| 1. |
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| 2. |
- Auvray, Xavier, 1986, et al.
(author)
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The effect gas composition during thermal aging on the dispersion and NO oxidation activity over Pt/Al2O3 catalysts
- 2013
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In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 129, s. 517-527
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Journal article (peer-reviewed)abstract
- The aging of a model 1 wt.% Pt/Al2O3 catalyst was performed stepwise under different reactive atmosphere to study the evolution of metal dispersion and NO oxidation activity. After each aging step the dispersion was evaluated by CO chemisorptions and the activity of the catalyst for NO oxidation was measured using 500 ppm NO and 8%O-2 diluted in Ar. After a degreening step at 500 degrees C, aging was performed at 600, 700,800 and 900 degrees C. Five wash-coated cordierite monoliths were aged in Ar, 10% O-2, 1% H-2 30 ppm SO2 and 30 ppm SO2 + 10% O-2, respectively. The general trend showed a linear decrease in dispersion when increasing the aging temperature for the lower aging temperatures and for the highest ones the dispersion levels off. When the platinum dispersion decreased the NO oxidation activity increased, due to that the reaction is structure sensitive. H-2 seemed to hinder sintering at low aging temperature. Interestingly, after aging in 10% oxygen at 600 degrees C the NO oxidation activity was significantly higher compared to the Ar aged sample, although the dispersions were similar. Aging in oxygen at higher temperatures resulted in a decrease of dispersion and a slightly decreasing NO oxidation activity. Moreover lower dispersion limit was reached with oxygen aging. Aging in SO2 provoked a severe dispersion drop at low aging temperature meanwhile the activity increased only moderately. However, activity kept increasing with further treatments at higher temperature. The combination of O-2 and SO2 enabled to decrease rapidly the dispersion and to greatly enhance the catalytic NO oxidation activity after the first aging step at only 600 degrees C. The best overall conversion was obtained for the catalyst treated with this mixture after aging at 800 degrees C. A 22-h aging at 250 degrees C in a mixture containing 500 ppm NO, 10% O-2 and 30 ppm SO2 led to a significant decrease of Pt dispersion, which shows the ability of SO2 to promote platinum sintering already 250 degrees C. The low temperature sintering was confirmed with STEM measurements. Several larger particles were observed, but also many small particles remained. Thus the SO2 + O-2 induced low temperature sintering results in a large variation of particle sizes. This treatment resulted in an increase of the maximum NO conversion (after reduction of the sample) from 45% to 76%. The different aging experiments show that it is beneficial to add SO2 during aging and the reason is the increased particle size, but also a clear chemical effect was observed.
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| 3. |
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| 4. |
- Fridell, Erik, 1963, et al.
(author)
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Model studies of NOx storage
- 2001
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In: ENVICAT2001, Amolfi, Italy, May 2-6, 2001.
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Conference paper (peer-reviewed)
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| 5. |
- Fridell, Erik, 1963, et al.
(author)
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Model studies of NOx storage and sulphur deactivation of NOx storage catalysts
- 2001
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In: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 16-17:1-4, s. 133-137
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Journal article (peer-reviewed)abstract
- The storage of NOx under lean conditions in model NOx storage catalysts as well as the deactivation by sulphur have been studied. We find that NO2 plays an important role in the storage mechanism as an oxidising agent. Two different mechanisms for this are discussed: the formation of surface peroxides and the oxidation of nitrites to nitrates, FTIR studies show that NOx is stored as surface nitrates, The sulphur deactivation is found to be more severe when SO2 is added during the rich phase than when SO2 is added during the lean period. FTIR shows the formation of bulk sulphates both under lean and rich conditions.
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| 6. |
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| 7. |
- Fridell, Erik, 1963, et al.
(author)
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Platinum oxidation and sulphur deactivation in NOx storage catalysts
- 2004
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In: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30-31:1-4, s. 143-146
-
Journal article (peer-reviewed)abstract
- Flow reactor experiments and X-ray photoelectron spectroscopy (XPS) measurements were used to investigate the importance of platinum oxide formation on Pt/BaO/Al2O3 NOx storage catalysts during reactions conditions. The reaction studied was NO(g) + 1/2 O-2(g) NO2 (g). During NO2 exposure of the catalyst the NO2 dissociation rate decreased during the reaction. This activity decrease with time was also studied with XPS and it was found to be due to platinum oxide formation. The influence of sulphur exposure conditions on the performance of the NOx storage catalysts was studied by exposing the samples to lean and/or rich gas mixtures, simulating the conditions in a mixed lean application, containing SO2 The main results show that all samples are sensitive to sulphur and that the deactivation proceeds faster when SO2 is present in the feed under rich conditions than under lean or continuous SO2 exposure. Additionally, the influence of the noble metals present in the catalysts was investigated regarding sulphur sensitivity and it was found that a combination of platinum and rhodium seems to be preferable to retain high performance of the catalyst under SO2 exposure and subsequent regeneration. Finally, the behaviour of micro-fabricated model NOx storage catalysts was studied as a function of temperature and gas composition with area-resolved XPS. These model catalysts consisted of a thin film of Pt deposited on one-half of a BaCO3 pellet. It was found that the combination of SO2 and O-2 resulted in migration of Pt on the BaCO3 support up to one mm away from the Pt/BaCO3 interface.
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| 8. |
- Jonsson, Rasmus, 1989, et al.
(author)
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Chemical poisoning by zinc and phosphorous of Pt/Ba/Al2O3 NOx storage catalysts
- 2019
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In: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 571, s. 158-169
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Journal article (peer-reviewed)abstract
- The effects of phosphorous and zinc on the performance of Pt/Ba/Al2O3 catalysts were investigated through wet impregnation of ammonium phosphate and zinc acetate aqueous solutions. Six different sample combinations were studied; 1 wt-% P, 1 wt-% Zn, 1 wt-% P with 1 wt-% Zn, 2 wt-% P, 2 wt-% Zn, 2 wt-% P with 2 wt-% Zn. NOx storage and reduction (NSR) activity and NO2 temperature programmed desorption (TPD) profiles were measured before and after impregnation of P and Zn. Samples containing P performed significantly worse than samples only containing Zn in both NSR activity and TPD measurements. The increased NOx slip during lean phase in activity measurements for P-poisoned samples is mainly related to an increased slip of NO2. This was found for both NO and NO2 in the gas feed during lean phase and suggests that it is mainly the storage component that is poisoned and not the noble metal. Furthermore, the combination (1 wt-% P and 1 wt-% Zn) proved to result in slightly worse performance than only 1 wt-% P, however this was not the case for samples containing 2 wt-%, where the addition of zinc reduced the negative effect of phosphorous. Measurements from NO2-TPD experiments showed that NOx release at low temperature was not affected by the addition of P, while desorption in the temperature range 425–475 °C was significantly reduced. It can therefore be concluded that the poisoning mainly is related to barium NOx storage sites and not to alumina sites. Moreover, X-ray diffraction measurements indicate that some of the barium species are affected by phosphorous. Images from scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDX) mapping were in line with the results seen in both the activity tests and NO2-TPD experiments. Phosphorous was concentrated at the same position as barium in the observed images, whereas zinc was more evenly distributed over the surface. For the sample with both 2 wt-% P and 2 wt-% Zn, X-ray photoelectron spectroscopy measurements indicate that Zn and P have a low interaction and this suggests that most of the zinc and phosphorous are separated. However, STEM-EDX showed agglomerates of some zinc and phosphorous, which could be zinc phosphates. This is a plausible explanation of the decreased deactivation observed after introducing 2 wt-% Zn compared to the sample only containing 2 wt-% P.
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| 9. |
- Jonsson, Rasmus, 1989, et al.
(author)
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Gas-phase phosphorous poisoning of a Pt/Ba/Al2O3 NOx storage catalyst
- 2018
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In: Catalysts. - : MDPI AG. - 2073-4344. ; 8:4
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Journal article (peer-reviewed)abstract
- The effect of phosphorous exposure on the NO x storage capacity of a Pt/Ba/Al 2 O 3 catalyst coated on a ceramic monolith substrate has been studied. The catalyst was exposed to phosphorous by evaporating phosphoric acid in presence of H 2 O and O 2 . The NOx storage capacity was measured before and after the phosphorus exposure and a significant loss of the NO x storage capacity was detected after phosphorous exposure. The phosphorous poisoned samples were characterized by X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), N 2 -physisorption and inductive coupled plasma atomic emission spectroscopy (ICP-AES). All characterization methods showed an axial distribution of phosphorous ranging from the inlet to the outlet of the coated monolith samples with a higher concentration at the inlet of the samples. Elemental analysis, using ICP-AES, confirmed this distribution of phosphorous on the catalyst surface. The specific surface area and pore volume were significantly lower at the inlet section of the monolith where the phosphorous concentration was higher, and higher at the outlet where the phosphorous concentration was lower. The results from the XPS and scanning electron microscopy (SEM)-energy dispersive X-ray (EDX) analyses showed higher accumulation of phosphorus towards the surface of the catalyst at the inlet of the monolith and the phosphorus was to a large extent present in the form of P 4 O 10 . However, in the middle section of the monolith, the XPS analysis revealed the presence of more metaphosphate (PO 3 – ). Moreover, the SEM-EDX analysis showed that the phosphorous to higher extent had diffused into the washcoat and was less accumulated at the surface close to the outlet of the sample
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| 10. |
- Olsson Månsson, Emma, 1992, et al.
(author)
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Removal of Inorganic Impurities in the Fast Pyrolysis Bio-oil Using Sorbents at Ambient Temperature
- 2024
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In: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 38:1, s. 414-4254
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Journal article (peer-reviewed)abstract
- Fast pyrolysis bio-oil (FPBO) sourced from residual biomass waste (such as sawdust) is a promising feedstock that may be used for biofuel production. Their inorganic elements may, however, vary and cause deactivation of the catalysts in the hydrodeoxygenation (HDO) upgrading biorefinery unit. It was found that the use of zeolite Y and strong acidic ion-exchange resins as adsorbents was almost equally efficient in lowering the concentrations of Ca from <10 to <1 ppm and of Fe, K, and Mg to <0.3 ppm in FPBO at 30 °C, atmospheric pressure, and 4 h adsorption time. The removal efficiency of zeolite and resins exceeded 85–98% (detection limit) of these particular elements. For the first time for the FPBO, phosphorus was reported as being successfully targeted by aluminum oxide, being lowered from 1 ppm to <0.1 ppm, which is a reduction of at least 90%. Characterization of the oil and sorbents suggests that the surface acidity affects the removal efficiency of these elements from FPBO. Organic compounds in the pyrolysis oil, including isopropanol, lactic acid, hydroxy acetone, furfural, guaiacol, and levoglucosan, were semiquantified using two-dimensional gas chromatography coupled with mass spectrometry (GCxGC-MS). Compared to the fresh oil, the compositions and contents of these organic compounds were not impacted significantly by the sorbents under these mild operating conditions. This research indicates that inorganic impurities present in bio-oils can be removed, and thus, they may be considered feedstocks for producing biofuels with less deactivation of HDO catalysts.
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| 11. |
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| 12. |
- Achour, Abdenour, 1980, et al.
(author)
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Evaluation of kraft and hydrolysis lignin hydroconversion over unsupported NiMoS catalyst
- 2023
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In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 453
-
Journal article (peer-reviewed)abstract
- Catalytic hydroconversion of Kraft and hydrolysis lignins was for the first time compared in a batch reactor over an unsupported NiMoS-SBA catalyst. We also report the effect of key reaction parameters on the yields and properties of the products. The results obtained at 20 wt% catalyst loading for hydrolysis lignin showed the highest monomer yield of 76.0 wt%, which consisted of 39 wt% aromatics with the lowest alkylphenolics yield of 10.1 wt%. Identical operating conditions, 400 °C, 80 bar, 5 h at 10 wt% catalyst loading, were used to compare both lignins and the highest monomer yield (64.3 wt%) was found for the hydrolysis lignin, consisting of 16.0 wt% alkylphenolics and 20.1 wt% aromatic compounds. These values are considerably higher than those for Kraft lignin with its 47.0 wt% monomer yield. We suggest that the reason for high yields of monomeric units from hydrolysis lignin is that it is more reactive due to its lower ash and sulfur contents and the chemical structural differences compared to the Kraft lignin. More precisely, the bio-oil from hydrolysis lignin contained higher yields of small molecules, sourced from ring-opening of cellulose in the hydrolysis lignin, which could stabilize the reactive oligomeric groups. These yields were two to seven times higher from kraft and hydrolysis lignin, respectively, compared to those obtained without catalyst. The results showed that the NiMoS-SBA catalyst is a promising catalyst for reductive depolymerization of lignin and in addition that the regenerated catalyst had good stability for multiple reaction cycles.
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| 13. |
- Achour, Abdenour, 1980, et al.
(author)
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Towards stable nickel catalysts for selective hydrogenation of biomass-based BHMF into THFDM
- 2023
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In: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437 .- 2213-2929. ; 11:2
-
Journal article (peer-reviewed)abstract
- Selective transformation of BHMF (2,5-bis(hydroxymethyl)furan) to THFDM (tetrahydrofuran-2,5-dimethanol) over a variety of structured Ni/Sx-Z1−x catalysts was investigated. The effects of support, Ni loading, solvent, temperature, pressure, and particle size on the conversion and selectivity were studied. Among them, the 10 wt% Ni catalyst supported on the SiO2:ZrO2 weight ratio of 90:10 (10NiS90Z10) exhibits the best performance in terms of BHMF conversion and THFDM selectivity. Its good performance was attributed to its well-balanced properties, that depend upon the ZrO2 content of the support in combination with SiO2, the active Ni sites-support interaction, and acidity/basicity ratio of each catalyst resulting in different Ni dispersions. Importantly, the 10NiS90Z10 catalyst showed a stable selectivity to THFDM (>94%), with 99.4% conversion of BHMF during 2 h reaction time. Poor catalytic activity resulted from excessive ZrO2 content (>10 wt%). The structural, textural, and acidity properties of NiSi100−y-Zry catalysts, tuned by selectively varying the Ni amount from 5 to 15 wt%, were critically investigated using numerous material characterization techniques. Catalyst recycling experiments revealed that the catalyst could be recycled several times without any measurable loss of catalytic activity.
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| 14. |
- Adermark, Louise, 1974, et al.
(author)
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Ethanol acutely decreases astroglial gap junction permeability in primary cultures from defined brain regions
- 2004
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In: Neurochemistry International. - : Elsevier BV. - 0197-0186. ; 45:7, s. 971-978
-
Journal article (peer-reviewed)abstract
- The acute effect of hyperosmotic ethanol on gap junction permeability was examined in astroglial cells in primary culture from five different brain regions. Gap junction permeability was analyzed by measuring dye spreading from cell to cell with the low molecular weight dye Lucifer Yellow. Ethanol concentrations 25-300 mM significantly decreased dye spreading in cultures from the cerebral cortex in a dose-dependent but time-independent manner for up to 60 min. Besides cerebral cortex, exposure to 150 mM ethanol decreased dye spreading in astroglial cultures from the hippocampus and from the brain stem, while cultures from the olfactory bulb and from the hypothalamus were not significantly affected. The ethanol-induced decrease in dye spreading in cultures from the cerebral cortex was not mediated through changes in cell volume, osmolarity, protein kinase C (PKC) phosphorylation, intracellular pH, or intracellular calcium concentration ([Ca 2+ ] i ). The decrease in dye spreading was abolished upon incubation in sodium-reduced buffer, and after blockage of the Na + /K + /2Cl - cotransporter with furosemide. The results presented here indicate that ethanol-mediated decrease in dye spreading is directly or indirectly dependent on sodium. © 2004 Elsevier Ltd. All rights reserved.
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| 15. |
- Adermark, Louise, 1974, et al.
(author)
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Implications for glycine receptors and astrocytes in ethanol-induced elevation of dopamine levels in the nucleus accumbens.
- 2011
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In: Addiction biology. - : Wiley. - 1369-1600 .- 1355-6215. ; 16:1, s. 43-54
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Journal article (peer-reviewed)abstract
- ABSTRACT Elevated dopamine levels are believed to contribute to the rewarding sensation of ethanol (EtOH), and previous research has shown that strychnine-sensitive glycine receptors in the nucleus accumbens (nAc) are involved in regulating dopamine release and in mediating the reinforcing effects of EtOH. Furthermore, the osmoregulator taurine, which is released from astrocytes treated with EtOH, can act as an endogenous ligand for the glycine receptor, and increase extracellular dopamine levels. The aim of this study was to address if EtOH-induced swelling of astrocytes could contribute to elevated dopamine levels by increasing the extracellular concentration of taurine. Cell swelling was estimated by optical sectioning of fluorescently labeled astrocytes in primary cultures from rat, and showed that EtOH (25-150 mM) increased astrocyte cell volumes in a concentration- and ion-dependent manner. The EtOH-induced cell swelling was inhibited in cultures treated with the Na(+)/K(+)/2Cl(-) cotransporter blocker furosemide (1 mM), Na(+)/K(+)-ATPase inhibitor ouabain (0.1 mM), potassium channel inhibitor BaCl(2) (50 microM) and in cultures containing low extracellular sodium concentration (3 mM). In vivo microdialysis performed in the nAc of awake and freely moving rats showed that local treatment with EtOH enhanced the concentrations of dopamine and taurine in the microdialysate, while glycine and beta-alanine levels were not significantly modulated. EtOH-induced dopamine release was antagonized by local treatment with the glycine receptor antagonist strychnine (20 microM) or furosemide (100 microM or 1 mM). Furosemide also prevented EtOH-induced taurine release in the nAc. In conclusion, our data suggest that extracellular concentrations of dopamine and taurine are interconnected and that swelling of astrocytes contributes to the acute rewarding sensation of EtOH.
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| 16. |
- Andersson, Anna, et al.
(author)
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Lactate contributes to ammonia-mediated astroglial dysfunction during hyperammonemia.
- 2009
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In: Neurochemical research. - : Springer Science and Business Media LLC. - 1573-6903 .- 0364-3190. ; 34:3, s. 556-65
-
Journal article (peer-reviewed)abstract
- Even though ammonia is considered to underlie nervous system symptoms of dysfunction during hyperammonemia, lactate, which increases as a metabolic consequence of high ammonia levels, might also be a contributing factor. The data presented here show that NH4Cl (5 mM) mediates astroglial cell swelling, and that treatment with NH4Cl or lactate (25 mM) causes rearrangements of actin filaments and reduces astroglial glutamate uptake capacity. Co-application with BaCl2, which blocks astroglial uptake of NH4+, prevents NH4Cl-mediated cell swelling and rearrangement of actin filaments, but does not reduce NH4Cl-induced glutamate uptake capacity inhibition. Neither NH4Cl nor lactate affected glutamate uptake or protein expression in microglial cultures, indicating that astroglial cells are more susceptible to the neurotoxic affects of ammonia. Our results suggest that ammonium underlies brain edema, but that lactate can contribute to some of the cellular dysfunctions associated with elevated cerebral levels of ammonia.
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| 17. |
- Andonova, Stanislava, 1977, et al.
(author)
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Chemical deactivation by phosphorous under lean hydrothermal conditions over Cu/BEA NH3-SCR catalysts
- 2014
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In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 147, s. 251-263
-
Journal article (peer-reviewed)abstract
- To obtain a better understanding of the deactivation of SCR catalysts that may be encountered due to the presence of P-containing impurities in diesel exhausts, the effects induced by P over Cu/BEA NH3-SCR catalysts were studied as functions of the temperature of poisoning and P concentration in the feed. Cu/BEA catalysts with different Cu loadings (4 and 1.3 wt% Cu) were exposed to P by controlled evaporation of H3PO4 in the presence of 8% O2 and 5% H2O at 573 and 773 K. The reaction studies were performed by NH3-storage/TPD, NH3/NO oxidation and standard NH3-SCR. In addition, a combination of several characterisation techniques (ICP–AES, BET surface area, pore size distribution, H2-TPR and XPS) was applied to provide useful information regarding the mechanism of P deactivation. Pore condensation of H3PO4 in combination with pore blocking was observed. However, the measured overall deactivation was found to occur mostly by chemical deactivation reducing the number of the active Cu species and hence deteriorating the redox properties of the Cu/BEA catalysts. The process of P accumulation on the surface preferentially occurs on the “over exchanged” Cu active sites with the formation of phosphate species. This is likely the reason for the more severe deactivation of the 4% Cu/BEA compared to 1.3% Cu/BEA. Further, the higher NOx reduction performance at 773 K of the P-poisoned Cu/BEA catalysts was found to originate from the lower selectivity towards NH3 oxidation, which occurs predominately on the “over-exchanged” sites.
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| 18. |
- Andonova, Stanislava, 1977, et al.
(author)
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Enhanced Low Temperature NOx Reduction Performance Over Bimetallic Pt/Rh-BaO Lean NOx Trap Catalysts
- 2013
-
In: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 56:1-8, s. 68-74
-
Journal article (peer-reviewed)abstract
- The overall NSR operation was tested over a bimetallic Pt/Rh-BaO lean NO (x) trap (LNT) catalyst in the range of 473-673 K with simulated diesel exhausts and compared to monometallic 1 wt% Pt/BaO/gamma-Al2O3 and 0.5 wt% Rh/BaO/gamma-Al2O3 samples. The results showed the beneficial effect of the simultaneous presence of 0.5 wt% Pt and 0.25 wt% Rh on the catalytic performance under lean-burn conditions at low temperatures. It was observed that both Pt/BaO/gamma-Al2O3 and Rh/BaO/gamma-Al2O3, which both were mildly aged, have limited NO (x) reduction capacity at 473 K. However, combining Pt and Rh in the NO (x) storage catalyst assisted the NO (x) reduction process to occur at lower temperatures (473 K). One possible reason could be that the combined Pt and Rh sample was more resistant to aging. In addition, the NO2-TPD data showed that the presence of Rh into the Pt/BaO/gamma-Al2O3 system has a considerable effect on the spill-over process of NO (x) , accelerating the release of NO (x) at lower temperatures. These results were in a good agreement with the observed higher rate of oxygen release of the bimetallic Pt/Rh catalyst, leaving a significant number of noble metal sites available for adsorption at lower temperatures than that of the monometallic Pt sample. The superior NSR performance of the bimetallic Pt/Rh/BaO/gamma-Al2O3 catalyst under lean-burn conditions suggested the existence of synergetic promotion effect between the Pt and Rh components, increasing the NO (x) reduction efficiency in comparison with that of the monometallic Pt and Rh-BaO LNT catalysts.
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| 19. |
- Andonova, Stanislava, 1977, et al.
(author)
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Mechanistic investigations of the promoting role of Rh on the NSR performance of NOx storage BaO-based catalysts
- 2013
-
In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 132, s. 266-281
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Journal article (peer-reviewed)abstract
- To determine the promoting effect of Rh on the overall NOx storage and reduction (NSR) performance, the studies in the current work were directed toward investigating the storage and release ability over Rh NOx storage BaO-based catalysts compared to Pt. In terms of the metal surface dispersion and the ability of the noble metals to release oxygen at lower temperatures, the synthesized catalysts were characterized by means of dynamic CO chemisorption (RT) and N2O dissociation (RI - 773 K). The NOx storage capacity and the thermal stability of the NOx adsorbed species formed on the surface were analyzed via NOx storage tests and temperature programmed desorption (TPD) without and in the presence of CO2 and H2O. In addition, experiments with lean and rich cycling were conducted at 473,573 and 673 K. The results from the N2O dissociation experiments showed the superior ability of Rh/Al and Rh/Ba/Al catalysts compared to Pt toward O-2 release from the catalytic surface at lower temperatures. In this work, we show that the presence of Rh into the BaO/gamma-Al2O3 system has a considerable effect on the spill-over process of NOx to the precious metal, controlling the subsequent desorption of NOx to occur at lower temperatures in comparison with that of the Pt catalysts. It is suggested a mechanism of NOx desorption where the lower temperature of O-2 release from the surface of Rh catalysts could leave a significant number of noble metal sites accessible for adsorption. Thus this could facilitate the rate of spill-over of NOx from the storage site (the surface sites on gamma-Al2O3 and those on BaO) to the noble metal and their desorption at lower temperatures. The limited NOx storage ability of the Rh-based BaO/gamma-Al2O3 catalysts under lean-burn conditions was found to originate from both low NO oxidation activity and NOx reduction activity, while the main limiting factor for the low NSR performance of the Pt-based catalysts was the limited regeneration ability during rich period.
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| 20. |
- Andonova, Stanislava, 1977, et al.
(author)
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Micro-calorimetric studies of NO2 adsorption on Pt/BaO-supported on gamma-Al2O3 NOx storage and reduction (NSR) catalysts-Impact of CO2
- 2017
-
In: Molecular Catalysis. - : Elsevier BV. - 2468-8231. ; 436, s. 43-52
-
Journal article (peer-reviewed)abstract
- The adsorption of NO2 on Pt/BaO/gamma Al2O3 catalyst has been investigated by micro calorimetry at atmospheric pressure, NOx storage tests and temperature-programmed desorption (TPD). The heat of adsorption of NO2 (Delta H-ads(NO2)) was determined over a wide range of NOx coverages, as the catalyst was exposed to 500/900 ppm NO2 in the absence/presence of 5% CO2 in the range of 423-773 K. The temperature dependent changes of Delta H-ads(NO2) verified the presence of energetically different NOx storage sites with different binding strength. The Delta H-ads(NO2) was found to follow a linear correlation versus temperature, ranging for example from -134.5 to -178.8 kJ/mol for NOx storage over Pt/BaO/gamma Al2O3 at 423-673 K. Thus, at high temperature mostly strongly bound nitrates were formed, while at lower temperature more loosely bound species were also present. Interestingly, the heat of adsorption was higher when using higher NO2 concentration, indicating more bulk barium nitrate formation. This is consistent with the TPD data where a clear high temperature peak was visible after adsorption using 900 ppm NO2 at 423 and 473 K, which was not the case for 500 ppm NO2. Moreover, the micro-calorimetric data also provided evidence in support of the detrimental effect of CO2 on the NOx uptake process. The heat released during the NOx storage in 500 ppm NO2 + 5% CO2 was determined to be significantly reduced ca. -97.8 kJ mol(-1) at 423 K, but ca. -134.5 kJ mol(-1) without CO2. Furthermore, our results show that it is critical to measure heat of adsorption for surface compounds since they are significantly different compared to thermodynamic data for bulk materials.
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| 21. |
- Andonova, Stanislava, 1977, et al.
(author)
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The effect of iron loading and hydrothermal aging on one-pot synthesized Fe/SAPO-34 for ammonia SCR
- 2016
-
In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 180, s. 775-787
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Journal article (peer-reviewed)abstract
- The current commercially-available technique for NOx reduction for diesel engines is the selective catalytic reduction (SCR) of NOx with NH3 over Cu zeolites. One of the problems of this technique is their limited ability to convert NOx at diesel particulate filter (DPF) regeneration temperatures. In addition, during regeneration of the DPF there is a risk of thermally deactivating the SCR catalyst. Thus, the aim of the current work was the development of a catalytic system that can reduce NOx both at low as well as high temperature and in addition is stable at high temperature. In order to reach this goal, a Fe/SAPO-34 with chabazite (CHA) structure was combined in a system with a commercial Cu/CHA catalyst. Earlier studies have shown that it is difficult to ion-exchange Fe into CHA structures due to steric hindrance, and we have therefore used a novel synthesis procedure which incorporated iron directly into the zeolite structure. Fe/SAPO-34 with three different Fe-loadings (0.27; 0.47 and 1.03 wt.% Fe) were synthesized and the catalysts were characterized using inductively coupled plasma atomic spectroscopy (ICP-AES), N-2 adsorption-desorption isotherms, BET area measurements and X-ray diffraction (XRD). The chemical composition, porous and crystalline structure of the parent SAPO-34 sample were found to be only slightly affected by addition of small amounts of Fe in the framework zeolite structure. However, more visible changes in the crystallinity were observed in the Fe/SAPO-34 catalysts with higher Fe content, which were attributed to the unit cell size expansion provoked by integration of higher amounts of Fe into the zeolite SAPO-34 framework. The Fe/SAPO-34 with the lowest Fe-loading (0.27 wt.%) was found to be the best catalyst when considering activity as well as high temperature stability. The synthesized Fe/SAPO-34 catalyst demonstrated a significantly improved NOx reduction performance at high temperatures (600-750 degrees C) when compared to a commercial Cu/CHA SCR system, and the combined system (Fe/SAPO-34+ Cu/CHA) exhibited a very good performance in a large temperature interval (200-800 degrees C) that encompasses most diesel exhaust gas conditions.
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| 22. |
- Andriopoulos, Thanos, et al.
(author)
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Commencement of and Retention in Web-Based Interventions and Response to Prompts and Reminders : Longitudinal Observational Study Based on Two Randomized Controlled Trials
- 2021
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In: Journal of Medical Internet Research. - : JMIR Publications. - 1438-8871. ; 23:3
-
Journal article (peer-reviewed)abstract
- Background: Web-based interventions are effective for several psychological problems. However, recruitment, adherence, and missing data are challenges when evaluating these interventions. Objective: This study aimed to describe the use patterns during the commencement phase, possible retention patterns (continuation of data provision), and responses to prompts and reminders among participants in 2 randomized controlled trials (RCTs) evaluating web-based interventions. Methods: Data on use patterns logged in 2 RCTs aiming to reduce symptoms of anxiety and depression among adult patients recently diagnosed with cancer (AdultCan RCT) and patients with a recent myocardial infarction (Heart RCT) were analyzed. The web-based intervention in the AdultCan trial consisted of unguided self-help and psychoeducation and that in the Heart trial consisted of therapist-supported cognitive behavioral therapy. In total, 2360 participants' use patterns at first log-in, including data collection at baseline (ie, commencement) and at 2 follow-ups, were analyzed. Both the intervention and comparison groups were analyzed. Results: At commencement, 70.85% (909/1283) and 86.82% (935/1077) of the participants in AdultCan and Heart RCTs, respectively, logged in and completed baseline data collection after receiving a welcome email with log-in credentials. The median duration of the first log-in was 44 minutes and 38 minutes in AdultCan and Heart RCTs, respectively. Slightly less than half of the participants' first log-ins were completed outside standard office hours. More than 80% (92/114 and 103/111) of the participants in both trials explored the intervention within 2 weeks of being randomized to the treatment group, with a median duration of 7 minutes and 47 minutes in AdultCan and Heart RCTs, respectively. There was a significant association between intervention exploration time during the first 2 weeks and retention in the Heart trial but not in the AdultCan trial. However, the control group was most likely to retain and provide complete follow-up data. Across the 3 time points of data collection explored in this study, the proportion of participants responding to all questionnaires within 1 week from the prompt, without a reminder, varied between 35.45% (413/1165) and 66.3% (112/169). After 2 reminders, up to 97.6% (165/169) of the participants responded. Conclusions: Most participants in both RCTs completed the baseline questionnaires within 1 week of receiving the welcome email. Approximately half of them answered questions at baseline data collection outside office hours, suggesting that the time flexibility inherent in web-based interventions contributes to commencement and use. In contrast to what was expected, the intervention groups generally had lower completion rates than the comparison groups. About half of the participants completed the questionnaires without a reminder, but thereafter, reminders contributed to both baseline and follow-up retention, suggesting they were effective. Strategies to increase commencement of and retention in eHealth interventions are important for the future development of effective interventions and relevant research.
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| 23. |
- Arora, Prakhar, 1987, et al.
(author)
-
Investigating the effect of Fe as a poison for catalytic HDO over sulfided NiMo alumina catalysts
- 2018
-
In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 227, s. 240-251
-
Journal article (peer-reviewed)abstract
- The effect of iron (Fe) as poison present in renewable feeds was studied during hydrodeoxygenation (HDO) overmolybdenum based sulfided catalysts. The study was carried out at 6 MPa and 325 °C in batch reaction conditions. Different concentrations of Fe in the feed were tested over MoS2/Al2O3 and NiMoS/Al2O3. A notable drop in activity for the conversion of oxygenates was observed for both catalyst systems with an increased concentration of Fe in the feed. However, the changes in selectivity of products was opposite for unpromoted and Nipromoted catalysts. In the case of the NiMoS catalyst, at higher Fe concentration, the decarbonated product (C17 hydrocarbons) decreased while the direct hydrodeoxygenation product (C18 hydrocarbons)increased. On the contrary, for the base catalyst (MoS2), there was a decrease in the yield of direct hydrodeoxygenation (C18 hydrocarbons) products and an increase in yield of decarbonated products (C17 hydrocarbons). These sulfided catalysts have different sites for these two different reaction routes and they interacted differently with Fe during the deactivation process. With surface deposition of Fe, the ability of these catalysts to create active sites i.e. via sulfur vacancies deteriorated. TEM-EDX results suggested that the effect of Ni as a promoter for the decarbonation route was nullified and a resultant FeMo phase explains the drop in activity and change in selectivity.
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| 24. |
- Arora, Prakhar, 1987, et al.
(author)
-
Kinetic study of hydrodeoxygenation of stearic acid as model compound for renewable oils
- 2019
-
In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 364, s. 376-389
-
Journal article (peer-reviewed)abstract
- The kinetics during hydrodeoxygenation (HDO) of stearic acid (SA) was investigated to explore the fundamental chemistry and the reaction scheme involved for the reaction with a sulfide NiMo/Al2O3catalyst. Intermediates like octadecanal (C18 O) and octadecanol (C18 OH) were used to resolve the reaction scheme and explain the selectivity for the three major reaction routes (decarboxylation, decarbonylation and direct-HDO). Several reaction parameters, like temperature, pressure, feed concentration and batch-reactor stirring rate, were explored for their effect on changes in rate of conversion and selectivity. A weaker dependence on pressure (40–70 bar) and strong dependence on temperature (275–325 °C) was found for the product distribution during HDO of SA. A model based on Langmuir–Hinshelwood type kinetics was developed to correlate the experimental data. The model well predicted trends in variation of selectivities with the reaction conditions, in part by including intermediates like octadecanol and octadecanal and it predicted phenomenon like inhibiting effects of the fatty acid. The proposed kinetic model is expected to be applicable to liquid phase HDO of different renewable feeds containing long chain fatty acids, methyl esters and triglycerides etc.
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| 25. |
- Arora, Prakhar, 1987, et al.
(author)
-
The role of catalyst poisons during hydrodeoxygenation of renewable oils
- 2021
-
In: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 367, s. 28-42
-
Journal article (peer-reviewed)abstract
- Hydrodeoxygenation (HDO) activity of NiMo catalysts have been evaluated in the presence of catalyst poisons in bio-based feedstocks. An in-house synthesized NiMo/Al2O3 catalyst was placed in a refinery unit for biofuel production. Iron (Fe), phosphorus (P) and metals were identified as major contaminants. Calcination treatment was explored to recover the activity of spent catalysts. The effect of Fe, K and phospholipid containing P and Na on catalyst deactivation during hydrodeoxygenation of stearic acid was simulated at lab-scale. Fe caused the most deactivation where the highest feed concentration of the Fe compound resulted in 1480 ppm Fe deposited on the catalyst. Elemental distribution along the radial axis of spent catalysts indicated: Fe deposited only to a depth of 100 μm irrespective of concentration while P and Na from phospholipid and K penetrated deeper in catalyst particles with a distribution profile that was found to be concentration dependent.
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| 26. |
- Auvray, Xavier, 1986, et al.
(author)
-
Aging of Cu/SSZ-13 for NH3 SCR in mixed lean condition
- 2018
-
Conference paper (other academic/artistic)abstract
- Two catalytic methods have been developed to remove the NOx emissions from diesel vehicles and comply with the emission regulations: the NOx storage and reduction process (NSR) and the reduction of NOx with NH3 (SCR). Advanced systems combining these two methods for an optimum efficiency are now studied. SCR catalysts are subjected alternating lean and rich conditions as well as to high temperatures in rich conditions during deSOx of the LNT material. The purpose of the present work is therefore to determine the response of a Cu/SSZ-13 to several aging treatments at 800°C involving rich and/or lean exposure. Deactivation was observed after all types of aging. However strong differences in deactivation degree exists between aging procedures. Lean aging, for 8h at 800°C, was the most moderate aging tested although it brought about significant activity loss below 250°C. Alternating between long lean periods and short rich periods caused slightly stronger deactivation, which was most significant at 200°C. However, the switching frequency between lean and rich had negligible influence on subsequent activity. As shown in Figure 1, SCR activity after 8h exposure in H2 was outstandingly low. It increased monotonically with temperature to reach a maximum of 58% NO conversion. Further investigation pertaining to the rich treatment was performed. The aging time was reduced to 2h and, for direct comparison, a 32h cycling aging was performed, implying a total rich time of 2h. Both samples were severely impacted over the whole temperature range. It revealed that 2h in rich conditions led to stronger deactivation than 8h in lean and lean/rich conditions, emphasizing the deterioration power of H2. Aging caused by rich conditions was so dominant that additional 30h in lean has negligible influence on SCR below 300°C. However, the long additional exposure to lean conditions lowered significantly the SCR activity between 400 and 500°C.
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| 27. |
- Auvray, Xavier, 1986, et al.
(author)
-
Comparative Study of SO 2 and SO 2 /SO 3 Poisoning and Regeneration of Cu/BEA and Cu/SSZ-13 for NH 3 SCR
- 2021
-
In: Emission Control Science and Technology. - : Springer Science and Business Media LLC. - 2199-3629 .- 2199-3637. ; 7:4, s. 232-246
-
Journal article (peer-reviewed)abstract
- Two copper-exchanged zeolites, Cu/SSZ-13 and Cu/BEA, were studied as catalysts for the selective reduction of NOx by NH3 (NH3-SCR). Their activities for standard SCR (NOx = NO) and fast SCR (NOx = 50% NO + 50% NO2) were measured before and after sulfur poisoning at 250 °C. The effect of 30 ppm SO2 and a mixture of 24 ppm SO3 + 6 ppm SO2 was evaluated. The repetition of subsequent activity measurements served as regeneration method in SCR conditions. SO2 deactivated Cu/SSZ-13 whereas Cu/BEA was only moderately affected. SO3 led to stronger deactivation of both catalysts than SO2. However, also for this case, the Cu/BEA was significantly less affected than Cu/SSZ-13, even though Cu/BEA contained larger amount of stored sulfur. One possible reason for this could be the large pores of Cu/BEA, where the sulfur species possibly resulted in less sterical hindrance than in the small pore SSZ-13 structure. NH3 temperature-programmed desorption (NH3-TPD) showed no loss of storage sites upon sulfur treatment and subsequent regeneration. Partial activity recovery was observed after a period in SCR conditions at 400 °C and 500 °C. Temperature at 300 °C was insufficient to regenerate the catalysts. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of NO adsorption suggested that SO2 interacts with the ZCuOH sites on Cu/SSZ-13, causing the strong poisoning.
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| 28. |
- Auvray, Xavier, 1986, et al.
(author)
-
Deactivation of Cu/SSZ-13 NH3-SCR catalyst by exposure to CO, H2, and C3H6
- 2019
-
In: Catalysts. - : MDPI AG. - 2073-4344. ; 9:11
-
Journal article (peer-reviewed)abstract
- Lean nitric oxide (NOx)-trap (LNT) and selective catalytic reduction (SCR) are efficient systems for the abatement of NOx. The combination of LNT and SCR catalysts improves overall NOx removal, but there is a risk that the SCR catalyst will be exposed to high temperatures and rich exhaust during the LNTs sulfur regeneration. Therefore, the effect of exposure to various rich conditions and temperatures on the subsequent SCR activity of a Cu-exchanged chabazite catalyst was studied. CO, H2, C3H6, and the combination of CO + H2 were used to simulate rich conditions. Aging was performed at 800 °C, 700 °C, and, in the case of CO, 600 °C, in a plug-flow reactor. Investigation of the nature of Cu sites was performed with NH3-temperature-programed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) of probe molecules (NH3 and NO). The combination of CO and H2 was especially detrimental to SCR activity and to NH3 oxidation. Rich aging with low reductant concentrations resulted in a significantly larger deactivation compared to lean conditions. Aging in CO at 800 °C caused SCR deactivation but promoted high-temperature NH3 oxidation. Rich conditions greatly enhanced the loss of Brønsted and Lewis acid sites at 800 °C, indicating dealumination and Cu migration. However, at 700 °C, mainly Brønsted sites disappeared during aging. DRIFT spectroscopy analysis revealed that CO aging modified the Cu2+/CuOH+ ratio in favor of the monovalent CuOH+ species, as opposed to lean aging. To summarize, we propose that the reason for the increased deactivation observed for mild rich conditions is the transformation of the Cu species from Z2Cu to ZCuOH, possibly in combination with the formation of Cu clusters. © 2019, MDPI AG. All rights reserved.
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| 29. |
- Auvray, Xavier, 1986, et al.
(author)
-
Effect of enhanced support acidity on the sulfate storage and the activity of Pt/γ-Al2O3 for no oxidation and propylene oxidation
- 2014
-
In: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 144:1, s. 22-31
-
Journal article (peer-reviewed)abstract
- NO oxidation and propylene oxidation were studied on standard and acidity-enhanced Pt/Al 2 O 3 catalyst. Deactivation by platinum oxide formation was suppressed by the presence of chlorine and sulfates. After a long SO 2 exposure, the activity of modified catalysts was higher than the standard catalyst. The aged chlorinated sample showed the best propylene oxidation activity while the sulfated one exhibited the best NO conversion. © 2013 Springer Science+Business Media New York.
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| 30. |
- Auvray, Xavier, 1986, et al.
(author)
-
Enhancement of NO and C3H6 oxidation by SO2 treatment over Pt/Al2O3
- 2013
-
In: 23rd Meeting of the North American Catalysis Society, Louisville, KY, June 2013.
-
Conference paper (other academic/artistic)abstract
- Oxidation catalyst is used in automotive exhaust treatment to convert CO and hydrocarbons into CO2 and water. They also have the specific function of converting NO into NO2 in Diesel vehicles, which increases the efficiency of NOx-removal system and participates in the particle filter regeneration. Automotive catalysts are affected by thermal treatments and gas composition. SO2 is one of the undesirable compounds of exhaust gases that is able to store on the catalyst [1] and hinder the reaction. Despite its low concentration, SO2 affects significantly the catalyst. Ageing in SO2-containing atmosphere has shown to promote platinum migration and increase the ability of Pt/Al2O3 catalysts to oxidize NO in dry conditions [2]. In the present work, model catalysts were aged in presence of SO2 at 250 °C and tested for NO and C3H6 oxidation in wet conditions. Various reductive treatments were performed after ageing in order to shed a light on the stability and impact on activity of the different types of adsorbed sulfur species. The hysteresis phenomenon observed for both reactions was also affected by the presence of surface sulfur.The performance of a typical oxidation catalyst was improved by pretreatment in presence of SO2 and subsequent elimination of the less stable stored sulfur species. Further activity was gained during the cooling for both NO and C3H6 oxidation after complete removal of sulfur.
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| 31. |
- Auvray, Xavier, 1986, et al.
(author)
-
Enhancement of NO and C3H6 oxidation by SO2 treatment over Pt/Al2O3
- 2013
-
In: Energirelaterad fordonsforskning 2013, Örebro, April 2013.
-
Conference paper (other academic/artistic)abstract
- The oxidation of NO and C3H6 over a 1wt% Pt/Al2O3 catalyst was studied. Ageing of the catalyst at 250 °C for 22 h with a gas flow containing 30 ppm SO2 decreased the dispersion and increased the catalytic activity for the two reactions. Two types of sulfur species were formed during ageing, the less stable of which have to be eliminated to recover high activity. The most stable species, probably sulfates stored on the support, affect the conversion during extinction only.
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| 32. |
- Auvray, Xavier, 1986, et al.
(author)
-
Kinetic modeling of NH3-SCR over a supported Cu zeolite catalyst using axial species distribution measurements
- 2015
-
In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 163, s. 393-403
-
Journal article (peer-reviewed)abstract
- In this study, a kinetic model is developed for NH3-SCR over a honeycomb-monolith-supported Cu-zeolites using intra-catalyst axial species distribution measurements. An ammonia TPD experiment, together with micro calorimetry data were used for tuning the ammonia adsorption and desorption properties. The spatial distribution for NO oxidation, NH3 oxidation and NH3 "Standard" SCR were modeled between 200 and 400 degrees C. Four-step protocol measurements were employed in order to validate the transient functions of the model. The resulting kinetic model provides good spatiotemporal simulation of the SCR reaction and component reactions throughout the monolith catalyst system.
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| 33. |
- Auvray, Xavier, 1986, et al.
(author)
-
Lean and rich aging of a Cu/SSZ-13 catalyst for combined lean NO x trap (LNT) and selective catalytic reduction (SCR) concept
- 2019
-
In: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:9, s. 2152-2162
-
Journal article (peer-reviewed)abstract
- © 2019 The Royal Society of Chemistry. In the combined lean NO x trap (LNT) and selective catalytic reduction (SCR) concept, the SCR catalyst can be exposed to rich conditions during deSO x of the LNT. Aging of Cu/SSZ-13 SCR catalysts, deposited on a cordierite monolith, was therefore studied in rich, lean and cycling lean/rich operations at 800 °C (lean condition: 500 ppm NO, 8% O 2 , 10% H 2 O and 10% CO 2 ; rich condition: 500 ppm NO, 1% H 2 , 10% H 2 O and 10% CO 2 ). The structure of the catalyst was investigated by X-ray diffraction (XRD), surface area measurements and scanning transmission electron microscopy (STEM). In general, aging decreased the SCR activity and NH 3 oxidation. However, rich conditions showed a very rapid and intense deactivation, while lean aging led to only a small low-temperature activity decrease. The XRD results showed no sign of structure collapse, but the number of active sites, as titrated by NH 3 temperature-programed desorption (NH 3 -TPD) and in situ DRIFTS, revealed an important loss of acid sites. NH 3 storage was significantly more depleted after rich aging than after lean aging. The Lewis sites, corresponding to exchange Cu 2+ , were preserved to some extent in lean conditions. Lean aging also decreased the enthalpy of NH 3 adsorption from -158 kJ mol -1 to -136 kJ mol -1 . Moreover, a comparison of aging in lean-rich cycling conditions with aging only in rich conditions revealed that adding lean events did not hinder or reverse the deactivation, and it was mainly the time in rich conditions that determined the extent of the deactivation. The STEM images coupled with elemental analysis revealed the formation of large Cu particles during rich aging. Conversely, Cu remained well dispersed after lean aging. These results suggest that the copper migration and agglomeration in large extra-framework particles, accelerated by the action of hydrogen, caused the observed severe deactivation.
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| 34. |
- Auvray, Xavier, 1986, et al.
(author)
-
Local ammonia storage and ammonia inhibition in a monolithic copper-beta zeolite SCR catalyst
- 2012
-
In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 126, s. 144-152
-
Journal article (peer-reviewed)abstract
- Selective catalytic reduction of NO with NH3 was studied on a Cu-beta zeolite catalyst, with specific focus on the distributed NH3 capacity utilization and inhibition. In addition, several other relevant catalyst parameter distributions were quantified including the SCR zone, or catalyst region where SCR occurs, and NO and NH3 oxidation. We show that the full NH3 capacity (100% coverage) is used within the SCR zone for a range of temperatures. By corollary, unused NH3 capacity exists downstream of the SCR zone. Consequently, the unused capacity relative to the total capacity is indicative of the portion of the catalyst unused for SCR. Dynamic NH3 inhibition distributions, which create local transient conversion inflections, are measured. Dynamic inhibition is observed where the gas phase NH3 and NO concentrations are high, driving rapid NH3 coverage buildup and SCR. Accordingly, we observe dynamic inhibition at low temperatures and in hydrothermally aged states, but predict its existence very near the catalyst front in higher conversion conditions where we did not specifically monitor its impact. While this paper addresses some general distributed SCR performance parameters including Oxidation and SCR zone, our major new contributions are associated with the NH3 capacity saturation within the SCR zone and dynamic inhibition distributions and the associated observations. These new insights are relevant to developing accurate models, designs and control strategies for automotive SCR catalyst applications.
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| 35. |
- Auvray, Xavier, 1986, et al.
(author)
-
Stability and activity of Pd-, Pt- and Pd-Pt catalysts supported on alumina for NO oxidation
- 2015
-
In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 168, s. 342-352
-
Journal article (peer-reviewed)abstract
- The association of palladium and platinum supported on alumina was studied for diesel oxidation catalyst application. The effect of propene, water and their combination on NO oxidation activity was investigated in flow reactor over Pt/Al2O3, Pd/Al2O3 and two Pt-Pd/Al2O3 catalysts, prepared by co-impregnation and sequential impregnation of the metals. Contrary to Pd/Al2O3, activity improvement due to the repetition of activity test was observed on Pt/Al2O3 and both Pt-Pd/Al2O3. Metal sintering during activity test was revealed by CO chemisorption. The bimetallic catalysts reached their final stability and activity before Pt/Al2O3. The presence of water decreased the NO oxidation activity of all catalysts and the propene completely inhibited NO oxidation at low temperature until propene combustion occurred. The addition of palladium to Pt/Al2O3 was found very efficient to oxidize propene and therefore significantly limited the inhibition of NO oxidation by propene. A mechanism was proposed to explain the NO oxidation promotion lying behind the addition of Pd. DRIFT measurements and flow reactor experiments showed that propene was less stable and able to react with surface nitrates on Pd-containing catalyst at low temperature (175 degrees C). On Pt/Al2O3, however, the propene consumption proceeded initially through selective catalytic reduction of NO, which took place at higher temperature (240 degrees C). In this way, propene combustion and consequently NO oxidation occurred at lower temperature on bimetallic catalysts than on Pt/Al2O3.
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| 36. |
- Auvray, Xavier, 1986, et al.
(author)
-
Sulfur Dioxide Exposure: A Way To Improve the Oxidation Catalyst Performance
- 2013
-
In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 52:41, s. 14556-14566
-
Journal article (peer-reviewed)abstract
- The oxidation of nitric oxide and propylene was studied over a model alumina-supported platinum catalyst. Two treatments (22 h at 250 degrees C and 2 h at 800 degrees C) involving sulfur dioxide were performed in order to understand the effect of SO2 aging. The role and stability of sulfur species stored during aging were investigated by the reduction of sulfated samples at 500 degrees C and temperature-programmed reduction (TPR) up to 800 degrees C. The low activity obtained after aging without reduction revealed the poisoning effect of surface sulfur species. The reduction at 500 degrees C released half of the surface species, which increased the catalytic activity for both NO and C3H6 oxidation. The TPR removed the most stable sulfur species and improved the activity during cooling. The catalyst aged in SO2 at high temperature showed the greatest activity for both reactions because of SO2 exposure and low sulfur storage.
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| 37. |
- Auvray, Xavier, 1986, et al.
(author)
-
The addition of alkali and alkaline earth metals to Pd/Al2O3 to promote methane combustion. Effect of Pd and Ca loading
- 2018
-
In: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 299, s. 212-218
-
Journal article (peer-reviewed)abstract
- Methane catalytic combustion was studied on Pd/Al2O3 catalysts modified with alkali and alkaline earth metals (K, Na, Ca and Ba). Temperature-programmed reactions were performed in flow reactor on washcoated monolithic samples. CO chemisorption was carried out and BET surface area was measured in order to characterize the catalysts. Addition of alkaline metals was either beneficial or detrimental for methane oxidation, depending on the catalyst composition and pretreatment. High loading of alkaline modifiers and cooling in reaction mixture increased the light-off temperature of methane oxidation. However, promotion was achieved by doping with calcium after cooling in inert atmosphere. Furthermore, calcium doping was more beneficial in presence of NO, which inhibits the methane oxidation. Higher Pd loading enhanced CH4 oxidation, whereas the effect of calcium depends on Ca and Pd loading. Indeed, the promotion by calcium was more pronounced on catalysts with 5% Pd than with 2.5% Pd. On 2.5% Pd catalyst, high Ca loading was detrimental for CH4 oxidation. In contrary, on 5% Pd catalyst, even 1.51 wt% calcium (the highest loading used) induced promotion, which demonstrates a correlation between Ca: Pd ratio and promotion/inhibition effect. Samples with a mass ratio of 0.15 showed the best activity.
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| 38. |
- Auvray, Xavier, 1986, et al.
(author)
-
The effect of gas composition during thermal aging on the dispersion and NO oxidation activity over Pt/Al2O3 catalyst
- 2012
-
In: CapoC 9, August 2012, Brussels, Belgium.
-
Conference paper (other academic/artistic)abstract
- The effect of aging atmosphere (Ar, H2, O2, SO2, SO2+O2) during thermal aging of Pt/Al2O3 model diesel oxidation catalysts was studied. More specifically, the impact of the aging on the NO oxidation activity and platinum dispersion was investigated. Thermal aging caused a decrease in dispersion and an increase in NO oxidation performance. However, the aging behavior was strongly correlated with the nature of the ageing atmosphere. Catalysts with similar dispersion could have very different NO oxidation activity, depending on which atmosphere that they were aged with.
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| 39. |
- Azis, Muhammad Mufti, 1983, et al.
(author)
-
Evaluation of H2 effect on NO oxidation over a diesel oxidation catalyst
- 2015
-
In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 179, s. 542-550
-
Journal article (peer-reviewed)abstract
- The influence of H2 on NO oxidation over Pt/Al2O3 as a model DOC catalyst was evaluated with various DOC feed mixtures. Discrimination of surface chemistry and exothermal effects due to addition of H2 was made based on differences in time scales of transient responses. H2 was proposed to retard Pt oxide formation mainly at low temperatures (ca.
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| 40. |
- Bergvall, Niklas, et al.
(author)
-
Upgrading of fast pyrolysis bio-oils to renewable hydrocarbons using slurry- and fixed bed hydroprocessing
- 2024
-
In: Fuel processing technology. - : Elsevier B.V.. - 0378-3820 .- 1873-7188. ; 253
-
Journal article (peer-reviewed)abstract
- Liquefaction of lignocellulosic biomass through fast pyrolysis, to yield fast pyrolysis bio-oil (FPBO), is a technique that has been extensively researched in the quest for finding alternatives to fossil feedstocks to produce fuels, chemicals, etc. Properties such as high oxygen content, acidity, and poor storage stability greatly limit the direct use of this bio-oil. Furthermore, high coking tendencies make upgrading of the FPBO by hydrodeoxygenation in fixed-bed bed hydrotreaters challenging due to plugging and catalyst deactivation. This study investigates a novel two-step hydroprocessing concept; a continuous slurry-based process using a dispersed NiMo-catalyst, followed by a fixed bed process using a supported NiMo-catalyst. The oil product from the slurry-process, having a reduced oxygen content (15 wt%) compared to the FPBO and a comparatively low coking tendency (TGA residue of 1.4 wt%), was successfully processed in the downstream fixed bed process for 58 h without any noticeable decrease in catalyst activity, or increase in pressure drop. The overall process resulted in a 29 wt% yield of deoxygenated oil product (0.5 wt% oxygen) from FPBO with an overall carbon recovery of 68%.
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| 41. |
- Bjerregaard, Joachim, 1996, et al.
(author)
-
Interpretation of H 2 -TPR from Cu-CHA Using First-Principles Calculations
- 2024
-
In: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 128:11, s. 4525-4534
-
Journal article (peer-reviewed)abstract
- Temperature-programmed reduction and oxidation are used to obtain information on the presence and abundance of different species in complex catalytic materials. The interpretation of the temperature-programmed reaction profiles is, however, often challenging. One example is H2 temperature-programmed reduction (H2-TPR) of Cu-chabazite (Cu-CHA), which is a material used for ammonia assisted selective catalytic reduction of NOx (NH3-SCR). The TPR profiles of Cu-CHA consist generally of three main peaks. A peak at 220 °C is commonly assigned to ZCuOH, whereas peaks at 360 and 500 °C generally are assigned to Z2Cu, where Z represents an Al site. Here, we analyze H2-TPR over Cu-CHA by density functional theory calculations, microkinetic modeling, and TPR measurements of samples pretreated to have a dominant Cu species. We find that H2 can react with Cu ions in oxidation state +2, whereas adsorption on Cu ions in +1 is endothermic. Kinetic modeling of the TPR profiles suggests that the 220 °C peak can be assigned to Z2CuOCu and ZCuOH, whereas the peaks at higher temperatures can be assigned to paired Z2Cu and Z2CuHOOHCu species (360 °C) or paired Z2Cu and Z2CuOOCu (500 °C). The results are in good agreement with the experiments and facilitate the interpretation of future TPR experiments.
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| 42. |
- Cheah, You Wayne, 1993, et al.
(author)
-
Role of transition metals on MoS 2 -based supported catalysts for hydrodeoxygenation (HDO) of propylguaiacol
- 2021
-
In: Sustainable Energy and Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 5:7, s. 2097-2113
-
Journal article (peer-reviewed)abstract
- Transition metal sulfides (TMSs) are typically used in the traditional petroleum refining industry for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) applications. Bio-oils require an upgrading process like catalytic hydrodeoxygenation (HDO) to produce advanced biofuels and chemicals. Herein, MoS /γ-Al O promoted by transition metals like nickel (Ni), copper (Cu), zinc (Zn), and iron (Fe) was evaluated for the HDO of a bio-oil model compound, 4-propylguaiacol (PG) in a batch reactor at 340 °C under 50 bar H pressure. The catalyst screening results showed that the sulfided Ni-promoted catalyst gave a high 94% yield of deoxygenated cycloalkanes, however for the sulfided Cu-promoted catalyst, 42% of phenolics remain in the reaction medium after 5 h. The results also revealed that the sulfided Zn and Fe-promoted catalysts gave a final yield of 16% and 19% at full PG conversion, respectively, for deoxygenated aromatics. A kinetic model considering the main side reactions was developed to elucidate the reaction pathway of demethoxylation and dehydroxylation of PG. The developed kinetic model was able to describe the experimental results well with a coefficient of determination of 97% for the Ni-promoted catalyst system. The absence of intermediates like 4-propylcyclohexanone and 4-propylcyclohexanol during the reaction implies that direct deoxygenation (DDO) is the dominant pathway in the deoxygenation of PG employing sulfided catalysts. The current work also demonstrated that the activity of the transition metal promoters sulfides for HDO of PG could be correlated to the yield of deoxygenated products from the hydrotreatment of Kraft lignin. 2 2 3 2
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| 43. |
- Cheah, You Wayne, 1993, et al.
(author)
-
Slurry co-hydroprocessing of Kraft lignin and pyrolysis oil over unsupported NiMoS catalyst: A strategy for char suppression
- 2023
-
In: Chemical Engineering Journal. - 1385-8947. ; 475
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Journal article (peer-reviewed)abstract
- Pyrolysis oil (PO) assisted Kraft lignin (KL) liquefaction over an unsupported NiMoS catalyst in a paraffin solvent was explored in this work. A paraffin solvent was used to represent hydrogenated vegetable oil (HVO) which is a biofuel. We have for the first time showed that when co-processing Kraft lignin with pyrolysis oil in a paraffin solvent the char formation could be completely suppressed. The complex composition of PO, containing various compounds with different functional groups, was able to aid the depolymerization pathways of lignin by obstructing the condensation path of reactive lignin derivatives. To further understand the role of different functional groups present in pyrolysis oil during lignin liquefaction, we investigate the co-hydroprocessing of Kraft lignin with various oxygenate monomers using unsupported NiMoS. 4-propylguaiacol (PG) was found to be the most efficient monomer for stabilizing the reactive lignin intermediates, resulting in a low char yield (3.7%), which was 4 times lower than the char production from Kraft lignin hydrotreatment alone. The suppressed rate of lignin fragment repolymerization can be attributed to the synergistic effect of functional groups like hydroxyl (-OH), methoxy (-OCH3), and propyl (-C3H7) groups present in PG. These groups were found to be able to stabilize the lignin depolymerized fragments and blocked the repolymerization routes enabling efficient lignin depolymerization. It was found that the presence of a co-reactant like PG during the heating period of the reactor acted as a blocking agent facilitating further depolymerization routes. Finally, a reaction network is proposed describing multiple routes of lignin hydroconversion to solid char, lignin-derived monomers, dimers, and oligomers, explaining why the co-processing of pyrolysis oil and Kraft lignin completely suppressed the solid char formation.
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| 44. |
- Cheah, You Wayne, 1993, et al.
(author)
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Thermal annealing effects on hydrothermally synthesized unsupported MoS2 for enhanced deoxygenation of propylguaiacol and kraft lignin
- 2021
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In: Sustainable Energy and Fuels. - 2398-4902. ; 5:20, s. 5270-5286
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Journal article (peer-reviewed)abstract
- Catalytic hydrodeoxygenation (HDO) is an important hydrotreating process that is used to improve the quality of bio-oils to produce biomass-derived fuel components and chemicals. Molybdenum disulfide (MoS2) has been widely used as a catalyst in hydrodesulfurization (HDS) applications for several decades, which can be further improved for effective unsupported catalyst synthesis. Herein, we studied a universally applicable post-annealing treatment to a hydrothermally synthesized MoS2 catalyst towards developing efficient unsupported catalysts for deoxygenation. The effect of the annealing treatment on the catalyst was studied and evaluated for HDO of 4-propylguaiacol (PG) at 300 °C with 50 bar H2 pressure. The annealing of the as-synthesized catalyst under nitrogen flow at 400 °C for 2 h was found to enhance the HDO activity. This enhancement is largely induced by the changes in the microstructure of MoS2 after the annealing in terms of slab length, stacking degree, defect-rich sites and the MoS2 edge-to-corner site ratio. Besides, the effect of hydrothermal synthesis time and acid addition combined with the annealing treatment on the MoS2 catalytic activity was also studied for the same model reaction. The annealed MoS2 with a synthesis time of 12 h under an acidic environment was found to have improved crystallinity and exhibit the highest deoxygenation degree among all the studied catalysts. An acidic environment during the synthesis was found to be crucial in facilitating the growth of MoS2 micelles, resulting in smaller particles that affected the HDO activity. The annealed unsupported MoS2 with the best performance for PG hydrodeoxygenation was further evaluated for the hydrotreatment of kraft lignin and demonstrated a high deoxygenation ability. The results also indicate a catalyst with high activity for deoxygenation and hydrogenation reactions can suppress char formation and favor a high lignin bio-oil yield. This research uncovers the importance of a facile pretreatment on unsupported MoS2 for achieving highly active HDO catalysts.
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| 45. |
- Cheah, You Wayne, 1993, et al.
(author)
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Upgrading of triglycerides, pyrolysis oil, and lignin over metal sulfide catalysts: A review on the reaction mechanism, kinetics, and catalyst deactivation
- 2023
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In: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437 .- 2213-2929. ; 11:3
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Research review (peer-reviewed)abstract
- Human activities such as burning fossil fuels for energy production have contributed to the rising global atmospheric CO2 concentration. The search for alternative renewable and sustainable energy sources to replace fossil fuels is crucial to meet the global energy demand. Bio-feedstocks are abundant, carbon-rich, and renewable bioresources that can be transformed into value-added chemicals, biofuels, and biomaterials. The conversion of solid biomass into liquid fuel and their further hydroprocessing over solid catalysts has gained vast interest in industry and academic research in the last few decades. Metal sulfide catalysts, a common type of catalyst being used in the hydroprocessing of fossil feedstocks, have gained great interest due to their low cost, industrial relevance, and easy implementation into the current refining infrastructures. In this review, we aim to provide a comprehensive overview that covers the hydrotreating of various bio-feedstocks like fatty acids, phenolic compounds, pyrolysis oil, and lignin feed using sulfided catalysts. The main objectives are to highlight the reaction mechanism/networks, types of sulfided catalysts, catalyst deactivation, and reaction kinetics involved in the hydrotreating of various viable renewable feedstocks to biofuels. The computational approaches to understand the application of metal sulfides in deoxygenation are also presented. The challenges and needs for future research related to the valorization of different bio-feedstocks into liquid fuels, employing sulfided catalysts, are also discussed in the current work.
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| 46. |
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| 47. |
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| 48. |
- DAWODY, JAZAER, 1959, et al.
(author)
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Sulfur Deactivation of Pt/SiO2, Pt/BaO/Al 2O3 and BaO/Al2O3 NOx Storage Catalysts: Influence of SO2 Exposure Conditio
- 2005
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In: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 234:1, s. 206-218
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Journal article (peer-reviewed)abstract
- Flow reactor experiments were performed to study the effect Of SO2 + O-2 and SO2 + H-2 exposures on the NOx storage performance of Pt/BaO/Al2O3 and BaO/Al2O3 catalysts. In addition, Pt/SiO2 samples were used to study the interaction between Pt and SO2 under the two exposure conditions. For BaO/Al2O3 the two SO2 exposure conditions caused similar deactivation of the NO, storage capacity, whereas for Pt/BaO/Al2O3 the decline in the NOx storage capacity was faster during the SO2 + H-2 exposure than for SO2 + O-2 exposure. The presence of Pt enhances the adsorption Of SO2 for both SO2 exposure conditions. Quantitative analysis of sulfur showed that exposure to SO2 + O-2 caused higher accumulation of sulfur in Pt/BaO/Al2O3 samples in comparison with SO2 + H-2 exposure. Thus there is no correlation between the total amount of adsorbed sulfur in the samples and the reduction of the NOx storage capacity, probably because of the adsorption of sulfur on sites not necessarily important for the NOx storage process.
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| 49. |
- De Abreu Goes, Jesus, 1989, et al.
(author)
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Chapter 5: Mechanism and Kinetics of NOx Storage
- 2018
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In: RSC Catalysis Series. - Cambridge : Royal Society of Chemistry. - 1757-6725. ; , s. 127-156
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Book chapter (other academic/artistic)abstract
- In this chapter, experimental studies and kinetic models are presented to elucidate the fundamental mechanisms for NOxstorage on the NOxstorage and reduction (NSR) catalysts. A well-accepted reaction pathway for NOxstorage includes, as an initial step, the oxidation of NO to NO2under lean conditions, and subsequently storage on the NOxstorage sites in the form of nitrites or nitrates. NO can also be stored directly in the presence of NO and oxygen, in the so-called nitrite route. However, the NOxstorage process is largely influenced by the primary gas components in the exhaust stream, such as CO2, H2O and SO2. In particular, significant attention has been focused on sulphur poisoning and the interaction of SO2with different NSR components due to its large potential of harming NSR catalyst activity. Finally, a kinetic model describing in detail the sulphur poisoning over a commercial LNT catalyst is discussed. The model can well describe the gradual deactivation of the catalyst during sulphur exposure.
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| 50. |
- De Abreu Goes, Jesus, 1989, et al.
(author)
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Correlation between Vehicle- and Rapid- Aged Commercial Lean NOx Trap Catalysts
- 2017
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In: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 10:4, s. 1613-1626
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Conference paper (other academic/artistic)abstract
- Even though substantial improvements have been made for the lean NOx trap (LNT) catalyst in recent years, the durability still remains problematic because of the sulfur poisoning and sintering of the precious metals at high operating temperatures. Hence, commercial LNT catalysts were aged and tested in order to investigate their performance and activity degradation compared to the fresh catalyst, and establish a proper correlation between the aging methods used. The target of this study is to provide useful information for regeneration strategies and optimize the catalyst management for better performance and durability. With this goal in mind, two different aging procedures were implemented in this investigation. A catalyst was vehicle-aged in the vehicle chassis dynamometer for 100000 km, thus exposed to real conditions. Whereas, an accelerated aging method was used by subjecting a fresh LNT catalyst at 800 °C for 24 hours in an oven under controlled conditions. Engine dynamometer studies were performed with a Volvo mid-sized diesel engine with the purpose of testing the NOx storage and reduction performance, as well as the THC and CO conversion activity of the catalysts under controlled conditions. The aged catalysts activity was shown to be significantly degraded, mainly at low working temperatures compared to the fresh LNT, and one reason for this could be limited NO oxidation. In addition, the oven-aged sample was found to be well correlated to the vehicle-aged catalyst. On top of that, several vehicle emission cycles were carried out in the vehicle chassis dynamometer with a 2.0 l Volvo XC90 diesel vehicle in order to study the catalysts performance under real driving conditions and monitor the gradual deterioration of the vehicle-aged catalyst during the vehicle aging testing.
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