| 1. |
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| 2. |
- Auvray, Xavier, 1986, et al.
(författare)
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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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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 129, s. 517-527
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Tidskriftsartikel (refereegranskat)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. |
- Fridell, Erik, 1963, et al.
(författare)
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Fundamental studies of NOx storage catalysis
- 2002
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Ingår i: EUCHEM Conference on Environmental Catalysis, Hindås, Sweden, November 27-December 1, 2002.
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Konferensbidrag (refereegranskat)
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| 4. |
- Fridell, Erik, 1963, et al.
(författare)
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Model studies of NOx storage
- 2001
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Ingår i: ENVICAT2001, Amolfi, Italy, May 2-6, 2001.
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Konferensbidrag (refereegranskat)
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| 5. |
- Fridell, Erik, 1963, et al.
(författare)
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Model studies of NOx storage and sulphur deactivation of NOx storage catalysts
- 2001
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Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 16-17:1-4, s. 133-137
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Platinum oxidation and sulphur deactivation in NOx storage catalysts
- 2004
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Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30-31:1-4, s. 143-146
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Chemical poisoning by zinc and phosphorous of Pt/Ba/Al2O3 NOx storage catalysts
- 2019
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Ingår i: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 571, s. 158-169
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Gas-phase phosphorous poisoning of a Pt/Ba/Al2O3 NOx storage catalyst
- 2018
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 8:4
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Removal of Inorganic Impurities in the Fast Pyrolysis Bio-oil Using Sorbents at Ambient Temperature
- 2024
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Ingår i: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 38:1, s. 414-4254
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Evaluation of kraft and hydrolysis lignin hydroconversion over unsupported NiMoS catalyst
- 2023
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 453
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Towards stable nickel catalysts for selective hydrogenation of biomass-based BHMF into THFDM
- 2023
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Ingår i: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437 .- 2213-2929. ; 11:2
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Ethanol acutely decreases astroglial gap junction permeability in primary cultures from defined brain regions
- 2004
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Ingår i: Neurochemistry International. - : Elsevier BV. - 0197-0186. ; 45:7, s. 971-978
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Addiction biology. - : Wiley. - 1369-1600 .- 1355-6215. ; 16:1, s. 43-54
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Lactate contributes to ammonia-mediated astroglial dysfunction during hyperammonemia.
- 2009
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Ingår i: Neurochemical research. - : Springer Science and Business Media LLC. - 1573-6903 .- 0364-3190. ; 34:3, s. 556-65
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Chemical deactivation by phosphorous under lean hydrothermal conditions over Cu/BEA NH3-SCR catalysts
- 2014
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 147, s. 251-263
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Enhanced Low Temperature NOx Reduction Performance Over Bimetallic Pt/Rh-BaO Lean NOx Trap Catalysts
- 2013
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 56:1-8, s. 68-74
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Mechanistic investigations of the promoting role of Rh on the NSR performance of NOx storage BaO-based catalysts
- 2013
-
Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 132, s. 266-281
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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
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Ingår i: Molecular Catalysis. - : Elsevier BV. - 2468-8231. ; 436, s. 43-52
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Tidskriftsartikel (refereegranskat)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.
(författare)
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The effect of iron loading and hydrothermal aging on one-pot synthesized Fe/SAPO-34 for ammonia SCR
- 2016
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 180, s. 775-787
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Journal of Medical Internet Research. - : JMIR Publications. - 1438-8871. ; 23:3
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Investigating the effect of Fe as a poison for catalytic HDO over sulfided NiMo alumina catalysts
- 2018
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 227, s. 240-251
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Kinetic study of hydrodeoxygenation of stearic acid as model compound for renewable oils
- 2019
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 364, s. 376-389
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Tidskriftsartikel (refereegranskat)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.
(författare)
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The role of catalyst poisons during hydrodeoxygenation of renewable oils
- 2021
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 367, s. 28-42
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Tidskriftsartikel (refereegranskat)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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