1. |
- Abdelaziz, Omar Y., et al.
(författare)
-
Oxidative Depolymerisation of Lignosulphonate Lignin into Low-Molecular-Weight Products with Cu–Mn/δ-Al2O3
- 2019
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 62, s. 639-648
-
Tidskriftsartikel (refereegranskat)abstract
- Lignin depolymerisation receives great attention due to the pressing need to find sustainable alternatives to fossil sources for production of fuels and chemicals. In this study, alumina-supported Cu–Mn and Ni–Mo catalysts were tested for oxidative depolymerisation of a technical lignin stream—sodium lignosulphonates—to produce valuable low-molecular-weight aromatics that may be considered for applications in the fuels and chemicals sector. The reactions were performed at elevated temperature and oxygen pressure, and the product mixtures were analysed by size exclusion chromatography, two-dimensional nuclear magnetic resonance spectroscopy and supercritical fluid chromatography mass spectrometry. The best performance was obtained with Cu–Mn/δ-Al 2 O 3 , which was thoroughly characterised before and after use by nitrogen physisorption, scanning electron microscopy, energy dispersive spectroscopy, powder X-ray diffraction, thermal gravimetric analysis, inductively coupled plasma optical emission spectrometry and X-ray photoelectron spectroscopy. Major products identified were vanillin, p-hydroxybenzaldehyde, vanillic acid and p-hydroxybenzoic acid as well as smaller aliphatic aldehydes, acids and lactones.
|
|
2. |
- Abdulhamid, Hussam, 1974, et al.
(författare)
-
Influence of the type of reducing agent (H2, CO, C3H6 and C3H8) on the reduction of stored NOX in a Pt/BaO/Al2O3 model catalyst
- 2004
-
Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30-31:1-4, s. 161-168
-
Tidskriftsartikel (refereegranskat)abstract
- In this investigation, a comparative study for a NOx storage catalytic system was performed focusing on the parameters that affect the reduction by using different reductants (H2, CO, C3H6 and C3H8) and different temperatures (350, 250 and 150 degrees C), for a Pt/BaO/Al2O3 catalyst. Transient experiments show that H2 and CO are highly efficient reductants compared to C3H6 which is somewhat less efficient. H2 shows a significant reduction effect at relatively low temperature (150 degrees C) but with a low storage capacity. We find that C3H8 does not show any NOx reduction ability for NOx stored in Pt/BaO/Al2O3 at any of the temperatures. The formation of ammonia and nitrous oxide is also discussed.
|
|
3. |
- Adams, Emma, 1989, et al.
(författare)
-
Passive SCR: The effect of H2 to NO ratio on the formation of NH3 over alumina supported platinum and palladium catalysts
- 2016
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 59:10-12, s. 970-975
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the relationship between the H2:NO ratio and NH3 formation over alumina supported Pt and Pd catalysts. By kinetic studies and in situ infrared spectroscopy, we report that NH3 formation is not only sensitive to the catalyst formulation but equally dependent on the feed gas composition and tem- perature. Specifically, we identify that hydrogen plays an important role in the dissociation of NO at low tem- perature. We also show that the support material itself plays a vital role in the ammonia formation mechanism due to the redox behaviour of NO adsorption at low temperature. This was unexpected as the noble metal is generally considered to be the active phase for the reaction of NO and H2.
|
|
4. |
- Albertazzi, Simone, et al.
(författare)
-
Deactivation of a Ni-Based Reforming Catalyst During the Upgrading of the Producer Gas, from Simulated to Real Conditions
- 2011
-
Ingår i: Topics in catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 54:10, s. 746-754
-
Tidskriftsartikel (refereegranskat)abstract
- The deactivation of a nickel reforming catalyst during the upgrading of the producer gas obtained by gasification of lignocellulosic biomass was studied. The research involved several steps: the selective deactivation of the catalyst in a laboratory scale; the streaming of the catalyst with the producer gas of a downdraft and an oxygen/steam circulating fluidized bed (CFB) gasifier; and tests in a reformer placed in a slipstream of the CFB gasifier. The information obtained allowed to elucidate the catalyst deactivation mechanisms taking place during the reforming of the producer gas: physical deactivation by deposition of fine ashes, aerosol particulate or carbon; poisoning by H2S and HCl present in the gas phase and thermal sintering because of the high operation temperatures required to avoid the chemical deactivation. These physical and chemical effects depended on the composition of the biomass fuel.
|
|
5. |
- Andersson, Mike, et al.
(författare)
-
Investigations on the possibilities of a MISiCFET sensor system for OBD and combustion control utilizing different catalytic gate materials
- 2004
-
Ingår i: Topics in catalysis. - 1022-5528 .- 1572-9028. ; 30-31:1, s. 365-368
-
Tidskriftsartikel (refereegranskat)abstract
- Different catalytic materials, like Pt and Ir, applied as gate contacts on metal insulator silicon carbide field effect transistors — MISiCFET—facilitate the manufacture of gas sensor devices with differences in selectivity, devices which due to the chemical stability and wide band gap of SiC are suitable for high temperature applications. The combination of such devices in a sensor system, utilizing multivariate analysis/modeling, have been tested and some promising results in respect of monitoring a few typical exhaust and flue gas constituents, in the future aiming at on board diagnostics (OBD) and combustion control, have been obtained.
|
|
6. |
- Andonova, Stanislava, 1977, et al.
(författare)
-
Enhanced Low Temperature NOx Reduction Performance Over Bimetallic Pt/Rh-BaO Lean NOx Trap Catalysts
- 2013
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 56:1-8, s. 68-74
-
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.
|
|
7. |
- Barrientos, Javier, et al.
(författare)
-
Deactivation of Ni/gamma-Al2O3 Catalysts in CO Methanation : Effect of Zr, Mg, Ba and Ca Oxide Promoters
- 2017
-
Ingår i: Topics in catalysis. - : Springer. - 1022-5528 .- 1572-9028. ; 60:17-18, s. 1276-1284
-
Tidskriftsartikel (refereegranskat)abstract
- Catalyst deactivation is one of the major concerns in the production of substitute natural gas (SNG) via CO methanation. Catalysts in this application need to be active at low temperatures, resistant to polymeric carbon formation and stable at high temperatures and steam partial pressures. In the present work, a series of alumina-supported nickel catalysts promoted with Zr, Mg, Ba or Ca oxides were investigated. The catalysts were tested under low temperature CO methanation conditions in order to evaluate their resistance to carbon formation. The catalysts were also exposed to accelerated ageing conditions at high temperatures in order to study their thermal stability. The aged catalysts lost most of their activity mainly due to sintering of the support and the nickel crystallites. Apparently, none of these promoters had a satisfactory effect on the thermal resistance of the catalyst. Nevertheless, it was found that the presence of Zr can reduce the rate of polymeric carbon formation.
|
|
8. |
- Barrientos, Javier, et al.
(författare)
-
Fischer-Tropsch Synthesis Over Zr-Promoted Co/gamma-Al2O3 Catalysts
- 2017
-
Ingår i: Topics in catalysis. - : SPRINGER/PLENUM PUBLISHERS. - 1022-5528 .- 1572-9028. ; 60:17-18, s. 1285-1298
-
Tidskriftsartikel (refereegranskat)abstract
- Two Zr-modified alumina supports were synthetized containing the same amount of Zr but a different distribution of this modifier over the alumina surface. These supports, together with the unmodified alumina carrier, were used to prepare three cobalt-based catalysts which were characterized and tested under relevant Fischer-Tropsch conditions. The three catalysts presented very similar porosity and cobalt dispersion. The addition of Zr nor its distribution enhanced the catalyst reducibility. The catalyst activity was superior when using a carrier consisting of large ZrO2 islands over the alumina surface. The use of a carrier with a homogeneous Zr distribution had however, a detrimental effect. Moreover, a faster initial deactivation rate was observed for the Zr-promoted catalysts, fact that may explain this contradictory effect of Zr on activity. Finally, the addition of Zr showed a clear enhancement of the selectivity to long chain hydrocarbons and ethylene, especially when Zr was well dispersed.
|
|
9. |
- Becker, Elin, 1981, et al.
(författare)
-
Methane oxidation over alumina and ceria supported platinum
- 2009
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 52:13-20, s. 1957-1961
-
Tidskriftsartikel (refereegranskat)abstract
- Oxidation of methane over Pt/Al(2)O(3) and Pt/CeO(2) catalysts was studied by transient gas-flow reactor and in situ FTIR spectroscopy experiments. The Pt/CeO(2) catalyst is generally more active, indicating more efficient CH(4) dissociation, especially during oxygen pulsing, which likely is connected to the higher oxygen storage capacity/mobility of ceria.
|
|
10. |
- Bernas, Andreas, et al.
(författare)
-
Catalytic transformation of abietic acid to hydrocarbons
- 2012
-
Ingår i: Topics in catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 55:7-10, s. 673-679
-
Tidskriftsartikel (refereegranskat)abstract
- Catalytic and thermal conversion of abietic acid was investigated in a laboratory scale high-pressure autoclave. Fractionation of crude tall oil produces rosin acids of which abietic acid is the main compound. Tall oil rosin acid, a forest product industry residue, is an abundant, inexpensive and chemically desirable feedstock for production of lighter hydrocarbons that can be used as diesel fuel additives. The carboxylic acid functionality of the main reactant, abietic acid, must first be removed, followed by double bond hydrogenation of the remaining aromatic rings. In this study, a number of catalytic and non-catalytic reaction steps in the conversion of abietic acid were investigated. The aim was to study hydrogenation and decarboxylation reactions of abietic acid in order to produce lighter hydrocarbons. The experiments were performed by using toluene as a solvent as well as with neat abietic acid, in the absence of any solvent. Hydrogenation of abietic acid to tetrahydroabietic acid in toluene was successfully performed over palladium on carbon catalyst at the temperature range of 100-200 A degrees C and at 30 bar hydrogen pressure. Thermal non-catalytic decarboxylation of abietic acid in toluene takes place at 200-300 A degrees C resulting in one main product. The hydrocarbon products were further hydrogenated under hydrogen pressure. Catalytic decarboxylation of abietic acid in toluene was achieved over 5 wt% Ru/C, giving a wider product distribution than thermal decarboxylation.
|
|
11. |
- Birgersson, Henrik, et al.
(författare)
-
Deactivation and regeneration of spent three-way automotive exhaust gas catalysts (TWC)
- 2004
-
Ingår i: Topics in catalysis. - 1022-5528 .- 1572-9028. ; 30-1:1-4, s. 433-437
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of oxidation, oxy-chlorination and reduction treatments at elevated temperatures on the dispersion of palladium (Pd) and rhodium (Rh) for commercially aged three-way automotive exhaust gas catalysts (TWC) has been investigated. The catalytic activity of treated samples was compared with a reference sample, which was taken from the corresponding aged TWC and tested using a 'mini-cuts' reactor simulating real driving conditions. In the case of oxygen, the improvement of the noble metal dispersion on the catalysts was dependent on the noble metal loading and the degree of metal sintering. Adding chlorine to the oxygen atmosphere facilitates the restructuring of the metals with an improved increase in the noble metal dispersion. The temperature and the composition of the gas used during these thermal treatments proved to be of importance not only to increase the metal dispersion, but also to prevent possible losses of noble metals, in the form of volatile MOxCly compounds. TEM-EDS techniques indicated changes in the size of the largest noble metal agglomerates of Lip to 100 nm in size after thermal gas treatment. BET porosity and XRD analyses were employed to investigate restructuring of the washcoat and showed a decrease in pore size distribution and an increase in surface area.
|
|
12. |
- Bisagni, Serena, et al.
(författare)
-
Exploring the Substrate Specificity and Enantioselectivity of a Baeyer-Villiger Monooxygenase from Dietzia sp D5: Oxidation of Sulfides and Aldehydes
- 2014
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 57:5, s. 366-375
-
Tidskriftsartikel (refereegranskat)abstract
- Baeyer-Villiger monooxygenases (BVMOs) are valuable enzymes for specific oxyfunctionalization chemistry. They catalyze the oxidation of ketones to esters, but are also capable of oxidizing other chemical functions, namely aldehydes and heteroatoms such as sulfur, nitrogen, selenium and boron. The oxidation specificity and enantioselectivity of a newly characterized BVMO (BVMO4) from a strain of Dietzia towards sulfide- and aldehyde substrates have been studied. BVMO4 could react with sulfides containing an aromatic group. The presence of a substituent on the aromatic group was tolerated when they were in the meta- and para position and the oxidations yielded predominantly the (R)-sulfoxides. Similarly, BVMO4 displayed a higher activity for aldehydes containing a phenyl group, but long aliphatic aldehydes, namely octanal and decanal, were also accepted as substrate by this enzyme. The major oxidation products of the aldehyde substrates were the respective carboxylic acids in contrast to formate ester that was obtained in most of the previous reports. The Baeyer-Villiger oxidation of the substrate 2-phenylpropionaldehyde was studied in further detail and the corresponding acid product was obtained with good regio- and enantioselectivity. This is a unique feature for BVMO4 and is of great interest for further exploration of an alternative biocatalytic process.
|
|
13. |
- Bleken, Bjørn Tore L., et al.
(författare)
-
Unit cell thick nanosheets of zeolite H-ZSM-5 : Structure and activity
- 2013
-
Ingår i: Topics in catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 56:9-10, s. 558-566
-
Tidskriftsartikel (refereegranskat)abstract
- nosheets of zeolite H-ZSM-5 were synthesized and characterized by X-ray diffraction, transmission electron microscopy (TEM), N2- physisorption, FT-IR spectroscopy, 27Al and 29Si MAS NMR spectroscopy in addition to catalytic testing in conversion of methanol to hydrocarbons (MTH). It was found that Rietveld analysis, involving anisotropic broadening parameters, gave average crystallite dimensions in good agreement with TEM images. The selectivities in MTH is intact in the mesoporous nanosheet H-ZSM-5 with the largest difference being a higher C3/C2 ratio compared to regular H-ZSM-5.
|
|
14. |
- Blomberg, S., et al.
(författare)
-
Comparison of AP-XPS and PLIF Measurements during CO Oxidation over Pd Single Crystals
- 2016
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 59:5-7, s. 478-486
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction between the gas-phase molecules and a catalyst surface is crucial for the surface structure and are therefore important to consider when the active phase of a catalyst is studied. In this study we have used two different techniques to study the gas phase during CO oxidation over Pd single crystals. Gas-phase imaging by planar laser-induced fluorescence (PLIF) shows that a spherical boundary layer with a decreasing gradient of CO2 concentration out from the surface, is present close to the surface when the Pd crystal is highly active. Within this boundary layer the gas composition is completely different than that detected at the outlet of the chamber. The PLIF images of the gas-phase distribution are used to achieve a better understanding of the gas composition between the surface and the detector of a set-up for ambient pressure X-ray photoelectron spectroscopy (AP-XPS), a common technique for surface structure determination of model catalysts. The results show that also the gas-phase peaks present in the AP-XPS spectra truly represent the gas closest to the surface, which facilitates the interpretation of the AP-XPS spectra and thereby also the understanding of the mechanism behind the reaction process.
|
|
15. |
- Bounechada, Djamela, 1984, et al.
(författare)
-
Enhanced methane conversion under periodic operation over a Pd/Rh based TWC in the exhausts from NGVs
- 2013
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 56:1-8, s. 372-377
-
Tidskriftsartikel (refereegranskat)abstract
- The enhancement of methane oxidation performances under periodic operation over a commercial Pd–Rh based three way catalyst (TWC) is investigated at different temperatures. Results confirm that under conditions with periodic oscillating feed around stoichiometry (λ = 1 ± 0.02), higher and more stable CH4 conversion are obtained than under conditions with constant stoichiometric feed. In particular higher CH4 conversion is obtained in the rich part of the cycle than in the lean one, the difference being more pronounced at high temperature. A narrow turning point for the TWC activity is finally observed under slightly rich conditions, which is characterised by a marked increase of CH4 conversion, paralleled by total consumption of O2 and NO and formation of small amounts of CO, H2 and NH3. Results suggest that the oxidation state of palladium plays a key role in the observed enhancement of catalyst performances.
|
|
16. |
- Brandin, Jan, 1958-, et al.
(författare)
-
Poisoning of SCR Catalysts used in Municipal Waste Incineration Applications
- 2017
-
Ingår i: Topics in catalysis. - : Springer. - 1022-5528 .- 1572-9028. ; 60:17-18, s. 1306-1316
-
Tidskriftsartikel (refereegranskat)abstract
- A commercial vanadia, tungsta on titania SCRcatalyst was poisoned in a side stream in a waste incinerationplant. The effect of especially alkali metal poisoning was observed resulting in a decreased activity at long times of exposure. The deactivation after 2311 h was 36% whilet he decrease in surface area was only 7.6%. Thus the major cause for deactivation was a chemical blocking of acidic sites by alkali metals. The activation–deactivation model showed excellent agreement with experimental data. The model suggests that the original adsorption sites, from the preparation of the catalyst, are rapidly deactivated but are replaced by a new population of adsorption sites due to activation of the catalyst surface by sulphur compounds (SO2, SO3) in the flue gas.
|
|
17. |
- Bäckvall, Jan-Erling
(författare)
-
Preface
- 2010
-
Ingår i: Topics in catalysis. - New York : Springer. - 1022-5528 .- 1572-9028. ; 53:13-14, s. 831-831
-
Tidskriftsartikel (refereegranskat)
|
|
18. |
- Carlsson, Per-Anders, 1972, et al.
(författare)
-
Low-temperature CO oxidation over a Pt/Al2O3 monolith catalyst investigated by step-response experiments and simulations
- 2004
-
Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30/31:1-4, s. 375-381
-
Tidskriftsartikel (refereegranskat)abstract
- The ignitionextinction processes for CO oxidation over a Pt/Al2O3 monolith catalyst have been studied by flow-reactor experiments and simulations. The study was performed by stepwise changes of the inlet O2 concentration ranging 020 vol% while the CO concentration and the inlet gas temperature were kept constant at 1.0 vol% and 423 K, respectively. Several features observed experimentally are qualitatively simulated with our model: (i) the ignition of the CO oxidation demands 8.0vol% O2 (ii) corresponding to a catalyst ignition temperature of 433 K (due to the exothermicity of the reaction) and (iii) occurs in the rear part of the monolith where (iv) a local reaction zone is formed which (v) moves towards the reactor inlet as a function of time on stream. Additionally, the simulations show first order kinetic phase transitions, i.e. rapid adsorbate concentration changes, where the catalyst surface is predominantly CO covered in the low reactive state and almost completely oxygen covered in the high reactive state. For the ignition process the kinetic phase transition occurs after the actual catalytic ignition. However, the extinction process is more difficult to simulate dynamically without changing the model parameters for O2 adsorption in the low and high reactive state, respectively. The influence of diffusion limitations and the role of formation of a less reactive Pt state under oxidising conditions is discussed.
|
|
19. |
- Carlsson, Per-Anders, 1972, et al.
(författare)
-
Periodic control for improved low-temperature catalytic activity
- 2001
-
Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 16-17:1-4, s. 343-347
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of transient changes in the gas composition on the low-temperature activity of a commercial three-way catalyst and a Pt/Al2O3 model catalyst has been studied. By introducing well-controlled periodic O2 pulses to simple gas mixtures of CO or C3H6 (in N2), a substantial improvement of the low temperature oxidation activity was observed for both catalysts. The reason for low activity at low temperatures is normally attributed to self-poisoning by CO or hydrocarbons. The improved catalytic performance observed here is suggested to origin from the transients causing a surface reactant composition that is favourable for the reaction rate.
|
|
20. |
- Carlsson, Per-Anders, 1972, et al.
(författare)
-
Virtual control for high conversion of methane over supported Pt
- 2009
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 52:13-20, s. 1962-1966
-
Tidskriftsartikel (refereegranskat)abstract
- A transient model for oxidation of methane over Pt/Al2O3 monolith catalysts has been developed by rigorous consideration of mass- and heat transport and mean-field treatment of the reaction kinetics. By coupling a virtual regulator using the reactant slip, methane or oxygen partial pressures, or oxygen surface coverage as feedback variable(s) as such or in combinations for control of feed composition, the influence of gas composition changes on the methane conversion has been investigated.
|
|
21. |
- Chávez, Georgina, et al.
(författare)
-
Baeyer-Villiger Oxidation of Cyclohexanone in Aqueous Medium with In Situ Generation of Peracid Catalyzed by Perhydrolase CLEA
- 2014
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 57:5, s. 349-355
-
Tidskriftsartikel (refereegranskat)abstract
- A perhydrolase, immobilized as a cross linked enzyme aggregate (CLEA), was employed to catalyze the in situ formation of peracetic acid (PAA) from ethylene glycol diacetate (EGDA) and hydrogen peroxide. The produced PAA was used for the Baeyer-Villiger oxidation of cyclohexanone, which afforded caprolactone in 63 % yield. The effect of type and amount of acyl donor, solvent, pH, temperature and ratio of cyclohexanone to hydrogen peroxide on the production of caprolactone was studied. The highest caprolactone yield was obtained with 100 mM EGDA as the acyl donor at pH 6 and room temperature using a ratio of cyclohexanone to hydrogen peroxide ratio of 1:4. Interestingly, the perhydrolase CLEA exhibited the highest activity in aqueous medium in contrast to the well studied lipase B from Candida antarctica. The perhydrolase CLEA proved to be a very efficient catalyst; the K (m) and V-max values were 118 mM and 56.3 mu mol min(-1), respectively.
|
|
22. |
- Chen, Lin, 1990, et al.
(författare)
-
Interpretation of NH 3 -TPD Profiles from Cu-CHA Using First-Principles Calculations
- 2019
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 62:1-4, s. 93-99
-
Tidskriftsartikel (refereegranskat)abstract
- Temperature-programmed desorption (TPD) with ammonia is widely used for zeolite characterization revealing information on acidity and adsorption sites. The interpretation of TPD measurements is, however, often challenging. One example is the NH 3 -TPD profile from Cu-chabazite (Cu-CHA) which generally is deconvoluted in three peaks with contributions from NH 3 on Lewis acid sites, copper sites and Brønsted acid sites. Here, we use density functional theory calculations combined with kinetic simulations to analyze this case. We find a large number of possible species, giving rise to overlapping features in the NH 3 -TPD. The experimental low-temperature peak (below 200∘C) is assigned to NH 3 desorption from Lewis acid sites together with NH 3 desorption from a [Cu(II)(OH)(NH3)3]+ complex. The intermediate-temperature peak (250-350∘C) is attributed to decomposition of a linear [Cu(I)(NH3)2]+ complex and a residual from [Cu(II)(OH)(NH3)3]+. The high-temperature peak is predicted to have contributions from Brønsted acid sites (NH4+), [Cu(I)NH3]+ and [Cu(II)(NH3)4]2+. The present work shows that NH 3 -TPD from Cu-CHA can be reconciled with copper complexes as NH 3 storage sites.
|
|
23. |
|
|
24. |
- De Gracia Triviño, Juan Angel, et al.
(författare)
-
The Role of Counterions in Intermolecular Radical Coupling of Ru-bda Catalysts
- 2022
-
Ingår i: Topics in catalysis. - : Springer Nature. - 1022-5528 .- 1572-9028. ; 65:1-4, s. 383-391
-
Tidskriftsartikel (refereegranskat)abstract
- Intermolecular radical coupling (also interaction of two metal centers I2M) is one of the main mechanisms for O-O bond formation in water oxidation catalysts. For Ru(bda)L-2 (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylate, L = pyridine or similar nitrogen containing heterocyclic ligands) catalysts a significant driving force in water solution is the hydrophobic effects driven by the solvent. The same catalyst has been successfully employed to generate -N2 from ammonia, also via I2M, but here the solvent was acetonitrile where hydrophobic effects are absent. We used a classical force field for the key intermediate [(RuN)-N-VI(bda)(py)(2)](+) to simulate the dimerization free energy by calculation of the potential mean force, in both water and acetonitrile to understand the differences and similarities. In both solvents the complex dimerizes with similar free energy profiles. In water the complexes are essentially free cations with limited ion paring, while in acetonitrile the ion-pairing is much more significant. This ion-pairing leads to significant screening of the charges, making dimerization possible despite lower solvent polarity that could lead to repulsion between the charged complexes. In water the lower ion pairing is compensated by the hydrophobic effect leading to favorable dimerization despite repulsion of the charges. A hypothetical doubly charged [(RuIN)-I-VI(bda)py(2)](2+) was also studied for deeper understanding of the charge effect. Despite the double charge the complexes only dimerized favorably in the lower dielectric solvent acetonitrile, while in water the separated state is more stable. In the doubly charged catalyst the effect of ion-pairing is even more pronounced in acetonitrile where it is fully paired similar to the 1+ complex, while in water the separation of the ions leads to greater repulsion between the two catalysts, which prevents dimerization.
|
|
25. |
- Engvall, Klas, et al.
(författare)
-
Upgrading of raw gas from biomass and waste gasification : Challenges and opportunities
- 2011
-
Ingår i: Topics in catalysis. - : Springer-Verlag New York. - 1022-5528 .- 1572-9028. ; 54:13-15, s. 949-959
-
Forskningsöversikt (refereegranskat)abstract
- The depletion of fossil fuel-based resources and concerns for increasing emissions of CO2 call for newways of producing environmentally- friendly substitutes for motor fuels and chemicals. Thermo-chemical conversion of biomass andwaste using gasification is a strong candidate tomeet these challenges. For efficient and cost-effective application of this technique, novel solutions for hot gas cleaning are needed. This review highlights some important areas for improvement of upgrading technologies for pressurised fluidised bed gasification systems using biomass as a fuel.
|
|