| 1. |
- Atakan, Aylin, et al.
(författare)
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Time evolution of the CO2 hydrogenation to fuels over Cu-Zr-SBA-15 catalysts
- 2018
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 362, s. 55-64
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Tidskriftsartikel (refereegranskat)abstract
- Time evolution of catalytic CO2 hydrogenation to methanol and dimethyl ether (DME) has been investigated in a high-temperature high-pressure reaction chamber where products accumulate over time. The employed catalysts are based on a nano-assembly composed of Cu nanoparticles infiltrated into a Zr doped SiOx mesoporous framework (SBA-15): Cu-Zr-SBA-15. The CO2 conversion was recorded as a function of time by gas chromatography-mass spectrometry (GC-MS) and the molecular activity on the catalyst’s surface was examined by diffuse reflectance in-situ Fourier transform infrared spectroscopy (DRIFTS). The experimental results showed that after 14 days a CO2 conversion of 25% to methanol and DME was reached when a DME selective catalyst was used which was also illustrated by thermodynamic equilibrium calculations. With higher Zr content in the catalyst, greater selectivity for methanol and a total 9.5% conversion to methanol and DME was observed, yielding also CO as an additional product. The time evolution profiles indicated that DME is formed directly from methoxy groups in this reaction system. Both DME and methanol selective systems show the thermodynamically highest possible conversion.
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| 2. |
- Behravesh, Erfan, et al.
(författare)
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Synthesis and characterization of Au nano particles supported catalysts for partial oxidation of ethanol : Influence of solution pH, Au nanoparticle size, support structure and acidity
- 2017
-
Ingår i: Journal of Catalysis. - : Elsevier. - 0021-9517 .- 1090-2694. ; 353, s. 223-238
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Tidskriftsartikel (refereegranskat)abstract
- Partial oxidation of ethanol to acetaldehyde was carried out over gold catalysts supported on various oxides and zeolites by deposition precipitation. The special focus of this work was on the influence of H-Y zeolite surface charge on Au cluster size and loading linking it to activity and selectivity in ethanol oxidation and comparing with other studied catalysts. The catalysts were characterized by nitrogen physisorption, transmission electron microscopy (TEM), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDXA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and zeta potential measurements. pH of the solution governed the Au NPs size within the range of 5.8–13.2 nm with less negatively charged surfaces leading to formation of smaller clusters. Au loading on H-Y zeolite with silica to alumina ratio of 80 was increased by raising the pH. In fact, H-Y-12 and H-Beta-25 were selective towards diethyl ether while acetaldehyde was the prevalent product on less acidic H-Y-80. The results demonstrated strong dependency of the catalytic activity on the Au cluster size. Namely turn over frequency (TOF) decreased with an increase in metal size from 6.3 to 9.3 nm on H-Y-80. Selectivity towards acetaldehyde and ethyl acetate did not change significantly on H-Y-80 within 6.3–9.3 nm Au particle size range. On Al2O3 support, however, selectivity towards acetaldehyde increased considerably upon diminishing Au average particle size from 3.7 to 2.1 nm.
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| 3. |
- Chen, Lin, 1990, et al.
(författare)
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Activation of oxygen on (NH3–Cu–NH3)+ in NH3-SCR over Cu-CHA
- 2018
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 358, s. 179-186
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Tidskriftsartikel (refereegranskat)abstract
- Cu-CHA materials are efficient catalysts for NH 3 –SCR of NO x in oxygen excess. A crucial step in the reaction is oxygen (O 2 ) activation, which still is not well understood. Density functional theory calculations in combination with ab initio thermodynamics and molecular dynamics are here used to study O 2 dissociation on Cu(NH 3 ) 2 + species, which are present under NH 3 –SCR conditions. Direct dissociation of O 2 is found to be facile over a pair of Cu(NH 3 ) 2 + complexes whereas dissociation on a single Cu(NH 3 ) 2 + species is unlikely due to a high activation energy. The presence of NO promotes oxygen dissociation on both single and pairs of Cu(NH 3 ) 2 + complexes. Nitrites and nitrates are easily formed as O 2 dissociates, and NO adsorption over nitrates leads to facile formation of NO 2 . The results stress the importance of ligand-stabilized Cu species in Cu-CHA catalysts for NH 3 –SCR.
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| 4. |
- Fashandi, Hossein, et al.
(författare)
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Applicability of MOS structures in monitoring catalytic properties, as exemplified for monolayer-iron-oxide-coated porous platinum films
- 2016
-
Ingår i: Journal of Catalysis. - : Elsevier. - 0021-9517 .- 1090-2694. ; 344, s. 583-590
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Tidskriftsartikel (refereegranskat)abstract
- Metal Oxide Semiconductor (MOS) capacitor devices comprised of monolayer iron oxide-coated as well as non-coated polycrystalline Pt deposited on oxidized silicon carbide substrates have been fabricated and their usefulness as realistic model systems in catalyst studies development was evaluated. The CO oxidation characteristics of both iron oxide- and non-coated Pt catalysts were investigated using mass spectrometry, monitoring the carbon dioxide production rate for different combinations of carbon monoxide (CO) and oxygen concentrations at various temperatures. Additionally, the output capacitance of the MOS model catalysts was recorded for each individual CO oxidation activity. A low-temperature shift in CO oxidation characteristics for the monolayer-coated compared to the non-coated Pt catalysts was observed, similar to that previously reported for monolayer iron oxide grown on single-crystalline Pt substrates. A strong correlation between the output capacitance of the MOS structures and the CO oxidation characteristics was found for both monolayer- and non-coated model catalysts. Furthermore, the devices exhibit retained MOS electrical output and CO oxidation characteristics as well as an unaffected catalyst surface composition, as confirmed by photoelectron spectroscopy, even after 200 h of continuous model catalyst operation. In addition to the implications on practical applicability of monolayer iron oxide coating on widely used polycrystalline Pt films in real-world catalysts and sensors, the findings also point to new possibilities regarding the use of MOS model systems for in situ characterization, high throughput screening, and tailoring of e.g. catalyst- and fuel-cell-electrode materials for specific applications.
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| 5. |
- Garlisi, Corrado, et al.
(författare)
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N-TiO2/Cu-TiO2 double-layer films : Impact of stacking order on photocatalytic properties
- 2017
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Ingår i: Journal of Catalysis. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0021-9517 .- 1090-2694. ; 353, s. 116-122
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we report for the first time a unique configuration of N-doped and Cu-doped TiO2 bilayer. The activity of TiO2 was improved by combining Cu- and N-doping in a layered thin-film structure. The impact of the stacking order was studied, pointing out how the best arrangement is by far the one with Cu-TiO2 as the top layer. The results reveal a unique and simple way to enhance the photocatalytic response of TiO2 in the visible domain.
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| 6. |
- Hus, Matej, 1988, et al.
(författare)
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Dipole effect on ethylene epoxidation: Influence of alkali metals and chlorine
- 2018
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 363, s. 18-25
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Tidskriftsartikel (refereegranskat)abstract
- Ethylene epoxidation is one of the most important selective oxidation reactions in industry and is almost invariably carried out on silver catalysts. Empirically it is known that moderate selectivity of silver can be greatly enhanced with cesium and chlorine dopants, whereas a mechanistic understanding of the underlying reason remains elusive. In this work, we present a first-principles explanation of the dipole effect on reaction selectivity, which could, in principle, be effected by alkali metals. We show that, on a silver surface, alkali metals work in a similar fashion thanks to their low electronegative character. The selectivity is impacted by inducing electric dipoles on the catalytic surface, whereas the electronic properties of the catalyst remain largely unperturbed. Cesium, as the least electronegative metal, shows the most pronounced effect. This effect is shown to persist when alkali metals are treated as “naked” atoms or, more realistically, when oxidized. Additionally, alkali metals increase activity of the catalyst by favoring the rate-determining step of oxygen dissociation. Chlorine, which is strongly electronegative, acts differently. Subsurface chlorine would increase selectivity through the same mechanism, while surface chlorine stabilizes alkali metals and moderately increases selectivity. Interplay of both dopants is needed to precisely tailor the catalyst for the best performance.
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| 7. |
- Intikhab, Saad, et al.
(författare)
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Stoichiometry and surface structure dependence of hydrogen evolution reaction activity and stability of MoxC MXenes
- 2019
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Ingår i: Journal of Catalysis. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0021-9517 .- 1090-2694. ; 371, s. 325-332
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Tidskriftsartikel (refereegranskat)abstract
- The exploration of non-precious catalysts for the hydrogen evolution reaction (HER) remains critical in the commercialization of electrochemical energy storage and conversion technologies. Two-dimensional transitional metal carbides called MXenes have been found to have great potential as electrocatalysts for HER. In this work, we synthesize two molybdenum-based MXenes: Mo1.33CTz and Mo2CTz, and measure their HER activity and operational durability. The ordered divacancies on the basal planes of Mo1.33CTz cause a marked decrease in HER activity compared to Mo2CTz. The stoichiometry and atomic surface structure of MXenes is found to be critically important for catalytic activity while having less of an impact on operational durability. This work provides insight for the development of active 2D materials, in general and MXenes in particular for HER and other technologically relevant electrochemical reactions. (C) 2019 Elsevier Inc. All rights reserved.
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| 8. |
- Konwar, Lakhya Jyoti, et al.
(författare)
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Shape selectivity and acidity effects in glycerol acetylation with acetic anhydride : selective synthesis of triacetin over Y-zeolite and sulfonated mesoporous carbons
- 2015
-
Ingår i: Journal of Catalysis. - : Elsevier. - 0021-9517 .- 1090-2694. ; 329, s. 237-247
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Tidskriftsartikel (refereegranskat)abstract
- Abstract 100% triacetin selectivity was achieved in glycerol acetylation with acetic anhydride in 20–50 min in the presence of catalytic amounts of mesoporous sulfonated carbons and zeolite H-Y. Experimental results obtained over a range of solid acids with varying structure and acidic properties indicate that selectivity to triacetin was influenced mainly by the pore structure and catalyst surface acid site density. The shape selectivity effect over microporous zeolites was verified from the molecular dimensions of glycerol, monoacetin, diacetin and triacetin obtained from DFT calculations; on the contrary in mesoporous catalyst surface acid site density was responsible for determining triacetin selectivity.
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| 9. |
- Kwong, Wai Ling, et al.
(författare)
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High-performance iron (III) oxide electrocatalyst for water oxidation in strongly acidic media
- 2018
-
Ingår i: Journal of Catalysis. - : Academic Press. - 0021-9517 .- 1090-2694. ; 365, s. 29-35
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Tidskriftsartikel (refereegranskat)abstract
- Stable and efficient oxygen evolution reaction (OER) catalysts for the oxidation of water to dioxygen in highly acidic media are currently limited to expensive noble metal (Ir and Ru) oxides since presently known OER catalysts made of inexpensive earth-abundant materials generally suffer anodic corrosion at low pH. In this study, we report that a mixed-polymorph film comprising maghemite and hematite, prepared using spray pyrolysis deposition followed by low-temperature annealing, showed a sustained OER rate (>24 h) corresponding to a current density of 10 mA cm−2 at an initial overpotential of 650 mV, with a Tafel slope of only 56 mV dec−1 and near-100% Faradaic efficiency in 0.5 M H2SO4 (pH 0.3). This performance is remarkable, since iron (III) oxide films comprising only maghemite were found to exhibit a comparable intrinsic activity, but considerably lower stability for OER, while films of pure hematite were OER-inactive. These results are explained by the differences in the polymorph crystal structures, which cause different electrical conductivity and surface interactions with water molecules and protons. Our findings not only reveal the potential of iron (III) oxide as acid-stable OER catalyst, but also highlight the important yet hitherto largely unexplored effect of crystal polymorphism on electrocatalytic OER performance.
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| 10. |
- Liao, Rong-Zhen, et al.
(författare)
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Possible water association and oxidation mechanisms for a recently synthesized Mn4Ca-complex
- 2017
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 354, s. 169-181
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Tidskriftsartikel (refereegranskat)abstract
- The laboratory synthesis of complexes to mimic the structure of the Mn4Ca cluster in the oxygen evolving complex (OEC) of photosystem II is a very challenging task to accomplish. The most encouraging breakthrough in this field was recently achieved with the synthesis of a Mn4Ca complex (Zhang et al., 2015) that shows a very similar core structure to the OEC. On the basis of density functional calculations, the structure and the redox potentials of this Mn4Ca complex in acetonitrile are obtained with very good agreement to experiments. A possible mechanism for water oxidation is more problematic. If only the thermodynamics is considered and assuming a standard state of 1 mol/L, it turns out that up to five water molecules can be inserted into the complex with only a small cost. This leads to a barrier for O-O bond formation which is 22.8 kcal/mol with an applied potential of 1.3 V. However, a study of the kinetics for the insertion of the critical water bridge between Mn3 and Mn4 indicates that the barrier for that process is quite high with 24.6 kcal/mol. A model where this water is not inserted also led to a rather high barrier for O-O bond formation with 31.7 kcal/mol with an applied potential of 1.3 V. However, the barrier decreases significantly to only 13.4 kcal/mol with an applied potential of 1.7 V. The different barrier originates from the different energetic penalty for the formation of the catalytic competent S-4 state. A major experimental problem discussed below, is the instability of the complex, which does not allow a high water concentration. The best calculated overall mechanism obtained is essentially the same as the leading suggestion for the OEC, where the critical O-O bond formation takes place at the S-4 state (formally Mn-4(IV,IV,IV,IV)) via direct coupling of a Mn-IV-oxyl radical and a di-Mn bridging oxo group.
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| 11. |
- Lögdberg, Sara, et al.
(författare)
-
Further insights into methane and higher hydrocarbons formation over cobalt-based catalysts with γ-Al2O3, α-Al2O3 and TiO2 as support materials
- 2017
-
Ingår i: Journal of Catalysis. - : Academic Press. - 0021-9517 .- 1090-2694. ; 352, s. 515-531
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Tidskriftsartikel (refereegranskat)abstract
- A range of cobalt-based catalysts varying in Co loading and prepared by incipient wetness impregnation of traditional support materials (γ-Al2O3, α-Al2O3 and TiO2), have been studied in the Fischer-Tropsch reaction at industrially relevant process conditions (483 K, 20 bar, H2/CO = 2.1). A high selectivity to C5+ hydrocarbons (SC5+) is to a great extent connected with a high site activity, but not exclusively. We propose that the ratio of monomer-production rate to C–C coupling rate of a catalyst determines chain-growth probability by means of governing the coverage of the monomer on the cobalt surface. We speculate that this ratio depends on e.g. shape, strain and size of the Co crystallites and, therefore, is highly dependent on the choice of support material. No general relationship between Co particle size and SC5+ is found, but individual correlations exist for each support material. Within each support material, there are indications of negative correlations between the chain-growth probability of the C1 ∗ surface intermediate (αC1) and the higher αCn values. This can be rationalized by assuming that the majority of methane is formed by a different mechanism, separate from chain growth, but connected with chain growth through a common carbon pool. We propose that the monomers and the majority of methane are produced at sites different from the ones involved in chain growth. There is no general correlation between αC1 and SC5+ for catalysts with different support materials, possibly due to small differences in cobalt surface coverage of hydrogen. For the TiO2-supported catalysts, a dramatically increased αC1 value observed for catalysts with Co particles smaller than approx. 15 nm, is probably associated with strong metal-support interactions (SMSI). This phenomenon apparently limits the effect (reduction) on the SC5+ when moving toward smaller Co particles.
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| 12. |
- Murzin, Dmitry Yu., et al.
(författare)
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Hemicellulose arabinogalactan hydrolytic hydrogenation over Ru-modified H-USY zeolites
- 2015
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 330, s. 93-105
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Tidskriftsartikel (refereegranskat)abstract
- The hydrolytic hydrogenation of hemicellulose arabinogalactan was investigated in the presence of protonic and Ru (1-5 wt.%)-modified USY zeolites (Si/Al ratio = 15 and 30). The use of the purely acidic materials was effective in depolymerizing the macromolecule into free sugars. While the latter partly dehydrated into 5-hydroxymethylfurfural and furfural, the generation of high molecular-weight compounds (aggregates of sugars and humins) was not favored, in contrast to previous evidences over beta zeolites. Application of the bifunctional Ru/USY catalyst, comprising well-dispersed metallic nanopartides on the aluminosilicate support, resulted in the formation of galactitol and arabitol, in the suppression of dehydration side products, and further inhibition of polymerization reactions, which only yielded low molecular-weight oligomers. Detailed analysis of the reaction pathways as well as kinetic modeling of hydrolytic hydrogenation was performed with an advanced reaction mechanism.
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| 13. |
- Nilsson, Johan, 1987, et al.
(författare)
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Methane oxidation over Pd/Al2O3 under rich/lean cycling followed by operando XAFS and modulation excitation spectroscopy
- 2017
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 356, s. 237-245
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Tidskriftsartikel (refereegranskat)abstract
- Rich/lean cycling is used to study the total oxidation of methane over a Pd/Al2O3 catalyst at different oxi- dation states. Time-resolved energy-dispersive X-ray absorption fine structure is used in a modulation excitation approach to monitor the chemical state of the palladium nanoparticles during the cycling, and the resulting spectra are demodulated using phase sensitive detection. Cycling is performed using oxygen pulses with a concentration of 0.15, 0.25, and 1.5% over a constant flow of 0.1% methane. For the two lowest oxygen concentrations the methane conversion is generally low but increases at the switches between the rich and the lean periods, while for the highest oxygen concentration the conver- sion is highest during the lean periods. The oxidation state of Pd changes rapidly but to a limited extent for the two lowest oxygen concentrations, whereas for the high oxygen concentration the oxidation appears to proceed via a two-step process, where the first step is rapid and the second step is slower. EXAFS fitting of the demodulated spectra is used to quantify the Pd oxidation state, the first rapid oxida- tion step is assigned to surface oxidation, while the second step is assigned to bulk oxidation of Pd. A low methane conversion is observed when the Pd nanoparticles are covered with chemisorbed oxygen or sur- face oxide, the methane conversion is higher when the Pd nanoparticles are bulk oxidized.
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| 14. |
- Oberhauser, Werner, et al.
(författare)
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Glycerol to lactic acid conversion by NHC-stabilized iridium nanoparticles
- 2018
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 368, s. 298-305
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen reduction of an Ir(I) complex featured by a bulky N-heterocyclic carbene (NHC) ligand in dichloromethane gave small-sized (1.8 nm) Ir nanoparticles (NPs) decorated with NHC ligands (IrNHC). 1,4-Dioxane solutions of the latter particles were successfully applied to convert glycerol into lactic acid in the presence of NaOH (i.e. 1 mol equivalent with respect to glycerol). IrNHC showed an atom-related TOF value of almost 104 h−1, an almost exclusive formation of liquid reaction products, a high selectivity for lactic acid (93.0%) and a complete recyclability in air atmosphere. Attempts to synthesize analogous NHC-stabilized Ir NPs on a high surface area carbon support (CK) by reducing the same Ir(I) precursor, supported onto CK, prior to the hydrogen reduction in water, gave almost naked CK-supported Ir NPs (1.4 nm). Their catalytic activity tested for the same reaction in water as reaction medium, exhibited much lower catalytic activity (4 × 103 h−1), a lower percentage of liquid reaction products (i.e. 27.0% of the converted glycerol) and a lower selectivity for lactic acid compared to IrNHC.
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| 15. |
- Rozmyslowicz, Bartosz, et al.
(författare)
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Selective hydrogenation of fatty acids to alcohols over highly dispersed ReOx/TiO2 catalyst
- 2015
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 328, s. 197-207
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Tidskriftsartikel (refereegranskat)abstract
- Production of fatty alcohols through selective hydrogenation of fatty acids was studied over a 4% ReOx/TiO2 catalyst. Stearic acid was hydrogenated to octadecanol at temperatures and pressures between 180-200 degrees C and 2-4 MPa, with selectivity reaching 93%. A high yield of octadecanol was attributed to a strong adsorption of the acid compared to alcohol on the catalyst, which inhibits further alcohol transformation to alkanes. Low amounts (<7%) of alkanes (mainly octadecane) were formed during the conversion of stearic acid. However, it was found that the catalyst could be tuned for the production of alkanes. The reaction intermediates were octadecanal and stearyl stearate. Based on the reaction products analysis and catalyst characterization, a reaction mechanism and possible pathways were proposed.
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| 16. |
- Stefanov, Bozhidar, et al.
(författare)
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Gas-phase photocatalytic activity of sputter-deposited anatase TiO2 films : Effect of <001> preferential orientation, surface temperature and humidity
- 2016
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 335, s. 187-196
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Tidskriftsartikel (refereegranskat)abstract
- We present a systematic in situ study of the environmental reaction conditions on the photocatalytic activity of sputter deposited anatase TiO2 films with controlled amounts of preferential <001> orientation. In particular, the effects of relative humidity (RH) and substrate temperature ( ) are investigated. It is found that {001} facets, which are present in higher abundance on highly oriented samples, exhibit an order of magnitude higher reactivity for gas-phase photocatalytic oxidation of the indoor air pollutant acetaldehyde (CH3CHO) than {101} facets do, and a functional dependence of the reaction rate on facet orientation is determined. It is proposed that water adsorbed on the film contributes with two counteracting effects on the photocatalytic activity: (i) It provides hole acceptors to complete the photo-induced redox cycle and subsequent OH– radical formation for pollutant degradation, and (ii) it creates a diffusion barrier between the catalyst interface and pollutant molecules adsorbed in the water layer. As a consequence, increasing at high RH has the beneficial effect of removing excess water and reducing the diffusion barrier, thereby improving the photocatalytic activity. A comparison is also made with a commercial anatase TiO2 film, with less developed surface crystallinity and random facet distribution, where the improvement is even more pronounced. Films with a higher degree of orientation exhibit much more stable performance over a range of operating conditions, which suggests that it is possible to tune the effects of water and exposed facet orientation to achieve optimum activity and making TiO2 films amenable to a larger (RH, ) parameter space for practical applications.
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| 17. |
- Vucetic, Nemanja, et al.
(författare)
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Preparation and characterization of a new bis-layered supported ionic liquid catalyst (SILCA) with an unprecedented activity in the Heck reaction
- 2019
-
Ingår i: Journal of Catalysis. - : Elsevier. - 0021-9517 .- 1090-2694. ; 371, s. 35-46
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Tidskriftsartikel (refereegranskat)abstract
- A new bis-layered supported ionic liquid catalyst (SILCA) loaded with palladium was designed and successfully applied for the Heck reaction of iodobenzene and methyl acrylate. The silica modified catalyst consisting of the first ionic liquid layer - covalently anchored imidazolium bromide - on which the second layer, made of pyridine-carboxylic acid balanced with tetramethylguanidinium cation was attached, resulted in a catalyst with high activity. High turnover frequencies of 22,000 h(-1) were achieved in reactions with a low palladium loading as 0.009 mol %. Lower TOFs, indicating on palladium dimerization was detected when higher amounts were used. The TMG cation had a purpose to recapture and stabilize the Pd nanoparticles thus followed a release and catch mechanism. In order to get a full understanding of the catalyst structure and behaviour, the catalyst was characterized by means of nitrogen physisorption, thermal gravimetric analysis, infrared spectroscopy, scanning electron and transmission electron microscopes, solid-state NMR, X-ray photoelectron spectroscopy and inductively coupled plasma spectroscopy. The catalyst preserved good activity in five cycles.
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| 18. |
- Wang, Lei, et al.
(författare)
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A nickel (II) PY5 complex as an electrocatalyst for water oxidation
- 2016
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 335, s. 72-78
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Tidskriftsartikel (refereegranskat)abstract
- A Ni-PY5 [PY5 = 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine)] complex has been found to act as an electrocatalyst for oxidizing water to dioxygen in aqueous phosphate buffer solutions. The rate of water oxidation catalyzed by the Ni-PY5 is remarkably enhanced by the proton acceptor base HPO42-, with rate constant of 1820 M-1 s(-1). Controlled potential bulk electrolysis with Ni-PY5 at pH 10.8 under an applied potential of 1.5 V vs. normal hydrogen electrode (NHE) resulted in dioxygen formation with a high faradaic efficiency over 90%. A detailed mechanistic study identifies the water nucleophilic attack pathway for water oxidation catalysis.
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| 19. |
- Xia, Changjiu, et al.
(författare)
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Irreversible deactivation of hollow TS-1 zeolite caused by the formation of acidic amorphous TiO2-SiO2 nanoparticles in a commercial cyclohexanone ammoximation process
- 2016
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 338, s. 340-348
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Tidskriftsartikel (refereegranskat)abstract
- Commercial deactivated HTS zeolite has been investigated by multiple characterization methods and catalytic evaluations. These indicate that structural and textural properties are not mainly ascribed to the irreversible deactivation, but some framework Ti species are transformed into Ti-rich nanoparticles. Both Bronsted and Lewis acid sites are observed in deactivated HTS zeolite, which agrees well with the spectroscopic characterization results and Tanabe's acidity theory on mixed binary oxides. Hence the acidic Ti-rich aggregates are attributed to the amorphous TiO2-SiO2 nanoparticles located on the external surface of the zeolite. Furthermore, it is demonstrated that the catalytic performance of deactivated HTS zeolite in phenol hydroxylation is seriously dependent on its acidity properties, which can accelerate the decomposition of H2O2. As a consequence, we conclude that the irreversible deactivation of HTS zeolite in the ammoximation process is caused by the formation of acidic amorphous TiO2-SiO2 nanoparticles catalyzing the fast H2O2 decomposition reaction.
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