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Sökning: L773:2044 4753 > (2015-2019)

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1.
  • Aftab, Umair, et al. (författare)
  • The chemically reduced CuO-Co3O4 composite as a highly efficient electrocatalyst for oxygen evolution reaction in alkaline media
  • 2019
  • Ingår i: Catalysis Science & Technology. - : ROYAL SOC CHEMISTRY. - 2044-4753 .- 2044-4761. ; 9:22, s. 6274-6284
  • Tidskriftsartikel (refereegranskat)abstract
    • The fabrication of efficient, alkaline-stable and nonprecious electrocatalysts for the oxygen evolution reaction is highly needed; however, it is a challenging task. Herein, we report a noble metal-free advanced catalyst, i.e. the chemically reduced mixed transition metal oxide CuO-Co3O4 composite, with outstanding oxygen evolution reaction activity in alkaline media. Sodium borohydride (NaBH4) was used as a reducing agent for the mixed transition metal oxide CuO-Co3O4. The chemically reduced composite carried mixed valence states of Cu and Co, which played a dynamic role in driving an excellent oxygen evolution reaction process. The X-ray photo-electron spectroscopy (XPS) study confirmed high density of active sites in the treated sample with a large number of oxygen vacancies. The developed electrocatalyst showed the lowest overpotential of 144.5 mV vs. the reversible hydrogen electrode (RHE) to achieve the current density of 40 mA cm(-2) and remained stable for 40 hours throughout the chronoamperometry test at the constant potential of 1.39 V vs. RHE. Moreover, the chemically reduced composite was highly durable. Electrochemical impedance spectroscopy (EIS) confirmed the low charge transfer resistance of 13.53 ohms for the chemically reduced composite, which was 50 and 26 times smaller than that of Co3O4 and untreated CuO-Co3O4, respectively. The electrochemically active surface area for the chemically reduced composite was found to be greater than that for pristine CuO, Co3O4 and untreated pristine CuO-Co3O4. These findings reveal the possibility of a new gateway for the capitalization of a chemically reduced sample into diverse energy storage and conversion systems such as lithium-ion batteries and supercapacitors.
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2.
  • Arvidsson, Adam, 1990, et al. (författare)
  • First-principles microkinetic study of methane and hydrogen sulfide catalytic conversion to methanethiol/dimethyl sulfide on Mo 6 S 8 clusters: Activity/selectivity of different promoters
  • 2019
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:17, s. 4573-4580
  • Tidskriftsartikel (refereegranskat)abstract
    • A large fraction of the global natural gas reserves is in the form of sour gas, i.e. contains hydrogen sulfide (H2S) and carbon dioxide (CO2), and needs to be sweetened before utilization. The traditional amine-based separation process is energy-intensive, thereby lowering the value of the sour gas. Thus, there is a need to find alternative processes to remove, e.g., hydrogen sulfide. Mo6S8 clusters are promising candidates for transforming methane (CH4) and hydrogen sulfide into methanethiol (CH3SH) and dimethyl sulfide (CH3SCH3), which are high-value sulfur-containing products that can be further used in the chemical industry. Here first-principles microkinetics is used to investigate the activity and selectivity of bare and promoted (K, Ni, Cl) Mo6S8. The results show that methanethiol is produced via two different pathways (direct and stepwise), while dimethyl sulfide is formed via a competing pathway in the stepwise formation of methanethiol. Moreover, there is an increase in activity and a decrease in selectivity when adding an electropositive promoter (K), whereas the reverse behaviour is observed when adding an electronegative promoter (Cl). When adding Ni there is also a decrease in activity and an increase in selectivity; however, Ni is acting as an electron donor. The results provide insights and guidance as to what catalyst formulation is preferred for the removal of hydrogen sulfide in sour gas.
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3.
  • Arvidsson, Adam, 1990, et al. (författare)
  • Metal dimer sites in ZSM-5 zeolite for methane-to-methanol conversion from first-principles kinetic modelling: is the [Cu-O-Cu]2+ motif relevant for Ni, Co, Fe, Ag, and Au?
  • 2017
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:7, s. 1470-1477
  • Tidskriftsartikel (refereegranskat)abstract
    • Direct methane-to-methanol conversion is a desired process whereby natural gas is transformed into an energy-rich liquid. It has been realised at ambient pressure and temperature in metal ion-exchanged zeolites, where especially copper-exchanged ZSM-5 has shown promising results. The nature of the active sites in these systems is, however, still under debate. The activity has been assigned to a [Cu-O-Cu]2+ motif. One remaining question is whether this motif is general and also active in other metal-exchanged zeolites. Herein, we use first-principles microkinetic modelling to analyse the methane-to-methanol reaction on the [Cu-O-Cu]2+ motif, for Cu and other metals. First, we identify the cluster model size needed to accurately describe the dimer motif. Starting from the [Cu-O-Cu]2+ site, the metal ions are then systematically substituted with Ni, Co, Fe, Ag and Au. The results show that activation of Ag and Au dimer sites with oxygen is endothermic and therefore unlikely, whereas for Cu, Ni, Co and Fe, the activation is possible under realistic conditions. According to the kinetic simulations, however, the dimer motif is a plausible candidate for the active site for Cu only. For Ni, Co and Fe, close-to-infinite reaction times or unreasonably high temperatures are required for sufficient methane conversion. As Ni-, Co- and Fe-exchanged ZSM-5 are known to convert methane to methanol, these results indicate that the Cu-based dimer motif is not an appropriate model system for these metals.
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4.
  • Auvray, Xavier, 1986, et al. (författare)
  • Lean and rich aging of a Cu/SSZ-13 catalyst for combined lean NO x trap (LNT) and selective catalytic reduction (SCR) concept
  • 2019
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:9, s. 2152-2162
  • Tidskriftsartikel (refereegranskat)abstract
    • © 2019 The Royal Society of Chemistry. In the combined lean NO x trap (LNT) and selective catalytic reduction (SCR) concept, the SCR catalyst can be exposed to rich conditions during deSO x of the LNT. Aging of Cu/SSZ-13 SCR catalysts, deposited on a cordierite monolith, was therefore studied in rich, lean and cycling lean/rich operations at 800 °C (lean condition: 500 ppm NO, 8% O 2 , 10% H 2 O and 10% CO 2 ; rich condition: 500 ppm NO, 1% H 2 , 10% H 2 O and 10% CO 2 ). The structure of the catalyst was investigated by X-ray diffraction (XRD), surface area measurements and scanning transmission electron microscopy (STEM). In general, aging decreased the SCR activity and NH 3 oxidation. However, rich conditions showed a very rapid and intense deactivation, while lean aging led to only a small low-temperature activity decrease. The XRD results showed no sign of structure collapse, but the number of active sites, as titrated by NH 3 temperature-programed desorption (NH 3 -TPD) and in situ DRIFTS, revealed an important loss of acid sites. NH 3 storage was significantly more depleted after rich aging than after lean aging. The Lewis sites, corresponding to exchange Cu 2+ , were preserved to some extent in lean conditions. Lean aging also decreased the enthalpy of NH 3 adsorption from -158 kJ mol -1 to -136 kJ mol -1 . Moreover, a comparison of aging in lean-rich cycling conditions with aging only in rich conditions revealed that adding lean events did not hinder or reverse the deactivation, and it was mainly the time in rich conditions that determined the extent of the deactivation. The STEM images coupled with elemental analysis revealed the formation of large Cu particles during rich aging. Conversely, Cu remained well dispersed after lean aging. These results suggest that the copper migration and agglomeration in large extra-framework particles, accelerated by the action of hydrogen, caused the observed severe deactivation.
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5.
  • Azis, Muhammad Mufti, 1983, et al. (författare)
  • On the role of H2 to modify surface NOx species over Ag-Al2O3 as lean NOx reduction catalyst: TPD and DRIFTS studies
  • 2015
  • Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 55:1, s. 296-309
  • Tidskriftsartikel (refereegranskat)abstract
    • Formation and stability of surface NOx species related to the promotional effect of H2 over Ag–Al2O3 as NOx reduction catalyst were investigated with temperature-programmed desorption and DRIFT spectroscopy. Formation of two groups of surface NOx species was found: a less thermally stable group of “low temperature (LT) species” and a more thermally stable group of “high temperature (HT) species”. The LT NOx was attributable to the decomposition of surface NOx species formed on the active sites where its elimination by addition of H2 or thermal decomposition correlated with higher NO oxidation and NOx reduction conversion. Under reaction conditions, these possibly inhibiting LT NOx species were stable up to about 300 °C and their formation depended on donation of oxygen from surface oxides. Removal of LT nitrate species by H2 accounted for only a fraction of the increased NO oxidation and NOx reduction conversion by co-feeding H2. Furthermore, it was also found that H2 facilitates formation of HT NOx that primarily corresponded to the decomposition of spectator species on the Al2O3 support identified as monodentate nitrate species. From TPD studies of C3H6-SCR, it was shown that H2 not only eliminated LT NOx but also promoted formation of greater quantities of adsorbed hydrocarbons.
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6.
  • Benzi, Federico, et al. (författare)
  • Transient structural and catalytic behaviour of Pt-particles probed by operando spectroscopy during a realistic driving cycle
  • 2017
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:18, s. 3999-4006
  • Tidskriftsartikel (refereegranskat)abstract
    • Pt-based diesel oxidation catalysts were investigated for CO oxidation activity under rapid transient temperature conditions based on a realistic driving cycle, which is presently a focal point in exhaust gas aftertreatment. Experiments were performed in a microreactor setup allowing rapid heating/cooling coupled with operando Turbo X-ray absorption spectroscopy (T-XAS) and on-line product analysis by mass spectrometry. Significant differences were observed in catalyst structure and performance depending on the temperature ramp rate. Particularly for Pt/Al2O3, the Pt oxidation state followed a dynamic hysteresis profile during CO oxidation light-off and light-out. In contrast, in Pt-CeO2/Al2O3, ceria acted as an oxygen storage buffer, reducing the width of the Pt oxidation/reduction hysteresis loop as a function of the temperature ramp rate. Ceria also supplied oxygen to the Pt surface, helping to maintain high activity during cooling down and at lower temperatures during transient conditions. This study shows the potential insights into the reaction mechanism available when considering transient temperature as an experimental condition during operando spectroscopic studies in exhaust gas catalysis. The current method is applicable to virtually any rapid transient temperature driving cycle.
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7.
  • Chaoquan, Hu, 1981, et al. (författare)
  • Selectivity and kinetics of methyl crotonate hydrogenation over Pt/Al2O3
  • 2015
  • Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 5:3, s. 1716-1730
  • Tidskriftsartikel (refereegranskat)abstract
    • The hydrogenation of gas-phase methyl crotonate (MC) over Pt/Al2O3 was investigated with the aim to understand C=C hydrogenation in unsaturated methyl esters. Three Pt/Al2O3 catalysts with different Pt dispersions were prepared by varying calcination temperature and evaluated for MC hydrogenation. The main products were found to be methyl butyrate (MB) and methyl 3-butenoate (M3B), resulting from hydrogenation and shift of the C=C bond in MC, respectively. The measured activity for both hydrogenation and shift of the C=C in MC was found to depend on the Pt dispersion where higher Pt dispersion favors the C=C hydrogenation reaction. The effect of reactant concentrations on the activity and selectivity for MC hydrogenation over the Pt/Al2O3 catalyst was examined in detail. Under the investigated conditions, the C=C hydrogenation was found to have a negative reaction order with respect to MC concentration but a positive H2 order. Further understanding of the MC hydrogenation was provided from H2 chemisorption experiments over the catalyst with and without pre-adsorbed MC and from transient experiments using alternating MC and H2 feeds. Based on the present experimental results, a reaction pathway was proposed to describe gas-phase MC hydrogenation over Pt/Al2O3. In order to gain more insight into the reaction, a kinetic analysis of MC hydrogenation was performed by fitting a power-law model to the kinetic data, moreover, dissociative H2 adsorption on the catalyst was found to be the rate-determining step by comparing the power-law model with the overall rate expressions derived from mechanistic considerations.
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8.
  • Chen, Lin, 1990, et al. (författare)
  • Effect of Al-distribution on oxygen activation over Cu-CHA
  • 2018
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 8:8, s. 2131-2136
  • Tidskriftsartikel (refereegranskat)abstract
    • Cu(NH 3 ) 2 + -pairs in chabazite (CHA) have been suggested to activate oxygen during lowerature selective catalytic reduction of nitrogen oxides with ammonia (NH 3 -SCR). As charge neutrality requires that each Cu-complex is associated with a framework Al, the Al-distribution may affect Cu(NH 3 ) 2 + -pair formation and subsequent oxygen activation. Here, density functional theory calculations in combination with ab initio molecular dynamics simulations are used to explore Cu(NH 3 ) 2 + -pair formation and oxygen activation in Cu-CHA. The Al-distribution is found to markedly affect the probability for Cu(NH 3 ) 2 + -pair formation. Moreover, the molecular dynamics simulations reveal a low-energy reaction path for O 2 activation and dissociation. The facile O 2 dissociation suggests that Cu-pair formation rather than O 2 activation governs the lowerature NH 3 -SCR activity. The results indicate that precise synthesis of Cu-exchanged chabazite with respect to Al-distribution may enhance the catalytic activity.
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9.
  • Finnveden, Maja, et al. (författare)
  • Mono-substitution of symmetric diesters: selectivity of Mycobacterium smegmatis acyltransferase variants
  • 2019
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry. - 2044-4753 .- 2044-4761.
  • Tidskriftsartikel (refereegranskat)abstract
    • A method for selectively reacting one, out of two identical carboxylic esters in a symmetric diester has been developed. An esterase from Mycobacterium smegmatis (MsAcT) has a restricted active site resulting in a narrow acyl donor specificity. This constraint was used to develop a selective synthesis route from divinyl adipate (a symmetric diester) towards mixed vinyl adipate esters. To find a suitable catalyst, the wild type (wt) MsAcT and two MsAcT variants: a single point mutant (L12A) and a double point mutant (T93A/F154A), were immobilized and studied under solvent-free conditions. Out of the tested catalysts, MsAcT L12A was the most selective for mono-transesterification of divinyl adipate. When divinyl adipate was reacted with 1.5 equivalents of a hydroxyl vinyl ether full conversion of DVA was observed yielding over 95% mixed diester. Furthermore, the limitations for longer dicarboxylic esters were studied, showing that MsAcT T93A/F154A tolerated up to at least dimethyl sebacate.
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10.
  • Florén, Carl-Robert, 1988, et al. (författare)
  • Modelling complete methane oxidation over palladium oxide in a porous catalyst using first-principles surface kinetics
  • 2018
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 8:2, s. 508-520
  • Tidskriftsartikel (refereegranskat)abstract
    • A comprehensive model is developed for complete methane oxidation over supported palladium. The model is based on first-principles microkinetics and accounts for mass and heat transport in a porous catalytic layer. The turnover frequency (TOF) is simulated for wet exhaust gas compositions, exploring the effects of temperature and total pressure on the TOF. Three different temperature regimes are identified each with different dependency on the total pressure. The regimes originate from temperature and pressure dependent coverages of carbon dioxide and water, which are the most abundant surface species hindering methane dissociation at low temperatures. The TOF is controlled by surface kinetics below 400 °C whereas above 500 °C and up to 8 atm, internal mass transport is controlling. A combination of kinetics, external and internal mass transport controls the TOF at other reaction conditions. The physically meaningful model paves the way for extrapolation and optimization of catalyst design parameters for high catalytic efficiency.
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11.
  • Florén, Carl-Robert, 1988, et al. (författare)
  • Multiscale reactor modelling of total pressure effects on complete methane oxidation over Pd/Al2O3
  • 2019
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:12, s. 3055-3065
  • Tidskriftsartikel (refereegranskat)abstract
    • A two-dimensional multiscale model is developed for complete methane oxidation in a continuous flow reactor. The model considers mass and heat transfer for a porous alumina supported palladium catalyst coated on a ceramic monolith substrate and the surface kinetics are described by a first-principles microkinetic model for complete methane oxidation over PdO(101). The temperature dependent conversion for a synthetic exhaust gas composition shows a delayed ignition but a higher conversion at elevated temperatures when the total pressure is increased from 1 to 10 atm. The simulations reveal a temperature and total pressure dependent operating point where the methane conversion is maximized. Analysis of the kinetics shows that the reaction is suppressed by bicarbonates, hydroxyl species and water originating from adsorbed carbon dioxide and water from the gas phase. The reaction order with respect to water and carbon dioxide at 1 atm is -0.94 and -0.99, respectively, and decreases with increasing total pressure. The developed model paves the way for exploring how design parameters and reaction conditions influence the complete methane oxidation reaction.
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12.
  • Gao, Yuxi, et al. (författare)
  • Sulphation and ammonia regeneration of a Pt/MnOx-CeO2/Al2O3 catalyst for NOx-assisted soot oxidation
  • 2018
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 8:6, s. 1621-1631
  • Tidskriftsartikel (refereegranskat)abstract
    • The sulphur resistance and regeneration strategy of soot oxidation catalysts are critical to the application of catalytic diesel particulate filters (CDPFs). In the present work, Pt/MnOx-CeO2/Al2O3, Pt/Al2O3 and MnOx-CeO2/Al2O3 catalysts were sulphated and regenerated with ammonia. The soot oxidation activity of poisoned Pt/MnOx-CeO2/Al2O3 was recovered completely after 30 min reduction in 500 ppm NH3 at 550 degrees C. The amount, distribution and structure of sulphates were studied comprehensively for the sulphated and regenerated samples by thermogravimetric analysis (TGA), infrared (IR) spectroscopy, CO chemisorption and transmission electron microscopy (TEM). The NO oxidation of Pt catalysts was found to depend strongly on the particle size distribution, surface exposure and oxidation state of the precious metal. This, as well as the effect of the remaining surface sulphates, helped the regenerated catalysts achieve even higher catalytic activity for soot oxidation.
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13.
  • Gemo, Nicola, et al. (författare)
  • The influence of catalyst amount and Pd loading on the H2O2 synthesis from hydrogen and oxygen
  • 2015
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 5:7, s. 3545-3555
  • Tidskriftsartikel (refereegranskat)abstract
    • Palladium catalysts with an active metal content from 0.3 to 5.0 wt.% and supported on a strongly acidic, macroporous resin were prepared by ion-exchange/reduction method. H2O2 direct synthesis was carried out in the absence of promoters (acids and halides). The total Pd amount in the reacting environment was varied by changing A) the catalyst concentration in the slurry and B) the Pd content of the catalyst. In both cases, smaller amounts of the active metal enhance the selectivity towards H2O2, at any H-2 conversion, with option B) better than A). In case A), the Pd(II)/Pd(0) molar ratio (XPS) in the spent catalysts was found to decrease at lower catalyst Pd content. With these catalysts and this experimental set-up the dynamic H-2(1)/Pd molar ratio, the metal loading and the metal particle size were the key factors controlling the selectivity, which reached 57% at 60% H-2 conversion, and 80% at lower conversion.
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14.
  • Goncalves, Leticia C. P., et al. (författare)
  • Boosting photobioredox catalysis by morpholine electron donors under aerobic conditions
  • 2019
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry. - 2044-4753 .- 2044-4761. ; 9:10, s. 2682-2688
  • Tidskriftsartikel (refereegranskat)abstract
    • Light-driven reduction of flavins, e.g. FAD or FMN, by sacrificial electron donors emerged as a convenient method to promote biocatalytic transformations. However, flavin activation has been restricted to oxygen-free conditions to prevent enzyme deactivation caused by reactive oxygen species (ROS). Herein, we show that the photoreduction of FMN by morpholines, including 3-(N-morpholino)propanesulfonic acid (MOPS), lessens the deactivation of the enoate reductase XenB from Pseudomonas sp. during the stereoselective asymmetric enzymatic reduction of a model ,-unsaturated diketone under aerobic conditions, leading to a 91% GC-yield and a stereoselectivity greater than 94%. The kinetic stability of the thermolabile XenB was increased by more than 20-fold in MOPS buffer compared to that in Tris-HCl buffer, and a pronounced positive effect on the transition midpoint temperature was observed. The reactive form of the FMN photocatalyst is stabilized by the formation of a (3)[FMN--MOPS+] ensemble, which reduces the formation of hydrogen peroxide and other ROS in the presence of oxygen. These results contribute to broaden the application of photobiocatalytic transformations using flavin-dependent reductases.
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15.
  • Goncalves, Leticia C. P., et al. (författare)
  • Morpholine-based buffers activate aerobic photobiocatalysis via spin correlated ion pair formation
  • 2019
  • Ingår i: Catalysis Science & Technology. - : ROYAL SOC CHEMISTRY. - 2044-4753 .- 2044-4761. ; 9:6, s. 1365-1371
  • Tidskriftsartikel (refereegranskat)abstract
    • The use of enzymes for synthetic applications is a powerful and environmentally-benign approach to increase molecular complexity. Oxidoreductases selectively introduce oxygen and hydrogen atoms into myriad substrates, catalyzing the synthesis of chemical and pharmaceutical building blocks for chemical production. However, broader application of this class of enzymes is limited by the requirements of expensive cofactors and low operational stability. Herein, we show that morpholine-based buffers, especially 3-(N-morpholino)propanesulfonic acid (MOPS), promote photoinduced flavoenzyme-catalyzed asymmetric redox transformations by regenerating the flavin cofactor via sacrificial electron donation and by increasing the operational stability of flavin-dependent oxidoreductases. The stabilization of the active forms of flavin by MOPS via formation of the spin correlated ion pair (3)[flavin(-)-MOPS+] ensemble reduces the formation of hydrogen peroxide, circumventing the oxygen dilemma under aerobic conditions detrimental to fragile enzymes.
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16.
  • Gonzalez-Fabra, J., et al. (författare)
  • Entropic corrections for the evaluation of the catalytic activity in the Al(iii) catalysed formation of cyclic carbonates from CO2 and epoxides
  • 2019
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:19, s. 5433-5440
  • Tidskriftsartikel (refereegranskat)abstract
    • The reaction mechanism for formation of cyclic carbonates from CO2 and 1,2-epoxyhexane catalyzed by an [Al(amino-triphenolate)]/NBu4I binary system has been investigated by using density functional theory (DFT) based methods. A monometallic mechanism is proposed and the main steps of the reaction are described in detail. The energetic span model (delta E) was used to theoretically determine the turnover frequencies (TOFs) of the catalytic cycle and to evaluate the efficiency of the aluminum complex in mediating the CO2 addition reaction. Our findings indicate that entropy changes in solution must be included in order to compute the TOF values in line with the experimental results.
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17.
  • Gustafson, Karl P. J., et al. (författare)
  • Water oxidation mediated by ruthenium oxide nanoparticles supported on siliceous mesocellular foam
  • 2017
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry. - 2044-4753 .- 2044-4761. ; 7:1, s. 293-299
  • Tidskriftsartikel (refereegranskat)abstract
    • Artificial photosynthesis is an attractive strategy for converting solar energy into fuel. In this context, development of catalysts for oxidation of water to molecular oxygen remains a critical bottleneck. Herein, we describe the preparation of a well-defined nanostructured RuO2 catalyst, which is able to carry out the oxidation of water both chemically and photochemically. The developed heterogeneous RuO2 nanocatalyst was found to be highly active, exceeding the performance of most known heterogeneous water oxidation catalysts when driven by chemical or photogenerated oxidants.
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18.
  • Henych, Jiri, et al. (författare)
  • Solar light decomposition of warfare agent simulant DMMP on TiO2/graphene oxide nanocomposites
  • 2019
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry. - 2044-4753 .- 2044-4761. ; 9:8, s. 1816-1824
  • Tidskriftsartikel (refereegranskat)abstract
    • Solar light-induced photodecomposition of organophosphorus warfare agent simulant dimethyl methylphosphonate (DMMP) on the surfaces of TiO2/graphene oxide (GO) nanocomposites was studied by in situ DRIFT spectroscopy. Nanocomposites containing 1 and 2 wt% GO, respectively, were prepared by two different aqueous methods. All nanocomposites were shown to effectively adsorb and partly dissociate DMMP as shown by the formation of surface coordinated methoxy groups. Solar light illumination induced rapid decomposition of the adsorbed species to yield various ionic and surface coordinated formate and carbonate species as the main intermediate products. Both the kinetics of adsorbed species decomposition and the formation of various intermediates were strongly affected by the presence of GO, as compared to pure TiO2 nanoparticles. The two synthesis routes yielded nanocomposites with different degrees of reduction of GO that correlated with their reactivity towards DMMP adsorption and photodegradation. Upon illumination, rapid depletion of water was observed on the TiO2/GO nanocomposites and was attributed to a water splitting reaction, which competed with the DMMP photo-oxidation reaction.
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19.
  • Hu, Guangzhi, et al. (författare)
  • Atomistic understanding of the origin of high oxygen reduction electrocatalytic activity of cuboctahedral Pt3Co-Pt core-shell nanoparticles
  • 2016
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 6:5, s. 1393-1401
  • Tidskriftsartikel (refereegranskat)abstract
    • PtM-based core-shell nanoparticles are a new class of active and stable nanocatalysts for promoting oxygen reduction reaction (ORR); however, the understanding of their high electrocatalytic performance for ORR at the atomistic level is still a great challenge. Herein, we report the synthesis of highly ordered and homogeneous truncated cuboctahedral Pt3Co-Pt core-shell nanoparticles (cs-Pt3Co). By combining atomic resolution electron microscopy, X-ray photoelectron spectroscopy, extensive first-principles calculations, and many other characterization techniques, we conclude that the cs-Pt3Co nanoparticles are composed of a complete or nearly complete Pt monolayer skin, followed by a secondary shell containing 5-6 layers with similar to 78 at% of Pt, in a Pt3Co configuration, and finally a Co-rich core with 64 at% of Pt. Only this particular structure is consistent with the very high electrocatalytic activity of cs-Pt3Co nanoparticles for ORR, which is about 6 times higher than commercial 30%-Pt/Vulcan and 5 times more active than non-faceted (spherical) alloy Pt3Co nanoparticles. Our study gives an important insight into the atomistic design and understanding of advanced bimetallic nanoparticles for ORR catalysis and other important industrial catalytic applications.
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20.
  • Jørgensen, Mikkel, 1990, et al. (författare)
  • Connection between macroscopic kinetic measurables and the degree of rate control
  • 2017
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:18, s. 4034-4040
  • Tidskriftsartikel (refereegranskat)abstract
    • Catalytic reactions are commonly characterized by measuring reaction orders and apparent activation energies. In the present work, these macroscopic measurables are related to the degree of rate control (χi), which describes how the overall kinetics is influenced by the elementary reactions. The reaction orders are found to be χi-weighted sums over the microscopic rates, derived with respect to pressure. Similarly, the apparent activation energy is shown to be a sum over the individual reaction-energy-barriers, weighted by χi. The results couple macroscopic kinetics to the microscopic scale, which can facilitate analysis of catalytic reaction kinetics.
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21.
  • Kannisto, Hannes, 1979, et al. (författare)
  • Direct observation of atomically-resolved silver species on a silver alumina catalyst active for selective catalytic reduction of nitrogen oxides
  • 2019
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:22, s. 6213-6216
  • Tidskriftsartikel (refereegranskat)abstract
    • We characterize the size and state of the silver species in a 2 wt% silver alumina catalyst, which is highly active for the selective catalytic reduction of nitrogen oxides with ammonia or hydrocarbons as reductant. The silver alumina catalyst is prepared by a single-step sol-gel method and characterized with X-ray photoelectron and ultraviolet-visible spectroscopy, and high-resolution transmission electron microscopy. We show, for the first time, direct observations of atomically-resolved silver species and silver clusters on the silver alumina catalyst. The results determine the existence of these silver species on the alumina support, which corroborate previously reported indirect observations, and strengthen the hypothesis of small silver clusters as active sites for the selective catalytic reduction of nitrogen oxides.
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22.
  • Konwar, Lakhya Jyoti, et al. (författare)
  • Efficient C-C coupling of bio-based furanics and carbonyl compounds to liquid hydrocarbon precursors over lignosulfonate derived acidic carbocatalysts
  • 2018
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry. - 2044-4753 .- 2044-4761. ; 8:9, s. 2449-2459
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper demonstrates the catalytic potential of novel Na-lignosulfonate (LS) derived meso/macroporous solid protonic acids upon C–C coupling of bio-based furanics and carbonyl compounds. The materials demonstrated catalytic activity for solventless hydroxyalkylation/alkylation (HAA) of 2-methylfuran with furfural, acetone, butanal, cyclohexanone, levulinic acid and α-angelica lactone under mild reaction conditions (50–60 °C) producing branched-chain C12–C16 hydrocarbon precursors in yields approaching 96%. Moreover, the carbon materials exhibiting high total acidity (6–6.4 mmol g−1) outperformed sulfonic acid resins (Amberlyst®70, Amberlite®IR120 and LS resin), zeolites and liquid acids (p-toluenesulfonic acid, acetic acid and phenol). In fact, the most active carbocatalyst (60LS40PS350H+) exhibited the same turnover frequency as p-toluenesulfonic acid (186 h−1) upon furfural conversion but with an improved HAA product yield (up to 88%) and reusability, maintaining 98% of its original activity up to seven reaction cycles. The observed catalytic activity and operational stability of the LS derived acidic carbocatalysts were attributed to the strongly Brønsted acidic –SO3H groups covalently incorporated into their structural carbon framework and the promotional effects of hydrophilic surface functional groups (–COOH and –OH) favoring adsorption of oxygenated reactant molecules.
  •  
23.
  • Kumar, S., et al. (författare)
  • Dominant {100} facet selectivity for enhanced photocatalytic activity of NaNbO3 in NaNbO3/CdS core/shell heterostructures
  • 2017
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:2, s. 481-495
  • Tidskriftsartikel (refereegranskat)abstract
    • Design and engineering of crystalline advanced photocatalysts with specific facets is one of the most challenging tasks to enhance the photocatalytic performance. The surface energy of different facets is different in a crystal which leads to a corresponding change in their photocatalytic behaviour. The present study provides an experimental as well as theoretical understanding of the role of different facets of NaNbO3 in cubic and orthorhombic phases with crystals showing cubic and cuboctahedron morphologies in enhancing the photocatalytic activity of NaNbO3/CdS core/shell heterostructures. Herein, we discuss the importance of the approach of facet-selective synthesis and trace the origin of enhanced photoelectrochemical (PEC) water splitting and photocatalytic dye degradation activity for calculated surface energies of the {100} family of facets of the cubic phase and the (110) and (114) facets of the orthorhombic phase of NaNbO3. We propose that different mechanisms contribute to the enhancement of catalytic activity in these two phases. In the prepared core/shell heterostructures containing NaNbO3 as the core material, the presence of highly reactive facets of the cubic phase contributes to higher photocatalytic activity as compared to the orthorhombic phase which has a spatial charge separation assisted inter-facet charge transfer mechanism.
  •  
24.
  • Kärkäs, Markus D., et al. (författare)
  • Molecular ruthenium water oxidation catalysts carrying non-innocent ligands : mechanistic insight through structure-activity relationships and quantum chemical calculations
  • 2016
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 6:5, s. 1306-1319
  • Tidskriftsartikel (refereegranskat)abstract
    • Robust catalysts that mediate H2O oxidation are of fundamental importance for the development of novel carbon-neutral energy technologies. Herein we report the synthesis of a group of single-site Ru complexes. Structure-activity studies revealed that the individual steps in the oxidation of H2O depended differently on the electronic properties of the introduced ligand substituents. The mechanistic details associated with these complexes were investigated experimentally along with quantum chemical calculations. It was found that O-O bond formation for the developed Ru complexes proceeds via high-valent Ru-VI species, where the capability of accessing this species is derived from the non-innocent ligand architecture. This cooperative catalytic involvement and the ability of accessing Ru-VI are intriguing and distinguish these Ru catalysts from a majority of previously reported complexes, and might generate unexplored reaction pathways for activation of small molecules such as H2O.
  •  
25.
  • Li, Yunguo, et al. (författare)
  • Review of two-dimensional materials for photocatalytic water splitting from a theoretical perspective
  • 2017
  • Ingår i: Catalysis Science & Technology. - : ROYAL SOC CHEMISTRY. - 2044-4753 .- 2044-4761. ; 7:3, s. 545-559
  • Forskningsöversikt (refereegranskat)abstract
    • Two-dimensional (2D) materials have shown extraordinary performances as photocatalysts compared to their bulk counterparts. Simulations have made a great contribution to the deep understanding and design of novel 2D photocatalysts. Ab initio simulations based on density functional theory (DFT) not only show efficiency and reliability in new structure searching, but also can provide a reliable, efficient, and economic way for screening the photocatalytic property space. In this review, we summarize the recent developments in the field of water splitting using 2D materials from a theoretical perspective. We address that DFT-based simulations can fast screen the potential spaces of photocatalytic properties with the accuracy comparable to experiments, by investigating the effects of various physical/ chemical perturbations. This, at last, will lead to the enhanced photocatalytic activities of 2D materials, and promote the development of photocatalysis.
  •  
26.
  • Liao, Rong-Zhen, et al. (författare)
  • On the mechanism of water oxidation catalyzed by a dinuclear ruthenium complex : a quantum chemical study
  • 2016
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 6:13, s. 5031-5041
  • Tidskriftsartikel (refereegranskat)abstract
    • The development of efficient and robust catalysts for H2O oxidation is an essential element in solar water splitting. The reaction mechanism for a previously reported dinuclear Ru water oxidation catalyst (1) has been investigated in detail through quantum chemical calculations. The predicted mechanism starts from a Ru-2(III,III) complex with two aqua ligands. After three sequential oxidations, O-O bond formation occurs at a formal Ru-2(IV,V) state via the direct coupling of two adjacent oxo moieties while the water nucleophilic attack mechanism was found to be associated with a higher energy barrier. Two H2O molecules are then inserted with subsequent release of O-2, which was found to be the rate-limiting step with a barrier of 22.7 kcal mol(-1). In a previous work, it was revealed that the ligand scaffold in the studied Ru complex has a non-innocent function. Here, we further highlight this behavior, where the ligand was shown to mediate proton transfer events and accept/donate electrons during the catalytic cycle, which can significantly decrease the redox potentials and facilitate the access to high-valent redox states. This study provides further insight into the H2O oxidation mechanism and principles for designing improved catalysts for activation of small molecules, such as H2O.
  •  
27.
  •  
28.
  • Martin, Natalia Mihaela, 1984, et al. (författare)
  • Catalytic hydrogenation of CO2 to methane over supported Pd, Rh and Ni catalysts
  • 2017
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:5, s. 1086-1094
  • Tidskriftsartikel (refereegranskat)abstract
    • As a step in production of so-called electrofuels, ambient pressure CO2 hydrogenation has been investigated over different catalytic model systems based on metal particles (Pd, Rh and Ni) supported on various metal oxides (SiO2, Al2O3 and CeO2) and aluminosilicates (ZSM-5 and MCM-41) at different specific reactant ratios and temperatures between 150 and 450 degrees C. Catalytic activity and selectivity measurements in a flow reactor show that the highest CO2 conversion towards methane is obtained for the Rh/Al2O3 and Rh/CeO2 catalysts, followed by Ni/CeO2. Generally, the results suggest that both the support material and reaction conditions play an important role in the hydrogenation process. Further, in situ diffusive reflectance infrared Fourier transform spectroscopy reveals the intermediate species during transient CO2 hydrogenation over the Rh and Ni containing catalysts. Adsorption and dissociation of CO2 occurs over the Rh/Al2O3 catalyst in the presence of H-2, resulting in the formation of linear Rh-CO species, while formates and carbonates are formed over the Rh/CeO2 and Ni/CeO2 catalysts, likely at the metal-support interface.
  •  
29.
  • Martin, Natalia Mihaela, 1984, et al. (författare)
  • Structure-function relationship during CO2 methanation over Rh/Al2O3 and Rh/SiO2 catalysts at atmospheric pressure conditions
  • 2018
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 8:10, s. 2686-2696
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of support material and chemical state of Rh for Rh/Al2O3 and Rh/SiO2 model catalysts during CO2 hydrogenation were studied by a combined array of in situ characterisation techniques including diffuse reflectance infrared Fourier transform spectroscopy, energy-dispersive X-ray absorption spectroscopy and high-energy X-ray diffraction at 250-350 °C and atmospheric pressure. The CO2 methanation proceeds via intermediate formation of adsorbed CO species on metallic Rh likely followed by their hydrogenation to methane. Linearly-bonded CO species is suggested to be a more active precursor in the hydrogenation compared to the bridge-bonded species, which seems to relate to particle size effects: for larger particles mainly the formation of inactive bridge-bonded CO species takes place. Further, analysis of the chemical state of Rh during reaction conditions reveal a minor formation of RhOx from dissociation of CO2 , which is a consequence of the increased activity observed over Rh/Al2O3 catalyst.
  •  
30.
  • Martin, Natalia M., et al. (författare)
  • Structure-function relationship for CO2 methanation over ceria supported Rh and Ni catalysts under atmospheric pressure conditions
  • 2019
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry. - 2044-4753 .- 2044-4761. ; 9:7, s. 1644-1653
  • Tidskriftsartikel (refereegranskat)abstract
    • In situ structural and chemical state characterization of Rh/CeO2 and Ni/CeO2 catalysts during atmospheric pressure CO2 methanation has been performed by a combined array of time-resolved analytical techniques including ambient-pressure X-ray photoelectron spectroscopy, high-energy X-ray diffraction and diffuse reflectance infrared Fourier transform spectroscopy. The ceria phase is partially reduced during the CO2 methanation and in particular Ce3+ species seem to facilitate activation of CO2 molecules. The activated CO2 molecules then react with atomic hydrogen provided from H-2 dissociation on Rh and Ni sites to form formate species. For the most active catalyst (Rh/CeO2), transmission electron microscopy measurements show that the Rh nanoparticles are small (average 4 nm, but with a long tail towards smaller particles) due to a strong interaction between Rh particles and the ceria phase. In contrast, larger nanoparticles were observed for the Ni/CeO2 catalyst (average 6 nm, with no crystallites below 5 nm found), suggesting a weaker interaction with the ceria phase. The higher selectivity towards methane of Rh/CeO2 is proposed to be due to the stronger metal-support interaction.
  •  
31.
  • Martin, Natalia Mihaela, 1984, et al. (författare)
  • Structure-function relationship for CO2 methanation over ceria supported Rh and Ni catalysts under atmospheric pressure conditions
  • 2019
  • Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 9:7, s. 1644-1653
  • Tidskriftsartikel (refereegranskat)abstract
    • In situ structural and chemical state characterization of Rh/CeO 2 and Ni/CeO 2 catalysts during atmospheric pressure CO 2 methanation has been performed by a combined array of time-resolved analytical techniques including ambient-pressure X-ray photoelectron spectroscopy, high-energy X-ray diffraction and diffuse reflectance infrared Fourier transform spectroscopy. The ceria phase is partially reduced during the CO 2 methanation and in particular Ce 3+ species seem to facilitate activation of CO 2 molecules. The activated CO 2 molecules then react with atomic hydrogen provided from H 2 dissociation on Rh and Ni sites to form formate species. For the most active catalyst (Rh/CeO 2 ), transmission electron microscopy measurements show that the Rh nanoparticles are small (average 4 nm, but with a long tail towards smaller particles) due to a strong interaction between Rh particles and the ceria phase. In contrast, larger nanoparticles were observed for the Ni/CeO 2 catalyst (average 6 nm, with no crystallites below 5 nm found), suggesting a weaker interaction with the ceria phase. The higher selectivity towards methane of Rh/CeO 2 is proposed to be due to the stronger metal-support interaction.
  •  
32.
  • Mihai, Oana, 1975, et al. (författare)
  • The effect of water on methane oxidation over Pd/Al2O3 under lean, stoichiometric and rich conditions
  • 2017
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:14, s. 3084-3096
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, the effect of oxygen concentration and the presence of water on methane oxidation were examined over a Pd/Al2O3 catalyst. The physicochemical properties of the catalyst were investigated in detail using BET, XRD, STEM, O-2-TPO and CH4-TPR. Ramping experiments from 150 to 700 degrees C were conducted using rich, stoichiometric and lean gas mixtures in the absence and presence of water. It was found that increasing the oxygen concentration in a dry atmosphere resulted in higher methane oxidation activity, which can be connected to the facilitation of palladium oxide formation. The TPO data showed that only minor amounts of PdO up to 700 degrees C were decomposed; however, in the stoichiometric and rich reaction mixture, PdO was still decomposed because of the oxygen limitation. This fact resulted in a "negative activation" during cooling, with increased activity because of palladium re-oxidation. Moreover, methane steam reforming and water gas shift reactions were important reactions under rich conditions over the metallic palladium sites. A significant inhibiting effect of water on the Pd-catalyst with loss of methane activity was found. Interestingly, the inhibition effect was much greater using high oxygen concentration in the gas mixture (500 ppm CH4, 8% O-2, 5% H2O) than that at lower oxygen levels (800-1200 ppm) and we propose that the hydroxyl species formation, which blocks the active sites, are facilitated by a large oxygen excess. In addition, the re-oxidation of palladium occurring during the cooling ramp in dry feed using rich and stoichiometric gas mixtures was also significantly suppressed in the presence of a large amount of water. Thus, water impedes the oxidation of palladium, which significantly deactivates the Pd catalyst.
  •  
33.
  • Mir, Showkat H., et al. (författare)
  • A comparative study of hydrogen evolution reaction on pseudo-monolayer WS2 and PtS2 : insights based on the density functional theory
  • 2017
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry. - 2044-4753 .- 2044-4761. ; 7:3, s. 687-692
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, we investigated the catalytic activity of ultrathin PtS2 and WS2 nanostructures for the hydrogen evolution reaction by electronic structure calculations based on the spin-polarised density functional theory. We also explored the effect of van der Waals interactions on the surface-adsorbate interactions. Using the adsorption free energy of H-2 as an activity descriptor, we tuned the photocatalytic water splitting activity of PtS2 and WS2 by functionalizing the individual systems with different transition metals such as Ru, Rh, Pd, Ag, Ir, Au, and Hg. The density of states was calculated along with the band structure to find the effect of different dopants on the fundamental band gap, which is one of the primary parameters in the photocatalytic water splitting.
  •  
34.
  • Mousazade, Younes, et al. (författare)
  • Water oxidation by a manganese-potassium cluster : Mn oxide as a kinetically dominant "true" catalyst for water oxidation
  • 2018
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 8:17, s. 4390-4398
  • Tidskriftsartikel (refereegranskat)abstract
    • Nature uses an Mn cluster for water oxidation, and thus, water oxidation using Mn clusters is interesting when used in artificial water-splitting systems. An important question is whether an Mn cluster is a true catalyst for water oxidation or not. Herein, an Mn-K cluster was investigated for electrochemical water oxidation to find the true and the kinetically dominant catalyst using X-ray absorption spectroscopy, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and electrochemical methods. The experiments showed that conversion into nanosized Mn oxide occurred for the cluster, and the nanosized Mn oxides are the true catalyst for water oxidation.
  •  
35.
  • Ng, Chun Hin, et al. (författare)
  • Mechanistic studies of the photo-electrochemical hydrogen evolution reaction on poly(2,2'-bithiophene)
  • 2016
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 6:9, s. 3253-3262
  • Tidskriftsartikel (refereegranskat)abstract
    • The realisation of poly(2,2’-bithiophene) (PBTh) as an effective photo-electrocatalyst for the hydrogen evolution reaction is a novel discovery [Ng et al., Int. J. Hydrogen Energy, 2014, 39, 18230]; however, the underlying mechanism of this catalysis remains unknown. In this article, studies using electrochemical, photo-electrochemical, Raman spectroscopy and computational modelling are undertaken to shed some light on the mechanistic process. From these studies, a compelling reaction scheme is proposed involving the protonation of the PBTh chain via the sulphur atom and subsequent intersystem crossing to a long-lived triplet state for the reaction to form H-2. This suggested mechanism is tentative but cohesively integrates all experimental and computational findings. Importantly, these insights into the PBTh system form an important mechanistic milestone study and will help inspire new developments and applications for polythiophenes and conducting polymers.
  •  
36.
  • Riedel, J. N., et al. (författare)
  • H-2/D-2 exchange reaction on mono-disperse Pt clusters: enhanced activity from minute O-2 concentrations
  • 2016
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 6:18, s. 6893-6900
  • Tidskriftsartikel (refereegranskat)abstract
    • The H-2/D-2 exchange reaction was studied on mono-disperse Pt-8 clusters in a mu-reactor. The chemical activity was studied at temperatures varying from room temperature to 180 degrees C using mass spectrometry. It was found that minute amounts of O-2 in the gas stream increased the chemical activity significantly. XPS and ISS before and after reaction suggest little or no sintering during reaction. A reaction pathway is suggested based on DFT. H-2 desorption is identified as the rate- limiting step and O-2 is confirmed as the source of the increased activity. The binding energy of platinum atoms in a SiO2 supported Pt-8 cluster is found to be comparable to the interatomic binding energies of bulk platinum, underlining the stability of the model system.
  •  
37.
  • Sá, Jacinto, et al. (författare)
  • Controlling dark catalysis with quasi half-cycle terahertz pulses
  • 2017
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:5, s. 1050-1054
  • Tidskriftsartikel (refereegranskat)abstract
    • This study reports the changes in the platinum electronic structure induced by a strong electric field originated from quasi half-cycle THz pulses, which forces the C-O molecule to dissociate. The changes could be rationalized via a simple analysis of the local density-of-states and easily characterised via high resolution X-ray absorption spectroscopy (HR-XAS). Thus, conferring half-cycle THz pulses the capability of triggering dark catalytic processes required to follow real time catalytic bond rupture or formation, i.e., time-resolved measurements using THz as the pump and HR-XAS as the probe.
  •  
38.
  • Say, Zafer, et al. (författare)
  • Sulfur-tolerant BaO/ZrO2/TiO2/Al2O3 quaternary mixed oxides for deNOX catalysis
  • 2017
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:1, s. 133-144
  • Tidskriftsartikel (refereegranskat)abstract
    • Advanced quaternary mixed oxide materials in the form of BaO/Al2O3/ZrO2/TiO2 functionalized with Pt active sites (i.e. Pt/BaO/AZT) were synthesized and structurally characterized via XRD and BET in comparison to a conventional Pt/20BaO/Al benchmark NSR/LNT catalyst. The interactions of these catalysts' surfaces with SOx and NOx gases were monitored via in situ FTIR and TPD. There exists a delicate trade-off between NOx storage capacity (NSC) and sulfur uptake/poisoning which is strongly governed by the BaO loading/dispersion as well as the surface structure and acidity of the support material. Flow reactor measurements performed under realistic catalytic conditions show the high NOx activity for the Pt/20BaO/AZT catalyst at 573 K. After sulfur poisoning and subsequent regeneration at 773 and 973 K, Pt/20BaO/AZT surpassed the NOx catalytic performance at 573 K of all other investigated materials including the conventional Pt/20BaO/Al benchmark catalyst. © The Royal Society of Chemistry 2017.
  •  
39.
  • Singh, Deobrat, et al. (författare)
  • 2D-HfS2 as an efficient photocatalyst for water splitting
  • 2016
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 6:17, s. 6605-6614
  • Tidskriftsartikel (refereegranskat)abstract
    • Two dimensional monolayer nanostructures for water splitting solar photocatalysts are drawing more attention due to their extraordinary properties. Using first principles calculations we have systematically investigated the structural, electronic and vibrational properties of corresponding HfS2 monolayers in both hexagonal (1H) and trigonal (1T) phases. The most stable adsorption configurations and adsorption energies are calculated. The adsorption energy of H2O on the substrate is 646.53 kJ mol(-1) for the 1H-phase and 621.65 kJ mol(-1) for the 1T-phase of HfS2. This shows that H2O molecules have a stronger interaction with the HfS2 substrate. The calculated redox potentials of H2O splitting lie properly astride the valence and conduction bands, suggesting that the monolayers of 1H- and 1T-HfS2 show the same characteristics as a photocatalyst for water splitting. Furthermore, we also calculated that the optical band gaps for the 1H and 1T phases of HfS2 are 2.60 eV and 3.10 eV, respectively. We have also calculated Raman spectrum signatures of the monolayer 1H and 1T-phase of the in-plane vibrational mode of the Hf and S atoms (E1g) and the out-of-plane vibrational mode of S atoms (A(1g) and A(2u)). Our work suggests that a lot more research and attention in this field is needed for the practical application of the material as visible light active photocatalysts.
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40.
  • Tahira, Aneela, et al. (författare)
  • An efficient bifunctional electrocatalyst based on a nickel iron layered double hydroxide functionalized Co3O4 core shell structure in alkaline media
  • 2019
  • Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry. - 2044-4753 .- 2044-4761. ; 9:11, s. 2879-2887
  • Tidskriftsartikel (refereegranskat)abstract
    • Developing highly active nonprecious metal and binder free bifunctional electrocatalysts for water splitting is a challenging task. In this study, we used a simple strategy to deposit a nickel iron layered double hydroxide (NiFeLDH) onto cobalt oxide (Co3O4) nanowires. The cobalt oxide nanowires are covered with thin nanosheets of NiFeLDH forming a core shell structure. The Co3O4 nanowires contain the mixed oxidation states of Co2+ and Co3+, and the surface modification of Co3O4 nanowires has shown synergetic effects due to there being more oxygen defects, catalytic sites, and enhanced electronic conductivity. Further, the core shell structure of Co3O4 nanowires demonstrated a bifunctional activity for water splitting in 1 M KOH aqueous solution. From the hydrogen evolution reaction (HER), a current density of 10 mA cm - 2 is achieved at a potential of - 0.303 V vs. reversible hydrogen electrode (RHE). Meanwhile for the case of the oxygen evolution reaction (OER), a current density of 40 mA cm - 2 is measured at a potential of 1.49 V vs. RHE. Also, this electrocatalyst has shown a considerable long- term stability of 15 h for both the HER and the OER. Importantly, electrochemical impedance spectroscopy has shown that the NiFeLDH integration onto cobalt oxide exhibited around 3 fold decrease of charge transfer resistance for both the HER and the OER in comparison with pristine cobalt oxide films, which reveals an excellent electrocatalytic activity for both faradaic processes. All these results confirm that the proposed electrocatalyst can be integrated into an efficient water splitting system.
  •  
41.
  • Taifan, W., et al. (författare)
  • CH4 and H2S reforming to CH3SH and H-2 catalyzed by metal-promoted Mo6S8 clusters: a first-principles micro-kinetic study
  • 2017
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:16, s. 3546-3554
  • Tidskriftsartikel (refereegranskat)abstract
    • Direct processing of sour, e.g. containing large amounts of acidic H2S and/or CO2 molecules, natural gas is of direct interest as vast amounts of it are available and accessible but are underutilized. While sour natural gas is still treated using energy-intensive amine absorption/desorption, here we propose and describe a first step in catalytically producing a value added chemical and energy carrier, CH3SH and H-2, respectively. For this purpose, we performed Density Functional Theory (DFT) and microkinetic modelling of CH4 and H2S reaction pathways to form CH3SH and H-2 as a first step in elucidating complex yet not explored pathways in oxygen-free sour gas reforming. For this purpose, we utilized bare unpromoted and K-or Nipromoted Mo6S8 clusters. CH4 dissociation was found to be the rate-determining step above 1100 K on Ni-promoted Mo6S8 while H-2 formation was the rate-determining step on the bare and K-promoted Mo6S8. At lower reaction temperatures between 800 and 1100 K, CH3SH formation becomes an important step, especially on Ni-Mo6S8. This method presents an interesting route of direct catalytic sour natural gas processing which potentially leads to high-value hydrocarbons, such as ethylene, using CH3SH as a reactive intermediate.
  •  
42.
  • Vandichel, Matthias, 1985, et al. (författare)
  • A dimer path for CO dissociation on PtSn
  • 2019
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:3, s. 695-701
  • Tidskriftsartikel (refereegranskat)abstract
    • Density functional theory calculations are used to investigate CO adsorption, dissociation and SnOX formation on Pt3Sn. We find that direct CO dissociation is prevented by high activation energies. An energetically feasible path is instead CO dimer formation followed by C-O bond cleavage. Dimers are formed in the presence of Sn adatoms which effectively stabilize anionic OCCO- species. The presence of Sn adatoms is crucial as dimers are unstable on Pt-only systems. The proposed mechanism may explain recent experimental observations of SnOX and C-C formation as PtxSn is exposed to CO.
  •  
43.
  • Wijayanti, Kurnia, 1979, et al. (författare)
  • Deactivation of Cu-SSZ-13 by SO2 exposure under SCR conditions
  • 2016
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 6:8, s. 2565-2579
  • Tidskriftsartikel (refereegranskat)abstract
    • A deactivation study of Cu-SSZ-13 has been conducted using SO2 exposure under SCR conditions and examining its effect on different reactions involving NH3-SCR. Several reactions, including NH3 storage/TPD, NO/NH3 oxidation, standard SCR, fast SCR and SCR with 75% NO2, as well as NH3-NO2 storage/TPD, were investigated at a temperature range of 100-400 degrees C after exposing the catalyst to 30 ppm SO2 under SCR conditions at 300 degrees C for 90 min. The catalyst was characterized using XRD, BET, ICP-SFMS and H-2-TPR. The BET surface area and pore volume decreased after the sulfur treatment presumably due to blocking by sulfur and/or ammonium-sulfur species. It was found that sulfur was not uniformly deposited along the monolith channel. The deposition occurred from the inlet towards the outlet, as evident from ICP-SFMS measurements. Part of the sulfur was removed after an SCR experiment up to 400 degrees C. However, this removal was observed only in the inlet half of the sample and not in the outlet. Ammonia TPD experiments revealed that the sulfur poisoning resulted in additional sites that were capable of adsorbing ammonia, resulting in increased ammonia storage. Moreover, standard SCR was significantly deactivated by SO2 poisoning under SCR conditions. Due to the site-blocking effect of the ammonium-sulfur species, fewer copper sites are likely available for the redox SCR cycle. Furthermore, the effect of sulfur poisoning on NH3 oxidation and NO2-SCR as well as N2O production in various SCR reactions were observed. Finally, it was found that the conditions for the sulfur poisoning were critical in which SO2 deactivation under SCR conditions (NH3 + NO+ O-2 + H2O) was more severe compared to SO2 poisoning in O-2 + H2O alone.
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44.
  • Woo, Jung Won, 1980, et al. (författare)
  • Effect of various structure directing agents (SDAs) on low-temperature deactivation of Cu/SAPO-34 during NH3-SCR reaction
  • 2018
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 8:12, s. 3090-3106
  • Tidskriftsartikel (refereegranskat)abstract
    • Cu/SAPO-34 and Cu/SSZ-13 having chabazite structure (CHA) have attracted significant attention because of their high activity and N2selectivity during SCR reaction as well as superior resistance to hydrocarbon poisoning. Cu/SAPO-34 has shown better hydrothermal durability than Cu/SSZ-13 at high temperature. However, we have observed earlier that Cu/SAPO-34 prepared using morpholine as a structure directing agent (SDA) deteriorated under water exposure at low temperature, where the NOxconversion activity decreased from 87% to 6% after 9 h of low temperature exposure. In this study, Cu/SAPO-34 catalysts prepared using three different SDAs, i.e., morpholine (MO), triethylamine (TEA), and tetraethylammonium hydroxide (TEAOH), were prepared by the incipient wetness impregnation (IWI) method. A commercially purchased SAPO-34 (SAPO-34(ACS)) was also used for comparison purposes. After low temperature water deactivation, Cu/SAPO-34(TEA) and (TEAOH) mostly recovered their activities while Cu/SAPO-34(MO) and (ACS) only regained part of their activities after regeneration tests under a series of experimental conditions for the NH3-SCR reaction. Solid-state MAS NMR was employed to study the impact of SDAs on the coordination of Al, P, and Si in the SAPO-34 supports and Cu/SAPO-34 catalysts. CO-DRIFTS, NO-DRIFTS, and H2-TPR employed in this study collectively propose the presence of two different Cu locations in Cu/SAPO-34(MO, TEA, TEAOH, and ACS). It is suggested that the concentrations of Cu in two distinct locations within Cu/SAPO-34 catalysts characterized by CO-DRIFTS, NO-DRIFTS, and H2-TPR studies are significantly influenced by the choice of SDA, which will be important for understanding the deactivation mechanism of Cu/SAPO-34 catalysts during low temperature NH3-SCR reaction.
  •  
45.
  • Woo, Jung Won, 1980, et al. (författare)
  • Understanding the mechanism of low temperature deactivation of Cu/SAPO-34 exposed to various amounts of water vapor in the NH3-SCR reaction
  • 2019
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:14, s. 3623-3636
  • Tidskriftsartikel (refereegranskat)abstract
    • The low temperature hydrothermal stability of Cu/SAPO-34 catalysts for the NH3-SCR reaction, prepared by three different structure directing agents (SDAs), i.e., morpholine (MO), triethylamine (TEA), and tetraethylammonium hydroxide (TEAOH), was investigated by exposing them to various amounts of water vapor. XRD and BET studies indicate that there was no sign of Cu/SAPO-34 catalyst's chabazite (CHA) structural collapse due to water vapor exposure up to 55 h regardless of SDA choice. However, a multinuclear solid-state magic angle spinning (SS-MAS) NMR study of Cu/SAPO-34(MO, TEA, TEAOH) suggests that the water vapor exposure had significantly altered the coordination environment of Al, P, and Si, the extent of which depends on the choice of SDA along with water vapor exposure time. NO-DRIFTS and H-2-TPR studies suggest different mobility for Cu ions between the 6MR and 8MR of the CHA structure in Cu/SAPO-34(MO, TEA, TEAOH) as the result of water vapor exposure and during the NH3-SCR reaction. The mechanisms for low temperature deactivation of Cu/SAPO-34 were proposed as follows: 1) irreversible Si condensation in the support and 2) Cu migration to less accessible sites and/or formation of CuOx clusters depending on Cu mobility.
  •  
46.
  • Yang, Xiaoyong, et al. (författare)
  • Probing the active sites of newly predicted stable Janus scandium dichalcogenides for photocatalytic water-splitting
  • 2019
  • Ingår i: Catalysis Science & Technology. - : ROYAL SOC CHEMISTRY. - 2044-4753 .- 2044-4761. ; 9:18, s. 4981-4989
  • Tidskriftsartikel (refereegranskat)abstract
    • The Janus structures of transition metal dichalcogenides with intrinsic dipoles have recently drawn attention as efficient candidates in the class of non-precious metal photocatalysts for water splitting. Here, we have proposed Janus ScXY (X/Y = S, Se, or Te, X not equal Y) monolayers as promising catalysts for the hydrogen evolution reaction (HER). We have thoroughly investigated the structural stabilities of the ScXY monolayers, as a primary step to understand the splitting mechanism more accurately. It has been observed that Janus ScSSe and ScSeTe monolayers are dynamically, thermally and mechanically stable, whereas the ScSTe monolayer is dynamically unstable. Moreover, based on hybrid functional (HSE06) calculations, these stable ScSSe and ScSeTe monolayers are semiconductors with direct band gaps of 1.810 and 0.921 eV, respectively. Considering spin-orbit coupling on top of the HSE06 calculations results in an insignificant change in the band gaps. The steady optical responses of Janus ScSSe and ScSeTe, respectively, in the visible and near IR spectra demonstrate their photocatalytic activities in the respective regions. Interestingly, we have observed excellent performance shown by the ScSeTe monolayer, where both surfaces are catalytically active, and maintain close to thermoneutral conditions with near-zero adsorption free energy at different H* coverages. Comparatively, the ScSSe monolayer shows poor performance for the HER due to strong bonds with the adsorbed hydrogen. Also, it has been confirmed that even the application of +/- 2% strain on the ScSSe monolayer does not enhance its HER activity. Our theoretical predictions demonstrate that out of all the Janus ScXY monolayers studied here, ScSeTe is the most active catalyst for the HER to efficiently split water, which certainly could make it worth performing further experimental investigations.
  •  
47.
  • Yuan, Ning, et al. (författare)
  • In situ XAS study of the local structure and oxidation state evolution of palladium in a reduced graphene oxide supported Pd(ii) carbene complex during an undirected C-H acetoxylation reaction
  • 2019
  • Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:8, s. 2025-2031
  • Tidskriftsartikel (refereegranskat)abstract
    • In situ X-ray absorption spectroscopy (XAS) investigations have been performed to provide insights into the reaction mechanism of a palladium(ii) catalyzed undirected C-H acetoxylation reaction in the presence of an oxidant. A Pd(ii) N-heterocyclic carbene complex π-stacked onto reduced graphene oxide (rGO) was used as the catalyst. The Pd speciation during the catalytic process was examined by XAS, which revealed a possible mechanism over the course of the reaction. Pd(ii) complexes in the as-synthesized catalyst first go through a gradual ligand substitution where chloride ions bound to Pd(ii) are replaced by other ligands with a mean bond distance to Pd matching Pd-C/N/O. Parallel to this the mean oxidation state of Pd increases indicating the formation of Pd(iv) species. At a later stage, a fraction of the Pd complexes start to slowly transform into Pd nanoclusters. The mean average oxidation state of Pd decreases to the initial state at the end of the experiment which means that comparable amounts of Pd(0) and Pd(iv) are present. These observations from heterogeneous catalysis are in good agreement with its homogeneous analog and they support a Pd(ii)-Pd(iv)-Pd(ii) reaction mechanism.
  •  
48.
  • Yuan, Ning, et al. (författare)
  • In Situ XAS Study of the Local Structure and Oxidation State Evolutions of Palladium in a Reduced Graphene Oxide Supported Pd(II) Carbene Complex during an Undirected C−H Acetoxylation Reaction
  • 2019
  • Ingår i: Catalysis Science & Technology. - 2044-4753 .- 2044-4761. ; 9:8, s. 2025-2031
  • Tidskriftsartikel (refereegranskat)abstract
    • In situ X-ray absorption spectroscopy (XAS) investigations have been performed to provide insights into the reaction mechanism of a palladium(II) catalyzed undirected C–H acetoxylation reaction in the presence of an oxidant. A Pd(II) N-heterocyclic carbene complex p-stacked onto reduced graphene oxide (rGO) was used as catalyst. The Pd speciation during the catalytic process was examined by XAS, which revealed a possible mechanism over the course of the reaction. Pd(II) complexes in the as-synthesized catalyst first go through a gradual ligand substitution where chloride ions bound to Pd(II) are replaced by other ligands with a bond distance to Pd corresponding to carbon, nitrogen and/or oxygen (L). Parallel to this the mean oxidation state of Pd increases indicating the formation of Pd(IV) species. At a later stage, a fraction of the Pd complexes start to slowly transform into Pd nanoclusters. The mean average oxidation state of Pd decreases to the initial state at the end of the experiment which means that comparable amounts of Pd(0) and Pd(IV) are present. These observations from heterogeneous catalysis are in good agreement with its homogeneous analog and they support a Pd(II)-Pd(IV)-Pd(II) reaction mechanism.
  •  
49.
  • Land, Henrik, et al. (författare)
  • One-pot biocatalytic amine transaminase/acyl transferase cascade for aqueous formation of amides from aldehydes or ketones
  • 2016
  • Ingår i: catalysis science & technology. - : Royal Society of Chemistry. - 2044-4753. ; 6, s. 2897-2900
  • Tidskriftsartikel (refereegranskat)abstract
    • An efficient one-pot one-step biocatalytic amine transaminase/acyl transferase cascade for the formation of amides from the corresponding aldehydes and ketones in aqueous solution has been developed. N-benzyl-2-methoxyacetamide has been synthesized utlilizing the developed cascade in conversions up to 97%. The cascade was also evaluated for the synthesis of chiral amides.
  •  
50.
  • Vargas-Salfate, S., et al. (författare)
  • System justification enhances well-being : A longitudinal analysis of the palliative function of system justification in 18 countries
  • 2018
  • Ingår i: British Journal of Social Psychology. - : John Wiley & Sons. - 0144-6665 .- 2044-8309. ; 57:3, s. 567-590
  • Tidskriftsartikel (refereegranskat)abstract
    • According to the palliative function of ideology hypothesis proposed by System Justification Theory, endorsing system-justifying beliefs is positively related to general psychological well-being, because this fulfils existential, epistemic, and relational needs. We discuss and address three main issues: (1) the role of societal inequality, (2) comparisons by social status, and (3) cross-sectional versus longitudinal research. We used a longitudinal survey of representative online samples (N=5,901) from 18 countries. The results supported the main argument proposed by the theory, in that system justification was positively and significantly related to life satisfaction and negatively related to anxiety and depression. The pattern of results suggested that the palliative function of system justification is more homogeneously distributed across individual and collective measures of social status than proposed by the theory, because the function was unaffected either by society-level inequality or by individual-level social status. These results allow us to infer that one of the reasons for the high stability of social arrangements is located in the psychological domain of palliative effects.
  •  
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