| 1. |
- Abdelgaid, Mona, et al.
(författare)
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Multiscale modeling reveals aluminum nitride as an efficient propane dehydrogenation catalyst
- 2023
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Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 13:12, s. 3527-3536
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Tidskriftsartikel (refereegranskat)abstract
- Nonoxidative propane dehydrogenation (PDH) is a promising route to meet the steadily increasing demand for propylene, an important building block in the chemical industry. Wurtzite group-IIIA metal nitrides are potential catalysts for PDH with high chemical, thermal, and mechanical stability alongside inherent Lewis acid-base properties that can activate the C-H bond of alkanes. Herein, we investigate the catalytic behavior of pristine (AlN) and gallium-doped (Ga/AlN) aluminum nitride for PDH via concerted and various stepwise mechanisms using density functional theory (DFT) calculations and microkinetic modeling (MKM). The reaction profiles investigated with DFT calculations are used in MKM, which reveals that the stepwise mechanisms produce >99% of propylene on both AlN and Ga/AlN. AlN has approximately one order of magnitude higher activity than Ga/AlN due to lower barriers along the dominant PDH reaction pathway. In summary, we propose the potential application of AlN as an efficient dehydrogenation catalyst for the conversion of light alkanes into valuable olefins. In addition, we show that multiscale simulations are essential to evaluate the catalytic behavior of complex alkane conversion reaction networks and obtain activity trends for dehydrogenation catalysts.
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| 2. |
- Aftab, Umair, et al.
(författare)
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The chemically reduced CuO-Co3O4 composite as a highly efficient electrocatalyst for oxygen evolution reaction in alkaline media
- 2019
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Ingår i: Catalysis Science & Technology. - : ROYAL SOC CHEMISTRY. - 2044-4753 .- 2044-4761. ; 9:22, s. 6274-6284
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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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| 3. |
- Arvidsson, Adam, 1990, et al.
(författare)
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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
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:17, s. 4573-4580
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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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| 4. |
- Arvidsson, Adam, 1990, et al.
(författare)
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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
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:7, s. 1470-1477
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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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| 5. |
- Auvray, Xavier, 1986, et al.
(författare)
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Lean and rich aging of a Cu/SSZ-13 catalyst for combined lean NO x trap (LNT) and selective catalytic reduction (SCR) concept
- 2019
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:9, s. 2152-2162
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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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| 6. |
- Azis, Muhammad Mufti, 1983, et al.
(författare)
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On the role of H2 to modify surface NOx species over Ag-Al2O3 as lean NOx reduction catalyst: TPD and DRIFTS studies
- 2015
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Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 55:1, s. 296-309
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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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| 7. |
- Baruah, Sunandan, et al.
(författare)
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Development of a visible light active photocatalytic portable water purification unit using ZnO nanorods
- 2012
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Ingår i: Catalysis Science & Technology. - 2044-4753 .- 2044-4761. ; 2:5, s. 918-921
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Tidskriftsartikel (refereegranskat)abstract
- A ZnO nanorods based water purification unit was designed which operates with solar energy as the source of activation. The purifier was tested on two model bacteria Escherichia coli and Staphylococcus aureus with concentration as high as 1010 colony forming units (CFU) per litre, which is about 105 times higher than the bacterial concentration in tap water. Up to 99% (0.99 × 1010 CFU L−1) removal of viable bacterial cells was achieved under sunlight activation.
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| 8. |
- Baruah, Sunandan, et al.
(författare)
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Development of a visible light active photocatalytic portable water purification unit using ZnO nanorods
- 2012
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Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 2:5, s. 918-921
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Tidskriftsartikel (refereegranskat)abstract
- A ZnO nanorods based water purification unit was designed which operates with solar energy as the source of activation. The purifier was tested on two model bacteria Escherichia coli and Staphylococcus aureus with concentration as high as 10(10) colony forming units (CFU) per litre, which is about 10(5) times higher than the bacterial concentration in tap water. Up to 99% (0.99 x 10(10) CFU L-1) removal of viable bacterial cells was achieved under sunlight activation.
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| 9. |
- Benzi, Federico, et al.
(författare)
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Transient structural and catalytic behaviour of Pt-particles probed by operando spectroscopy during a realistic driving cycle
- 2017
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Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:18, s. 3999-4006
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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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| 10. |
- Boje, Astrid, 1991, et al.
(författare)
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First-principles-informed energy span and microkinetic analysis of ethanol catalytic conversion to 1,3-butadiene on MgO
- 2021
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 11:20, s. 6682-6694
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Tidskriftsartikel (refereegranskat)abstract
- Kinetic modeling of single-step catalytic conversion of ethanol to 1,3-butadiene is necessary to inform accurate process design. This paper uses first-principles-informed energy span and microkinetic analysis to explore the reaction free energy landscapes and kinetic limitations of competing reaction pathways on a MgO (100) step-edge. Previous studies suggested mechanisms proceeding via both dehydrogenation and dehydration of ethanol, and highlighted sensitivity to conditions and catalyst composition. Here, we use the energy span concept to characterize the theoretical maximum turnover and degree of turnover frequency control for states in each reaction pathway, finding the dehydration route to be less active for 1,3-butadiene, and suggesting rate-determining states in the dehydrogenation, dehydration, and condensation steps. The influence of temperature on the relative rate contribution of each state is quantified and explained through the varying temperature sensitivity of the free energy landscape. A microkinetic model is developed to explore competition between pathways, interaction with gas-phase species, and surface coverage limitations. This suggests that the turnover may be significantly lower than predicted solely based on energetics. Turnover frequency determining states found to have high surface coverage include adsorbed ethanol and two longer, oxygenated hydrocarbons. The combined energy span and microkinetic analysis permits investigation of a complex system from two perspectives and helps elucidate conflicting observations of rate determining steps and product distribution by considering both energetic and kinetic limitations. The impact of uncertainty in the energy landscape is quantified using a correlated error model. While the range of predictions is large, the average performance and trends are similar.
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| 11. |
- Chaoquan, Hu, 1981, et al.
(författare)
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Catalytic hydrogenation of C=C and C=O in unsaturated fatty acid methyl esters
- 2014
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 4:8, s. 2427-2444
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Forskningsöversikt (refereegranskat)abstract
- Biodiesel derived from edible and non-edible oils has received much attention as a chemical feedstock or as a raw fuel alternative to the traditional diesel due to its renewability and biodegradability. However, the crude biodiesel containing large amounts of polyunsaturated fatty acid methyl esters (FAMEs) is susceptible to oxidation upon exposure to heat, light, and oxygen. Catalytic hydro-genation of biodiesel has been considered as a feasible and powerful technique to improve the oxidative stability of biodiesel and hence to provide stable raw materials for industrial applications. The catalytic hydrogenation of FAMEs is a complex process but basically consists of hydrogenation of C=C or C=O, depending on the desirable properties of final products. In this review, we summarize recent developments in hydrogenation of C=C and C=O in FAMEs with focus on catalysts, reaction mechanisms, and reactor conditions. The features of hydrogenation of FAMEs are generalized and the opportunities for future research in the field are outlined.
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| 12. |
- Chaoquan, Hu, 1981, et al.
(författare)
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Selectivity and kinetics of methyl crotonate hydrogenation over Pt/Al2O3
- 2015
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Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 5:3, s. 1716-1730
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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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| 13. |
- Chen, Lin, 1990, et al.
(författare)
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Effect of Al-distribution on oxygen activation over Cu-CHA
- 2018
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 8:8, s. 2131-2136
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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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| 14. |
- Chen, Zheng, et al.
(författare)
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Reaction pathways on N-substituted carbon catalysts during the electrochemical reduction of nitrate to ammonia
- 2022
-
Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry. - 2044-4753 .- 2044-4761. ; 12:11, s. 3582-3593
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical reduction of nitrate into ammonia is one potential strategy to valorize pollutants needed to close the nitrogen cycle. The understanding of carbonaceous materials as metal-free representatives of electrocatalysts is of high importance to ensure sufficient activity and target selectivity. We report on the role of defects in cellulose-derived nitrogen-doped carbon (NDC) materials, produced by ammonolysis at different temperatures, to obtain efficient electrocatalysts for the nitrate reduction reaction (NO3RR). Carbon catalyst ammonolysis at 800 °C (NDC-800) yields the highest electrochemical performance, exhibiting 73.1% NH4+ selectivity and nearly 100% NO3− reduction efficiency with a prolonged NO3RR time (48 h) at −1.5 V vs. Ag/AgCl in a 0.1 M Na2SO4 electrolyte. We provide support to our findings by undertaking complementary structural analyses with scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, low-temperature N2 adsorption, and theoretical studies based on multi-scale/level calculations. Atomistic molecular dynamics simulations based on a reactive force field combined with quantum chemistry (QC) calculations on representative model systems suggest possible realistic scenarios of the material structure and reaction mechanisms of the NO3− reduction routes.
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| 15. |
- Cornelius Chukwu, Eugenia, et al.
(författare)
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Engineered Aldolases Catalyzing Stereoselective Aldol Reactions Between Aryl-Substituted Ketones and Aldehydes
- 2023
-
Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry. - 2044-4753 .- 2044-4761.
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Tidskriftsartikel (refereegranskat)abstract
- An A129G/R134V/S166G triple mutant of fructose 6-phosphate aldolase (FSA) from Escherichia coli was further engineered with the goal to generate new enzyme variants capable of catalyzing aldol reactions between aryl substituted ketones and aldehydes. Residues L107 and L163 were subjected to saturation mutagenesis and the resulting library of FSA variants was screened for catalytic activity with 2-hydroxyacetophenone and phenylacetaldehyde as substrates. A selection of aldolase variants was identified that catalyze the synthesis of 2,3-dihydroxy-1,4-diphenylbutanone. The most active enzyme variants contained an L163C substitution. An L107C/L163C variant was further tested for activity with substituted phenylacetaldehydes, and was shown to afford the production of the corresponding diphenyl substituted butanones with good diastereoselectivities (anti : syn dr of 10 to 30) and reasonable to good enantioselectivities of syn enantiomers (er of 5 to 25).
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| 16. |
- Domen, K., et al.
(författare)
-
Editorial
- 2013
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 3:7, s. 1659-
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Tidskriftsartikel (refereegranskat)
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| 17. |
- Finnveden, Maja, et al.
(författare)
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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.
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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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| 18. |
- Florén, Carl-Robert, 1988, et al.
(författare)
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Modelling complete methane oxidation over palladium oxide in a porous catalyst using first-principles surface kinetics
- 2018
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 8:2, s. 508-520
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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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| 19. |
- Florén, Carl-Robert, 1988, et al.
(författare)
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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
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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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| 20. |
- Florén, Carl-Robert, 1988, et al.
(författare)
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Total oxidation of methane over Pd/Al2O3at pressures from 1 to 10 atm
- 2020
-
Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 10:16, s. 5480-5486
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of total methane oxidation over a 0.15 wt% Pd/Al2O3 monolith catalyst has been measured during temperature programmed methane oxidation experiments at total pressures from 1 to 10 atm and compared with multiscale simulations. The methane conversion can be significantly enhanced by increasing the total pressure at temperatures above 350 °C, which is thanks to a longer residence time that dominates over decreased bulk gas diffusion rates and product inhibition. For the present catalyst, the external mass transfer impacts the methane conversion above 4 atm. With increasing total pressure, the observed methane reactions order decreases at 350 °C whereas it increases at 450 °C due to a more pronounced product inhibition at the lower temperatures. This is also reflected in the apparent activation energy, which increases with increasing total pressure. The multiscale simulations capture the general trends of the experimental results but overestimate the methane conversion at higher temperatures and total pressures. The overestimated activity indicates of an overestimated number of active sites and/or an underestimated external mass transfer resistance.
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| 21. |
- Fouladvand, Sheedeh, 1984, et al.
(författare)
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A transient in situ infrared spectroscopy study on methane oxidation over supported Pt catalysts
- 2014
-
Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 4:10, s. 3463-3473
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Tidskriftsartikel (refereegranskat)abstract
- Catalysts with platinum dispersed on alumina, ceria and mixed alumina-ceria have been prepared by incipient wetness impreg- nation, characterized with transmission electron microscopy and X-ray diffraction, and evaluated for total oxidation of methane under both stationary and transient gas compositions (oxygen pulsing). Further, in situ diffuse reflectance Fourier transformed infrared spectroscopy has been used to monitor the evolution of surface species during precise transient gas composition changes using high-speed gas switching valves. The results show that platinum interacts sufficiently strong with all the supports so as to form small platinum particles. The smallest sizes are observed for the Pt/Ce sample. The alumina con- taining samples show, in contrast to the Pt/Ce sample, a decreased methane conversion with the increasing oxygen concentration and a clear kinetic bistability between increasing and decreasing oxygen concentrations. The bistable kinetics is likely connected to oxidation and reduction of platinum occurring at different stoichiometric gas mixtures depending on the history of the system, for which an oxidation of the platinum particles effectively inhibits the dissociative adsorption of methane leading to low reaction rate. It is shown for the alumina containing samples that the adverse effects of oxygen excess can be circumvented by the use of periodic operation so that the the average methane conversion is improved. Further, Pt/Ce seems to exhibit additional active sites at the platinum-ceria interface explaining the generally higher conversion of methane for this sample.
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| 22. |
- Fouladvand, Sheedeh, 1984, et al.
(författare)
-
Inside front cover
- 2014
-
Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 4:10, s. 3396-3396
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Tidskriftsartikel (refereegranskat)
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| 23. |
- Gao, Yuxi, et al.
(författare)
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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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| 24. |
- 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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| 25. |
- 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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| 26. |
- 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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| 27. |
- 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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| 28. |
- 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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| 29. |
- 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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| 30. |
- Hirschmann, Max, et al.
(författare)
-
Bi-functional and mono-component organocatalysts for the ring-opening alternating co-polymerisation of anhydride and epoxide
- 2023
-
Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 13:24, s. 7011-7021
-
Tidskriftsartikel (refereegranskat)abstract
- Bi-functional organocatalysts constituted by a (thio-)urea moiety and an iminophosphorane moiety were synthesized and optimised for the ring-opening alternating co-polymerisation of phthalic anhydride with three different epoxides: cyclohexene oxide, propylene oxide and butylene oxide. The most effective catalyst featured a cyclohexyl urea moiety, an iminophosphorane moiety with three 2,4-dimethyl-3-methoxy phenyl substituents, and a short spacer length of two carbon atoms between them. All tested epoxides reached quantitative conversion within 24 hours with ester-selectivities up to >97%. NMR and DFT experiments reveal that the catalysts exist in solution as dimers that dissociate during the initiation of the polymerisation. During the polymerisation, the catalyst is coordinated to the growing chain and further modulates its reactivity through reversible protonation/deprotonation suppressing transesterification side reactions even at prolonged polymerisation times without the need for a co-catalyst. The rate-determining step of the polymerisation is the ring-opening of the epoxide by the carboxylate chain end, and accordingly, higher temperatures (up to 150 °C) and higher concentrations of epoxide and catalyst increase polymerisation rates.
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| 31. |
- Hong, Sungil, et al.
(författare)
-
First-principles microkinetic modeling of partial methane oxidation over graphene-stabilized single-atom Fe-catalysts
- 2023
-
Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 13:24, s. 6999-7010
-
Tidskriftsartikel (refereegranskat)abstract
- Catalytic conversion of CH4 to transportable liquid hydrocarbons via partial oxidation is a promising avenue towards efficient utilization of natural gas. Single Fe atoms on N-functionalized graphene (FeN4/GN) have recently been shown to be active for partial CH4 oxidation with H2O2 at room temperature. Here, density functional theory (DFT) calculations combined with mean-field microkinetic modeling (MKM) have been applied to obtain kinetic understanding of partial CH4 oxidation with H2O2 to CH3OH and CH3OOH over FeN4/GN. CH3OH and CH3OOH are found to be minor and major reaction products, respectively, with a selectivity in agreement with reported experimental data. The kinetic modeling reveals two pathways for CH3OH production together with a dominant catalytic cycle for CH3OOH formation. The selectivity is found to be sensitive to the temperature and H2O2 concentration, with the CH3OH selectivity increasing with increasing temperature and decreasing H2O2 concentration. Turnover frequencies of both CH3OH and CH3OOH are found to decrease over time, due to a change in the Fe formal oxidation state from +6 to +4; Fe(+6) is more active, but less stable than Fe(+4). The present work unravels the detailed reaction mechanism for partial oxidation of methane by FeN4/GN, rationalizes experimental observations and provides guidance for efficient room-temperature methane conversion by single-atom Fe-catalysts.
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| 32. |
- 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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| 33. |
- Isapour Toutizad, Ghodsieh, 1986, et al.
(författare)
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In situ DRIFT studies on N2O formation over Cu-functionalized zeolites during ammonia-SCR
- 2022
-
Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 12:12, s. 3921-3936
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of the zeolite framework structure on the formation of N2O during ammonia-SCR of NOx was studied for three different copper-functionalized zeolite samples, namely Cu-SSZ-13 (CHA), Cu-ZSM-5 (MFI), and Cu-BEA (BEA). The evolution of surface species during the SCR reaction at different temperatures was monitored with step-response experiments using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) at different reaction conditions. Also, density functional theory (DFT) calculations were performed to assist the interpretation of the experimental results. The DRIFTS results indicate that NO+ and nitrate species are the main products formed during NO oxidation, and NO appears to adsorb on both Cu-Lewis and Al-Lewis acid sites. The DFT calculations for NO adsorption on the SSZ-13 sample reveal adsorption at Bronsted acid sites with similar adsorption energies but with a slight difference in NO+ stretching vibrations in the DRIFT spectra. Within the standard SCR reaction, in the O-H stretching region, the number of NH3 molecules adsorbed on the Bronsted acid sites is higher for the small-pore size sample compared to the medium- and large-pore zeolites. The obtained DRIFTS results for nitrate species are supported by DFT calculations by simulating the IR spectra of mobile and framework bound nitrate species, which both have a signature at 1604 cm(-1) associated with the O-N bond on NO3-. It is revealed that N2O is produced in a higher amount at lower temperatures for all three samples irrespective of the NO/NO2 ratio. Furthermore, the obtained results from both DRIFTS studies and flow reactor experiments show the higher formation of N2O for the large-pore zeolite compared to the medium- and small-pore zeolite.
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| 34. |
- Jørgensen, Mikkel, 1990, et al.
(författare)
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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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| 35. |
- 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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| 36. |
- Kannisto, Hannes, 1979, et al.
(författare)
-
On the performance of Ag/Al2O3 as a HC-SCR catalyst – influence of silver loading, morphology and nature of the reductant
- 2013
-
Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 3:3, s. 644-653
-
Tidskriftsartikel (refereegranskat)abstract
- This study focuses on the performance of Ag/Al2O3 catalysts for hydrocarbon selective catalytic reduction (HC-SCR) of NOx under lean conditions, using complex hydrocarbons as reductants. The aim is to elucidate the correlation towards the silver loading and morphology, with respect to the nature of the reductant. Ag/Al2O3 samples with either 2 or 6 wt% silver loading were prepared, using a sol–gel method including freeze-drying. The catalytic performance of the samples was evaluated by flow reactor experiments, with paraffins, olefins and aromatics of different nature as reductants. The physiochemical properties of the samples were characterized by scanning electron microscopy/energy dispersive X-ray spectroscopy, scanning transmission electron microscopy/high angle annular dark field imaging, X-ray photoelectron spectroscopy and N2-physisorption. The 2 wt% Ag/Al2O3 sample was found to be the most active catalyst in terms of NOx reduction. However, the results from the activity studies revealed that the decisive factorfor high activity at low temperatures is not only connected to the silver loading per se. There is also a strong correlation between the silver loading and morphology (i.e. the ratio between low- and high- coordinated silver atoms) and the nature of the hydrocarbon, on the activity for NOx reduction. Calculated reaction rates over the low-coordinated step and high- coordinated terrace sites showed that the morphology of silver has a significant role in the HC-SCR reaction.For applications which include complex hydrocarbons as reductants (e.g. diesel), these issues need to be considered when designing highly active catalysts.
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| 37. |
- Kirilin, Alexey V., et al.
(författare)
-
Aqueous-phase reforming of xylitol over Pt/C and Pt/TiC-CDC catalysts : catalyst characterization and catalytic performance
- 2014
-
Ingår i: Catalysis Science & Technology. - : RSC Publishing. - 2044-4753. ; 4:2, s. 387-401
-
Tidskriftsartikel (refereegranskat)abstract
- The aqueous phase reforming (APR) of xylitol was studied over five Pt/C catalysts. The correlation between physico-chemical properties of the catalysts and catalytic performance was established. The Pt/C catalysts have different textural properties as well as different mean Pt cluster sizes and surface acidity. The average Pt cluster size was investigated by means of CO chemisorption as well as by TEM. The reaction was found to be structure sensitive and TOF linearly increases with increasing average Pt cluster size in the studied domain. The catalysts which possess higher surface acidity favoured higher rates of hydrocarbon production. On the contrary the Pt/C materials with lower acidities generated hydrogen with high selectivity and TOF.
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| 38. |
- Klacar, Simon, 1984, et al.
(författare)
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H-2 dissociation over Ag/Al2O3: the first step in hydrogen assisted selective catalytic reduction of NOx
- 2013
-
Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 3:1, s. 183-190
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrogen assisted selective catalytic reduction of NOx over Ag/Al2O3 with either hydrocarbons or ammonia as reducing agents is an emerging technology for lean NOx reduction. Herein, we present a density functional theory study of H-2 dissociation over a representative set of sites present on the Ag/Al2O3 catalyst. Whereas H-2 dissociation over supported Ag ions and oxidized Ag surfaces is found to be facile, dissociation over metallic Ag, defect free Al2O3 and alumina-supported Ag is associated with high barriers. The results are rationalized by analysis of the electronic structure.
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| 39. |
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| 40. |
- Konwar, Lakhya Jyoti, et al.
(författare)
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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.
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| 41. |
- Koroidov, Sergey, et al.
(författare)
-
Chemisorbed oxygen or surface oxides steer the selectivity in Pd electrocatalytic propene oxidation observed by operando Pd L-edge X-ray absorption spectroscopy
- 2021
-
Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 11:10, s. 3347-3352
-
Tidskriftsartikel (refereegranskat)abstract
- Controlled electrochemical oxidation of hydrocarbons to desired products is an attractive approach in catalysis. Here we study the electrochemical propene oxidation under operando conditions using Pd L-edge X-ray absorption spectroscopy (XAS) as a sensitive probe to elucidate surface processes occurring during catalysis. Together with ab initio multiple-scattering calculations, our XAS results enable assignment of characteristic changes of the Pd L-edge intensity and energy position in terms of a mechanistic understanding of the selective oxidation of propene. The results, supported by electrochemical density functional theory DFT simulations, show that in the potential range of 0.8–1.0 V vs. the reversible hydrogen electrode (RHE), selective oxidation of propene to acrolein and acrylic acid occurs on the metallic Pd surface. These reactions are proposed to proceed via the Langmuir–Hinshelwood mechanism. In contrast, for the potential range of 1.1–1.3 V vs. RHE, selective oxidation of propene to propylene glycol takes place on a Pd oxide surface.
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| 42. |
- Kosem, Nuttavut, et al.
(författare)
-
Photobiocatalytic H(2)evolution of GaN:ZnO and [FeFe]-hydrogenase recombinantEscherichia coli
- 2020
-
Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 10:12, s. 4042-4052
-
Tidskriftsartikel (refereegranskat)abstract
- The need for sustainable, renewable and low-cost approaches is a driving force behind the development of solar-to-H(2)conversion technologies. This study aims to develop a new strategy using a visible-light photocatalyst coupled to a biocatalyst for H(2)production. Photocatalytic methyl viologen (MV2+) reduction activity was investigated to discover active oxynitrides. In comparative studies with LaTiO2N, BaTaO2N and Ta3N5, it was revealed that the suitable surface area, band gap and band edge potentials are some physical factors that are responsible for the photocatalytic behaviors of GaN:ZnO in MV(2+)reduction. The activity is enhanced at higher concentrations and the alkaline pH of triethanolamine (TEOA). The expression of an active [FeFe]-hydrogenase fromEscherichia coli(Hyd(+)E. coli) as a recombinant biocatalyst was confirmed by its MV & x2d9;(+)-dependent H(2)production activity. In the photobiocatalytic system of GaN:ZnO and Hyd(+)E. coli, the rate of H(2)production reached the maximum level in the presence of MV(2+)as an electron mediator at neutral pH as a biocompatible condition. The present work reveals a novel hybrid system for H(2)production using visible-light active GaN:ZnO coupled to Hyd(+)E. coli, which shows the feasibility of being developed for photobiocatalytic H(2)evolution under solar light.
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| 43. |
- 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.
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| 44. |
- Kusema, Bright T, et al.
(författare)
-
Kinetics of L-arabinose oxidation over supported gold catalysts with in situ catalyst electrical potential measurements
- 2012
-
Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753. ; 2, s. 423-431
-
Tidskriftsartikel (refereegranskat)abstract
- The kinetics of L-arabinose selective oxidation over Au/Al2O3 catalysts was studied with simultaneous in situ catalyst electrical potential measurements. An oxidative dehydrogenation mechanism was proposed and a kinetic model taking into account the catalyst potential changes was developed. The kinetic model was implemented into the three-phase system and validated with the experimental observations. The agreement of the kinetic model to the experimental data, in line with the suggested reaction mechanism, was satisfactory.
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| 45. |
- Kärkäs, Markus D., et al.
(författare)
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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.
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| 46. |
- Li, Yucheng, et al.
(författare)
-
Facile synthesis of a high-efficiency NiFe bimetallic catalyst without pre-reduction for the selective hydrogenation reaction of furfural
- 2022
-
Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 13:2, s. 457-467
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Tidskriftsartikel (refereegranskat)abstract
- A high-efficiency nickel-iron bimetallic catalyst (Ni3Fe1 alloy) was synthesized by a facile solvothermal reaction and directly used in furfural hydrogenation without pre-reduction. When the total metal acetate was 6 mmol (Ni : Fe = 4 : 2) with 2 mmol sodium acetate under reaction conditions of 1 MPa H2 pressure at 130 °C for 1 h, the conversion for furfural and selectivity for furfuryl alcohol were both more than 98%. XRD, BET, H2-TPD, SEM, HRTEM, EDS, ICP-MS and ex/in situ XPS were used to characterize the catalysts. Compared to the monometallic Ni catalyst, the introduction of Fe not only enhanced the hydrogen adsorption capacity of Ni but also forms NiFe2O4 on the surface of the catalyst to protect the internal crystals from further oxidation and maintain hydrogenation ability. Moreover, the introduction of Na increased the purity of the Ni3Fe1 crystal of the catalyst and reinforced the interaction between Ni and Fe, resulting in an improvement in hydrogenation performance. Based on density functional theory (DFT) calculations, the reaction mechanism was systematically investigated. The results of five recycling tests show excellent catalyst stability. The environmentally friendly synthetic process, high stability, catalytic efficiency and the ability to function without a pre-reduction step make the nickel-iron bimetallic catalyst an ideal, commercial candidate for the furfural hydrogenation reaction.
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| 47. |
- Li, Yunguo, et al.
(författare)
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Review of two-dimensional materials for photocatalytic water splitting from a theoretical perspective
- 2017
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Ingår i: Catalysis Science & Technology. - : ROYAL SOC CHEMISTRY. - 2044-4753 .- 2044-4761. ; 7:3, s. 545-559
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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.
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| 48. |
- Li, Yunguo, et al.
(författare)
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Single-layer MoS2 as an efficient photocatalyst
- 2013
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 3:9, s. 2214-2220
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Tidskriftsartikel (refereegranskat)abstract
- The potential application of the single-layer MoS2 as a photocatalyst was revealed based on first-principles calculations. It is found that the pristine single-layer MoS2 is a good candidate for hydrogen production, and its catalysing ability can be tuned by the applied mechanical strain. Furthermore, the p-type doping could make the single layer a good photocatalyst for the overall water splitting.
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| 49. |
- Liao, Rong-Zhen, et al.
(författare)
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On the mechanism of water oxidation catalyzed by a dinuclear ruthenium complex : a quantum chemical study
- 2016
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Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 6:13, s. 5031-5041
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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.
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| 50. |
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