Synergistic effect of the metal-support interaction and interfacial oxygen vacancy for CO_(2) hydrogenation to methanol over Ni/In_(2)O_(3) catalyst:A theoretical study

Indium oxide supported nickel catalyst has been experimentally confirmed to be highly active for CO_(2) hydrogenation towards methanol.In this work,the reaction mechanism for CO_(2) hydrogenation to methanol has been investigated on a model Ni/In_(2)O_(3) catalyst,i.e.,Ni_(4)/In_(2)O_(3),via the density functional theory(DFT)study.Three possible reaction pathways,i.e.,the formate pathway,CO hydrogenation and the reverse water-gas-shift(RWGS)pathways,have been examined on this model catalyst.It has been demonstrated that the RWGS pathway is the most theoretically-favored for CO_(2) hydrogenation to methanol.The complete RWGS pathway follows CO_(2)+6 H→COOH+5 H→CO+H_(2)O+4 H→HCO+H_(2)O+3 H→H_(2)CO+H_(2)O+2 H→H_(3)CO+H_(2)O+H→H_(3)COH+H_(2) O.Furthermore,it has been also proved that the interfacial oxygen vacancy can serve as the active site for boosting the CO_(2) adsorption and charge transfer between the nickel species and indium oxide,which synergistically promotes the consecutive CO_(2) hydrogenation towards methanol.

First-principles characterization of formate and carboxyl adsorption on stoichiometric CeO_2(111)and CeO_2(110) surfaces

Molecular adsorption of formate and carboxyl on stoichiometric CeO2（111） and CeO2（110） surfaces was studied using periodic density functional theory （DFT＋U） calculations. Two distinguishable adsorption modes （strong and weak） of formate are identified. The bidentate configuration is more stable than the monodentate adsorption configuration. Both formate and carboxyl bind at the more open CeO2（110） surface are stronger. The calculated vibrational frequencies of two adsorbed species are consistent with the experimental measurements. Fi- nally, the effects of U parameters on the adsorption of formate and carboxyl over both CeO2 surfaces were investigated. We found that the geometrical configurations of two adsorbed species are not affected by different U parameters （U = 0, 5, and 7）. However, the calculated ad- sorption energy of carboxyl pronouncedly increases with the U value while the adsorption energy of formate only slightly changes （〈0.2 eV）. The Bader charge analysis shows the opposite charge transfer occurs for formate and carboxyl adsorption where the adsorbed formate is neg- atively charge while the adsorbed carboxyl is positively charged. Interestingly, with the increasing U parameter, the amount of charge is also increased.

Integrating Zeolite and Layered Double Hydroxide for Highly Selective Catalytic Production ofγ-Valerolactone

The production ofγ-valerolactone(GVL)from biomass derivatives levulinic acid(LA)based on acidbase metallic catalysts offers a sustainable pathway to the synthesis of valuable chemicals and biofuels.However,the development of efficient metallic catalysts with tunable Lewis acid–base and Brønsted acid sites remains a challenge.Herein,for the first time,we integrated zeolite and layered double hydroxide(LDH),in a core–shell structure,wherein zeolite and CoFe-LDH provided the Brønsted acidic sites and Lewis acid sites,respectively.Meanwhile,oxygen vacancies(OV_(x))acting as Lewis bases were generated on the surface of LDH via Ga doping.An efficient cascade catalytic reaction from LA to GVL was successfully achieved over the designed Beta@LDH-OVx catalyst,affording a superior conversion of LA(>99.9%)and an impressive selectivity to GVL(89.18%).Importantly,the“memory effect”of LDH endowed the catalyst with excellent regeneration of metal active sites.Density functional theory calculations revealed that the introduced OVx facilitated the adsorption of carbonyl oxygen in LA and boosted the production of GVL through the synergistic effect of acid/base sites in the composite catalyst.This work presents a rational design route for the construction of multifunctional catalysts by coupling zeolites and LDHs for highly selective catalytic conversion of biomass.

La ions-enhanced NH_(3)-SCR performance over Cu-SSZ-13 catalysts

Lanthanum(La)ions are generally recognized to cause a decline of the catalytic performance for Cu-SSZ-13 zeolite in the selective catalytic reduction of NO_(x)with NH_(3)(NH_(3)-SCR).Herein,we demonstrate that the NH_(3)-SCR performance and hydrothermal stability of Cu-La-SSZ-13 zeolites can be enhanced with the incorporation of a small amount of La ions.The incorporation of La ions into SSZ-13 favors more Z_(2)Cu^(2+)ions at six-membered rings(6MRs),which results in higher hydrothermal stability of Cu-La-SSZ-13 than that of Cu-SSZ-13.The NO conversion of Cu-La-SSZ-13 achieves 5%–10%higher than that of Cu-SSZ-13 at the temperature range of 400–550℃ after hydrothermal ageing.While introducing excess amount of La ions in SSZ-13 may cause the formation of inactive CuO_(x),leading to the decrease of catalytic activity and hydrothermal stability.Notably,the low-temperature activity of Cu-SSZ-13 with a low Cu content(≤2 wt.%)can be boosted by the introduction of La ions,which is largely due to the improved redox ability of Cu active sites modified by La ions.Density functional theory(DFT)calculations indicate that La ions prefer to locate at eight-membered rings(8MRs)and thus promoting the formation of more Z_(2)Cu^(2+)ions.Meanwhile,the existence of La ions in SSZ-13 inhibits the dealumination process and the transformation from Z_(2)Cu^(2+)to CuO_(x),resulting in its enhanced hydrothermal stability.The present work sheds a new insight into the regulation of secondary metal cations for promoting high NH_(3)-SCR performance over Cu-SSZ-13 zeolite catalysts.

Air-Steam Etched Construction of Hierarchically Porous Metal-Organic Frameworks

The introduction of mesoporosity into the microporous metal-organic frameworks(MOFs)is expected to expand their applications.Herein,we report a green and facile method to obtain hierarchically porous MOF structures by using an air-steam etching process.By virtue of the protonation reaction between the imidazole moiety and water vapor,the protonated imidazole related linkers leave the framework,resulting in the formation of mesopores in the zeolitic imidazolate frameworks(ZIFs),as exemplified by ZIF-8.Given the mild etching process,the materials'structural integrity and crystallinity are well maintained.Accordingly,the hierarchical porous ZIF-8 exhibited enhanced performance in the dye removal as well as CO_(2) cycloaddition reaction with epichlorohydrin in comparison with microporous ZIF-8,owing to the accelerated mass transfer arising from mesoporous structures.Remarkably,the proposed steam etching approach is generally applicable,which can be readily extended to other ZIFs,such as ZIF-14,ZIF-69,and ZIF-71,thus representing a powerful strategy to construct hierarchically porous MOF materials.

Thermodynamic and kinetic roles of H2 in structure evolution of urchin-like Co:A density functional theory study

Small gas molecules acting as good capping agents play important roles in controlling the morphologies and surface structures of metal nanocrystals.In the present work,the thermodynamic and kinetic roles of H2 molecules in the morphology of Co nanocrystals were systematically studied by density functional theory(DFT).The Gibbs surface free energies of Co(100),Co(110),and Co(111)at different hydrogen surface coverages were determined by ab initio thermodynamics.The phase diagram of stable H coverage on each plane was obtained and morphology evolution of the Co nanocrystals with various surface hydrogen coverages was predicted by the Wulff construction.Addition of H2 changes the facet stability,generating diverse morphological Co nuclei.The kinetic role of H2 in adatom Co surface diffusion at different H coverages was investigated by DFT.The results suggest that surface H hinders Co surface diffusions,except for Co(100)at 0.56 monolayer coverage.The projected density of states gives deeper insight into the electronic structures of Co adatoms with addition of the surface H atoms,which affect its surface diffusion ability.