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This work gives an insight into combined experimental and DFT study of water gas shift reaction on Ni catalysts at moderately elevated temperatures. The relative reactivity of surface adsorbed species O*, OH* and H* with CO* and their catalytic consequence in reaction mechanism and kinetics was studied. DFT investigation and microkinetic analysis pointed out that the favorable reaction pathway depends on the relative reactivity of O*, OH* and H* with CO* on the surface. It rationalizes the experimental observed changes in kinetics with hydrogen pressure. • Experimental and DFT study leads to WGS reaction mechanism insight on Ni catalyst. • It reveals dependency of the reaction mechanism and kinetics on hydrogen pressure. • Reaction pathway is dependent on relative reactivity of O*, OH* and H* with CO*. • DFT studies rationalize the experimental changes in kinetics with H 2 pressure. This paper presents a combined experimental and density functional theory study of the relative reactivity of surface species O*, OH*, and H* with CO* on nickel catalysts and their catalytic consequence in reaction mechanism and kinetics of water gas shift reaction. The kinetic study illustrates the hydrogen reaction order changes from 0.5 at relatively low hydrogen pressures to -1 at high hydrogen pressures. Detailed kinetic analysis indicated a hydrogen-induced change of the corresponding reaction pathway from hydrogen assisted CO activation to the redox mechanism with CO*+O* as a rate-determining step. The DFT investigation revealed that the surrounding surface H* atoms destabilize more significantly O* adsorption than H* adsorption, thus enhance more the reactivity of O* than H* towards reaction with CO* at high H* coverage. This kinetic study provides an insightful depiction for the future study of CO activation on other transition metals and the catalyst development for WGS reaction. [ABSTRACT FROM AUTHOR]

Understanding the chain growth mechanism is of vital importance for the development of catalysts with enhanced selectivity towards long-chain products in cobalt-catalyzed Fischer-Tropsch synthesis. Herein, we discriminate various C1 + C1 coupling reactions by theoretical calculations and kinetic isotope experiments. CHx(x=0−3), CO, HCO, COH, and HCOH are considered as the chain growth monomer respectively, and 24 possible coupling reactions are first investigated by theoretical calculations. Eight possible C1 + C1 coupling reactions are suggested to be energetically favorable because of the relative low reaction barriers. Moreover, five pathways are excluded where the C1 monomers show low thermodynamic stability. Effective chain propagation rates are calculated by deconvoluting from reaction rates of products, and an inverse kinetic isotope effect of the C1 + C1 coupling reaction is observed. The theoretical kinetic isotope effect of CO + CH2 is inverse, which is consistent with the experimental observation. Thus, the CO + CH2 pathway, owing to the relatively lower barrier, the high thermodynamic stability, and the inverse kinetic isotope effect, is suggested to be a favorable pathway. [ABSTRACT FROM AUTHOR]