The water-gas shift reaction on Pt/γ-Al2O3 Catalyst: Operando SSITKA-DRIFTS-mass spectroscopy studies

Steady-state isotopic transient kinetic analysis (SSITKA) experiments coupled with in situ DRIFTS and mass spectrometry (operando) were performed for the first time to study essential mechanistic aspects of the water-gas shift reaction (WGSR) over a 0.5 wt.% Pt/gamma-Al2O3 catalyst. The chemical structure of active and inactive reaction intermediate species present in the carbon-path (C-path) from CO to the CO2 product gas (Use Of (CO)-C-13) and in the hydrogen-path (H-path) from H2O to the H-2 product gas (use of D2O) of the reaction mechanism were determined. In addition, the concentrations (mu mol/g) of active species in both the C-path and H-path of the WGSR at 350 degrees C were measured. Based on the large concentration of active species present in the H-path (OH/H located on the alumina support), the latter being larger than 28 equivalent monolayers of the exposed Pt metal surface, the small concentration of OH groups along the periphery of metal-support interface, and the significantly smaller concentration (mu mol/g) of active species present in the C-path (adsorbed CO on Pt and COOH species on the alumina support and/or the metal-support interface), it might be suggested that diffusion of OH/H species on the alumina support surface towards Pt catalytic sites present in the H-path of reaction (back-spillover process) might be considered as a slow reaction step. The latter process was evidenced after conducting the WGS reaction (CO/H2O) in a partially deuterated alumina surface (Pt/gamma-Al2O3). At least two kinds of formate (-COOH) species residing on the alumina surface have been identified, one of which was active and leads to the formation of CO2(g) and H-2(g), whereas the other kind(s) is/are considered as inactive (spectator) adsorbed reaction intermediate species. (C) 2008 Elsevier B.V. All rights reserved.