PNNL

Abstract

Reforming of methane with H2S is a promising path to directly utilize sour natural gas reserves, although some aspects of the mechanism and structure–function relations remain elusive. Here we show that metal oxides of group 4–6 elements, which are inert for steam and dry methane reforming reactions, are active and stable (pre)catalysts for the H2S reforming of methane. The key active sites are sulfur species (S*) that are dynamically bound to metal cations during catalysis. Similar H/D isotope exchange patterns and universal rate inhibition by H2 on representative catalysts indicate that H2S decomposition and recombination of surface hydrogen atoms are quasi-equilibrated, whereas CH4 dissociation steps are reversible, yet not quasi-equilibrated. An in-depth analysis of the kinetic data and isotopic substitution effects identifies S*-mediated C–H bond cleavage as the most plausible rate-limiting step common for all catalysts, with subtle yet essential differences between 3d and 4d/5d catalysts in the thermodynamic stability of S*. This work was financially supported by Evonik Industries. J.A.L. acknowledges support by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences (Impact of catalytically active centers and their environment on rates and thermodynamic states along reaction paths, FWP 47319). We thank L. Wahl and X. Hecht for the construction of the reaction device, S. Ren and F. Chew for catalyst screening, R. Weindl, A. Wellmann (Technical University of Munich) and J. Hu (Xiamen University) for transmission electron microscopy and Raman characterizations.