Influence of sulfur on the carbon deposition in steam reforming of liquid hydrocarbons over CeO2-Al2O3 supported Ni and Rh catalysts

This study was performed to elucidate the influence of sulfur on the carbon deposition in steam reforming of liquid hydrocarbons over CeO2-Al2O3 supported Ni and Rh catalysts at 800 degrees C. The characteristics of the carbon deposits on the used catalysts after the reactions without and with sulfur were investigated by temperature-programmed oxidation (TPO), transmission electron microscopy (TEM), scanning transmission X-ray microscopy (STXM), temperature-programmed hydrogenation (TPH), X-ray absorption near edge structure (XANES), and scanning electron microscopy (SEM). Though abundant carbon deposits can accumulate on the pure CeO2-Al2O3 support due to fuel thermal cracking, the addition of Ni or Rh metal greatly reduced the carbon deposition in the sulfur-free reaction. The presence of sulfur increased the carbon deposition on both catalysts, which has a much more significant impact for the Ni catalyst. Carbon XANES study on the used catalysts revealed that graphitic carbon was dominant in the presence of sulfur, while oxidized carbon species (quinone-like carbon, carboxyl and carbonate) prevailed without sulfur. Meanwhile, the formation of carboxyl and carbonate more dramatically dropped on the Ni catalyst than that on the Rh catalyst. Our results strongly suggest that (I) the presence of sulfur can suppress carbon gasification and promote the formation of graphitic carbon on reforming catalysts due mainly to its poisoning effect on metals, and (II) Rh catalyst possesses stronger capability to maintain carbon gasification activity than Ni catalyst in the presence of sulfur. (C) 2010 Elsevier B.V. All rights reserved.