Selective Production of Hydrogen for Fuel Cells Via Oxidative Steam Reforming of Methanol Over CuZnAl Oxide Catalysts: Effect of Substitution of Zirconium and Cerium on the Catalytic Performance

Abstract

H₂ fuel, for fuel cells, is traditionally produced from methanol by the endothermic steam reforming of methanol (SRM). Partial oxidation of methanol (POM), which is highly exothermic, has also been suggested as a route to extract H₂ from methanol. In both these reactions a considerable amount of CO is produced as a byproduct, which is a poison to the Pt anode of the fuel cell. A combined steam reforming and partial oxidation of methanol, which has been termed “oxidative steam reforming of methanol” (OSRM), reported recently is considered to be more efficient and convenient for the selective production of H₂ at a relatively low temperature. The catalysts used in the OSRM reaction were CuZnAl mixed oxides derived from hydroxycarbonate precursors containing hydrotalcite (HT)-like layered double hydroxides (LDHs)/aurichalcite phases. Substitution of Zr for Al in the CuZnAl oxide system was found to improve the catalytic performance. In the present study, the role of added Zr was investigated in detail by employing spectroscopic methods such as X-ray diffraction (XRD), temperature-programmed reduction (TPR), electron paramagnetic resonance (EPR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (AES). The detailed spectroscopic studies revealed that substitution of Zr for Al improved the reducibility and dispersion of copper species due to the operation of a synergistic interaction between copper and zirconium as a consequence of the formation of a “Cu²⁺-O-Zr⁴⁺-O-” solid solution. The higher catalytic performance of CuZn-based catalysts containing Zr in the OSRM reaction was attributed to the ease of reducibility and enhanced dispersion of copper particles on the support. The substitution of Ce in the CuZnAl system, on the other hand, did not alter the catalytic performance greatly.