Activity and stability enhancement of copper–alumina catalysts using cerium and zinc promoters for the selective production of hydrogen via steam reforming of methanol

Abstract

The catalytic activity and hydrogen selectivity of cerium and zinc promoted copper–alumina catalysts have been investigated for the selective production of hydrogen via steam reforming of methanol (SRM). The SRM was carried out in a fixed bed tubular reactor at atmospheric pressure over a temperature range 200–300 °C. The major reaction products were hydrogen and carbon dioxide with traces of carbon monoxide. Catalysts of varying compositions were prepared by the wet impregnation method and characterized by atomic absorption spectroscopy (AAS), BET surface area, pore volume, pore size, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and thermogravimetry analysis (TGA). Results revealed that the methanol conversion, hydrogen selectivity and carbon monoxide formation varied with the type of promoter and content of copper in the catalyst. Cerium promoted Cu–Zn–Ce–Al-oxide catalysts improved the activity and hydrogen selectivity greatly and also kept the CO formation very low. Using cerium the SRM could be carried out at lower temperature with high methanol conversion, results in suppression of methanol decomposition and reverse water gas shift reactions eventually end-up with the low carbon monoxide and hydrogen rich product stream. Cerium also stabilizes the copper–alumina catalysts effectively that was confirmed by deactivation studies in which cerium promoted Cu–Zn–Ce–Al-oxide catalysts gave the consistent performance for a long run-time compared to catalysts containing only zinc promoter. The optimum operating conditions for SRM have been investigated by detailed study of effects of reaction temperature, contact time and steam to methanol molar ratio on methanol conversion, hydrogen selectivity and CO formation. Reaction pathway has been proposed for the SRM based on results obtained.