Oxidative Steam Reforming of Methanol over CuZnAl(Zr)-Oxide Catalysts for the Selective Production of Hydrogen for Fuel Cells: Catalyst Characterization and Performance Evaluation

Abstract

A new series of CuZnAl(Zr)-oxide catalysts were prepared by the decomposition of CuZnAl(Zr)-hydroxycarbonate precursors containing hydrotalcite (HT)-like layered double hydroxide (LDH)/aurichalcite phases around 450°C. The physicochemical properties of the catalysts were investigated by X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), temperature-programmed reduction (TPR), electron paramagnetic resonance (EPR) spectroscopy, and surface area measurements. XRD of the catalysts indicated the presence of a mixture of poorly crystallized CuO and ZnO phases whose crystallinity increased with decreasing Al content. TPR results demonstrated that substitution of Zr for Al improved the copper reducibility and dispersion. UV–vis DRS and EPR results revealed that isolated Cu2+ ions interacting with Al were formed in the Al-rich samples, while mostly bulk-like or cluster-like Cu2+ species were present in the Zr-rich samples. The oxidative steam reforming of methanol reaction was performed over these catalysts in the temperature range 180° to 290°C at atmospheric pressure using H2O/CH3OH, molar ratio=3. Initially, the Cu : Zn : Al metallic composition was optimized and it was found that catalytic performance in terms of methanol conversion and H2 production rate increased with decreasing Al content. Among CuZnAl-oxide catalysts the one with Cu : Zn : Al=37.6 : 50.7 : 11.7 (wt%) was found to be the most active. Replacement of Al either partially or completely by Zr further improved the catalytic performance. The higher catalytic performance of Zr-containing catalysts was attributed to the improved Cu reducibility, higher Cu metal surface area, and dispersion. Studies of the effect of MeOH contact time on the catalytic performance over a Zr-containing catalyst revealed that both CO and CO2 were produced as primary products, and CO was subsequently transformed into CO2+H2 by the water–gas shift reaction/and CO oxidation.