Oxidative steam reforming of methanol over CuZnAl(Zr)-oxide catalysts for the selective production of hydrogen for fuel cells: Catalyst characterization and performance evaluation

A new series of CuZnAl(Zr)-oxide catalysts were prepared by the decompositi on of CuZnAl(Zr)-hydroxycarbonate precursors containing hydrotalcite (HT)-l ike layered double hydroxide (LDH)/aurichalcite phases around 450 degrees C . The physicochemical properties of the catalysts were investigated by X-ra y diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), tempera ture-programmed reduction (TPR), electron paramagnetic resonance (EPR) spec troscopy, and surface area measurements. XRD of the catalysts indicated the presence of a mixture of poorly crystallized CuO and ZnO phases whose crys tallinity increased with decreasing Al content. TPR results demonstrated th at substitution of Zr for Al improved the copper reducibility and dispersio n. 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 clust er-like Cu2+ species were present in the Zr-rich samples, The oxidative ste am reforming of methanol reaction was performed over these catalysts in the temperature range 180 degrees to 290 degrees C at atmospheric pressure usi ng H2O/CH3OH, molar ratio = 3. Initially, the Cu:Zn:Al metallic composition was optimized and it was found that catalytic performance in terms of meth anol conversion and Hz 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 ca talytic performance of Zr-containing catalysts was attributed to the improv ed Cu reducibility, higher Cu metal surface area, and dispersion. Studies o f the effect of MeOH contact time on the catalytic performance over a Zr-co ntaining catalyst revealed that both CO and CO2 were produced as primary pr oducts, and CO was subsequently transformed into CO2 + H-2 by the water-gas shift reaction/and CO oxidation, (C) 2000 Academic Press.