Selective production of hydrogen by partial oxidation of methanol over catalysts derived from CuZnAl-layered double hydroxides

Hydrogen production by partial oxidation of methanol (POM) reaction (CH3OH + (1/2)O-2 reversible arrow 2H(2) + CO2) was investigated over a series of CuZnAl ternary oxide catalysts derived from CuZnAl hydroxycarbonate precursors containing hydrotalcite-like layered double hydroxide as a major phase. These catalysts exhibited a good catalytic activity and high H-2 selectivity. A methanol conversion of about 40-60% was obtained at 200(degrees)C with high selectivity of H-2 and CO2. The undesirable by-product, CO was virtually not produced over most of the catalysts at this temperature. The catalytic activity was found to decrease with increasing (Cu+Zn)/Al atomic ratio in the precursor and, was correlated with Cu metal surface areas, Cu dispersion and Cu particle sizes, which were calculated by both XRD and TPR-N2O passivation methods. The catalyst with higher Cu surface areas and Cu dispersion displayed a higher catalytic activity. Lifetime experiments showed that these catalysts were stable over a period of 24 h of continuous operation. Catalyst precursors containing hydroxycarbonates other than LDH as a major phase offered considerable amount of dimethyl ether as a by-product.