A comparative study of reactions of methanol over catalysts derived from NiAl- and CoAl-layered double hydroxides and their Sn-containing analogues

Ni- and Co-based catalysts derived from NiAl- and CoAl-layered double hydro xides were tested in four kinds of reactions of methanol, namely decomposit ion of methanol (DCM), partial oxidation of methanol (POM), steam reforming of methanol (SRM), and oxidative steam reforming of methanol (OSRM), for t he purpose of H-2 production for fuel cells. H-2, CO and/or CO2 were the pr edominant products with minor amounts of dimethyl ether (DME) and CH4 depen ding on the reaction temperature. Among the four kinds of reactions tested, the OSRM reaction was found to be more effective in terms of MeOH conversi on and H-2 selectivity over these catalysts. Higher selectivity of H-2 and CO2 with only traces of CO could be obtained at about 100% methanol convers ion around 300 C-degrees in the OSRM reaction over the catalyst derived fro m CoAl-LDH. Substitution of a part of Al by Sn in the NiAl- and CoAl-LDH sy stems was found to be inhibiting the methanol conversion. On the other hand , the selectivities to DME and CH4 were declined with a consequent increase in the selectivity to H-2. In addition, considerable amount of formaldehyd e was also noticed, especially over the catalyst derived from CoAlSn-LDH at lower reaction temperatures. The observed difference in the catalytic perf ormance upon Sn incorporation was attributed to an improved redox capabilit y of the Ni- and Co-based oxide catalysts, as determined by temperature-pro grammed reduction (TPR) experiments.