Hydrogen production over highly active Pt based catalyst coatings by steam reforming of methanol: Effect of support and co-support

The effect of metal oxide (CeO2, Al2O3 and ZrO2) support and In2O3 co-supported Pt catalysts has been investigated on steam reforming of methanol in microreactors. CeO2, Al2O3 and ZrO2 were prepared by the sol-gel method and they were used as a support, which was impregnated with In2O3 as co-support followed by the introduction of Pt species via the wet impregnation method. The size and dispersion of the Pt nanoparticles on In2O3/support have been examined by transmission electron microscopy. From these TEM and XPS results, it was found that the addition of In2O3 supports the formation of a high concentration of metallic Pt nanoparticles with enhanced dispersion and controlled particle size on the surface. The activity and stability of all the developed catalysts were tested for the steam reforming of methanol in microreactors at different temperatures. Under reforming conditions without prior reduction, a Pt/CeO2 catalyst containing 15 wt % of Pt exhibited complete methanol conversion and high selectivity towards hydrogen at 350 °C. However, the CO formation was found to be very high (7.0 vol %) for this catalyst. Upon addition of In2O3 as a co-support to this formulation the formation of CO decreased considerably. Pt/In2O3/CeO2 catalyst containing 15 wt % of Pt and 15 wt % of In2O3 showed excellent catalytic performance at much lower concentration of CO. This change could be closely associated with the formation of metallic Pt nanoparticles with smaller size, higher dispersion with strong interaction between Pt, In2O3 and support, which creates more oxygen vacancies to activate the water molecule which then react with methanol to produce H2 and CO2 suppressing the CO formation. Moreover, CeO2 supported Pt/In2O3 catalyst displayed higher stability with lowest CO formation under continuous steam reforming operation of 100 h. The superior performance of this catalyst is thought to be due to the relative abundance of redox sites on the CeO2 surface, which is able to create an oxygen vacancy as it possesses higher oxygen storage capacity and oxygen exchange capacity. This work demonstrates that the nature of support plays a crucial role for the continuous activation of reactants and determines the catalytic stability during methanol steam reforming.