Hydrogen production by oxidative methanol reforming on Pd/ZnO

Pd/ZnO catalysts with Pd loadings of between 1 and 45% were prepared by impregnation and coprecipitation methods; their catalytic performances during oxidative methanol reforming for the production of hydrogen were investigated under various reaction conditions. The prepared catalysts showed high activity and selectivity towards hydrogen formation. At higher Pd loading (exceeding 5%), the coprecipitation method was superior to the impregnation method for the preparation of the catalyst. Highly active Pd/ZnO that is comparable to commercial Cu-Zn catalyst can be obtained with high Pd loadings. On the other hand, CO formation was greatly reduced by increasing the Pd loading. Excess amounts of Pd on the ZnO decreased the conversion of methanol and increased CO formation. XRD characterization of freshly prepared and spent catalysts confirmed the formation of the Pd-Zn alloy. The sizes of both the ZnO and the Pd-Zn crystallites affect the catalytic performance. A strong interaction between the Pd-Zn alloy and the ZnO support is believed to be essential for the selective formation of hydrogen. The reaction mechanism and the CO formation route are also discussed, based on the results that we obtained.