Hydrogen Production from Methanol over Gold Supported on ZnO and CeO₂ Nanoshapes

Abstract

In the present study we have found that gold supported on CeO2 and ZnO with well-defined crystal structures or shapes is an excellent catalyst for the low-temperature (175−225 °C) steam reforming of methanol (SRM). We have compared the active nature of gold dispersed on {0001} surfaces of ZnO nanorods and polyhedra to our previous work, which demonstrates that TEM-invisible gold dispersed on the {110} surfaces of CeO2 catalyzes the SRM reaction in a cooperative mechanism with CeO2. Similar to Au−CeO2, we have found that Au−O bonds are essential species for SRM over Au−ZnO and the same apparent activation energy (110−120 kJ·mol−1) of the reaction was calculated for both catalysts. On the basis of temperature-programmed surface reaction/mass spectrometry analysis, we determined that the SRM reaction on both Au−ZnO and Au−CeO2 involves methanol dehydrogenation, methyl formate hydrolysis, and formic acid decomposition steps to produce CO2 and H2. Better than 95% catalyst selectivity to CO2 was found over the temperature range from 175 to 250 °C for both catalysts. In the presence of methanol, the water−gas shift reaction is suppressed and is not part of the mechanism at temperatures below 250 °C. The SRM stability of the Au−ZnO and Au−CeO2 systems is good for practical application of this type catalyst.