Steam reforming of methanol over CeO2- and ZrO2-promoted Cu-ZnO catalysts supported on nanoparticle Al2O3

Methanol steam reforming was studied over several ZrO2- and CeO2-promoted catalysts prepared by deposition of copper and zinc oxide precursors onto nanoparticle Al2O3 and ZrO2 supports. The catalysts were characterized using temperature programmed reduction (TPR), Brunauer–Emmett–Teller (BET) surface area measurements, N2O decomposition, and X-ray diffraction (XRD) and the results were compared to a commercially available Cu/ZnO/Al2O3 catalyst. It was found that the catalyst activities and CO selectivities are very dependent on both the catalyst preparation method and the ZrO2 precursor. The best performing catalyst was prepared by co-impregnating Cu and ZnO precursors onto a physical mixture of nanoparticle ZrO2 and nanoparticle Al2O3. This catalyst resulted in a highly active reforming catalyst which also suppressed CO production. The turnover frequencies of catalysts containing ZrO2 nanoparticles were notably higher than those of similar catalysts which contained impregnated ZrO2, and dramatically higher than the commercially available reference catalyst. This indicates that the presence of ZrO2 nanoparticles promotes a highly active copper surface. Addition of high surface area alumina was necessary to assure a reasonable Cu surface area. However, the catalytic activities of the catalysts in this study did not correlate with Cu surface area, total surface area, or reduction temperature. It is therefore postulated that the presence of a monoclinic ZrO2 phase, which is a result of using a monoclinic nanoparticle ZrO2 precursor, promotes methanol reforming and also suppresses methanol decomposition, both of which are desired in methanol reforming catalysts.