Production of hydrogen from oxidative steam reforming of methanol: II. Catalytic activity and reaction mechanism on Cu/ZnO/Al 2O 3 hydrotalcite-derived catalysts

Abstract

Cu/ZnO/Al 2O 3 catalysts derived from a hydrotalcite precursor were studied for oxidative steam reforming of methanol (OSRM), with O 2:H 2O:CH 3OH molar ratios = 0.12:1.1:1. The results were compared with those obtained in nonoxidative steam reforming (SRM) and in partial oxidation (POM) of methanol. The catalysts were highly active for OSRM, giving total CH 3OH conversion at 350–400 °C with GHSV = 0.6 – 1.2 × 10 5 h − 1 . They also showed high selectivity, giving H 2 yield of 2.5 mol per mole CH 3OH, with CO concentration below 500 ppm. Besides the main products, CH 2O and (CH 3) 2O were also observed at all temperatures, while some CH 4 was produced at T > 300 °C . The catalytic activity increased with increasing heating rate of the catalyst precursor. High selectivity was observed also in SRM, but with lower conversion. On the other hand, POM appeared faster than SRM, but produced CO concentrations of a few percent at T > 300 °C , due to CH 3OH decomposition. The production of CO was strongly reduced in the presence of water vapor. The reaction network was described in detail. The interaction methanol catalyst was studied by IR spectroscopy. IR spectra showed the presence of adsorbed methoxy groups, that were converted into formate groups at high temperature, and then decomposed into H 2 and CO in the absence of O 2 and/or H 2O, while in their presence CO was probably oxidized to CO 2 before desorption, due to the action of Cu(II) species.