Platinum supported on alkaline and alkaline earth metal-doped alumina as catalysts for dry reforming and partial oxidation of methane

Pt catalysts with low metal loadings (0.02, 0.1 and 0.5 wt%) supported on alkaline (Na and K) or alkaline earth (Mg) metals-doped alumina were tested in the catalytic partial oxidation and dry reforming of methane. Supports were characterized by X-ray diffraction and also by determining their BET surface area, temperature-programmed desorption of CO2, and isopropanol dehydration; while catalysts were characterized by X-ray diffraction, temperature programmed reduction, tests of cyclohexane dehydrogenation, temperature-programmed oxidation, and transmission electronic microscopy. The presence of the dopants modified the thermal stability of the gamma-Al2O3 phase by calcination at 1000 degrees C and the acidity of the support. The gamma -> theta transition took place for K- and Na-doped catalysts, the acidity being almost suppressed. Conversely, the Mg-doped gamma-Al2O3 was thermally stable, and the catalysts still showed some acidic sites. The catalytic performances in both partial oxidation and dry reforming processes were dependent on the support dopants, with a more notable effect observed at low-noble-metal loadings. K- and Na-doped catalysts showed poor activities in the catalytic partial oxidation reaction, whereas the presence of Mg in the alumina promoted the catalytic activity. In the dry reforming reaction an improvement was found in the catalytic activity for the sample with the highest Pt content; moreover, the K-doped catalysts were slightly more efficien