Propane combustion over supported Pd catalysts

We prepared Pd catalysts supported on various metal oxides, viz. gamma-Al2O3, alpha-Al2O3, SiO2-Al2O3, SiO2, CeO2 and TiO2 by an incipient wetness method and applied them to propane combustion. Several techniques: N-2 physisorption, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), CO chemisorption, temperature-programmed reduction (TPR) and temperature-programmed oxidation (TPO) were employed to characterize the catalysts. Pd/SiO2-Al2O3 showed the least catalytic activity at high temperatures among Pd catalysts supported on irreducible metal oxides, viz. SiO2, Al2O3 and SiO2-Al2O3. Pd/gamma-Al2O3 was much superior for this reaction to Pd/alpha-Al2O3. The Pd catalyst supported on reducible metal oxides (CeO2 and TiO2) with a less specific surface area showed the higher catalytic activity compared with that supported on reducible metal oxides with a higher specific surface area, even though the former had a less Pd dispersion than the latter. In the case of Pd/SiO2-Al2O3, the initially reduced Pd catalyst was superior to the fully oxidized one. The oxidation of metallic Pd occurred in the presence of O-2 with increasing reaction temperature, which resulted in the change in the catalytic activity.