Propane combustion over supported Pd catalysts

摘要

We prepared Pd catalysts supported on various metal oxides, viz.yAl_20_3, α-Al_20_3, Si0_2-Al_20_3, Si0_2, CeO_2 and TiO_2 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 temperatureprogrammed oxidation (TPO) were employed to characterize the catalysts. Pd/Si0_2–Al_20_3 showed the least catalytic activity at high temperatures among Pd catalysts supported on irreducible metal oxides, viz. Si0_2, Al_20_3 and Si0_2–Al_20_3. Pd/y-Al_20_3 was much superior for this reaction to Pd/α- Al_2O_3. The Pd catalyst supported on reducible metal oxides (CeO_2 and Ti0_2) 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/SiO_2–Al_20_3, the initially reduced Pd catalyst was superior to the fully oxidized one. The oxidation of metallic Pd occurred in the presence of 0_2 with increasing reaction temperature, which resulted in the change in the catalytic activity.