Synthesis of nanostructured pt/CeO_2-ZrO_2-Al_2O_3 catalysts by a two-step sol-gel method

摘要

Porous Pt/CeO_2-ZrO_2-Al_2O_3 catalysts were synthesized by a two-step sol-gel method in which noble metal nanoparticles were first prepared as a dispersed colloid in an aqueous medium, then mixed with aluminum isopropoxide (AIP), Ce(NO_3)_4 and Zr(NO_3)_4, and condensed into a gel. After calcination at 800 deg C for 3 h, these composite catalysts showed large specific surface areas (150-160 m~2 g~(-1)) and a narrow pore size distribution of 10-12 nm as determined from the nitrogen adsorption/desorption isotherms. XPS and TEM scans showed that the active component of the catalyst was well dispersed, with the Pt nanoparticles (particle size 3-5 nm) confined to the pores. It was found that changing the template surfactants from ionic cetyltrimethylammonium bromide (CTAB) to non-ionic polyethylene glycol P-l,l,3,3-tetramethylbutylphenyl ether (TritonX-100) did not change either the specific surface area or the pore structure, but lowered the CO-to-CO_2 reaction temperature by nearly 60 deg C. Measurements of CO conversion proved that the catalyst prepared with TritonX-100 as the template had the highest catalytic activity: the onset of the conversion of CO to CO_2 began at 158 deg C and was complete at 192 deg C. The possible mechanism of the anti-aggregation of nanoparticles and high catalyst activity has been discussed.