| Popis: |
The effects of CeO 2 and MoO 3 on the surface interaction in the Pt/γ-Al 2 O 3 system were studied by selective chemisorption of CO on Pt to measure the dispersion, sintering and redispersion of PtO 2 on 3.6% CeO 2 /γ-Al 2 O 3 and 5.3% MoO 3 /γ-Al 2 O 3 supports. Chemisorption data of CO on Pt/CeO 2 /γ-Al 2 O 3 and Pt/MoO 3 /γ-Al 2 O 3 reduced at 300 ° C, show that the presence of CeO 2 and MoO 3 increases the dispersion limit (the saturation concentration in the disperssed phase) of PtO 2 on γ-Al 2 O 3 . In each case, the dispersion limit of PtO 2 at 500 ° C is increased about 2–3 fold compared to that in Pt/γ-Al 2 O 3 . Temperature programmed reductions of Pt/CeO 2 /γ-Al 2 O 3 and Pt/MoO 3 /γ-Al 2 O 3 by H 2 show that the presence of Pt lowers significantly the temperatures for the removal of capping oxygen anions of CeO 2 and MoO 3 on γ-Al 2 O 3 . All these observations are attributed to the enhanced metal oxide-support interaction in the Pt/CeO 2 /γ-Al 2 O 3 and Pt/MoO 3 /γ-Al 2 O 3 catalysts. Reduction at 500 ° C by H 2 generally decreases the amount of CO chemisorption and lowers the surface coverage of Pt on CeO 2 /γ-Al 2 O 3 and MnO 3 /γ-Al 2 O 3 . While the sintered Pt/γ-Al 2 O 3 can be completely redispersed by heating in O 2 at 500 ° C, the sintered Pt/CeO 2 -γ-Al 2 O 3 and Pt/MoO 3 /γ-Al 2 O 3 show only partial redispersion, or none at all, under the same conditions. |
