Nature and catalytic performance of PtSAPO-5 molecular sieve catalyst synthesized by one step

Pt catalysts supported on silicoaluminophosphate molecular sieves were synthesized by adding platinum salts directly to the gel mixture of SAPO. The synthesized products were marked as PtSAPO-5, in order to distinguish with the SAPO-5 supported platinum catalyst prepared by impregnation, which was marked as Pt/SAPO-5. The as-synthesized and calcined PtSAPO-5 samples were characterized by XRD,29Si MAS NMR,129XeNMR and NH3-TPD, and their catalytic activities were evaluated by the hydroisomerization of n-hexane. The results revealed that in PtSAPO-5, the platinum could catalyze the removal of the templates entrapped in the as-synthesized samples. The presence of Pt in the gel mixture can increase silicon content in the framework of SAPO-5, and the acid sites. In the activated PtSAPO-5 catalyst, Pt was highly dispersed in the channel of SAPO-5 molecular sieve. Pt exists in the form of big particles outside of the channel of Pt/SAPO-5 prepared by impregnating method, and impregnation with H2PtCl6 improved the strength of acid sites. PtSAPO-5 has a higher activity and selectivity than Pt/SAPO-5 in the hydroisomerization of n-hexane. This is because the former has medium acid sites and high dispersion of Pt, while the channel of Pt/SAPO-5 is somewhat retarded by the big platinum particles, and the acid sites are stronger than the former.