NATURE AND CATALYTIC PERFORMANCE OF PTSAPO-5 MOLECULAR-SIEVE CATALYSTSYNTHESIZED BY ONE-STEP

Pt catalysts supported on silicoaluminophosphate molecular sieves were synthesized by adding platinum salts directly to the gel mixture of S APO. The synthesized products were marked as PtSAPO-5, in order to dis tinguish with the SAPO-5 supported platinum catalyst prepared by impre gnation, which was marked as Pt/SAPO-5. The as-synthesized and calcine d PtSAPO-5 samples were characterized by XRD, Si-29 MAS NMR,Xe-129 NMR and NH3-TPD, and their catalytic activities were evaluated by the hyd roisomerization of n-hexane. The results revealed that in PtSAPO-5, th e platinum could catalyze the removal of the templates entrapped in th e as-synthesized samples. The presence of Pt in the gel mixture can in crease silicon content in the framework of SAPO-S,and the acid sites. In the activated PtSAPO-5 catalyst, Pt was highly dispersed in the cha nnel 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. PtS APO-5 has a higher activity and selectivity than Pt/SAPO-5 in the hydr oisomerization 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 so mewhat retarded by the big platinum particles, and the acid sites are stronger than the former.