Influence of template on Si distribution of SAPO-11 and their performance for n-paraffin isomerization

Abstract

SAPO-11 molecular sieves were synthesized using single agent (i.e. diethylamine (DEA), di- iso-propylamine (DIPA) and di- n-propylamine (DPA)) or a mixture of DEA and DIPA (named DEPA) as the template under hydrothermal conditions. XRD indicated that the directing effect of different templates for AEL structure decreased in the order of DEPA > DPA > DIPA > DEA. 29Si MAS NMR showed that although all SAPO-11 samples synthesized at same Si content, that prepared with the mixed template contained more Si (4Al) sites, whereas Si ( nAl, 4- nSi, 0 < n < 4) environments were predominant in the samples synthesized with single template. The results indicated that the mixed template led to a better Si dispersion and then increased the number of total acid sites of SAPO-11. In the isomerization of n-tetradecane over different Pt/SAPO-11 catalysts, the sample prepared with DEPA showed high catalytic activity and selectivity for i-C 14, which were related to the most abundant weak acid sites of the sample.