Isomorphous substitution and the generation of catalytic activity in VPI-5

VPI-5 and substituted derivatives containing silicon or magnesium have been synthesized, analyzed, and tested for their catalytic activity. By means of [sup 29]Si solid-state NMR, it could be shown that SAPO-VPI-5 prepared with polyphosphoric acid as a phosphorus source exhibits both [open quotes]silica patches[close quotes] and isolated silicon atoms incorporated in the framework. Broensted acid sites in SAPO-and MAPO-VPI-5 could be detected by means of infrared spectroscopy in combination with pyridine adsorption. The isomorphously substituted VPI-5 samples were active in the hydroconversion of n-heptane, giving both cracking and isomerization products. The highest activity and the highest yield in iso-heptane, however, were observed with AlPO-VPI-5 as a catalyst. The catalytic activity could be ascribed to the presence of unreacted alumina. Upon treatment with an EDTA solution the Al/P atomic ratio decreased from 1.29 to 1.07, and the purified AlPO-VPI-5 showed considerably reduced catalytic activity. 28 refs., 6 figs., 2 tabs.