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 29Si solid-state NMR, it could be shown that SAPO-VPI-5 prepared with polyphosphoric acid as a phosphorus source exhibits both “silica patches” and isolated silicon atoms incorporated in the framework. Brønsted 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 hydroconverston 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. © 1993 Academic Press, Inc.