Vanadosilicates having the pentasil structure were prepared by the rapid crystallization method using the following starting vanadium salts; NH4VO3(V5+), VOSO4(V4+), VOC2O4(V4+), VCl3(V3+), and V(C5H7O2)3(V3+). No vanadium ions were incorporated for NH4VO3 salt, because the vanadium ion from NH4VO3 could not interact strongly with the gel and because the vanadium ion was excluded from the crude crystal during the course of crystallization in the hydrothermal condition. The vanadium ion from other salts was considerably incorporated and atomically dispersed in the crystal. However, the crystallinity, morphology, BET surface area, and acidic property changed with the kind of starting vanadium salts. The V(C5H7O2)3 salt was the most effective for preparing a vanadosilicate having high crystallinity, large BET surface area, large number of strong acid sites, and uniform crystalline size. The VCl3 salt exhibited characteristics opposite to the V(C5H7O2)3 salt. Although Al ions from the raw materials of catalysts were considered to be partly responsible for the formation of strong acid site, the incorporated vanadium ions were found to control the number of strong acid sites. In accordance with these changes in the physical properties of the vanadosilicates, the catalytic performance changed greatly with the kind of starting vanadium salts. The vanadosilicate from VCl3 salt did not exhibit high activity even at the beginning of the reaction and deactivated rapidly with increasing time on stream. On the other hand, the vanadosilicate from V(C5H7O2)3 showed high activity for more than 10 h on stream and was the best among the vanadosilicates. It was also found that the incorporated vanadium ion accelerates the combustion of the deposited coke with air in the regeneration process.
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