Vanadium species and their effect on the catalytic behavior of an FCC catalyst

Samples of a commercial FCC catalyst impregnated with 3000 ppm vanadium and subjected to oxidative and reductive treatments, were characterized by electron spin resonance (ESR) and tested in a microactivity test (MAT) to study the effect of different oxidation states of vanadium on the catalytic behavior when processing an atmospheric residue from the North Sea. MAT testing at 524 °C shows that samples containing a substantial part of V4+ combined with a strong part of V3+ or lower oxidation states give a considerably less catalytic effect of vanadium than samples containing mainly V5+. The test results indicate that V4+ and V5+ have quite similar dehydrogenation activities, while V3+ or lower oxidation states have almost no dehydrogenation effect. It has been found that different oxidation states of vanadium (V3+ or lower, V4+ and V5+) co-exist when treating the catalyst samples in 5% hydrogen in nitrogen at elevated temperatures up to 760 °C. The initial conversion to V3+ or lower oxidation states occurs no later than after only one-third of the vanadium is converted from V5+ to V4+. A relatively higher concentration of V4+ is allowed when treating the catalyst in 5% carbon monoxide in nitrogen.