Distribution of chromium species in catalysts supported on ZrO2/Al2O3 and performance in dehydrogenation

Chromium catalysts (2–3 wt% Cr) supported on Al2O3 and ZrO2/Al2O3, prepared with Cr(NO3)3·9H2O or K2CrO4, were characterized and studied in the isobutane dehydrogenation. Depending on the chromium salt and the support, CrO3, Cr2O3, and K2CrO4 species were observed in the calcined samples, and amorphous Cr2O3 remained after reduction with H2. The preparation of ZrO2/Al2O3 support yields zirconia dispersed on the surface of alumina. In the Cr/ZrO2/Al2O3 calcined catalysts, the chromium sites were distributed on the ZrO2 and Al2O3 surfaces. The O2 chemisorption and the activity and selectivity to isobutene were also affected by the chromium species distribution. The addition of potassium decreased the O2 chemisorption. In the isobutane dehydrogenation, the turnover number and selectivity to isobutene increased for the catalysts prepared with K2CrO4.