Distribution of chromium species in catalysts supported on ZrO 2/Al 2O 3 and performance in dehydrogenation

Abstract

Chromium catalysts (2–3 wt% Cr) supported on Al 2O 3 and ZrO 2/Al 2O 3, prepared with Cr(NO 3) 3·9H 2O or K 2CrO 4, were characterized and studied in the isobutane dehydrogenation. Depending on the chromium salt and the support, CrO 3, Cr 2O 3, and K 2CrO 4 species were observed in the calcined samples, and amorphous Cr 2O 3 remained after reduction with H 2. The preparation of ZrO 2/Al 2O 3 support yields zirconia dispersed on the surface of alumina. In the Cr/ZrO 2/Al 2O 3 calcined catalysts, the chromium sites were distributed on the ZrO 2 and Al 2O 3 surfaces. The O 2 chemisorption and the activity and selectivity to isobutene were also affected by the chromium species distribution. The addition of potassium decreased the O 2 chemisorption. In the isobutane dehydrogenation, the turnover number and selectivity to isobutene increased for the catalysts prepared with K 2CrO 4.