Stabilizing effect of α-Cr2O3 on highly active phases and catalytic performance of a chromium alumina catalyst in the process of isobutane dehydrogenation

Abstract

• Stabilization of active phases of amorphous Cr 2 O 3 and polychromates by α-Cr 2 O 3 • Cr 2 O 3 -phases prevent agglomeration of active phase particles • Cr 2 O 3 -phases contribute of high catalytic performance The demand for C 3 -C 5 olefins is constantly growing, that is why it is important to improve the performance of catalysts for dehydrogenation of light alkanes. The study regards the influence of the supports porous system, the contribution of α-Cr 2 O 3 particles to the state of the active phase and the catalytic performance of the chromia-alumina catalysts in the isobutane dehydrogenation reaction. The catalysts were synthesized by impregnating the support with chromic acid. The supports and the catalysts were studied by the following techniques: low-temperature nitrogen adsorption, temperature-programmed desorption and reduction; UV-Vis- and Raman-spectroscopy, X-ray phase and X-ray fluorescence analyses. It was found that crystals of α-Cr 2 O 3 are formed on a support with 56 m 2 /g specific surface area and 7.1% (m/m) chromium content, that contributes to stabilization of the particles of highly active phases of amorphous Cr 2 O 3 and polychromates and catalytic performance. Meanwhile, no α-Cr 2 O 3 particles are formed on a support with a 103 m 2 /g specific surface area and 7.4% (m/m) chromium content. Therefore, in the course of 54 regeneration reactions cycles, the rates of isobutylene formation and isobutylene selectivity are significantly reduced due to agglomeration of amorphous Cr 2 O 3 particles, formation of di-, tri- chromates, and migration of part of chromium into the support structure.