Initial catalytic behavior of chromium oxide during induction period of fluidized dehydrogenation of propane

Abstract

Fluidized-bed propane dehydrogenation (PDH) has the advantage being energy efficient; however a new catalyst-design concept that overcomes short reaction time is required. While Pt and Cr are excellent catalysts for PDH, the formation of propylene is delayed for a few seconds due to the formation of CH4, CO and CO2. To better understand this induction period, we developed a reaction system for monitoring products on the second timescale and an analytical method (TPO) for distinguishing different oxygen species that develop over the Cr/Al2O3. A detailed correlation between the initial selectivity to propylene and the formation of oxygen species on a chromium-alumina catalyst was established by O2-TPO and Raman analysis. The properties of the oxygen species were found to depend on the degree of redox catalyst dispersion, and that lattice oxygen accumulated over the monolayer results in an oxidation reaction that is responsible for the induction period. We also introduce a catalyst-development strategy for fluidization process that reduces the induction period by control of oxygen species on catalyst and increases propylene selectivity within 3 s of the commencement of the reaction.