Catalytic activity of laser-synthesized CrO_x/Al₂O₃ nanocatalysts with different particle sizes in isobutane dehydrogenation

CrO_x/Al₂O₃ model catalysts in the form of nanopowders with the chromium content of 0.96 wt% and the mean particle size 5.5, 7.3, 11.7, 13.1, and 20.5 nm were synthesized by a laser vaporization technique. CrO_x/Al₂O₃ nanocatalysts are mainly represented by softly agglomerated particles with a sphere-like morphology. It was shown that a considerable increase in the mean particle size from 5.5 to 20.5 nm with the corresponding decrease in specific surface area from 297 to 80 m²/g of the freshly prepared catalysts decreased isobutane conversion and selectivity to isobutylene at 550 °C by 2–4% and 10–15 mol.%, respectively. The laser synthesis was found to produce Al₂O₃ nanoparticles with stable highly dispersed Cr₂O₃ clusters on their surface, which serves as the active catalytic centers. The presence of such highly dispersed clusters with a size of 2–4 nm was confirmed by the HRTEM method. The catalytic properties of the tested nanocatalysts with the established steady state were stable in isobutane dehydrogenation over 25–30 dehydrogenation-regeneration cycles. On the nanocatalysts that reached a steady state, an increase in the mean particle size led to a decrease in isobutane conversion by 7 and 6%; selectivity to isobutene decreased by 11 and 10 mol.% at the reaction temperatures 560 and 580 °C, respectively.