The Nature of the Isolated Gallium Active Center for Propane Dehydrogenation on Ga/SiO2

Single-site Ga/SiO2 catalysts exhibit up to 99% C3H6 selectivity at 4% propane conversion with an initial rate of 5.4 × 10−4 (mole C3H6) (mole Ga)−1 s−1 during propane dehydrogenation (PDH) at 550 °C. Following pre-treatment in H2 at 550 °C, only four-coordinate, Ga3+–O Lewis acid sites are observed under reaction conditions. At 650 °C in H2, an additional isolated Ga site with lower Ga–O coordination (N Ga−O < 4) is formed and leads to a 30% decrease in the initial PDH rate per total moles of Ga. The PDH rates are equivalent when normalized by the amount of surface, four-coordinate Ga3+–O, regardless of catalyst pre-treatment conditions, which indicates that these isolated Ga3+ centers are the catalytically relevant sites. Isolated, Lewis acidic Ga3+ cations present as four-coordinate Ga3+–O centers exhibit up to 99% C3H6 selectivity during propane dehydrogenation (PDH) at 550 °C. An additional isolated Ga site with lower Ga–O coordination is formed during H2 treatment at elevated temperatures, but is inactive for PDH and reversibly decomposes under reaction conditions.