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

Abstract: 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. Graphical Abstract: 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. [Figure not available: see fulltext.].