Ga-Doped and Pt-Loaded Porous TiO₂–SiO₂ for Photocatalytic Nonoxidative Coupling of Methane

Abstract

Photodriven nonoxidative coupling of CH₄ (NOCM) is a potential alternative approach to clean hydrogen and hydrocarbon production. Herein, a Mott-Schottky photocatalyst for NOCM is fabricated by loading Pt nanoclusters on a Ga-doped hierarchical porous TiO₂-SiO₂ microarray with an anatase framework, which exhibits a CH₄ conversion rate of 3.48 μmol g^-1 h^-1 with 90% selectivity toward C₂H₆. This activity is 13 times higher than those from microarrays without Pt and Ga. Moreover, a continuous H₂ production (36 μmol g^-1) with a high CH₄ conversion rate of ∼28% can be achieved through a longtime irradiation (32 h). The influence of Ga on the chemical state of a surface oxygen vacancy (Vo) and deposited Pt is investigated through a combination of experimental analysis and first-principles density functional theory calculations. Ga substitutes for the five-coordinated Ti next to Vo, which tends to stabilize the single-electron trapped Vo and reduce the electron transfer from Vo to the adsorbed Pt, resulting in the formation of a higher amount of cationic Pt. The cationic Pt and electron-enriched metallic Pt form a cationic-anionic active pair, which is more efficient for the dissociation of C-H bonds. However, the presence of too much cationic Pt results in more C₂₊ product with a decrease in the CH₄ conversion rate due to the reduced charge-carrier separation efficiency. This study provides deep insight into the effect of the doping/loading strategy on the photocatalytic NOCM reaction and is expected to shed substantial light on future structural design and modulation.