Design of frustrated Lewis pair in defective TiO2 for photocatalytic non-oxidative methane coupling

Abstract

The efficient C–H polarization is the prerequisite for the low-temperature photocatalytic CH 4 conversion, which is restricted by the poor C–H stretching ability of short-distance adjacent lattice atoms. Here, a frustrated Lewis pair (FLP) composed of doped metal in TiO 2 as Lewis acid (LA) and neighboring Ti–OH as Lewis base (LB) with a long distance (0.31–0.37 nm) was designed through DFT calculation and fabricated by hydrogenation treatment of metal-doped TiO 2 –SiO 2 with macroporous-mesoporous structure. Benefitting from the long LA-LB distance and matched acid-base intensity, hydrogenated Ga-doped composite achieves superior C–H stretching with a high photocatalytic CH 4 conversion rate (139 μmol g −1 h −1 ). The photo-irradiation causes electron excitation from Ga to Ti–OH according to the time-dependent DFT calculation and in situ EPR analysis, which promotes the formation and coupling of ·CH 3 . This work provides a key underpinning for regulating the characteristics of FLP for C–H activation and C–C coupling via light irradiation. • Frustrated Lewis pair (FLP) in defective TiO 2 was designed by DFT calculation • 139 μmol g −1 h −1 CH 4 conversion rate in NOCM is achieved under irradiation • FLP with long distance and suitable Lewis intensity is conducive to C–H stretching • Photo-irradiation promotes the formation and coupling of CH 3 The serious greenhouse effect caused by the massive use of fossil energy is an inevitable environmental problem in today’s world. In particular, the greenhouse effect of methane is 25 times that of CO 2 . However, the traditional methane conversion process consumes a great deal of energy. This study emphasizes the efficient conversion of methane driven by green and renewable solar energy under mild conditions. Its fundamental principle is to generate a charge by using light in semiconductors. The efficient conversion of methane is attributed to the unique active sites designed on TiO 2 , such as magnets, which attract C and H, respectively, effectively break the C–H bond, and generate high-value products under the action of a photogenerated charge. This research does not require the high temperature and high pressure of traditional industry and is of great significance to realize energy development and environmental protection that is beneficial to all. Long LA–LB distance and strong acid and base intensities promote the stretching of the C–H bond. The effect of light irradiation on improving the intensities of LA Ga and LB Ti–OH was confirmed based on the electron transition from LA to LB, which is the key to forming methyl and hydrogen radicals for the further coupling production of C 2 H 6 .