Solar energy-driven C−H activation of methanol for direct C−C coupling to ethylene glycol with high stability by nitrogen doped tantalum oxide

Abstract

Direct photocatalytic coupling of methanol to ethylene glycol (EG) is highly attractive. The reported photocatalysts for this reaction are all metal sulfide semiconductors, which may suffer from photocorrosion and have low stability. Thus, the development of non-sulfide photocatalysts for efficient photocatalytic coupling of methanol to EG and H2 with high stability is urgent but extremely challenging. Herein, the first metal oxide photocatalyst, tantalum-based semiconductor, is reported for preferential activation of C−H bond within methanol to form hydroxymethyl radical (•CH2OH) and subsequent C−C coupling to EG. Compared with other metal oxide photocatalysts, such as TiO2, ZnO, WO3, Nb2O5, tantalum oxide (Ta2O5) is unique in that it can realize the selective photocatalytic coupling of methanol to EG. The co-catalyst free nitrogen doped tantalum oxide (2%N-Ta2O5) shows an EG formation rate as high as 4.0 mmol gcat−1 h−1, about 9 times higher than that of Ta2O5, with a selectivity higher than 70%. The high charge separation ability of nitrogen doped tantalum oxide plays a key role in its high activity for EG production. This catalyst also shows excellent stability longer than 160 h, which has not been achieved over the reported metal sulfide photocatalysts. Tantalum-based photocatalyst is an environmentally friendly and highly stable candidate for photocatalytic coupling of methanol to EG.