High‐Selectivity Tandem Photocatalytic Methanation of CO<sub>2</sub> by Lacunary Polyoxometalates‐Stabilized *CO Intermediate
Qian Zhu, Zhaohui Li, Tao Zheng, Xingxing Zheng, Si Liu, Shen Gao, Xionghui Fu, Xiaofang Su, Yi Zhu, Yuanming Zhang, Yongge Wei
Abstract
Abstract Stabilizing specific intermediates to produce CH 4 remains a main challenge in solar‐driven CO 2 reduction. Herein, g‐C 3 N 4 is modified with saturated and lacunary phosphotungstates (PW x , x =12, 11, 9) to tailor the CO 2 reduction pathway to yield CH 4 in high selectivity. Increased lacuna of phosphotungstates leads to higher CH 4 yield and selectivity, with a superior CH 4 selectivity of 80 % and 40.8 μmol ⋅ g −1 ⋅ h −1 evolution rate for PW 9 /g‐C 3 N 4 . Conversely, g‐C 3 N 4 and PW x alone show negligible CH 4 production. The conversion of CO 2 to CH 4 follows a tandem catalytic process. CO 2 is initially activated on g‐C 3 N 4 to form *CO intermediates, meanwhile photogenerated electrons derived from g‐C 3 N 4 transfer to PW x . Then the reduced PW x captures *CO, which is subsquently hydrogenated to CH 4 . With the injection of two photogenerated electrons, PW 9 is capable of adsorbing and activating *CO. However, the reduced PW 12 and PW 11 are incapable of adsorbing *CO due to the small energy of occupied molecular orbitals, which is the reason for the poorer activity of PW x /g‐C 3 N 4 ( x =12, 11) compared with that of PW 9 /g‐C 3 N 4 . This work provides new insights to regulate highly selective CO 2 photoreduction to CH 4 by utilizing lacuna of polyoxometalates to enhance the interaction of metals in polyoxometalates with key intermediates.