Insight into mechanism of divalent metal cations with different d-bands classification in layered double hydroxides for light-driven CO2 reduction

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2022-01, Vol.427, p.130863, Article 130863
• Main Authors: Wang, Ruonan, Qiu, Zhongyong, Wan, Shipeng, Wang, Yanan, Liu, Qiang, Ding, Jie, Zhong, Qin
• Format: Article
• Language: English
• Subjects: D-band center; Divalent metal cations; Layered double hydroxide; Photocatalytic CO2 reduction
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2021.130863

[Display omitted] •MAl-LDHs (M = Mg, Ni, Cu, Zn) were prepared for solar-driven CO2 conversion.•The effects of d orbitals structure of M2+ on activity and stability were inspected.•The possible reaction mechanism on LDHs surface was proposed.•The relevance between d-band center and photocatalytic activity was established.•Hard and soft acid base theory was used to explain the stability distinction. By varying divalent-metal cations (M = Mg2+, Ni2+, Cu2+, Zn2+) with different d-bands classification, MAl-LDHs were prepared and inspected for solar-driven CO2 conversion. The CO and CH4 yields over these LDHs followed an order of: NiAl-LDHs > CuAl-LDHs > ZnAl-LDHs > MgAl-LDHs. Coupled with multiple characterizations, the activity distinction was revealed from three crucial perspectives: (i) light harvesting, (ii) charge separation and transfer, (iii) surface reactions. The results affirmed that when d orbital was partially occupied with active electrons, both activation of CO2 and excitation of electrons were much easier to achieve. In-situ DRIFTS manifested that NiAl-LDHs and CuAl-LDHs exhibited more active reaction with CO2, which may be related to the upward shifts of the d-band center determined by Valence-band XPS. Particularly, these LDHs exhibited various catalytic stabilities, which was explained by Pearson׳s hard and soft acid–base (HSAB) principle for the first time in this field.