Activity and selectivity regulation through varying the size of cobalt active sites in photocatalytic CO2 reduction

Abstract

The development of efficient and economical catalysts for photocatalytic reduction of CO₂ into chemical feedstocks is highly desirable for addressing both the global energy crisis and carbon emission problem. Herein, a series of carbonized cobalt composites derived from bimetallic Zn/Co zeolitic imidazolate frameworks (C-BMZIFs) are synthesized and used as the co-catalysts for [Ru(bpy)₃]²⁺ mediated photocatalytic CO₂ reduction under visible light irradiation. Varying the Zn/Co ratio allows regulation of the size of Co active sites, which further differentiates their catalytic activity towards CO₂ reduction and H₂ evolution, resulting in tunable CO/H₂ ratio in the produced syngas. Among all investigated configurations, the C-BMZIF with a Zn/Co ratio of 3 : 1 demonstrates the highest CO yield of 1.1 × 10⁴ μmol g⁻¹ h⁻¹, owing to the optimal balance between the quantity of active sites and the activity of each individual site. Consequently, this work provides insight into the design of stable MOF-derived co-catalysts for efficient photo-reduction of CO₂, and offers an alternative solution for photocatalytic syngas production with tunable CO/H₂ ratio.