Microwave-assisted deposition of a highly active cobalt catalyst on mesoporous silica for photochemical CO₂ reduction

Abstract

Coupling with robust surfaces is a promising approach to improve the stability and recyclability of highly active molecular catalysts. This study builds on our prior success to deposit a Co(iii) cyclam complex, where cyclam is 1,4,8,11-tetraazacyclotetradecane, on mesoporous silica via a microwave-assisted process. The Co(iii) complex was successfully deposited on the silica surface through reacting with silanol groups in the silica mesopores. The resulting surface Co(iii) catalyst was characterized by different techniques and tested in photochemical CO reduction in the presence of p-terphenyl as a photosensitizer. The synthesized Co(iii) catalyst showed significantly higher activity and selectivity than the unbound Co(iii) cyclam complex and a surface Co(iii) catalyst prepared by other methods. Microwave-assisted heating was found to be essential for the deposition of uniform Co(iii) sites in the silica mesopores, which likely accounts for the superior activity and selectivity of the synthesized surface Co(iii) catalyst.

Molecular catalysis of CO2 reduction: recent advances and perspectives in electrochemical and light-driven processes with selected Fe, Ni and Co aza macrocyclic and polypyridine complexes

“…205 Further grafting of the Co-cyclam onto silica by a microwave-assisted process afforded a uniform distribution of the Co III active sites in the silica mesopores, boosting the activity for CO production (TON CO = 312) under similar conditions, and TON was increased over 500. 206 In a different strategy, a [Mn(CO) 5 Br] complex was attached onto bipyridyl-containing periodic mesoporous silica (bpy-PMO, Scheme 6), resulting in isolated Mn-carbonyl centers coordinated to the bipyridine functionalities of bpy-PMO. Employing [Ru(bpy) 3 ]Cl 2 as PS and BIH as SD, the hybrid can complete the photo-stimulated reduction of CO 2 with TONs of 484 and 239 for formate and CO respectively.…”

Well-defined surface catalytic sites for solar CO2reduction: heterogenized molecular catalysts and single atom catalysts

“…Based on this discovery, we employed a microwave-assisted synthesis to achieve uniform deposition of Co-cyclam on an unfunctionalized mesoporous SiO 2 . 85 The resulting CoX/SiO 2 demonstrated superior activity in CO 2 reduction using p -terphenyl as a photosensitizer. A TON more than 300 was obtained for CO after photocatalytic CO 2 reduction for 4 h (Fig.…”

Immobilized Molecular Catalysts for CO2Photoreduction

“…Microwave‐assisted heating in the process of supporting the molecular complex to SBA‐15 produced a material with uniform distribution of the active centers and enhanced the TON up to 312. [ 107 ] Since the same amounts of photosensitizer ( p ‐terphenyl) and electron donors (TEOA and methanol) were used in all photocatalytic experiments, increasing the loading of Co(III), the ratio between the concentration of photosensitizer and electron donors to Co(III) decreases, which might influence the CO 2 reduction photocatalyst. Since the Co(III) centers are deposited on the silica surface upon reacting with surface silanol groups, another contributing factor could be related to the Co(III) sites on silica surfaces, which has been studied in detail through different techniques.…”