Defects in nanosilica catalytically convert CO₂to methane without any metal and ligand

Abstract

Active and stable metal-free heterogeneous catalysts for CO2fixation are required to reduce the current high level of carbon dioxide in the atmosphere, which is driving climate change. In this work, we show that defects in nanosilica (E′ centers, oxygen vacancies, and nonbridging oxygen hole centers) convert CO2to methane with excellent productivity and selectivity. Neither metal nor complex organic ligands were required, and the defect alone acted as catalytic sites for carbon dioxide activation and hydrogen dissociation and their cooperative action converted CO2to methane. Unlike metal catalysts, which become deactivated with time, the defect-containing nanosilica showed significantly better stability. Notably, the catalyst can be regenerated by simple heating in the air without the need for hydrogen gas. Surprisingly, the catalytic activity for methane production increased significantly after every regeneration cycle, reaching more than double the methane production rate after eight regeneration cycles. This activated catalyst remained stable for more than 200 h. Detailed understanding of the role of the various defect sites in terms of their concentrations and proximities as well as their cooperativity in activating CO2and dissociating hydrogen to produce methane was achieved.

Nearly free surface silanols are the critical molecular moieties that initiate the toxicity of silica particles

“…Silica is ubiquitous in the Earth's crust and universally used, both in crystalline and amorphous forms, mostly for its surface properties. Silicas are used in industrial productions and processes, including ceramics, glass, paints, plastics, construction products, catalysis, nanofabrication, and biomedical applications, in which the surface assumes a fundamental role (9)(10)(11)(12). Some of us have recently shown that specific surface moieties of amorphous silica can catalyze amide bond formation, which has implications for prebiotic chemistry and the origin of life from silica minerals (13).…”

Defective TiO2for photocatalytic CO2conversion to fuels and chemicals

“…Efforts to produce C 2 and higher products by utilizing the advantages provided by the defects present on the surface of TiO 2 are needed. Recent work by Chen et al 90 who reported the activation of CO 2 over defective Bi 2 O 3 for the production of the dimethyl carbonate using methanol, and Polshettiwar et al 91 who reported activation of CO 2 using defective dendritic fibrous nanosilica (DFNS) without any metal sites, could be a way forward for defect engineering in other catalytic materials.…”

Transformation of Stöber Silica Spheres to Hollow Nanocatalysts

“…Even though not proved thoroughly yet, hollow pure silica structure may also demonstrate catalytic activity without any form of functionalization since it was revealed very recently that a highly porous defect‐containing nanosilica owns innate active sites (i. e., oxygen vacancies and nonbridging oxygen hole centers) which can drive chemical reactions such as CO 2 to methane conversion …”