Photocatalytic Reduction of Carbon Dioxide to Methane over SiO2-Pillared HNb3O8

Abstract

Carbon dioxide (CO2) photoreduction by gaseous water over silica-pillared lamellar niobic acid, viz. HNb3O8, was studied in this work. The physicochemical characteristics of samples were examined by techniques such as XRD, FT-IR, SEM, TEM, and UV–visible diffuse reflectance spectroscopy. Aspects that influence CO2 photoreduction, such as the layered structure, the protonic acidity, silica pillaring, and cocatalyst loading, were investigated in detail. Pt loading obvious promoted the activity for CO2 photoreduction to methane. The loading of Pt also promoted the formation of methane from catalyst associated carbon residues, although this contributes insignificantly to the overall amount of methane produced. The layered structure and the protonic acidity of the lamellar niobic acid have significant influences on CO2 photoreduction by water in gas phase. With layered structure, expanded interlayer distance, and stronger intercalation ability to water molecules, the silica pillared niobic acid showed much higher activity than the nonpillared niobic acid, Nb2O5, and TiO2. Because of the unique adsorption ability to water molecules through hydrogen bonding, the activity of silica pillared HNb3O8 increased more remarkably with elevated water content than the mostly investigated TiO2 photocatalyst.