New optimized mesoporous silica incorporated isolated Ti materials towards improved photocatalytic reduction of carbon dioxide to renewable fuels

Abstract

In the present work, novel isolated Ti-SBA-15-spherical and Ti-KIT-6 (Si/Ti=200, 100 and 50) photocatalysts have been synthesized; optimized through N2-adsorption/desorption, SEM, EDX, UV–Vis, FT-IR, XPS and TEM analysis techniques; and explored for the photocatalytic reduction of greenhouse gas CO2 to renewable fuels. The Ti-KIT-6 (Si/Ti=100) showed better CH4 production rate (4.15μmolgcat.−1h−1) than the corresponding Ti-KIT-6-dried (2.63μmolgcat.−1h−1) and the Ti-SBA-15-calcined/dried (1.85, 3.45μmolgcat.−1h−1, respectively) in the initial optimization reactions. CH3OH, CO, and H2 are the other main fuel products produced by the Ti-KIT-6-calcined (Si/Ti=100). The increased surface concentration of OH groups found in the Ti-KIT-6-calcined (Si/Ti=100) than the other two ratios (Si/Ti=200, 50), the presence of more accessible surface reaction active sites due to the lower number of Ti–O–Ti or TiO2 agglomerates, and the more isolated Ti species which are uniformly dispersed on the 3-D KIT-6 mesoporous silica support without collapsing the mesoporous structure, have boosted the higher activity, which is even higher than the best commercial Aeroxide P25 TiO2. The reaction has been preceded by the competitive adsorption of CO2 and H2O vapors. The UV light source/intensity, H2O/CO2 ratios and catalyst shapes are the key factors that influence the performance of the catalyst, and therefore, these parameters have been optimized to boost the fuel products.