Highly dispersed tetrahedrally coordinated Ti species incorporated in silica are efficient for photocatalytic reduction of CO2 by water vapour [1]. In application of a Ti-functionalized 2D mesoporous material SBA-15 [2], hydrocarbons such as methane, ethane and ethene have been detected, all be it at low concentrations. In the presentation several strategies for improvement of the activity of Ti-functionalized SBA-15 based catalysts will be presented. First, the accessibility of the mesoporous network will be demonstrated to affect the performance. A 1% Ti loading was found to be more effective (30-35%) in a siliceous 3D mesoporous material TUD-1 [3], as compared to SBA-15. Characterization results indicate the presence of Ti in the form of isolated centers [(-Si-O)3-Ti-O-] in both catalysts. These were previously reported to be essential for a high activity per Ti-site [1]. Nanoparticles of TiO2 in TUD-1 were found ineffective for the reaction. A second modification of the catalytic material was based on a recent study [4], in which it was shown that ZnO supported on silica exhibits a high adsorption capacity for CO2. ZnO-Ti-TUD-1 was prepared with 10% Zn loading and 1% Ti, to investigate the ability of the isolated Ti centers to initiate conversion of (concentrated) CO2, adsorbed on neighboring ZnO particles. Unfortunately, the photocatalytic activity of ZnO-Ti-TUD-1 was lower than of Ti-TUD-1. This suggests the adsorbed CO2 molecules on ZnO are not easily converted by reactive species formed on the isolated Ti centers. An additional reason for the detrimental effect of the presence of ZnO, is the increase in rates of back reactions (from hydrocarbons to CO2 and H2O), which will be extensively discussed.

Photocatalytic conversion of CO<sub>2</sub> into hydrocarbons over catalyst centers in mesoporous silicas

245th National Meeting (2013)

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Photocatalytic conversion of CO2 into hydrocarbons over catalyst centers in mesoporous silicas

Photocatalytic conversion of CO₂ into hydrocarbons over catalyst centers in mesoporous silicas