Photocatalytic Reduction of CO₂ with H₂O on Titanium Oxides Anchored within Micropores of Zeolites:  Effects of the Structure of the Active Sites and the Addition of Pt

Abstract

Titanium oxide species anchored within the Y-zeolite cavities by an ion-exchange method exhibit a high and unique photocatalytic reactivity for the reduction of CO2 with H2O at 328 K with a high selectivity for the formation of CH3OH in the gas phase. The in situ photoluminescence, ESR, diffuse reflectance absorption, and XAFS (XANES and FT-EXAFS) investigations indicate that the titanium oxide species are highly dispersed within the zeolite cavities and exist in a tetrahedral coordination. The charge transfer excited state of the anchored titanium oxide species plays a significant role in the reduction of CO2 with H2O with a high selectivity for the formation of CH3OH, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species show a high selectivity to produce CH4, being similar to reactions on the powdered TiO2 catalysts. The addition of Pt to the anchored titanium oxide catalysts promotes the charge separation which leads to an increase in the CH4 yields in place of CH3OH formation.

Understanding the Reaction Mechanism of Photocatalytic Reduction of CO2 with H2O on TiO2-Based Photocatalysts: A Review

“…the intermediates to generate CH 3 OH. Anpo et al (1997) reported a unique role of Pt metal on Ti/Y-zeolites for CO 2 photoreduction, besides the conventional role of Pt in promoting charge transfer. They found that carbon radials and H atoms were generated on the same Pt metal sites, and thus CH 4 formation was facilitated by Pt.…”

Functioning devices for solar to fuel conversion

“…Scientific challenges in the domain of storing solar energy by CO 2 conversion are larger than for hydrogen synthesis. CO 2 conversion in the presence of water can lead to different products, such as methane or methanol, and little is known about the role of the chemical composition and surface structure of electrocatalytic and photo-catalytic converters in triggering selectivity [19][20][21][26][27][28][29]. In the following case studies we will further address the options for chemical storage of solar energy.…”

“…While some interesting results have been reported, productivity is still beyond the limit to design a viable process. Besides studies on crystalline TiO 2 based catalysts, Ti-containing siliceous materials, such as TS-1, Ti-MCM-41, Ti-MCM-48 and Ti-SBA-15 were found to yield high methane production rates in gas phase photocatalytic CO 2 reduction [5,[26][27][28][29]. The production yield of highly dispersed titanium oxide catalysts (in mol/g-Ti/h), was increased 10-300 times as compared to crystalline TiO 2 .…”

Photocatalytic Hydrogenation on Semiconductor Particles

“…Therefore, the photocatalytic hydrogenation of CO2 upon semiconductor powders has received much attention [9][10][11][44][45][46][47][48][49][50][51][52][53][54][55][56]. Among the earliest studies on the photocatalytic hydrogenation of CO2, Inoue et al examined a wide range of semiconductors (WO3, TiO2, ZnO, CdS, GaP, and SiC in 200 -400 mesh) in aqueous solution [44].…”

“…Among those, methanol is the most valuable product because it can be directly used as a fuel or a building block. High efficiency and selectivity in the preparation of methanol were obtained by the use of Ti-oxide/Y-zeolite catalysts containing highly dispersed tetrahedral titanium oxide species under UV irradiation [53,54]. The charge-transfer excited state of these species played an important role in the selectivity for producing CH3OH, in contrast to the different selectivity giving CH4 on bulk TiO2 photocatalyst.…”