Ultrathin TiO 2 nanosheet (NST) with abundant Ti 3+ sites is developed as a photocatalyst which exhibits a high yield (147.2 μmol g −1 h −1 ) and selectivity (96.8%) for CO 2 to CH 4 . The results of in situ FTIR, in situ EPR and density functional theory (DFT) calculation suggest that CO 2 would be selectively activated on NST surface via forming the bridging Ti···CO 2 − ···Ti coordination species which not only lowers the activation energy barrier, but also determines the selectivity of CH 4 . Additionally, NST with the better separation and transfer ability for photogenerated electrons-holes can fleetly supply the electrons to CO 2 molecules for high efficiently producing CH 4 via the Ti-C coordination bond. Finally, a possible mechanism of the synergistic effect about coordination-activation and photocatalysis is discussed at a molecule level. This work would offer a perspective for designing an effective photocatalyst and tailoring the selectivity of products by coordination activation.
Yanan Liu,Chenglin Miao,Pengfei Yang,Yufei He,Junting Feng,Dianqing Li
The ultrathin TiO 2 nanosheets (TiO 2 -U) with abundant defects were successfully fabricated as substrates to support well-dispersed Pt nanoparticles with low metal loading by photochemical route (P), with impregnated Pt/TiO 2 -U, Pt/TiO 2 -bulk and photoreduced Pt/TiO 2 -bulk as control samples, to focus on studying the inductive effect of oxygen vacancy-rich ultrathin TiO 2 on highly dispersed Pt nanoparticles, and their synergetic promotional effect for CO 2 photoreduction. As expected, P-Pt/TiO 2 -U exhibited excellent photocatalytic efficiency for the selective conversion of CO 2 into CH 4 and CO. The ultrathin TiO 2 nanosheets with a large number of low coordinative sites and ultralarge surface area promoted the rate of electron-transfer. The ultrafine Pt nanoparticles induced by photochemical strategy facilitated the efficient separation of electron–hole pairs. Furthermore, the synergy of metal and support improved the adsorption ability of CO 2 . These three factors were considered to drive jointly the enhancement of catalytic performance in this system. This work offers deep insights for the design of highly efficient catalysts with coordinatively unsaturated sites for CO 2 photoconversion in the presence of H 2 O.
Xiaoqing Gao,Shanhui Zhu,Mei Dong,Jianguo Wang,Weibin Fan
Highly efficient synthesis of valuable γ-valerolactone (GVL) by levulinic acid (LA) hydrogenation is still a challenge for Ru-based catalysts under mild condition. In this work, we have reported that ultrathin TiO 2 nanosheets supported Ru nanoparticles showed extraordinarily high catalytic activity, GVL yield (99.1%) and reusability owing to the formation of Ru O Ti interfacial structure. The turnover frequency (TOF) reached as high as 19,045 h −1 at 100 °C, much higher than those of Ru/SiO 2 , Ru/GO, Ru/MoS 2 , and commercial Ru/C. DFT calculation elucidates that the dominant reaction pathway of LA hydrogenation to GVL is preferentially hydrogenated to CH 3 CHOCH 2 CH 2 COOH*, followed by cyclization to CH 3 (OH)C 4 OH 4 OH* (GVL − OH) and final dehydroxylation, irrespective of surface structure. Compared to Ru (0 0 2) facet, Ru/TiO 2 interfacial structure changes the rate-determining step from initial hydrogenation to cyclization, which greatly declines the activation barrier from 0.81 eV to 0.48 eV.
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