CO2 hydrogenation over ultradispersed Mo/TiO2 catalysts

MICROSCOPIE+CDURABLE:CATREN:ING+TLN:PAF:LCS:NPR:MAO:FMO:LPINational audienceEnvironmental concerns impose the reduction of CO2 emissions in the atmosphere. A promising strategy consists in the valorisation of effluent CO2 through catalytic hydrogenation [1]. In particular, CO2 can be converted into methanol on the Cu/ZnO/Al2O3 syngas-to-methanol catalyst, but the latter is sensitive to water and prone to deactivation. Single-atom or subnanometric cluster-based catalysts are a promising class of materials, which potentially offer maximum atom-efficiency and distinct catalytic properties [2,3]. In this work, we show that Mo ultradispersed on TiO2 catalyses CO2 hydrogenation. We focus on the effect of Mo loading and TiO2 properties on catalyst activity and selectivity to methanol, and on the identification of surface species. Mo/TiO2 catalysts with 0.1-10 wt% loading were prepared by wet impregnation – reduction using (NH4)6Mo7O24 as precursor and homemade rutile TiO2 nanorods (RNR) together with various commercial forms as supports. The catalysts were characterized by various techniques, including aberration-corrected scanning transmission electron microscopy (AC-STEM), operando Raman and X-ray absorption spectroscopies, and near ambient pressure X-ray photoelectron spectroscopy. The catalytic performances were measured using a flow fixed-bed reactor with a H2/CO2/N2 ratio of 3:1:1 at 3 MPa total pressure and 275 °C. Whereas previous works reported the absence of CO2 hydrogenation activity of Mo/TiO2-P25 [4,5], this work reveals promising performances for selected materials, the most active and methanol-selective catalyst being Mo/RNR. Carbon monoxide, methane, dimethyl ether and methanol are formed with different selectivities depending on the support. The methanol formation turnover frequency (per Mo atom) greatly increases at lower Mo loadings, i.e. 0.1-1 wt%. STEM studies show that single Mo atoms (oxometallate monomers) replace small clusters (multimers) as the Mo loading decreases, which suggests that isolated MoOx species anchored on TiO2 are the most active ones for methanol production. In this communication, based on several complementary characterization data, we will provide insights on the catalytic performance in relation to the nature of MoOx species and the physicochemical properties of the titania surface. 1. Ganesh, I., Renewable Sustainable Energy Rev. 31, 221 (2014). 2. Wang, A., Li, J., and Zhang. T. Nat. Rev. Chem 2, 65 (2018). 3. Dessal, C., Len, T., Morfin, F., Rousset, J.L., Aouine, M., Afanasiev, P., Piccolo, L., ACS Catal. 9, 5752 (2019). 4. Toyao, T., Kayamori, S., Maeno Z., Hakim Siddiki, S.M.A., Shimizu, K., ACS Catal. 9, 8187 (2019). 5. Barrault, J., Urresta, J., C. R. Acad. Sci. Paris, 2, 167 (1999)