Photocatalytic reduction of CO2 with H2O vapor for CO production in a temperature range of 50-170 oC was studied using porous MgO/TiO2 microspheres as the photocatalysts with the benefits of improved CO2 adsorption by incorporating MgO and enhanced products/intermediates desorption at a higher temperature. The MgO/TiO2 microspheres were fabricated by two methods: (1) one-step spray pyrolysis method using TiO2 (P25) nanoparticles dispersed in Mg(NO3)2 solution as the precursors (Mg/Ti-SP), and (2) spray pyrolysis synthesis of pure TiO2 (P25) microspheres first and then wet-impregnated with MgO (Mg/Ti-WI). We found that the temperature, surface MgO dispersion and CO2 adsorption/desorption dynamics significantly affected the performance of MgO/TiO2 in CO2 photoreduction. When the temperature increased from 50 to 150 oC, Mg/Ti-SP demonstrated 10 times higher activity toward CO production. The two material synthesis methods led to different MgO dispersion on the TiO2 surface. For Mg/Ti-SP, the strong aggregation of MgO nanoparticles caused a rough surface of the MgO/TiO2 microsphere; while for Mg/Ti-WI, MgO was more uniformly deposited leading to a much smoother surface of the microsphere. At the same MgO concentration, Mg/Ti-SP had more than two times higher activity than Mg/Ti-WI, and most importantly, little deactivation of the catalyst was observed on Mg/Ti-SP while Mg/Ti-WI started to deactivate after 1 to 2 h when the reactor was operating in a continuous flow mode. The results from in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed two advantages of Mg/Ti-SP over Mg/Ti-WI: (1) more abundant bicarbonates (important intermediates for CO production) on the surface and (2) easier desorption/transformation of intermediates.

Effects of temperature, surface MgO dispersion, and CO2 adsorption/desorption dynamics on CO2 photoreduction with H2O vapor by porous MgO/TiO2 ?microspheres

247th National Meeting (2014)

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