Abstract
Photocatalytic gas-phase hydrogenation of CO2 into alkanes was achieved over TiO2-supported Ni nanoparticles under LED irradiation at 365 nm, 460 nm and white light. The photocatalysts were prepared using photo-assisted deposition of Ni salts under LED irradiation at 365 nm onto TiO2 P25 nanoparticles in methanol as a hole scavenger. This procedure yielded 2 nm Ni particles decorating the surface of TiO2 with a nickel mass content of about 2%. Before the photocatalytic runs, Ni/TiO2 was submitted to thermal reduction at 400 °C in a 10% H2 atmosphere which induced O-defective TiO2−x substrates. The formation of oxygen vacancies, Ti3+ centers and metallic Ni sites upon photocatalytic CO2 hydrogenation was confirmed by operando EPR analysis. In situ XPS under reaction conditions suggested a strong metal–support interaction and the co-existence of zero and divalent Ni states. These photoactive species enhanced the photo-assisted reduction of CO2 below 300 °C to yield CO, CH4 and C2H6 as final products.
Highlights
IntroductionPhotocatalysis involves a greener vision of chemical processes, including the smart and selective transformation of chemicals into fuels and/or chemical intermediates of interest.[8,9,10] The use of photocatalysts leads to an effective depletion of organic pollutants, either in the form of wastewater or as organic volatile compounds.[11,12] photocatalysis takes advantage of sunlight as an abundant and inexpensive energy source, providing a sustainable approach to solving the most pressing environmental issues
The overall depletion of fossil fuels and the overwhelming evidence of the impact of greenhouse gas emissions on the global environment are among the major challenges of the humankind today[1,2] and demand a swi transition to renewable and sustainable processes
Paper contains the ionic precursor of the material to be deposited and at least one liquid component that can act as a hole scavenger
Summary
Photocatalysis involves a greener vision of chemical processes, including the smart and selective transformation of chemicals into fuels and/or chemical intermediates of interest.[8,9,10] The use of photocatalysts leads to an effective depletion of organic pollutants, either in the form of wastewater or as organic volatile compounds.[11,12] photocatalysis takes advantage of sunlight as an abundant and inexpensive energy source, providing a sustainable approach to solving the most pressing environmental issues. Ni-based nanosized particles have been deposited on the surface of TiO2 nanoparticles by a photodeposition method in methanol as a hole scavenger These materials have been successfully tested in the gas-phase photocatalytic hydrogenation of CO2 in a xed-bed reactor under LED irradiation at different wavelengths, including the full visible spectrum. In situ XPS studies were performed using a customized system incorporating a hemispherical analyzer (SPECS Phoibos 100), a non-monochromatized X-ray source (Al Ka; 1486.6 eV, Mg Ka, 1253.6 eV) and a high temperature–high pressure cell (SPECS-HPC-20) that allows sample heating and gas ow. A er the treatment the sample was cooled to room temperature under the reaction atmosphere, evacuated down to 10À7 mbar in less than two minutes and transferred back to the spectrometer chamber for analysis, avoiding ambient exposure. DC current was set at 0.9 A and 12 V during LED irradiation for all tested materials
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