Wide spectral response enables efficient photochemistry-assisted selective hydrogenation of butadiene over Pd/N-TiO2

Abstract

Selective hydrogenation driven by heat is a critical industrial process for purifying alkene feedstocks with serious problems of energy and H₂ consumption. Photochemistry-assisted strategy offers a sustainable alternative owing to its superiority of H₂-free reaction under ambient temperature, unfortunately, with a challenging demand on efficient catalysts. Herein, a wide-spectrum-responsive Pd/N-TiO₂ photo-thermal catalyst was developed by a solvothermal method for photochemistry-assisted selective hydrogenation of butadiene in propene. It shows an excellent catalytic performance, with 100 % alkenes selectivity and 100 % butadiene conversion under irradiation of full-light (i.e., 320 nm∼780 nm). Notably, over 53 % butadiene conversion with 100 % alkenes selectivity was successfully retained on Pd/N-TiO₂ after shortening the wavelength range to visible light, much superior to that on Pd-TiO₂ (i.e., <1 % butadiene conversion). Further exploration reveals that the nitrogen doping extends the light-responsive wavelength of titanium oxide from ∼380 nm to above 500 nm owing to the formation of Ti³⁺ and oxygen vacancies, which later create a defect energy level (i.e., ∼-0.53 to -0.12 eV) between the valence-conduction band of TiO₂. The wide spectral response of N-TiO₂ enhances the water photolysis to produce intermediate hydrogen ([H]) that acts as the hydrogen source for the tandem butadiene hydrogenation over the Pd surface. The work indicates that developing a dual-functional catalyst with an expanded light-responsive wavelength is an efficient way to enhance the photochemistry-assisted selective hydrogenation.