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| - Size-Dependent Hydrogenation Selectivity of Nitrate on Pd−Cu/TiO2 Catalysts
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| Abstract
| - Catalytic hydrogenation of nitrate (NO3−) in water on Pd−Cu ensembles has been denoted as a promising denitridation method, but its hydrogenation selectivity remains challenging. In this study, the hydrogenation selectivity of nitrate on the Pd−Cu/TiO2 systems was discussed mainly concerning the size effect of Pd−Cu ensembles in a gas−liquid cocurrent flow system. Demonstrated by their TEM images, homogeneous morphologies as well as narrow size distributions of Pd−Cu ensembles on titania have been prepared by a facile photodeposition process, and the size of the ensembles was controlled and varied with the total metal loadings. The different XRD patterns and XPS spectra of Pd−Cu/TiO2 catalysts from their corresponding monometallic counterparts suggested the formation of Pd−Cu complex on the surface of TiO2. It is first indicated that the hydrogenation selectivity of nitrate generally depends on the size of active phase with critical size of approximately 3.5 nm, below which NO2− becomes the predominant product instead of nitrogen. Ammonium production was increasing slowly throughout the reaction, but this can be efficiently restrained by bubbling CO2. The optimal catalytic activity and nitrogen selectivity of 99.9% and 98.3% respectively could be achieved on the Pd−Cu/TiO2 catalyst with average size of 4.22 nm under the modification of CO2 after approximately 30 min reduction. The catalytic activities of nitrite on several Pd−Cu bimetallic catalysts were examined to strongly depend on the size of active metal, as is well responsible for the observed distinct hydrogenation selectivity of nitrate.
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| - Size-Dependent Hydrogenation Selectivity of Nitrate
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