The Sol–Gel Metal-Oxide Skeleton Affects the Catalytic Properties of In Situ Formed Metal Nanoparticles

The interaction between the mesoporous metal-oxide matrix and the adsorbed/entrapped active metal species attracts attention and curiosity due to its critical role in defining catalytic performance. Herein, the effects of TiO₂, Al₂O₃, and SiO₂ sol–gel matrices on the catalytic properties of encapsulated Cu⁰ and Ni⁰ species catalyzing the dehalogenation of the hazardous disinfection byproducts, chloro and bromoacetic acids, are reported. A precatalyst approach is employed in which a matrix is prepared by incorporating M(II) species into the pores of the sol–gel, which are later reduced to the active catalyst, M(0), during the reduction reaction by BH₄^–. The synthesized precatalysts are thoroughly studied using BET isotherms, X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, and scanning electron microscopy. The results point out that the relative effect of the metal-oxide environment on the adsorbed active metal species affects the process studied: for example, in the dechlorination of chloroacetic acid by Cu⁰-NPs, the order of activities is SiO₂ > Al₂O₃ > TiO₂; whereas for the analogous processes catalyzed by Ni⁰-NPs, the order of reactivities is Al₂O₃ > SiO₂ > TiO₂. For the other processes studied, other orders of activity are observed. Thus, the results indicate that the different sol–gel materials encapsulating the catalytic metals affect the reduction reactions differently.