Effect of ammonia addition on the dispersion and activity of supported copper species on porous silica–alumina hollow spheres for catalytic decomposition of nitrous oxide

Abstract

In this work, we investigated the influence of ammonia addition in the immersion process of active species on the dispersion and activity of copper-supported porous hollow silica–alumina sphere catalysts for decomposition of nitrous oxide. The porous hollow sphere support was prepared using surfactant micelles and oil droplets in an aqueous solution as dual templates, and active copper species were supported on the resulting hollow spheres via the immersion process. The amount of supported copper species on the hollow sphere support tended to increase with increasing amount of aqueous ammonia solution used in the immersion process, suggesting that the formation of copper ammine complexes induced strong interactions between the complexes and silica surface from the results of EDS and XPS analyses. Specific surface areas and pore volumes of the copper-supported hollow spheres tended to increase with increasing the amount of aqueous ammonia solution identified from the results of nitrogen sorption measurements, indicating that the confined active copper species in the nanospaces in the hollow spheres’ shells increased with increasing the amount of aqueous ammonia solution. A significantly high amount of pores with a diameter of around 3 nm were observed in the copper-supported hollow spheres prepared with the amount of aqueous ammonia solution of 2.64 mL from the estimation of their pore size distributions, indicating that the confined active copper species in the nanospaces in the shells did not completely plug the pores. The catalytic activity of the copper-supported hollow sphere catalyst for the decomposition of nitrous oxide depended on the dispersion of the active species, and the catalyst prepared with the amount of aqueous ammonia solution = 2.64 mL exhibited the highest activity and included highly dispersed active copper species even after the catalytic reaction from the result of the XRD profiles.