Enhanced catalytic activity of the Rh/gamma-Al2O3 pellet catalyst for N2O decomposition using high Rh dispersion induced by citric acid

摘要

Two types of egg-shell-type Rh-based spherical gamma-alumina pellets were prepared by simple impregnation and incipient wetness methods with citric acid as an additive. In the case of the simple impregnation method, most of the Rh precursor molecules were selectively located in the outermost region of the spherical gamma-alumina pellet because of strong interactions between the Rh precursor and alumina. Thus, it formed a very thin Rh shell (Rh/Al2O3-Thin) around the pellet. On the other hand, the Rh precursor molecules were widely dispersed in the outer part of the spherical gamma-alumina pellet when citric acid was used as an additive. This method led to the formation of a thick Rh shell (Rh/Al2O3-Thick). The two samples were characterized via N-2 adsorption isotherms and CO chemisorption, and used as catalysts for the decomposition of N2O under different reaction conditions and at varying gas hourly space velocities. The N2O conversion achieved using the Rh/Al2O3-Thick catalyst was higher than that attained with the Rh/Al2O3-Thin catalyst. This implied that Rh dispersion is an important factor governing the performance of Rh-based spherical gamma-alumina pellet catalysts in N2O decomposition. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.