Insight into the effects of different ageing protocols on Rh/Al 2O3 catalyst

In this work, a catalyst of Rh loaded on Al₂O₃ was prepared by impregnating method with rhodium nitrate aqueous solution as the Rh precursor. The catalyst was aged under different protocols (lean, rich, inert and cyclic) to obtain several aged samples. All the Rh/Al₂O ₃ samples were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) method, CO-chemisorption, H₂-temperature programmed reduction (H₂-TPR), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). It was found that a specific ageing treatment could strongly affect the catalytic activity. The N₂ aged and the H₂ aged samples had a better catalytic activity for CO + NO reaction than the fresh sample while the air aged and the cyclic aged samples exhibited much worse activity. More surface Rh content and better reducibility were obtained in the N₂ and the H₂ aged samples and the Rh particles existed with an appropriate size, which were all favorable to the catalytic reaction. However, the air and the cyclic ageing protocols induced a strong interaction between Rh species and the Al ₂O₃ support, which resulted in a severe sintering of particles of Rh species and the loss of active sites. The structure evolution scheme of the catalysts aged in different protocols was also established in this paper. © 2014 Elsevier B.V.