Ru/CeO2 catalysts for combustion of mixture of light hydrocarbons: Effect of preparation method and metal salt precursors

Abstract

Two preparation methods and two metal salt precursors (chlorine containing and chlorine-free) were used to synthesize Ru/CeO2 catalysts and their catalytic behaviour has been evaluated in combustion of propane, n-butane and isobutane mixture. In the first method, Ru nanoparticles (Ru NPs) deposited on CeO2 were synthesized by a microwave-assisted polyol method using RuCl3 as a metal precursor and ethylene glycol as a reducing agent. In the second, Ru/CeO2 catalysts were prepared by traditional incipient wetness impregnation method using RuCl3 or Ru(NO)(NO3)3. ICP-AES, N2 adsorption-desorption, H2-TPR, XRD, HRTEM and SEM-EDS techniques were used to characterize the catalysts. In all the Ru/CeO2 catalysts only highly dispersed Ru nanoparticles (1–2nm) were present. The catalytic data show that the preparation method and the nature of the metal precursor have a significant influence on catalytic performance of the Ru/CeO2 catalysts. The VOC reactivity order (iso-butane >n-butane > propane) show that propane is the most difficult to oxidize. The Ru(NPs)/CeO2 and impregnated Ru(N)/CeO2 catalyst exhibited much higher activity and stability than that of impregnated Ru(Cl)/CeO2. It was found that the Ru(NPs)/CeO2 nano-catalyst was free of chlorine species although it had been prepared from RuCl3. The differences in the activity have been ascribed to the presence of Cl− ions on the Ru(Cl)/CeO2 catalyst and to much better reducibility of the chlorine-free Ru(NPs) and Ru(N) catalysts. The Cl species have a negative impact on the redox properties of CeO2, they have some influence on Ru agglomeration during long-term activity tests (50h), and consequently, the chlorinated catalyst exhibited a poorer activity and stability compared with those of the Cl-free catalysts.