Ceramic-foam-structured Rh/CeO2 catalysts: in-situ combustion deposition and biogas reforming performance

The application of ceramic foams as structured catalyst supports is clearly expanding due to their interesting specific properties (large exchange area, low pressure drops, high mass and heat transfer properties). In the present work, alumina open-cell foams (OCFs) with different pore density (20,30 and 40 ppi) were coated with Rh/CeO2 catalyst via a two steps synthesis method involving i) the solution combustion synthesis (SCS) to in-situ deposit the CeO2 carried and the ii) wet impregnation (WI) of the Rh active phase. The coated structures were characterized by SEM/EDX and TEM analysis to analyze the morphological characteristics of the deposited films; the mechanical stability was analyzed using ultrasound tests; the permeability and form coefficient were derived from the pressure drop data. The activity and stability of the structured catalysts were investigated towards the steam reforming (SR) and oxy-steam reforming (OSR) of biogas at atmospheric pressure varying temperature (700-900°C), space velocity (35,000-230,000 Nml•g-1•h-1) and time-on-stream (up to 200 h). Catalytic tests were carried out at S/CH4=3 for SR experiments and S/CH4=1 and O2/CH4=0.2 for OSR experiments. Homogeneous, thin (5-40 μm) and high-resistance coating layers were obtained. Structured catalysts showed high activity, following the order 20 ppi < 30 ppi ≈ 40 ppi. External mass transfer diffusion, evaluated by Damköhler and Carberry numbers, could be improved by reducing the pore diameter of the OCF structures, whereas Damköhler and Weisz-Prater numbers confirmed the absence of internal mass transport limitation due to thin coating thickness provided by SCS method. Good stability was observed over 200 h for both SR and OSR processes.