Influence of ceria and nickel addition to alumina-supported Rh catalyst for propane steam reforming at low temperatures

Abstract

Kinetic studies reveal that loading ceria and Ni onto alumina-supported Rh dramatically increases the propane reforming rates; adding CeO 2 promotes steam and propane adsorption and activation, while adding Ni mainly enhances C 3 H 8 adsorption and activation. The influence of ceria and nickel addition to alumina-supported Rh catalyst for steam reforming of propane at low temperatures has been studied by preparing and examining 2 wt%Rh/Al 2 O 3 , 2 wt%Rh/20 wt%CeO 2 –Al 2 O 3 , and 2 wt%Rh–5 wt%Ni/20 wt%CeO 2 –Al 2 O 3 . TPR characterization showed that adding ceria makes rhodium oxide easier to reduce and the presence of rhodium also makes ceria easier to reduce through Rh–Ce interaction, whereas the addition of Ni makes Rh 2 O 3 and ceria more difficult to reduce, likely due to Rh–Ni and Ce–Ni interactions. Adding ceria and nickel significantly improved the catalytic activity of Rh catalyst for propane conversion at 475 °C. Kinetic study at different temperatures (450–650 °C) indicated that the addition of ceria and Ni can greatly increase the propane reforming rates by lowering the activation energies from 67.6–68.8 kJ/mol for 2Rh/Al to 50.1–50.4 kJ/mol for 2Rh/20CeAl and to 42.1–42.5 kJ/mol for 2Rh5Ni/20CeAl. The feed steam/carbon molar ratios corresponding to maximum reaction rates at 475 °C increased from 2.0 for 2Rh/Al to 3.0 for 2Rh/20CeAl and 4.5 for 2Rh5Ni/20CeAl catalyst. A kinetic equation based on Langmuir–Hinshelwood model best fitting the experimental data was applied for the propane steam reforming over the Rh-based catalysts. Kinetic results at different partial pressures of propane and steam revealed that the addition of ceria could enhance the steam and propane adsorption, while the addition of Ni could significantly promote the propane adsorption, probably through working with Rh as propane adsorption sites.