A study of Ni/La-Al2O3 catalysts: A competitive system for CO2 methanation

Ni/La-gamma-Al2O3 samples containing 13.6 wt.% Ni and a variable amount of lanthana (0, 4, 14 and 37 wt.%) were prepared by incipient wetness impregnation, using silica-free gamma-Al2O3 support. The materials were characterized, as such or after reaction, with XRD, H-2-TPR, IR,UV-vis-NIR, XPS and FE-SEM techniques. They were tested as catalysts for CO2 methanation at atmospheric pressure at GHSV 55000 h(-1). The reaction is under kinetic control at T < 650-673 K, while the product mixture is under thermodynamic control above this temperature range. Lanthanum addition strongly increases the activity of Ni/gamma-Al2O3 for CO2 methanation. Methane selectivity is increased to nearly 100% at low temperatures (T < 650 K). The CO2 methanation reaction on La-doped Ni/gamma-Al2O3 occurs with similar activation energies (80 kJ/mol), and with slightly higher reaction order for hydrogen and lower reaction order for CO2 than those observed for undoped Ni/gamma-Al2O3. Lanthanum acts as a promoter because of the stronger basicity of the lanthana-alumina support allowing stronger adsorption of CO2 as surface carbonates that can be act as "reactant reservoirs". The Ni/La-alumina catalysts studied here are similarly effective as Ru/alumina catalysts for the selective CO2 methanation at low temperature and atmospheric pressure.