Evaluation of lanthanide-group promoters on Co-Ni/Al₂O ₃ catalysts for CH₄ dry reforming

The influence of lanthanide group (Ce, Pr and Sm) promoters on alumina-supported bimetallic Co-Ni catalysts for CH₄ dry reforming in a fixed-bed reactor was investigated. Lanthanide doping did not appear to affect CH₄ and CO₂ consumption rate, however, H ₂ and CO production rates increased suggesting better utilisation of surface carbonaceous species. Carbon deposition on the promoted catalysts was substantially reduced (by up to 50%), with Ce providing the greatest anti-coking resistance followed by Pr and Sm. The beneficial effects of the promoted catalysts may be attributed to the interaction of the deposited but unconverted C_xH_1-x species with the lanthanide oxide in redox reactions, as well as smaller active particle size of the promoted catalysts which was unfavourable for carbon formation. In general, the study shows that attributes (such as product (H₂ and CO) formation rate constants and the associated reaction orders as well as the enthalpy and entropy of CH ₄ adsorption) of the promoted catalysts compared favourably to those of the unpromoted counterpart and are reasonably correlated with the Pauling electronegativity of the dopants. TPR-TPO of used catalysts suggests the presence two types of carbonaceous deposits - a reactive species which is lower in the promoted catalysts, and a relatively unreactive carbon which is present in similar quantities for all the catalysts.