Comparative Study of Supported Ni and Co Catalysts Prepared Using the All-in-One Method in the Hydrogenation of CO₂: Effects of Using (Poly)Vinyl Alcohol (PVA) as an Additive

Two series of Ni and Co catalysts supported onto La-Al2O3 were prepared and the CO2 hydrogenation reactions investigated. The catalytic performance was evaluated in terms of the evolution with the reaction temperature of the CO2 conversion and product (CH4 and CO) yields, as well as specific activities (TOF) and apparent activation energies. CH4 was the favored product over both metals while the TOF for CH4 formation was about three times higher for Ni than Co at 240-265 degrees C. Metallic particle size effects were found, with the TOF for CH4 formation decreasing over both Ni and Co as the mean metallic size decreased. In contrast, the TOF for CO formation tended to increase at a decreasing particle size for the catalysts with the smallest Ni particle sizes. The apparent activation energies for Ni and Co were very similar and significantly decreased to values of 73-79 kJ/mol when the metallic dispersion increased. The catalysts were prepared using the all-in-one method, resulting in (poly)vinyl alcohol (PVA) being a key additive that allowed us to enhance the dispersion of Ni and Co to give very effective catalysts. This comparative study joins the few existing ones in the literature in which catalysts based on these metals operated under strictly the same reaction conditions.