CO2 Valorization by CH4 Tri-Reforming on Al2O3-Supported NiCo Nanoparticles

CO2 valorization from real feedstocks through CH4 tri-reforming (CH4-TR), combining steam reforming (SR), dry reforming (DR), and partial oxidation (CPO) of methane in a single process, is a desirable strategy for greenhouse gas mitigation and syngas (CO + H2) production. NiCo/γ−Al2O3 catalysts prepared by impregnation at different relative metal contents (Ni50Co50 and Ni30Co70) were investigated for CH4-TR in a fixed-bed reactor under conventional heating and characterized by XRD, FESEM, and Raman spectroscopy after catalytic runs. This study focused on the role of the Ni/Co ratio and feed composition on selectivity for CO2 valorization, syngas yield, and deactivation resistance. Both the catalysts showed high activity, with a superior performance of Ni50Co50 confirming Ni metal species as the active sites. While in DR, a slow deactivation occurred due to coke deposition, in CH4-TR, the addition of small O2 and/or H2O amounts stabilized activity and selectivity due to surface carbon removal. Large O2 and H2O amounts strongly inhibited CO2 conversion due to competition with CPO and SR, in the order CPO ≥ DR > SR. Interestingly, the stoichiometric CH4-to-oxidants ratio favored the DR pathway, giving very high CO2 conversion. Modulating CH4 addition into real flue mixtures renders CH4-TR on NiCo/γ-Al2O3 catalysts a favorable strategy for effective valorization of CO2 industrial or biomass-derived streams.