Exploring new catalysts for the valorisation of carbon dioxide from biogas

New Ni-based catalysts have been developed and applied for the steam dry reforming (SDR) and the methanation reaction of clean biogas, exploring the possibility of converting its CO2 fraction into a useful product (syngas or biomethane) instead of separating and discharging it. The catalysts were prepared from hydrotalcite-type precursors through co-precipitation, with the addition of promoters (Ru, Rh, La) or basic sorbents (CaO). Then, they were deeply characterised before and after reaction by BET, XRD, H2-TPR, CO2-TPD analyses, and Raman spectroscopy. The results obtained for SDR at low temperature (700°C) showed that, although the catalysts synthetised were active and stable in terms of CH4 conversion, the conversion values reached were not yet compatible with the industrial requirements. On the other hand, a promising Ni-Ru bimetallic catalyst was developed for high temperature SDR (900°C), presenting a convenient alternative to the already studied Ni-Rh and Ni-Ir formulations. The synergic effect of the two metals significantly enhanced the catalyst stability and resistance toward coke formation, while achieving high methane and carbon dioxide conversions and producing syngas with a H2/CO ratio compatible with downstream applications such as Fischer-Tropsch or methanol synthesis. Finally, the feasibility of the direct methanation of clean biogas was assessed, using a Ni-La catalyst. Its activity was studied simulating the industrial conditions for the reaction, achieving CO2 conversions up to 90% with a total selectivity for methane production.