Coke-Resistant Rh and Ni Catalysts Supported on g-Al2O3 and CeO2 for Biogas Oxidative Steam Reforming

2020 Abstract: The depletion of fossil fuels and the growing concerns related to the environmental impact of their processing has progressively switched the interest towards the utilization of biomass-derived materials for a large variety of processes. Among them, biogas, which is a CH 4 -rich gas deriving from anaerobic digestion of biomass, has acquired a lot of interest as a feedstock for reforming processes. The main issue in employing biogas is related to the carbon deposition and active metal sintering, which are both responsible for the deactivation of the catalyst. In this work, bimetallic and monometallic Rh- and Ni-based formulations were supported on alumina and ceria with the aim of evaluating their activity and stability in biogas oxidative steam reforming. The Rh addition to the monometallic Ni/  -Al 2 O 3 formulation enhances its catalytic performances; nevertheless, this induces a higher coke deposition, thus suggesting a preferential coke formation on Rh sites. The initial activity of the CeO 2 -supported catalysts was found to be lower than the Al 2 O 3 supported catalysts, but the 5%Ni/CeO 2 sample showed a very good stability during the test and, despite the lower activity, 0.5%Rh-5%Ni/CeO 2 did not show coke deposition. The results suggest that the promotion of Ni/CeO 2 catalysts with other active metals could lead to the selection of a highly stable and performing formulation for biogas oxidative for the alumina-supported catalysts: CeO 2 -supported samples did not produce CO 2 during the TPO experiment, thus confirming the lack of coke deposition in the catalytic bed; for this reason, these latter profiles are not shown below. As it is possible to see, the results are in agreement with the hypotheses made when observing the pressure drop trends: the sample 0.5%Rh/Al 2 O 3 induced the highest coke formation, while a smaller production was observed on 0.5%Rh-5%Ni/Al 2 O 3 ; and a very small quantity of coke was gasified during TPO on the 5%Ni/Al 2 O 3 sample, thus again suggesting metal sintering as a different reason for the catalyst deactivation. Furthermore, these results suggest that coke deposition occurs preferentially on Rh sites rather than Ni ones.