Biogas as a source of renewable syngas production: advances and challenges

Biogas produced by the anaerobic digestion of biomass is a valuable renewable energy source. It can be exploited directly as a fuel for small-to-medium-scale combined heat and power production, or as a raw material for the production of synthesis gas and/or hydrogen for industrial syntheses or energetic purposes. Since biogas contains CH4 and CO2 as two main components, it can be processed to a syngas according to a well-reported technological process called CO2 reforming of methane (dry reforming). We highlight the dry reforming of biogas as one area of activity where catalysts are already a significant focus of worldwide research efforts. The subject is demanding and recognized as a top priority for providing key solutions for a sustainable energy future. Nickel catalysts are highly active for reforming reactions and their cost is much lower compared with noble metals, which makes them suitable for a cost-effective commercial reforming process. For this reason, Ni-based catalysts are extensively studied, with emphasis on the effect of catalyst composition, preparation method and pretreatment. Unfortunately, nickel is more prone to carbon deposition. Improvement in the performance of Ni-based catalysts by incorporation of a second metal to catalyst composition and use of different Ni catalyst precursors is discussed in some detail. The challenges for catalysts applied to the dry reforming of biogas (activity, sulfur poisoning, carbon formation and sintering) are also examined, in order to reveal the specific needs and responses for the reforming process. An overview is provided of the research strategies and approaches adopted in the search for catalysts that respond to the above challenges.