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Innovative renewable routes are potentially able to sustain the transition to a decarbonized energy economy. Green synthetic fuels, including hydrogen and natural gas, are considered viable alternatives to fossil fuels. Indeed, they play a fundamental role in those sectors that are difficult to electrify (e.g., road mobility or high-heat industrial processes), are capable of mitigating problems related to flexibility and instantaneous balance of the electric grid, are suitable for large-size and long-term storage and can be transported through the gas network. This article is an overview of the overall supply chain, including production, transport, storage and end uses. Available fuel conversion technologies use renewable energy for the catalytic conversion of non-fossil feedstocks into hydrogen and syngas. We will show how relevant technologies involve thermochemical, electrochemical and photochemical processes. The syngas quality can be improved by catalytic CO and CO2 methanation reactions for the generation of synthetic natural gas. Finally, the produced gaseous fuels could follow several pathways for transport and lead to different final uses. Therefore, storage alternatives and gas interchangeability requirements for the safe injection of green fuels in the natural gas network and fuel cells are outlined. Nevertheless, the effects of gas quality on combustion emissions and safety are considered.

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The research work leading to this paper [...]

Fuel cells powered by biogas for decentralised cogeneration of heat and power are an attractive alternative to combustion technologies. However, biogas contains sulfur-based compounds (H2S, COS, DMS, siloxanes), which are harmful to fuel cells. This work was carried out in the framework of the European project Waste2Watts, involving the laboratories of Politecnico di Torino, ENEA, and PSI. The aim is to design and test a flexible and cost-effective cleaning unit to remove impurities for the use of biogas in high-efficiency fuel cell systems. The focus is on small- to medium-sized farms for which deep cleaning of biogas by adsorption materials is a suitable techno-economic solution to avoid intensive gas processing treatments. The ability of commercial adsorption materials (activated carbons, metal oxides, and metal hydroxides) to remove hydrogen sulphide and carbonyl sulphide was tested under different biogas compositions (oxygen and humidity). After evaluating the results, three plant configurations were proposed to optimally utilise the potential of the sorbents. Indeed, the RGM3 sorbent has proven to be an effective solution for removing H2S and COS under humid conditions (50% RH), whilst R7H and R8C sorbents are better suited for removing H2S and COS, respectively, in dry biogas conditions. Graphical abstract