Biogas, with its high carbon dioxide content (30–50 vol%), is an attractive feed for catalytic methanation with green hydrogen, and is suitable for establishing a closed carbon cycle with methane as energy carrier. The most important questions for direct biogas methanation are how the high methane content influences the methanation reaction and overall efficiency on one hand, and to what extent the methanation catalysts can be made more resistant to various sulfur-containing compounds in biogas on the other hand. Ni-based catalysts are the most favored for economic reasons. The interplay of active compounds, supports, and promoters is discussed regarding the potential for improving sulfur resistance. Several strategies are addressed and experimental studies are evaluated, to identify catalysts which might be suitable for these challenges. As several catalyst functionalities must be combined, materials with two active metals and binary oxide support seem to be the best approach to technically applicable solutions. The high methane content in biogas appears to have a measurable impact on equilibrium and therefore CO₂ conversion. Depending on the initial CH₄/CO₂ ratio, this might lead to a product with higher methane content, and, after work-up, to a drop in-option for existing natural gas grids.

This study used quantitative biogas measurements from four full-scale biogas plants to determine which trace components can be expected in biogas from biogenic agricultural or municipal residues. The objective was to identify trace compounds that could damage the catalyst when biogas is used as a feedstock for a catalytic conversion. Knowing the exact composition of the biogas, including for example all sulfur-containing molecules, is therefore essential for the process's operational expenditures (OPEX). The results of this investigation add to a database of fully measured biogases and can be used to select suitable biogas purification steps. Trace compounds found in all measured biogas samples were ethanol, acetone, toluene, alpha-pinene and 3-methylfuran. However, biogases from different substrates contain distinctive trace components. The biogas from organic waste shows the highest amount of S-containing molecules (up to 14.7ppm in total), while the biogas from wastewater sludge shows higher amounts of siloxanes (50 mg m^-3STP) and the biogases from agricultural waste contain oxygenates like acetone and 2-butanone. Measurements taken at various points along the process chain indicate that activated carbon is sufficient for removing most of the trace components from biogas. However, it was observed in one plant that the activated carbon must be replaced before it reaches its adsorption limit to avoid the desorption of volatile organic compounds. Biogas or the biogenic CO₂ are well-suited to be used in downstream processes, but analytical monitoring of the biogas composition and a suitable connection between plant and downstream process are required.