Catalytic conversion of biomass waste to methane without external hydrogen source

Abstract

Methane, the primary constituent of natural gas, shale gas, and flammable ice, serves as a crucial carbon-based energy source and chemical feedstock. Traditional gas reserves are universally acknowledged as limited and non-renewable resources over an extended timespan stretching from decades to millennia. Biomethane, with its unique renewable properties, showcases remarkable development potential and presents a compelling supplement and even alternative for fossil fuel. Although catalytic hydrothermal processes appear as promising valorization routes to transfer biomass to sustainable methane, the safety and supply source of high-pressure hydrogen remain key factors restricting the widespread application. Herein, a catalytic approach without an external hydrogen source was developed to transform waste biomass resources into CH₄ under the Ni-Mo catalyst. The total carbon yield of gas products reached up to 92.2%, of which the yield of methane and C₂–C₄ hydrocarbons were 44.9% and 3.0%, respectively. And it's calculated that approximately 343.6 liters of CH₄ could potentially be generated from 1 kilogram of raw biomass. Ni-based catalysts exhibited the robust activity in cleaving C–C and C–O bonds. And the introduction of an appropriate amount of molybdenum significantly enhanced catalytic performance of reforming and subsequent methanation reaction, likely due to the high adsorption capacity of highly dispersed Ni-Mo catalysts for carbon monoxide and hydrogen molecules, facilitating the methanation reaction. The pathway of catalytic methane production might be inferred that CO, H₂ and a large number of oxygen-containing intermediates were formed via decarbonylation, dehydrogenation, and retro-aldol condensation reaction under hydrothermal condition. These intermediates then underwent the reforming reaction to generate H₂ and CO₂, ultimately forming CH₄ through the methanation reaction.