Direct Catalytic Methanation of Biomass at Mild Conditions by a Sustainable Hydrochar-Supported Metal Catalyst

Abstract

Direct conversion of waste biomass into methane via catalytic methanation at low and ambient temperatures is an attractive albeit elusive route in the quest for an effective, inexpensive, and sustainable catalyst. In this study, we tried to tackle this challenging task by designing a series of efficient yet cost-effective Ce-doped hydrochar-supported Ni catalysts. The optimized Ni_0.02/Ce_0.05-HC under optimal reaction conditions exhibited a markedly high activity at low temperature (350 °C) and atmospheric pressure for the direct methanation reaction, with 90.7% CH₄ selectivity, 33.5 MJ/Nm³ LHV_g, and 3629 mL/g CH₄ yield. On the basis of catalytic studies as well as structural characterizations, the active sites responsible for this exceptional activity can be associated with highly dispersed metallic Ni species maximized by the Ce dopant as well as favored electronic metal–support interactions. Moreover, the stable Ce-doped hydrochar framework and its covalently bridged oxygen-containing functional groups cooperatively contribute to the improved stability during the direct methanation process. These findings may provide a strong reference for developing more high-efficiency yet low-cost catalysts toward biomass methanation, thus leveraging the existing natural gas infrastructure to facilitate a seamless transition from fossil fuels to sustainable energy sources.