Solar-driven coupled system for the co-production of hydrogen and 4-hydroxybenzoic acid from methane and CO₂.

Professor Fei Qiang's team at Xi'an Jiaotong University (XJTU) recently achieved a breakthrough at the intersection of C1 biomanufacturing and photocatalysis. They developed a solar-driven bio-photocatalytic coupled system that converts CH₄ and CO₂ into 4-hydroxybenzoic acid (4-HBA) and H₂. This research provides a novel technical path for the high-value utilization of decentralized C1 resources, carbon emission reduction, and renewable energy development.

The study, titled Bio-Photocatalytic Synergy Enables Valorization of CH₄ and CO₂ into Hydrogen and 4-Hydroxybenzoate in Engineered Methanotrophic Bacteria, was published as a hot paper in the international journal Angewandte Chemie International Edition.

China possesses abundant decentralized C1 gas resources, such as biogas and coke oven gas. However, due to their small scale at single points, scattered distribution, and high CO₂ content, traditional thermal catalysis is often inefficient and uneconomical.

While aerobic methanotrophs (methane-oxidizing bacteria) can convert methane into bio-based products under mild conditions, they face two major bottlenecks: limited reducing power and carbon loss via metabolic by-products.

To address these hurdles, the team engineered a dual-function system. It regulated the methane assimilation pathways in methanotrophs to optimize carbon flux between formic acid accumulation and 4-HBA synthesis, and designed metal-complex photocatalysts that function under cellular growth conditions.

These catalysts use formic acid as a substrate to generate H2 and photo-generated electrons. These electrons serve as a supplementary reducing power to drive methane oxidation and 4-HBA synthesis within the bacteria.

To further minimize the carbon footprint, the team integrated an artificial carbon sequestration pathway to recapture CO₂ released during the photocatalytic process.

Under optimal conditions, the system achieved a 4-HBA yield of 472.36 µg/L and a hydrogen yield of 0.59 mmol H2/mol CH₄. The integrated system achieved a total carbon emission reduction of over 50 percent.

This progress overcomes critical challenges in carbon flux regulation, bio-inorganic compatibility, and power supply reduction in methanotrophic cell factories.