Biomass-based green ammonia: Pathways, technologies, and sustainability for a carbon-neutral future

Ammonia plays a pivotal role in the global economy, serving as a hydrogen carrier, carbon-free fuel, and a key component in nitrogen fertilizers that enhance agricultural productivity. However, the conventional Haber-Bosch (H-B) process, which relies on methane (natural gas) as a source of hydrogen, contributes approximately 2 % of global CO 2 emissions, underscoring the need for sustainable alternatives. This review explores biomass as a renewable feedstock for green ammonia production, focusing on thermochemical and biochemical conversion processes through two pathways: (1) Indirect, using renewable based hydrogen from steam methane reforming of syngas, bio-oil, biogas and glycerol obtained from biomass gasification, pyrolysis, anaerobic digestion and transesterification processes, respectively, and (2) Direct, converting nitrogen-rich biomass into ammonia through catalytic or laser-driven pyrolysis, or recovering ammonia from biohydrogen or biogas effluents via stripping. While the biochemical process has higher technology readiness, thermochemical methods, especially biomass steam gasification, are more widely used due to higher green hydrogen yields. Novel integrations, such as process simulations, cascaded designs, chemical looping, and external energy sources like solar, biomass, wind, or hybrid systems, enhance ammonia production. Green ammonia reduces CO 2 emissions by approximately 65–66 % and is less costly than conventional processes, depending on system configuration and biomass feedstock. This review examines technological advancements, economic feasibility, and environmental impacts, concluding that biomass-based green ammonia is essential for sustainable energy systems. While earlier reviews have provided broad overviews of green ammonia production, they often overlook the specific potential of biomass-based routes. This review addresses that gap by systematically analyzing biomass-driven pathways, along with their technological, economic, and environmental dimensions, to underscore the distinctive contribution of biomass to sustainable ammonia production. • Conventional Haber-Bosch process contributes ∼2 % CO 2 emissions, 1–2 % global energy consumption. • Biomass is a sustainable, renewable feedstock for producing green ammonia. • Green ammonia is produced directly or indirectly through thermochemical and biochemical process. • Biochemical process has higher readiness but produces less ammonia than thermochemical. • Biomass steam gasification offers an eco-friendly, cost-effective method for green H 2 to ammonia.