Enhancing hydrogen production from the pyrolysis-gasification of biomass by size-confined Ni catalysts on acidic MCM-41 supports

Hydrogen, currently produced from the reforming of fossil fuel resources, is a significant source for clean energy and the chemical industry. It is promising to develop a high-efficiency hydrogen production process from renewable biomass for sustainable development. This research reports that catalyst support acidity could strongly enhance the hydrogen production from the biomass gasification of wood sawdust. For minimizing the influence of the Ni particle size for the biomass gasification, the uniform Ni nanoparticles around 2–3 nm were loaded into one type of mesoporous support MCM-41 with various acidity. Ni/H-[Al] MCM-41 with a large amount of Brϕnsted acid sites contributed 2–3 times higher hydrogen yield (21.6 mmol H₂ g⁻¹ sample) than that on Ni/H-[Si]MCM-41 with a small amount of very weak acidic surface SiOH groups (9.8 mmol H₂ g⁻¹ sample) and that on nonacidic Ni/Na-[Si]MCM-41 (6.7 mmol H₂ g⁻¹ sample). The surface acid sites on supports could generate bifunctional catalysts and were proposed to show two functions for enhancing the hydrogen production: 1) help to crack and transfer the pyrolysis chemicals into smaller compounds for more efficient reforming on the Ni surface inside nanopores; 2) enhance the support and Ni interaction for better reduction property and surface activity of Ni nanoparticles and improve the reforming performance. The obtained Ni/MCM-41 catalysts were quite stable and no sintering has been observed after the gasification at 800 °C, and only a low coke deposition has been detected.