CO2 assisted steam gasification for hydrogen-rich syngas from rice straw: Evolution of carbon structure and its effect

CO 2 -assisted steam gasification of rice straw (RS) offers a promising approach for both the sustainable utilization of rice straw and the reduction of CO 2 emissions. This study investigates the transformation of RS during pyrolysis and gasification in a fixed-bed reactor, with structural changes observed through solid-state 13 C nuclear magnetic resonance and Fourier-transform infrared (FT-IR) spectroscopy. The gas composition is analyzed by gas GC, and covalent bonds are quantified through carbon structure and elemental analysis. The results demonstrate that steam acts as a key reactant in the gasification process, significantly enhancing the pyrolysis of RS and leading to higher hydrogen yields. CO 2 serves as an oxidant above 500°C, oxygenating aromatic rings and initiating ring-opening reactions to form active C(O) intermediates that are crucial for hydrogen production. The hydrogen yield increases similarly to H 2 O gasification, while methane and carbon monoxide decrease significantly after gasification over 700°C. The H 2 /CO ratio improves from 0.64 in N 2 to 1.46 in H 2 O, and further to 1.71 in CO 2 -H 2 O at 700°C. CO 2 -assisted steam gasification optimizes the reactive interface activity, promoting the selective formation of hydrogen and improving the efficiency of the gasification process. Furthermore, CO 2 plays a pivotal role in enhancing the formation of active C(O) intermediates, which further facilitates the production of high-purity hydrogen. The process also induces the formation of a regular micro-pore structure, improving the overall efficiency and selectivity of directional hydrogen generation. • Steam is acted as the reactant and catalyst for gasification of RS. • CO 2 -assisted steam gasification significantly enhances hydrogen yield and purity. • CO 2 -assisted steam gasification optimizes reactive interface activity for gas reaction. • CO 2 improves the active C(O) intermediates for Hydrogen production.