Hydrogen-rich gas production by catalytic steam gasification of rice husk using CeO2-modified Ni-CaO sorption bifunctional catalysts

Hydrogen-rich gas production from rice husk via steam gasification and catalytic reforming using CeO2-modified Ni-CaO sorption bifunctional catalysts synthesized by sol-gel method in a two-stage system was investigated. The results show that the Ce0.7Ni1Ca5 catalyst achieves maximum H-2 concentration (85.81(+/- 0.39) vol.%) and H-2 yield (35.82(+/- 0.28) mmol g(biomass)(-1)) under a condition of 500 ?C, S/C (steam/carbon in biomass) molar ratio of 5, catalyst/biomass mass ratio of 2.5, producing the lowest content of CO2 (3.62(+/- 0.16) vol.%), CO (4.27(+/- 0.11) vol.%), CH4 (4.49(+/- 0.18) vol.%), and C2-C3 (1.81(+/- 0.09) vol.%), correspondingly. Ce0.7Ni1Ca5 also exhibits excellent cyclic stability in H-2 production, CO2 sorption, and inhibition of carbon deposition. The H-2 concentration and H-2 yield remain above 81.88 vol% and 32.11 mmol g(biomass)(-1), respectively, and CO2 emission keeps below 4.85 vol% during 10 cyclic tests. The carbon deposition of Ce0.7Ni1Ca5 is only about 30% of that of Ni1Ca5 after 10 cycles and hardly increased after 5 cycles. It is found that well-dispersed CeO2 can effectively prevent the sintering of NiO and delay agglomeration of CaO species, stabilizing CaO carbonation and CO2 sorption, and the strong Ni-O-Ce interaction induces the creation of oxygen vacancies that facilitate the fracture of O-H bonds of water for the formation of H-2. Furthermore, the high oxygen transport capacity of CeO2 not only forms abundant mesopores structure to promote WGS and SMR reactions for enhancing H-2 production, but also contributes to reforming the carbon deposited on the catalyst surface by lowering the oxidation temperature of amorphous carbon containing low-molecular aromatic or aliphatic compounds with lower degree of graphitization.

Automated summary

This study investigates the production of hydrogen-rich gas from rice husk using CeO2-modified Ni-CaO sorption bifunctional catalysts synthesized by sol-gel method. The Ce0.7Ni1Ca5 catalyst achieves the highest H2 concentration and yield, as well as exhibits excellent cyclic stability and inhibition of carbon deposition.