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

[Display omitted] • Two-stage steam gasification and catalytic reforming of rice husk for H 2 -rich gas. • Ce 0.7 Ni 1 Ca 5 catalyst achieves 85.81 vol% H 2 with H 2 yield of 35.82 mmol g-1 biomass. • Ce 0.7 Ni 1 Ca 5 exhibits excellent cyclic stability and inhibition of carbon deposition. • High oxygen transport capacity of CeO 2 helps to promote WGS and SMR reactions. • CeO 2 prevents the sintering of NiO and CaO particles, stabilizing CO 2 sorption. Hydrogen-rich gas production from rice husk via steam gasification and catalytic reforming using CeO 2 -modified Ni-CaO sorption bifunctional catalysts synthesized by sol–gel method in a two-stage system was investigated. The results show that the Ce 0.7 Ni 1 Ca 5 catalyst achieves maximum H 2 concentration (85.81(±0.39) vol.%) and H 2 yield (35.82(±0.28) mmol g-1 biomass) 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 CO 2 (3.62(±0.16) vol.%), CO (4.27(±0.11) vol.%), CH 4 (4.49(±0.18) vol.%), and C 2 -C 3 (1.81(±0.09) vol.%), correspondingly. Ce 0.7 Ni 1 Ca 5 also exhibits excellent cyclic stability in H 2 production, CO 2 sorption, and inhibition of carbon deposition. The H 2 concentration and H 2 yield remain above 81.88 vol% and 32.11 mmol g-1 biomass , respectively, and CO 2 emission keeps below 4.85 vol% during 10 cyclic tests. The carbon deposition of Ce 0.7 Ni 1 Ca 5 is only about 30% of that of Ni 1 Ca 5 after 10 cycles and hardly increased after 5 cycles. It is found that well-dispersed CeO 2 can effectively prevent the sintering of NiO and delay agglomeration of CaO species, stabilizing CaO carbonation and CO 2 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 CeO 2 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. [ABSTRACT FROM AUTHOR]