Reduction mechanism study on sorption enhanced chemical looping gasification of biomass waste rice husk for H2 production over multi-functional NixCa1−xO particles

The sorption enhanced chemical looping gasification (SECLG) of rice husk (RH) with NixCa1−xO particles was studied in this work. NixCa1−xO particles were prepared by the sol-gel method. The experimental results showed that the ratio of Ni/Ca in NixCa1−xO had a great effect on the SECLG of RH. NixCa1−xO in a Ni/Ca ratio of 1 exhibited the best catalytic activity for the production of H2 and CO. The SECLG process could be interpreted by a sorption enhanced in situ reduction reaction mechanism, showing that Ni was the real active center for SECLG of RH to hydrogen. NiO was firstly reduced by CO released from SECLG of RH to Ni metal with a side product of CO2, and CO2 reacted with CaO to form CaCO3. These coupled reactions significantly enhanced the generation rate of metallic Ni, the real catalytic active center, which accelerated the reaction rate. •A series of NixCa1−xO particles have been synthesized, and their activities for SECLG of RH were evaluated.•The release rate of H2 in SECLG with Ni0.5Ca0.5O is higher than that with other NixCa1−xO particles.•NiO was firstly reduced by CO released from SECLG of RH to Ni metal with a side product of CO2.