Synthesis of CH4 by catalytic reforming of rice husk pyrolysis gas over NiO/CuO-CeO2 catalysts

Targeted conversion of biomass pyrolysis gas to CH4 using rational catalytic means is an effective way to realize high-value utilization of biomass. In this paper, an experimental study on the synthesis of CH4 by catalytic reforming of pyrolysis gas was carried out using the gas product of rice husk pyrolysis as the raw material, KOH as the primary in-situ catalyst and NiO/CuO-CeO2 as the secondary non-in-situ catalyst. The results showed that the in-situ catalysis increased the H2 content in pyrolysis gas to lay the feedstock basis for the subsequent methanization conversion, and the non-in-situ catalysis further achieved higher CO conversion and CH4 yield. Under the optimal process parameters, the low heat value of the obtained gas was 19.75 MJ/Nm3, the CH4 content and yield reached 40.78 vol % and 6.81 mmol/g, respectively, and the CO conversion reached 92.67 %. In addition, the catalytic and deactivation mechanisms of the catalysts were preliminarily explored by various characterization analyses. The high dispersion of the active component NiO and the high CO adsorption capacity due to the large number of oxygen vacancies contained in the carrier CeO2 are important reasons for the better catalytic effect of methanation. The additive Cu can further play a role in promoting the dispersion of Ni species and improving the surface chemical state of Ni and Ce elements. The high stability of the carrier and the generation of singlet Ni during the catalytic cycle prolonged the catalyst lifetime. Catalyst deactivation is mainly related to the covering of carbon deposits, sintering of active component Ni, and irreversible changes in the surface chemical state. The present study is useful for the design and industrial application of biomass methanation catalysts, and also provides new ideas for the high-value utilization of biomass pyrolysis gas products.