CO2-assisted two-step pyrolysis fabrication of hierarchical porous Ni/ZrO2 catalyst for low-temperature dry reforming of methane.

A new strategy for preparing highly dispersed, richer oxygen vacancies Ni/ZrO2 catalysts derived from UiO-66-NH2 is reported via pyrolysis-calcination removal of the ligands under N2, CO2, and Air atmospheres followed by loading Ni with 5 wt.% via wet impregnation method. Subsequently, the low-temperature dry reforming of methane (DRM) reaction over the obtained Ni/ZrO2 catalysts was preliminarily investigated. The results indicated that the Ni/ZrO2C catalyst, obtained by two-step pyrolysis in CO2, contained smaller Ni particles with a size of only 5-7 nm and possessed a hierarchical porous structure, as well as richer oxygen vacancies and basic active sites compared to the other two catalysts. Its catalytic activity in the DRM reaction presented the highest initial conversion of CH4 (35 %) and CO2 (26 %) at 600 °C, which was 5 % higher than that of the Ni/ZrO2N and Ni/ZrO2O catalysts obtained by two-step pyrolysis under an N2 atmosphere and one-step pyrolysis under an air atmosphere, respectively. Meanwhile, an in-situ DRIFTS experiment revealed that Ni/ZrO2C could enhance the adsorption and activation of CO2 by promoting the formation of formate as an intermediate of CO hydrogenation and reverse water-gas shift (RWGS) reactions, which in turn facilitates the decomposition of CH4.