Hydrogen Production from Biogas: Development of an Efficient Nickel Catalyst by the Exsolution Approach

Hydrogen production from biogas over alumina-supported Ce1-xNixO2-x catalysts was studied in a temperature range of 600-850 degrees C with an initial gas composition of CH4/CO2/H2O of 1/0.8/0.4. To achieve a high and stable hydrogen yield, highly dispersed Ni catalysts were prepared through the exsolution approach. A solid solution of Ce1-xNixO2-x was firstly formed on the surface of Al2O3 and then activated in H-2/Ar at 800 degrees C. The genesis and properties of the Ce1-xNixO2-x/Al2O3 catalysts were established using X-ray fluorescence analysis, thermal analysis, N-2 adsorption, ex situ and in situ X-ray diffraction, Raman spectroscopy, electron microscopy, EDX analysis, and temperature-programmed hydrogen reduction. The performance of Ce1-xNixO2-x/Al2O3 catalysts in biogas conversion was tuned by regulation of the dispersion and reducibility of the active component through variation of content (5-20 wt.%) and composition (x = 0.2, 0.5, 0.8) of Ce1-xNixO2-x as well as the mode of its loading (co-impregnation (CI), citrate sol-gel method (SG)). For the 20 wt.% Ce1-xNixO2-x/Al2O3 catalyst, the rate of the coke formation decreased by a factor of 10 as x increased from 0.2 to 0.8. The optimal catalyst composition (20 wt.% Ce0.2Ni0.8O1.8/80 wt.% Al2O3) and preparation mode (citrate sol-gel method) were determined. At 850 degrees C, the 20 wt.% Ce0.2Ni0.8O1.8/Al2O3-SG catalyst provides 100% hydrogen yield at full CH4 conversion and 85% CO2 utilization.