Development of nano Ni_xMg_yO solid solutions with outstanding anti-carbon deposition capability for the steam reforming of methanol

In this study, different types of nano Ni_xMg_yO solid solutions for the steam reforming of methanol were prepared via three different preparation methods. The solid solutions were characterised systematically by using a suite of characterisation techniques. TEM analysis demonstrated that Ni particles in these solid solutions were in nano-scale with an average size of 9.6–12 nm. The catalytic performance of these catalysts was evaluated using a fixed-bed reactor operated under atmospheric pressure at four different temperatures, i.e., 400, 500, 600 and 700 °C, and at two steam-to-carbon ratios (S/C), i.e., S/C = 1 and 3. Results showed that the nano Ni_xMg_yO material (Ni_xMg_yO-hydro), which was prepared using a hydrothermal method, achieved the highest methanol conversion efficiency of 97.4% and hydrogen yield of 58.5% under a S/C ratio of 3. The evaluation on carbon deposition resistance showed that nano Ni_xMg_yO-hydro had no detectable carbon deposited under a S/C ratio of 3. In addition, physical and chemical properties of these catalysts were also studied by using H₂-Temperature-Programmed Reduction/Desorption(H₂-TPR/D), CO₂-Temperature- Programmed Desorption(CO₂-TPD) and X-ray Photoelectron Spectroscopy(XPS). The outstanding carbon deposition resistance of Ni_xMg_yO-hydro was attributed to the “isolation effect” of the Ni_xMg_yO solid solution structure, which restricts Ni nano particles from aggregation. The high basicity of the surface of Ni_xMg_yO-hydro catalyst also resulted in the enhanced adsorption of CO₂ and therefore contributed to anti-carbon deposition by providing oxygen to promote the gasification reaction between carbon and CO₂.