Obtaining well-dispersed Ni/Al2O3 catalyst for CO2 methanation with a microwave-assisted method

•Microwave method was used to prepare Ni20-Al2O3-M catalyst with high Ni dispersion.•The comparison catalyst (Ni20-Al2O3-I) was prepared with an impregnation method.•XRD, HRTEM, TPR and TPD confirmed that Ni20-Al2O3-M has a better Ni dispersion.•Ni20Al2O3-M showed a better activity for CO2 methanation compared with Ni20Al2O3-I.

The Ni dispersion of the catalysts is essential to the catalytic activity for CO2 methanation, which could be affected by preparation process and treatment method of the catalysts. Accordingly, a microwave-assisted method was used to synthesize Ni/Al2O3 catalysts (Ni20-Al2O3-M) because the microwave technique is an efficient route for high dispersion of inorganic salts onto supports. Polyvinyl pyrrolidone (PVP) and distilled water was used as surfactant and microwave absorbent to improve the dispersivity of Ni nanoparticles on γ-Al2O3. The comparison catalyst (Ni20-Al2O3-I) was prepared with an impregnation method. XRD, Raman spectrum and HRTEM collectively confirmed the good Ni dispersion of Ni20-Al2O3-M, while H2-TPR and CO2-TPD results indicated that the Ni20-Al2O3-M catalysts obtained more Ni active sites under low temperature of H2 pretreatment and strengthened basicity. Therefore, the CO2 methanation activity over Ni20-Al2O3-M was evidently enhanced at lower temperature. The corresponding CH4 selectivity was also well maintained over the whole temperature region. Moreover, Ni20Al2O3-M showed good stability for CO2 methanation at 325 °C during the 72 h lifetime test.