Methanation of CO2 on Ni/γ-Al2O3: Influence of Pt, Pd or Rh promotion

• Published in: Catalysis today 2018-05, Vol.306, p.294-299
• Main Authors: Mihet, Maria, Lazar, Mihaela D.
• Format: Article
• Language: English
• Subjects: Bimetallic Ni based catalyst; CO2 methanation; CO2-TPD; H2-TPD; Hydrogen; Supported Ni catalyst
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2016.12.001

[Display omitted] •Ni(10%)/Al2O3 promoted by Pt, Pd, Rh (0.5%) were tested in the CO2 methanation process.•Promotion by Pt, Pd or Rh enhances the metal dispersion.•The catalytic activity decreases in the series: Ni-Pd/Al2O3≥Ni-Pt/Al2O3>Ni/Al2O3>Ni-Rh/Al2O3.•Stability tests proved all catalysts to be stable over the entire tested time range. Methanation of carbon dioxide was carried out in a plug flow reactor (CO2:H2=1:4, GHSV=5700h−1) over a series of noble metal promoted Ni/γ-Al2O3 catalysts, prepared by the co-impregnation method: Ni(10wt.%)-Pt(0.5wt.%)/γ-Al2O3, Ni(10wt.%)-Pd(0.5wt.%)/γ-Al2O3, and Ni(10wt.%)-Rh(0.5wt.%)/γ-Al2O3. Characterization of catalysts was performed by N2 adsorption–desorption isotherms at −196°C (BET), X-ray powder diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption of H2 (H2-TPD), and CO2 (CO2-TPD). Promotion by noble metals resulted in better reducibility of NiO (Ni-Rh>Ni-Pt>Ni-Pd>Ni), enhanced metal dispersion and H2 chemisorption capacity (Ni-Pt>Ni-Rh>Ni-Pd>Ni), with no significant influence upon the support intrinsic activity given by the CO2 adsorption capacity. Catalytic activity of the promoted catalysts compared to the unpromoted one was performed by temperature programmed reactions (TPRea, 30–300°C) and stability tests at 250°C, under atmospheric pressure, and was evaluated in relation with the structural and functional properties of the catalysts. Promotion by Pt and Pd of Ni/γ-Al2O3 resulted in enhanced CO2 conversion and CH4 selectivity values in the 180–270°C domain, while Ni-Rh/γ-Al2O3 was inferior to Ni/γ-Al2O3. Considering the stability, all catalysts show stable catalytic performance over the investigated time range, with CH4 selectivity values above 90%. Ni-Pd/γ-Al2O3 is the most efficient catalyst, with stable CO2 conversion of 74.6% and CH4 selectivity of 96.6% at 250°C, in addition to the maximum values of 90.5% and 98.7%, respectively, at 300°C, obtained during temperature programmed reaction runs.