Catalytic Activity For CO2 Methanation Research Articles

Ni/Al2O3 catalysts for CO methanation: Effect of Al2O3 supports calcined at different temperatures

The correlation between phase structures and surface acidity of Al2O3 supports calcined at different temperatures and the catalytic performance of Ni/Al2O3 catalysts in the production of synthetic natural gas (SNG) via CO methanation was systematically investigated. A series of 10 wt% NiO/Al2O3 catalysts were prepared by the conventional impregnation method, and the phase structures and surface acidity of Al2O3 supports were adjusted by calcining the commercial γ-Al2O3 at different temperatures (600–1200 °C). CO methanation reaction was carried out in the temperature range of 300–600 °C at different weight hourly space velocities (WHSV = 30000 and 120000 mL·g−1·h−1) and pressures (0.1 and 3.0 MPa). It was found that high calcination temperature not only led to the growth in Ni particle size, but also weakened the interaction between Ni nanoparticles and Al2O3 supports due to the rapid decrease of the specific surface area and acidity of Al2O3 supports. Interestingly, Ni catalysts supported on Al2O3 calcined at 1200 °C (Ni/Al2O3-1200) exhibited the best catalytic activity for CO methanation under different reaction conditions. Lifetime reaction tests also indicated that Ni/Al2O3-1200 was the most active and stable catalyst compared with the other three catalysts, whose supports were calcined at lower temperatures (600, 800 and 1000 °C). These findings would therefore be helpful to develop Ni/Al2O3 methanation catalyst for SNG production.

Effect of ZrO 2 promoter on structure and catalytic activity of the Ni/SiO 2 catalyst for CO methanation in hydrogen-rich gases

Ni-based catalysts supported on SiO 2 aerogel that is unpromoted (Ni/SiO 2) or promoted (Ni/ZrO 2–SiO 2) with ZrO 2 are prepared by the incipient-wetness impregnation method. Their catalytic activities for CO methanation in hydrogen-rich gases with 1 vol.% CO are studied with a continuous flowing microreactor. It is found that the Ni/ZrO 2–SiO 2 catalyst shows higher catalytic activity, over which CO can be completely converted into CH 4 at 240 °C. However, CO cannot be completely converted until the temperature was raised to 320 °C over the Ni/SiO 2 catalyst under the same reaction conditions. Characterizations using FT-IR, XRD, TEM, NH 3-TPD, H 2-TPR and H 2-TPD suggest that the formation of Si–O–Zr bond results in stronger acid strength and larger amounts of acid of the ZrO 2–SiO 2 support. The changes of acidity lead to the increase of the interaction between NiO species and the ZrO 2–SiO 2 support and then enhance the dispersion degree and the reduction degree of NiO species. Thus, the Ni/ZrO 2–SiO 2 catalyst possesses smaller Ni crystallite size, higher Ni dispersion, more active Ni species and stronger adsorption ability for H 2, which may contribute to its higher catalytic activity for CO methanation.

Effect of ZrO 2 promoter on the catalytic activity for CO methanation and adsorption performance of the Ni/SiO 2 catalyst

The catalytic activities for CO methanation and adsorption performances of the Ni/SiO 2 and Ni/ZrO 2-SiO 2 catalysts were investigated by a continuous flowing microreactor apparatus and in-situ diffuse reflectance Fourier transform infrared spectroscopy. The results showed that CO was completely converted at 200°C over the Ni/ZrO 2-SiO 2 catalyst under the reaction condition of 1% of CO, GHSV of 5000 h −1, and the atmospheric pressure. However, the CO conversion was only 35% over the Ni/SiO 2 catalyst under the same reaction condition, and CO was not completely converted until 270°C, which suggested that the catalytic activity of the Ni/ZrO 2-SiO 2 catalyst increased with the addition of ZrO 2 promoter. Meanwhile, the addition of ZrO 2 promoter enhanced the CO adsorption capacity of the Ni/ZrO 2-SiO 2 catalyst. In the presence of H 2, a large number of bridged carbonyl hydrides were formed over the Ni/ZrO 2-SiO 2 catalyst at lower temperatures, resulting in high catalytic activity for CO methanation. In CO methanation, the breaking of C—O bond over catalysts was by multihydrogen carbonyl hydride rather than by direct breaking.