Effect of MoO_3 on the heat resistant performances of nickel based MCM-41 methanation catalysts

摘要

Several Ni-Mo based catalysts with Mo content from 1 wt% to 7 wt% were prepared by the impregnation method with MCM-41 as the support. The effect of Mo content on the activity of the catalyst was investigated for syngas methanation in a fixed-bed reactor. The addition of MoO_3 could obviously improve catalytic activity of Ni/M catalyst at low temperature of 250 ℃ with the CO conversion and the CH_4 selectivity from about 20%, 16% to 100%, about 80%, respectively. Ni-3%Mo/M catalyst showed the best activity with a CO conversion of 100% and a CH_4 selectivity of 94% at 350 ℃ under 1.0 MPa and 12000 ml/g/h with a 3:1 molar ratio of H_2 to CO. Compared with Ni/M catalyst, Ni-Mo/M catalysts showed higher resistance to sintering and no decrease in the catalytic activity after calcination at 700 ℃ for 2 h. In the 100 h stability test under atmospheric pressure, the CO conversion and the CH_4 selectivity obtained on Ni-3%Mo/M catalyst maintained at about 100% and 89%, respectively, suggesting an excellent catalytic stability of this catalyst. The catalysts were characterized by N_2 adsorption-desorption, CO chemisorptions, TEM, SEM-EDS, ICP, XRD, H_2-TPR and XPS, and the results showed that electron transfer from MoO_3 to metal nickel was the main cause of activity improvement of Ni-Mo/M catalysts at low reaction temperature of 250 ℃. The addition of MoO_3 could obviously improve the heat resistant performance of Ni/M catalyst. The results of TPR, SEM-EDS and XRD showed that the addition of MoO_3 could enhance the interaction between metal nickel and the support in the way of Ni-Mo alloy, which inhibited the catalyst sintering.