Study On Surface Modification Of Ni Based Catalysts For Partial Oxidation Of Methane To Syngas

The catalytic partial oxidation of methane (POM) to syngas (CO+H2) has been extensively investigated since the selectivity of syngas and methane conversion are high at high space velocity and the syngas produced with a molar ratio of H2/CO as 2:1 can be directly used as feed for methanol or Fischer- Tropsch synthesis. The key problem limiting the further industrial production of syngas by POM process is the catalytic deactivation due to carbon deposition. In this paper, the surface modification of Ni catalyst by adding promoters and plasma treatment was studied.The support effect was tested first and the results showed that Al2O3 support was better than other oxides. Among the Al2O3 support tested, Ni/θ- Al2O3 catalyst is the best catalyst in both of activity and selectivity and Ni/α-Al2O3 catalyst has higher activity and lower CO selectivity. Both the activity and the selectivity of Ni/γ-Al2O3 catalyst were low. The results of 250h decay experiment indicated that the catalytic stability of 10%Ni/(-Al2O3 is better than 10%Ni/(-Al2O3 catalyst. The specific surface area and XRD measurements for the catalysts before and after reaction were done and the results revealed that on 10% Ni/(-Al2O3 catalysts the decrease of surface area and carbon deposition was one of the factors resulting in the decrease of the catalytic activity. We choose the Ni/(-Al2O3 and Ni/(-Al2O3 as based catalysts for further modification experiments. The modification study of promoters showed that the effect of promoters on Ni/α-Al2O3 is better than that of promoters on Ni/(-Al2O3. Ce and La were better promoters than Ca for the catalytic performance and the optimum Ce and La loading was 1% and 2% respectively. When La and Ce were in optimum loading, La exhibited better performance against carbon deposition.The air plasma modification experiments showed that the plasma treatment could improve the catalytic activity, the specific surface and the Ni dispersion but couldn't change the crystal structure of these catalysts. Helium plasma treatment could improve the catalytic activity and stability significantly. Also, plasma treatment could increase the resistance of carbon deposition on the catalysts.