Study On Surface Modification Of Catalysts For Partial Oxidation Of Methane To Syngas By Plasma Treatment

The catalytic partial oxidation of methane (POM) to syngas has been extensively investigated since the high selectivity and the syngas can be produced at a molar ratio of H2/CO of 2/1, which can be directly used as feed for the methanol or Fischer- Tropsch synthesis. Two groups of catalysts have been reported to be active and selective towards this process. One group is noble metal such as Rh, Ru, Pt, Ir and the other is transition metal such as Ni, Co and Fe among which Ni based catalyst exhibits high activity. However, Ni catalyst deactivates with time by the carbon deposition and the nickel sintering at high temperature, which limit its further industrial application. Although many researchers managed to improve the catalytic stability of Ni catalyst by addition of alkaline-earth metal and alkali metals to the catalyst, no breakthrough was obtained.Cold plasma treatment has been extensively used in the surface modification of polymers. However, few researchers pay attention to the study on surface modification of supported metal catalyst by cold plasma. Our research indicated that plasma treatment can increase the CH4 conversion and CO selectivity and couldn't alter the crystal structure. Also, the plasma treatment improved the catalytic stability.As the process of plasma treatment is complex, many treatment conditions will affect the catalytic activity. It was found that highest CH4 conversion was obtained for 10%Ni/(-Al2O3 catalyst when the discharge power was 60 W and the plasma treatment time was 3 min. The plasma treatment order and the kinds of discharge gas have no much effect on the treatment result. Moreover, the particle size of the catalysts affects the treatment result.Surface modification by plasma treatment was extended to the noble metal catalyst Pt. It was found that He plasma treatment can also increase the catalytic activity of Pt catalyst and Pt dispersion, and couldn't alter the oxidative and reductive performance of the catalyst and the crystal structure. So, it was concluded that plasma treatment affected only surface and subsurface regions. It may alter the specific surface areas, external structure and metal dispersion of the catalysts but couldn't change the crystal structure. The main reason of the increase of the catalytic activity was the increase of the active metal dispersion after plasma treatment.