On The Plasma Treatment Of Nickel Catalyst For Methanation

In consideration of the fuel resources and environment, the methanation of coal becomes a hot topic nowadays. Nickel is a good metal for catalyst. It has good activity to many reactions. And its low price and availability enable it to get wide use in industry. In order to improve the activity and stability, large quantities of work have been conducted. Optimization has been promoted for each process of preparation of the catalyst. In previous studies, plasma has been employed to prepare many kinds of supported metal catalyst. The products have good dispersion, better activity, and improved stability. In present work, glow discharge plasma was used to modify the nickel supported by silica. The catalyst was used in methanation reaction. As the result showed, it has smaller nickel particles, narrower size distribution and better activity towards the methantion. Compared to conventional catalyst, the one treated by plasma brought down the temperature by 25 ?C. After reaction, the TEM showed that the catalyst by plasma show better anti-coke performance, and it still kept good dispersion and no obvious aggregation was observed.Thermal analysis was used to characterize the precursor of nickel catalys. It was concluded that plasma treatment induced dehydration and partial decomposition of the precursor and there was a shift to higher temperature for the decomposition of sample by plasma. It was the first time to make quantitive analysis to compare the difference between the precursors with or without plasma treatment.In order to magnify the treatment of catalyst by plasma, another type of plasma: dielectric barrier discharge plasma was studied in comparison of glow discharge plasma. The samples were tested by CO methanation of hydrogen-rich gas. After 1-h's treatment, both the two types of plasma promoted the activity of catalys. XRD result showed that nickel particles of both the samples have particle size of 20 nm, smaller than conventional one (22 nm). Smaller particles account mainly for the better activity.With the help of atomic force microscopy (AFM), we carried out study on a model catalyst of supported nickel. We made ex situ obvervation on the change of nickel species at each process of the preparation. The plasma treatment didn't change the morphology and particle size of nickel species directly. But it changed the support to enhance the surface tension, so during the calcination and reduction at high temperature, it stabilized the nickel spcecies at the surface of support with smaller size and better activity. Besides, there was a significant change in the morphology of nickel particles after plasma treatment. It became flattened and has a much smaller height. This kind of particle edge improved the activity.