(394f) Carbon Dioxide Reforming of Methane Over Nickel Supported Mesoporous Material Catalysts with Superior Stability

Catalytic reforming of methane with carbon dioxide, also known as dry reforming, has recently attracted considerable attention due to simultaneous utilization and reduction of two types of greenhouse gases, CO2 and CH4. The synthesis gas (syngas) produced has a lower H2/CO ratio than those available from steam reforming and partial oxidation of methane; the lower ratio is preferred for the synthesis of valuable oxygenated chemicals and long-chain hydrocarbons [1, 2].

Our group has extensively explored the feasibility of catalyzing the dry reforming with nickel supported mesoporous molecular sieve catalysts. Highly ordered Ni-MCM-41 catalysts with nickel ions incorporated into the silica framework of MCM-41 have been prepared and studied for the reforming of methane with carbon dioxide [3]. Significant catalytic activity can be obtained at temperatures as low as 500oC. The results also indicated that the presence of a suitable amount of nickel in Ni-MCM-41 was beneficial for maintaining high catalytic activity and long-term stability. The improved catalytic performance was suggested to closely associate with both the amount of active centers on the pore wall surface and the stabilized dispersion of these active sites by the silica matrix and/or the surrounding unreduced nickel ions. This anchoring effect facilitated the formation of the active Ni nano-clusters with high dispersion under reaction conditions. Hence the reforming reaction is favored and the carbon formation is suppressed. All Zr-promoted Ni-MCM-41 catalysts exhibited comparable or enhanced initial activity compared to Ni-MCM-41. Adding Zr4+ remarkably improved the long-term stability whereas the decreased initial activity and stability were observed for Ti- and Mn- substituted catalysts. It was observed that adding Zr4+ enhanced the structure stability and the dispersion of active Ni sites. The strong anchoring effect of Zr4+ and partial activation of CO2 by Zr4+ contributed to the high catalytic activity and long-term stability. However, the decoration of Ni clusters with TiOx and MnOx species in Ni-Ti and Ni-Mn catalysts hindered the accessibility of Ni active centers, thus decreasing their catalytic performance. The crystalline transformation of silica in Ni-Mn, Ni-Ti and Ni-MCM-41 catalysts also played a negative role in catalytic performance [4].

In this contribution, we report a novel method to prepare nickel catalysts supported mesoporous materials. Nickel supported on MCM-41 and SBA-15 mesoporous molecular sieves were synthesized by grafting using nickel acetylacetonate as precursor. The grafted Ni catalysts were characterized using various techniques. The catalytic results indicated that Ni grafted catalysts provided high catalytic activity, superior stability and reasonable H2/CO ratios in the product which was ascribed to the stabilized dispersion of these active sites on the silica matrix. Furthermore, nickel grafted SBA-15 was more active compared to MCM-41 implying that the structure and stability of support played a vital role. It is believed that the interconnected pores and the thick pore walls of SBA-15 may have an advantage on the catalytic performance over the MCM-41 with thin pore wall and isolated pores. Subsequently, a detailed comparative study will be performed to evaluate the catalytic performance of grafted and impregnated nickel species on both MCM-41 and SBA-15.

References

1. J.R.H. Ross, A.N.J. van Keulen, M.E.S. Hegarty, K. Seshan, Catal. Today 30 (1996) 193-199.

2. I. Wender, Fuel Processing Techn. 48 (1996) 189-297.

3. D. Liu, et al., Appl Catal A: Gen (2009), doi:10.1016/j.apcata.2008.12.044

4. D. Liu, et al., J. Catal. (revision)