(626e) Selective Deposition of Ni on Mo2c That Has Been Supported on Al2O3: Enhanced Stability for Dry Reforming of Methane

In recent years, there has been much greater incentive to reduce greenhouse gas (GHG) emissions, CH₄ and CO₂ being the most potent offenders [1]. Biogas, which contains both GHGâ??s, is a largely under-utilized and passively emitted resource that may be used for energy production; therefore utilizing biogas represents not only an environmental benefit, but also a significant economic opportunity. One way to utilize biogas and provide a distributable source of energy is to catalytically convert it into liquid fuels. This may be achieved by first (dry) reforming CH₄ with CO₂ to form CO and H_2­, followed by liquid fuel production reaction such as Fischer-Tropsch or dimethyl ether (DME) synthesis. Although there are a few cases in which dry reforming of biogas has been scaled to demonstration-sized facilities [2], it has not attained full scale production. One of the main barriers is catalyst deactivation due to coking [3]. In this presentation, we address this issue by both choice of support and preparation method of Ni-based catalysts.

Oxide-supported Ni catalysts have been modified by others using Mo₂C in appropriate amounts to improve stability and activity [4, 5]. The enhanced stability has been attributed to a redox cycle where Mo₂C is oxidized by CO₂ which is then followed by recarburization from the coke deposited on Ni to re-form Mo₂C [4]. However, no efforts have been made to ensure intimate contact between Ni and Mo₂C when both are supported on a metal oxide surface. We demonstrate that Ni may be selectively deposited on Mo₂Caggregates that have been previously supported on Al₂O₃; the enhanced interaction between Ni and Mo₂C improve stability and provide more efficient utilization of the catalyst. Electroless deposition (ED) is used to selectively deposit Ni on Mo₂C by activation of a reducing agent on the Mo₂C surface to reduce a Ni²⁺ precursor in solution. Strong electrostatic adsorption (SEA) of the Ni²⁺ precursor on the Al₂O₃ surface is prevented by adjusting the pH of the solution to maintain the Al₂O₃ surface in a positive state. Thus, it is critical to avoid SEA of Ni on Al₂O₃ and to deposit Ni only on Mo₂C.

The resulting catalysts have been evaluated for dry reforming of methane; activities and stabilities are compared with catalysts prepared by conventional co-impregnation. XRD, TPR, and CO chemisorption have been used to determine bulk and surface compositions. The selectivity of Ni deposition on Mo₂C has been confirmed by STEM images.

References

[1] Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 â?? 2014, in: E.P. Agency (Ed.), 2016.

[2] A. Corradini, J. McCormick, Process and system for converting biogas to liquid fuels, in, Google Patents, 2012.

[3] C. Papadopoulou, H. Matralis, X. Verykios, Utilization of biogas as a renewable carbon source: dry reforming of methane, in: Catalysis for Alternative Energy Generation, Springer, 2012, pp. 57-127.

[4] S. Zhang, C. Shi, B. Chen, Y. Zhang, Y. Zhu, J. Qiu, C. Au, Catalytic role of β-Mo 2 C in DRM catalysts that contain Ni and Mo, Catalysis Today, 258 (2015) 676-683.

[5] W. Li, Z. Zhao, P. Ren, G. Wang, Effect of molybdenum carbide concentration on the Ni/ZrO 2 catalysts for steam-CO 2 bi-reforming of methane, RSC Advances, 5 (2015) 100865-100872.