(573c) Dry Reforming of Methane over Nickel-Based Catalysts for Syngas Production

B. R. DE VASCONCELOS¹, D. PHAM MINH¹, P. SHARROCK¹, A. NZIHOU¹

¹Mines Albi, CNRS, Centre RAPSODEE, Univ. Toulouse, Campus Jarlard, F-81013 Albi Cedex 09, France

Climate changes caused by greenhouse gases emissions, especially CO₂, have driven scientists to develop technologies for CO₂ utilization. Moreover, increases in energy demand and depletion of carbon-based resources have shown the need of substitution of fossil fuels for renewable energies. The valorization of CO₂in more valuable chemicals and fuels has become an environmentally interesting option [1][2].

Among the several chemical processes that are able to convert CO₂ into chemicals, the dry reforming of methane (Equation 1) has gained much attention. In this reaction, CO₂reacts with methane to form syngas, from which many other chemicals, such as methanol, dimethyl ether, hydrogen and liquid hydrocarbons can be produced [3]. DRM is also an interesting option for the valorization of natural gas and biogas, which are composed mainly of carbon dioxide and methane. The economic aspect is also propitious. Natural gas reserves, for example, are larger than petroleum reserves [1][4][5]. Biogas, formed by anaerobic digestion of organic biomass and wastes, is largely produced at different scales [6][7][8]. DRM reaction and its side reactions are expressed in equations (1-5):

Dry reforming of methane:

CH₄ + CO₂â?? 2CO + 2H₂ (1)

Side reactions:

Water-gas shift reaction:

CO₂ + H₂â?? H₂O + CO (2)

Boudouard reaction:

2CO â?? C_(s) + CO₂ (3)

Methane cracking reaction:

CH₄â?? C_(s) + 2H₂ (4)

Carbon gasification:

H₂O + C_(s)â?? CO + H₂ (5)

Despite the economic and environmental benefits, no technical solution for DRM has emerged at industrial scale yet. The main reason is the catalytic deactivation by carbon deposition (Equations 3-5) and the sintering of both support and metal particles [9].

Supported nickel catalysts have been widely studied due to their low cost, high availability (compared to noble metals) and high catalytic activity. Nevertheless, they were reported to be prone to carbon deposition on the catalyst active surface. So, much effort has been spent on the design of a stable Ni catalyst for DRM. Parameters such as support chemical composition and promoters are key parameters for the development of a performing catalyst [9]. Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) has gained much attention as catalyst support due to its high chemical and thermal stabilities and its ability to undergo several substitutions in its crystal lattice. So, this work focused on the development of a performing Ni supported on hydroxyapatite catalyst for DRM.

The catalyst was synthesized by incipient wetness impregnation method with a Ni loading of 5.7wt.%. Then, its performance on DRM was tested in a fixed-bed tubular reactor at 700°C for 50 h of time-on-stream (TOS) with WHSV = 15882mLh^-1g_cat^-1. The catalyst showed both methane and CO₂conversion around 80% and no deactivation was detected during the 50h of TOS.

In order to compare the performance of the Ni/hydroxyapatite catalyst synthesized in this work with the ones of the catalysts already used at industrial scale in similar reforming processes, two alumina-based catalysts (5%wt.Ni/Al₂O₃ and 5%wtNi/MgO-Al₂O₃) were also synthesized and tested on DRM in the same conditions. Ni/hydroxyapatite showed similar catalytic performance that Ni/ MgO-Al₂O₃ and better performance that Ni/ Ni/Al₂O₃. These results show that the hydroxyapatite-based catalyst could be a promising catalyst for DRM.

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