(544fb) Non-Oxidative Direct Conversion of Methane over Fe(C)SiO2 Catalyst with Controlling Radical-Based Reaction

Many researches on methane conversion into valuable chemicals have been conducted due to the abundance of natural gas resources [1,2]. Because dissociation of C-H bond of methane requires high temperatures exceeding 700 ^oC, methane direct conversion has low carbon efficiency by coke formation [3]. In this area, Fe©SiO₂ catalyst with single iron sites has been recently suggested and exhibited high methane conversion without deactivation at 1293 K [4]. However, the catalytic function is still controversial because radical-based reaction is dominant under the reaction conditions. It is also difficult to control the radical-based reaction that occurs on both gas phase and on catalyst surface. In this work, we prepared Fe©SiO₂ catalyst with lattice confined iron using fayalite as an iron-silicate precursor, and it was applied to methane direct conversion.

Nano crystallized fayalite (Fe₂SiO₄) with high purity was prepared by sol-gel method [5]. It was mixed with quartz and melt-fused to yield Fe©SiO₂ catalyst. Fe©SiO₂ catalyst exhibited low coke selectivity (< 5%) and stable catalytic performance during 50 h-reaction. From the TEM images of spent catalysts, it was observed that Fe carbide particles were highly dispersed in the spent Fe©SiO₂ catalyst. This indicates that Fe©SiO₂ obtained confined Fe carbide particle and avoided sintering during the reaction, which induced high catalytic stability.

By changing particle size of a-cristobalite, the effect of surface area on coke formation was investigated. We have observed that coke formation is predominantly related to the surface area of a-cristobalite. The Fe©SiO₂, however, required high Fe dispersion for high selectivity to hydrocarbons. Therefore, we further investigated the effect of preparation method showing how the physicochemical properties of Fe-silicate precursor affect the activity of Fe©SiO₂. The effect of particle size of precursors on Fe dispersion and catalytic activity was also investigated. Overall, with the various characterization, strategies to effectively convert methane with controlling radical-based reaction over Fe©SiO₂ catalyst were suggested.

[1] S. Ma et al, J. Energy Chem. 22 (2013) 1–20.

[2] A. Galadima et al, J. Ind. Eng. Chem. 37 (2016) 1–13.

[3] N. Kosinov et al, J. Catal. 346 (2017) 125–133.

[4] X. Guo et al, Science 344 (2014) 616-619.

[5] M.T. Deangelis et al, Am. Mineral. 97 (2012) 653-656.