Oxidative Coupling of Methane over Mn2O3-Na2WO4/SiC Catalysts

Jieun Kim,Eun Duck Park,La-Hee Park,Jeong-Myeong Ha

doi:10.3390/catal9040363

Abstract

The oxidative coupling of methane (OCM) is operated at high temperatures and is a highly exothermic reaction; thus, hotspots form on the catalyst surface during reaction unless the produced heat is removed. It is crucial to control the heat formed because surface hotspots can degrade catalytic performance. Herein, we report the preparation of Mn2O3-Na2WO4/SiC catalysts using SiC, which has high thermal conductivity and good stability at high temperatures, and the catalyst was applied to the OCM. Two Mn2O3-Na2WO4/SiC catalysts were prepared by wet-impregnation on SiC supports having different particle sizes. For comparison, the Mn2O3-Na2WO4/SiO2 catalyst was also prepared by the same method. The catalysts were analyzed by nitrogen adsorption–desorption, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The transformation of SiC into α-cristobalite was observed for the Mn2O3-Na2WO4/SiC catalysts. Because SiC was completely converted into α-cristobalite for the nano-sized SiC-supported Mn2O3-Na2WO4 catalyst, the catalytic performance for the OCM reaction of Mn2O3-Na2WO4/n-SiC was similar to that of Mn2O3-Na2WO4/SiO2. However, only the surface layer of SiC was transformed into α-cristobalite for the micro-sized SiC (m-SiC) in Mn2O3-Na2WO4/m-SiC, resulting in a SiC@α-cristobalite core–shell structure. The Mn2O3-Na2WO4/m-SiC showed higher methane conversion and C2+ yield at 800 and 850 °C than Mn2O3-Na2WO4/SiO2.

Highlights

The utilization of natural gas as a chemical feedstock has drawn attention because of the increased production of shale gas, a new and abundant gas resource [1,2,3]
We have found that the Mn/Na2 WO4 catalyst supported on micro-sized Silicon carbide (SiC) retained the SiC core and showed a better catalytic activity than the conventional Mn2 O3 -Na2 WO4 /SiO2 catalyst in the temperature range of 800–850 ◦ C
The SiC was stable after calcination in air at 800 ◦ C, the surface of the SiC was oxidized to α-cristobalite after the impregnation of the active components (Mn2 O3 -Na2 WO4 ) on the SiC

Summary

Introduction

The utilization of natural gas as a chemical feedstock has drawn attention because of the increased production of shale gas, a new and abundant gas resource [1,2,3]. Catalysts 2019, 9, 363 chemical processes, such as the Fisher–Tropsch reaction [10,11,12], methanol synthesis [13,14,15], and dimethyl ether (DME) production [16,17] processes. Because syngas synthesis via steam reforming consumes significant energy, much attention has been paid to the direct methane conversion technologies, such as the direct oxidation of methane into methanol or the oxidative coupling of methane (OCM) into olefins. The OCM reaction has drawn particular attention because olefins, such as ethylene and propylene, can be synthesized from methane directly without any intermediates, such as methanol or DME. The one-pass yield is still low, so the development of highly active catalyst for the OCM reaction is required.

Methods

Results

Conclusion