A review of recent progress on CO2 hydrogenation to methane by Ni-based catalysts supported on carbon materials

Abstract

Recent research progress on the use of Ni-based catalysts supported by various carbon materials, such as carbon nanotubes, graphene, and activated carbon, for the hydrogenation of CO2 to CH4 is summarized. The influence of additives and surface modification methods on improving their catalytic performance is discussed as is the reaction mechanism, especially the structure-function relationship produced by the carbon. The review provides a comprehensive directory for the rational design of carbon-supported Ni-based catalysts for the methanation of CO2.

1. Introduction

The ongoing development of society and the economy, along with the enhancement of living standards, has led to the excessive utilization of fossil fuels and enormous carbon dioxide (CO2) emissions. The emission of CO2 has caused a series of irrevocable environmental issues, including the greenhouse effect and ocean acidification[1–4]. However, CO2 is also a cheap and abundant ideal carbon inorganic resource, which can be chemically converted into high-value chemicals and fuels. The transformation of CO2 driven by chemical strategy not only alleviates the environmental pressure caused by greenhouse gas emissions but also provides a non-fossil feedstock route for chemical synthesis and fuel production[5–10]. Recently, thermal catalysis-based CO2 hydrogenation technology has attracted considerable research attention due to its high CO2 conversion efficiency and targeted product yield. Additionally, the rapid advancement of electrolytic hydrogen production using clean and renewable energy sources, such as wind, solar and tidal energy, has made cost-effective hydrogen (H2) more readily available for CO2 hydrogenation[11–13]. In comparison with the hydrogenation of CO2 to other high-value products, such as liquid fuel, light olefins and oxygenates, the hydrogenation of CO2 to methane (CH4) is preferential due to the higher targeted CH4 selectivity (usually higher than 90%) and lower product separation cost[14]. Moreover, CH4, as the main component of natural gas, has a broad market demand. It can be used directly as a fuel and raw material for synthesizing other important chemicals, such as aromatics and ethylene, which are widely used in chemical industries and hold significant economic and practical value (Fig. 1).

The rational design of efficient catalysts has been considered a key factor in boosting methanation efficiency. Ni-based, Fe-based, Co-based, Ru-based and Rh-based catalysts are generally employed for hydrogenating CO2 to CH4[15]. Among them, Ru-based and Rh-based catalysts deliver high CO2 conversion and targeted CH4 selectivity, but the high price hampers their industrial applications. Even though the Fe-based and Co-based catalysts are relatively low-cost, the low CH4 activation capability and poor stability during the reaction process are bottlenecks for large-scale utilization[16]. Notably, Ni-based catalysts are the most extensively studied catalysts for CO2 hydrogenation to CH4 due to their excellent C―O bond activation capability, superior H2 dissociation capability, outstanding targeted CH4 selectivity, and relatively low cost[17–19]. However, Ni nanoparticles are prone to sintering at high reaction temperatures, which leads to rapid deactivation during the catalytic process. Therefore, choosing appropriate support is crucial to enhance the sintering tolerance of Ni-based active sites, as the physicochemical properties of the supports could significantly influence the dispersion, stability and catalytic efficiency of the metallic active sites. In recent years, carbon materials have gained considerable attention as potential catalyst supports.