Direct non-oxidative methane decomposition over silica-supported Co/Ni/Mo catalysts

Materials for Renewable and Sustainable Energy https://doi.org/10.1007/s40243-024-00289-0 (2025) 14:15 ORIGINAL PAPER Direct non‑oxidative methane decomposition over silica‑supported Co/Ni/Mo catalysts Siddharth Parashar1 · Sharad M. Sontakke1 Received: 26 July 2024 / Accepted: 18 December 2024 © The Author(s) 2025 Abstract Typically, the methods for converting methane can be categorized into two primary groups: direct and indirect. Among these, the direct non-oxidative conversion of methane to higher hydrocarbons has received a lot of interest in recent years due to its distinct advantages over the indirect routes. Several catalysts based on transitional metals such as Ni, Fe, Co, Mo, etc. have been reported for the methane conversion, employing different supports. This study focuses on the direct nonoxidative decomposition of methane using monometallic catalysts based on silica. The catalysts, specifically Co, Ni, and Mo, were impregnated to the pre-synthesized silica support. The synthesized catalysts were characterized for crystallite size, surface area, morphology and thermal stability using X-ray diffraction, porosimeter, scanning electron microscope and thermogravimetric analysis, respectively. The effect of reaction temperature, amount of catalyst, methane preheating, flow rate of methane and presence of promotors on the decomposition reaction was investigated. Keywords Non-oxidative · Methane conversion · Catalysts · SiO2 Introduction Population growth, industrialization, and urbanization have been primarily responsible for the substantial increase in global energy consumption over the past century. Based on the findings of the British Petroleum (BP) statistical review of 2022, India was the third-largest energy consumer in the world in 2021 after China and the United States [1]. Fossil fuels continue to make up the majority of the world's energy supply. The largest energy source is oil which is followed by coal and natural gas. Considering that fossil fuel reserves are depleting along with their impact on the environment, it is necessary to find an alternative low cost, abundant and environmentally benign source of energy. Natural gas has emerged as a key source of conventional energy due to improvements in excavation technology along with incredibly low emissions as compared to other fossil fuels, and large reserves that are currently available in nature [2, 3]. * Sharad M. Sontakke 1 Sharad’s Lab (δ‑Alpha Research Group), Department of Chemical Engineering, Birla Institute of Technology and Science, Pilani, K. K. Birla Goa Campus, Goa 403726, India Natural gas comprises of a variety of hydrocarbon gases, with its composition varying based on its geographical origin. In the past, natural gas that was obtained while extracting petroleum could not be sold for a profit, so it was simply flared off at the oil field. As the value of the gas has appreciated, conservation efforts have grown and gas flaring has decreased significantly. Currently, the majority of gas generated at production sites is transported to the market via high-pressure pipelines. Nevertheless, the economic viability of transporting natural gas over large distances is limited. Consequently, considerable efforts have been dedicated to the advancement of methodologies for the on-site conversion of natural gas to transportable value-added chemicals, including olefins, aromatics, and hydrogen [2–4]. Since, natural gas is primarily methane, various strategies for the conversion of methane are investigated and reported in the literature. In general, the routes for methane conversion can be classified into: (1) direct, and (2) indirect. There are several drawbacks associated with the indirect processes [5, 6]. The partial oxidation of methane to syngas are limited by safety issues [5]. The production of syngas by reforming is a highly endothermic process and is typically carried out at temperatures as high as 1100 K over alumina-supported nickel catalysts. To generate these high temperatures, almost Vol.:(0123456789) 15 Page 2 of 10 25% of the feed (natural gas) is consumed resulting in high operating expenses. About 60% of the capital expense for converting syngas to methanol is estimated to be incurred during the syngas production process. As a result, the syngas production is an expensive and energy-intensive process. Heat transfer is another critical challenge since there is a significant temperature differential between the methane reforming stage and the subsequent conversion to methanol. Additionally, steam methane reforming needs to be regulated to prevent excessive methane oxidation via the water gas shift reaction, which will result in high C O2 emissions and lower carbon atom usage [5, 6]. Therefore, the primary focus of current research in this field is the development of suitable direct conversion routes. The direct approaches involve the elimination of the intermediary syngas generation stage, enabling the conversion of methane into value-added products in a single step. This reduces the overall processing costs and enhances the carbon utilization efficiency. The reported direct methane conversion routes can be broadly categorized into oxidative (in presence of oxygen) and nonoxidative (in absence of oxygen) processes. The oxidative conversion of methane is thermodynamically more favorable than under non-oxidative conditions. However, the direct oxidative processes are limited by the low conversion of methane, formation of undesired products such as C O2, and low selectivity towards hydrocarbons [6–8]. Further, a mixture of methane and oxygen has serious safety concerns [5]. Therefore, direct non-oxidative conversion of methane to higher hydrocarbons has gained significant attention in the recent years. The specific advantages of direct non-oxidative conversion of methane are: oxygen-free safer reaction conditions, improved carbon utilization efficiency, improved selectivity towards hydrocarbons, reduced catalyst deactivation due to coking, and reduced overall processing costs. Several studies have reported the application of different supports for the direct non-oxidative conversion of methane, employing various transitional metal-based catalysts such as Nickel (Ni), Iron (Fe), Cobalt (Co), Molybdenum (Mo), among others [5, 9]. The use of HZSM-5 (Hydrogen form, or protonic type, of Zeolite Socony Mobil-5) supported catalysts, particularly Mo/HZSM-5, has been extensively documented and demonstrated for the direct non-oxidative conversion of methane to aromatic compounds. The influence of the SiO2 and Al2O3 composition on the activity of HZSM-5 catalysts has also been reported [6, 10]. Despite numerous efforts, coking-induced catalyst deactivation continues to be a major drawback. Solymosi and Cserényi demonstrated the application of metal oxide-based catalysts for the non-oxidative decomposition of methane [11]. The researchers investigated the catalytic behavior of iridiu (...truncated)