Catalytic decomposition of methane is a viable method of producing hydrogen and carbon nanomaterials. Hydrogen gas is mainly used as a reactant in the chemical industry, i.e., petrochemicals, glass, and pharmaceutical industries, whereas carbon may be used in direct carbon fuel cells or marketed as a filamentous carbon. Demand for carbon monoxide (CO)–free hydrogen continues to rise due to the increase in the number of its applications. Currently, a significant amount of hydrogen comes from gasification of natural gas, oxidation, and steam reforming of hydrocarbons. In all these technologies, CO is formed as a by‐product that requires tedious and costly processes to separate hydrogen from syngas. Herein, the recent literature on methane decomposition, methane reaction kinetics, catalyst performance, hydrogen yield, and formation of carbon nanomaterial are reviewed. The scope of this work is limited to direct conversion of methane into carbon and hydrogen; therefore, processes involving synthesis gas as intermediate products are not covered. Finally, catalysts that are often used in methane decomposition, their deactivation, and regeneration are discussed with the aim of documenting the foundation upon which an entirely new class of catalysts can be built to enhance their activity, selectivity, and yield.

Summary Bulk of present day hydrogen comes from gasification of coal, steam reforming, and partial oxidation of hydrocarbons. Steam reforming accounts for over 50% of world hydrogen production despite producing carbonaceous gases which are harmful to the environment. In this work, five different supported molten metal catalysts comprising varying quantities of nickel and lithium supported on calcium oxide were synthesized and designated according to weight % as; 50%Ni/CaO, 37.5%Ni‐12.5%Li/CaO, 25.0%Ni‐25.0%Li/CaO, 12.5%Ni‐37.5%Li/CaO, and 50%Li/CaO. The synthesized catalysts were characterized by scanning electron microscopy, X‐ray diffraction, Brunauer‐Emmett‐Teller, and transmission electron microscopy and tested for methane decomposition. During decomposition experiments, the performance of each catalyst under different temperature conditions was evaluated in terms of methane conversion, carbon, and hydrogen yield. From experimental data obtained, catalyst 37.5%Ni‐12.5%Li/CaO recorded 65.7% methane conversion and 38.3%hydrogen yield, while catalyst 50%Ni/CaO recorded the lowest methane conversion of 60.2% and a hydrogen yield of 35.7% at 650°C. This confirms that the molten environment aided catalyst activity in methane decomposition reaction.

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Mature hydrogen producing technologies like steam methane reforming, coal combustion, and hydrogenation of hydrocarbons are leading emitters of greenhouse gases into the atmosphere. Catalytic decomposition of methane into carbon and hydrogen is a sure way of controlling the net emission of this greenhouse gas into the atmosphere. In this study, we present an environmentally benign approach of producing hydrogen from methane over a supported molten metal oxide catalyst. Catalyst systems were prepared by incipient wetness impregnation and characterized for crystallinity, shape and size, and surface area using various techniques. Methane conversion experiments were done in a packed bed reactor over three different catalyst systems synthesized from nickel oxide, lithium hydroxide, and calcium oxide (CaO) under various process conditions. Gaseous products from the reactor were analyzed using gas chromatography. Using catalyst 38N12L, 45.9% hydrogen yield was obtained at 650°C and GHSV of 1.2 Lg−1cath−1. The molten environment provided by LiOH enhanced hydrogen yields by 12.6% through surface reaction and chemisorption. Calcium oxide played a bifunctional role as a catalyst support and an adsorbent of in situ generated CO/CO2 gases thereby improving hydrogen quality.

Non-oxidative conversion of methane (NOCM) is an environmentally benign route for producing carbon and valuable petrochemicals from methane. Unlike other methane conversion processes like Fischer-Tropsch and methanol synthesis which have been scaled up to commercial level, NOCM process development remains at laboratory scale due to various challenges such as catalyst deactivation due to coking, process thermodynamics, low conversion, and limited selectivity towards useful products. In this present work, a study of non-oxidative conversion of methane into carbon and petrochemicals was done over Fe, W, & Mo catalyst systems supported on activated carbon (AC) and HZSM-5. The catalyst systems were prepared by various techniques at different metal loadings. The prepared catalysts were characterized for phase identification, structural properties, surface area, presence of functional groups, and tested for non-oxidative methane conversion at different operating conditions in a packed bed reactor. Products from non- oxidative conversion of methane were analysed using gas chromatography. To accomplish the research objectives, synthesized binary catalyst systems were developed step by step. Phase one of the study involved synthesis of 24 single metal catalyst systems supported on activated carbon and HZSM-5 between 1.8-7.2% metal loading and tested for non-oxidative methane conversion. Prepared catalysts were screened based on methane conversion. Phase two of the study involved synthesis of 5.4% bimetallic catalyst systems supported on AC/ HZSM-5 and applied for non-oxidative methane conversion. Catalytic activity of Fe-Mo, W-Mo and Fe- W on AC and HZSM-5 supports were evaluated based on methane conversion and product distribution. In the final phase of the study, trimetallic binary catalyst systems (Fe-W-Mo) on AC and HZSM-5 supports were synthesized, characterized, and their catalytic activity evaluated at different metal loading, different metal composition, and different process conditions. The effect of support and catalyst preparation method on catalyst activity was also evaluated. Based on the results obtained, catalyst Fe-Mo/HZSM-5 showed little activity in terms of methane conversion with low C2 and high coke formation whereas catalyst W-Mo/HZSM-5 was very active in methane conversion but less selective towards C2 and aromatic hydrocarbons. On the other hand, catalyst Fe-W showed low methane conversion and low coke formation but exhibited high selectivity toward aromatics. A 5.4% binary catalyst system (Fe-W-Mo/HZSM-5) with equal metal loading did not show much improvement on methane conversion, selectivity towards C2 hydrocarbons, aromatics, and coke. However, when Fe and W metal loading were higher than Mo in this 5.4% binary catalyst system, there was notable increase in methane conversion and coke but C2 formation decreased. On the contrary, when Mo loading was increased and Fe and W metal loading reduced, there was a subsequent decrease in methane conversion and coke formation but C2 and aromatics formation increased by a big margin. From X-ray diffraction (XRD) results, M2C on HZSM-5 produced by transformation of highly dispersed MoO3, was the most active site for the activation of the C-H bond in methane molecules, but these sites were less active for further decomposition of CH∗ radicals. Based on methane conversion, catalytic activity of Fe-W-Mo 3 catalyst systems showed the same trend both on AC and HZSM-5 although methane conversion values were higher on AC than on HZSM-5 support. A wider range of product distribution was realized on catalysts supported on HZSM-5 than on AC support. This was attributed to the HZSM-5 zeolite channel structure and its inherent acidity which promoted shape selectivity towards benzene and its derivatives. Further, methane reacted with Mo6+ on HZSM-5 zeolite to produce CH3+ (a methoxy species on the Bronsted acid sites of the zeolite) and [Mo-H]5+ which were further transformed into a molybdenum-carbene species (Mo=CH2). These species further reacted with CH4 to produce C2 intermediates. The Bronsted acid sites located inside the zeolite channels and shape selectivity of HZSM-5 zeolite were responsible for activation of C- H bond and conversion of the C2 intermediates into benzene and other higher carbon hydrocarbons. Despite intensive research in this area, and to the best of the author’s knowledge, no work on the development of a catalyst system for quantitative control of methane conversion and product distribution using Fe, W, and Mo catalyst systems loaded on AC/HZSM-5 has been reported. Therefore, the novelty in this work lies in the development of a tuneable binary catalyst system for quantitative control of product distribution in methane conversion to carbon and petrochemicals.