A critical literature review of the advances in methane dehydroaromatization over multifunctional metal-promoted zeolite catalysts

• Published in: Applied catalysis. A, General General, 2020-11, Vol.608 (C), p.117870, Article 117870
• Main Authors: Menon, Unmesh, Rahman, Mustafizur, Khatib, Sheima J.
• Format: Article
• Language: English
• Subjects: Benzene; Catalysts; Catalytic converters; Coking; Configurations; Conversion; Deactivation; Dehydroaromatization; Dopants; Literature reviews; Methane; Multifunctional; Naphtha; Natural gas; Optimization; Process intensification; Reactors; Shale gas; Stability; Synthesis gas; Zeolites
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2020.117870

[Display omitted] •Adding metals to Mo/ZSM-5 confers multifunctionality to the catalysts enhancing their performance in MDA.•Transition metal additives, Fe, Co, Ni, can change the nature of the C deposits formed in reaction.•Noble metal additives, Pt, Rh, Pd, Ir, Ru, Cu, hydrogenate carbon deposits formed in reaction in situ.•Metals additives like Cr, Ag, can enhance the acid-assisted heterolytic splitting of methane.•Multifunctional Mo-X/ZSM-5 catalysts must be coupled with process intensified reactor configurations to optimize MDA. The drastic rise in shale gas production has encouraged the quest for alternative uses of methane as a chemical feedstock in the manufacturing industry. While two-step syngas routes for methane valorization are deployed commercially, direct one-step routes for methane conversion are attracting much attention. As steam cracking installations have shifted from using oil-based naphtha to shale-based natural gas liquids, production of aromatics has dropped. Methane dehydroaromatization (MDA) is a one-step reaction capable of valorizing methane to hydrogen and benzene. Challenges with the MDA reaction are two-fold: the reaction is thermodynamically limited with low one-pass methane conversion and even the best catalytic systems, Mo/zeolites, suffer rapid deactivation from coking. A catalyst design strategy to improve stability is the use of multifunctional Mo-X/zeolite systems where X is a dopant capable of modulating the stability. In this paper we provide a complete overview of the main Mo-X/zeolite systems used in MDA and critically draw connections among the different types of dopants (X) employed, as a function of the role they play in the reaction/deactivation pathway. We have also dedicated a section to emerging trends with non-Mo based catalysts. The goal of this review article is to establish a basis that will facilitate the identification of useful multifunctional catalytic systems, and recognize gaps in the knowledge of these systems that deserve more attention. Improving MDA systems to the point to which they can be commercially deployed requires a multifaceted approach that combines optimization of the designs of both the catalyst and the reactor configuration. We therefore also provide a brief overview of the most recent advances in process intensification strategies employed with different reactor configurations.