Dehydroaromatization of methane over noble metal loaded Mo/H-ZSM-5 zeolite catalysts

Abstract

Dehydroaromatization of methane (MDA) reaction was investigated over platinum modified Mo/H-ZSM-5 catalysts which were pre-carbided at 750 °C. The influence of platinum on the catalytic performance and product selectivity of Mo/H-ZSM-5 catalysts for the MDA reaction at 700 °C were studied. The presence of platinum led to a slight decrease in methane conversion from 7.5 to 4.2%. Aromatic selectivities above 90% were obtained with catalysts containing low platinum loadings (0.5 and 1.0 wt.%), with benzene being the most prominent product. A decrease in coke selectivity and coke deposits was noted with the platinum modified Mo/H-ZSM-5 zeolite catalysts. A comparative study was performed to compare platinum, palladium and ruthenium promoted Mo/H-ZSM-5 zeolite catalysts with un-promoted Mo/H-ZSM-5. The ruthenium promoted catalyst proved to be superior in catalytic performance, with a higher methane conversion obtained than that found for platinum promoted and palladium promoted Mo/H-ZSM-5 catalysts. Benzene selectivity of about 60% was obtained for ruthenium and palladium promoted Mo/H- ZSM-5 catalysts and the total aromatic selectivity was maintained at 90%. TGA results showed a total reduction of 50% by weight of carbon deposited on the promoted Mo/H-ZSM-5 catalyst. Graphic abstract

Catalytic Routes for Direct Methane Conversion to Hydrocarbons and Hydrogen: Current State and Opportunities

“…In the current review we summarize the best results obtained with different catalysts reported during the last 25 years: methane conversion, C 2 products, and benzene yields, as well as the operating conditions (Figure and Table ). ,,− ,,,− As can be seen from Table , the Mo/HZSM-5 is the most investigated catalyst for the MDA reaction since the very first report in 1993 . Usually, the MDA reaction is carried out at temperatures from 650 to 800 °C, leading to an average benzene selectivity of 70%. ,,− Other catalysts for the MDA with lower performance including Fe/HZSM-5, GaN/SBA-15, TaH/SiO 2 , and bimetallic Pt-X/HZSM-5 have been reported.…”

“…The introduction of several metals promoters to tune the performance of the Mo/HZSM-5 catalysts has been reported; in particular, the nature, concentration of mono- or bi-metallic promoters. The total benzene yield on bimetallic Mo-X/HZSM-5 catalysts and the first order deactivation rate constant of benzene formation are summarized in Table . ,− ,,,,− The bimetallic Mo-X/HZSM-5 based catalysts contain palladium, ruthenium, iridium, zinc, copper, chromium, tungsten, platinum, iron, cobalt, nickel, rhenium, or gallium (Table ). In most of the studies, mono- and bimetallic catalysts with an increase of the total metallic content were compared.…”

“… a Bold: monometallic catalysts used as references for the catalyst series; 1 benzene produced (%) is calculated by integration of a range of T.O.S specified for each case. Refs ,− ,,,,− . …”

“…Effect of the concentration of cometal promoters (Fe, Co, Ni, Pt, Zn, Pd, and Rh) of Mo/HZSM-5 catalysts in comparison with the monometallic molybdenum catalyst (Mo/HZSM-5 reference, dashed red line) on benzene yield. Data taken for △, from ref ; ◀, from ref ; ▶, from ref ; □, from ref ; ●, from ref ; ○, from ref ; ⬟, from ref ; ▲, from ref ; ▼, from ref ; ■, from ref ; ◆, from ref .…”

“…Furthermore, knowing that the production of large amounts of coke is currently unavoidable, focused efforts to address this issue have been devoted. Possible approaches consist of partial coke removal under soft conditions and use of reductive atmosphere in order to avoid structural damages of the catalyst. , Pretreatment of the catalyst under a reductive atmosphere is also a way to prevent migration of the active metallic sites. − Finally, strategies to improve benzene yields as the addition of metallic promoters ,− and mixture of other molecules in the feed have been explored. − As will be shown in the next sections, the catalytic performances can be improved by displacing the thermodynamic equilibrium, resulting in coke reduction and higher benzene yields.…”