Simultaneous Conversion of Methane and Methanol into Gasoline over Bifunctional Ga‐, Zn‐, In‐, and/or Mo‐Modified ZSM‐5 Zeolites

Abstract

In response to increased energy demands, worldwide efforts have been made over the past 2-3 decades to develop alternative methods for the conversion of methane (a main constituent of natural gas, coal-bed gas, and biogas) into value-added products. These include ethylene (by oxidative coupling of methane), [1][2][3] syngas (by partial oxidation with or without simultaneous steam-and/or CO 2 -mediated methane reformation), [4][5][6][7][8] and gasoline/liquid hydrocarbon fuels [9][10][11][12][13][14] that involve either oxidative [1][2][3][4][5][6][7][8][9][10] or nonoxidative [11][12][13][14][15] methane activation. As methane and carbon dioxide are key greenhouse gases responsible for global warming, the current industrial practice of emission and/or flaring of produced methane will be banned in the near future. The methane produced in remote places must therefore be converted into easily transportable energy sources like liquid hydrocarbon fuels at the sites of methane production. The most important approach for the transformation of methane into liquid hydrocarbons is the well-established and already commercially proven route: [16] methane!syngas!methanol!gasoline, based on the methanol-to-gasoline (MTG) process developed by Mobil. [16][17][18] In 1985, Mobil successfully operated a commercial plant in New Zealand for MTG conversions. However, its operation had to be discontinued as a result of unfavorable process economics. [18][19][20] The cost of the syngas production step (by steam reforming) is about twice the cost of the MTG production step.The MTG process could become economically viable if it were possible to convert a significant portion of the methane into gasoline without the intermediate steps of conversion into syngas and methanol. Herein, we show that this very difficult goal can be met through the nonoxidative activation of methane and its simultaneous conversion with methanol into gasoline-range hydrocarbons over bifunctional Ga-, In-, Zn-, and/or Mo-modified ZSM-5 type zeolites that have both dehydrogenation and acid functions. We also show that the amount of methane converted can be equimolar to the amount of methanol converted in this novel process, depend-

Water‐Promoted Hydrocarbon Activation Catalyzed by Binuclear Gallium Sites in ZSM‐5 Zeolite

“…[3] An additional appealing example is the incorporation of methane into gasoline products in the MTG process over Ga/HZSM-5. [4] A catalytic issue relates to the nature of the cationic clusters. Are the alkanes activated by isolated cations, or do the extraframework oxygen atoms also play a role?…”

Co-conversion of Ethane and Methanol into Higher Hydrocarbons over Ga/H-ZSM-5, Mo/H-ZSM-5 and Ga-Mo/H-ZSM-5

“…The catalytic experiments are designed to resemble the methane and methanol co-conversion experiments performed by Choudhary et al [15].…”

“…All the catalysts were pretreated at 550°C prior to test. The Ga/H-ZSM-5 catalyst was pretreated in a flow of He for 2 h, while the molybdenum containing catalysts were pretreated in a H 2 /CH 4 mixture (6% H 2 ) for 4 h to produce the catalytically active molybdenum carbide [15]. Tests were carried out at atmospheric pressure and at an oven temperature of 500°C.…”

“…In a different study, Choudhary et al [15] investigated the co-conversion of methane and methanol over Ga-, Zn-, In-, and Mo-modified H-ZSM-5 zeolites in the production of olefins and aromatics. Choudhary et al reported that the conversion of methane was highly promoted by the presence of methanol in the feed.…”

“…In principle, a thermoneutral reaction can be obtained in this way. The working hypothesis is that the alkane is activated by a combination of the dehydrogenating metal sites and the methanol generated hydrocarbon species on the catalyst [15].…”