Effect of Addition of K, Rh and Fe Over Mo/HZSM-5 on Methane Dehydroaromatization Under Non-oxidative Conditions
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Effect of Addition of K, Rh and Fe Over Mo/HZSM-5 on Methane Dehydroaromatization Under Non-oxidative Conditions Vaidheeshwar Ramasubramanian1 · Daniel J. Lienhard1 · Hema Ramsurn1 · Geoffrey L. Price1 Received: 28 November 2018 / Accepted: 31 January 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract Methane dehydroaromatization was studied over a series of K, Rh and Fe promoted 10 wt% Mo/HZSM-5 catalysts with different promoter loadings of 0.5, 1 and 1.5 wt% at 750 °C in a recirculating batch reactor. All the catalysts were reduced in H2 at 750 °C prior to methane activation. K, Rh and Fe- promoted Mo/HZSM-5 catalysts were prepared by sequential impregnation. N-propylamine-temperature programmed desorption confirmed the significant modification in the acidity of the catalyst upon addition of K. Compared to 10 wt% Mo/HZSM-5, the conversion of CH4 remained nearly unchanged for 1 wt% K-promoted catalyst but decreased by ~ 46% for 1 wt% Rh promoted catalyst and by ~ 4.3% for Fe-promoted catalyst after 255 min of reaction. The conversion of C H4 further decreased with increase in K and Rh loading but increased with increase in Fe loading. Compared to Rh and Fe-promoted catalysts, K-promoted catalyst exhibited better selectivity for C6H6 after 255 min of reaction. The temperature programmed oxidation results revealed that K promoted catalyst significantly reduced coking. 1 wt% K added to 10 wt% Mo/HZSM-5 exhibited optimum performance, where the conversion of CH4 was ~ 28%, selectivity of C6H6 was ~ 50% while the selectivity of carbon was ~ 47% after 255 min of reaction. Graphical Abstract
Keywords Methane dehydroaromatization · Promoters · K-Mo/HZSM-5 · H2 pretreatment · β−Mo2C
* Hema Ramsurn hema‑[email protected] 1
Russell School of Chemical Engineering, The University of Tulsa, 800 South Tucker Drive, Tulsa, OK 74104, USA
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1 Introduction The low cost of natural gas has created an interest in its conversion to high value chemicals and fuels. The major component of natural gas is methane which generally consists of about 70–90% by volume of the total. This methane can be converted into valuable chemicals by both direct and indirect routes. The indirect conversion of methane by Fisher-Tropsch to methanol followed by methanolto-gasoline is currently a more commercially viable process than the direct conversion of methane to aromatics and has been practiced on large scales for decades [1, 2]. Direct methane conversion technologies include oxidative coupling of methane, partial oxidation of methane and methane dehydroaromatization (MDA). These processes have barriers to commercialization including limited conversions, poor selectivity to desired products and catalyst deactivation. Direct conversion of methane to aromatics under non-oxidative conditions was first studied by Wang et al. [3] in 1993. MDA effectively occurs over a transition-metal incorporated in a bifunctional zeolite catalyst. Past studies investigated various metals which include Mo
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