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Surface hydrophobicity and acidity effect on alumina catalyst in catalytic methanol dehydration reaction.

ABSTRACT: BACKGROUND:Methanol to dimethyl ether (MTD) is considered one of the main routes for the production of clean bio-fuel. The effect of copper loading on the catalytic performance of different phases of alumina that formed by calcination at two different temperatures was examined for the dehydration of methanol to dimethyl ether (DME). RESULTS:A range of Cu loadings of (1, 2, 4, 6, 10 and 15% Cu wt/wt) on Al2O3 calcined at 350 and 550?°C were prepared and characterized by TGA, XRD, BET, NH3-TPD, TEM, H2-TPR, SEM, EDX, XPS and DRIFT-Pyridine techniques. The prepared catalysts were used in a fixed bed reactor under reaction conditions in which the temperature ranged from 180-300?°C with weight hourly space velocity (WHSV)?=?12.1?h-1. It was observed that all catalysts calcined at 550?°C (?-Al2O3 support phase) exhibited higher activity than those calcined at 350?°C (?-AlOOH), and this is due to the phase support change. Furthermore, the optimum Cu loading was found to be 6% Cu/?-Al2O3 with this catalyst also showing a high degree of stability under steady state conditions and this is attributed to the enhancement in surface acidity and hydrophobicity. CONCLUSION:The addition of copper to the support improved the catalyst properties and activity. For all the copper modified catalysts, the optimum catalyst with high degree of activity and stability was 6% copper loaded on gamma alumina. © 2017 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

SUBMITTER: Osman AI

PROVIDER: S-EPMC5698741 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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Surface hydrophobicity and acidity effect on alumina catalyst in catalytic methanol dehydration reaction.

Osman Ahmed I AI Abu-Dahrieh Jehad K JK Rooney David W DW Thompson Jillian J Halawy Samih A SA Mohamed Mohamed A MA

Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986) 20170908 12

<h4>Background</h4>Methanol to dimethyl ether (MTD) is considered one of the main routes for the production of clean bio-fuel. The effect of copper loading on the catalytic performance of different phases of alumina that formed by calcination at two different temperatures was examined for the dehydration of methanol to dimethyl ether (DME).<h4>Results</h4>A range of Cu loadings of (1, 2, 4, 6, 10 and 15% Cu wt/wt) on Al<sub>2</sub>O<sub>3</sub> calcined at 350 and 550 °C were prepared and charac ...[more]

PMID: 29200585

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Project description:A better fundamental understanding of the plasma-catalyst interaction and the reaction mechanism is vital for optimizing the design of catalysts for ammonia synthesis by plasma-catalysis. In this work, we report on a hybrid plasma-enhanced catalytic process for the synthesis of ammonia directly from N2 and H2 over transition metal catalysts (M/Al2O3, M = Fe, Ni, Cu) at near room temperature (?35 °C) and atmospheric pressure. Reactions were conducted in a specially designed coaxial dielectric barrier discharge (DBD) plasma reactor using water as a ground electrode, which could cool and maintain the reaction at near-room temperature. The transparency of the water electrode enabled operando optical diagnostics (intensified charge-coupled device (ICCD) imaging and optical emission spectroscopy) of the full plasma discharge area to be conducted without altering the operation of the reactor, as is often needed when using coaxial reactors with opaque ground electrodes. Compared to plasma synthesis of NH3 without a catalyst, plasma-catalysis significantly enhanced the NH3 synthesis rate and energy efficiency. The effect of different transition metal catalysts on the physical properties of the discharge is negligible, which suggests that the catalytic effects provided by the chemistry of the catalyst surface are dominant over the physical effects of the catalysts in the plasma-catalytic synthesis of ammonia. The highest NH3 synthesis rate of 471 ?mol g-1 h-1 was achieved using Ni/Al2O3 as a catalyst with plasma, which is 100% higher than that obtained using plasma only. The presence of a transition metal (e.g., Ni) on the surface of Al2O3 provided a more uniform plasma discharge than Al2O3 or plasma only, and enhanced the mean electron energy. The mechanism of plasma-catalytic ammonia synthesis has been investigated through operando plasma diagnostics combined with comprehensive characterization of the catalysts using N2 physisorption measurements, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), NH3-temperature-programmed desorption (TPD), and N2-TPD. Four forms of adsorbed NH x (x = 0, 1, 2, and 3) species were detected on the surfaces of the spent catalysts using XPS. It was found that metal sites and weak acid sites could enhance the production of NH3 via formation of NH2 intermediates on the surface.

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Surface hydrophobicity and acidity effect on alumina catalyst in catalytic methanol dehydration reaction.

Publications

Surface hydrophobicity and acidity effect on alumina catalyst in catalytic methanol dehydration reaction.

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