A DRIFTS Study of Catalyzed Dehydration of Alcohols by Alumina-supported Heteropoly Acid
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A DRIFTS Study of Catalyzed Dehydration of Alcohols by Alumina-supported Heteropoly Acid Leming Cheng Æ X. Philip Ye
Received: 8 December 2008 / Accepted: 31 January 2009 / Published online: 4 March 2009 Ó Springer Science+Business Media, LLC 2009
Abstract Selectively catalyzed dehydration of ethanol, 1,2-propylene glycol, and glycerol on supported heteropoly acid (HPA) was studied using transient diffuse reflectance infrared fourier transform spectroscopy (DRIFTS). Tungstosilicic acid (H4[SiW12O40] denoted as H4SiW), supported on neutral mesoporous alumina as a catalyst, was studied to investigate the formation of intermediate products and desired dehydration products on the catalyst surface. Both ethylene-containing species and surfacebound carboxyl species were detected for all three alcohols. The formation of ethylene was promoted at lower temperatures while an increased reaction temperature facilitated the formation of acetate products when ethanol was used. When 1,2-propylene glycol was used, surfacebound carboxyl species were found as major intermediate products; these might have formed from propanal produced from the hydration reaction catalyzed by acid sites on HPA. Intermediate species from more complicated reactions were detected on the catalyst surface when glycerol was used, including aldehyde, surface-bound carboxyl species, and alkene species. The results indicated that acid dehydration might be facilitated either by the addition of water or lowering the reaction temperature. The work provides insight into reaction pathways for bio-polyols, and therefore is informative for designing cost-effective and efficient chemical catalysis systems for the conversion of bio-renewables.
L. Cheng X. P. Ye (&) Department of Biosystems Engineering and Soil Science, The University of Tennessee, 2506 E. J. Chapman Dr., Knoxville, TN 37996-4531, USA e-mail: [email protected]
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Keywords Alcohols Glycerol Dehydration Ethylene Acrolein Heteropoly acids Catalysis DRIFTS
1 Introduction The main challenges for the current fossil-fuel-dependent energy structure are carbon dioxide emissions and resource shortages. There are several promising alternatives to fossil resources; bio-polyols—including bio-ethanol from biomass fermentation, glycerol from bio-diesel production, and other compounds from renewable resources containing multiple hydroxyl groups such as carbohydrates from biomass hydrolysis—are among those alternatives. These biorenewables have the potential to provide for the production of both clean fuel and value-added chemicals, with the added advantage of nearly neutral CO2 emissions [1, 2]. One of the unique characteristics of these bio-renewables is the existence of multiple hydroxyl groups in their molecular structures, as distinct from the structures of chemical compounds in petroleum or coal. These multiple hydroxyl groups present a unique conversion pathway to the production of fuel and value-added chemicals; however, the catalytic chemistry behind the pathway is not yet fully understood. Furt
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