Journal
ACS CATALYSIS
Volume 6, Issue 2, Pages 939-948Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.5b02672
Keywords
hydroxyapatite; ethanol coupling; acetaldehyde; butanol; Guerbet reaction
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Funding
- Office of Science, Office of Basic Energy Sciences of the U.S. Department of Energy [DE-AC02-05CH11231]
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The mechanism and kinetics for ethanol coupling to n-butanol over hydroxyapatite (HAP) were investigated at 573-613 K. In situ titration experiments show that the active sites for acetaldehyde and butanol formation are different. In combination with FTIR studies, it was found that ethanol dehydrogenation is catalyzed by Ca-O sites, whereas condensation of acetaldehyde is catalyzed by CaO/PO43- pairs. Measurements of the reaction kinetics at various ethanol (3.5-9.4 kPa) and acetaldehyde (0.055-0.12 kPa) partial pressures reveal that direct condensation involving two ethanol molecules does not play a significant role in butanol formation; instead, n-butanol is formed via a Guerbet pathway. At a constant acetaldehyde pressure, enolate formation is rate-limiting, and ethanol inhibits acetaldehyde condensation rates by competitive adsorption. A model of the reaction kinetics consistent with all experimental observations is developed.
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