Acetic acid hydrogenation over supported platinum catalysts

Article abstract of DOI:10.1006/jcat.2000.2863

The kinetic behavior of acetic acid hydrogenation over platinum supported on TiO₂, SiO₂, η-Al₂O₃, and Fe₂O₃ was studied in a differential, fixed-bed reactor at 423-573 K, 100-700 torr hydrogen, and 7-50 torr acetic acid. The interaction of acetic acid with the oxide support played a major role in determining the kinetics of the reaction, and platinum served as a source of mobile, activated hydrogen atoms. During hydrogenation at low conversions, carbon-containing products consisted of about 50% CO and 50% CH₄ over Pt/SiO₂; 50% ethanol, 30% ethyl acetate, and 20% ethane over Pt/TiO₂ reduced at 473 or 773 K; 40% CH₄, 10% ethane, 8% ethanol, 4% ethyl acetate, 33% CO, and 5% CO₂ over Pt/η-Al₂O₃; and 80% acetaldehyde and 20% ethanol over Pt/Fe₂O₃. Pt/TiO₂ catalysts were the most active, with activities and turnover frequencies being ≤ 2 orders of magnitude larger than those for the other catalysts. The apparent reaction order with respect to H₂ varied between 0.4 and 0.6, while that with respect to acetic acid was 0.2-0.4. This study provided evidence that acetic acid hydrogenation over supported Pt catalysts can be described by a Langmuir-Hinshelwood-type mechanism invoking two sites, one on the metal to activate H₂ and one on the oxide to molecularly adsorb acetic acid. The kinetic rate expression derived from this reaction model fitted the data well with thermodynamically consistent parameters.