Journal
ACS CATALYSIS
Volume 3, Issue 11, Pages 2644-2653Publisher
AMER CHEMICAL SOC
DOI: 10.1021/cs400569v
Keywords
IR spectroscopy; Pd-Au catalyst; CO heat of adsorption; cyclohexene hydrogenation; Temkin adsorption; CO oxidation; selective hydrogenation
Categories
Funding
- U.S. National Science Foundation [CHE-1012395, CHE-0449549]
- Welch Foundation [W-0031]
- Camille and Henry Dreyfus Foundation
- French Agence Nationale de la Recherche (ANR) [ANR-11-JS07-0007]
- European COST program [COST-MP0903]
- Directorate For Engineering
- Div Of Chem, Bioeng, Env, & Transp Sys [1160217] Funding Source: National Science Foundation
- Agence Nationale de la Recherche (ANR) [ANR-11-JS07-0007] Funding Source: Agence Nationale de la Recherche (ANR)
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Incorporating small amounts of Pd into supported Au catalysts has been shown to have beneficial effects on selective hydrogenation reactions, particularly 1,3-butadiene hydrogenation and the hydrogenation of nitroaromatics, especially p-chloronitrobenzene. Appropriate Pd incorporation enhances hydrogenation activity while maintaining the desirable high selectivity of supported Au catalysts. To better understand this phenomenon, a series of alumina-and titania-supported Au and dilute Pd-Au catalysts were prepared via urea deposition-precipitation. The catalysts were studied with infrared spectroscopy of CO adsorption, CO oxidation catalysis, and cyclohexene hydrogenation catalysis with the goal of understanding how Pd affects the catalytic properties of Au. CO adsorption experiments indicated a substantial amount of surface Pd when the catalyst was under CO. Adsorption experiments at various CO pressures were used to determine CO coverage; application of the Temkin adsorbate interaction model allowed for the determination of adsorption enthalpy metrics for CO adsorption on Au. These experiments showed that Pd induces an electronic effect on Au, affecting both the nascent adsorption enthalpy (Delta H-0) and the change in enthalpy with increasing coverage. This electronic modification had little effect on CO oxidation catalysis. Michaelis-Menten kinetics parameters showed essentially the same oxygen reactivity on all the catalysts; the primary differences were in the number of active sites. The bimetallic catalysts were poor cyclohexene hydrogenation catalysts, indicating that there is relatively little exposed Pd when the catalyst is under hydrogen. The results, which are discussed in the context of the literature, indicate that a combination of surface composition and Pd-induced electronic effects on Au appear to increase hydrogen chemisorption and hydrogenation activity while largely maintaining the selectivities associated with catalysis by Au.
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