Metal-Support Effects on Intramolecular Selectivity During Acetophenone Hydrogenation over Pt Catalysts

Abstract

The choice of support to disperse a metal can have a significant effect in certain reactions, and one of the best examples of metal-support interactions (MSI) is the hydrogenation of C[double bond]O bonds over noble metals such as Pt. It was first shown that the turnover frequency (TOF) for CH[sub 4] formation on Pt from CO and H[sub 2] could be increased by two orders of magnitude using TiO[sub 2] as a support. This reaction is structure insensitive and the TOF is independent of crystallite size. The explanation the authors have preferred for this behavior is the creation of special sites at the metal-support interface which interact with the oxygen end of the molecule to enhance the reactivity of the C[double bond]O bond towards hydrogen. As further support of this concept, the hydrogenation of acetone to isopropanol also showed marked enhancements in TOF (ca. 500-fold) over Pt/TiO[sub 2] catalysts, and the intramolecular selectivity during crotonaldehyde hydrogenation was altered by favoring hydrogenation of the carbonyl bond compared to the C[double bond]C double bond to increase the crotyl alcohol/butyraldehyde product ratio. The next step in examining the influence of MSI on intramolecular selectivity was a comparison of the rates of hydrogenation ofmore » a carbonyl bond vs an aromatic ring, and acetophenone (C[sub 6]H[sub 5]COCH[sub 3]) represents one of the simplest molecules containing these two types of bond systems which also has a high enough vapor pressure to allow a vapor-phase reaction to be utilized. These results are reported here. 34 refs., 1 fig., 2 tabs.« less