Transformation of Styrene Oxide on Bi-Functional Ni, Co and Cu Catalysts Supported on Zirconia-Alumina: Effect of Depositing Zirconia on Alumina

Abstract

2-phenyl ethanol (2-PEA) and 2-phenylacetaldehyde (PAA) are important perfumery chemicals which are prepared by hydrogenation and isomerization of styrene oxide (SO) respectively. Activities of Ni, Co and Cu supported on a set of zirconia-alumina supports with varying ZrO₂:Al₂O₃ molar ratio are compared for these reactions. Zirconia was deposited on γ-alumina by deposition-precipitation. All catalysts were characterized by XRD, NH₃-TPD, H₂-TPR, N₂ physisorption, XPS and Raman spectroscopy. Increasing the zirconia content significantly influenced catalyst characteristics. These are correlated with reactivity: i) surface concentration of Ni, Co and Cu (XPS) decreased, which affected conversion of styrene oxide and selectivity to 2-PEA ii) 1 1 1 plane of Cu (XRD) was suppressed which enhanced selectivity of styrene by-product relative to 2-PEA iii) acidity (NH₃-TPD) decreased, which adversely affected yield of PAA. Product space time yields (STY) of 2-PEA and PAA correlated well with surface concentration of active metals (XPS) and acidity (NH₃-TPD) respectively. Various by-products were identified. Styrene appeared to form by deoxygenation of SO. TPR and Raman spectroscopy indicated strong interaction of Co and Ni with alumina while Cu showed strong interaction with zirconia. This reflected in their XRD crystallite size. Cu has different electronic properties than Co and Ni, which reflected in differences in their behavior. This study directly compares the performance of these transition metals in continuous flow studies and correlates catalyst characteristics with reactivity.