Catalytic and physicochemical characterizations of novel oxide-supported copper catalysts. Part 1.—Hydrosol-prepared Cu/TiO2 and effects of prereduction on hydrogenation and oligomerization of acetone

Abstract

Catalytic conversions of acetone, allied to transmission electron microscopy (TEM), electron spectroscopy for chemical applications (ESCA) and temperature-programmed desorption (TPD) techniques have been used to characterize titanium-dioxide-supported copper preformed by the reduction of aqueous copper malonate with hydrazine. Scanning electron microscopy (SEM) and TEM showed aggregates of 30 ± 10 nm TiO₂ particles edged by smaller copper particles (ca. 10 nm). The coexistence of copper and TiO₂ in such aggregates was confirmed by energy dispersive X-ray analysis (EDXA). Comparisons of the X-ray photoelectron spectroscopy (XPS) Cu 2p_3/2 and X-ray excited Auger electron spectroscopy (XAES) Cu L₃M_4,5M_4,5 features of the ‘as-stored’ materials with those after in situ reduction at 453, 503 and 548 K, confirmed that Cu²⁺ was converted to Cu + after reduction at 503 K. Significant amounts of Cu⁺ were also present after reduction at 503 K, but little or no Cu⁰. At 423 K < T_rx < 453 K over samples prereduced at 473 K, only acetone hydrogenation to isopropyl alcohol was detected, with single-pass conversion increasing with T_rx until approximating to the equilibrium-limited conversion at 453 K. A strong metal/support interaction (SMSI) type inhibition of this selective hydrogenation capability was observed after high-temperature reduction at 773 K (HTR₇₇₃). At 483K < T_rx < 513K further catalytic activity of the lowtemperature reduction (LTR) materials emerged, namely that for aldol-condensation-type conversions of the acetone and H₂ reactants to yield mainly C(6) and C(9) saturated ketones. This was not inhibited by prior HTR.