Catalytic and physicochemical characterizations of novel oxide-supported copper catalysts. Part 1.—Hydrosol-prepared Cu/TiO2and 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 2p3/2 and X-ray excited Auger electron spectroscopy (XAES) Cu L3M4,5M4,5 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 < Trx < 453 K over samples prereduced at 473 K, only acetone hydrogenation to isopropyl alcohol was detected, with single-pass conversion increasing with Trx 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 < Trx < 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.