Low temperature precursors for metal oxide catalysts

Abstract

Scope and Method of Study: The purpose of the investigation conducted in this project was to establish a simple, cost-effective, environmentally benign method, utilizing the distinctive thermal instability of the metal complexes of pyruvic acid oxime (PAO) ligand, for the synthesis of high surface area, porous, nanocrystalline metal oxide ceramics and testing them as heterogeneous catalyst systems and adsorbents for the remediation of arsenate in aqueous medium. The metal complexes of PAO were readily prepared in aqueous medium via ligand exchange strategy. Structural characterization of these complexes was to verify their formation on the basis of their infrared (IR) and solid-state 13c nuclear magnetic resonance (NMR) spectra, X-ray powder diffraction (XRD), single crystal X-ray diffraction, and thermal gravimetric and differential thermal analyses (TGA and DTA). IR and XRD analyses were used to confirm the formation of metal oxides as the final products of the pyrolysis of the metal complexes of PAO. The crystallite size, the surface properties (acidity, basicity and BET surface area), and the morphology of the metal oxides were to be determined by XRD, the adsorption of base and acid probe molecules, and by scanning and transmission electron microscopes (SEM and TEM), respectively. Some of the metal oxides were to have their catalytic activity examined with either Friedel-Crafts alkylation or Claisen-Schmidt condensation in Teflon bomb reactors at 150 oC. The analyses of the products were to be executed by gas chromatography/mass spectrometry technique. The adsorption ability of some of the metal oxides for arsenate in aqueous solution was to be performed in the natural pH range of water (6.8-7.1) at room temperature. The equilibrium concentration of arsenic was to be determined using a water analysis test kit (EM Science, Gibbstown, NJ, USA).

Findings and Conclusions: Zinc oxide was very good catalyst for the coupling reaction between benzaldehyde and acetophenone. It was the first time that zinc oxide was used for this kind of reactions. Nickel zinc ferrite was an excellent catalyst for the selective N-methylation of aniline using either methanol or dimethyl carbonate as a methylating agent. Tricobalt tetraoxide was the first oxide used for the allylation of benzene. Allybenzene was obtained in very high yield along with a small amount of diallyl ether. Iron, cobalt, and zinc oxides were excellent adsorbent for arsenate in aqueous medium. The cobalt oxide was also used for the first time in such an application. The adsorption capacity of the oxide was found to depend on its surface properties. It appeared that surface acidity played a key role in determining the capacity of the oxide.