The acid-base properties of metal oxides play a key role in catalysis . The adsorption and reaction of alcohols on metal surfaces plays an important role in determining the surface chemistry of a number of important catalytic processes because of its application to produce a various intermediates and compounds . In the past few years, various reduction reactions in gas phase have been studied to synthesize valuable intermediate products on fine chemicals . Benzaldehyde reduction is one of theses reactions who can provide information about nature and properties of surface centers .
The present work deals with acid-base properties of alkali-earth metal oxide catalysts (MgO, CaO, BaO, SrO). Isopropanol decomposition and benzaldehyde reduction were used as probe reactions for characterizing the surface properties. They were characterized by their BET specific area, XRD and FTIR spectra. The catalytic performances were carried out in a quartz fixed bed reactor with 0,2g samples (P= 1 atm, Treaction = 100 – 350°C) after H2 or N2 pre-treatment at 350°C.
The results obtained by isopropanol decomposition show propene and acetone were produced competitively with yields depending on nature of the oxide and reaction temperature. The obtained order of acetone productivity was attributed to basic surface and propene productivity to acid surface character of alkali earth metal oxides. The different studies have provided evidence of the dissociative adsorption of isopropanol and the formation of isopropoxide species which decompose at high temperature to acetone and/or propene.
The results obtained by benzaldehyde reduction show that benzyl alcohol is produced by the Cannizzaro reaction under nitrogen flow on MgO oxide and by direct hydrogenation under dihydrogen on irreducible oxides such as CaO, BaO, and SrO. The Cannizzaro reaction involves the basic hydroxyl groups and is followed by the reduction of benzoate species by H2 to benzaldehyde. Toluene and benzene were produced at high temperature reaction under nitrogen and dihydrogen flow over alkali earth oxides from a reaction involving benzyl alcoholate species, under H2 by means of consecutive reduction reactions and under N2 by alkoxy species.
Key words: reduction, alkali earth metal oxide, benzaldehyde, isopropanol.
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