Property and Activity of Molybdates Dispersed on Silica Obtained from Various Synthetic Procedures

Antonella Gervasini, Laura Wahba, Manuel Dario Finol, Jean-François Lamonier

Dipartimento di Chimica Fisica ed Elettrochimica (DCFE), Centro Interdipartimentale Materiali e Interfacce Nanostrutturati (CIMaINa), Università degli Studi di Milano, Milano, Italy.
Unité de Catalyse et Chimie du Solide UCCS UMR CNRS 8181, Université de Lille 1 Sciences and Technologies, Villeneuve d’Ascq, Lille, France..

DOI: 10.4236/msa.2012.34030                

Abstract

The synthesis and characterization of several dispersed molybdena catalysts on silica support (MoO₃-SiO₂) prepared from a variety of precursors (Mo(VI)-acetylacetonate, oxo-peroxo Mo-species, hydrated ammonium heptamolybdate) and preparation methods (deposition of the Mo-phase on finite SiO₂ support by aqueous and methanol impregnations, by adsorption, by oxo-peroxo route-like, and by one-step synthesis of MoO₃-SiO₂ system with molecular precursors) are presented. The molybdena concentration on silica was comprised in a large interval (1.5 - 14 wt%) depending on the preparation method which governed the Mo-loading on silica. Convenient comparisons among samples at similar Mo-concentration have been made discussing the morphologic-structural (XRD, XPS, UV-vis-DRS, and N₂-adsorption) and physicochemical (TG-DTG, TPR, and n-butylamine-TPD) sample properties. Polymeric octahedral polymolybdate aggregates predominated in the samples prepared by aqueous and methanol impregnations, which were at high Mo-concentration. On the contrary, isolated Mo(VI) species in distorted T_d symmetry predominated in the sample prepared by adsorption which was at very low Mo-concentration. The sample acidity was composed of a weak acidy site population, associated with the silica support, and a strong acid site population associated with the Mo-dispersed phase. Oxidation tests of formaldehyde, an oxygen-containing VOC (Volatile Organic Compound), were performed to determine the prevalent redox or acidic function of the Mo-species at the surface of the catalysts.

Keywords

MolybdenCharacterization; Catalytic Oxidation; Formaldehydea-Silica Mixed Oxides; Molybdenum Dispersed Phase; Catalyst Preparation; Catalyst

Conflicts of Interest

The authors declare no conflicts of interest.

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