Al13–[X–Mo/WOn] (X = Al, Co, V, P) composites as catalysts in clean oxidation of aromatic sulfides

Abstract

Several phases of general formula Al13–[XMo6] (X=Al(III), Co(III), Cr(III), V(V) and Al13–P/[WO4]n) were prepared by combining the [AlO4Al12(OH)24(H2O)12]7+ (Al13) Keggin-type isopolycation with different iso or heteropolymetalates such as [(Al/Co/V)Mo6O24(H6)]x−, [Co2Mo10O38H4]6−, [H2W12O40]6− and [PW9O34]9−. The characterization was carried out by means of XRD, 27Al NMR, FTIR and Raman Microprobe techniques. The catalytic activity of bulk composites, structurally constituted by an ordered distribution of the condensed metallic species in an Al(III) oxidic matrix, were proved in two aromatic sulfide oxidation reactions: diphenylsulfide (DPS) to diphenylsulfone in presence of H2O2 and dibenzothiophene (DBT) to dibenzothiophenone by means of tert-butyl hydroperoxide (t-BuOOH). Both reactions were carried out in batch at 80 and 75°C respectively. Results indicated that oxidation activity improved as the electronic density of the sulfur substrate increased, being higher for DPS (over 90%) than for DBT. Composites based on Anderson heteropolymolybdates presented a better performance in both reactions. 27Al MAS NMR spectroscopic properties can be associated to the catalytic behavior. On the other hand, catalysts based on polytungstates did not show activity except for that containing P as heteroatom. Besides, by 27Al NMR and Raman Microprobe, it was verified that these phases kept their structure after reaction showing an interesting possibility of being re-used.