Patrick Graffin

Photocatalytic degradative oxidation of Diuron in organic and semi-aqueous systems over titanium dioxide catalyst

The photocatalytic degradation of Diuron in organic and semi-aqueous media is compared. The rates of disappearence fit Langmuir–Hinshelwood kinetics and the parameters k and K have been determined. A main intermediate was detected in all cases and its structure has been determined. This product is obtained by oxidation of a methyl group of the urea moiety. Several compounds [trichloroaniline, dichloronitrobenzene, N-(3,4-dichlorophenyl)formamide, dimethylurea . . .] were detected by GC-MS analysis in both media while hydroxylated compounds were only observed in the semi-aqueous medium.

Selective photocatalytic oxidation of hydrocarbon compounds over zeolites

Abstract The photocatalytic oxidation of various hydrocarbon compounds (alkyl and alkenylbenzenes) over irradiated semiconductor with wavelengths λ>300 nm has been studied at room temperature first using TiO 2 and then using TiO 2 and zeolites. Alkylbenzenes led essentially to the corresponding α-ketones while for alkenylbenzenes there is a cleavage of the double bond with formation of the corresponding carbonyl compounds and oxygen addition leading to epoxide. Addition of acidic zeolite led to an increased or a decreased oxidation rate depending on the substrates but an increased selectivity was observed in all cases. The various results and the opposite effects observed with zeolite-added TiO 2 are consistent with two different intermediates involved in the photoxidation mechanisms of alkylbenzenes and of alkenylbenzenes.

Zeolite effect on the oxidation of hydrocarbons with irradiated TiO2 semiconductor

The effect of an acidic zeolite on the photocatalytic oxidation of isopropylbenzene and α-methylstyrene over irradiated TiO2 leads to either an increase or a decrease in oxidation rate depending on the substrate but, in both cases, an increase in selectivity is observed.

23-P-13 - heterogeneous base catalysis: characterization of zeolites and mixed oxides using nitromethane as a NMR probe molecule and activity in the Michaël condensation of nitromethane and cyclohex-2-en-1-one

Publisher Summary This chapter discusses the use of nitromethane as a probe of basicity of zeolites (NaX, CsX, and CsX 9Cs) and mixed oxides [Mg(Al)O]. Various species (physisorbed nitromethane, aci-anion nitromethane, and methazonate salt analog) formed upon nitromethane adsorption are characterized by 13C magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Heterogeneous base catalysis of the Michael addition of nitromethane on cyclohex-2-en-l-one is also studied. Low rates are obtained for catalysts showing only nitromethane physisorption. Formation of aci-anion nitromethane is observed for the solids of medium efficiency; correlation of the chemical shift with the initial rate is established. The decrease of Lewis acidity and concomitant increase of basicity leads to methazonate formation and to the more efficient catalysts.

Probing the basicity of oxide surfaces by FTIR spectroscopy of isocyanic acid generated in situ by thermal decomposition of nitromethane

Infrared spectroscopy of isocyanic acid generated insitu by the thermal decomposition of nitromethane provides an efficient and easy method to probe the basic strength of the surface of oxides. The frequencies of the adsorbed isocyanate species are directly correlated with the heats of adsorption of carbon dioxide determined by microcalorimetry.