Michel Blanchard

Metathesis of alkynes by a molybdenum hexacarbonyl–resorcinol catalyst

A mixture of molybdenum hexacarbonyl and a phenol reagent is an active and selective homogeneous catalyst for the metathesis of aromatic disubstituted alkynes.

Catalytic gas-phase fluorination of 1,1,1-trifluoro-2-chloroethane over chromium (III) oxide: Preparation of hydrofluoroalkanes

Abstract The transformation of CF3CH2Cl over bulk chromium(III) oxide, fluorinated or not, leads mainly to the fluorination product CF3CH2F and to the alkene CF2=CHCl. In the presence of HF, CF3CH2F is the main product. In absence of HF this product is also obtained with HF formed in the elimination reaction of CF3CH2Cl to CF2=CHCl. At the same time a part of HF is used for the fluorination of chromium oxide. The XPS analysis of fluorinated catalysts with HF gives surface fluorine atomic contents which correspond to a F/Cr ratio of 0.36. A survey of the effect of partial pressures of HF and of CF3CH2Cl shows a zero order for HF and a 0.6 order for CF3CH2Cl. The fluorination reaction could occur on a partially fluorinated chromium(III) oxide involving HF oligomer species previously postulated by Rowley et al. [L. Rowley, J. Thomson, G. Webb and J.M. Winfield, Appl. Catal. A, 79 (1991) 89–103].

Catalytic oxidation of o-xylene

Abstract Oxidation of o -xylene to phthalic anhydride over V 2 O 5 -TiO 2 catalyst has been studied in order to detect the intermediates of this conversion. The oxidation of alcohols such as o -methylbenzyl alcohol and o -xylene-α,α′-diol yields the same compounds as those obtained from the hydrocarbon in the same conditions, whereas oxidation of o -toluic acid yields mainly the lactone, phthalide. Moreover, a competitive oxidation of inactive o -methylbenzyl alcohol, and o -xylene (methyl- 14 C) results in the formation of o -tolualdehyde, phthalide, and phthalic anhydride, having different specific radioactivities, and demonstrates that different reaction paths are involved. A mechanism is proposed in which the selective incorporation of oxygen occurs after abstraction of one hydrogen atom so as to produce a surface alcoholate ion, whereas degradation into maleic anhydrides and carbon oxides arises from substitution of hydrogen atoms of the aromatic nucleus by oxygen.

Hydrocarbon selectivity in fischer-tropsch synthesis in relation to textural properties of supported cobalt catalysts

Abstract Cobalt catalysts for the synthesis of paraffins from carbon monoxide and hydrogen have been prepared by low temperature thermal treatment of dicobalt octacarbonyl impregnated porous supports (alumina, silica-alumina). An catalysts exhibited high selectivities for restrained hydrocarbon cuts, provided there was a low metal loading. The chain length of hydrocarbons was clearly related to the mean pore diameter of the supports and the hydrocarbon cut was restrained by the design of the supports. Adsorption-desorption kinetics have shown that pore condensation and filling can occur at a chain length related to the pore size and thus modify the residence times of hydrocarbons on the catalyst. It is proposed that this physical effect of the support is the limiting factor of the chain length because of the subsequent hydrogenolysis of the condensed hydrocarbons inside the pores when light paraffins are not retained and can easily desorb. With high amounts of metal and conventional catalysts, the metal is mainly at the external surface of the support and this effect can not be seen.

Heterogeneous catalytic reactions of chlorofluorocarbons

Abstract The reactions of 1,1,2-trichloro-1,2,2-trifluoroethane, CCl2FCClF2 (F113), were studied on three catalysts, Cr2O3 on active charcoal, AlF3 and Cr2O3 on AlF3, in the presence and absence of hydrogen fluoride. Without hydrogen fluoride two reactions occur, disproportionation (exchange of halogen) and isomerization. With hydrogen fluoride fluorination is the main reaction, the selectivity of which (symmetric or asymmetric compounds) is governed by the acidity of the catalyst.

Liquid-phase fluorination and dehydrochlorination of 1,1,1-trichloroethane

Abstract During the liquid-phase fluorination of 1,1,1-trichloroethane with SbCl 5 · HF, 1,1-dichloroethene is formed. This reacts to give linear and branched oligomers. The hydrolysis of these by-products affords 3,4-dichlorophenol, 6-methyl-4-chloro-2-pyran-2-one and 2- methyl-5,7-dichlorochromone whose source is the acid-catalyzed reaction of water with the trimer and pentamer of 1,1-dichloroethene.

CATALYTIC OXIDATION OF FURAN ON A MOLYBDENUM-TITANIUM-OXYGEN CATALYST. INFRARED AND THERMODESORPTION STUDY

The adsorption and oxidation of furan, an intermediate in the conversion of 1-butene to maleic anhydride, were studied on a catalyst containing 15.6% molybdenum as trioxide on titanium dioxide that yielded 53% maleic anhydride at 63% conversion. The results showed at furan adsorbed in two distinct modes, of which one was observed only on oxidized surface and the other was always present but depended on the degree of reduction. The adsorbed furan was oxidized in the presence of oxygen at temperatures above 235/sup 0/C, but it desorbed only above 320/sup 0/C. The Mo=O species did not seem to be important in the oxidation of furan to maleic anhydride.

Preparation of substitutes for CFCs. Catalytic properties of chromia for halogen exchange involving hydrogen fluoride and trifluorochloroethane

The catalytic activity of chromia for F to Cl exchange in trifluorochloroethane is proportional to the number of chromium atoms which are reversibly oxidized.