Thomas P. Wilson

The oxidative dehydrogenation of ethane over catalysts containing mixed oxides of molybdenum and vanadium

Mixed oxide catalysts, containing molybdenum and vanadium (MoV) together with another transition metal oxide (Ti, Cr, Mn, Fe, Co, Ni, Nb, Ta, or Ce), are active as low as 200 °C for the oxydehydrogenation of ethane to ethylene. A material composed of oxides of composition Mo0.61V0.31Nb0.08 appears to be optimum for the reaction. The better MoV catalysts are characterized by a broad X-ray diffraction band near 4.0 A. The presence of niobium stabilizes the catalyst structure against oxidation and reduction and permits a very strongly oxidized or reduced catalyst to be returned more readily to its original state. The oxydehydrogenation of ethane may involve formation of a surface ethoxide intermediate, since ethanol gives a mixture of both ethane and ethylene with the catalyst in the absence of oxygen. At superatmospheric pressures, acetic acid appears as a product of the subsequent oxidation of ethylene. The kinetics of the process are described. The reaction rates to acetic acid and carbon oxides were found to be dependent on the ethylene concentration but independent of ethane. The catalysts are the basis of a very efficient process for the production of ethylene and acetic acid from ethane. Higher hydrocarbons are nearly completely burned.

Synthesis gas conversion over supported rhodium and rhodium-iron catalysts

Abstract When used as a catalyst for conversion of synthesis gas at pressures above 25 atm, supported rhodium produces two-carbon oxygen-containing compounds, specifically acetic acid, acetaldehyde, and ethanol, with chemical efficiencies on the order of 50%. The other major product is methane. These results are strikingly different from those obtained with other Group VIII metals and from those previously reported for rhodium. Reasons for the differences from earlier work are discussed. Addition of iron to the rhodium catalysts sharply reduces the yields of acetic acid and acetaldehyde. Ethanol becomes the principal two-carbon product and methanol appears as a major product. Hydrocarbon production remains low, at least up to an iron to rhodium mole ratio of unity.

A soluble chromium-based catalyst for ethylene trimerization and polymerization

Abstract The catalyst formed by the interaction of chromium (III) 2-ethylhexanoate or related compounds with partially hydrolyzed triisobutyl aluminum, in paraffinic solvents, polymerizes ethylene to linear polyethylene at ethylene turnover numbers of the order of 30 sec−1 atm−1. The polyethylene appears to be formed by what has come to be considered a conventional Ziegler olefin polymerization mechanism [Novaro et al., J. Catal. 41, 91 (1976)]. Hexene-1 can also be produced, at rates comparable to those of polyethylene formation. The mechanism of hexene-1 formation differs from that of polyethylene formation, as shown by differences in the pressure and temperature dependence of the two rates and by the inhibition of hexene-1 formation, but not polyethylene formation, by small quantities of dienes. Some mechanistic implications of the hexene-1 formation kinetics are discussed. Information relating to the structure of poly(isobutyl aluminum oxide) is also presented. Some structures for the catalytically active centers are proposed, and reactions by which such structures could be produced are suggested.

The state of manganese promoter in rhodium-silica gel catalysts

The ESR spectra of MnSiO2 and Rh-MnSiO2 compositions were investigated to learn more about the mode of action of the Mn used as a promoter for acetic acid and acetaldehyde formation from synthesis gas over RhSiO2 catalysts. The MnSiO2 catalyst showed a moderately strong, unresolved Mn2+ signal while Rh-MnSiO2 catalysts showed little signal of any kind when they were reduced in H2 at 500 °C and evacuated. Adding H2O vapor at room temperature resulted in the appearance of a moderately intense, resolved sextet Mn2+ signal from both catalysts. Subsequent treatment of the Rh-MnSiO2 with a CO + H2O mixture led to a threefold increase in intensity of the resolved Mn2+. The same gas mixture had no effect on the signal from the MnSiO2 catalyst. It is suggested that these observations are consequences of the Mn being concentrated on the surface of the Rh crystallites in the Rh-MnSiO2 catalysts, probably as a mixed surface oxide with the Rh which stabilizes Rh+ on the metal surface. The change in Rh surface chemistry resulting from this strong interaction with Mn2+ could be responsible for the effectiveness of Mn as a promoter in these catalysts.