Madan Mohan Bhasin

Synthesis of ethylene via oxidative coupling of methane. I. Determination of active catalysts

Ethylene and ethane (C2s) have been synthesized by catalytic oxidative coupling of methane at atmospheric pressure and temperatures of 500–1000°C. A great number of metal oxides, supported on an α-alumina support, have been screened for activity and selectivity in the normal, concurrent feeding mode of reactants, as well as, in the sequential or feed programming mode. The concurrent feeding experiments gave low selectivities of 0–20%, while feed programming experiments gave selectivities of ~50%. In the latter case, however, a stainless-steel reactor became catalytically active for burning of methane to carbon oxides. Although a stainless-steel reactor was used in most of the work reported here, a quartz reactor was found to be inert. The most active catalysts for C2 formation were the oxides of Sn, Pb, Sb, Bi, Tl, Cd and Mn, while Li, Mg, Zn, Ti, Zr, Mo, Fe, Cr, W, Cu, Ag, Pt, Ce, V, B and Al showed little or no activity. The low C2-forming activity of Pt and Ce, however, may be due to the secondary burning of C2s on the stainless-steel reactor walls. This also makes it difficult to quantify the C2-forming selectivity of the active metal oxides. The active metals seem to exhibit a common characteristic: they can cycle between at least two oxidation states. Although there are differences in selectivities in C2 formation and carbon oxides formation, no correlation seems to exist with the free-energy changes in the oxidation states. A possible mechanism for C2 formation from methane is proposed.

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.

Auger electron spectroscopic study of the surface poisoning of copper catalysts

Abstract Two samples of commercial copper catalysts were examined by Auger electron spectroscopy in search of an explanation for the difference in their performance as characterized by their ability to catalyze the reaction of methyl chloride with silicon metal. The poorly performing copper catalyst (Lot “B”) was found to have at least three times the surface lead concentration that the good copper catalyst (Lot “A”) did. The actual lead analysis (using the 92 eV NOO transition) on the surface of Lot B was 4.9 surface atomic percent as against 1.7% for Lot A. This low-energy transition has been shown to be more sensitive to surface analysis than the high-energy, 2275 eV, MNN transition. In relation to copper only, the lead level is about 13% in Lot B. These analyses represent analysis of the top few (1–2) layers of atoms. Such a high level of lead in Lot B catalyst is sufficient to substantially reduce or completely kill the catalytic activity. Examination of these catalysts by conventional physical and chemical analysis, scanning electron microscope and chemical analysis by EDAX, had failed to reveal any significant differences. Apparently, lead is migrating to the catalyst surface during a catalyst manufacturing step or steps and thus concentrating on the catalyst surface.

Auger spectroscopic study of the poisoning of a commercial palladium-alumina hydrogenation catalyst

Abstract A commercial palladium-alumina catalyst used for the selective hydrogenation of diolefins in an olefin-aromatic-paraffin stream had lost most of its hydrogenation activity. It was examined by Auger electron spectroscopy after other typical physical measurements on the spent catalyst had failed to clearly establish the cause or causes of catalyst deactivation. Surface areas and levels of S and Cl in the fresh and the spent catalysts were not significantly different. However, iron to the extent of 1.7% by weight was found on the spent catalyst. This level of iron on a ~200 m 2 /g surface area support is not necessarily a poison. However, Auger surface analysis has now revealed that iron was coating a majority of the palladium catalyst surface thereby masking (and poisoning) the active Pd surface atoms as well as the atoms of the promoters like Cr and Mo. The iron deposited on the catalyst came from a bad batch of feedstock. The surface analysis by Auger electron spectroscopy also revealed substantial amounts of surface Ca and large gradients of Pd, Cr, and Mo, from the outside to the inside of the pellets. The spent catalyst also had much higher amounts of iron on the outside than the interior surface of the catalyst pellets.