Title Catalysts Research Articles

ChemInform Abstract: In Situ Mössbauer Spectroscopic Characterization of Fe/Al2O3 and Fe/ThO2 Fischer‐Tropsch Catalysts.

AbstractMössbauer spectroscopy has been used to study in situ the transformation of the title catalysts under different stages of calcination, reduction, carbu?zation, and Fischer‐Tropsch reactions.

ChemInform Abstract: Effect of Pretreatment on Pt/Al2O3 and Pt + Re/Al2O3 Catalyst Deactivation.

AbstractThe calcination and reduction temp. seem to play a relatively insignificant role in the deactivation characteristics of the title catalysts.

Why do homogeneous analogs of phillips (CrO3/SiO2) and union carbide (Chromocene/SiO2) polyethylene catalysts fail? Some answers from ir investigations

Both title catalysts show strong i.r. bands after adsorption of CO, which are assigned to bridging CO molecules. These CO i.r. bands are at 2120, 2100 and 2035 cm −1 at low temperatures (−145 °C) for the CO-reduced Phillips catalyst (Zecchina , 1975) or at 1920, 1825 and 1620 cm −1 (Union Carbide catalyst).Single-bonded CO is observed showing i.r. bands at 2190, 2186 and 2179 cm −1 —shifted to higher wavenumbers than CO gas (2143 cm −1 ), in contrast to bridging CO — or at 2046 and 1974 cm − (and 2008 cm −1 ), respectively. The single-bonded CO is replaced at low temperatures (Phillips catalyst) or after some days at room temperature (Union Carbide catalyst) by bridging CO molecules. These findings support not only the presence of dinuclear chromium surface complexes, but also further indicate that such surface complexes represent the majority ofthe chromium. The CO i.r. studies make it possible to propose detailed models of the dinuclear chromium surface complexes. The initiation reaction for the polymerization of ethylene could be the addition of one ethylene molecule to one dinuclear surface complex by forming a bridge. Homogeneous analogs for the title catalysts should therefore consist of coordinatively unsaturated dinuclear complexes, which was not the case in previous studies.

Deuteration of methyl linoleate with nickel, palladium, platinum and copper‐chromite catalysts

AbstractSamples taken during deuteration of methyl linoleate with the title catalysts were separated into saturate, monoene and diene fractions. Monoenes were further separated intocis andtrans fractions. A comparison of the double bond distribution in monoenes with those from hydrogenation of alkaliconjugated linoleate indicated that up to 59% of the linoleate was reduced through a conjugated intermediate with nickel catalyst. The respective percentages for palladium and platinum catalysts were 51 and 23. Copper catalysts have previously been shown to reduce linoleate solely through conjugated intermediates. Copper‐chromite catalyst showed infinite selectivity for the reduction of linoleate, because stearate did not form. The decreasing order of various catalysts for the selective reduction was copper‐chromite>>>Ni at 195 C>Pd>Ni at 100 C>Pt. Computer simulation of platinum reduction indicated that ca. 20% of the linoleate was directly reduced to stearate through a shunt. Geometrical isomers of linoleate were formed during reduction with all catalysts except copper‐chromite. Nickel catalyst formed bothtrans,trans‐ andcis,trans‐isomers, as well as nonconjugatable dienes. These isomers were favored at the higher temperature and deuterium was incorporated into them. Palladium and platinum did not isomerize linoleate to nonconjugatable dienes. Because conjugated dienes are more reactive than linoleate, they were not found in appreciable amounts during reduction. Conjugated dienes were the only isomers formed with copper‐chromite catalyst. Deuterium was found in these conjugated dienes, which were also extensively isomerized. As a result of isomerization and exchange during reduction of linoleate‐as well as further exchange between deuterium and monoenes‐a wide distribution of isotopic isomers in monoenes was found with nickel, palladium and platinum catalysts. Since isomerization of monoenes with copper‐chromite is negligible, the isotopic distribution of monoenes must be due to exchange of intermediate conjugated dienes followed by addition.