Nature Of Cocatalyst Research Articles

Characterization of Pd/C and Cu Catalysts for the Oxidation of Methane to a Methanol Derivative

Carbon-supported Pd catalysts with a copper compound for the oxidation of methane to a methanol derivative, CF3COOCH3, in the presence of CO and O2 were characterized. The bulk structure and chemical environment of palladium and copper were determined by XRD and XAFS, respectively. In this reaction system, the nature of cocatalyst, the presence of Cl−, and the solvent composition changed the structure of the palladium species and affected the yield of CF3COOCH3. In the presence of a copper compound and Cl−, the metallic palladium can be partly oxidized into Pd(II) species, which resulted in higher yields of CF3COOCH3. For the active catalyst system, the copper compound was present as CuCl. Pd(II) species coordinated with Cl− appeared to be essential for the selective activation of methane and the metallic palladium for the in situ generation of H2O2 from CO, H2O, and O2.

Morphological Study of HDPE Prepared with the Highly Active Silica Supported TiCl4/MgCl2 Catalyst

Kinetic investigations were carried out on the effects of polymerization conditions and nature of aluminium alkyl cocatalyst on the morphology (size, shape, density, and texture) of nascent polyethylene synthesized with TiCl4/MgCl2/SiO2 catalyst. Depending on the nature of the cocatalyst, considerably different kinetic profiles are obtained. Fibrillar, globular, cobweb, ribbon-like, worm-like, and lamellar structures are identified according to the catalyst system and polymerization conditions. The formation of a worm-like texture is a common feature of the catalyst combined with Al(C2H5)3 at high catalyst efficiency, while globular texture is obtained at low catalyst efficiency. Polymerization at optimum temperature (80°C) and Al(C2H5)3 concentration (Al/Ti=60) without the addition of hydrogen produces a well-defined crystalline structure, folded lamella globule. A cobweb structure is observed when AlEt2Cl is used as the cocatalyst. The effect of polymerization conditions on the particle size distribution of nascent polyethylene is also investigated. Replication phenomenon was observed to depend on the catalyst yield and polymerization time. Generally, the average particle size of polymer particles becomes large as the rate of polymerization increases.

Catalytic reactions involving butadiene: III. Oligomerisation with cationic bis(triphenylphosphine)(η 3-allyl) complexes

The bis(triphenylphosphine)(η 3-crotyl)nickel cation is a catalyst precursor for the oligomerisation of butadiene to cyclic or linear dimers. Polymers and oligomers are also produced in variable amounts. The product distributions depend strongly on the type of solvent used and on the nature of co-catalysts. In the aprotic polar solvent DMF, the starting complex undergoes disproportionation, leading finally to a zerovalent nickel-phosphine catalyst. In protic solvents (alcohols) a cationic hydridonickel-phosphine catalyst is produced, but addition of sodium methoxide induces the formation of the zerovalent nickel-phosphine, therefore accounting for the changes in product selectivities.

Catalytic reactions involving butadiene III. Oligomerisation with cationic bis(triphenylphosphine)(η3-allyl) complexes

Abstract The bis(triphenylphosphine)(η 3 -crotyl)nickel cation is a catalyst precursor for the oligomerisation of butadiene to cyclic or linear dimers. Polymers and oligomers are also produced in variable amounts. The product distributions depend strongly on the type of solvent used and on the nature of co-catalysts. In the aprotic polar solvent DMF, the starting complex undergoes disproportionation, leading finally to a zerovalent nickel-phosphine catalyst. In protic solvents (alcohols) a cationic hydridonickel-phosphine catalyst is produced, but addition of sodium methoxide induces the formation of the zerovalent nickel-phosphine, therefore accounting for the changes in product selectivities.