No abstract

Owing to shifting market demands, it is important to convert ethylene to propylene. One attractive way to achieve this conversion is the dimerization of ethylene to 1‐butene, followed by isomerization to 2‐butene and subsequent metathesis of 2‐butene/ethylene olefin. Our contribution focuses on combining the first two steps. Herein, we report a highly selective tandem dimerization/isomerization of ethylene to 2‐butene catalyzed by homogeneously dissolved cationic nickel complexes. These catalysts can be efficiently immobilized by using the supported ionic liquid phase technology. Such supported ionic liquid phase materials have been tested under continuous gas phase conditions and demonstrated attractive catalytic performance with respect to both catalyst stability and productivity after the optimization of support, ionic liquid, ligand, and process parameters. The limited thermal stability of the nickel complexes and olefin condensation at too low temperatures require a careful thermal management of the fixed‐bed reactor.

The ionic liquid 1‐ethyl‐3‐methylimidazolium ethylsulfate [EMIM][EtOSO3] was supported on Pd‐Al2O3 to yield a solid catalyst with ionic liquid layer (SCILL) material. During the hydrogenation of ethene, it was found that ethene was incorporated into the imidazolium moiety in a reaction catalyzed by the palladium surface. The formation of 1,2‐diethyl‐3‐methylimidazolium ethylsulfate was confirmed ex situ by means of NMR spectroscopy. Moreover, the reaction itself could be monitored in situ by diffuse reflection infrared Fourier transformation (DRIFT) spectroscopy. A reaction mechanism involving surface carbene species was proposed on the basis of the analytical data.

(PPh 3 OdiMePh = (2-(2,6-dimethylphenoxy)phenyl)diphenylphosphine) 3 were immobilized as Supported Ionic Liquid Phase (SILP) catalysts and applied for the tandem dimerization/isomerization of ethylene to 2-butene in a fluidized bed reactor. The better heat removal in the fluidized bed improves the catalyst stability and allows for a more detailed investigation of the deactivation mechanism. Based on kinetic studies, a second order deactivation mechanism is proposed, in which two nickel complexes dimerize if the supply of ethene is insufficient.

Today's catalytic forecast: migrating front and hot spots The cover picture shows the conversion of ethylene to 1-butene and 2-butene by using a fixed-bed reactor with the catalyst bed consisting of supported ionic liquid phase (SILP) catalyst particles. In their Full Paper on p. 162 ff., P. Wasserscheid et al. describe that the applied homogeneous nickel complex exhibits a high activity and selectivity to 2-butene. The observed catalyst deactivation is attributed to a migrating reaction/deactivation front travelling through the catalyst bed in combination with hot spot formation. The time until catalyst deactivation could be heavily prolonged by optimization of catalytic and process parameters.