Heterolytic Activation of C–H Bonds on CrIII–O Surface Sites Is a Key Step in Catalytic Polymerization of Ethylene and Dehydrogenation of Propane

Understanding surface site structures and properties by first principles calculations: an experimental point of view!

Computational Chemistry is key for the molecular-level understanding of active sites in heterogeneous catalysis paving the way to the rational design and development.

The influence of functional groups on the ethylene polymerization performance of silsesquioxane-supported Phillips-type catalysts

A series of silsesquioxane-supported Phillips-type molecular catalysts for ethylene polymerization were synthesized by introducing various functional groups in proximity to monoalkylated Cr(iii).

Insights into Cr/SiO2 catalysts during dehydrogenation of propane: an operando XAS investigation

In situ and operando XAS spectroscopic methods were applied to monitor the variations in the oxidation state and in the local structure of the chromium sites in a 2.0Cr/SiO_2-DHS catalyst during propane dehydrogenation under non-oxidative and different oxidative conditions.

Real-time Analysis of a Working Triethylaluminium-Modified Cr/Ti/SiO2 Ethylene Polymerization Catalyst with In Situ Infrared Spectroscopy

A diffuse reflectance infrared Fourier-transform (DRIFT) study has been conducted at 373 K and 1 bar on an industrial Cr/Ti/SiO2 Phillips-type catalyst modified with, and without, triethylaluminium (TEAl) as co-catalyst. The reaction rate of the polymerization of ethylene, as monitored by the increase in the methylene stretching band of the growing polyethylene (PE), has been investigated as a function of the titanium content. After an initial period of mixed kinetics, with the reaction rate significantly higher for the TEAl-modified catalysts compared with the non-modified catalysts, the polymerization proceeded as a pseudo-zero-order reaction with a reaction rate that increased as a function of titanium loading. Furthermore, it was found that the higher Ti loading caused the appearance of more acidic hydroxyl groups and modified the Cr sites by making them more Lewis acidic, ultimately shortening the induction time and increasing the initial polymerization rate.

Organometallic model complexes elucidate the active gallium species in alkane dehydrogenation catalysts based on ligand effects in Ga K-edge XANES

Ga(iii)-alkyl and alkoxide model compounds demonstrate XANES edge energy shifts similar to those in Ga dehydrogenation catalysts without a change in Ga oxidation state.

Amorphous SiO2 surface models: energetics of the dehydroxylation process, strain, ab initio atomistic thermodynamics and IR spectroscopic signatures

Realistic amorphous SiO₂ models of 2.1 × 2.1 nm with silanol densities ranging 1.1–7.2 OH per nm² are obtained by means of ab initio calculations via the dehydroxylation of a fully hydroxylated silica surface.