Temporary deactivation

A higher concentration of basic and polar molecules, i.e. nitrogen compounds that are readily adsorbed on to the catalyst acidic sites, leading to an instant, but temporary deactivation. Polycyclic aromatics also strongly contribute to coke formation. 

Demchenko and co-workers demonstrated that STaz glycosides can be engaged in stable non-ionizing transition-metal complexes. This observation served as a basis for the development of a temporary deactivation technique for oligosaccharide synthesis (Scheme 28).158 The deactivation of the otherwise reactive building block was... 

SCHEME 29. Synthesis of pneumococcal oligosaccharides serogroup 14 by temporary deactivation technique.159... 

P. Pomsuriyasak, N. P. Rath, and A. V. Demchenko, 4-(Pyridin-2-yl)thiazol-2-yl thioglycosides as bidentate ligands for oligosaccharide synthesis via temporary deactivation, Chem. Commun., (2008) 5633-5635. 

The following questions can in principle be addressed with spectroscopy (1) Zeolite synthesis what are the mechanisms of ZSM-5 synthesis and how do they influence the quality of the catalyst synthesized (2) Catalyst characterization what are the structure and composition of the zeolite, and what is the configuration of the active site for methanol conversion (3) How do methanol and dimethylether interact with the active sites i.e. what species are present in the catalyst in the initial stages of methanol conversion (4) What are the subsequent reaction pathways leading to the final alkane, alkene and aromatic products (5) What causes catalyst deactivation This question concerns both the temporary deactivation associated with coke formation, which can be reversed by oxidative regeneration, and the permanent deactivation which occurs after repeated deactivation-regeneration cycles. 

Typically, CRP processes rely on the temporary deactivation of the radical chains into a dormant form. Consequently, the probability of bimolecular termination... 

Remarkably, the same key concept applies in living radical polymerizations. It has been suggested that the term temporary deactivation is more appropriate than reversible termination, to emphasize control (20). 

Living polymerization is defined as chain polymerization in which chain termination and irreversible chain transfer are absent. The rate of chain initiation is usually larger than the rate of chain propagation with the result that the number of kinetic-chain carriers is essentially constant throughout the reaction. Reversible (temporary) deactivation of active centers can take place in a living polymerization, and all the macromolecules formed possess the potential for further growth. The term controlled polymerization, on the other hand, indicates control of a certain kinetic feature of a polymerization or structural aspect of the polymer. ... 

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