Case studies turnover

Heterogenization of homogeneous metal complex catalysts represents one way to improve the total turnover number for expensive or toxic catalysts. Two case studies in catalyst immobilization are presented here. Immobilization of Pd(II) SCS and PCP pincer complexes for use in Heck coupling reactions does not lead to stable, recyclable catalysts, as all catalysis is shown to be associated with leached palladium species. In contrast, when immobilizing Co(II) salen complexes for kinetic resolutions of epoxides, immobilization can lead to enhanced catalytic properties, including improved reaction rates while still obtaining excellent enantioselectivity and catalyst recyclability. 

Despite the obvious versatility of light-activated key steps and their numerous advantages for the biomimetic modeling of natural systems, up to now, only very few examples are known, where such types of photosensitized processes have been successfully combined to complete reaction cycles with reasonable catalytic turnovers 6). In the last section, we are therefore briefly presenting two case studies which describe some recent work performed in our own group focusing on bioinspired catalytic systems that can be controlled and driven by visible light. 

Akzo Nobel has its headquarters in Arnhem, the Netherlands. In 1998 it had a turnover of Eur 11256 million. There are 292 production sites employing 69000 people in 70 countries worldwide, and although the operating countries are not named, the annual report does identify that 64% of the workforce work in Europe, 15% in North America, 7% in Latin America, 11% in Asia/Pacifk and 3% in other regions. Although there are cases studied in the CER that indicate the nature of company activities, the full scope of operations of the four main sectors can only be determined from the annual report ... 

Many people are familiar with the Bhopal disaster in December 1984, and as is usually the case, there were multiple problems and failures leading up to the catastrophic release of methyl isocyanate (MIC). For this case study, we will focus on the organizational issues related to personnel turnover to provide an example of how such changes can contribute to process safety incidents. 

The three case study industries differed widely in the specific effects of deregulation on human performance and human capital. In the aviation industry, rapid industry growth created significant growth in total employment. As a result, human performance problems were generally associated with relatively inexperienced personnel and high turnover rates, especially at smaller carriers. 

There are case studies which highlight a mtmber of tangible benefits. These benefits are obviously extremely attractive to employers, and include increased productivity, increased profitability through an overall cut in expenses, and lowering of absenteeism rates. Further benefits are a reduction in staff turnover, and a reduction in workers compensation claims. 

Palladium(II) complexes provide convenient access into this class of catalysts. Some examples of complexes which have been found to be successful catalysts are shown in Scheme 11. They were able to get reasonable turnover numbers in the Heck reaction of aryl bromides and even aryl chlorides [22,190-195]. Mechanistic studies concentrated on the Heck reaction [195] or separated steps like the oxidative addition and reductive elimination [196-199]. Computational studies by DFT calculations indicated that the mechanism for NHC complexes is most likely the same as that for phosphine ligands [169], but also in this case there is a need for more data before a definitive answer can be given on the mechanism. 

Our results do not support the protein stress model. However, this model may apply in cases where stress is intermittent and results in tissue loss, as observed in the study of crows (Hobson and Clark 1992). Low protein levels throughout life after weaning may have produced overall slow and reduced rate of growth rather than tissue loss. Adult rats fed protein-deficient diets after maturation show systematic losses of nitrogen from most tissues that are in proportion to their turnover rates and masses (Uezu et al. 1983). Perhaps tissue nitrogen isotope enrichment may occur under these conditions. New experiments are needed to evaluate this hypothesis. 

It is already evident that the turnover rate of a transmitter is only a crude measure of its release rate. Further limitations are that there is appreciable intraneuronal metabolism of some neurotransmitters notably, the monoamines. In such cases, turnover will overestimate release rate. Another problem, again affecting monoamines, is that some of the released neurotransmitter is taken back into the nerve terminals and recycled. This leads to an underestimate of release rate. Despite these drawbacks, studies of turnover rates uncovered some important features of transmitter release. In particular, they provided the first evidence for distinct functional pools of monoamines, acetylcholine and possibly other neurotransmitters a release pool, which could be rapidly mobilised for release, and a storage or reserve pool which had a slower turnover rate. 

The kinetics of ethylene hydrogenation on small Pt crystallites has been studied by a number of researchers. The reaction rate is invariant with the size of the metal nanoparticle, and a structure-sensitive reaction according to the classification proposed by Boudart [39]. Hydrogenation of ethylene is directly proportional to the exposed surface area and is utilized as an additional characterization of Cl and NE catalysts. Ethylene hydrogenation reaction rates and kinetic parameters for the Cl catalyst series are summarized in Table 3. The turnover rate is 0.7 s for all particle sizes these rates are lower in some cases than those measured on other types of supported Pt catalysts [40]. The lower activity per surface... 

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