Intrinsic site activity

Bertole, C.J., Mims, C.A., and Kiss, G. Support and rhenium effects on the intrinsic site activity and methane selectivity of cobalt Fischer-Tropsch catalysts. Journal of Catalysis, 2004, 221, 191. 

A comparison of the surface residence times, x, reveals no significant difference for the experiments. From this observation, it can be concluded that the variation in methane 5deld is due to a difference in the amount of active sites. The intrinsic site activity for the methanation reaction remains unchanged after the water treatment, and it is also unaffected by the presence of the rhenium promotor. It is proposed that rhenium supports the reduction of cobalt, but the water pretreatment leads to a reoxidation of the active metal, particularly the fraction of the cobalt metal that is reduced only when rhenium is present. 

Steady-state isotopic transient kinetic analysis (SSITKA) shows that the deactivation of the methanation reaction after water treatment is due to a decrease in the number of active sites, while the intrinsic site activity apparently remains unchanged. 

Rhenium promotion of the Co/Al Oj catalyst results in a significantly higher activity, both for methane and higher hydrocarbons. The promoted catalyst shows no better tolerance for the presence of water. The intrinsic site activity for methane formation is equal to the values found for the unpromoted catalyst. 

It would be highly desirable to be able to determine the intrinsic site activity of a catalyst in order to evaluate its site efficiency relative to other catalysts active for a reaction of interest - unbiased by the amount of catalyst used, by the concentration of active sites per weight or volume of catalyst, or even, in the ideal, by the concentration of reactants or products. This intrinsic activity would thus reflect the catalytic essence of the reaction site. Use of such a site activity would permit discrimination between a poor catalyst candidate and an excellent one for further study that, for whatever reason, might have only a few super active sites. One could work to determine the nature/structure of those very active sites and seek a way to design a catalyst having an increased concentration of such sites. 

The results showed that K promotion resulted in almost 50 times the increase in the reaction rate. TOF based on the amount of hydrogen chemisorption increased by about two orders of magnitude with K-promotion. However, the intrinsic TOF based on SSITKA increased only by a factor of 16. The increase in activity with K promotion was actually due to both a significant increase by a factor of 3 in the surface concentration of intermediates, and an increase by a factor of 16 in the average intrinsic site activity. 

These observations are explained by the conversion of CO to CO2 on sites active for CO conversion, as the intrinsically produced CO makes its way out of the catalyst bead by diffusion. The greater the diffusion limitation, the more the CO conversion. Weisz gave the mathematical solution for two special cases of these phenomena and demonstrated that the above interpretation was correct. 

The success of treating tumours, especially solid tumours, by systemic therapy depends on various characteristics of the tumour. Besides the importance of intrinsic drug activity and the potential targets within the tumour cells, drug pharmacokinetics and whole body distribution, site of delivery and the ability of site-specific targeting (affinity) are important features. 

In comparison to the level of cellular serine or threonine phosphorylation, protein tyrosine phosphorylation occurs at quite low levels in normal cells but dramatically increases upon oncogenic transformation or stimulation. Since the first discovery in 1978 that the transforming protein from Rous sarcoma virus (pp60vsrc) exhibited intrinsic kinase activity/5 protein kinase activity has also been shown to be inherent to other growth factor receptors such as epidermal growth factor receptor and the insulin receptor,[6 91 and to involve autophosphorylation processes. The diverse biochemical activity exhibited by protein tyrosine phosphorylation has stimulated the development of chemical methods for the preparation of phosphorylated peptides for use as substrates in elucidating the biochemical and physiological activity of phosphorylated site(s). 

Large-pore titanosilicates developed after TS-1, for example, Ti-beta, Ti-ITQ-7, Ti-MCM-41 and Ti-MCM-48, have been claimed to have advantages for the oxidation of bulky alkenes because of their pore size [15-17, 66, 67]. However, none of them is intrinsically more active than TS-1 in the reactions of small substrates that have no obvious diffusion problem for the medium pores. Therefore, in parallel with developing large pore titanosilicates, the search for more intrinsically active ones than TS-1 is also an important research subject. The catalytic performance of Ti-MWW is compared in the oxidation of 1-hexene with H202 with that of TS-1 and Ti-beta. Consistent with the results reported elsewhere [15-17], TS-1 showed higher conversion than Ti-beta with a similar Ti content. However, Ti-MWW exhibited activity about three times as high as TS-1 based on the specific conversion per Ti site (TON). 

Salicylates Interference with renal excretion of drugs that undergo active tubular secretion. Salicylate renal excretion dependent on urinary pH when large doses of salicylate used. Aspirin (but not other salicylates) interferes with platelet function. Large doses of salicylates have intrinsic hypoglycemic activity. Salicylates may displace drugs from plasma protein binding sites. Carbonic anhydrase inhibitors [NE] Increased acetazolamide serum concentrations increased salicylate toxicity due to decreased blood pH. 

Powders possessing relatively high surface area and active sites can be intrinsically catalytically active themselves. Powders of nickel, platinum, palladium, and copper chromites find broad use in various hydrogenation reactions, whereas zeolites and metal oxide powders are used primarily for cracking and isomerization. All of the properties important for supported powdered catalysts such as particle size, resistance to attrition, pore size, and surface area are likewise important for unsupported catalysts. Since no additional catalytic species are added, it is difficult to control active site location however, intuitively it is advantageous to maximize the area of active sites within the matrix. This parameter can be influenced by preparative procedures. 

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