Modification of acidity

Other modifications of acid wool dyes have groups which react by nucleophilic substitution of basic groups ia proteia fibers (NH2 groups, etc). The iatroduction of Procion dyes by ICI ia 1956 was the most important development ia the field of technological azo dye chemistry. Chemically, many of the reactive dyes are prepared from the group of the anionic monoazo dyes (see Dyes, reactive). 

As illustrated by the examples, the eatalytie properties of POMs may benefit from the assoeiation with the matrix, and in some eases both enhanced activity and selectivity have resulted from immobilization. That is often the ease of POMs embedding in silica matrix and may be attributed to a eonstrained environment effect . However, it is still very difficult to predict the catalytic performance after immobilization, and only experiment ean clarify this matter. Meanwhile, a rational modification of acid-base and/or hydrophobic-hydrophilic properties of a support is possible in some cases and may tune the catalytic properties. 

To develope the scientific bases of zeolite catalysts preparation for selective organic and petrochemical synthesis, the elaboration of methods of directed modification of acid properties of these systems seems to be very important, namely, the creation in them of acid sites of different nature and the determination of their irole in multi-route catalytic transformations. 

Tsai T-H, Yen S-C. Localized corrosion effects and modifications of acidic and alkaline slurries on copper chemical mechanical polishing. Appl Surf Sci 2003 210(3-4) 190. 

Figure 7 shows an improvement of catalyst stability after the stabilization treatment. This clearly indicates that modification of acidity by steaming can enhance the stability of HZSM-5. The coke deposited on the catalysts were analyzed and divided by the total number of acid sites determined by ammonia TPD. It was expressed as the amount of coke per number of acid site and the result is shown in Figure 8. The figure demonstrates that there is no change in the amount of coke produced by the acid site after the stabilization treatment. This may suggest the nature of coke-forming sites for both stabilized and unstabilized catalysts are identical. Therefore we do not expect predominant passivation of some of the acid sites with certain strength and nature.

We have not determined the change in the location of zinc and its nature. Accordingly, our results do not contravene the contribution of zinc modification. However, we believe that modification of acid property plays an important role in increasing the catalyst stability. 

These results imply the production or modification of acid sites by irradiation, both with y-rays and with heavy particles. The site can hardly be acid, because the reactions (except in one instance) were studied between 149° and 400°, and acid was observed to have a half-life of 1 to 1.5 hour at 100°. A radiation-produced site similar to acid might be more stable in silica-alumina, but some of the above experiments were on pure silica. At —78°, irradiated silica gel catalyzed the polymerization of isobutylene (7d). Since the loss of this catalytic activity on annealing paralleled the loss in acidity, the activity is probably attributable to acid. 

The modification of acidic properties of zeolite catalysts through the isomorphous substitution of trivalent species into tetrahedral framework positions has generated great interest recently fl-3). Gallium analogues of ZSM-5, in particular, have been shown to act as acid catalysts for several reactions L4-6J. However, the knowledge about the temporal course of the crystallization process is still incomplete. The present paper reports on the influence of the crystallization time on the synthesis of gallosllicates (Ga-ZSM 5) and on their catalytic properties. 

Thomas, K.A., Ortega, S., Soderman, D., Schaeffer, M.-T., DiSalvo, J., Giminez-Gallego, G., Linemeyer, D., Kelly, L. and Menke, J. (1991) Structural modifications of acidic fibroblast growth factor alter activity, stability, and heparin dependence. Ann. N. Y. Acad. Sci. 638 9-17. 

Iij lijima, T., Fukuda, W., Tomoi, M. Modification of acid anhydride-cured epoxy resins by N-phenylmaleimide-styrene copolymers and N-phenylmaleimide-styrene-p-hydroxy-styrene ter-polymers. Polym. Intern. 42 (1997) 57-66. 

Obtaining evidence for theories - observable properties of acids and bases have led to the modification of acid-base theories... 

Depending on the legislation, various adjustments such as the addition of sugar or modification of acidity can be made to juice before the initiation of fermentation. These adjustments should be limited to avoid disequilibrating the wine. 

Song Y Sun C, Shen W, Lin L. Hydrothermal post-synthesis of HZSM-5 zeolite to enhance the coke-resistance of Mo/HZSM-5 catalyst for methane dehydroaromatization reaction reconstruction of pore structure and modification of acidity. Appl Catal A 2007 317 266-74. 

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