Sites density

Attachment site density effects in inorganic primer films... 

We can anticipate that the highly defective lattice and heterogeneities within which the transformations are nucleated and grow will play a dominant role. We expect that nucleation will occur at localized defect sites. If the nucleation site density is high (which we expect) the bulk sample will transform rapidly. Furthermore, as Dremin and Breusov have pointed out [68D01], the relative material motion of lattice defects and nucleation sites provides an environment in which material is mechanically forced to the nucleus at high velocity. Such behavior was termed a roller model and is depicted in Fig. 2.14. In these catastrophic shock situations, the transformation kinetics and perhaps structure must be controlled by the defective solid considerations. In this case perhaps the best published succinct statement... 

Table 6-4. Association constants for complexes between carboxylic acids and nitrogen bases in aprotic solvents and corresponding association constants and site densities for binding of the base to a molecu-larly imprinted polymer.

Zeolites as cracking catalysts are characterized hy higher activity and better selectivity toward middle distillates than amorphous silica-alumina catalysts. This is attrihuted to a greater acid sites density and a higher adsorption power for the reactants on the catalyst surface. 

A conventional FCC unit can be an olefin machine with proper operating conditions and hardware. Catalysts with a low unit cell size and a high silica/alumina ratio favor olefins. Additionally, the addition of ZSM-5, with its lower acid site density and very high framework silica-alumina ratio, converts gasoline into olefins. A high reactor temperature and elimination of the post-riser residence time will also produce more olefins. Mechanical modification of the FCC riser for millisecond cracking has shown potential for maximizing olefin yield. 

Calculate the specific surface site concentration (moles of surface sites per gram) for quartz (Si02) particles 1 jum in diameter. Assume a site density, ris, of 5 sites/nm (1 nm = 10 m). What will be the concentration of silica surface sites if the suspended quartz is present at 2 ppm (mg/L) ... 

Fig. 4 Number of atoms normalized by the site density plotted as a function of T for the surface model.

McQueen, JK, Wilson, H, Sumner, BEH and Fink, G (1999) Serotonin transporter (SERT) mRNA and binding site densities in male rat brain affected by sex steroids. Molec. Brain Res. 63 241-247. 

Table 2 also lists the noble metal surface areas normalized to the total mass of the catalyst. The surface areas were calculated directly from the dispersion data taking into account the different mass of noble metal in each cataly and assuming a constant site density of 1x10 /m As with dispersion, no clear correlation exists between mass-specific noble metal surface areas and CO/NOx cross-over efficiencies. 

As we demonstrate in this chapter, enzymes can be extremely active electrocatalysts at ambient temperatures and mild pH, and have significantly higher reaction selectivity than precious metals. The main disadvantage in applying redox enzymes for electrocatalysis arises from their large size, which means that the catalytic active site density is low. Enzymes also have a relatively short hfetime (usually not more than a few months), making them more suited to disposable applications. 

NMDA on the affinity and binding site density by Scatchard analysis, as described in the note with table 4. 

Zeng, L. Z., and J. F. Kausner, 1993, Nucleation Site Density in Forced Convection Boiling, Trans. ASME, J. Heat Transfer 115 215-221. (4)... 

The results of the catalyst testing are shown in Table 3. The data listed in the table show, that on a per proton basis, catalyst A (based on 7% DVB) has higher activity as compared to resin materials, crosslinked with 12% DVB. This result is in accord with the finding by Petrus et al.,3 that at temperatures higher than 120 °C the hydration is under into particle diffusion limitation and as such, a more flexible polymeric matrix will provide better access to the acidic sites. On a dry weight basis, catalyst D showed the highest activity, which correlates well with the high acid site density found for this resin (Table 2). On a catalyst volume basis, catalyst A has the best performance characteristics followed by catalyst D. 

The maximum adsorption density of semi-rigid xanthan is not very sensitive to the nature of the adsorbent surface provided that the surface has a homogeneous adsorption site density. This maximum level is close to the value calculated for a closely-packed monolayer of xanthan molecules. 

Letchworth S.R., Nader M.A., Smith H.R., Friedman D.P., Porrino LJ. Progression of changes in dopamine transporter binding site density as a result of cocaine self-administration in rhesus monkeys. J. Neurosci. 21 2799, 2001. 

The results collected in Table 2 show that the average activity is also dependent on the architectural system of channels. Thus, samples with close pore size, Ni and acid sites density, but with different topology showed very different catalytic behavior Ni-MCM-48 (with a 3D pore system) was more active than Ni-MCM-41 (with a ID pore system). In fact, the three-dimensional interconnecting mesopore system is very beneficial with respect to the molecular diffusion of heavy products in the pore channels. 

From Table 2 it can also be observed that the selectivity towards different hydrocarbon groups strongly depended on the acid properties of solids. Large amounts of C4 and C6 olefins were obtained for the mesoporous NiMCM-41 and NiMCM-48 catalysts with the lowest acid site concentration. In this case, a near Schulz-Flory-type product distribution (C4>C6>C8>Cio) was observed. The increase in acid site density (for the catalysts NiY, NiMCM-36, NiMCM-22) results in decrease of C 6/C8 ratio. These results are in agreement with the reaction network proposed in Scheme 1. 

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