Adsorption sites available for

The retention in NPLC increases with increasing polarity (activity) and is proportional to the specific surface area. As, which controls the number of the adsorption sites available for contact with the sample solutes in the column. Water in mobile phases deactivates the adsorbent (decreases oc ), as the sites with strongly held adsorbed water are no longer available for adsorption of moderately polar organic compounds. The elution times of analytes generally increase in the following sequence alkanes < alkenes < aromatic hydrocarbons chloroalkanes < alkylsul-phides < ethers < ketones aldehydes esters < alcohols < amides phenols, amines, carboxylic acids. The... 

There are B equivalent sites available for adsorption in the first layer. 

The effect of electronegative additives on the adsorption of ethylene on transition metal surfaces is similar to the effect of S or C adatoms on the adsorption of other unsaturated hydrocarbons.6 For example the addition of C or S atoms on Mo(100) inhibits the complete decomposition (dehydrogenation) of butadiene and butene, which are almost completely decomposed on the clean surface.108 Steric hindrance plays the main role in certain cases, i.e the addition of the electronegative adatoms results in blocking of the sites available for hydrocarbon adsorption. The same effect has been observed for saturated hydrocarbons.108,109 Overall, however, and at least for low coverages where geometric hindrance plays a limited role, electronegative promoters stabilize the adsorption of ethylene and other unsaturated and saturated hydrocarbons on metal surfaces. 

We can think of a heterogeneous catalyst as a collection of active sites (denoted by ) located at a surface. The total number of sites is constant and equal to N (if there is any chance of confusion with N atoms, we will use the symbol N ). The adsorption of the reactant is formally a reaction with an empty site to give an intermediate I (or more conveniently R if we explicitly want to express that it is the reactant R sitting on an adsorption site). All sites are equivalent and each can be occupied by a single species only. We will use the symbol 6r to indicate the fraction of occupied sites occupied by species R, making N6r the number of occupied sites. Hence, the fraction of unoccupied sites available for reaction will be 1 - 0r The following equations represent the catalytic cycle of Fig. 2.7 ... 

Greater adsorption of trace metals is found at higher pH and C02(g) concentrations. Sites available for Zn2+ sorption are less than 10% of the Ca2+ sites on the calcite surface, and Zn adsorption is independent of surface charge. This indicates a surface complex with a covalent character (Zachara et al., 1991). Furthermore, the surface complex remains hydrated and labile because Zn2+ is rapidly exchangeable with Ca2+, Zn2+ and ZnOH. At the dolomite-solution interface, the carbonate(C03)-metal (Ca/Mg) complex dominates surface speciation at pH > 8, but at pH 4-8, hydroxide (OH) -metal (Ca/Mg) dominates surface speciation (Pokrovsky et al., 1999). Calcite has an observed selectivity sequence Cd > Zn > Mn > Co > Ni > Ba = Sr, but their sorption reversibility is correlated with the hydration energies of the metal sorbates. Cadmium and Mn dehydrate soon after adsorption to calcite and form a precipitate, while Zn, Co and Ni form surface complexes, remaining hydrated until the ions are incorporated into the structure by recystallization (Zachara et al., 1991). 

The results of adsorption and desorption of CO mentioned above suggest that for the reaction at low temperature, the sites for relatively weakly chemisorbed CO are covered by the deposited carbon and the reaction occurs between molecularly adsorbed CO and oxygen on the carbon-free sites which are the sites for relatively strongly chemisorbed CO. Therefore, the definition of the turnover rate at 445 K remains as given in Equation 1. For the reaction at 518 K, however, this definition becomes inappropriate for the smaller particles. Indeed, to obtain the total number of Pd sites available for reaction, we now need to take into consideration the number Trp of CO molecules under the desorption peak. Furthermore, let us assume that disproportionation of CO takes place through reaction between two CO molecules adsorbed on two adjacent sites, and let us also assume that the coverage is unity for the CO molecules responsible for the LT desorption peak, since this was found to be approximately correct on 1.5 nm Pd on 1012 a-A O (1). Then, the number Np of palladium sites available for reaction at 518 K is given by HT/0 + NC0 LT s nce t ie co molecules under the LT desorption peak count only half of the available sites. Consequently, the turnover rate at 518 K should be defined as ... 

Ligand effect CO adsorption is lowered by alloying, thus decreasing CO coverage and increasing sites available for H2 adsorption/ dissociation and oxidation. 

Some polymer molecules can be regarded to maintain their approximate solution conformation upon adsorption (19). Adsorption of a nonionic polymer would lead to a coiled adsorbed polymer configuration with a small number of polymer segments in actual contact with the surface. The number of surface sites available for surfactant adsorption would remain quite large. 

The tungsten (110) surface is one of the best studied of all surfaces, especially in field emission and field ion microscopy for many reasons. It is a very stable surface without surface reconstruction or phase transformation. It is also inert to contaminations. For the study of adatom-adatom interactions, it is a very smooth plane with the largest density of adsorption sites available of any W surface. Lesser restrictions are imposed on the adatom-adatom separation. As the surface is structurally very smooth, wave mechanical interference effects are least affected by the surface atomic structure. 

In this expression, U(t) is relative rate of uptake and Cx is relative to equilibrium, i.e. the sites available for ion exchange or adsorption for the specified ratio Vim. Thus, the absolute rate is a coupled result of kinetics and equilibrium. Note that in a solid diffusion-controlled process, U(t) is relative to the ease of movement of the incoming species in the solid phase (through Ds). 

In view of the linearity of the curves presented in Figure 8 and the high activation energies obtained by using Equation 1 at constant values of there seems to be considerable justification for the chemisorption model of volatile matter release. The fact that the initial rates of H2 release show a zero-order dependency may be attributed to the fact that for raw anthracite the fraction of surface coverage is practically unity. Under these conditions, where almost all of the sites available for H2 adsorption are filled, Equation 1 leads to the result that the rate of change of coverage with respect to time is initially constant. 

Organic matter deposited onto the suspended sediment has a large influence on the specific surface area. On one hand, it appears that organic matter blocks some sites available for physical adsorption of inert gas (BET adsorption) and, on the other hand, it probably partly causes flocculation and agglomeration of particles in the upper estuary, such floes and agregates being destroyed downstream in the salinity intrusion zone. 

The polymeric chains are assumed to grow on sites available for propylene oxide monomer but not on oxygen adsorption sites. 

While previous work has often been conducted under conditions where only trace quantities of lead or other heavy metals have been placed in contact with an adsorbent, very few of these approaches have dealt with the problems faced as the adsorbent sites begin to be filled. The usefulness of the VSC-VSP model in taking this into account is illustrated here by demonstration of the effect of charged adsorbed species on the electrostatic potential which acts on the adsorbing ions. When a given number of equivalents of adsorbent are placed in contact with a comparatively large number of moles of cations, some of which will attach to the adsorbent, adsorption will be further opposed in two ways. First, of course, the process of adsorption will reduce the number of sites available for further adsorption. Second, the Gouy potential is said by Bowden ad. (7) to decrease from the... 

The layer effect will play a part when on the solid surface the number of sites available for adsorption is not unlimited so that for unrestricted adsorption more than one layer has to be considered. In the below we investigate whether this assumption intervenes with the results of Jantti s procedure. 

The number of sites available for adsorption on the solid we refer to as The number of molecules in the first and second layer are n, and respectively. The total number n of the adsorbed molecules satisfies ... 

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