Adsorption mechanisms for

Hydroxotitanate anion, however, has never been detected in the course of hydrolysis of titanium alkoxides. On the basis of electron microscopy data, Diaz-Guemes et al. [477] suggested the two-step adsorption mechanism for the above reaction. According to his assumption hydrolysis of titanium alkox-ide results in a gel of hydrated titanium oxide, which is further diffused by M2+ cations to form crystalline MDTi03 ... 

Fairly recently it has been established that a set of pseudo-steady-state equations for complex catalytic reactions can have several solutions only when their detailed mechanisms involve as one step an interaction between various intermediates [22], The simplest catalytic mechanism possessing this property is an adsorption mechanism. For example... 

Hance, R.J. (1971). Complex formation as an adsorption mechanism for linuron and atrazine. Weed Res., 11 106-110. 

The first boundary condition is equivalent to the Levich approach, given elsewhere as ca=1 for r co [8]. Eq. (4b) has been proposed by Coutelieris et al. [1] to ensure continuity of concentration at the outer boundary of the cell for any Peclet number. Moreover, eq. (4c) and (4d) represent the axial symmetry assumption considered for this problem. The last boundary condition describes a typical instantaneous adsorption mechanism for the component A upon the solid surface. 

Adsorption mechanisms for retention of nonionic polar organic molecules, such as phenylcarbamates and substituted ureas used as herbicides, are illustrated in Figure 13. The great importance of hydrogen bonding in retention is suggested. Other adsorption mechanisms include van der Waals... 

Specific adsorption is an important adsorption mechanism for trace substances in water, but not for major ionic species. Define specific adsorption and explain this statement with examples. 

FIGURE 7.14 Schematic representation of the adsorption mechanisms for SDS/C[2EOg mixtures on kaolinite. (From Xu, Q. and Somasundaran, R, Miner. Metal. Processing, 9, 29, 1992. With permission.)... 

The protein concentration in the sublayer c(Fi) can be determined via the adsorption isotherm Eqs. (2.117) to (2.119). The Eq. (4.38) is quite complicated for a further analysis and simplifications are necessary. From experimental data, it is known that the adsorption of proteins at the air/water interfaces follows a diffusion-controlled mechanism, at least for small surface pressures n < 2 mN/m [71, 72, 73, 74, 75]. Moreover, the so-called induction time t, the time at which the surface pressure FI starts to increase, can be used for an estimation of the adsorption mechanism. For this time interval the relation cH s const should hold [71, 74, 76]. A diffusion model for the range of small F as approximation was given in [77]... 

For a modelling of adsorption processes the well-known integro-differential equation (4.1) derived by Ward and Tordai [3] is used. It is the most general relationship between the dynamic adsorption r(t) and the subsurface concentration e(0,t) for fresh non-deformed surfaces and is valid for kinetic-controlled, pure diffusion-controlled and mixed adsorption mechanisms. For a diffusion-controlled adsorption mechanism Eq. (4.1) predicts different F dependencies on t for different types of isotherms. For example, the Frumkin adsorption isotherm predicts a slower initial rate of surface tension decrease than the Langmuir isotherm does. In section 4.2.2. it was shown that reorientation processes in the adsorption layer can mimic adsorption processes faster than expected from diffusion. In this paragraph we will give experimental evidence, that changes in the molar area of adsorbed molecules can cause sueh effectively faster adsorption processes. 

Bridges et al. (33) obtained lower chromia areas by CO adsorption than by O2 adsorption, and they attributed this result to a two-site adsorption mechanism for CO, and a single-site mechanism for Og. If one takes into account the ratio of the number of available double sites to single sites in the clusters of Table VI, then one may deduce the... 

In some of the studies attempts have been made to elucidate the details of the adsorption mechanisms for particular pesticides. Two different approaches have been used in these studies some workers have used whole organic soils as the sorbents in their experiments, whereas others have used humic acids extracted from soils. The whole soils are certainly heterogeneous, and it has been shown that the humic acids extracted from them consist of fractions of different molecular weight and different chemical structure (15). In systems in which heterogeneous... 

Another weak adsorption mechanism for either anionic or polar organic functional groups is water bridging, which involves complexation with the... 

M. G. Browman and G. Chesters, The solid-water interface Transfer of organic pollutants across the solid-water interface. Advan. Environ. Sci. Technol. 8(1) 49 (1977). The adsorption mechanisms for pesticides in soils are discussed in the first three sections of this review article. 

M. M. Mortland, Clay-organic complexes and interactions, Advan. Agron. 22 75 (1970). This classic review article remains the best comprehensive introduction to adsorption mechanisms for organic compounds. 

Several observations discussed in the following sections support either the film breaking or the adsorption mechanism for the nonstationary or stationary conditions of the passive film. 

Several experimental results support the adsorption mechanism for stationary conditions of the passive layer. Even the stationary passive current density depends on the composition of the electrolyte. For iron in 0.5 M H2SO4, the passive current density is 7 pA cm , whereas less than lpAcm is detected in 1 M HCIO4. From these observations, a catalysis for the transfer of Fe + from the passive layer to the electrolyte by S04 ions was concluded [55, 56]. Similarly, the dissolution Ni + from passive nickel and nickel base alloys is accelerated by organic acids hke formic acid and leads to a removal of NiO from the passive layer [57]. Additions of citrate to the electrolyte cause the thinning of passive layers on stainless steel and increase its Cr content [58]. Apparently Fe and Ni ions are complexed at the surface of the passive film, which causes an enhancement of their dissolution into the electrolyte. It should be mentioned that the dissolution of Cr " " apparently is not catalyzed by these anions and remains... 

M. Ozacar, 1. A. engil, H. Tiirkmenler, Equilibrium and kinetic data, and adsorption mechanism for adsorption of lead onto valonia tannin resin. Chem Eng J 2008,143 (1), 32-42. 

FIGURE 15.8 Adsorption kinetics according to the random sequential adsorption mechanism for spherical and ellipsoidal particles having varying aspect ratios (a/b). 

The well-known adsorption mechanism for the oxidation of carbon monoxide over platinum at constant partial pressures of oxygen and carbon monoxide,... 

The main result is that real multiplicity of steady states—the existence of two internal stable steady states and one internal unstable steady state—can be explained using one of the four mechanisms shown in Table 7.3. If the experimentally observed steady-state reaction rate is characterized by two different branches, and multiplicity of steady states is observed, one of these four mechanisms can be used to interpret the data. We prefer to use mechanism B because its steps are characterized by overall reaction orders that are not larger than two. In fact, this mechanism is identical to the mechanism represented by Eq. (7.102), an example of which is the adsorption mechanism for the oxidation of carbon monoxide (Eq. (7.103)). We will return to this mechanism in Chapter 11, in which the problem of critical simplification is discussed. 

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