Interfacial reactions capacity

Fendorf SE, Jardine PM, Taylor DL, Brooks SC, Rochette EA (1998) Auto-inhibition of oxide mineral reductive capacity toward Co(II)EDTA. ACS Symp Ser 715 (Mineral-Water Interfacial Reactions), American Chemical Society, Washington, DC, p 358-371... 

Therefore the lattice-gas model has proved most useful for the study of those processes in which the ionic double layer plays a major role, and there are quite a few. So it has been used to investigate the interfacial capacity, electron and ion-transfer reactions, and even such complex processes as ion pairing and assisted ion transfer. Because of its simplicity we carmot expect this model to give quantitative results for particular systems, but it is ideally suited to qualitative investigations such as the prediction of trends and orders of magnitude for various effects. 

Huber et al. [12] investigated the same model by Monte Carlo simulations however, they focused on a different aspect the dependence of the interfacial capacity on the nature of the ions, which in this model is characterized by the interaction constant u. Samec et al. [13] have observed the following experimental trend the wider the potential window in which no reactions take place, the lower the interfacial capacity. Since the width of the window is determined by the free energy of transfer of the ions, which is 2mu in this model, the capacity should be lower, the higher u. ... 

Unfortunately the development of models is hindered by a lack of reliable experimental data. For example, the rates of ion-transfer reactions measured at different times and by different groups vary widely. Also, it has been suggested that the high interfacial capacities that are measured in certain systems are an experimental artifact [13]. While this is frustrating for the researcher who wants to decide between competing models, it can also be viewed as a sign that the electrochemistry of liquid-liquid interfaces is an active field, where fundamental issues are just being explored. 

In the ideal situation of 100% utilization x = 1.0), the capacity corresponding to the above anode half reaction is 372 mA h g However, due to the low ion conductivity of the polymer electrolyte and the high interfacial impedance between it and the graphite electrode, this elegant example of electrochemical preparation of lithiated graphite is of limited practical significance. 

Burch and Flambard (113) have recently studied the H2 chemisorption capacities and CO/H2 activities of Ni on titania catalysts. They attributed the enhancement of the catalytic activities for the CO/H2 reaction (after activation in H2 at 450°C) to an interfacial metal-support interaction (IFMSI). This interaction is between large particles of Ni and reduced titanium ions the Ti3+ is promoted by hydrogen spillover from Ni to the support, as pictured in Fig. 8. The IFMSI state differs from the SMSI state since hydrogen still chemisorbs in a normal way however, if the activation temperature is raised to 650°C, both the CO/H2 activity and the hydrogen chemisorption are suppressed. They define this condition as a total SMSI state. Between the temperature limits, they assumed a progressive transition from IFMSI to SMSI. Such an intermediate continuous sequence had been... 

Ultrasound is known for its capacity to promote heterogeneous reactions (Ley and Low, 1989) mainly through greatly increased mass transport, interfacial cleaning and thermal effects. In addition, homogeneous chemical reactions have been reported to be modified (Suslick et ai, 1983 Luche, 1990 Colarusso and Serpone, 1996) for example the sonochemical generation of radical species in aqueous media is important in environmental detoxification (Kotronarou et al., 1991 Serpone et al., 1994). 

The fluidized bed characteristics of high solids heat capacity, large interfacial heat transfer area, and good solids mixing allow the assumptions of thermal equilibrium between the solids and the gas, uniform bed temperature and negligible heat capacitance of the gas. An additional assumption required to use equation (9) is that the reactions do not change the gas volume. 

Thus assumption of the same value for interfacial area in physical and chemical absorption leads to uncertainty, especially if the mass transfer coefficient is deduced from k a measured by physical absorption or desorption and from a in chemical absorption. The effective interfacial area in the case of a fast-reaction system where the absorbing capacity is increased by a chemical reactant is substantially larger than the effective interfacial area for physical absorption or desorption, as pointed out by Joosten and Danckwerts (JIO). These authors introduced a correction factor y, the ratio between the increase in liquid absorption capacity and the increase in mass transfer due to chemical reaction ... 

Ultrasound and electrochemistry provide a powerful combination for several reasons. Ultrasound is well known for its capacity to promote heterogeneous reactions, mainly through increased mass-transport, interfacial cleaning, and thermal effects. Effects of ultrasound in electrochemistry may be divided into several important branches (1) Ultrasound greatly enhances mass transport, thereby altering the rate, and sometimes the mechanism, of the electrochemical reactions. 

The cathodic Tafel slope corresponding to reaction (19.33) in the reverse direction is close to —0.120 V per decade at 25°C. For both cathodic and anodic reactions, the interfacial capacity results in 30—35 xF cm. This figure is consistent with a low surface coverage by chlorine atoms. 

In slurry systems, similar to fluidized beds, the overall rate of chemical transformation is governed by a series of reaction and mass-transfer steps that proceed simultaneously. Thus, we have mass transfer from the bubble phase to the gas-liquid interface, transport of the reactant into the bulk liquid and then to the catalyst, possible diffusion within the catalyst pore structure, adsorption and finally reaction. Then all of this goes the other way for product. Similar steps are to be considered for heat transfer, but because of small particle sizes and the heat capacity of the liquid phase, significant temperature gradients are not often encountered in slurry reactors. The most important factors in analysis and design are fluid holdups, interfacial area, bubble and catalyst particle sizes and size distribution, and the state of mixing of the liquid phase. ... 

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