Poisoning, homogeneous

When homogeneous poisoning occurs, since no reaction will be possible on the poisoned fraction ( , say, as shown in Fig. 3.11) of active surface it is reasonable to suppose that the intrinsic activity of the catalyst is in proportion to the fraction of active surface remaining unpoisoned. To find the ratio of activity of the poisoned catalyst to the activity of an unpoisoned catalyst one would compare the stationary flux of reactant to the particle surface in each case. For a first-order reaction... 

A fraction ( of the active surface of some porous slab-shaped catalyst pellets becomes poisoned. The pellets are used to catalyse a first-order isothermal chemical reaction. Find an expression for the ratio of the activity of the poisoned catalyst to the original activity of the unpoisoned catalyst when (a) homogeneous poisoning occurs, (b) selective poisoning occurs. 

They considered deactivation to occur by either pore-mouth (shell-progressive) or uniform (homogeneous) poisoning and examined the effect these types of deactivation had on overall activity and production rates for a single catalyst pellet. Analytical solutions were obtained for the production per pore by considering the time dependence of activity. Their results will be used here as the basis for the development of models for deactivation in fixed bed reactors. 

Corroaon products play a minor role and make up to about 1 percent of the total solid content of the HLW solution. If gadolinium is used as homogeneous poison for criticality control, it will significantly increase the total solid content of the waste. 

If the species giving rise to the poisoning reaction must make several collisions with the catalyst surface before adsorption can occur, these molecules will have a chance to diffuse deep into the catalyst pore structure before chemisorbing on the surface. Here deactivation of the catalyst will occur uniformly throughout the pore structure (homogeneous poisoning). If we denote the fraction of the surface that is poisoned by a, the fraction that is intrinsically capable of promoting reaction is equal to 1 - a. For a first-order reaction, the rate per unit surface area will then be k"(l - a)C. 

Criticality Cont> ol in Large Spent-Fuel Dissolvers Using Homogeneous Poison, Richard L. Brunnenmeyer (Bechtel-San Francisco)... 

According to the results of trend and serial correlation tests, a trend was noticed as interpreted from the convexity of the curve. The test for the serial correlation showed no correlation in general. Therefore, non-homogeneous Poison process it the best way for reliability analysis. In this research, the... 

Apart from the activation of a biphasic reaction by extraction of catalyst poisons as described above, an ionic liquid solvent can activate homogeneously dissolved transition metal complexes by chemical interaction. 

Mercury is a classical test to identify heterogeneous catalysts (bulk metal or colloids) due to its ability to poison metal(O) heterogeneous catalysts by formation of amalgam or adsorption on the metal surface [23]. If the catalytic activity remains unaffected when mercury is present, this fact represents an evidence for a homogeneous catalyst. But mercury can induce side reactions [23c] and also react with some molecular complexes [23c,24]. Consequently, the results obtained with mercury are not enough to conclude about the catalyst nature. From a practical point of view, it is important to use a large excess of Hg(0) with respect to the catalyst to favour the contact with it. 

An elegant complementary test to mercury poison is the use of dienes as selective poisons for homogeneous catalysts, due to their strong coordination to metal centres yielding inert catalytic complexes. In addition, their interaction with metal surfaces is weak. If the presence of diene (dienemetal =1 1) inhibits the catalytic process and Hg test does not, homogeneity can be strongly supported. 

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