Deactivators of catalysts

Thermal Degradation and Sintering Thermally iaduced deactivation of catalysts may result from redispersion, ie, loss of catalytic surface area because of crystal growth ia the catalyst phase (21,24,33) or from sintering, ie, loss of catalyst-support area because of support coUapse (18). Sintering processes generally take... 

Deactivation of catalysts is an important and complex phenomenon, which can have many causes. It can be kept to a minimum by carefully purifying the feed and by keeping process conditions optimal, which often implies a temperature as low as possible. 

For some processes, though they would not be classified as batch processes, the period of continuous production will be limited by gradual changes in process conditions such as, the deactivation of catalysts or the fouling of heat-exchange surfaces. Production will be lost during the periods when the plant is shut down for catalyst renewal or equipment clean-up, and, as with batch process, there will be an optimum cycle time to give the minimum production cost. 

However, it should not necessarily be concluded that the reactor should be operated at low temperature, as the rate of reaction has yet to be considered. Also, catalysts and the deactivation of catalysts have yet to be considered. 

Carbon Deposition. The processing of hydrocarbons always has the potential to form coke (soot). If the fuel processor is not properly designed or operated, coking is likely to occur. Carbon deposition not only represents a loss of carbon for the reaction but more importantly also results in deactivation of catalysts in the processor and the fuel cell, due to deposition at the active sites. 

Hydrothermal Deactivation of Catalyst Impregnated with Different Levels of Metal... 

Deactivation of catalysts in the reforming of liquid fuels is caused principally by two processes the formation of carbon-containing deposits and sulfur poisoning. This section examines the thermodynamics and the literature dealing with these processes. 

Reaction Studies. There have been a significant number of studies on the deactivation of catalysts in the reforming of liquid fuels, especially the formation of elemental carbon and coke. Collectively, these studies show that the... 

MAS NMR experiments characterizing catalysts in reaction environments in flow systems may be carried out under conditions close to those of industrial processes. The formation of catalytically active surface species and the cause of the deactivation of catalysts can be characterized best under flow conditions. When flow techniques are used for the investigation of reactions under steady-state conditions, a continuous formation and transformation of intermediates occurs. The lifetime of the species under study must be of the order of the length of the free-induction decay, which is ca. 100 ms for " C MAS NMR spectroscopy. 

In Section V, deactivation of catalyst pellets and reactor beds during residuum hydroprocessing is considered. The chemical nature of the metal deposits is described, including a discussion of the physical distribution of these poisons in aged catalysts and reactor beds. Models to predict... 

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