Views: 82 Author: Site Editor Publish Time: 2021-08-20 Origin: Site
Although the definition of catalyst is that the catalyst will not be consumed during the chemical reaction, the catalyst will maintain its original chemical state before and after the reaction and will continue to play a catalytic role.
However, in practice, catalysts cannot be used indefinitely and will be deactivated after repeated use because they will undergo a series of physical and chemical changes under certain temperature, pressure and chemical reactions, such as catalyst fragmentation, lattice deformation, changes in pore structure and specific surface area, loss of active components, covering of active sites and coking or carbon accumulation of reaction products on the surface.
Catalytic stability refers to the change of catalyst activity and selectivity over time and can be used to measure the ability of catalysts to maintain activity and selectivity, often using parameters such as service life, number of cycles, thermal decomposition temperature, acid and base resistance and mechanical strength.
The catalyst life is defined as the time to maintain a certain activity level under service conditions (one-way life) or the cumulative time to return to the required activity level after each activity drop by regeneration (total life); life is a general description of the stability of a catalyst. Testing the activity and selectivity of a catalyst takes little time, while understanding its stability takes a great deal of time.
① Chemical stability: the chemical composition and chemical state of the catalyst is stable during the catalytic process, and the active components and additives do not react or are lost. Of course, for a specific catalytic environment, the catalyst is required to be resistant to alkalis, acids or strong oxidizing properties, etc.
② Heat resistance stability: the catalyst does not undergo changes such as sintering, microcrystalline growth and crystalline phase transformation during the catalytic process; a good catalyst should be able to have a certain level of activity under high temperature and harsh reaction conditions for a long time.
Most catalysts have a limit temperature for use, beyond which the activity decreases or even deactivates completely. The thermal stability of a catalyst is measured by gradually increasing the operating temperature and recording how high the catalyst can endure and how long it can maintain the same activity, the higher and longer the thermal temperature, the longer the life of the catalyst.
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