Catalytic cracking catalyst
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Why does the coking degree of catalytic cracking catalysts decrease upon the addition of rare earths?
Rare earths play many roles in cracking catalysts. Firstly, rare earths, as cocatalyst materials, can enhance the activity and thermal stability of zeolite catalysts. Secondly, once the catalyst becomes deactivated due to prolonged use, it must be regenerated through high-temperature hydrothermal treatment to burn off the increasing amount of carbon that fills the active pores of the zeolite; rare earth elements possess good hydrothermal stability and play an important role in this process. Furthermore, the use of rare earth zeolite catalysts in petroleum catalytic cracking offers many advantages, including large processing capacity, high yield of light oils, good quality, high activity, low coking rate, low catalyst loss, and good selectivity.
For catalysts, rare earth elements are generally introduced through rare earth molecular sieves. The higher its content, the better the catalyst activity, but the coking rate also tends to be higher. How can the degree of coking be reduced? I don’t understand some of it.
The characteristic reactions of catalytic cracking catalysts include cracking, hydrogen transfer, and condensation reactions; however, coke is generated as a result of the condensation and hydrogen transfer reactions. Since rare earths can increase the activity of molecular sieves, this may also lead to an increase in coking activity, thereby reducing the catalyst’s activity. At the same time, rare earths can also enhance the thermal stability of catalysts, allowing them to maintain better activity during high-temperature hydrothermal treatment to remove carbon deposits.
Rare earths can enhance the acidity of catalysts, right?
It has a high rare earth content, resulting in good stability of the zeolite; however, its activity and selectivity are poor, and the coke yield is relatively high. During the preparation of zeolites, it is important to control and adjust the appropriate RE/H ratio as a key method to improve catalyst activity and selectivity.