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← ScienceWhich phenomenon causes decreased catalytic activity in zeolites with high aluminum content used in catalytic cracking?
A)Framework dealumination during thermal treatment
B)Increased Brønsted acidity leading to coking
C)Formation of extra-framework aluminum species✓
D)Reduced hydrophobicity hindering reactant access
💡 Explanation
When zeolites have high aluminum content, the isomorphic substitution of Si with Al creates charge imbalance, promoting formation of extra-framework aluminum species (EFAL) during reaction because EFAL lowers the catalytic activity. Therefore, EFAL formation decreases activity rather than dealumination, coking, or hydrophobicity changes, which have distinct conditions.
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