Influence of alkali cations on the inter-conversion of extra-framework aluminium species in dealuminated zeolites

• Poisoning Na+ effect is the consequence of its activity as of Lewis acid.
• Na+ cation changes the activation energy of the EFAL reactions.
• The barrier variation depends on the oxygen atom type to be coordinated.
• The concert mechanism for the limiting stage of the EFAL transformation.

The common main factor of the Na+ influence on the extra-framework aluminum (EFAL) transformations was observed while modeling partly hydrated zeolites at both periodic and cluster computational levels. It can be characterized as the attack of Lewis acid (Na+) toward electron pairs of different O atoms. The limiting step of EFAL formation is assigned to the transformation between the AlOH2+ and Al(OH)2+ species. It allows the explanation of the poisoning effect of Na+ on the cracking reactions known experimentally. The role of electrostatic factor is also discussed.

The concert mechanism for proton and Na+ exchange for the explanation of Na+ effect at the limiting stage of the EFAL transformation.Figure optionsDownload as PowerPoint slide