Structural analysis of Cu/Zeolite with controlled Si/Al ratio and the resulting thermal stability

Cu-loaded zeolite (Cu/Zeolite or Cu/CHA) has been prepared from USY (SiO2/Al2O3 =30) through hydrothermal conversion using trimethyladamantylammonium ion (TMAda) as an organic structure directing agent. Simple control over the concentration of mineralizing agent in the hydrothermal synthesis from 0.2 to 0.6 with respect to SiO2, changed the Si/Al ratio in the resulting zeolite, CHA with a decrease of overall yield. The result of 29Si NMR and 27Na spectrum of the synthesis gel and mother liquor suggested the zeolite formation through hydrothermal conversion did not occur when the monomeric Si species was increased significantly while TMAdaOH can lead to the formation of CHA similar to the synthesis of conventional silica source. Still, the textural properties and crystallographic structure of the obtained CHA have remained the same but the fraction of the strong acidity was increased significantly with the increase of the Si/Al ratio. High silica CHA shows superior hydrothermal stability in selective catalytic reduction of NOx, consistent with the result of lattice optimization using General Utility Lattice program (GULP) with the core-shell potential. Further, the results of the molecular dynamics simulation using Car-Parrinello method indicated the rapid migration of proton in CHA with a low Si/ Al ratio while monovalent alkali metal ions stabilized near the double six membered rings, implying proton hopping can affect the stability of the zeolite.

Automated summary

Cu-loaded zeolite (Cu/Zeolite or Cu/CHA) was prepared using hydrothermal conversion with trimethyladamantylammonium ion (TMAda) as an organic structure directing agent. Control over the concentration of mineralizing agent resulted in changes to the Si/Al ratio in the resulting zeolite, and affected the formation process. High silica CHA showed superior hydrothermal stability in selective catalytic reduction of NOx.