(403h) Modulation of Framework Al Distribution of Mse-Type Zeolite By Site-Selective Dealumination

MSE-type zeolites have 12-ring straight channels that intersect dual independent zigzag 10-ring channels as well as supercages (18×12-ring) that are accessible only through 10-ring windows¹⁾. There are two types of MSE-type zeolites which use the different organic structure-directing agent (OSDA); MCM-68²⁾ and UZM-35³⁾. We have reported on the clarification of the location of the acid sites in MSE-type zeolites based on ²⁷Al MQMAS NMR and in situ IR measurements; there is a marked difference in the distribution of the acid sites between MCM-68 and UZM-35⁴⁾. Meanwhile, post acid-treatment of zeolite leads to the “dealumination”, resulting in the change in the chemical composition of framework.

In this study, the post acid-treatment of MCM-68 and UZM-35 were conducted in order to clarify the impact of acid sites distribution on the dealumination behavior. Consequently, highly-selective dealumination of the Al atoms located at 12-ring in the MSE framework has successfully achieved. Finally, the catalytic properties of the post-modified zeolites were also evaluated.

Experimental

MCM-68 was hydrothermally synthesized using N,N,N’,N’-tetraethylbicyclo[2.2.2]oct-7-ene-2,3:5,6-dipyrrolidinium iodide, (TEBOP(I)₂) as an OSDA⁵⁾. UZM-35 was synthesized using dimethyldipropylammonium hydroxide (DMDPAOH, 40 wt%) as an OSDA according to the reports with a slight modification⁶⁾.

The post acid-treatment of MCM-68 and UZM-35 was carried out using nitric acid under reflux conditions. The number of Brønsted acid sites located at 12- and 10-ring in MSE-type zeolites was estimated by IR spectroscopy with pyridine (Py) and 2,6-di-tert-butylpyridine (DTBPy) as probe molecules.

Results and Discussion

From XRD patterns, the MSE-type phase was confirmed in the obtained MCM-68 and UZM-35. The number of Brønsted acid sites located at 12- and 10-ring in MSE-type zeolites were listed in Table1. From ICP-AES measurement, it was found that dealumination more easily happened in MCM-68 than UZM-35. It is good agreement with the variation of the number of Brønsted acid sites from FT-IR measurements. In UZM-35, acid sites at 10-ring were preferentially removed because it had more acid sites at 10-ring compared to 12-ring. However, the number of acid sites at 12-ring was largely decreased when the concentration of HNO₃ was increased from 0.2 to 1.0 M. The post acid-treatment of the as-made samples will be reported. Our findings would diversify the application of the MSE-type zeolites with unique Al dsirtibution.

Table 1 Acidic properties of MCM-68 and UZM-35

REFERENCES

[1] http://www.iza-structure.org/databases/

[2] D. C. Calabro, et al., U. S. Patent, 6049018 (2000).

[3] J. G. Moscoso and D. Y. Jan, U. S. Patent, 7922997 (2011).

[4] H. Toyoda, et al., Phys. Chem. Chem. Phys., 24 (2022) 4358.

[5] R. Otomo, et al., J. Phys. Chem. C., 122 (2018) 1180.

[6] J. Yin, et al., Micropor. Mesopor. Mater., 305 (2020) 110321.