Catalytic applications and FTIR investigation of zeolite SSZ-33 after isomorphous substitution

• Borosilicate SSZ-33 was isomorphously substituted into Al, Fe and Ga form.
• Modified zeolites were studied by FTIR spectroscopy using different probe molecules.
• Acid strength of zeolites decreased in the series: [Al] > [Ga] > [Fe]-SSZ-33.
• Zeolites SSZ-33 were studied in toluene disproportionation and toluene alkylation.
• Toluene conversion decreased in the order Al > Ga > Fe-SSZ-33 in both tested reactions.

Zeolite SSZ-33 (topology: CON, borosilicate as-synthesized) contains access to the internal void spaces via 10- and 12-ring pores. Borosilicate SSZ-33 was transformed by isomorphous substitution to Al, Ga and Fe form. The acid sites of zeolite samples were investigated using infrared spectroscopy. The different probes (d3-acetonitrile, pivalonitrile, pyridine and 2,6-di-tert-butyl-pyridine) were used in this study. Brønsted acidity confirms the isomorphous substitution of B by Al, Ga and Fe in the SSZ-33 framework. It was found that the strength of Brønsted acid sites of zeolites under study decreased in the series: [Al]-SSZ-33 > [Ga]-SSZ-33 > [Fe]-SSZ-33. Upon adsorption of 2,6-di-tert-butyl-pyridine a part of Brønsted acid sites was not accessible (51% [Al]-SSZ-33, 76% [Ga]-SSZ-33 and 78% [Fe]-SSZ-33).The catalytic performance was studied in toluene disproportionation and toluene alkylation with isopropyl alcohol. Toluene conversions decreased in the order: [Al]-SSZ-33 > [Ga]-SSZ-33 > [Fe]-SSZ-33 in all tested reactions. Selectivities to sum of xylene isomers in toluene disproportionation was as follows: [Al]-SSZ-33 > [Ga]-SSZ-33 > [Fe]-SSZ-33. Zeolite [Al]-SSZ-33 and [Fe]-SSZ-33 exhibited the highest ratio xylene/benzene 0.75. In the case of toluene alkylation, the highest selectivities to cymenes were achieved over [Fe]-SSZ-33 and [Ga]-SSZ-33 at 200 °C. In the case of [Fe]-SSZ-33 almost no n-propyltoluene was found in the reaction mixture.

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