Acid catalytic function of mesopore walls generated by MFI zeolite desilication in comparison with external surfaces of MFI zeolite nanosheet

Abstract

Mesopores with zeolite walls were generated through desilication of bulk crystals of MFI zeolite in a NaOHsolution in the presence or absence of cetyltrimethylammonium surfactant, as reported in the literature.Catalytic functions of the Brønsted acid sites existing on the mesopore walls were evaluated in comparisonwith external surfaces of 2.5-nm thick MFI zeolite nanosheets, which were hydrothermally synthesizedusing a meso-micro dual structure-directing surfactant. Acid sites were characterized with respect to thestrength and concentration by31P NMR signals of adsorbed tributylphosphine oxide. Catalytic functionswere evaluated for decalin cracking, and acetal formation of benzaldehyde with pentaerythritol. Theresult from desilication was quite sensitive to the particle diameters of the initial zeolite samples. In ourbest case of desilication, the mesopore walls exhibited similar catalytic activity for the acetal formationto the external surfaces of MFI nanosheets. In contrast to the condensation reaction occurring at mild ormoderate acid sites, the result for decalin cracking requiring strong acid sites indicated that the desilicatedzeolite corresponded to about 60% of the MFI nanosheets.