Synthesis, characterization, and catalytic properties of H-Al-YNU-1 and H-Al-MWW with different Si/Al ratios

摘要

H-Al-MWW with different Si/Al ratios has been synthesized in the presence of hexamethyleneimine by the postsynthesis method with the ion-exchange of Na~+ with NH_4~+ unnecessary. However, irrespective of the framework Si/Al ratio, the as-synthesized Al-MWW lamellar precursor was not transformed into the Al-YNU-1 phase by the method used for preparing Ti-YNU-1 [W. Fan, P. Wu, S. Namaba, T. Tatsumi, Angew. Chem. Int. Ed. 43 (2004) 236]. This may be due to the difficulty in removing hardly oxidized hexamethyleneimine molecules by acid treatment, as shown by TG/DTA measurement results. In combination with ~(13)C CP/MAS NMR spectroscopy, it was indicated that these hardly oxidized hexamethyleneimine molecules might strongly interact with the zeolite framework or be tightly constrained between the layers. Nevertheless such a type of templating molecules could be washed away by acid when piperidine was used as a template. As a result, H-Al-YNU-1 with a pore opening intermediate between those of H-Al-MOR and H-Al-Beta was successfully prepared in the way adopted for preparing Ti-YNU-1. This material showed much higher activity than H-USY, H-Al-MOR, H-Al-Beta, H-Al-MWW, H-Al-ZSM-5, and interlayer-expanded H-Al-MWW through silylation in alkylation of anisole with benzyl alcohol and acylation of anisole with acetic anhydride as a result of its enlarged pore opening connected to supercages and predominant moderately strong Br?nsted acid sites. The benefit of the large pore opening of H-Al-YNU-1 was also confirmed by the catalytic results obtained in the Baeyer-Villiger reaction of cyclohexanone with bulkiness corresponding to 12 membered-ring pore openings.