Post-synthesis incorporation of Al into germanosilicate ITH zeolites : the influence of treatment conditions on the acidic properties and catalytic behavior in tetrahydropyranylation

M. S. thanks the Czech Science Foundation for support through the project 14-30898P. M. O. acknowledges the Czech Science Foundation for the project 13-17593P. R. E. M. thanks the EPSRC for funding (EP/K025112/1 and EP/L014475/1).Post-synthesis alumination of germanosilicate medium-pore ITH zeolites was shown to be an effective procedure for tuning their acidity. Treatment of ITH zeolites synthesized with different chemical compositions (i.e. Si/Ge = 2.5, 4.4 and 5.8) with aqueous Al(NO3)3 solution led to the formation of strong Brønsted and Lewis acid sites and an increasing fraction of ultramicro- and meso-pores in Ge-rich ITH samples (Si/Ge = 2.5 and 4.4). The concentration of Al incorporated into the framework increases with decreasing Si/Ge ratio of the parent ITH. The increasing temperature of alumination from 80 to 175 °C (HT conditions) resulted in (1) a 1.5-2-fold increase in the concentration of Brønsted acid sites formed and (2) a decreasing fraction of framework Al atoms detectable with base probe molecules (i.e. pyridine, 2,6-di-tert-butylpyridine), i.e. an increased concentration of the "inner" acid sites. The activity of prepared Al-substituted ITH zeolites in tetrahydropyranylation of alcohols is enhanced with increasing amount of accessible acid sites in bulky crystals (e.g. alumination at lower temperature) or with increasing total concentration of acid centres within tiny ITH crystals (e.g. alumination under HT conditions). This trend became more prominent with increasing kinetic diameter of the substrate molecules under investigation (methanol <1-propanol <1-hexanol).PostprintPeer reviewe

Annulation of phenols: Catalytic behavior of conventional and 2D zeolites

Catalytic behavior of MFI zeolites differing in thickness of nanosheets and ordering was studied in annulation of phenols, and compared with 3D zeolites BEA and MFI containing large or medium pores as well as with micro/mesoporous zeolite USY. The highest conversions of phenols studied were achieved over ordered hexagonally mesostructured zeolite with 1.7 nm wall size, followed by materials possessing 2.1 and 2.7 nm of nanosheets thickness. This corresponds to decreasing surface area of materials studied. The preferences of materials with zeolitic layers and high surface areas over bulky zeolites BEA and especially MFI in annulation of phenols is more prominent for substrates with larger kinetic diameters [phenol(0.66 nm)<1-naphthol (0.80 nm)<2-naphthol (0.89 nm)]. USY zeolite exhibited higher conversions (32, 6, 25% for phenol, 1-and 2-naphthol, respectively, after 300 min time on stream) than BEA (23, 6, 8%) and MFI (13, 0, 0%) not overcoming hexagonally mesostructured MFI (45, 36, 55%).115161sciescopu

Mesoporous MFI Zeolite Nanosponge as a High-Performance Catalyst in the Pechmann Condensation Reaction

A zeolite nanosponge possessing MFI framework type was hydrothermally prepared by a seed-assisted synthesis method using C22H45-N+(CH3)2-C6H12-N+(CH3)2-C6H13 as a structure-directing agent. The nanosponge morphology was composed of a three-dimensional disordered network of MFI nanolayers with 2.5 nm thickness supporting each other. Catalytic performance of the MFI nanosponge was investigated in the Pechmann condensation of bulky reactants (pyrogallol and resorcinol) with ethyl acetoacetate and compared with conventional zeolites MFI, BEA, and USY) and also layered MFI, pillared MFI, and self-pillared MFI. The investigation revealed outstanding catalytic performance of the MFI nanosponge, which can be attributed to the contribution of strong acid sites located on the external surfaces accessible for the reaction of bulky reactants. (Chemical Equation Presented). © 2015 American Chemical Society129331sciescopu