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

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 Bronsted 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 degrees C (HT conditions) resulted in (1) a 1.5-2-fold increase in the concentration of Bronsted 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).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 aqueous5529732984Czech Science Foundation [14-30898P, 13-17593P

Annulation of phenols with methylbutenol over MOFs: The role of catalyst structure and acid strength in producing 2,2-dimethylbenzopyran derivatives

The catalytic behavior of metal-organic frameworks of different structures (Fe(BTC), MIL-100(Fe), MIL-100(Cr) and Cu-3(BTC)(2)) was investigated in annulation reaction between 2-methyl-3-buten-2-ol and phenols differing in size (phenol, 2-naphthol). MIL-100(Fe) possessing intermediate Lewis acidity, perfect crystalline structure, and the highest S-BET surface area showed the highest activity (TOF = 0.7 and 1.4h(-1) for phenol and 2-naphthol, respectively) and selectivities to target benzopyran (45% and 65% at 16% of phenol and 2-naphthol conversion, respectively). The increasing strength of Lewis acid centers for MIL-100(Cr) was found to result in the dramatically decreased activity of the catalyst, while negligible conversion of phenols was found over Fe(BTC), characterized by a less ordered framework.M.O. and J.C. acknowledge the Czech Science Foundation for the support (14-07101S) and RNDr. Libor Brabec, CSc. for SEM images.Shamzhy, MV.; Opanasenko, MV.; García Gómez, H.; Cejka, J. (2015). Annulation of phenols with methylbutenol over MOFs: The role of catalyst structure and acid strength in producing 2,2-dimethylbenzopyran derivatives. Microporous and Mesoporous Materials. 202:297-302. doi:10.1016/j.micromeso.2014.10.003S29730220

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

A zeolite nanosponge possessing <b>MFI</b> 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 <b>MFI</b> nanolayers with 2.5 nm thickness supporting each other. Catalytic performance of the <b>MFI</b> nanosponge was investigated in the Pechmann condensation of bulky reactants (pyrogallol and resorcinol) with ethyl acetoacetate and compared with conventional zeolites <b>MFI</b>, <b>BEA</b>, and USY) and also layered <b>MFI</b>, pillared <b>MFI</b>, and self-pillared <b>MFI</b>. The investigation revealed outstanding catalytic performance of the <b>MFI</b> nanosponge, which can be attributed to the contribution of strong acid sites located on the external surfaces accessible for the reaction of bulky reactants

Liquid metals for boosting stability of zeolite catalysts in the conversion of methanol to hydrocarbons

Methanol-to-hydrocarbons (MTH) process has been considered one of the most practical approaches for producing value-added products from methanol. However, the commonly used zeolite catalysts suffer from rapid deactivation due to coke deposition and require regular regeneration treatments. We demonstrate that low-melting-point metals, such as Ga, can effectively promote more stable methanol conversion in the MTH process by slowing coke deposition and facilitating the desorption of carbonaceous species from the zeolite. The ZSM-5 zeolite physically mixed with liquid gallium exhibited an enhanced lifetime in the MTH reaction, which increased by a factor of up to ~14 as compared to the parent ZSM-5. These results suggest an alternative route to the design and preparation of deactivation-resistant zeolite catalysts