Enormous Passivation Effect of Surrounding Zeolitic Framework on Pt Clusters for Catalytic Propane Dehydrogenation

Enclosing metal clusters into the inner of zeolite can enhance its catalytic performance due to the complex effects of the zeolitic environment surrounding them. Differently, here we report the enormous...

Seed- and solvent-free synthesis of ZSM-5 with tuneable Si/Al ratios for biomass hydrogenation

Seed- and solvent-free synthesis of MFI zeolites with tuneable Si/Al ratios (18-∞) was achieved. The key role of F− was evidenced that forming 6-coordinated “F–Al–O–Si” species drove the formation of the zeolitic framework during crystallization.

Fast room temperature lability of aluminosilicate zeolites

Aluminosilicate zeolites are traditionally used in high-temperature applications at low water vapour pressures where the zeolite framework is generally considered to be stable and static. Increasingly, zeolites are being considered for applications under milder aqueous conditions. However, it has not yet been established how neutral liquid water at mild conditions affects the stability of the zeolite framework. Here, we show that covalent bonds in the zeolite chabazite (CHA) are labile when in contact with neutral liquid water, which leads to partial but fully reversible hydrolysis without framework degradation. We present ab initio calculations that predict novel, energetically viable reaction mechanisms by which Al-O and Si-O bonds rapidly and reversibly break at 300 K. By means of solid-state NMR, we confirm this prediction, demonstrating that isotopic substitution of 17O in the zeolitic framework occurs at room temperature in less than one hour of contact with enriched water.

Introduction of Al into the HPM-1 Framework by In Situ Generated Seeds as an Alternative Methodology

An alternative method for the introduction of aluminum into the STW zeolitic framework is presented. HPM-1, a chiral STW zeolite with helical pores, was synthesized in the pure silica form, and an aluminum source was added by in situ generated seeds. Displacements of the peak positions in the Al samples were found in the X-ray diffractograms, indicating the possible incorporation of the heteroatom into the framework. Using an analysis of the 29Si and 27Al magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra, we concluded that the aluminum was effectively introduced into the framework. The (AlTETRAHEDRAL/AlOCTAHEDRAL) ratio and its textural properties were studied to explain the catalytic ethanol conversion results at medium temperatures. The sample with the lowest Si/Al ratio showed the best results due to its higher surface area and pore volume, in comparison to those observed for the sample with the highest Si/Al ratio, and due to its higher bulk tetrahedral aluminum content, in comparison to the intermediate Si/Al ratio sample. All catalysts were selective to ethylene and diethyl ether, confirming the presence of acidic sites.

Increasing the ion-exchange capacity of MFI zeolites by introducing Zn to aluminosilicate frameworks

Zn(ii) is incorporated into the zeolitic framework to improve the ion-exchange capacity of MFI zeolites beyond the aluminosilicates.