Oxygen-18 exchange between zeolite ZSM-5 and water

Nature and Topology of Metal–Oxygen Binding Sites in Zeolite Materials:17O High‐Resolution EPR Spectroscopy of Metal‐Loaded ZSM‐5

“…From the relative abundances of these three isotopomers, deduced by the simulation analysis, we estimate a local enrichment level of approximately 70 % (Supporting Information, Figure S5). Such a high level of enrichment under the adopted mild conditions reflects the high reactivity of the Al‐O‐Si bridging oxygens, in line with 18 O exchange experiments . Importantly, the presence of an 11‐line pattern demonstrates that two equivalent oxygen nuclei are interacting with the unpaired electron of Zn + , pointing to a situation where the metal cation is bound to two oxygen anions with a pseudo‐ C 2 v local symmetry.…”

“…Since the framework substitution of 16 O by 17 O relies on a mild steaming (120 °C for 2 h, in presence of H 2 17 O vapors), IR spectroscopy of adsorbed pyridine was used to verify that no dealumination of the framework occurs under these conditions (see Section S3 in the Supporting Information). It should be noted that 17 O isotopic enrichment can be extremely costly; however, for EPR purposes cost‐ and atom‐efficient protocols such that described can be used, exploiting the ready exchange of lattice oxide ions with the oxygen of adsorbed H 2 O, while keeping the highly crystalline frameworks . Experimental and computational details are provided in the Supporting Information (Section S2).…”

Violations of Löwenstein's rule in zeolites

“…The first is to use water, which has been shown to facilitate the making and breaking of –Si–O–Si– and –Al–O–Si–. 44 Long-term steeping of H-SSZ-13 in water could be expected to lead to the redistribution of Al in the framework, yielding –Al–O–Al– as the thermodynamically preferred arrangement. Potentially, very slightly acidic or basic water might enhance the rate of rearrangement without dealumination or desilication of the zeolite framework.…”

Catalytic fast pyrolysis of biomass: the reactions of water and aromatic intermediates produces phenols

“…72 It was shown that the oxygen in both Si-O-Al and Si-O-Si bridges of the zeolite was exchanged with oxygen from 18 O-labeled water. In this case, the oxygen in water will exchange with the framework oxygen as reported in a previous study.…”