NMR studies of the sorption of p-xylene, toluene, and benzene on ZSM5 zeolite

Journal Article · Thu Oct 19 00:00:00 EDT 1989 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100358a034· OSTI ID:6825283

Kustanovich, I; Vieth, H M; Luz, Z; Vega, S ^[1]

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1. Weizmann Institute of Science, Rehovot (Israel)

Deuterium NMR results of p-xylene-d{sub 6}, toluene-d{sub 3}, and benzene-d{sub 6} as well as proton MASS of p-xylene-d{sub 6} and -d{sub 4} sorbed in H-ZSM5 are reported. The analysis of the results shows that below room temperature the sorbed p-xylene molecules undergo at most reorientation about their para axis. When samples are heated above room temperature, an increasing fraction of the molecules become mobile and unlike in Na-ZSM5 a significant fraction undergoes rapid three-site jumps between intersecting channel segments. This reflects the much weaker hindering effect that H{sup +} ions have on the diffusion of the guest molecules compared with the larger sodium ions. Toluene behaves similar to p-xylene, but the appearance of the dynamic species starts at significantly lower temperatures. Sorbed benzene molecules in both Na- and H-ZSM5 undergo fast reorientation about their C{sub 6} axes even at the lowest temperature studied ({minus}120{degree}C). Above {minus}60{degree}C, new species appear in which the benzene C{sub 6} axes undergo fast but restricted local reorientation. No direct evidence for fast three-dimensional diffusion of the guest molecules within the zeolite channels was obtained, but this process cannot be ruled out for the species undergoing fast three-site jumps. Heating a sample of sorbed p-xylene in H-ZSM5 to above 100{degree}C results in a structural change in the zeolite framework and concomitantly a change in the distribution of the guest molecules toward more mobile species. Above room temperature, exchange between the aromatic hydrogens of p-xylene and the hydrogens in the zeolite framework takes place.

• OSTI ID: 6825283
• Journal Information: Journal of Physical Chemistry; (USA), Vol. 93:21; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BENZENE
SORPTIVE PROPERTIES
TOLUENE
XYLENES
DATA ANALYSIS
DEUTERATION
EXPERIMENTAL DATA
MEASURING INSTRUMENTS
MEASURING METHODS
NUCLEAR MAGNETIC RESONANCE
ALKYLATED AROMATICS
AROMATICS
CHEMICAL REACTIONS
DATA
HYDROCARBONS
INFORMATION
MAGNETIC RESONANCE
NUMERICAL DATA
ORGANIC COMPOUNDS
RESONANCE
SURFACE PROPERTIES
400201* - Chemical & Physicochemical Properties