Reactions of Propene on Zeolite HY Catalyst Studied by in Situ Variable-Temperature Solid-State Nuclear Magnetic Resonance Spectroscopy

Article abstract of DOI:10.1021/ja00188a016

The oligomerization reactions of propene on zeolite catalyst HY have been studied in detail by in situ variable-temperature ¹³C solid-state NMR with cross polarization (CP) and magic-angle spinning (MAS).Propene is shown to be highly mobile in the zeolite at temperature far below the onset of chemical reactivity.Alkoxy species formed between protonated alkenes and zeolite framework oxygens are found to be important long-lived intermediates in the reactions.Simple secondary or tertiary carbocations either do not exist as free ions in the zeolite at low temperature or are so transient that they are not detected by NMR even at temperatures as low as 163 K.There is, however, evidence for long-lived alkyl-substituted cyclopentenyl carbocations, which are formed as free ions in the zeolite at room temperature.These carbocations do not form until all of the propene is consumed and hence do not play a significant role in the oligomerization reactions.A detailed reaction mechanism is proposed to account for all of the experimental observations.Novel experimental techniques are introduced which will be applicable to the study of many highly reactive catalyst/adsorbate systems.