Effects of Ethene Pressure on the Deactivation of Ni‐Zeolites During Ethene Oligomerization at Sub‐ambient Temperatures. Issue 1 (29th November 2021)

• Record Type: Journal Article
• Authors: Caulkins, Richard; Joshi, Ravi; Gounder, Rajamani; Ribeiro, Fabio H.
• Is Part Of: ChemCatChem. Volume 14:Issue 1(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-11-29
• Subjects: capillary condensation -- deactivation -- nickel -- oligomerization -- zeolites; Catalysis -- Periodicals; 541.39505
• DOI: 10.1002/cctc.202101478
• Languages: English
• ISSNs: 1867-3880

Abstract

Abstract: Ni cation sites exchanged onto microporous materials catalyze ethene oligomerization to butenes and heavier oligomers but also undergo rapid deactivation. The use of mesoporous supports has been reported previously to alleviate deactivation in regimes of high ethene pressures and low temperatures that cause capillary condensation of ethene within mesoporous voids. Here, we reproduce these prior findings on mesoporous Ni‐MCM‐41 and report that, in sharp contrast, reaction conditions that nominally correspond to ethene capillary condensation in microporous Ni‐Beta or Ni‐FAU zeolites do not mitigate deactivation, likely because confinement within microporous voids restricts the formation of condensed phases of ethene that are effective at solvating and desorbing heavier intermediates that are precursors to deactivation. Deactivation rates are found to transition from a first‐order to a second‐order dependence on Ni site density in Ni‐FAU zeolites with increasing ethene pressure, suggesting a transition in the dominant deactivation mechanism involving a single Ni site to one involving two Ni sites, reminiscent of the effects of increasing H2 pressure on changing the kinetic order of deactivation in our prior work on Ni‐Beta zeolites. Abstract : Capillary condensation of ethene within mesoporous materials has been shown previously to suppress deactivation during ethene oligomerization at sub‐ambient temperatures in Ni‐MCM‐41 via the solvation and removal of heavy hydrocarbons that are precursors to deactivation, but analogous reaction conditions do not confer analogous stability in microporous materials (Ni‐Beta, Ni‐FAU), likely because liquid‐like ethene phases are unable to form within the spatial constraints imposed by microporous voids.