Effects of Ethene Pressure on the Deactivation of Ni‐Zeolites During Ethene Oligomerization at Sub‐ambient Temperatures

Abstract

AbstractNi 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.