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Dynamics of Copper-Containing Porous Organic Framework Catalysts Reveal Catalytic Behavior Controlled by the Polymer Structure
journal contribution
posted on 2020-08-07, 15:36 authored by Zhenwei Wu, Xu Zhang, Emmett D. Goodman, Weixin Huang, Andrew R. Riscoe, Sara Yacob, Matteo CargnelloThe structure of
enzyme catalytic centers often guides the synthesis
of heterogeneous catalysts. These structures are dynamic and provide
changes in the chemical environment and redox state of transition
metal centers that result in drastic changes in the catalytic behavior.
Inspired by these catalytic traits, porous polymers represent a versatile
platform for preparing catalysts by anchoring metals to organic functional
groups. Following this inspiration, we studied the structural evolution
of a series of catalysts containing atomically dispersed Cu ions grafted
onto imine-linked porous organic frameworks (IPOFs) during synthesis
and reaction. Cu species were found to be bound to the imine or diiminopyridine
units of IPOFs and to be active for oxidation of carbon monoxide.
Combining X-ray photoelectron spectroscopy (XPS) and in situ X-ray
absorption spectroscopy (XAS) showed that the metal centers could
gradually activate oxygen and change their oxidation state. Interestingly,
depending on the type of functional group responsible for binding
Cu, the active sites either reach a balanced redox turnover between
Cu(I) and Cu(II) states or get poisoned by CO and locked at a Cu(I)
state during reaction. Furthermore, samples with agglomerated Cu species
were found to be redispersed upon contact with the reaction mixture,
which promoted a high initial activity not seen in the original samples.
Overall, our results show that catalytic sites in porous polymers
can have very dynamic structures that are highly dependent on the
polymer functional groups as well as reaction conditions and show
how this strategy can be used to produce active catalysts with a wide
range of possible compositions and chemistries.
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results showredox stateredox turnoverXASPolymer Structurecarbon monoxideXPStransition metal centersdiiminopyridine unitsIPOFreaction mixtureagglomerated Cu speciesbinding CuCopper-Containing Porous Organic Fr...COchemical environmentcatalystCu speciesCu ionspolymerreaction conditionsX-ray absorption spectroscopymetal centersX-ray photoelectron spectroscopyoxidation state
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