Fine-Tuning the Activity of Metal–Organic Framework-Supported Cobalt Catalysts for the Oxidative Dehydrogenation of Propane

Abstract

Few-atom cobalt-oxide clusters, when dispersed on a Zr-based metal-organic framework (MOF) NU-1000, have been shown to be active for the oxidative dehydrogenation (ODH) of propane at low temperatures (<230 °C), affording a selective and stable propene production catalyst. In our current work, a series of promoter ions with varying Lewis acidity, including Ni(II), Zn(II), Al(III), Ti(IV) and Mo(VI), are anchored as metal-oxide,hydroxide clusters to NU-1000 followed by Co(II) ion deposition, yielding a series of NU-1000-supported bimetallic-oxo,hydroxo,aqua clusters. Using difference envelope density (DED) analyses, the spatial locations of the promoter ions and catalytic cobalt ions are determined. For all samples, the promoter ions are sited between pairs of Zr nodes along the MOF c-axis, whereas the location of the cobalt ions varies with the promoter ions. These NU-1000-supported bimetallic-oxide clusters are active for propane ODH after thermal activation under O to open a cobalt coordination site and to oxidize Co(II) to Co(III), as evidenced by operando X-ray absorption spectroscopy at the Co K-edge. In accord with the decreasing Lewis acidity of the promoter ion, catalytic activity increases in the following order: Mo(VI) < Ti(IV) < Al(III) < Zn(II) < Ni(II). The finding is attributed to increasing ease of formation of Co(III)-O species and stabilization of a cobalt(III)-oxyl/propane transition state as the Lewis acidity of the promoter ions decreases. The results point to an increasing ability to fine-tune the structure-dependent activity of MOF-supported heterogeneous catalysts. Coupled with mechanistic studies-computational or experimental-this ability may translate into informed prediction of improved catalysts for propane ODH and other chemical reactions.

Hybridization of Pd Nanoparticles with UiO‐66(Hf) Metal‐Organic Framework and the Effect of Nanostructure on the Catalytic Properties

“…MOF-MNP hybrids with diverse nanostructures with MNPs on the surfaceo fM OF [5] and/or inside pores were realized depending on the synthesis procedures( solution impregnation, [6] solid grinding, [7] chemical vapor deposition [8] etc.) adopted.…”

Metal‐Organic Frameworks as Platform for Lewis‐Acid‐Catalyzed Organic Transformations

“…The same group carried out further study on the previously synthesized Co‐SIM+NU‐1000 ( 35 ) to increase its catalytic efficiency and scope, by incorporating it with a range of inorganic catalytic promoter‐oxy clusters of Ni II , Zn II , Al III , Ti IV , and Mo VI . The finding of the group established that weakly Lewis acidic promoters can accelerate the cobalt‐mediated propane ODH, while strongly acidic metal oxides slow down the reaction.…”

Single‐Site, Single‐Metal‐Atom, Heterogeneous Electrocatalyst: Metal–Organic‐Framework Supported Molybdenum Sulfide for Redox Mediator‐Assisted Hydrogen Evolution Reaction

“…The node of the parent framework presents labile protons in the form of ligated hydroxo and aqua groups . The protons are readily displaceable upon introducing reactive metal precursors (molecular complexes) either through a vapor‐phase (in an atomic layer deposition‐like process) or condensed‐phase reaction …”