Metal–Organic Framework Supported Cobalt Catalysts for the Oxidative Dehydrogenation of Propane at Low Temperature

Abstract

Zr-based metal–organic frameworks (MOFs) have been shown to be excellent catalyst supports in heterogeneous catalysis due to their exceptional stability. Additionally, their crystalline nature affords the opportunity for molecular level characterization of both the support and the catalytically active site, facilitating mechanistic investigations of the catalytic process. We describe herein the installation of Co(II) ions to the Zr6 nodes of the mesoporous MOF, NU-1000, via two distinct routes, namely, solvothermal deposition in a MOF (SIM) and atomic layer deposition in a MOF (AIM), denoted as Co-SIM+NU-1000 and Co-AIM+NU-1000, respectively. The location of the deposited Co species in the two materials is determined via difference envelope density (DED) analysis. Upon activation in a flow of O2 at 230 °C, both materials catalyze the oxidative dehydrogenation (ODH) of propane to propene under mild conditions. Catalytic activity as well as propene selectivity of these two catalysts, however, is different under the same experimental conditions due to differences in the Co species generated in these two materials upon activation as observed by in situ X-ray absorption spectroscopy. A potential reaction mechanism for the propane ODH process catalyzed by Co-SIM+NU-1000 is proposed, yielding a low activation energy barrier which is in accord with the observed catalytic activity at low temperature.

Stabilizing a Vanadium Oxide Catalyst by Supporting on a Metal–Organic Framework

“…Metalation of Zr‐MOFs was recently achieved by a number of techniques, including vapor‐phase metalation by atomic layer deposition in MOFs (AIM) and an analogous condensed‐phase metalation by solvothermal deposition in MOFs (SIM) ,…”

“…NU‐1000, a Zr‐based MOF consisting of Zr 6 (μ 3 ‐O) 4 (μ 3 ‐OH) 4 (H 2 O) 4 (OH) 4 nodes and 1,3,6,8‐( p ‐benzoate)pyrene (TBAPy) linkers (Figure ), has proven to be an excellent support for metal‐oxide catalysts –. In addition, the 31 Å diameter mesopores enable efficient and homogeneous metalation on the zirconium nodes and also facilitate diffusive transport of substrates within the MOF crystallites during heterogeneous catalysis .…”

“…V‐NU‐1000 was prepared by a solution‐phase reaction (i.e., SIM),, in which tetrakis(dimethylamido)vanadium (TDMAV) reacts with the hydroxy functional groups available on the zirconium nodes of NU‐1000 with subsequent release of dimethylamine. To confirm the identity of the reaction site, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS, see Figure S2 in the Supporting Information) was used to monitor the bands characteristic of the v (OH) and v (μ 3 ‐OH) ( =3674 cm −1 ) stretches before and after metalation.…”

“…The highest achievable vanadium loading (i.e., after prolonged exposure to TDMAV solution) was found to be 3.7±0.2 V/Zr 6 , as determined by inductively coupled plasma optical emission spectroscopy (ICP‐OES). This number is consistent with the deposition of other metals by using a similar precursor, whereas a smaller and more reactive precursor can lead up to 8 V per Zr 6 . The powder X‐ray diffraction (PXRD) (Figure ) data of V‐NU‐1000 confirms that the crystallinity characteristics of NU‐1000 are retained after metalation.…”

Size effect of the active sites in UiO-66-supported nickel catalysts synthesized via atomic layer deposition for ethylene hydrogenation

“…15 The decoration can be accomplished via A LD i n M OFs (AIM) 16–18 or s olvothermal deposition i n M OFs (SIM) 19–22 —as well as by AIM and SIM in combination. 23 Depending, of course, on their specific chemical composition, the resulting MOF-supported clusters or single metal ions can be rendered competent for photocatalytic H 2 generation, 24 electrocatalytic O 2 production, 25 solution-phase alkene epoxidation, 26, 27 and gas-phase ethylene hydrogenation and oligomerization, 13, 21, 28 hexene polymerization, 20 and propane oxidative dehydrogenation, 29 among other reactions. 22, 30 …”