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Cite This: ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Highly Selective Acetylene Semihydrogenation Catalyzed by Cu Nanoparticles Supported in a Metal−Organic Framework Louis R. Redfern,† Zhanyong Li,† Xuan Zhang,† and Omar K. Farha*,†,‡ †
Department of Chemistry and International Institute of Nanotechnology, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States ‡ Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia
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S Supporting Information *
ABSTRACT: We describe herein the highly selective semihydrogenation of acetylene to ethylene using a Zr-based metal−organic framework (MOF; NU1000) with Cu−oxo clusters present on the nodes as precatalysts. The active form of the catalyst is MOF-supported Cu nanoparticles generated in situ upon a brief H2 reduction treatment at 200 °C. This composite material is stable for many catalytic cycles and effectively avoids overreduction to ethane, a common problem for many semihydrogenation catalysts.
KEYWORDS: semihydrogenation, Cu nanoparticle, metal−organic framework, catalysis, composite materials
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potential in developing supported catalysts because of their highly tunable nature and porosity.15−19 In addition to the built-in functionalities incorporated from de novosynthesis, postsynthetic modifications can impart various properties to these materials.20−22 Because of their high thermal and chemical stability,23 Zr-based MOFs can be subjected to harsh experimental conditions and reactive chemicals (such as water and hydrogen sulfide), allowing a variety of metal oxide24 or sulfide25 clusters to be anchored to the Zr6 nodes via atomic layer deposition or solvothermal impregnation.26 The crystallinity of MOFs enables the use of a suite of characterization techniques to elucidate the structure of the anchored species,27 while their robust stability and tremendous porosity lends them well to applications requiring exposure to water vapor, air, and other gases at a wide range of temperatures.28 One such Zr-based MOF, NU-1000, is a mesoporous material consisting of Zr6(μ3-O)4(μ3-OH)4(H2O)4(OH)4 nodes and tetratopic 1,3,6,8-tetrakis(p-benzoate)pyrene (TBAPy4−) linkers. Upon metalation with Cu(dmap)2 [dmap = (dimethylamino)-2-propoxide], Cu−oxo clusters are uniformly anchored to the Zr6 node of NU-1000 in high density. Following mild reduction in a flow of H2, Cu nanoparticles form inside the pores of NU-1000, resulting in a composite material (CuNPs@NU-1000) that has been extensively characterized using difference envelope density, pair distribution function (PDF) analysis, and X-ray photoelectron
olyethylene production for thermoplastics is the secondlargest downstream chemical process worldwide.1 These industrial polymerization reactions utilize Ziegler−Natta catalysts that are extremely sensitive to poisoning by alkynes. Therefore, acetylene contamination in ethylene from upstream processes must be removed prior to the polymerization process. In lieu of costly distillations to purify the mixture, conversion of acetylene to ethylene through semihydrogenationthat is, the partial reduction of an alkyne to an alkene is an attractive approach because it removes the contaminant while simultaneously producing more of the desired compound. However, exquisite catalyst selectivity is required to prevent the overreduction of acetylene and undesired consumption of ethylene in this process. Materials consisting of transition-metal active sites (Fe and Ni) or noble-metal catalysts such as Pd with Au, Ag, or Ga dopants to attenuate the reactivity and improve the selectivity have been developed for this purpose;2−5 however, overreduction remains problematic, with ∼10% ethane production typical for industrial catalysts and conditions.6 With higher earth abundancy than precious metal catalysts, supported Cu catalysts have garnered increasing attention for many applications where the activity and product selectivity can be finely tuned via active-site size modulation.7−10 Notably, Cu surfaces have demonstrated a propensity to interact strongly with acetylene gas,11 with recent computational support for the importance of the metal cluster size on the reactivity of Cu catalysts.12,13 Metal−organic frameworks (MOFs), hybrid materials composed of inorganic nodes linked via organic ligands forming 2D and 3D extended structures,14 exhibit great © XXXX American Chemical Society
Received: August 9, 2018 Accepted: September 11, 2018
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DOI: 10.1021/acsanm.8b01397 ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
Letter
ACS Applied Nano Materials
Figure 1. Installation of Cu−oxo clusters in NU-1000, followed by mild reduction, yielding Cu nanoparticles with diameters of ∼4 and
