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Multistep Engineering of Synergistic Catalysts in a Metal–Organic Framework for Tandem C–O Bond Cleavage
journal contribution
posted on 2020-02-28, 21:33 authored by Yang Song, Xuanyu Feng, Justin S. Chen, Carter Brzezinski, Ziwan Xu, Wenbin LinCleavage of strong
C–O bonds without breaking C–C/C–H
bonds is a key step for catalytic conversion of renewable biomass
to hydrocarbon feedstocks. Herein we report multistep sequential engineering
of orthogonal Lewis acid and palladium nanoparticle (NP) catalysts
in a metal–organic framework (MOF) built from (Al–OH)n secondary building units and a mixture of
2,2′-bipyridine-5,5′-dicarboxylate (dcbpy) and 1,4-benzenediacrylate
(pdac) ligands (1) for tandem C–O bond cleavage.
Ozonolysis of 1 selectively removed pdac ligands to generate
Al2(OH)(OH2) sites, which were subsequently
triflated with trimethylsilyl triflate to afford strongly Lewis acidic
sites for dehydroalkoxylation. Coordination of Pd(MeCN)2Cl2 to dcbpy ligands followed by in situ reduction produced orthogonal Pd NP sites in 1-OTf-PdNP as the hydrogenation catalyst. The selective and precise
transformation of 1 into 1-OTf-PdNP was characterized step by step using powder X-ray diffraction, transmission
electron microscopy, thermogravimetric analysis, inductively coupled
plasma mass spectrometry, infrared spectroscopy, and X-ray absorption
spectroscopy. The hierarchical incorporation of orthogonal Lewis acid
and Pd NP active sites endowed 1-OTf-PdNP with
outstanding catalytic performance in apparent hydrogenolysis of etheric,
alcoholic, and esteric C–O bonds to generate saturated alkanes
via a tandem dehydroalkoxylation–hydrogenation process under
relatively mild conditions. The reactivity of C–O bonds followed
the trend of tertiary carbon > secondary carbon > primary carbon.
Control experiments demonstrated the heterogeneous nature and recyclability
of 1-OTf-PdNP and its superior catalytic activity
over the homogeneous counterparts. Sequential engineering of multiple
catalytic sites in MOFs thus presents a unique opportunity to address
outstanding challenges in sustainable catalysis.