Recyclable nanocellulose-confined palladium nanoparticles with enhanced room-temperature catalytic activity and chemosel
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Published online 24 September 2020 | https://doi.org/10.1007/s40843-020-1438-9
Recyclable nanocellulose-confined palladium nanoparticles with enhanced room-temperature catalytic activity and chemoselectivity †
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Juan Meng , Yongzhuang Liu , Xiaochao Shi, Wenshuai Chen, Xianquan Zhang and Haipeng Yu ABSTRACT We describe the synthesis of even-dispersed palladium nanoparticles (Pd NPs) confined within a cellulose nanofiber (CNF) matrix for developing a high-performance and recyclable catalyst. The CNF matrix was composed of CNF-assembled mesoporous nanosheets and appeared as soft and hydrophilic foam. Ultrafine Pd NPs (~6 nm) with highloading (9.6 wt%) were in situ grown on these mesoporous nanosheets, and their dense spatial distributions were likely to generate nano-confinement catalytic effects on the reactants. Consequently, the CNF-confined Pd NPs (CNF-Pd) exhibited an enhanced room-temperature catalytic activity on the model reaction of 4-nitrophenol hydrogenation with a highest rate −3 −1 −1 constant of 8.8×10 s and turnover frequency of 2640 h . The CNF-Pd catalyst possessed good chemical stability and recyclability in aqueous media which could be reused for at least six cycles without losing activity. Moreover, chemoselective reduction of 3-nitrostyrene was achieved with high yield (80%–98%) of 3-aminostyrene in alcohol/water cosolvent. Overall, this work demonstrates a positive nanoconfinement effect of CNFs for developing stable and recyclable metal NP catalysts. Keywords: nanocellulose, deep eutectic solvents, palladium nanoparticles, catalysts, nano-confinement
INTRODUCTION Metal nanoparticles (NPs) as heterogeneous catalysts are used in a wide range of applications such as organic synthesis [1], biorefinery [2], electrocatalysis [3,4], and environmental protection [5]. In particular, palladium (Pd) NPs have been widely investigated in cross-coupling [6], oxidation [7], decarbonylation [8], hydrogenation [9] and related reactions [10,11]. However, Pd NPs are generally unstable due to their large active surface areas and
suffer from self-aggregation problems, which impair their properties and limit their catalytic applications [12–14]. In order to solve the above problems, various strategies have been attempted to stabilize Pd NPs including confinement of them in solids, polymers or ligands [15–18]. For example, carbon materials, including graphene [19], carbon nanotubes [20] and carbon fibers [21], have been used to load Pd NPs, and these carbon-loaded Pd NPs exhibit high catalytic turnover frequency (TOF) values of −1 1068–2520 h . Porous nanomaterials such as molecular sieves and metal-organic frameworks have also been used to anchor Pd NPs, and the Pd NPs confined within their nanopores exhibit excellent chemoselectivity of 99% at 353 K [22]. Recently, low-cost, nontoxic and biodegradable matters including chitosan, cellulose, and wood, have been used as natural templates for the syntheses of Pd NPs [23–26]. They are featured as having characteristics of renewability, sustainability, flexibi
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