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1.
Jinqiang Tan Huamei Zhu Shasha Cao Sisi Chen Yuanfu Tian Dachuan Ding Xuan Zheng Chuanqun Hu Tao Hu Chonggang Wu 《RSC advances》2020,10(70):43175
A poly(methyl methacrylate)-supported Pd0 nanocatalyst was successfully prepared from solution reaction of Pd(CH3COO)2 with a copolymer acid, poly(methyl methacrylate-ran-methacrylic acid) (MMA–MAA). The reaction was carried out in a benzene/methanol mixed solvent in the dark at room temperature (∼25 °C) in the absence of a typical chemical reductant. There was coordination between the Pd0 nanoclusters and MMA–MAA, resulting in Pd0 nanoclusters being stably and uniformly dispersed in the MMA–MAA matrix, with an average particle size of ∼2.5 ± 0.5 nm. Mechanistically, it can tentatively be proposed that PMMA-ionomerization of the Pd2+ ions produces intramolecular –2COO−–Pd2+ aggregate cross-links in the solution. On swelling of the chain-segments that are covalently bound via multiple C–C bonds, the resultant elastic forces cause instantaneous dissociation at the O–Pd coordination bonds to give transient bare (i.e., uncoordinated), highly-oxidative Pd2+ ions and H+-associative carboxylate groups, both of which rapidly scavenge electrons and protons, respectively, of the active α-H atoms abstracted from the methanol molecules of the solvent to make Pd0 nanoclusters supported by the re-formed MMA–MAA. The MMA–MAA acid copolymer, without itself undergoing any permanent chemical change, serves as a mechanical activator or catalyst for the mechanochemical reduction of Pd(CH3COO)2 under mild conditions. Compared with traditional Pd/C catalysts, this Pd0 nanocatalyst exhibited more excellent catalytic efficiency and reusability in the Heck reaction between iodobenzene and styrene, and it could be easily separated. The supported Pd0 nanocatalyst prepared using this novel and simple preparation method may display high-efficiency catalytic properties for other cross coupling reactions.A polymer-supported Pd0 nanocatalyst is prepared by using mechanochemical reduction as the driving force for the reaction. 相似文献
2.
A highly efficient heterogeneous catalyst was synthesized by delicate engineering of NH2-functionalized and N-doped hollow mesoporous carbon spheres (NH2–N-HMCS), which was used for supporting AuPd alloy nanoparticles with ultrafine size and good dispersion (denoted as AuPd/NH2–N-HMCS). Without using any additives, the prepared AuPd/NH2–N-HMCS catalytic formic acid dehydrogenation possesses superior catalytic activity with an initial turnover frequency value of 7747 mol H2 per mol catalyst per h at 298 K. The excellent performance of AuPd/NH2–N-HMCS derives from the unique hollow mesoporous structure, the small particle sizes and high dispersion of AuPd nanoparticles and the modified Pd electronic structure in the AuPd/NH2–N-HMCS composite, as well as the synergistic effect of the modified support.Anchoring ultrafine AuPd on NH2-functionalized and N-doped hollow mesoporous carbon spheres for formic acid dehydrogenation. 相似文献
3.
Chandan Chaudhari Katsutoshi Sato Yoshihide Nishida Tomokazu Yamamoto Takaaki Toriyama Syo Matsumura Yasuyuki Ikeda Kenji Terada Naoya Abe Kohei Kusuda Hiroshi Kitagawa Katsutoshi Nagaoka 《RSC advances》2020,10(72):44191
Monometallic (Pd, Ru or Rh) and bimetallic (Pd0.5–Ru0.5) alloy NPs catalysts were examined for the hydrogenation of quinoline. Pd–Ru alloy catalyst showed superior catalytic activity to the traditional Rh catalyst. The characterization of Pd0.5–Ru0.5 catalysts, HAADF-EDX mapping and XPS analysis suggested that the alloy state of PdRu catalysts remained unchanged in the recovered catalyst. Furthermore, the catalyst was highly selective for the hydrogenation of different arenes.Recyclable Pd0.5Ru0.5–PVP catalyst showed higher activity than monometallic Pd or Ru catalyst for the hydrogenation of quinoline. Furthermore, Pd0.5Ru0.5–PVP was able to hydrogenate different arenes.1,2,3,4-Tetrahydroquinolines are important building blocks for the synthesis of fine chemicals, pharmaceuticals and petrochemicals.1–3 Traditionally, 1,2,3,4-tetrahydroquinolines have been synthesized by catalytic cyclization or the Beckman rearrangement method.3–6 Direct hydrogenation of readily available quinoline by molecular hydrogen is a simple and atom-economical route for the hydrogenated quinoline compounds. Nevertheless, the hydrogenation of quinolines reaction suffers from catalyst deactivation caused by the strong interaction between the nitrogen atom of quinoline and active sites of the catalyst. Recently, several heterogeneous (Co, Au, Ru, Pt, Pd and Rh) catalysts have been developed to overcome the catalyst deactivation problem (Table S1†).7–24 Specifically, Rh catalysts exhibits remarkably excellent activity in comparison with other noble metal catalysts but some of them require high temperature (>80 °C)13,21 and/or high pressure (>10 bar).14–21 Later, Rh/AlOOH and Rh nanoparticles (NPs) catalysts have been reported for efficient hydrogenation of quinolines under ambient conditions (1 bar H2 and 25 °C).22–24 Although high selectivity and activity of Rh catalysts, the high cost of Rh make it unfavourable for the industrial purposes. From the economical and environmental point of view, the cost-effective catalyst is necessary for the hydrogenation of quinolines under mild condition.Solid-solution alloy method is a promising way for the synthesis of alloy NPs which offers an opportunity to control the electronic state of alloy by changing the composition ratio and/or different combinations of alloy in this method. In search of a cheap alternative for Rh catalyst, Pd and Ru are important metals because both metals are relatively cheaper than Rh metal and their well-known activity for hydrogenation reactions. We believe that Pd0.5–Ru0.5 solid solution alloy NPs could be alternative for the traditional Rh catalyst. However, a solid-solution alloy of Pd and Ru is a challenging task due to the immiscibility of Pd and Ru in bulk state.25,26 Recently, our research group led by H. Kitagawa has reported the first successful example of Pd0.5–Ru0.5 NPs via a chemical reduction method using a nano-size effect which showed almost similar catalytic activity than those of Rh for CO oxidation and automobile exhaust purification.27,28 As part of our continuing interest in the applications of Pd–Ru as pseudo Rh catalyst, we herein report that chemoselective hydrogenation of heteroarenes and arenes under mild condition.In preliminary experiments, we carried out the hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline as model reaction (27,28 We found the similar trend using Pd0.5Ru0.5 catalyst and it showed full conversion with 95% yield of 1,2,3,4-tetrahydroquinolines (entry 3). The effect of the solvent showed that the reactivity of Pd0.5Ru0.5 was improved using methanol as solvent. Probably, methanol provides the better dispersion of Pd0.5–Ru0.5 NPs in the reactions and/or high solubility of hydrogen gas in methanol. Next, we examined the activity of previously reported Rh catalyst. Although, the particle size of Rh and Pd0.5–Ru0.5 was similar, the moderate yield of tetrahydroquinoline was obtained in the presence of Rh–PVP (entry 7). Due to the high amount of PVP, the catalytic activity of Rh was slightly declined via less interaction between quinoline and metal sites.29Optimization of reaction conditions for hydrogenation of quinolinea
Open in a separate windowaReaction conditions: quinoline (1 mmol), catalyst (2 mol%), CH3OH (1 mL), 5 bar H2, 25 °C, 6 h, CH3OH.bDetermined by STEM analysis.cTHF.dToluene.e1,4-Dioxane.fRef. 38.The substrate scope of Pd0.5–Ru0.5PVP catalyst was explored under mild reaction conditions (5 bar H2 and 25 °C). As summarized in Entry Heteroarene Product Conv. (%) GC yield (%) 1 99 96 2 98 90 3 99 92 4 64 60 5 99 76 6 99 99 7 94 45b 8 99 80
Entry | Catalyst | Particle sizeb (nm) | Conv. (%) | GC yield (%) |
---|---|---|---|---|
1 | Ru–PVP | 8.4 ± 2.4 | 13 | 13 |
2 | Pd–PVP | 4.8 ± 0.8 | 41 | 32 |
3 | Pd0.5Ru0.5–PVP | 5.6 ± 1.6 | 99 | 95 |
4c | Pd0.5Ru0.5–PVP | 5.6 ± 1.6 | 63 | 60 |
5d | Pd0.5Ru0.5–PVP | 5.6 ± 1.6 | 45 | 40 |
6e | Pd0.5Ru0.5–PVP | 5.6 ± 1.6 | 21 | 13 |
7 | Rh–PVP | 5.4 ± 1.0f | 66 | 66 |