Zan Yifan, Ben Romdhane Ferdaous, Miche Antoine, Méthivier Christophe, Krafft Jean-Marc, Jolivalt Claude, Reboul Julien
Sorbonne Université, CNRS, Laboratoire de Réactivité de Surface (LRS), 4 Place Jussieu, Paris 75005, France.
Fédération de Chimie et Matériaux de Paris-Centre (FCMat), 4 Place Jussieu, Paris 75005, France.
ACS Appl Mater Interfaces. 2023 Aug 16;15(32):38716-38728. doi: 10.1021/acsami.3c08906. Epub 2023 Jul 31.
We report the synthesis of a stable heterogeneous catalyst based on copper metal nanoparticles with oxidized surface supported on ZIF-8 for the oxidation of benzyl alcohol under mild temperature and using air as a sustainable oxygen source as well as for the implementation of the tandem "one-pot" catalytic system allowing the sustainable synthesis of benzylidene malononitrile. The influence of the reduction process applied to form the nanoparticle upon the catalyst texture and its performances was extensively examined. After ZIF-8 impregnation with a copper chloride precursor, the reduction of cupric ions into Cu nanoparticles was carried out according to two procedures: (i) by soaking the solid into a solution of NaBH and (ii) by submitting it to a flow of gaseous H at 340 °C. The in-depth physicochemical characterization and comparison of the resulting two types of Cu/ZIF-8 materials reveal significant differences: the reduction with NaBH led to the formation of 16 nm sized Cu nanoparticles (NP) mainly localized on the external surface of the ZIF-8 crystals together with ZnO nanocrystallites, while the reduction under H flow resulted in Cu nanoparticles with a mean size of 22 nm embedded within the bulk of ZIF-8 crystals. More, when NaBH was used to reduce cupric ions, ZnO particles were highlighted by high-resolution microcospy imaging. Formation of ZnO impurities was confirmed by the photoluminescence analysis of ZIF-8 after NaBH treatment. In contrast, ZnO was not detected on ZIF-8 treated with H. Both types of Cu NPs supported on ZIF-8 were found to be active as catalysts toward the aerobic oxidation of benzyl alcohol under moderate temperature ( < 80 °C) and using air as a sustainable O source. Benzaldehyde yield of 66% and selectivity superior to 90% were obtained with the Cu/ZIF-8 catalyst prepared under H flow after 24 h under these conditions. The same material could be recycled 5 times without loss of activity, unlike the catalysts synthesized with NaBH, as a result of the leaching of the surface copper NPs over the consecutive catalytic cycles. Finally, the most stable catalyst was successfully implemented in a tandem "one-pot" catalytic system associating benzyl alcohol oxidation and Knoevenagel condensation to synthesize benzylidene malononitrile.
我们报道了一种基于负载在ZIF-8上的具有氧化表面的铜金属纳米颗粒的稳定多相催化剂的合成，该催化剂用于在温和温度下以空气作为可持续氧源氧化苯甲醇，以及用于实施串联“一锅法”催化体系以实现苄叉基丙二腈的可持续合成。广泛研究了用于形成纳米颗粒的还原过程对催化剂结构及其性能的影响。在用氯化铜前体浸渍ZIF-8后，根据两种程序将铜离子还原为铜纳米颗粒：（i）将固体浸泡在硼氢化钠溶液中，（ii）将其置于340℃的氢气气流中。对所得两种类型的Cu/ZIF-8材料进行的深入物理化学表征和比较揭示了显著差异：用硼氢化钠还原导致形成主要位于ZIF-8晶体外表面的16nm尺寸的铜纳米颗粒（NP）以及氧化锌纳米微晶，而在氢气气流下还原导致平均尺寸为22nm的铜纳米颗粒嵌入ZIF-8晶体的主体中。此外，当使用硼氢化钠还原铜离子时，通过高分辨率显微镜成像突出显示了氧化锌颗粒。通过硼氢化钠处理后ZIF-8的光致发光分析证实了氧化锌杂质的形成。相比之下，在用氢气处理的ZIF-8上未检测到氧化锌。发现负载在ZIF-8上的两种类型的铜纳米颗粒在中等温度（<80℃）下以空气作为可持续氧源时对苯甲醇的需氧氧化均具有催化活性。在这些条件下，在氢气气流下制备的Cu/ZIF-8催化剂在24小时后获得了66%的苯甲醛产率和优于90%的选择性。与用硼氢化钠合成的催化剂不同，由于表面铜纳米颗粒在连续催化循环中的浸出，相同的材料可以循环使用5次而不会损失活性。最后，最稳定的催化剂成功地应用于将苯甲醇氧化和Knoevenagel缩合相结合以合成苄叉基丙二腈的串联“一锅法”催化体系中。
