常温醇环境中离子交换原位还原制备Pd-核壳型玻璃微珠催化剂

This project aims to develop a novel in-situ method to prepare mono-dispersed palladium nanoparticles supported on porous glass beads with an egg-shell structure at room temperature. The innovation of this method mainly contains four points: firstly, palladium ions are loaded on the surface of the porous glass beads through the ion exchange process,it is easier to obtain nanoparticles with smaller size and narrow size distribution compared with the impregnation method; secondly, using porous glass beads as the solid base catalyst, the reduction of palladium ions is realized at room temperature instead of reducing by hydrogen gas at high temperature (573 K); thirdly, the change in solvent (from water to ethanol) weakens the competing effect of hydrogen ions, resulting in an larger loading amount of palladium nanoparticles; fourthly, the egg-shell structure would greatly enhanced mass transfer and selectivity. Preliminary results showed that in enthanol,the mono-dispersed Pd nanoparticles around 3.75 nm in diameter with a face-centered cubic structure have been successfully prepared. The adsorption capacity for palladium reached 55.0 mg/g in ethanol which was 26 times larger than that in water. This project will investigate the effects of the egg-shell structure, concentration of Pd2+ ions, type of solvent on the size and adsorption amount of Pd nanoparticles and explore the mechanism of coupling of the ion exchange and in-situ reduction; meanwhile, the catalytic activity of the prepared catalyst would be explored by the hydrogenation of anthraquinone.

该项目旨在发展一种在室温下制备钯核壳型催化剂的新方法，可以实现纳米钯颗粒在具有核壳结构的玻璃微珠上的单分散负载。该方法的创新性在于：通过离子交换将Pd负载在玻璃微珠上，与一般的浸渍法相比，有助于得到更小的Pd纳米颗粒；由于玻璃微珠具有碱性，可在常温下催化Pd离子和醇羟基的反应，使得Pd离子原位还原得到单质Pd，避免了使用高温氢气还原；通过改变溶剂环境（由水改变为乙醇）抑制了Pd离子解离，大大提高了Pd的负载量；核壳型结构可以减小扩散阻力，提高加氢反应选择性。初步的研究结果表明：在乙醇环境中得到的纳米钯颗粒拥有面心立方体结构且其平均粒径为3.75nm，玻璃微球上钯离子负载量可达55.0mg/g，与在水溶液中负载量相比提高了26倍。该项目拟研究核壳型结构、Pd初始浓度、醇种类等因素对Pd负载量和粒径的影响规律，探究离子交换原位还原的耦合机理，并以蒽醌加氢为实验体系，研究该新型催化剂的加氢性能。

改变亚临界水热刻蚀条件（温度和时间），成功实现了核壳结构多孔玻璃微珠的可控化制备，并具备孔、薄片阵列和纤维结构的三种形貌。该种新型核壳型多孔玻璃微球在水性环境中展现了对金属离子良好吸附性能。表面为孔的玻璃微珠对金属离子的吸附量最小，而表面为纤维时吸附量最高，且其对Cu2+、Ag+和Ni2+的最大吸附容量分别是81.33 mg/g、149.33 mg/g和42.96 mg/g，这主要是由于表面纤维结构的玻璃微珠具有最大的比表面积。基于核壳结构多孔玻璃微球的离子交换特性，发展了三种负载型金属纳米颗粒制备方法，同时成功制备了负载型Pd和Ni纳米催化剂，实现了其组成形貌的可控调备。实验得到的Pd纳米颗粒呈现面心立方体结构，平均粒径约为3.75 nm，同时在乙醇环境中多孔玻璃微球对Pd2+的负载量可高达75±0.55 mg/g，比在水相中的负载量提高了26倍。负载Ni催化剂中Ni的最大负载量可达46.4±0.9 mg/g，当Ni负载量在0.102 wt.% ~ 1.144 wt.%范围内变化时，Ni纳米颗粒的平均粒径约在1.8 nm左右；当负载时间从2 h增加至8 h，Ni纳米颗粒粒径大小从1.9 nm增长至3.7 nm。负载型金属Pd和Ni催化剂，在蒽醌加氢以及环己烯加氢反应中，均表现出了优异的催化加氢反应活性：当Pd负载量是0.34 wt%，蒽醌的转化率在不到2秒的停留反应时间中可以达到60%，相应的时空收率和氢化效率分别是3800 gH2O2/gPd/h和11.2 gH2O2/L；而对环己烯加氢反应，反应温度70 ℃，Pd负载量0.45 wt.%条件下，在2.76秒的停留反应时间内转化率可达到32.2%；对Ni催化剂，环己烯浓度1000 ppm，反应温度60 ℃，Ni负载是1.144 wt.%，在17.7秒的停留反应内实现了100%的转化率。综上，探究了核壳多孔玻璃微珠不同微观形貌的可控制备及其相应的高效离子交换性能，在乙醇环境中实现了负载于核壳结构多孔玻璃微珠表面的Pd2+和Ni2+还原，使得离子交换和离子还原的原位耦合，达到了以核壳多孔玻璃负载金属纳米颗粒加氢催化剂的绿色制备的目标。研究成果共发表了SCI学术论文25篇，其中以通讯作者发表的共计20篇，并获得第八届中国颗粒学会青年颗粒学奖和2016中国颗粒学会-赢创颗粒学创新奖。