| 摘要: | 在非貴金屬用於催化加氫反應的研究中，奈米鎳金屬(Ni NPs)因為其價格以及磁性而被廣泛研究。但在目前的技術中，如何去製備具有穩定且高度分散的奈米金屬粒子仍是個巨大的挑戰。在二氧化碳的氣相催化加氫反應研究中，透過鹼性濕式含浸法並以熱還原法還原金屬的方式，可將奈米鎳金屬(Ni NPs)有效的附載在具羧酸官能基修飾之二氧化矽材料SBA-16的籠型孔洞中。奈米鎳金屬(Ni NPs)的粒徑大小取決於Ni的含浸量，而在本研究中奈米鎳金屬的粒徑大小大約在2.7~4.7 nm之間。在適當的鹼性條件下(pH=9)，籠型孔洞上的羧酸官能基因去質子化的關係，可透過靜電相互作用力有效地將Ni2+嵌入SBA-16的籠型孔洞中，進而分散Ni NPs。籠型孔洞及其具官能基修飾的表面可以有效地固定Ni NPs並且控制其粒徑大小。籠型結構的SBA-16作為Ni NPs的載體增加更多的活性位點，提高對於CO以及CO2的吸附，因此造就高CO及CO2加氫催化反應速率。在本研究中，已成功探討出具高反應速率之以CH4進行CO2加氫催化反應的反應機構、催化動力學以及其活性位點。
另外，在硝基芳烴化合物的液相催化加氫反應裡，本研究進一步的探討2D及3D二氧化矽孔洞材料附載Ni NPs對於該反應的活性影響。藉由一鍋共縮合技術，可合成出兩種具羧酸官能基修飾表面的不同孔洞結構(2D六角形孔道:SBA-15C；3D籠型孔洞:SBA-16C)，並以此固定並控制超小奈米鎳金屬的成長。在不同孔洞材料SBA-15C以及SBA-16C中，奈米鎳金屬的粒徑範圍大概在3.0~11.1 nm(Ni-x/SBA-15C)及2.7~6.6 nm(Ni-x/SBA-16C)，而其粒徑大小取決於Ni所含浸的莫耳數。本研究在硝基芳烴化合物加氫轉化為氨基芳烴化合物的反應裡，發現Ni-x/SBA-16C相較於Ni-x/SBA-15C及Ni-x/SiO2具有較好的催化活性。而本研究也發現對於反應的催化活性受以下性質影響:奈米鎳金屬的粒徑大小、孔洞的結構、材料的結構性質以及鎳金屬的含量。此外，其磁性性質可促進催化劑的回收再利用。
為延續該研究的探討，本研究利用雙催化劑的概念使催化劑具有新的協同作用以提高現有催化劑的催化活性。透過快速的濕式含浸法，成功在具羧酸修飾表面的二氧化矽孔洞材料SBA-16中合成出銀參雜奈米鎳金屬顆粒，並在催化有毒的硝基芳烴化合物反應中具有高催化活性。在SBA-16上的羧酸官能基因其與Ag+與Ni2+的靜電相互作用力，使其可以有效的控制金屬顆粒在熱還原法中的生長。本研究透過不同的技術對於SBA-16C和Agx%Ni@SBA-16C進行材料鑑定，包含:固態核磁共振光譜(NMR)、傅立葉紅外光譜儀(FT-IR)、X光繞射圖譜(XRD)、等溫氮氣吸脫附圖譜(BET)、X射線光電子能譜(XPS)、高解析穿透式電子顯微鏡(HR-TEM)、超導量子干涉磁化儀（SQUID）。透過鑑定可發現在SBA-16C中超小銀參雜奈米鎳金屬顆粒具有高度的分散性，且具有磁性性質以利於回收再利用。在硝基芳烴化合物轉化為氨基芳烴化合物的催化反應中，雙金屬催化劑Agx%Ni@SBA-16C展現了它極高的催化活性，其原因包含:獨特的電子性質、銀參雜奈米鎳金屬的協同作用、極小的金屬顆粒大小、金屬的附載以及有利的結構性質。
除了以二氧化矽孔洞材料作為載體，本研究也利用金屬有機骨架材料(MOF)做為奈米銅金屬的載體。透過濕式含浸法，成功合成出一種具耐用及價格合理的優異奈米銅催化劑。本研究使用兩種分層微孔材料(單節點:ZIF-67、雙節點:ZIF-Co/Zn)做為控制小尺寸奈米銅金屬生長的載體。在催化有毒的硝基芳烴化合物水相加氫反應以及有毒有機染料降解的實驗中，可得知在催化活性上Cu(x)@ZIF-Co / Zn明顯表現出比Cu(x)@ZIF-67更高的成果。而造就Cu@ZIF-Co/Zn具有高催化活性的原因可能有:獨特電子性能、高體表面積、適當的銅含浸量以及穩定的微孔骨架。此外，該催化劑也在穩定性及再利用性都有優異的表現，在經過五次的循環利用後仍可保有高轉換率。
;The current drive to explore non-noble metal nanoparticles (NPs) utilized for the hydrogenation reaction encourages an extensive study of Ni NPs for their affordable price and magnetic properties. However, fabrication of stable and highly dispersed metal NPs against aggregation remains a great challenge. In the study of gaseous phase catalytic hydrogenation of CO2, nanocatalysts based on ultra-small Ni nanoparticles (Ni NPs) were controllably supported in the cage-type mesopores of −COOH functionalized mesoporous silica SBA-16 via wet impregnation under alkaline conditions, followed by thermal reduction. The particle sizes of the Ni NPs ranged from 2.7 to 4.7 nm, depending on the Ni loading. Under the appropriate alkaline conditions (i.e., pH=9) deprotonation of the carboxylic acid groups on the cage-type mesopore surfaces endowed the effective incorporation of Ni2+ species via favorable electrostatic interactions, and thus well-dispersed Ni NPs confined in the cage-type mesopores of SBA-16 were achieved. The combination of the cage-type mesopores and the surface functionality provided dual beneficial features to confine the immobilized Ni NPs and to tune their particle sizes. The cage-type SBA-16 support provided a positive effect for the Ni NPs to enrich the surface sites, which can strongly adsorb CO and CO2, thus leading to high catalytic rates for CO2 and CO hydrogenation. The reaction mechanism, catalytic kinetics, and active sites were investigated to correlate to the high reaction rate for CO2 hydrogenation to form CH4.
Besides, the support effect of 2D and 3D mesoporous silicas on the supported Ni NPs’ catalytic activity was further studied in the course of liquid phase catalytic hydrogenation of nitroarenes compounds. Carboxylic acid modified ordered mesoporous silicas with two distinctive pore architectures, so called 2D hexagonal channel SBA-15 (SBA-15C) and 3D cage-type SBA-16 (SBA-16C) synthesized by the one-pot co-condensation technique were utilized as the supports for the controllable confinement growth of ultra-small nickel nanoparticles (Ni NPs). The particle size of Ni NPs ranges from 3.0 to 11.1 nm and 2.7 to 6.6 nm for Ni-x/SBA-15C and Ni-x/SBA-16C, respectively, depending on molar amount of Ni loadings. The catalytic performances of the synthesized materials were evaluated with the hydrogenation of nitroarenes to aminoarenes and the catalytic activity of Ni-x/SBA-16C is found to be higher than that of Ni-x/SBA-15C and Ni-x/SiO2. It is found that the catalytic activity is greatly influenced by the particle size of Ni NPs, pore architectures, textural properties of the support and Ni amount. In addition, the magnetic properties allow a facile and rapid recovery of the catalysts for reuse.
For continuation of our works, a concept of binary catalyst system with its emerging synergistic effect was then introduced in order to significantly improve the catalytic activity of our present catalysts. In which, highly active Ag-doped Ni nanoparticles were successfully fabricated within carboxylic acid (–COOH) functionalized mesoporous silica SBA-16 by a facile wet incipient technique for catalytic conversion of toxic nitroaromatics. The –COOH groups on SBA-16 played a crucial role by enhancing the electrostatic interactions with Ag(I)/Ni(II) cations, that control the crystal growth during the thermal reduction. Systematic characterizations of SBA-16C and Agx%Ni@SBA-16C were performed by different techniques including solid state 13C and 29Si nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), N2 sorption, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and superconducting quantum interference device (SQUID). The highly dispersed ultrafine Ag-doped Ni NPs (~3 nm) were well-confined within SBA-16C and exhibit magnetic properties that were extremely beneficial for recycling. The bimetallic Agx%Ni@SBA-16C catalysts showed exceptionally high catalytic activity during catalytic conversion of toxic nitroaromatics to environmentally friendly amino-aromatics. The enhanced catalytic activity could be ascribed to the combined effects of unique electronic properties, synergistic effects of Ag-doped Ni, ultra-small size, metal loading, and favorable textural properties. These magnetically separable nanocatalysts showed excellent durability.
Apart from siliceous based mesoporous supports, metal organic frameworks (MOFs) were further studied as the support for the stabilization of Cu nanoparticles. An excellent, durable and affordable heterogeneous Cu-based nanocatalyst was developed through a facile wet impregnation method. Herein, hierarchically microporous single node ZIF-67 and binary nodes ZIF-Co/Zn were used as the supports to exclusively stabilize small size Cu nanoparticles. Their catalytic activities were comparatively evaluated and the Cu(x)@ZIF-Co/Zn apparently exhibited higher performance than that of Cu(x)@ZIF-67 in the aqueous phase hydrogenation of hazardous nitroarenes and degradation of toxic organic dyes. The unique electronic properties rising from the small sized Cu NPs embedded within bimetallic nodes ZIF-Co/Zn, higher surface area of support, appropriate Cu loading content and maintainable microporous frameworks could be the combination factors determining the catalytic enhancement for Cu@ZIF-Co/Zn. In addition, this catalyst showed excellent stability and recyclability which could retain the high conversion after 5 cycled reuse. |
