| 摘要: | 本論文主要分為兩大部分，在第一部分研究中，超小奈米鈷金屬還原在特殊三維孔道中孔洞材料KIT-6之中(命名為Co@KIT-6)，利用添加雙還原劑使金屬還原速率上升和KIT-6表面原有的羥基，使離子鈷金屬能快速平均披覆在KIT-6孔洞之中原位還原形成超小奈米金屬鈷。由於KIT-6高比表面積880m2g-1和孔洞體積0.9cm3g-1，使用KIT-6載體可以提高奈米鈷金屬分散率和附載率而提升催化活性。此外具有5nm的內部孔徑的KIT-6可以限制奈米鈷金屬成長範圍避免聚集。因為奈米鈷金屬在三維結構中受到調節，所以它可避免快速失活並且促進催化活性以達到高再利用時間。用於氨硼烷水解的Co @ KIT-6的轉換頻率和活化能（Ea）幾乎達到20 mol H2 /mol Co/min和26kJ mol-1。在這項研究中，Co @ KIT-6展示了用於從氨硼烷產生氫的高前景催化劑。
在第二部分研究中，透過浸泡法，超小奈米銅粒子可被固定附載在梭酸官能化及具擴孔的二氧化矽SBA-16籠型中孔洞中(命名為Cu@LP-S16C-x)。奈米銅粒子大小範圍為2至7奈米，在適當的鹼性條件下(pH 9.0)籠型中孔洞表面上的羧酸官能團會去質子化形成有利的靜電相互作用，吸引銅離子前驅物有效摻入。籠型中孔洞和表面官能基團的組合限制並固定奈米銅粒子和調整它們的粒子大小的雙重有益特徵。奈米銅粒子還原在LP-S16C-x材料中對4-硝基苯酚(4-nitrophenol)還原催化有極佳的結果，作為還原4-硝基苯酚的催化劑，Cu(x)@LP-S16C-x表現出非常高的催化活性，活性參數為1296.4s-1g-1，這種增強的催化活性歸因於銅奈米金屬顆粒大小和附載量，以及擴孔後的中孔洞SBA-16的高比表面積和籠型孔結構。
;There are two part of my study. In the first part, hydrogen is highly considered as the most important issue in fuel cell. Apart from this, ammonia borane is a popular reagent owing to its high hydrogen density up to ~19.6 wt%. In the field of catalytic hydrogen generation, cobalt nanoparticles (Co NPs) based materials are usually high potential candidates for hydrolysis of ammonia borane. However, the stability issue of Co NPs due to the particle aggregation resulting uncontrollable activity. Therefore, we here report the convenient way synthesis of Co NPs through one-step chemical reduction which is adsorbed in 3D mesoporous silica KIT-6 (denoted as Co@KIT-6) to keep maintain the high efficiency. Under wet impregnation process, KIT-6 support was immersed in cobalt ion precursor and the adsorbed cobalt ion into inside the pores was then chemically reduced using mixed reagent containing NaBH4 and NH3BH3 to obtain Co@KIT-6. It was found that the use of KIT-6 support can highly enhance the dispersion and efficiency due to its high surface area 880 m2g-1 and pore volume 0.9 cm3g-1. In addition, KIT-6 with the internal Pore size of 6 nm may separate confine the Co NPs and subsequently avoid the aggregation. Because cobalt is regulated in 3D structure, it can suffer from rapid deactivation and promote catalytic activity to reach high reuse times. According to X-ray diffraction pattern and TEM image, it can be confirmed that the particle size of Co NPs is about sub-1 nm and highly dispersed without aggregation. The turnover frequency (TOF) and activation energy (Ea) of Co@KIT-6 for the hydrolysis of ammonia borane reach almost 20 molH2 molCo-1 min-1 and 35 kJ mol-1. In this study, Co@KIT-6 exhibits a high promising catalyst for hydrogen generation from ammonia borane.
In the second part, ultra-small Cu nanoparticles (Cu NPs) are controllably supported in the cage-type mesopores of –COOH functionalized large pore mesoporous silica SBA-16 (denoted as Cu@LP-S16C-x) via wet impregnation under alkaline conditions, followed by the calcination-reduction process. The particle size of Cu NPs ranges from 2 to 7 nm, depending on the Cu loadings. Under an appropriate alkaline condition, i.e., pH 9, the deprotonation of carboxylic acid functional groups on the cage-type mesopore surface endows effective incorporation of the Cu2+ precursors via favorable electrostatic interactions. The combination of cage-type mesopores and surface functionality offers double beneficial features of confining the immobilized Cu NPs and tuning their particle sizes. The catalytic results of the Cu NPs based large pore SBA-16 materials towards 4-nitrophenol reduction show that both the particle size of Cu NPs and the textural properties of the support have important influence on the catalytic activity. As the catalyst for the reduction of 4-NP, the Cu@LP-S16C-x exhibited a very high catalytic activity with the activity parameter of 1296.4 s-1g-1, which is remarkably high as compared to the Cu based catalysts reported in the literature. This enhanced catalytic activity might be attributed to the size and loading amount of Cu NPs, and high specific surface area and cage-type pore structure of large pore SBA-16. |
