| dc.description.abstract |
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. | en_US |