The Synthesis Of Carbon Nanotube Based Nano-composite And Mechanism Study Of Catalysis For The Hydrolytic Dehydrogenation Of Ammonia Borane

Carbon nanotubes(CNTs) have attracted popular attention in hybrid materials, fuel cells, high efficient catalyst and nano-electron devices fields due to their unique structural properties and excellent physical and chemical properties. For carbon nanotubes, compositing with metal nanaoparticles is an effective way to improve their performance, and this composite are increasingly applied in hydrolytic dehydrogenation of ammonia borane, particularly, compositing with non-precious metal reduced the loading of precious metal and overcomed shortcomings such as high-cost and easyly be poisoned. Synchrotron radiation techniques are effective methods to study the electronic, atomic structure and chemical interaction of nano-materials, and they have wonderful advantages to investigate the mechanisum of catalysis for the hydrolytic dehydrogenation of ammonia borane.In this thesis, we prepared Ni-CNTs samples by physical and wet-chemical methods. Their electronic structures were probed by XANES and STXM techniques. They were also applied in the hydrolytic dehydrogenation of ammonia borane. The study provided experimental and theoretical evidence for the preparation of hybrids catalyst with superior performance. Main contents of this thesis include:We have probed the electronic structure of Ni-based NPs deposited on CNTs by STXM and transmission electron microscope(TEM) images. The results clearly reveal a strong interfacial interaction between Ni NPs and CNTs. In particular, the electronic structure of Ni NPs and CNTs may be tuned for optimum binding to the reactant to enhance catalytic performance. By tuning of Ni NP-CNT hybrids we indeed demonstrated catalytic enhancement in the hydrolysis of ammonia borane(AB, NH3BH3) adduct. The results showed that with strong interfacial interaction using thin CNTs(~20-50 nm OD, 5-10 nm ID), the hybrids delivered excellent performance(total turnover frequency(TOF) value of about 23.5 mol of H2 per mol of Ni per min) compared to that with weak interfacial interaction(using thick CNTs, >100 nm OD, ~5 nm ID, see below). The difference between thin and thick CNTs can be attributed to different surface chemical activity resulted from the curvature. Our results clearly reveal the existence of a tunable(buffer) electronic structure in NP-CNT system facilitating the catalytic process, which could be responsible for the excellent performance of carbon-supported materials and may shed light towards rational design of excellent catalysts in energy-related applications.The Pt-CNTs hybrids were also prepared. Interestingly, the catalyst with a Pt concentration of 2% showed a high performance for the hydrolysis of AB, which exhibited a TOF value of 577 comparable to the best value reported for Pt catalysts. It is also an interesting system requiring further investigation.