- 學位論文
改質鈷硼觸媒於硼氫化鈉水解產氫之研究
Hydrogen production from hydrolysis of sodium borohydride using modified CoB catalysts
摘要
本研究以硼氫化鈉為還原劑，醋酸鈷為前趨鹽類製備出鈷硼非晶相觸媒，用於硼氫化鈉溶液的水解反應，並以此為基礎加入不同添加劑於鈷硼觸媒中，藉由改變觸媒之物理及化學性質以提高產氫速率，此一系列之改質鈷硼觸媒以X-光繞射儀、氮氣吸附儀、穿透式電子顯微鏡、X-光光電子能譜儀等儀器鑑定其物理及表面性質。 CoB的活性（2230 ml/g‧min）遠大於NiB（140 ml/g‧min），再引入一系列不同鈷含量的NiCoB觸媒比較後，發現元素態鈷在硼氫化鈉水解反應中扮演著活性位置的角色，隨著鈷含量的提高，產氫速率亦隨之增加，加入鎳會降低CoB中的鈷含量，因此對反應有不利的作用。 加入鉬與鎢改質之後，不但元素態鈷的含量提高，表面積也隨之上升，而鉬與鎢均提供部分電子轉移給鈷，其氧化物提供良好的分散作用，降低了觸媒聚集的機率，因此活性激增為CoB的兩倍，MoCoB的活性達5050 ml/g‧min，WCoB的活性達5464 ml/g‧min。 改變促進劑的比例，發現MoCoB最好比例為莫耳比0.05:1:3，而WCoB最好比例為莫耳比1:1:3，CoB對鉬的參雜十分敏感，MoCoB (0.01:1:3)由於參雜的量太少，未達改質之目的，其活性與CoB一樣，繼續提高Mo的比例，反而造成元素態鈷減少，且表面積因太多活性位置被覆蓋而下降；提高鎢的比例，並未顯著增加元素態鈷，但觸媒表面積大幅提升，說明觸媒顆粒隨鎢的參雜而減小，然而過量的鎢，會覆蓋觸媒活性位置，造成活性下降。 以MoCoB或WCoB為核心，可設計出連續式產氫反應器，提供充足燃料給15瓦攜帶式燃料電池。 關鍵字：硼氫化鈉、產氫、非晶相觸媒、鈷、鉬、鎢
並列摘要
Amorphous CoB catalyst was prepared by cobalt acetate using sodium borohydride as the reducing agent in this research. The main reaction was hydrolysis of sodium borohydride solution. Different additives were added into CoB to modify its physical and chemical properties in favor of better hydrogen generation rate. The series of modified CoB catalysts were characterized by X-ray diffraction (XRD), BET (Brunauer-Emmett-Teller), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The catalytic activity of CoB (2230 ml/min•g) was higher than NiB (140 ml/min•g) catalyst. Comparing with a series of NiCoB catalysts, which contained different doping ratio of Co, it was obvious that Co played an important role as an active site in this reaction. With increasing Co content, hydrogen generation rate increased as well. Adding Ni would decrease Co content of CoB causing negative effect. Modified by Mo and W, not only metallic Co content but also surface area of CoB increased. Both Mo and W transferred partial electron to Co. Oxides of Mo and W provided good dispersion effect, so the probability of aggregation could be reduced. As a result, the activity of MoCoB and WCoB were 5050 ml/min•g and 5464 ml/min•g, respectively, more than double the activity of CoB. Among different doping ratio of additives, the optimum molar ratio for MoCoB and WCoB was 0.05:1:3 and 1:1:3, respectively. CoB was sensitive for doping of Mo. The activity of MoCoB (0.01:1:3) was closer to the activity of CoB due to its lower Mo content. Increasing Mo content would decrease metallic Co. The decrease in the surface area was observed owing to the cover of active sites by the additive; metallic Co did not significantly increase by adding more W. But the remarkable increase in the surface area observed was due to the smaller particle size of the nanoalloys. However, excess W still covered many active sites, directly caused reduction of activity. Based on this research, using MoCoB or WCoB as a core catalyst, a continuous hydrogen generator can be designed. This module was sufficient for 15W portable fuel cell. Key words: Sodium borohydride, hydrogen generation, amorphous catalyst, Co, Mo, W
參考文獻
延伸閱讀
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