雙胞反應器進行光催化固定氮並同步處理有機廢水

Photocatalytic Nitrogen Fixation and Simultaneous Organic Wastewater Treatment in a Twin Photo-reactor System

黃子恆(Tzu-Heng Huang)

指導教授 ： 吳紀聖

國立臺灣大學/工學院/化學工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202102350

摘要

本研究採用雙胞反應器系統，進行光催化反應固定氮氣生成氨並同步降解異丙醇。有別於目前工業上使用的哈伯法合成氨，須在高溫、高壓條件下進行，不只耗能且會產生大量溫室氣體，光催化反應是透過大自然無限的太陽光作為能量來源，並且可在常溫、常壓的溫和條件下進行。
實驗選用溴氧化鉍(BiOBr)以及非化學劑量比之氧化鎢(W18O49)系列觸媒作為固氮觸媒，並分別摻雜金屬鐵和鉬進行改質，異丙醇降解觸媒則選擇商用氧化鎢(WO3)。兩種固氮觸媒本身具有特殊的氧空缺結構，除了能減少電子電洞對再結合發生，還能作為反應活性點位，增加氮氣吸附量；過渡金屬的摻雜有助於弱化氮氣參鍵，活化氮氣，以上兩種改質手段皆有助於提升光催化的效率。
根據實驗結果找出最佳摻雜量，20 mol% Fe-BiOBr和1 mol% Mo-W18O49分別在兩系列觸媒中展現最佳活性，其中又以1 mol% Mo-W18O49固氮效果最佳，在雙胞反應器系統進行雙功全反應四小時，溶液中銨根離子最大平均產氨速率達28.0 μmol/gcat‧h，較單反應器系統提升66%。同時，初始濃度25 ppm的異丙醇也在氧化反應的第一個小時內被全數降解完畢。
在評判反應系統中可能出現之氮化合物的種類，並參考相關研究並對照實驗數據，推測除了銨根離子，應有其他氮化合物存在，如：NO3-、NO2-、NH2OH等，但主要的固氮產物確認為銨根離子。

關鍵字

光催化固定氮 ； 異丙醇降解 ； 氧空缺 ； 摻雜 ； 溴氧化鉍 ； 氧化鎢 ； 雙胞光反應器

並列摘要

In this study, a twin photo-reactor system was used to carry out photocatalytic nitrogen fixation and isopropanol degradation simultaneously. Different from the Haber-Bosch process for ammonia synthesis in industry, which consumes huge energy and generates greenhouse gas, photocatalytic reaction takes energy from un-limited sunlight and can be carried out under mild ambient condition.
In the experiment, bismuth oxybromide (BiOBr) and non-stoichiometric tungsten oxide (W18O49) series catalysts were used as nitrogen-fixation catalysts. Metallic iron and molybdenum were also doped, respectively, to modify two catalysts. Commercial tungsten oxide (WO3) was selected for isopropanol degradation. The structure of oxygen vacancy structure on BiOBr and W18O49 not only can reduce the recombination of electron-hole pairs, but also can serve as reactive sites, thus increase the amount of nitrogen adsorption. The doping of transition metals helps to weaken the nitrogen triple bonds and activate the nitrogen. Both of these modification techniques can improve the photocatalytic efficiency.
The optimal doping percentage was found experimentally to be 20 mol% Fe-BiOBr and 1 mol% Mo-W18O49 which show the best activity in two different series catalyst respectively. Among all catalysts, 1 mol% Mo-W18O49 shows the best nitrogen fixation performance. In the overall reaction in the twin reactor system for four hours, the maximum average production rate of ammonium ion in the solution reached 28.0 μmol/gcat‧h, which is 66% higher than that in the single-reactor system. At the same time, isopropanol with an initial concentration of 25 ppm was completely degraded in the first hour during oxidation reaction.
We have evaluated that some nitrogen-contained compounds may exist in the reaction system. According to related research reports and controlled experimental data, we conclude that ammonium ion is not the only product during nitrogen fixation process. Other compound also can be formed, for example, NO3-、NO2-、NH2OH, etc. However, the main product is certainly ammonium ion.

並列關鍵字

Photocatalytic nitrogen fixation ； Isopropanol degradation ； Oxygen vacancy ； Doping ； Bismuth oxybromide ； Tungsten oxide ； Twin photo-reactor

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