探討光觸媒固氮的應用潛力

Exploration of the Potential on Photocatalytic Nitrogen Fixation

陳凱婷(Tan Kai Ting)

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(2020年)

https://doi.org/10.6342/NTU202003070

摘要

固定氮在自然界是僅次光合作用的第二重要化學反應過程。自然固氮可通過閃電或固氮細菌進行，將大氣中的氮分子解離成可被動植物吸收的硝酸根及硝酸銨離子來進行生長。為了解決全球糧食危機，哈伯法廣泛的被應用在工業上生產氨，再進一步製成肥料。但過程中卻消耗了2%的全球總能源量及排放大量會造成溫室效應的二氧化碳。因此，發展低耗能及在不危害環境條件下進行光催化反應還原氨已成為探討的重要課題。本研究計劃以水為氫的來源及利用光源為驅動力以達到在低溫低壓條件下產氨，以解決環境與能源等問題。
本研究的宗旨為探討具有潛力應用於光催化固氮的光觸媒。石墨相氮化碳(CN)，（001）晶面二氧化鈦(TO)及氮化硼(BN)為主要探討的光觸媒，光催化反應在單胞反應器內進行。在所探討的觸媒中，VCN/N2 的氨產量最高，約143.03 μmolgcat-1h-1L-1。據其他文獻探討，以表面缺陷存在的氧缺位容易於（001）晶面的二氧化鈦形成，並有效提高電荷轉移能力，但它在本研究中並沒有發揮其角色。由於受氮化硼的疏水特性所限制，氮化硼的產氨效果在三組所探討的觸媒裡表現最差。此外，本研究也改良商用二氧化鈦(P25)，發現其產率高於以上三組所探討的光觸媒。最後，實驗時也發現以醇類當犧牲試劑會對納氏試劑造成干擾，造成嚴重的產物誤差。

關鍵字

固氮 ； 光催化還原 ； 氨 ； 氮化碳

並列摘要

Nitrogen fixation is the second most important chemical process in nature next to photosynthesis. In nature, nitrogen fixation is carried out either through lightning or the bacteria in soil to form nitrogen containing compounds for growth and development of living organisms. In industry, Haber-Bosch process is widely used to produce ammonia for the manufacture of fertilizer in order to solve global food crisis. However, this process consumes nearly 2% of world’s annual energy supply and releases millions of tons of carbon dioxide into atmosphere to cause serious global warming. Therefore, development of low-energy consumption and eco-friendly process to manufacture ammonia through the photocatalytic nitrogen fixation is urgently needed. This study proposed using water as hydrogen source and renewable sunlight as driving force in order to meet the goal of sustainable production of ammonia under mild condition.
The aim of this research is to explore the promising photocataysts on photocatalytic nitrogen reduction. Graphitic carbon nitride (CN), (001)-facet exposed TiO2 (TO) and boron nitride (BN) series of photocatalysts were investigated. Catalytic performance on the nitrogen reduction was carried out in a batch reactor system. The result showed that VCN/N2 generated the highest amount of ammonium among all the synthesized photocatalysts, which was approximately 143.03 μmolgcat-1h-1L-1. This was owing to the formation of nitrogen vacancies which could selectively adsorb nitrogen molecules. In spite of some literatures stated surface defects in the form of oxygen vacancies were widely available in the (001)-facets and they could enhance charge transfer ability, the (001)-facet exposed TiO2 series unexpectedly did not show outstanding performance in this research. Owing to the limitation of wettability of boron nitride, this series performed the worst in this research. Besides, commercial TiO2 (P25) was modified and found that it exhibited the best ammonium production if being compared with the main photocatalysts discussed in this research. Lastly, it was found that using sacrificial agents such as methanol caused serious interference effect on Nessler’s reagent if Nessler’s reagent was used as detection method.

並列關鍵字

Nitrogen Fixation ； Photocatalytic reduction ； Ammonia ； Carbon Nitride

參考文獻

1. Navarro-Gonzalez, R., C.P. McKay, and D.N. Mvondo, A possible nitrogen crisis for Archaean life due to reduced nitrogen fixation by lightning. Nature, 412 (2001) 61-64.

2. Medford, A.J. and M.C. Hatzell, Photon-Driven Nitrogen Fixation: Current Progress, Thermodynamic Considerations, and Future Outlook. ACS Catalysis, 7 (2017) 2624-2643.

3. Tuck, A.F., Production of nitrogen oxides by lightning discharges Quarterly Journal of the Royal Meteorological Society, 102 (1976) 749-755.

4. Lakna. What is the Difference Between Nitrogen Fixation and Nitrification. August 24, 2019; Available from: https://pediaa.com/what-is-the-difference-between-nitrogen-fixation-and-nitrification/.

5. Vu, M.H., M. Sakar, and T.O. Do, Insights into the Recent Progress and Advanced Materials for Photocatalytic Nitrogen Fixation for Ammonia (NH3) Production. Catalysts, 8 (2018)