應用Pd/TiO2, Rh/TiO2以及Ru/TiO2觸媒催化一氧化氮氫化生成氨氣

Abstract

氮氧化合物（NOx）是空氣中污染的來源，可能引起多種環境問題，包括光化學煙霧、酸雨、PM2.5和霧霾的形成。為了應對這些環境的挑戰，傳統上使用選擇性催化還原（SCR）反應將NOx轉化為無害的N2。與此同時，氨氣（NH3）作為合成含氮化合物的重要化學品，近來更成為氫儲存的載體。然而，NH3通常需要在高壓和高溫的條件下從N2和H2中合成（即Haber-Bosch製程）。為了解決與NOx（環境問題）和NH3（能源問題）相關的挑戰，我們提出了一種催化反應，可以在相對溫和的條件下將NO和H2轉化為NH3。以含浸法合成的2 wt% Pd/TiO2-R、2 wt% Rh/TiO2-R和2 wt% Ru/TiO2-R觸媒皆能在300℃達到NO轉化率約100%，值得注意的是，2Pd/TiO2-R相較2Rh/TiO2-R和2Ru/TiO2-R表現出更高的反應活性以及約95%的NH3選擇率。我們也透過程序升溫系列實驗得知，觸媒之反應活性與選擇率和NO的解離式吸附比例、H2與NH3在觸媒表面吸附能力強度息息相關，為了深入了解2Pd/TiO2-R觸媒上由NO和H2進行NH3合成的催化機制，包括NO和H2的活化過程，我們也進行了原位紅外光譜實驗，並發現了最容易反應之NO吸附型態為Pd-NO。這項研究有望為發展更有效地NOx轉化和NH3合成方法提供新的洞察。

Nitrogen oxides (NOx) serve as sources of air pollution, potentially leading to various environmental issues, including photochemical smog, acid rain, PM2.5, and haze formation. To address these environmental challenges, the traditional approach involves using Selective Catalytic Reduction (SCR) to convert NOx into harmless N2. Ammonia (NH3), an essential chemical for synthesizing nitrogen-containing compounds, has recently gained prominence as a carrier for hydrogen storage. However, the synthesis of NH3 typically requires harsh conditions, involving high pressure and temperature, through the Haber-Bosch process. In order to tackle challenges related to NOx (environment) and NH3 (energy), we propose a catalytic reaction capable of converting NO and H2 into NH3 under relatively mild conditions. There are three catalysts, 2 wt% Pd/TiO2-R, 2 wt% Rh/TiO2-R, and 2 wt% Ru/TiO2-R which synthesized by the impregnation method, achieved approximately 100% NO conversion at 300°C. It is noteworthy that 2Pd/TiO2-R exhibited higher reaction activity and around 95% NH3 selectivity compared to 2Rh/TiO2-R and 2Ru/TiO2-R. Through temperature programmed experiments, we discovered that the catalytic activity and selectivity are closely linked to the dissociative adsorption ratio of NO, and the surface adsorption strength of H2 and NH3 on the catalyst surface. To gain a deeper understanding of the catalytic mechanism of NH3 synthesis from NO and H2 on the 2Pd/TiO2-R catalyst, including the activation processes of NO and H2, we conducted in-situ infrared spectroscopy experiments. We found the most reactive NO adsorption form was identified as Pd-NO. This research holds the potential to provide new insights for the development of more effective methods for NOx conversion and NH3 synthesis.