GÜler Melih, VariŞli Dilek
Department of Chemical Engineering, Gazi University, Ankara Turkey.
Turk J Chem. 2020 Apr 1;44(2):309-324. doi: 10.3906/kim-1907-4. eCollection 2020.
In this study, microwave-assisted ammonia decomposition reaction was investigated over molybdenum incorporated catalysts. Due to the selective, volumetric, and noncontact heating properties of the microwave system, higher conversion values could be achieved at relatively lower reaction temperatures, which is important for on-site COx-free hydrogen production. Multiwall carbon nanotube-supported molybdenum catalysts were prepared following the impregnation procedure with different metal loading (3.5%-12.5% wt%), and inductively coupled plasma, nitrogen physisorption, X-ray diffraction, and transmission electron microscopic techniques were employed to characterize the fresh and used samples. Reaction experiments were performed under the flow of pure ammonia with a gas hourly space velocity of 36,000 mL/gh for both the microwave and conventionally heated reaction systems. It was found that ammonia conversion was obtained even at 400 °C, reaching 40%, and total conversion was observed even at 450 °C, while the activities of these catalysts were negligible at a reaction temperature lower than 550 °C, in the conventional heated system, which included an electrically heated furnace. Crystals of α-MoC as well as MoO were observed in the structures of the synthesized catalysts and the formation of nitride species was more easily observable under microwave heating, possibly due to the nitridation of molybdenum carbide species during the reaction.
在本研究中，对负载钼的催化剂上的微波辅助氨分解反应进行了研究。由于微波系统具有选择性、体积性和非接触式加热特性，在相对较低的反应温度下即可实现较高的转化率，这对于现场无COx制氢至关重要。采用浸渍法制备了不同金属负载量（3.5%-12.5% wt%）的多壁碳纳米管负载钼催化剂，并利用电感耦合等离子体、氮气物理吸附、X射线衍射和透射电子显微镜技术对新鲜样品和使用后的样品进行了表征。在微波和传统加热反应系统中，均在纯氨气流下进行反应实验，气体时空速为36,000 mL/gh。结果发现，在400℃时即可获得氨转化率，达到40%，在450℃时甚至可实现完全转化，而在传统加热系统（包括电加热炉）中，当反应温度低于550℃时，这些催化剂的活性可忽略不计。在合成催化剂的结构中观察到了α-MoC以及MoO晶体，并且在微波加热下更容易观察到氮化物物种的形成，这可能是由于反应过程中碳化钼物种的氮化作用。
