Exploring dynamic catalytic processes for low-temperature ammonia synthesis on Ru-supported nanoparticles
(2015)
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- Ammonia is one of the most produced chemicals in the world. Its industrial production emerged in the early 20th century as an alternative supply of nitrogen for fertilizer production, which today is the source of 50% of the human protein consumed. In theory, a high conversion of di-nitrogen and hydrogen into ammonia can be only reached at low ‘near room’ temperature, but the reaction requires catalytic materials that commonly operate at higher temperatures. High temperatures (300–500ºC) and high pressures (100–200 bar) have been set for the Haber-Bosch commercial process, operating with essentially the same iron based-catalyst developed over 100 years ago. In this work we study catalytic processes occurring at the highly active surface of Ruthenium nanoparticles, during ammonia synthesis at low temperature (< 200ºC) and low pressure (5 bar). The study provides valuable information to perform low-temperatures hydrogenation processes, with low energy consumption and high selectivity. We found that polydispersity and proximity between Ru nanoparticles are necessary conditions for high catalytic activity at low temperature. Processes of deposition and growth of RuO2 nanoparticles on γ-Al2O3 favor the synthesis of polysized-supported nanoparticles. A general Dynamic Mechanism of Catalytic Hydrogenation (DMCH) is proposed to operate during low-temperature hydrogenation processes on polydisperse metal supported nanoparticles, involving hydrogen transference between different-sized metal particles. For a more accurate description of these processes, we propose a kinetic model considering the overall reaction rate as a contribution of the rates reached on nearby metal particles of different sizes.
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Fernández Rojas, C. (2015). Exploring dynamic catalytic processes for low-temperature ammonia synthesis on Ru-supported nanoparticles. https://hdl.handle.net/2078.5/46788