Microwave Catalysis for Ammonia Synthesis Under Mild Reaction Conditions

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Abstract

A scalable, cost-effective catalytic process of ammonia synthesis is developed by using microwave excitation under mild reaction conditions. In this research project funded by DOE ARPA-E, our interdisciplinary team of WVU, NETL, PNNL, FSU and two industrial partners have demonstrated that ammonia synthesis can be carried out at 200-300 °C and ambient pressure. This transformational process integrates system elements of electromagnetic sensitive catalysts and microwave reactor design. Taking advantages of state-of-the art non-equilibrium microwave plasma technology, catalytic ammonia synthesis undergoes a new reaction pathway where the barrier for the initial dissociation of the dinitrogen is decoupled from the bonding energy of the intermediates.

In this project, catalytic ammonia synthesis was conducted under two microwave irradiation scenario: microwave and microwave plasma. Other than selective activation of dinitrogen to metastable radicals, the most obvious advantage that microwave irradiation affords in driving a heterogeneously catalyzed reaction is the ability to locally heat the catalytic sites. Many industrial processes utilizing heterogeneous catalysts are high-temperature processes wherein both components of the reaction (i.e., catalyst and medium) are heated to the temperature required for the reaction to occur.

Microwave irradiation is a facile and efficient means of generating plasmas and has been used for that purpose in a number of applications. The transformational chemistry is driven by the specific characteristics of plasma chemistry that leads to an energy efficient paradigm for the synthesis of ammonia. It is equally important to note that microwave irradiation, regardless of its accompanying plasma generation, has shown a profound impact on catalyzed and uncatalyzed gas-solid reactions. In particular, it has been demonstrated that microwave-specific effects can manifest themselves through the enhancement of reaction rates, changes in the position of equilibria and the distribution of products.

Specifically discussed in this presentation are the effects of electromagnetic properties of catalysts, microwave frequency and microwave energy absorbed on the conversion of nitrogen and ammonia yield. Energy efficiency and Technoeconomic analysis (TEA) relevant to microwave catalytic synthesis of ammonia will also be discussed to shed lights on commercial viability.

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