(486j) Microwave Catalysis for Ammonia Synthesis Under Mild Reaction Conditions

Microwave Catalysis for Ammonia Synthesis under Mild Reaction
Conditions

Jianli Hu, Hanjing Tian, Yan Luo, Xinwei Bai, West
Virginia University

Dushyant Shekhawat, Christina Wildfire, Victor
Abdel-Sayed, Michael Spencer, National Energy Technology Laboratory

Robert Dagle, Stephen Davidson, Pacific Northwest
National Laboratory

Al Stiegman, Florida State University

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^oC
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.

Figure 1. Illustration of microwave
catalytic synthesis of ammonia