(246c) Ab-Initio Design of Mild Temperature Ammonia Synthesis Catalysts Using Ni-Supported Metal Nitrides | AIChE

(246c) Ab-Initio Design of Mild Temperature Ammonia Synthesis Catalysts Using Ni-Supported Metal Nitrides

Authors 

Roy, P. - Presenter, Nanyang Technological University
Bukowski, B. C., Purdue University
Ammonia production is a pivotal industrial process with global significance. The potential for catalysts to produce significant ammonia yields at reduced temperatures and pressures could transform modern ammonia production, particularly in hydrogen storage and transportation. Metal nitrides, due to their ability to furnish surface nitrogen atoms for ammonia production, emerge as promising candidates in this pursuit. In this work, we employed periodic Density Functional Theory (DFT) to investigate the associative Mars-van Krevelen mechanism, involving sequential hydrogenation of adsorbed nitrogen on rocksalt-structured binary nitrides, leading to ammonia desorption. We opted for this mechanism over the dissociative pathway due to the energy-intensive nature of breaking the nitrogen-nitrogen bond, essential in the dissociative pathway.

We explored the correlation between ammonia adsorption energy and nitrogen vacancy formation energy for metal nitrides, crucial for understanding their catalytic behavior. Additionally, we investigated the influence of a quasi-one-dimensional Ni nanowire supported on a MnN substrate. The application of the nudged elastic band method on this system revealed a simplified ammonia formation mechanism, elucidating the potential of nanoparticles in enhancing catalytic efficiency. Through a detailed microkinetic model, we quantified reaction rates and species concentrations on Ni/MnN metal nitride surfaces, validated against experimental data for accuracy. Ultimately, we evaluated different phases and surfaces of manganese nitrides, constructing a surface phase diagram to determine the most energetically favorable structure under reaction conditions of nitrogen and hydrogen thermodynamic reservoirs. This ab-initio thermodynamic analysis guides the establishment of temperature and pressure conditions crucial for our chemical looping approach with metal nitride catalysts. By facilitating dynamic replenishment of vacancies in metal nitrides through phase transitions, this method enhances ammonia yields and offers catalyst regeneration potential.

Our research delves into the surface and reaction chemistry of metal nitrides, laying the groundwork for catalysts to produce higher ammonia yields under mild temperature and pressure conditions.

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