Multiscale modeling of the catalytic ammonia decomposition: From Mechanistic Insights to Industrial-Scale Reactor Design for Sustainable Hydrogen Production

This thesis explores novel approaches to understanding and optimizing catalytic ammonia decomposition, crucial for sustainable hydrogen production. The research employs an experimentally validated modeling framework integrating Density Functional Theory (DFT) calculations, microkinetic modeling, process modeling tools and data fitting. Firstly, the study investigates ammonia decomposition over Ru/CaO and Ru–K/CaO catalysts, unveiling a lowered activation barrier for ammonia adsorption on Ru–K/CaO. Microkinetic modeling predicts NH dissociation as the Rate-Determining Step (RDS) for Ru/CaO and NH3 dissociation for Ru–K/CaO, shedding light on the role of K promotion.

Secondly, the role of barium as a promoter for cobalt–cerium catalysts is examined, showcasing enhanced performance compared to Ru-based counterparts. Microkinetic modeling elucidates the kinetic contributions of Ba, highlighting its effect on N2 desorption and NH2 dehydrogenation. The study emphasizes the importance of considering thermodynamic consistency and avoiding oversimplifications in microkinetic modeling.

Third, the thesis explores opportunities for coupling ammonia decomposition in a membrane reactor, employing a multiscale modeling approach. Through parameter fitting and kinetic analysis, optimal catalyst and membrane configurations are identified, leading to significant ammonia conversion enhancements. The study underscores the paradigm shift in catalyst design facilitated by membrane reactor technology, offering insights for scaling up ammonia decomposition processes towards high-pressure, high-purity hydrogen production.

Lastly, chapter 4 delves into the repurposing of industrial reformers for H2 production via ammonia decomposition, employing a Co-Ba-Ce catalyst. Kinetic model refinement reveals significant dependencies of NH3 and H2 reaction orders on total pressure, enhancing accuracy for industrial-scale conditions. Optimization of a top-fired multi-tube industrial NH3 cracker demonstrates its viability, achieving a remarkable NH3 conversion rate of 98% and an H2 capacity of 7,000 Nm3 h–1. The detailed reactor design underscores the significance of comprehensive design considerations in lowering cost estimation by addressing real operational aspects.

In summary, this thesis contributes a holistic understanding of ammonia decomposition processes, from fundamental catalytic mechanisms to practical reactor design considerations, with implications for sustainable hydrogen production at industrial scales.


CE Ph.D. Candidate Natalia Realpe Munoz, supervised by Prof. Pedro Castaño

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16 Jul, 2024
02:00 PM - 04:00 PM
Building 2, Level 5, Room 5220