Singh Pragyansh, Li Qiang, Liu Yilang, Che Fanglin
Department of Chemical Engineering, University of Massachusetts, Lowell, Massachusetts 01854, United States.
ACS Catal. 2025 Apr 24;15(10):7690-7699. doi: 10.1021/acscatal.5c01829. eCollection 2025 May 16.
Ammonia catalytic cracking offers an efficient solution for hydrogen production, storage, and distribution, making it ideal for onboard hydrogen generation in maritime propulsion systems when integrated with fuel cells. However, conventional heating methods, even with highly active ruthenium (Ru) catalysts, require high temperatures to achieve satisfactory performance, posing a challenge for industrial implementation. A promising strategy to address this limitation is the application of strong external electric fields, which can lower the temperature requirement through interactions between fields and the dipoles of polarized species during ammonia cracking. To explore such a field-dipole effect, we developed a multiscale simulation framework that integrates density functional theory (DFT) calculations with microkinetic modeling. This framework provides mechanistic insights, identifies key rate-limiting steps, and optimizes conditions for field-enhanced ammonia catalytic cracking over Ru. Our results show that at 673 K, applying a -1 V/Å negative electric field dramatically increases the turnover frequency from 0.03 s (zero field) to 1435.2 s. Similarly, at a higher temperature of 823 K, the negative electric field enhances the turnover frequency by 4 orders of magnitude compared to the no field conditions. In addition, applying a -1 V/Å electric field reduces the operating temperature from 750 K (zero field) to 586 K while maintaining a given turnover frequency (e.g., 5 s). Sensitivity analysis further identifies NH dehydrogenation over Ru(1013) as the rate-limiting step across various electric fields and temperatures. This multiscale model enhances the understanding of field-enhanced catalysis, offering valuable insights into the development of more efficient hydrogen production processes.
氨催化裂化为氢气的生产、储存和运输提供了一种高效的解决方案，当与燃料电池集成时，它非常适合用于海上推进系统中的车载制氢。然而，传统的加热方法，即使使用高活性钌（Ru）催化剂，也需要高温才能实现令人满意的性能，这对工业应用构成了挑战。解决这一限制的一个有前景的策略是应用强外部电场，在氨裂解过程中，电场与极化物质的偶极子之间的相互作用可以降低温度要求。为了探索这种场-偶极子效应，我们开发了一个多尺度模拟框架，该框架将密度泛函理论（DFT）计算与微观动力学建模相结合。该框架提供了机理见解，确定了关键的速率限制步骤，并优化了在Ru上进行场增强氨催化裂解的条件。我们的结果表明，在673K时，施加-1V/Å的负电场可将周转频率从0.03s（零场）显著提高到1435.2s。同样，在823K的较高温度下，与无场条件相比，负电场使周转频率提高了4个数量级。此外，施加-1V/Å的电场可将操作温度从750K（零场）降低至586K，同时保持给定的周转频率（例如5s）。敏感性分析进一步确定，在Ru(1013)上的NH脱氢是各种电场和温度下的速率限制步骤。这种多尺度模型增强了对场增强催化的理解，为开发更高效的制氢工艺提供了有价值的见解。
