NSF-DFG Echem: Electrochemically enhanced low-temperature catalytic ammonia synthesis

小规模分布式氨合成作为集中式哈伯-博世的替代方案，具有很大的应用价值。避免非常高的压力降低了高资本成本，并且电化学促进可能实现无碳氨。前述研究是基于极化质子陶瓷电化学电池，在阳极上具有蒸汽电解或甲烷重整，质子传导陶瓷膜，并且在阴极上具有氨合成。因为平衡氨合成速率随着温度升高而大大降低，所以低温（例如，T< 450 °C）催化。然而，即使使用最好的催化剂，低于约500 °C的动力学限制也大大降低了合成。质子可能在催化中起重要作用。实际的质子陶瓷电化学电池通常在500 ° C至700 °C之间操作。电化学电池确实产生氨，但速率很低。这里提出的方法是不同的。我们将研究一种新型催化剂载体的直接电化学活化，以在低温下大大提高合成速率，其中该过程在动力学上受到N2活化的限制。卡尔斯鲁厄理工学院（KIT）和科罗拉多矿业学院（CSM）的联合项目的目标是开发和展示能够实现低温和低压氨合成的电化学增强。纳米相Ru分散在质子传导BCZY载体上。 用电场直接极化催化剂结构降低了N2活化的动力学限制势垒。虽然拟议的研究是科学基础，它具有巨大的技术潜力，具有成本效益的分布式生产氨。该研究的重点是假设，建模和验证拟议的化学行为。 预期电场通过两种协同机制降低限速N2解离势垒：1.电场影响质子传导BCZY载体，使得H2解离以形成可以活化气相N2的质子，直接形成所需的表面吸附物，例如NH（BCZY）。在0.1至1.0 V/cm 2范围内的场对分散的纳米Ru也降低了氮活化势垒。基于我们验证的Ba促进的Ru/YSZ反应机理，模拟表明，将N2解离能降低10 kJ mol-1将使氨的生成速率提高一个数量级。实现所提出的目标依赖于合作伙伴在多相催化，材料合成，表征和工艺演示（KIT）和基于物理的电化学、带电缺陷传输和催化（CSM）建模。

As an alternative to centralized Haber-Bosch, small-scale distributed ammonia synthesis has great value. Avoiding very high pressures reduces high capital cost, and electrochemical promotion potentially enables carbon-free ammonia. Foregoing research was based on polarized protonic-ceramic electrochemical cells, with either steam electrolysis or methane reforming on the anode, a proton-conducting ceramic membrane, and ammonia synthesis on the cathode. Because equilibrium ammonia synthesis rates decrease greatly as temperature increases, low-temperature (e.g., T< 450 °C) catalysis is needed. However, even with the best catalysts, synthesis is greatly reduced by kinetic limitations below about 500 °C. Protons likely play a significant role in catalysis. Practical protonic-ceramic electrochemical cells usually operate between 500 and 700 °C. Electrochemical cells do produce ammonia, but at low rates. The proposed approach here is different. We will study the direct electrochemical activation of a novel catalyst support to increase synthesis rates greatly at low temperatures where the process is kinetically limited by N2 activation. This objective of the joint project of Karlsruhe Institute of Technology (KIT) and Colorado School of Mines (CSM) is to develop and demonstrate electrochemical enhancement that enables low-temperature and low-pressure ammonia synthesis. Nanophase Ru is dispersed on a proton-conducting BCZY support. Directly polarizing the catalyst structure with an electric field decreases the kinetically limited barrier for N2 activation. Although the proposed research is scientifically fundamental, it has great technology potential for cost-effective distributed production of ammonia. The research focuses on postulating, modeling, and validating proposed chemical behaviors. The electrical field is expected to reduce rate-limiting N2 dissociation barriers via two synergistic mechanisms:1. Electrical fields affect the proton-conducting BCZY support, enabling H2 dissociation to form protons that can activate gas-phase N2, directly forming desired surface adsorbates such as NH(BCZY).2. Fields in the range of 0.1 to 1.0 V/Å on dispersed nano-Ru also reduce the nitrogen activation barrier. Based on our validated reaction mechanisms for Ba-promoted Ru/YSZ, simulations show that reducing the N2 dissociation energy by 10 kJ mol-1 will increase the ammonia formation rate by an order of magnitude.Achieving the proposed objectives relies on the combined, complementary, and unique expertise of the partners in the context of heterogeneous catalysis, materials synthesis, characterization and process demonstration (KIT) and physically based modeling of the electrochemistry, charged-defect transport, and catalysis (CSM).