Researchers are making strides toward alleviating the environmental threat posed by ammonia emissions through the development of innovative catalytic technology. A new bi-metallic catalyst composed of platinum and copper has been reported to significantly improve the selective catalytic oxidation (SCO) of ammonia (NH3) to nitrogen (N2), achieving remarkable efficiency and maintaining high selectivity during the process.
Developed by researchers from various institutions, including the EPSRC and EPFL, the catalyst known as PtSCuO/Al2O3 demonstrates its ability to convert ammonia at drastically lower temperatures compared to commercial alternatives. The study, published on June 15, 2025, highlights the advancements made possible through cooperative electronic interactions between platinum and copper sites, enhancing both the catalytic activity and selectivity for nitrogen.
Global ammonia emissions, largely resulting from vehicle exhaust and industrial processes, are estimated to exceed 220,000 tonnes per year, posing serious threats to environmental health and air quality. With ammonia commonly used as fuel across various transportation modes, emissions are set to increase dramatically. Consequently, there is heightened urgency for solutions capable of effectively eliminating NH3 emissions, particularly through catalytic methods.
The selective catalytic oxidation of ammonia has emerged as a preferred method to convert NH3 to N2—without incurring significant over-oxidation to harmful nitrogen oxides (NOx). Traditional noble metal catalysts, such as Pt/Al2O3, have proven effective but often fall short on selectivity, converting only about 50% of ammonia to nitrogen. Meanwhile, first-row transition metals like copper can offer higher nitrogen selectivity, though they typically operate at elevated temperatures of 300-500 °C.
The newly introduced PtSCuO/Al2O3 catalyst addresses these limitations, achieving full NH3 conversion at just 250 °C with noteworthy selectivity levels preserved throughout the reaction. During the study, operando X-ray absorption fine structure (XAFS) analyses revealed enhanced redox properties of the copper species, leading to the acceleration of the NH3-SCO reaction.
One of the standout characteristics of the PtSCuO/Al2O3 catalyst is its capacity to maintain over 90% selectivity to nitrogen across temperatures ranging from 150 to 450 °C, demonstrating stable performance even after 100 hours of continuous operation. This stability is coupled with its ability to efficiently mitigate NH3 emissions, making it particularly suitable for cold start applications typical of automotive exhaust systems.
Crucially, the synergy between platinum and copper plays a significant role, as the platinum atoms accelerate the redox activity of copper species, enabling more effective catalysis of the NH3-SCO reaction. By adjusting the ratio of platinum to copper during catalyst synthesis, researchers were able to optimize the surface coverage of platinum, enhancing catalytic performance even more.
Lu Chen, one of the lead researchers, remarked, "The intrinsic redox properties of the catalyst enable highly efficient ammonia oxidation, minimizing undesirable NOx formation." This notion underlines the importance of collaborative interactions between metal sites within catalytic frameworks, which has been partly responsible for the high selectivity observed.
Researchers also observed greater redox switching capabilities with the new catalyst compared to previous platinum-copper configurations, marking it as a transformative step forward for ammonia oxidation technologies. Concerns surrounding the oxidation states of Cu and Pt during reactions have been alleviated, showcasing how the facilitator roles of each metal augment overall catalyst efficiency.
Through comprehensive evaluations, the study has confirmed the PtSCuO/Al2O3 catalyst's superiority over conventional Pt/Al2O3 configurations, establishing it as one of the most effective solutions for ammonia oxidation currently available. The results promote broader applications of bi-metallic catalysis for not only reducing ammonia emissions but potentially paving the way for cleaner fuel technologies and enhanced industrial processes.
Overall, this research signifies the enormous potential held by bi-metallic catalysts for improving environmental outcomes associated with ammonia emissions. By deepening our understandings of how catalyst design can influence reactivity and selectivity, the team hopes to guide future endeavors toward refining these technologies for practical applications.