Enhanced Ammonia Decomposition by Tuning the Support Properties of Ni/GdxCe1-xO2-δ at 600 °C.

Ammonia decomposition is a promising method to produce high-purity hydrogen. However, this process typically requires precious metals (such as Ru, Pt, etc.) as catalysts to ensure high efficiency at relatively low temperatures. In this study, we propose using several Ni/GdxCe1-xO2-δ catalysts to improve ammonia decomposition performance by adjusting the support properties. We also investigate the underlying mechanism for this enhanced performance. Our results show that Ni/Ce0.8Gd0.2O2-δ at 600 °C can achieve nearly complete ammonia decomposition, resulting in a hydrogen production rate of 2008.9 mmol.g-1.h-1 with minimal decrease over 150 h. Density functional theory calculations reveal that the recombinative desorption of nitrogen is the rate-limiting step of ammonia decomposition over Ni. Our characterizations indicate that Ni/Ce0.8Gd0.2O2-δ exhibits a high concentration of oxygen vacancies, highly dispersed Ni on the surface, and abundant strong basic sites. These properties significantly enhance the associative desorption of N and strengthen the metal support interactions, resulting in high catalytic activity and stability. We anticipate that the mechanism could be applied to designing additional catalysts with high ammonia decomposition performance at relatively low temperatures.

Cu Species-Modified OMS-2 Materials for Enhancing Ozone Catalytic Decomposition under Humid Conditions.

Manganese oxide octahedral molecular sieves (OMS-2) exhibit an excellent performance in ozone catalytic decomposition in dry atmosphere conditions, which however is severely limited by deactivation in humid conditions. Herein, it was found that the OMS-2 materials modified with Cu species could obviously improve both the ozone decomposition activity and water resistance. Based on the characterization results, it was found that these CuOx/OMS-2 catalysts exhibited dispersed CuOx nanosheets attached and located at the external surface accompanied with ionic Cu species entering the MnO6 octahedral framework of OMS-2. In addition, it was demonstrated that the main reason for the promotion of ozone catalytic decomposition could be ascribed to the combined effect of different Cu species in these catalysts. On the one hand, ionic Cu entered the MnO6 octahedral framework of OMS-2 near the catalyst surface and substituted ionic Mn species, resulting in an enhanced mobility of surface oxygen species and formation of more oxygen vacancies, which act as the active sites for ozone decomposition. On the other hand, the CuOx nanosheets could serve as non-oxygen vacancy sites for H2O adsorption, which could alleviate the catalyst deactivation to some extent caused by the occupancy of H2O on surface oxygen vacancies. Finally, different reaction pathways for ozone catalytic decomposition over OMS-2 and CuOx/OMS-2 under humid conditions were proposed. The findings in this work may shed new light on the design of highly efficient catalysts for ozone decomposition with improved water resistance.