Uniform dispersion of ultrafine ruthenium nanoparticles on nano-cube ceria as efficient catalysts for hydrogen production from ammonia-borane hydrolysis

Ammonia-borane (NH3BH3, AB) is an valuable chemical hydrogen storage material due to its large hydrogen content of 19.6 wt%, superior stability, and environmental benignity. Highly active catalysts play an indispensable role in hydrogen production from AB hydrolysis. However, it remains a big challenge to achieve that kind of catalyst, i.e., small uniform size and homogeneous dispersion of metal particles on an oxide support. In this work, nano-cube ceria was successfully synthesized through a hydrothermal method. Two different catalysts, Ru/CeO2-NaBH4 and Ru/CeO2-H2/Ar, were prepared by loading ultrafine ruthenium nanoparticles on nano-cube ceria through the reduction of Ru3+ ions by NaBH4 in solution and H2/Ar mixed gas, respectively. The characterization results show that the ruthenium nanoparticles in a very narrow size range of 0.90-2.26 nm are uniformly dispersed on the surface of nano-cube ceria with the existence of Ce3+ and rich oxygen vacancies, thus providing a strong metal-support interaction. Therefore, even with a small amount of ruthenium (1.6 wt%), Ru/CeO2-H2/Ar exhibits a relatively low activation energy (Ea) of 42.98 kJ mol-1 and high catalytic activity with a turnover frequency (TOF) of 176.9 molH2 molRu-1 min-1 for the catalytic hydrolytic dehydrogenation of AB. Additionally, about 65.8% of catalytic activity is retained after five consecutive tests. This work provides a general strategy to achieve high-performance supported catalysts with ultrafine metal nanoparticles in a uniform distribution.

Automated summary

In this study, nano-cube ceria was synthesized through a hydrothermal method, and ultrafine ruthenium nanoparticles were loaded on the surface of nano-cube ceria to prepare two different catalysts. The ruthenium nanoparticles were uniformly dispersed on the ceria support, providing a strong metal-support interaction. The Ru/CeO2-H2/Ar catalyst showed high catalytic activity and relatively low activation energy for the hydrolytic dehydrogenation of ammonia-borane, and retained about 65.8% of its catalytic activity after five consecutive tests. This work presents a general strategy for achieving high-performance supported catalysts with ultrafine metal nanoparticles in a uniform distribution.