Polyol-Intermediated Facile Synthesis of B 5 -Site-Rich Ru-Based Nanocatalysts for CO x -Free Hydrogen Production via Ammonia Decomposition.

Herein, a B ₅ -site-rich Ru/MgAl ₂ O ₄ nanocatalyst for the production of CO _x -free hydrogen from ammonia (NH ₃ ) is synthesized using the polyol method. The polyol method enables size-sensitive Ru-nanoparticle growth and controlled B ₅ -site formation on the catalyst by tuning the carbon-chain length of the polyol solvent used, obviating the use of a separate stabilizer and enhancing electron donation from Ru (with a high surface electron density) and π-back bonding. The Ru/MgAl ₂ O ₄ (BG) catalyst synthesized using butylene glycol (a long-carbon-chain solvent) contains 2.5 nm Ru particles uniformly dispersed on its surface and abundant B ₅ sites at (0 0 2)/(0 1 1). Moreover, the Ru/MgAl ₂ O ₄ (BG) catalyst exhibits lower activation energy (48.9 kJ mol ^-1 ) and higher H ₂ formation rate (565-1,236 mmol g _cat ^-1 h ^-1 at 350-450 °C and a weight hourly space velocity of 30,000 mL g _cat ^-1 h ^-1 ) during the NH ₃ decomposition reaction than catalysts with a similar Ru particle size and high metal dispersion synthesized by the impregnation and deposition-precipitation methods. This high performance is possibly because the abundant electron-donating B ₅ sites on the catalyst surface accelerate the recombination-desorption of N ₂ , which is the rate-determining step of the NH ₃ decomposition reaction at low temperatures. Thus, this study facilitates clean hydrogen production.
(© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)