Polyol-Intermediated Facile Synthesis of B5-Site-Rich Ru-Based Nanocatalysts for COx-Free Hydrogen Production via Ammonia Decomposition

Herein, a B5-site-rich Ru/MgAl2O4 nanocatalyst for the production of COx-free hydrogen from ammonia (NH3) is synthesized using the polyol method. The polyol method enables size-sensitive Ru-nanoparticle growth and controlled B5-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/MgAl2O4 (BG) catalyst synthesized using butylene glycol (a long-carbon-chain solvent) contains 2.5 nm Ru particles uniformly dispersed on its surface and abundant B5 sites at (0 0 2)/(0 1 1). Moreover, the Ru/MgAl2O4 (BG) catalyst exhibits lower activation energy (48.9 kJ mol-1) and higher H2 formation rate (565-1,236 mmol gcat -1 h-1 at 350-450 °C and a weight hourly space velocity of 30,000 mL gcat -1 h-1) during the NH3 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 B5 sites on the catalyst surface accelerate the recombination-desorption of N2, which is the rate-determining step of the NH3 decomposition reaction at low temperatures. Thus, this study facilitates clean hydrogen production.Herein, a B5-site-rich Ru/MgAl2O4 nanocatalyst for the production of COx-free hydrogen from ammonia (NH3) is synthesized using the polyol method. The polyol method enables size-sensitive Ru-nanoparticle growth and controlled B5-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/MgAl2O4 (BG) catalyst synthesized using butylene glycol (a long-carbon-chain solvent) contains 2.5 nm Ru particles uniformly dispersed on its surface and abundant B5 sites at (0 0 2)/(0 1 1). Moreover, the Ru/MgAl2O4 (BG) catalyst exhibits lower activation energy (48.9 kJ mol-1) and higher H2 formation rate (565-1,236 mmol gcat -1 h-1 at 350-450 °C and a weight hourly space velocity of 30,000 mL gcat -1 h-1) during the NH3 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 B5