Hydrogen production from ammonia decomposition catalyzed by Ru nano-particles in alkaline molecular sieves under photothermal conditions

Abstract

Because the high electron cloud density around Ru is favorable for ammonia decomposition, gallium addition to it resulted in an alkaline molecular sieve carrier with a large specific surface area. It was revealed that GaOH not only elevated the electron cloud density near the active center of Ru but also encouraged NH bond breaking and hydrogen atoms’ binding on the catalyst surface. Furthermore, the molecular sieve's regular pore structure strongly inhibited the growth of Ru particles within it, resulting in a high degree of mono-dispersion of Ru nanoparticles and a reduction in the average particle size of the Ru active center to < 3 nm. For TOF >1, the above two factors combined to decrease the ammonia decomposition temperature to < 450 °C. Furthermore, under photothermal synergistic catalysis, the hydrogen production rate via ammonia decomposition was further elevated, and the reaction temperature was further decreased to < 380 °C with TOF > 1. In situ UV photoelectron spectroscopy clarified that the hydrogen atom concentration on Ru increased during photothermal catalysis. According to the FT-IR analysis of the surface intermediate of NH/NH2 formed by ammonia decomposition, photothermal synergistic catalysis can weaken the NH bond compared with pure heating, making it easier for H atoms to combine and form H2. The test results of the correlation between activation energy, reaction rate, and ammonia partial pressure show that, when compared to pure thermal catalysis, photothermal catalysis does not substantially alter the reaction path. The primary reason behind the increased hydrogen production rate of ammonia decomposition by photothermal catalysis was the thermal effect of the light source.