Efficient Low-Temperature H2 Production from HCOOH/HCOO– by [Pd0@SiO2-Gallic Acid] Nanohybrids: Catalysis and the Underlying Thermodynamics and Mechanism

Abstract

Hybrid Pd0-based nanoparticles have been synthesized in aqueous solution by two routes: (a) reduction of Pd ions by gallic acid (GA) producing Pd0-GA and (b) Pd0 formed on SiO2-GA nanohybrids where GA was covalently grafted on SiO2 nanoparticles (Pd0@SiO2-GA). In both protocols, Pd0 nanoparticles were formed in situ, under alkaline pH, via reduction of Pd2+ ions by GA radicals formed by atmospheric O2. XRD and TEM data show that the Pd0@SiO2-GA consists of 6.5 nm Pd0 nanoparticles finely dispersed on the SiO2-GA nanosupport, whereas Pd0-GA consists of aggregated 12 nm Pd0 nanoparticles. The two families of Pd0 nanohybrids have been studied for catalytic H2 production from formic acid/sodium formate in aqueous solution at near ambient temperatures 40–80 °C. Pd0@SiO2-GA achieves H2 production from NaCOOH/HCOOH at 19 mL/min per mg of Pd. This outperforms by a factor of 400% the H2 production by (Pd0-GA) particles, as well as all Pd0-SiO2 catalysts, so far reported in the literature. The Pd0@SiO2-GA catalyst ...