Catalytic water reduction at colloidal metal "microelectrodes". 2. Theory and experiment

Abstract

5336partitioning in the case of this relatively small hydrophilic monocation compared to the distinct binding observed with the larger, more hydrophobic C B P underlines the role of hydrophobic factors and once again reinforces the idea that these cations as well as probably many other polar organic molecules are solubilized or J. Am. Chem. SOC. 1981, 103, 5336-5341 interact with micelles by binding at hydrophobic-hydrophilic interfaces.Abstract: A simple theory based on electrochemical principles is presented which predicts some of the catalytic properties of the widely used colloidal metal dispersions. The theory has been specifically applied to the case of photocatalytic water reduction to H2. The model assumes that the kinetic properties of the system are governed by the current-potential curves of the half-reactions and that the reaction velocity can be determined by finding the common potential at which the current attributable to the mediator (e.g., methyl viologen) oxidation is equal to that for proton reduction at the metal surface. The effects of pH, mediator potential, and colloid size and composition can be predicted. These predictions have been experimentally verified with methyl viologen radical cation generated electrochemically and photochemically (via the Ru(bpy)?+-N-phenylglyche system) and with other mediators at colloidal dispersions of several metals.

Bimetallic Pt?Ni nanoparticles can catalyze reduction of aromatic nitro compounds by sodium borohydride in aqueous solution

“…It is now well known that metal particles can catalyze redox reactions; this could be explained in terms of electrochemical current potential [32,33]. Metallic particles, either monometallic or multimetallic, being electronically conducting solids, strongly catalyze the redox reaction.…”

Catalytic reduction of 4-nitrophenol by magnetically recoverable Au nanocatalyst

“…As has been known, the Au nanoparticles supported on the magnetic nanocarrier can serve as the electron relay between 4-nitrophenolate ion (oxidant) and BH 4 − (reductant), and electron transfer occurs via the Au nanoparticles [34,35]. Although a few studies on the catalytic properties of supported metal catalysts in colloidal solutions have been reported [36,37], relatively less efforts have been made on the fabrication and catalytic properties of metal nanoparticles supported on the magnetic nanocarrier.…”

Particle Size Effects in Electrocatalysis by Uniform Colloids of Ruthenium Dioxide Hydrate

“…'5 However, it may be shown that particle diffusion is so much slower than reactant diffusion that particle-particle collisions are unlikely to influence the kinetics of reaction l. 17 Coagulation increases the effective particle radius, but coagulation rate increases as the square of particle c o n c e n t r a t i~n ;~~,~~ so coagulation would tend to reduce reaction rates at higher catalyst concentrations rather than vice versa.…”