From metal vapor to supported single atoms, clusters and nanoparticles: Recent advances to heterogeneous catalysts

Swapping CO2 electro-reduction active sites on a nickel-based hybrid formed on a "guilty" covalent triazine framework

A homogeneous and almost monodisperse Ni/CTFph composite of ultrasmall Ni NPs (∼2.2 nm) has been prepared by Metal Vapor Synthesis (MVS) and deposited on a highly porous and high specific surface area covalent triazine network. Metal doping was deliberately carried out on a metal-free system exhibiting superior CO2RR selectivity towards the challenging CO2-to-HCOOH electroreduction. Electrochemical studies aimed at shedding light on the CO2RR performance of the ultimate composite have allowed speculation on the synergistic or exclusive action of the two potentially active phases (N-doped C-network vs. Ni NPs). In contrast to the generally exclusive CO2-to-CO reduction mechanism described for the state-of-the-art Ni NP-based CO2RR electrocatalysts, Ni/CTFph has unveiled the unprecedented ability of Ni NPs to promote the alternative and more challenging 2e- CO2-to-HCOOH reduction pathway, even at moderately reducing potentials (-0.3 V vs. RHE).

Effect of Pt Nanoparticle Morphology on the Aerobic Oxidation of Ethylene Glycol to Glycolic Acid in Water

Pt nanoparticles (diameter <3 nm), generated by metal vapor synthesis and supported on a high surface area carbon, were used to catalyze the aerobic oxidation of ethylene glycol to glycolic acid (GA) in water under neutral and basic reaction conditions. Controlled heat treatment of the catalyst under a nitrogen atmosphere brought about the formation of a morphologically well-defined catalyst. A combination of atomic resolution electron microscopy, CO stripping voltammetry, and XPS analyses conducted on as-synthesized and heat-treated catalysts demonstrated the crucial role of the nanoparticles' morphology on the stabilization of catalytically highly active Pt-OH surface species, which were key species for the Pt-catalyzed oxidation of the alcohol to the carbonyl functionality. The boosting effect of base on the catalyst' s activity and GA selectivity has been proved experimentally (autoclave experiments). The effect of base on the nonmetal-catalyzed reaction steps (i.e., aerobic oxidation of carbonyl to acid functionality) has been proved by DFT calculations.