Recent advances in the liquid‐phase synthesis of metal nanostructures of different sizes and shapes are reviewed regarding their catalytic properties. The controlled synthesis of nanostructures is based on the colloid chemistry techniques in the solution, which use organic nanoreactors and a variety of stabilizers. Their catalytic activity and selectivity depend on the particle's shape and size, as shown for Suzuki and Heck coupling, hydrogenations, hydrogenolysis, oxidations, and electron‐transfer reactions. The knowledge of a reaction's structure‐sensitivity relationship is important for the rational catalyst design in view of process intensification. Nanostructures can be used per se and in supported form to meet the requirements of an eventual process.

Metal nanoparticle (NP) co-catalysts on metal oxide semiconductor supports are attracting attention as photocatalysts for a variety of chemical reactions. Related efforts seek to make and use Pt-free catalysts. In this regard, we report here enhanced CH₄ formation rates of 25 and 60 μmol·g^–1·h^–1 by photocatalytic CO₂ reduction using hitherto unused ZnPd NPs as well as Au and Ru NPs. The NPs are formed by colloidal synthesis and grafted onto short n-type anatase TiO₂ nanotube arrays (TNAs), grown anodically on transparent glass substrates. The interfacial electric fields in the NP-grafted TiO₂ nanotubes were probed by ultraviolet photoelectron spectroscopy (UPS). Au NP-grafted TiO₂ nanotubes (Au-TNAs) showed no band bending, but a depletion region was detected in Ru NP-grafted TNAs (Ru-TNAs) and an accumulation layer was observed in ZnPd NP-grafted TNAs (ZnPd-TNAs). Temperature programmed desorption (TPD) experiments showed significantly greater CO₂ adsorption on NP-grafted TNAs. TNAs with grafted NPs exhibit broader and more intense UV–visible absorption bands than bare TNAs. We found that CO₂ photoreduction by nanoparticle-grafted TNAs was driven not only by ultraviolet photons with energies greater than the TiO₂ band gap, but also by blue photons close to and below the anatase band edge. The enhanced rate of CO₂ reduction is attributed to superior use of blue photons in the solar spectrum, excellent reactant adsorption, efficient charge transfer to adsorbates, and low recombination losses.