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.