The CO–H2 and CO–H2O reactions over TiO2 nanotubes filled with Pt metal nanoparticles

We have investigated the catalytic behavior of Pt encapsulated TiO2 nanotubes for the water gas shift reaction as well as the hydrogenation of CO. Pt–TiO2 nanotube catalysts were prepared by employing fine fiber shaped crystals of [Pt(NH3)4](HCO3)2 complex as a structure determining template material. The turnover frequencies (TOF) of these nanotube catalysts were more than one order of magnitude larger than conventional impregnation Pt/TiO2 catalysts, and the selectivity for methanol in CO–H2 reaction was extraordinary high compared to the impregnation catalysts. The XPS and XRD analyses of the nanotubes revealed characteristic electronic state of reduced TiO2 (Ti3+ in rutile structure) with zerovalent Pt even after the calcination at 773 K. In WGS reaction, electron rich Ti3+ on the nanotube wall may play an important role to activate water molecules for the oxidation of CO. In CO–H2 reaction, similar promotion effect of Ti3+ species may be operating for selective methanol formation by supplying active OH(a).