Supported Mesoporous and Hierarchical Porous Pd/TiO₂ Catalytic Coatings with Controlled Particle Size and Pore Structure

Control over the size of active metal particles and the structure of catalysts pore system is an essential requirement for the design of supported catalysts. Polymeric templates combined with a suitable metal-oxide precursor enable the synthesis of defined pore systems, whereas colloidal metal particles can provide access to the particle-size control. However, pore template, metal-oxide precursor, and colloidal metal particles combined in one synthesis solution are often not compatible with each other due to aggregation, precipitation, and dissolution processes. We present a new approach to the preparation of supported catalysts that permits the controlled coassembly of preformed colloidal metal nanoparticles, polymeric pore templates, and a metal-oxide precursor from a water-based solution. The synthesis is enabled by establishing under pH-neutral conditions the templating of defined pores using titanium(IV) bis(ammonium lactato) dihydroxide as an unconventional metal-oxide precursor. The presented approach provides a modular strategy for the precise control of the catalysts nanostructure. This is illustrated for the synthesis of mesoporous as well as hierarchically porous Pd/TiO 2 catalysts prepared from colloidal solutions of palladium nanoparticles. The catalysts show high activity and selectivity in the gas-phase hydrogenation of 1,3-butadiene.