Fabrication of ultrafine Pd nanoparticles on 3D ordered macroporous TiO2 for enhanced catalytic activity during diesel soot combustion

Abstract

Nanocatalysts consisting of three-dimensionally ordered macroporous (3DOM) TiO2-supported ultrafine Pd nanoparticles (Pd/3DOM-TiO2-GBMR) were readily fabricated by gas bubbling-assisted membrane reduction (GBMR) method. These catalysts had a well-defined and highly ordered macroporous nanostructure with an average pore size of 280 nm. In addition, ultrafine hemispherical Pd nanoparticles (NPs) with a mean particle size of 1.1 nm were found to be well dispersed over the surface of the 3DOM-TiO2 support and deposited on the inner walls of the material. The nanostructure of the 3DOM-TiO2 support ensured efficient contact between soot particles and the catalyst. The large interface area between the ultrafine Pd NPs and the TiO2 also increased the density of sites for O2 activation as a result of the strong metal (Pd)-support (TiO2) interaction (SMSI). A Pd/3DOM-TiO2-GBMR catalyst with ultrafine Pd NPs (1.1 nm) exhibited higher catalytic activity during diesel soot combustion compared with that obtained from a specimen having relatively large Pd NPs (5.0 nm). The T10, T50 and T90 values obtained from the former were 295, 370 and 415 °C. Both the activity and nanostructure of the Pd/3DOM-TiO2-GBMR catalyst were stable over five replicate soot oxidation trials. These results suggest that nanocatalysts having a 3DOM structure together with ultrafine Pd NPs can decrease the amount of Pd required, and that this approach has potential practical applications in the catalytic combustion of diesel soot particles.