Synthesis of Pd–alumina and Pd–lanthana Suspension for Catalytic Applications by One-step Liquid Flame Spray

Catalytic materials of alumina and lanthana supported nanosized palladium particles (7 wt%) in a water suspension were prepared by Liquid Flame Spray (LFS) method. The particle production rate was 90 g/h, using liquid precursors containing Al(NO₃)₃ · 9H₂O, La(NO₃)₃ · 6H₂O and Pd(NH₃)₄NO₃ in water solution. In the LFS method, a turbulent, high-temperature (T_max ∼ 2,700 °C) H₂–O₂ flame is used. The liquid precursor is atomized into micron sized droplets by high velocity H₂ flow and introduced into the flame where the droplets will evaporate. The evaporated compounds decompose and the reaction product re-condenses into particulate material. Here, the nanosized particles are formed by gas-to-particle conversion and the micron sized particles via liquid-to-solid route. In this study, the produced particulate material was collected by thermophoresis along with condensing water into a suspension (nanoparticles in water) in a one-step process. Thus, the whole suspension was produced from the end products of the flame. According to TEM-EDS analysis, the particulate material contained micron sized porous aluminum oxide or lanthanum oxide carrier particles, coated by nanosized palladium particles (∼2–10 nm). The surfactant (Rhodasurf-La 42) was injected into the suspension just after collection to reduce agglomeration. Catalytic performance of the produced Pd–lanthana containing suspension was tested in laboratory with synthetic gases, in order to use it as a possible raw material for three-way catalyst (TWC). The suspension was used as Pd raw material in TWC washcoat and dispersed onto a metallic honeycomb.