Increasing the Size-Selectivity in Laser-Based g/h Liquid Flow Synthesis of Pt and PtPd Nanoparticles for CO and NO Oxidation in Industrial Automotive Exhaust Gas Treatment Benchmarking

Abstract

PtPd catalysts are state-of-the-art for automotive diesel exhaust gas treatment. Although wet-chemical preparation of PtPd nanoparticles below 3 nm and kg-scale synthesis of supported PtPd/Al2O3 are already established, the partial segregation of the bimetallic nanoparticles remains an issue that adversely affects catalytic performance. As a promising alternative, laser-based catalyst preparation allows the continuous synthesis of surfactant-free, solid-solution alloy nanoparticles at the g/h-scale. However, the required productivity of the catalytically relevant size fraction <10 nm has yet to be met. In this work, by optimization of ablation and fragmentation conditions, the continuous flow synthesis of nanoparticles with a productivity of the catalytically relevant size fraction <10 nm of >1 g/h is presented via an in-process size tuning strategy. After the laser-based preparation of hectoliters of colloid and more than 2 kg of PtPd/Al2O3 wash coat, the laser-generated catalysts were benchmarked against an industry-relevant reference catalyst. The conversion of CO by laser-generated catalysts was found to be equivalent to the reference, while improved activity during NO oxidation was achieved. Finally, the present study validates that laser-generated catalysts meet the size and productivity requirements for industrial standard operating procedures. Hence, laser-based catalyst synthesis appears to be a promising alternative to chemical-based preparation of alloy nanoparticles for developing industrial catalysts, such as those needed in the treatment of exhaust gases.

Photoluminescence of Fully Inorganic Colloidal Gold Nanocluster and Their Manipulation Using Surface Charge Effects

“…[ 62 ] This supporting procedure of inorganic Au NC also leads to excellent model material for heterogeneous catalysis, which benefits from the high specific surface area of the inorganic metal NC as well as from their high surface charge. [ 63 ] Synthesis of supported catalysts from laser‐based synthesis routes was already demonstrated to be scalable to kilograms of catalysts for larger noble metal NPs [ 64 ] and transferability to Au NC with higher specific surface areas could be highly interesting. Note that surface charge tuning of ligand‐free, laser‐generated Au NCs has recently been demonstrated as an approach to understand the role of surface charge and size in heterogeneous catalysis of gold clusters supported on titania, evaluated for four different oxidation catalytic reactions.…”

Synthesis of gold, platinum, and gold-platinum alloy nanoparticle colloids with high-power megahertz-repetition-rate lasers: the importance of the beam guidance method

“…At high power MHz LSC, in-process fragmentation also contributes to a narrowed particle size distribution. Recently, it has been shown with the same polygon system that the mass fraction selectivity towards small particles is adjustable between 5 and 40% by balancing between the in-process fragmentation (downsizing) and ablation (overall productivity) particle formation pathway (Dittrich et al 2020).…”

“…The method makes alloy nanoparticles easily accessible, even in compositions difficult to produce by conventional methods, showing particular application potential and superior performance in heterogeneous catalysis (Reichenberger et al 2019). Recently, kg scale of laser-generated PtPd/Al 2 O 3 automotive exhaust gas catalysts were tested in reference reactions of CO and NO oxidation within an industrial test setting where the laser-made catalysts showed a comparable CO oxidation and even higher NO oxidation activity and durability (Dittrich et al 2020). An important contribution in the field of catalytic applications was made by Canadian researchers, who used gold-platinum alloy nanoparticles of various compositions prepared by LSC (Zhang et al 2012), (Oko et al 2014), (Oko et al 2015).…”

Time resolved studies reveal the origin of the unparalleled high efficiency of one nanosecond laser ablation in liquids

“…Laser ablation in liquid (LAL) is a versatile method for the synthesis of nanoparticles (NPs), that enables the production of ligand-free colloids 1−4 . Compared to chemically synthesized colloids, particles generated by LAL exhibit a higher signal-to-noise ratio for laser desorption ionization mass spectrometry 5 , are suitable as reference materials for nano-toxicological assays 6 , enable the decoration of microparticles for 3D printing 7,8 , and have high potential in heterogeneous catalysis 9 even in industrial settings of automotive exhaust gas catalyst testing 10 . Furthermore, with LAL it is possible to produce molar fraction series of alloy NPs from pressed micropowder targets, even if an element miscibility gap exists 11 .…”