Abstract
Since inter- and intra-particle heterogeneities in catalyst particles are more the rule than the exception, it is advantageous to perform high-throughput screening for the activity of single catalyst particles. A multiphase system (gas/liquid/solid) is developed, where droplet-based microfluidics and optical detection are combined for the analysis of single catalyst particles by safely performing a hydrogenation study on in-house synthesized hollow Pd/SiO2 catalyst microparticles, in a polydimethylsiloxane (PDMS) microreactor. A two-phase segmented flow system of particle-containing droplets is combined with a parallel gas-reactant channel separated from the flow channel by a 50 μm thick gas permeable PDMS wall. In this paper, the developed microreactor system is showcased by monitoring the Pd-catalyzed hydrogenation of methylene blue. A discoloration of blue to brown visualizes the hydrogenation activity happening in a high-throughput fashion on the single Pd/SiO2 spherical catalyst microparticles, which are encapsulated in 50 nL-sized droplets. By measuring the reagent concentration at various spots along the length of the channel the reaction time can be determined, which is proportional to the residence time in the channel. The developed experimental platform opens new possibilities for single catalyst particle diagnostics in a multiphase environment.
Highlights
In the search for more effective catalysts and reaction conditions, the use of highthroughput experimentation to monitor catalyst performance on a single particle level has gained increasing interest over the last decades.[1,2,3,4] A growing eld ofPaper research that has shown great potential for these types of experiments is lab-on-achip, and in particular droplet-based micro uidics.[5,6,7] When using two immiscible uids and speci c geometries such as a T-junction or ow focusing geometry, droplets can be created by a combination of surface tension and shear forces.[8]
For the hydrogenation to take place, the gaseous H2 has to travel from the gas channels through the PDMS wall and the uorinated oil (FC-40) continuous phase before it reaches the ethanol droplet
We concluded that H2 must rst diffuse into and through the PDMS wall before it can enter the ethanol droplet containing the catalyst
Summary
In the search for more effective catalysts and reaction conditions, the use of highthroughput experimentation to monitor catalyst performance on a single particle level has gained increasing interest over the last decades.[1,2,3,4] A growing eld ofPaper research that has shown great potential for these types of experiments is lab-on-achip, and in particular droplet-based micro uidics.[5,6,7] When using two immiscible uids and speci c geometries such as a T-junction or ow focusing geometry, droplets can be created by a combination of surface tension and shear forces.[8]. With an optical or spectroscopic detection method along the channel, the products formed per single particle can be analyzed by measuring all droplets passing through the detector.[14] This opens possibilities for the characterization of catalyst particles in liquid-phase reactions.
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