Microchannel wash-coated

To process the methanol and water mix, a CuZnAl catalyst was wash-coated onto the microchannel walls. The alumina was deposited by dipping the plates into a 20% alumina suspension, which also included a stabilizer and a binder. After any excess was wiped off, the plates were calcined at 600 °C for 1 h in air. Air was removed from the pores by placing the calcined plate in a vacuum. The alumina wash-... 

Figure 3.2 GPMR used for biocatalytic transformations with immobilized enzymes [22]. (a) the fully assembled microreactor, (b) microstructured multichannel plate, and (c) electron micrograph of the wash-coat layer of y-aluminum oxide covering the microchannel walls.

A microchannel reactor configuration, in which catalytic endothermic (hydrocarbon SR) and exothermic (hydrocarbon combustion) reactions can be coupled, is shown in Figure 11.8 [ 24]. The reactor is composed of parallel groups of endothermic and exothermic channels which are separated by thin solid walls. The reactive flows are considered to be co-current. Each channel is square shaped, and the inner walls of the channels are wash-coated with a porous supported metal catalyst specific for the reaction type. Washcoat thickness is assumed to be uniform... 

To make a fuel-processing reactor out of a microstructured plate heat exchanger, heterogeneous catalysts need to be introduced into the microchannels, usually by wash-coating, similar to the procedure established for automotive exhaust clean-up. 

Additives to suppress particle agglomeration may be added to the suspension. This is crucial for low particle sizes [129]. Pfeifer et al. described a technique for wash-coating copper/zinc oxide catalysts onto aluminium microchannels [135], Copper oxide nanoparticles of 41 nm average particle size were mixed with zinc oxide nanoparticles of 77 nm average particle size either by wet mixing with aqueous hydroxy ethyl cellulose or hydroxy propyl cellulose in isopropyl alcohol. Alternatively, the particles were typically milled and then dispersed in aqueous hydroxy ethyl cellulose. The dispersion then filled in the microchannels, resulting in a catalyst layer of 20 pm thickness, which was then calcined in air at 450 °C. The surface area of the samples was around 20 m g . ... 

Chen et al. prepared a hybrid copper/zinc oxide/alumina/palladium/zinc oxide catalyst by wash-coating a copper/zinc oxide catalyst supported by alumina into microchannels [192]. Palladium/zinc oxide powder was then coated onto this catalyst. 

Germani et al. prepared platinum/ceria water-gas shift catalysts in microchannels containing between 0.8 and 1.4wt.% platinum and between 8 and 20vrt.% ceria [308]. The sample containing 1.4wt.% platinum and 8 wt.% ceria showed the highest conversion, which was decreased when the catalyst was reduced prior to the activity test. Kolb et al. varied the platinum content of their platinum/ceria wash-coated catalysts between 1 and 5 wt.%, while the ceria content ranged between 6 and 40 wt.% [269]. The optimum platinum content was determined in the range between 3 and 5 wt.%, while the optimum ceria content was between 12 and 24 wt.%. 

Figure 10.2 Microchannels with catalyst prepared by wash coating with nanoparticles incorporation before assembling of a reactor.

Hernandez Carucci et of. [29] used a plug flow model for epoxidation of ethylene on silver/R-alumina catalysts. The silver/R-alumina catalysts were wash coated in stainless steel microchannels. Due to low conversions (<0.30% for kinetic experiments), the concentration and temperature gradients were small. The effect of internal diffiision could be neglected due to pure silver catalyst. The model was based on the competitive adsorption of ethylene and molecular oxygen over the silver surface. It was compared with experimental data in the microchaimels and had a very high degree of agreement (97%). 

In order to detect the analyte specifically, a complex has to be formed first. To this end, the revelation moiety (e.g. an enzyme-labelled antigen or antibody) is for instance incubated in the chip so as to bind to the analyte that has previously been captured within the microchannel. In another scheme, the analyte solution is first mixed with the revelation moiety, and the formed complex is then incubated in the chip in order to be captured on the bed of antibodies coating the walls of the micro-channel. After a washing step (to remove the excess affinity partner), the microchannel is filled with the substrate which shall thus react... 

Figure 11. Picture of an immunoassay chip with a H-shaped microchannel, and the sequential steps of an automatic lA processes. The surface of the reaction channel wall is coated with probing antigens. The solution delivery occurs in the dark colored channels whereas in the light colored channels, the solution remains stationary. The arrows indicate the flow direction, (a) Dispensing and incubation of the primary antibody (b) washing off the primary antibody by a buffer solution (c) dispensing and incubation of the secondary antibody (d) washing off the secondary antibody by a buffer solution.

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