Catalyst incorporation into microreactors

Sputtering has been used to incorporate a number of catal3 tic metals into microreactor devices. Examples include Pt, Zr, Mo, Pd, Ru, Rh, or alloys such as Pt-Ru. It is a convenient fabrication technique, although some researchers argue that the active surface area of the deposited catalyst is unsatisfactory. For many metals this problem can be overcome by sputtering using an oxygen-rich sputter gas rather than Ar alone. 

Packed-bed microreactors are prepared by filling catalyst powder into the microchannels of the reactor. Since this is the easiest and fastest way for the incorporation of the catalyst, this type of microreactor is frequently used for catalyst screening [82]. Another advantage over other types of catalytic beds is the possibility of using... 

Several methods for the incorporation of catalysts into microreactors exist, which differ in the phase-contacting principle. The easiest way is to fill in the catalyst and create a packed-bed microreactor. If catalytic bed or catalytic wall microreactors are used, several techniques for catalyst deposition are possible. These techniques are divided into the following parts. For catalysts based on oxide supports, pretreatment of the substrate by anodic or thermal oxidation [93, 94] and chemical treatment is necessary. Subsequently, coating methods based on a Uquid phase such as a suspension, sol-gel [95], hybrid techniques between suspension and sol-gel [96], impregnation and electrochemical deposition methods can be used for catalyst deposition [97], in addition to chemical or physical vapor deposition [98] and flame spray deposition techniques [99]. A further method is the synthesis of zeoUtes on microstructures [100, 101]. Catalysts based on a carbon support can be deposited either on ceramic or on metallic surfaces, whereas carbon supports on metals have been little investigated so far [102]. 

Multiphase packed-bed or trickle-bed microreactor [29, 30] Standard porous catalysts are incorporated in silicon-glass microfabricated reactors consisting of a microfluidic distribution manifold, a single micro-channel reactor or a microchannel array and a 25-pm microfllter. The fluid streams come into contact via a series of interleaved high aspect ratio inlet chaimels. Perpendicular to these chaimels, a 400-pm wide channel is used to deliver catalysts as a slurry to the reaction chaimel and contains two ports to allow cross-flow of the slurry. High maldistribution, pressure drop and large heat losses may occur... 

Unfortunately, the widely used flow reactors (for example, microreactors, multi-cell flow reactors, and disk reactors) do not tolerate solid particulates and precipitates, which would clog the miniaturized flow devices. Therefore, immobilization of the reagents/catalysts by a solid support is of significant importance in this field. Hence, a broad range of solid supports have been employed to incorporate the reagent/ catalyst into the reactors, including packed-beds, monoliths, and other systems that exploit the high surface-to-volume areas obtained in microchannel devices. 

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