Catalyst Coating on Prefabricated Capillary Microchannels for the Direct Synthesis of Hydrogen Peroxide

Abstract

The geometric surface area of capillary microchannels is insufficient for the direct deposition of a catalyst active phase to reach a sufficient level of microreactor activity. For this reason it is necessary to coat a porous layer of a catalyst support on the channel wall prior to the deposition of the active metallic species. This work addresses the challenges related to the preparation of well-adhered and uniform silica coatings inside closed capillary channels suitable for catalyst deposition for the direct synthesis of hydrogen peroxide. The method used to deposit a layer of coating suspension, which upon solvent evaporation and heating is transformed into a solid film, is known as dynamic gas displacement. Variation of coating parameters and properties of the coating solution could be used to produce microreactors coated with different silica loadings. The most critical aspect of coating is maintaining the film regularity during and after displacement of the coating fluid. The uniformity of the coating thickness is greatly affected not only by the ability to maintain the coating parameters constant, such as the coating velocity, temperature, and solvent evaporation rate during and after displacement of the coating solution, but also by the rheological properties of the coating fluid. Advantages and disadvantages of different coating techniques such as colloidal coating, sol–gel, and slurry coating are discussed in detail. Finally, we demonstrate that silica wall-coated layers with embedded Au–Pd colloidal alloy nanoparticles are active in catalyzing the direct synthesis of hydrogen peroxide.

Nopol Production Over Sn‐MCM‐41 Immobilized in a Wall‐Coated Microreactor using Formaldehyde Generated Ex‐Situ

“…Paunovic et al. (2015) [25] found that presynthesized catalyst incorporated in the washcoating suspension could be blocked by the binding material due to the closure of the catalyst pores. Therefore, it is preferable to deposit the active phase on the catalyst support layer previously deposited by washcoating methodology on the internal walls of the microreactor.…”

“…[23] The incorporation of the catalyst on the reactor walls could be carried out in two ways: i) starting with the catalyst support coated on the reactor wall and then to carry out the impregnation of the active phase, or ii) using a suspension that contains the previously synthesized catalysts. [24] Paunovic et al (2015) [25] found that presynthesized catalyst incorporated in the washcoating suspension could be blocked by the binding material due to the closure of the catalyst pores. Therefore, it is preferable to deposit the active phase on the catalyst support layer previously deposited by washcoating methodology on the internal walls of the microreactor.…”

In situ fabrication of layered double hydroxide film immobilizing gold nanoparticles in capillary microreactor for efficient catalytic carbonylation of glycerol

“…A microreactor can be fabricated as a chip or a capillary tube that exhibiting certain advantages of high surface-to-volume ratio, excellent mass and heat transfer properties [4]. However, the direct deposition of a catalytic active phase to reach a sufficient level of activity is hindered by the insufficient geometric surface area of capillary microchannels [5]. Therefore, porous SiO2 [6,7], porous TiO2 [8,9], ZnO nanorods [10], polydopamine [11], zeolites [12], [13], [14] and MOFs [15,16] have been introduced in microreactors to achieve the homogeneous dispersion and immobilization of catalytic active components, and realize supra-equilibrium conversions, resulting in improved reaction efficiency and intensified production processes.…”

Simple Method for Directly Synthesizing Ag Nanoparticles with Silver Ammonia and Polydopamine in a Microreactor toward the Conversion of 4-NP to 4-AP

“…However, these direct methods may cause unstable catalyst adhesion to the substrates, which leads to the peel-off and aggregation of the catalysts after long-term operation . Consequently, several scholars used a precursor solution for the in situ synthesis of catalysts on supporting materials, such as alumina, titania, carbon nanofibers, and silica . However, for better adhesion of the catalysts to the supporting materials, the preparation process usually requires high-temperature calcination, making it difficult to select the reactor materials.…”

“…22 Consequently, several scholars used a precursor solution for the in situ synthesis of catalysts on supporting materials, such as alumina, 23 titania, 24 carbon nanofibers, 25 and silica. 26 However, for better adhesion of the catalysts to the supporting materials, the preparation process usually requires high-temperature calcination, 16 reactor materials. Therefore, the development of a simple preparation method with low substrate selectivity and mild conditions is essential.…”