In cascade approach, products are made in more than one step through consecutive and independent reactions. In each step, the system would receive specific reactants and produce specific products depending on which catalyst is used. Nevertheless, in this multi-step approach, each catalyst should be synthesized, and the products should be transferred between one step and the other, associated with an increased production cost. Each catalyst can be directly used, usually supported on different materials. Among the possible supports, the hierarchical silica monoliths functionalized with metals are promising as they allow easy diffusion of the molecules within the different pore sizes. They are shown to be readily used as micro-reactors for catalysis, replacing traditional powdered materials. This work aims to show a general method for building new materials incorporating two well-separated different catalytic functions inside one silica monolith material, ideal for multi-step catalysis. To reach this goal, we adopted the High Internal Phase Emulsion (HIPE) synthesis, which is simple and easily functionalizable. Contrary to the classical synthesis, we constructed our material like a sandwich where each layer has a different function. The hierarchical porosity of the synthesized silica monoliths was verified by SEM. In addition, Diffuse Reflectance UV-Vis spectroscopy verified the presence of the metals. Then, a 2-step test-case of this new type of material, associated with two types of the desired functionalization, was identified and realized. As a demonstration case, sandwich monoliths of Co-Cu were tested as a catalytic reactor in continuous flow mode for a two-step reaction to form imines. The product obtained after passing through the monoliths was characterized with FTIR spectroscopy to demonstrate the specific catalytic activity. Four samples were tested: unfunctionalized monolith, Cu-monolith, Co-monolith, and Co-Cu monolith. Thus, the Co-Cu sandwich monolith spectrum was the only one that showed the singular peak of the C=N stretching bond, which confirms the imine formation. The same idea can be applied to synthesize three-layers monoliths.

Sandwich monoliths: A new strategy for multi-step catalysis

Where thousands of chemistry professionals meet to share ideas and advance scientific and technical knowledge. Spring 2023 abstracts, posters, and presentations will launch at the end of March.

ACS Spring 2023

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.