Low-temperature route for the structuring of catalysts and adsorbents via porous silica binders

Structured adsorbents and catalysts have gained increasing attention compared to conventional forms (such as beads, granules and pellets), as they allow a better control of macroscopic geometry, resulting in reduced pressure drop and improved mass transfer. In this work, structured catalysts and adsorbents were developed using a highly porous silica matrix as a binding phase. Two different case studies were investigated focusing on zeolites and Layered Double Hydroxides (LDHs) as active species. In the first case study, a silica-based system incorporating ZSM-5 zeolites was developed for the Selective Catalytic Reduction of nitrogen oxides. Monolithic samples were fabricated by Additive Manufacturing employing the Direct Ink Writing process and characterized using several techniques such as X-ray diffraction (XRD), pycnometry, Scanning Electron Microscopy (SEM) and gas physisorption, as well as compression tests to evaluate the mechanical properties. Furthermore, a scale-up of the 3D printed samples was carried out. In the second case study, the silica matrix was retained, while three different types of LDHs were employed as active phases for the adsorption of antibiotics from wastewater. The samples, produced in pellet form as an initial proof of concept, were extensively characterized showing that consolidation of the silica binder can be achieved via heat treatment at temperatures as low as 200°C, ensuring no damage to the organic functionalization employed on the LDHs. The results demonstrate that the proposed structuring strategies were successful, leading to mechanically stable adsorbents and catalysts while preserving high Specific Surface Area and accessibility of the active sites.