Straightforward Processing Route for the Fabrication of Robust Hierarchical Zeolite Structures

Abstract

Strong hierarchical porous zeolite structures are prepared by a sol–gel method using freeze gelation. Instead of conventional binders in powder form, such as bentonite or kaolin, it has been proven that using a freeze gelation method based on a colloidal silica sol is a more straightforward and easier-to-use-approach in fabricating highly mechanically stable zeolite monoliths. The resulting zeolite slurries possess superior rheological properties (not being pseudoplastic) and show low viscosities. This low viscosity of the slurry enables an increase in the solid content without compromising the extraordinary good flow behavior for casting applications. Additionally, in comparison to conventional powdery binders, zeolite samples prepared by using a colloidal silica sol exhibit a significantly higher mechanical strength. This mechanical strength can be further improved by either increasing the zeolite content or increasing the silica to zeolite ratio. Increasing the zeolite content leads to an increased volumetric adsorption capacity for CO 2 as the test gas, resulting from the increased amount of zeolite particles per unit volume. In addition, a higher solid content of the zeolite monoliths leads to higher compression strengths, while showing the same elastic deformation and brittle failure characteristics. In turn, increasing the silica to zeolite ratio does not affect the volumetric adsorption capacity for CO 2 . Nevertheless, higher silica contents lead to a significant increase in the elastic deformation and absorbed work until failure. Therefore, the proposed processing route based on freeze gelation presents an easy and unique tool to tune the mechanical and gas adsorptive properties of hierarchically structured zeolite monoliths, according to the application requirements.

Zeolite Nanocrystals Embedded in Microcellular Carbon Foam as a High‐Performance CO2 Capture Adsorbent with Energy‐Saving Regeneration Properties

“…Monolithic shapes of supported zeolite composites are desirable over powdery ones, as powders tend to suffer from gradual compaction over time, leading to pore blockage and significant drop in the diffusion kinetics. Embedding zeolites into macroporous monoliths thus gives supported zeolite composites with additional porosity on the larger length‐scales, giving access to a hierarchically porous system (macro‐micro or even macro‐meso‐microporosity), which maximizes the zeolite activity in terms of CO 2 adsorption per unit volume …”

Fabricating Mechanically Robust Binder‐Free Structured Zeolites by 3D Printing Coupled with Zeolite Soldering: A Superior Configuration for CO2 Capture

“…One is depositing active zeolite powders onto the surface of preprocessed macroporous supports, such as ceramic foams, [10] porous titanium alloy, [11] and cordierite. [13,14] Self-supporting is the other strategy through freeze casting, [15] sacrificial templating, [16] quasi-solid gel crystallization, [17] pulsed current processing, [18] which is an effective approach to enhance the volume efficiency of the fixed bed reactor. [13,14] Self-supporting is the other strategy through freeze casting, [15] sacrificial templating, [16] quasi-solid gel crystallization, [17] pulsed current processing, [18] which is an effective approach to enhance the volume efficiency of the fixed bed reactor.…”

“…The detailed surface area and pore volume data are summarized in Table S2 in the Supporting Information. Table S4 in the Supporting Information summarizes the mechanical performance of reported structured zeolites manufactured by 3D printing (0.05-1.54 MPa) [32,33] or other shaping strategies, such as direct extrusion (2.58 MPa), [50] sacrificial templating (0.085 MPa), [16] pulsed current processing (1.6-2.2 MPa), [34] freeze casting (0.045-1.38 MPa), [15,51,52] and slip casting (0.21-0.75 MPa). The external surface area and mesopore volume of ZM-BF are 40 m 2 g −1 and 0.040 cm 3 g −1 , respectively, which are higher than the parental NaX powders (S ext = 32 m 2 g −1 and V mes = 0.017 cm 3 g −1 ), as a result of the mesoporous character of ZM-BF.…”

“…Unfortunately, employing some of these porous supports obviously reduces the practical volume efficiency, especially in the case of a very low zeolite loading . Self‐supporting is the other strategy through freeze casting, sacrificial templating, quasi‐solid gel crystallization, pulsed current processing, which is an effective approach to enhance the volume efficiency of the fixed bed reactor. However, subjected to the inflexible configuration, complicated manufacturing process, and poor mechanical integrity, this strategy still faces many obstacles for their large‐scale implementation …”

“…Table S4 in the Supporting Information summarizes the mechanical performance of reported structured zeolites manufactured by 3D printing (0.05–1.54 MPa) or other shaping strategies, such as direct extrusion (2.58 MPa), sacrificial templating (0.085 MPa), pulsed current processing (1.6–2.2 MPa), freeze casting (0.045–1.38 MPa), and slip casting (0.21–0.75 MPa) . It is clear that ZM‐BF exhibits a much higher mechanical strength than most of the reported structured zeolites, which is only lower than that of 3D‐printed polymer‐zeolite composite monoliths .…”