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•3D-printed zeolite HZSM-5 and zeolite HY monoliths.•Secondary growth of the silicoaluminophosphate on the 3D-printed monoliths.•Superior stability in the n-hexane cracking and ...enhanced selectivity to light olefins on HZSM-5 monolithic catalyst.•Outstanding selectivity to benzene, toluene and xylene (BTX) on HY monolithic catalyst grown with SAPO-34.
Three dimensional (3D) printing manufacturing has attracted growing interests for material synthesis applied in various fields because of its rapid accomplishment, cost effectiveness, approach facilities and structure controllability. In this work, we present a facile and efficient method for the fabrication of 3D-printed HZSM-5 and HY monoliths with macro-meso-micorporosity as the heterogeneous catalysts for n-hexane cracking reaction. To modify and improve the performance of the monolithic catalysts, the silicoaluminophosphate with chabazite framework (SAPO-34) was grown on the zeolite monolith surface via secondary growth method. Characterization of the catalysts suggest that surface area, porosity, acidity and structure of the catalysts were influenced by both formulation into monolithic structures and growth of SAPO-34. The performance of the 3D-printed monolithic catalysts was investigated in catalytic cracking of n-hexane at 600 and 650 °C for 24 h time on stream. Our results indicated that HZSM-5 zeolite monolith exhibits more stable activity in n-hexane cracking and higher selectivity to light olefins than its powder counterpart. A highest selectivity to light olefins (53.0%) was found on HZSM-5 zeolite monolith at 650 °C whereas over HY zeolite monolith the highest selectivity was found to be 57.9% at 600 °C. SAPO-34 growth enhanced the activity all monolithic catalysts and significantly improved catalytic selectivity to BTX (benzene, toluene and xylene) over HY monoliths. The highest BTX selectivity reached 27.5% on SAPO-34 coated HY monolith at 600 °C.
3D monoliths have undergone great progress in the past decades in scientific and engineering fields. Especially, compressible and elastic 3D monoliths (CEMs) hold great promise in a series of ...applications, such as pressure/strain sensing, energy storage, oil/water separation, and thermal insulation, attributed to their unique mechanical properties and multifunctionality (e.g., conductivity, thermal stability, and high adsorption capacity). Recently, plenty of advanced CEMs have been developed from 1D and 2D building blocks, polymers, and biomass via various methods. Herein, the latest progress in controllable design and preparation of advanced CEMs, which mainly refer to aerogels, sponges, and foams, are reviewed in terms of their structural units and applications. The relationship between structure and mechanical performances of CEMs is discussed. Moreover, their applications in sensing, energy storage and conversion, water treatment, fire‐resistance, and electromagnetic interface shielding are presented. Finally, the challenges and future opportunities of CEMs are also discussed.
Recently, plenty of advanced three‐dimensional (3D) compressible and elastic monoliths (CEMs) have been developed. Herein, the latest progress in controllable design and preparation of CEMs beyond hydrogels is summarized. The relationship between structure and mechanical performances of CEMs is discussed, and their applications in sensing, energy storage and conversion, water treatment, fire‐resistance, and electromagnetic interface shielding are presented.
A highly efficient 3D wood‐derived carbon monolith reactor with a low tortuosity is demonstrated for high‐temperature reaction applications, using catalytic steam reforming of biomass tar as the ...model system. Outstanding catalytic activity is achieved as the reactant gases flow through this 3D natural wood‐derived catalyst, where over 99% toluene conversion and good stability at 700 °C are observed.
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•Cryptomelane-type manganese oxides were prepared by a solvent-free method.•Ceramic and metallic monoliths were washcoated with cryptomelane.•High catalytic activity of the structured ...materials was observed.•Thermal conductivity was the key factor to understand the results.•The different supports did not significantly change the activity of the catalyst.
Ceramic and metallic monoliths coated with cryptomelane-type manganese oxides were prepared and tested as catalysts for the oxidation of ethyl acetate. Several preparation conditions were optimized in order to enhance the activity of the monoliths. Monoliths with different cell sizes, prepared with the same number of immersions in the washcoating solution or with similar loadings were tested in order to evaluate the effect of this parameter on the adherence of the active phase and on the catalytic activity of the final monolith. Several characterization techniques were used to assess the properties of these monoliths and it was found that almost all properties of the active phase were maintained after the washcoating process.
The thermal conductivity of the structured supports must be taken into account in order to interpret the catalytic results in highly endothermic or highly exothermic reactions. The location of the measurement thermocouple is decisive when analyzing the results since it can give rise to apparent differences in activity. In our specific case, the available data suggest that the specific activity of the catalyst is not significantly altered by the deposition process or by the properties of the supports used.
Gelation is an effective way to realize the self‐assembly of nanomaterials into different macrostructures, and in a typical use, the gelation of graphene oxide (GO) produces various graphene‐based ...carbon materials with different applications. However, the gelation of MXenes, another important type of 2D materials that have different surface chemistry from GO, is difficult to achieve. Here, the first gelation of MXenes in an aqueous dispersion that is initiated by divalent metal ions is reported, where the strong interaction between these ions and OH groups on the MXene surface plays a key role. Typically, Fe2+ ions are introduced in the MXene dispersion which destroys the electrostatic repulsion force between the MXene nanosheets in the dispersion and acts as linkers to bond the nanosheets together, forming a 3D MXene network. The obtained hydrogel effectively avoids the restacking of the MXene nanosheets and greatly improves their surface utilization, resulting in a high rate performance when used as a supercapacitor electrode (≈226 F g−1 at 1 V s−1). It is believed that the gelation of MXenes indicates a new way to build various tunable MXene‐based structures and develop different applications.
Fast gelation of Ti3C2Tx MXenes is initiated by divalent metal ions in aquesous solution. Typically, Fe2+ ions eliminate the electrostatic repulsion, networking MXene nanosheets into a 3D structured hydrogel. The wet hydrogel avoids nanosheet restacking and is ideal for applications highlighting the surface utilization, especially as freestanding electrodes for high‐rate supercapacitors.
Assembly of 2D MXene sheets into a 3D macroscopic architecture is highly desirable to overcome the severe restacking problem of 2D MXene sheets and develop MXene‐based functional materials. However, ...unlike graphene, 3D MXene macroassembly directly from the individual 2D sheets is hard to achieve for the intrinsic property of MXene. Here a new gelation method is reported to prepare a 3D structured hydrogel from 2D MXene sheets that is assisted by graphene oxide and a suitable reductant. As a supercapacitor electrode, the hydrogel delivers a superb capacitance up to 370 F g−1 at 5 A g−1, and more promisingly, demonstrates an exceptionally high rate performance with the capacitance of 165 F g−1 even at 1000 A g−1. Moreover, using controllable drying processes, MXene hydrogels are transformed into different monoliths with structures ranging from a loosely organized porous aerogel to a dense solid. As a result, a 3D porous MXene aerogel shows excellent adsorption capacity to simultaneously remove various classes of organic liquids and heavy metal ions while the dense solid has excellent mechanical performance with a high Young's modulus and hardness.
A new MXene gelation method is demonstrated by assembling MXene flakes into a 3D hydrogel in the presence of graphene oxide and ethylene diamine. The resulting hydrogel shows an ultrahigh capacitance and an exceptionally high rate performance for supercapacitors and is ready to produce a MXene porous aerogel and dense solid with great promise in pollutant removal and compact energy storage.
This study illustrates a procedure for producing different high-performance liquid chromatography (HPLC) stationary phases, on demand, for silica monoliths. Two commercial first-generation analytical ...scale bare silica monoliths were subjected to a “remodification” process that involved the following: (1) coating of the silica through an in situ silylation procedure to bond ligands of choice to the surface, (2) periodic chromatographic characterization of the coated surface over 2,000 column volumes, and (3) removing the bonded ligands using a 0.1M hydrochloric (HCl) acid wash, to regenerate the initial silica surface.
This remodification protocol was repeated for three cycles to fabricate monoliths with selected functionalities. To test reproducibility, this study was conducted on two different commercial silica monoliths subjected to this treatment involving synthetic reactions with organo-silanes and subsequent stripping with acid washes. Both monoliths were functionalized with three different coatings, without significant degradation of the initial columns' silica infrastructure and excellent stability (tested up to 2,000 column volumes). One of the monoliths had measured theoretical plates per meter (N/m) of 57,000N/m for the original silica surface, 105,000N/m for the first cyano coating, and 60,000N/m for the third phenyl coating. The stationary phases prepared by remodification possessed similar selectivities to those synthesized from new silica monoliths. The results of the Tanaka test shows evidence of residual ligands of previous coatings. However, the methylene and phenyl selectivity proved to display the same characteristics as other modified monoliths of the same functionality, not subjected to the remodified process.
•Different stationary phases were prepared, on demand, on a single silica monolith.•Three selectivities were achieved without degradation of the initial infrastructure.•The stationary phases had similar retention to those made from new monoliths.
An improved hydrothermal process is developed to fabricate macroporous graphene monoliths (MGMs) using a soft template of organic droplets. The MGMs are constructed from closed‐cell distorted ...spherical pores. This unique microstructure makes MGMs that have low weight densities, good electrical conductivities, and excellent elasticity with rapid recovery rates.
Honeycomb monoliths loaded with metal–organic frameworks (MOFs) are highly desirable adsorption contactors because of their low-pressure drop, rapid mass-transfer kinetics, and high-adsorption ...capacity. Moreover, three-dimensional (3D)-printing technology renders direct material modification a realistic and economic prospect. In this study, 3D printing was utilized to impregnate kaolin-based monolith with UTSA-16 metal formation precursor (Co), whereupon an internal growth was facilitated via a solvothermal synthesis approach. The cobalt weight loading in the kaolin support was varied systematically to optimize the MOF growth while retaining monolith mechanical integrity. The obtained UTSA-16 monolith with 90 wt % loading exhibited similar textural features and adsorption characteristics to its powder analogue while improving upon structural integrity. In comparison to previously developed 3D-printed UTSA-16 monoliths, the UTSA-16-kaolin monolith not only showed higher MOF loading but also higher compression stress, indicative of its robust structure. Furthermore, the 3D-printed UTSA-16-kaolin monolith displayed a comparable CO2 adsorption capacity to the UTSA-16 powder (3.1 vs 3.5 mmol/g at 25 °C and 1 bar), which was proportional to its loading. Selectivity values of 49, 238, and 3725 were obtained for CO2/CH4, CO2/N2, and CO2/H2, respectively, demonstrating good separation potential of the 3D-printed MOF monolith for various gas mixtures, as determined by both equilibrium and dynamic adsorption measurements. Overall, this study provides a novel route for the fabrication of UTSA-16-loaded monoliths, which demonstrate both high MOF loading and mechanical integrity that could be readily applied to various CO2 capture applications.
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