Rational Design of Microporous and Mesoporous Solids for Catalysis: From the Molecule to the Reactor

3D printing of TiO2 nano particles containing macrostructures for As(III) removal in water

Nanomaterials play a crucial role in various areas due to their extraordinary chemical and physical properties. Loading microscopic nanomaterials onto macrostructures is inevitable for their implementation from laboratory experiments to practical applications. Nevertheless, the geometries of conventional supporting structures are usually limited and nanomaterials are easy to be inhomogeneously distributed, aggregated, and lost. Therefore, controllably configuring nanomaterials into sophisticated three-dimensional macroscopic structures without sacrificing their inherent properties remains challenging. Here we utilize the advantages of 3D printing technology to realize this purpose. As a proof-of-concept, the application of 3D stereolithography printed macrostructures containing TiO₂ nano particles (TiO₂ NPs) for direct adsorption removal of As(III) in water was demonstrated. The morphology and distribution of TiO₂ NPs mounted on printed macrostructures were initially characterized. Then batch adsorption experiments were conducted to investigate the effect of the 3D printing process, TiO₂ NPs doped concentration and TiO₂ NP size as well as adsorption kinetics and isotherms. We also demonstrated that 3D printed adsorption structures could be easily reused over 10 times and were effective for raw arsenic-polluted groundwater samples. Our findings show that 3D printing provides a promising route to design and fabricate customized macrostructures endowed with specific properties of nanomaterials.

Hierarchically Porous (Alumino)Silicates Prepared by an Imidazole-Based Surfactant and Their Application in Acid-Catalyzed Reactions

In this work, we developed a novel strategy to synthesize porous (alumino)silicate materials using a single structure-directing agent composed of an imidazole unit with a hydrophobic tail, namely, 1,2-dimethyl-3-hexadecyl-1H-imidazol-3-ium bromide (C₁₆dMImz). A wide range of products such as ordered mesoporous silicas, layered silica-alumina, and hierarchically porous mordenite zeolite were obtained by varying synthesis parameters such as temperature and aluminum concentration. By changing crystallization temperature, we could control the degree of silica condensation and tune the textural and morphological properties of the final materials. By varying the aluminum concentration in the gel, we can obtain mesoporous amorphous silica-alumina or crystalline mordenite zeolite with, respectively, weak and strong Brønsted acid sites. Obtained acidic silica-alumina materials displayed promising performance in catalytic reactions of linear paraffin hydroisomerization and Friedel-Crafts alkylation of benzene with benzyl alcohol.

Low-Temperature Continuous-Flow Dehydration of Xylose Over Water-Tolerant Niobia-Titania Heterogeneous Catalysts

The sustainable conversion of vegetable biomass-derived feeds to useful chemicals requires innovative routes meeting environmental and economical criteria. The approach herein pursued is the synthesis of water-tolerant, unconventional solid acid monolithic catalysts based on a mixed niobia-titania skeleton building up a hierarchical open-cell network of meso- and macropores, and tailored for use under continuous-flow conditions. The materials were characterized by spectroscopic, microscopy, and diffraction techniques, showing a reproducible isotropic structure and an increasing Lewis/Brønsted acid sites ratio with increasing Nb content. The catalytic dehydration reaction of xylose to furfural was investigated as a representative application. The efficiency of the catalyst was found to be dramatically affected by the niobia content in the titania lattice. The presence of as low as 2 wt % niobium resulted in the highest furfural yield at 140 °C under continuous-flow conditions, by using H₂ O/γ-valerolactone as a safe monophasic solvent system. The interception of a transient 2,5-anhydroxylose species suggested the dehydration process occurs via a cyclic intermediates mechanism. The catalytic activity and the formation of the anhydro intermediate were related to the Lewis acid sites (LAS)/Brønsted acid sites (BAS) ratio and indicated a significant contribution of xylose-xylulose isomerization. No significant catalyst deactivation was observed over 4 days usage.

Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes

The catalytic partial hydrogenation of substituted alkynes to alkenes is a process of high importance in the manufacture of several market chemicals. The present paper shortly reviews the heterogeneous catalytic systems engineered for this reaction under continuous flow and in the liquid phase. The main contributions appeared in the literature from 1997 up to August 2016 are discussed in terms of reactor design. A comparison with batch and industrial processes is provided whenever possible.

Formation of C–C, C–S and C–N bonds catalysed by supported copper nanoparticles

Copper nanoparticles on different supports are effective reusable catalysts for the palladium- and ligand-free coupling of aryl halides with alkynes, thiols and azoles.

Mesostructured zeolites: bridging the gap between zeolites and MCM-41

This feature article critically reviews the use of surfactants to introduce controlled mesoporosity in zeolites and their commercial applications.

F-assisted synthesis of a hierarchical ZSM-5 zeolite for methanol to propylene reaction: a b-oriented thinner dimensional morphology

A hierarchical ZSM-5 zeolite with a thinner dimension morphology has been synthesized in fluoride medium, and presents a superior performance in MTP reaction.

Novel windows for “solar commodities”: a device for CO2 reduction using plasmonic catalyst activation

A novel plasmonic reactor concept is proposed and tested to work as a visible energy harvesting device while allowing reactions to transform CO₂ to be carried out. Particularly the reverse water gas shift (RWGS) reaction has been tested as a means to introduce renewable energy into the economy. The development of the new reactor concept involved the synthesis of a new composite capable of plasmonic activation with light, the development of an impregnation method to create a single catalyst reactor entity, and finally the assembly of a reaction system to test the reaction. The composite developed was based on a Cu/ZnO catalyst dispersed into transparent aerogels. This allows efficient light transmission and a high surface area for the catalyst. An effective yet simple impregnation method was developed that allowed introduction of the composites into glass microchannels. The activation of the reaction was made using LEDs that covered all the sides of the reactor allowing a high power delivery. The results of the reaction show a stable process capable of low temperature transformations.

MFI-type zeolite nanosheets for gas-phase aromatics chlorination: a strategy to overcome mass transfer limitations

Mass transfer limitations and catalytic activity were studied for various ZSM-5 zeolite crystal sizes in the chlorination of deactivated arenes. An estimation of the quantity of mild acidic external silanol groups of zeolite nanosheets was made.

Visualization of hierarchically structured zeolite bodies from macro to nano length scales

A major challenge in the implementation of laboratory-designed catalysts is the scale-up into technically relevant forms. Advanced characterization is essential to understand and optimize catalyst assembly and function in industrial reactors. This Article presents an integrated approach to visualizing millimetre-sized extrudates and granules of a hierarchical MFI-type zeolite, displaying trimodal networks of micropores (0.56 nm), intracrystalline mesopores (∼10 nm) and macropores (∼200-300 nm). As exemplified for the conversion of methanol to olefins, the hierarchical zeolite yields a superior performance compared to its conventional analogue. The combination of dedicated specimen preparation with state-of-the-art optical, X-ray and electron-based microscopic and tomographic techniques proves a powerful methodology to reveal otherwise inaccessible information regarding structural organization over the whole range of length scales. It is expected that these tools will play a crucial role in the rationalization of scale-up principles in catalyst development.