In the field of heterogeneous catalysis, the successful integration of enzymes and inorganic catalysts could pave the way to multifunctional materials which are able to perform advanced cascade reactions. However, such combination is not straightforward, for example in the case of zeolite catalysts for which enzyme immobilization is restricted to the external surface. Herein, this challenge is overcome by developing a new kind of hybrid catalyst based on hollow zeolite microspheres obtained by the aerosol-assisted assembly of zeolite nanocrystals. The latter spheres possess open entry-ways for enzymes, which are then loaded and cross-linked to form cross-linked enzyme aggregates (CLEAs), securing their entrapment. This controlled design allows the combination of all the decisive features of the zeolite with a high enzyme loading. A chemo-enzymatic reaction is demonstrated, where the structured zeolite material is used both as a nest for the enzyme and as an efficient inorganic catalyst. Glucose oxidase (GOx) ensures the in situ production of H2O2 subsequently utilized by the TS-1 zeolite to catalyze the epoxidation of allylic alcohol toward glycidol. The strategy can also be used to entrap other enzymes or combination of enzymes, as demonstrated here with combi-CLEAs of horseradish peroxidase (HRP) and glucose oxidase. We anticipate that this strategy will open up new perspectives, leveraging on the spray-drying (aerosol) technique to shape microparticles from various nano-building blocks and on the entrapment of biological macromolecules to obtain new multifunctional hybrid microstructures.

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Hollow zeolite microspheres as a nest for enzymes: a new route to hybrid heterogeneous catalysts

Direct ring CH bond activation to produce cresols from toluene and hydrogen peroxide catalyzed by framework titanium in TS-1

Zeolites with ordered microporous systems, distinct framework topologies, good spatial nanoconfinement effects, and superior (hydro)thermal stability are an ideal scaffold for planting diverse active metal species, including single sites, clusters, and nanoparticles in the framework and framework-associated sites and extra-framework positions, thus affording the metal-in-zeolite catalysts outstanding activity, unique shape selectivity, and enhanced stability and recyclability in the processes of Brønsted acid-, Lewis acid-, and extra-framework metal-catalyzed reactions. Especially, thanks to the advances in zeolite synthesis and characterization techniques in recent years, zeolite-confined extra-framework metal catalysts (denoted as metal@zeolite composites) have experienced rapid development in heterogeneous catalysis, owing to the combination of the merits of both active metal sites and zeolite intrinsic properties. In this review, we will present the recent developments of synthesis strategies for incorporating and tailoring of active metal sites in zeolites and advanced characterization techniques for identification of the location, distribution, and coordination environment of metal species in zeolites. Furthermore, the catalytic applications of metal-in-zeolite catalysts are demonstrated, with an emphasis on the metal@zeolite composites in hydrogenation, dehydrogenation, and oxidation reactions. Finally, we point out the current challenges and future perspectives on precise synthesis, atomic level identification, and practical application of the metal-in-zeolite catalyst system.

Metal Sites in Zeolites: Synthesis, Characterization, and Catalysis.

In this Article, TS-1 was successfully synthesized on carbon nanotubes decorated nickel foam via in situ strategy forming the monolithic TS-1 (MTS-1). To the best of our knowledge, situ synthesis of the MTS-1 has not been reported. Carbon nanotubes decorated nickel foam has many aggregated pores (confined pores formed in aggregated structure) and a large surface area, and TS-1 particles could be dispersed on the surface of CNT@NF. MTS-1 had the characteristics of ultrafine nanoparticle and high content of skeleton titanium. High absorptive property and electrostatic interaction between CNT@NF and gels could accelerate the crystallization rate. The TS-1 particles were solidly immobilized on the CNT@NF, and the conversion rate was almost constant even after multiple reactions. The catalyst is easy to separate from liquid products after reaction, which offers an economical application prospect.

In Situ Synthesis of TS-1 on Carbon Nanotube Decorated Nickel Foam with Ultrafine Nanoparticles and High Content of Skeleton Titanium

Hierarchical iron-containing TS-1 zeolites (FTS) were successfully synthesized via post-treatment desilication over microporous Fe-TS-1, which were prepared through a one-step hydrothermal synthesi...

Iron-Containing TS-1 Zeolites with Controllable Mesopores by Desilication and Their Application in Phenol Hydroxylation

Green and efficient preparation of hollow titanium silicalite-1 by using recycled mother liquid

The spray-forming process of the nano-titanium silicalite (TS-1) zeolite was investigated and optimized in the lab in order to obtain materials with microsphere morphology and superior catalytic activity in cyclohexanone ammoximation on the industrial scale. The effects of spray-forming parameters, such as the state of the TS-1 raw material, load ratio, solid content, binder content, and calcination temperature, on the physicochemical and catalytic properties of TS-1 microspheres were investigated in detail. It was interesting to find that the shape of the spray-forming sample formed by wet powders was more intact than the sample formed by dried powders. Furthermore, the spray-forming process was successfully scaled up to a large spray device (LGZ-1000) according to the similarity principle of load ratio, and the shape of the TS-1 microspheres was as perfect as the spray-forming samples in the lab. The similarity principle of the load ratio for the spray-forming of titanium silicate was established and verified for the first time. The spray-forming TS-1 microspheres produced in the industry were used in cyclohexanone ammoximation, and ketone conversion and oxime selectivity were as high as 99.9 and 99.4%, respectively.

https://pubs.acs.org/doi/pdf/10.1021/acsomega.8b02561

Fabrication of Microspheres by Nano-TS-1 Crystals via a Spray-Forming Process: From Screening to Scale-up.

The invention provides a method for preparing a high-catalytic-activity Ti-MWW molecular sieve. The method comprises the steps of, at room temperature, mixing butyl titanate, silica sol, boric acid and water to obtain a gel precursor for synthesizing the molecular sieve; under ultraviolet irradiation, grinding the gel precursor obtained in the above step through a colloid grinder, adding in and uniformly mixing piperidine with the ground gel precursor to obtain a reacting gel, feeding the reacting gel into a hydrothermal crystallization synthesis reactor, increasing the temperature to 160-180 DEG C for crystallization synthesis for 72-120 hours, after reaction is completed, performing solid-liquid reaction, washing obtained solid through dilute nitric acid, and performing a drying process to obtain the high-catalytic-activity Ti-MWW molecular sieve in an MWW structure. Compared with conventional methods, the method for preparing the high-catalytic-activity Ti-MWW molecular sieve has the advantages of shortening the synthesizing time, greatly reducing boron consumption, significantly improving the catalytic activity.

Method for preparing high-catalytic-activity Ti-MWW molecular sieve

A hybrid kinetics integrating feed-consumption rate and product selectivity models for Fischer-Tropsch synthesis over an industrial cobalt-based catalyst

Congcong Niu

Papers

Green and efficient preparation of hollow titanium silicalite-1 by using recycled mother liquid

Fabrication of Microspheres by Nano-TS-1 Crystals via a Spray-Forming Process: From Screening to Scale-up.

Method for preparing high-catalytic-activity Ti-MWW molecular sieve

A hybrid kinetics integrating feed-consumption rate and product selectivity models for Fischer-Tropsch synthesis over an industrial cobalt-based catalyst

Enhanced catalytic activity and catalyst stability in cyclohexanone ammoximation by introducing anatase into TS-1 zeolite