Versatile Hollow ZSM-5 Nanoreactors Loaded with Tailorable Metal Catalysts for Selective Hydrogenation Reactions

Abstract

Zeolites are one of the most commonly used materials in the chemical industry, acting as catalysts or catalyst supports in different applications. Recently, the synthesis and functionalization of hollow zeolites have attracted many research interests, owing to the unique advantages of their hollow morphology. In the development of more sustainable processes, the hollow zeolites are often endowed with additional stability, selectivity, and activity. Herein, we present a stepwise synthetic protocol to prepare a range of complex hollow ZSM-5 catalysts with catalytic nanoparticles. Solid ZSM-5 crystals were first synthesized from Stöber silica spheres. This solid ZSM-5 sample was then loaded with transition metals via the impregnation method. A subsequent hollowing process was carried out in hydrothermal conditions in which hollow ZSM-5 crystals with confined transition metals inside were synthesized. More specifically, after the encapsulation of transition metals inside hollow ZSM-5, two different approaches have been further devised to allow the deposition of noble metals into the interior cavities or onto the exterior surfaces of the hollow ZSM-5. The deposition of Pt on the exterior surface was carried out by mixing the hollow ZSM-5 sample with presynthesized Pt nanoparticles. Loading of Pd in the interior was achieved by the galvanic replacement reaction between the Pd ions and embedded transition metals inside the hollow ZSM-5 sample. The catalytic performance of these reactor-like nanocatalysts has been evaluated with hydrogenation reactions in both liquid and gas phases, and their compositional and structural merits have been illustrated. For the hollow ZSM-5 sample with Pd loaded inside, liquid-phase selective hydrogenation of styrene over 4-vinylbiphenyl has been achieved with the ZSM-5 shell acting as a molecular sieve. The deposition of Pt on the exterior has improved the C2–C4 product yield when tested for the gas-phase CO2 hydrogenation reaction.

The Adsorption of VOCs by Honeycomb Ceramics Loaded with Molecular Sieves

“…Molecular sieve is a natural zeolite or synthetic aluminosilicate, which has the functions of sieving molecules, adsorption, ion exchange, and catalysis; it is mainly composed of silicon, oxygen, aluminum, and other metal cations, and it has high thermal stability and chemical stability [10,11]. Since the 1970s, a large number of artificial zeolite molecular sieves have been synthesized; because of their unique channel zeolite molecular sieves, they have become indispensable catalytic materials and adsorption materials in petrochemical and fine chemicals and are used in more and more fields.…”

Critical Review on Synthetic Routes and Catalytic Applications of Hollow Nanomaterials

“…[75] Zeng et al used porous polystyrene-divinylbenzene (PS-DVB) as template for the generation of multishelled titania hollow spheres. [76] Multishelled and sphere-in-sphere hollow structures of titania results after different heat treatment for the seeded polymerization of polystyrene-divinylbenzene and infiltration process of titania sol within polymer beads. [77] According to Gao and coworkers CdTe nanotubes may also prepared employing 1-D Cd-thioglycolic acid nanowire in the form of hard template.…”

Zeolite confinement-catalyzed cleavage of C–O/C–C bonds in biomass

“…On this basis, the encapsulation of multiple smaller Pd nanoparticles within the zeolite cavity, rather than one large metal particle, was realized by a further galvanic replacement reaction between Cu and Pd. 145 Furthermore, it is worth mentioning that the methods reported so far have only focused on the encapsulation of metals in MFI-type zeolites (S-1, ZSM-5) with high stability, as zeolites with low stability have a tendency to degrade in structure under alkaline heat treatment. In conclusion, based on this method, further improvements in the synthesis procedure to develop yolk–shell-structured catalysts of small metal particle size, improved diffusion hindrance and guaranteed molecular sieving would be welcome, and further applications to other types of zeolites should be explored.…”