Efficient methanation of CO2 relies on the development of more selective and stable heterogeneous catalysts. Herein, we present a simple and effective method to encapsulate Ni nanoparticles in zeolite silicalite‐1. In this method, the zeolite is modified by selective desilication, which creates intraparticle voids and mesopores that facilitate the formation of small and well‐dispersed nanoparticles upon impregnation and reduction. Transmission electron microscopy and X‐ray photoelectron spectroscopy analyses confirm that a significant part of the Ni nanoparticles are situated inside the zeolite rather than on the outer surface. The encapsulation results in increased metal dispersion and, consequently, high catalytic activity for CO2 methanation. With a gas hourly space velocity of 60 000 mL gcatalyst−1 h−1 and H2/CO2=4, the zeolite‐encapsulated Ni nanoparticles result in 60 % conversion at 450 °C, which corresponds to a site‐time yield of approximately 304 molCH4
molNi−1 h−1. The encapsulated Ni nanoparticles show no change in activity or selectivity after 50 h of operation, although postcatalysis characterization reveals some particle migration.
Zeolite encapsulated metal nanoparticle catalysts hold great promise for several green and sustainable processes, ranging from environmental remediation to renewable energy and biomass conversion. In particular, the microporous zeolite framework keeps the nanoparticles in a firm grip that can control selectivity and prevent sintering at high temperatures. While progress in the synthesis of mesoporous zeolites continues, the encapsulation of metal nanoparticles remains a challenge that often requires complex procedures and expensive additives. Here, we report a general method to encapsulate both base and noble metal nanoparticles inside the internal voids of a compartmentalized mesoporous zeolite prepared by carbon templating and steam-assisted Page 1 of 40 ACS Paragon Plus Environment ACS Applied Nano Materials 2 recrystallization. This results in a remarkable shell-like morphology that facilitates the formation of small metal nanoparticles upon simple impregnation and reduction. When the materials are applied in catalysis, we for instance demonstrate that zeolite encapsulated Ni nanoparticles are highly active, selective and stable catalysts for CO2 methanation (49% conversion with 93% selectivity at 450°C). A reaction where catalysts often suffer from sintering due to the high reaction temperatures. While the introduction of Ni nanoparticles prior to the steam-assisted recrystallization results in the formation of inactive nickel phyllosilicates, noble metals such as Pt do not suffer from this limitation. Therefore, we also demonstrate the synthesis of an active catalyst prepared by the formation of Pt nanoparticles prior to the shell synthesis. We tested the zeolite encapsulated Pt nanoparticles for hydrogenation of linear and cyclic alkenes with increased chain length. The catalysts are active for hydrogenation of oct-1-ene (66% conversion) and cyclooctene (79% conversion) but inactive for the large cyclododecane (<1% conversion), which show that this type of catalyst is highly selective in size selective catalysis. All catalysts are characterized by XRD, TEM, XPS and N2 physisorption.
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