Encapsulated Ni Nanoparticles within Silicalite-1 Crystals for Upgrading Phenolic Compounds to Arenes

Abstract

About 3−5 nm Ni nanoparticles were significantly encapsulated within different crystal sizes of a silicalite-1 matrix through tailoring the hydrothermal synthesis conditions and ratios of feeding materials, which were applied in the upgrading of phenolic compounds to arenes via the hydrogenolysis route. The smaller the sizes of Ni@silicalite-1 crystals with similar Ni contents and nanoparticles, the more obvious the active centers could be characterized. The enhancement in both phenol/m-cresol conversion and benzene/toluene selectivity was obtained with the decrease in crystal sizes of Ni@silicalite-1, which originated from the selective elimination of the hydroxyl group, hindrance of further hydrogenation of aromatics, and the formation of methane.

Toward Value-Added Arenes from Lignin-Derived Phenolic Compounds via Catalytic Hydrodeoxygenation

“…In an alternative strategy, the different crystal sizes of the Ni@S-1 catalysts were successfully designed using an in situ encapsulation method and applied in the upgrade of phenolics to arenes (Figure ). Surprisingly, the fabrication of Ni@silicalite-1 catalysts presented superior stability for 300 h during the conversion, leading to both a high phenol conversion of 78.4% and BTX yield of 73.1%. Ni nanoparticles encapsulated in zeolite provide a new strategy to modulate the reactant adsorption pattern to modify the arenes selective spatial effects.…”

“…Catalytic upgrading scheme of phenolics to BTX over different Ni@silicalite-1 catalysts. Reproduced from ref . Copyright 2021 American Chemical Society.…”

“…Arenes, such as benzene, toluene, and xylene (BTX), are a versatile class of raw materials for chemical production and are widely used in the fuel, rubber, fiber resin, pharmaceutical, textile, fragrance, and paper industries. − At present, the preparation of arenes is generally dependent on nonrenewable fossil resources (Figure a). − The excessive reliance on fossil feedstocks has led to the problems of an energy crisis and environmental deterioration, which promotes the development of green and sustainable energy sources. − Particularly, the production of arenes from renewable biomass has the advantages of low pollution and greenhouse gas emission, while the petroleum refining process produces large amounts of byproducts and other toxic gases and wastes, which seriously pollute the environment. Biomass, as a cheap and abundant renewable resource in nature, can be translated into various value-added functional chemicals and fuels. − Accordingly, under the global theme of advocating both carbon neutrality and low carbon economy, the utilization of biomass resources to produce high-valued arenes has attracted great interest and attention from researchers worldwide (Figure b). − …”

Highly Stable and Selective Catalysts for m-Cresol Hydrogenolysis to Aromatics

“…Among these metal catalysts, Ni-based catalysts are regarded as one of the most promising candidates based upon their relatively high hydrogenation activity, abundance supply, and low cost. Decreasing Ni sizes ,, and introducing the second oxophilic metals , through tailoring the preparation procedures have been proven as effective strategies to improve the selectivity of aromatics in vapor phenolics conversion. The highly coordinatively unsaturated surface Ni site of small Ni nanoparticles and the introduction of second oxophilic metals are responsible for C–O cleavage through hydroxyl adsorption in upgrading vapor m -cresol to toluene.…”

“…Metal nanoparticles encapsulated in zeolites have been demonstrated to show extreme stability in confined catalysis reactions. − Based upon our previous work, we tried to synthesize a 4.0 wt % Ni-confined catalyst that exhibited outstanding stability in hydroxyl hydrogenolysis of m -cresol for 300 h with 78.4% conversion and 73.1% aromatics yield at 350 °C in a space time of 0.67 g [catalyst] ·h·g [ m ‑cresol] –1 , which is mainly contributed by about 5.0 nm Ni nanoparticles confined in silicalite-1 (S-1) crystals. However, much lower activity of hydroxyl hydrogenolysis over 4.0 wt % Ni-confined catalysts was obtained than that of 5.0 wt % NiW/SiO 2 (87.1% conversion in 0.15 g [catalyst] ·h·g [ m ‑cresol] –1 ) at identical reaction temperature in vapor m -cresol conversion as well as toluene yield .…”