Hierarchical Porous WO₃@SiO₂ Self-Standing Monolithic Catalysts and Their Efficient Cycling “Cosolvent-Free” Friedel–Crafts Alkylation/Acylation Catalytic Properties

Abstract

Taking advantage of tungsten oxide inherent Brønsted–Lewis acidity, the first series of WO3–SiO2(HIPE) monolithic (MUB-104­(x) series) catalysts bearing multiscale porosity have been designed through integrative chemistry. At the microscopic length scale, beyond X-ray diffraction (XRD) revealing the WO3 monoclinic structure, local electron spin resonance (ESR) spectroscopy addresses g values clearly located at the frontier between extended WO3 phases and polyanion clusters, in agreement with scanning transmission electron microscopy high-angle annular dark field (STEM-HAADF) investigations. NH3-TPD shows that when the tungsten loading is increased from 10 wt % for MUB-104(1) to 24 wt % for MUB-104(3), the amount of acidic sites significantly decreases from 0.35 to 0.08 mmol of NH3 g–1, respectively, in agreement with the particle sizes. The MUB-104­(x) series offers efficient cosolvent-less heterogeneous cycling catalysis toward both Friedel–Crafts alkylation and acylation syntheses. MUB-104(1) carries the highest turnover number (TON) of 121 and turnover frequency (TOF) of 20 h–1, while for acylation, MUB-104(1) carries the highest TON of 117 and TOF of 26 h–1. Besides, we find out that the catalysts offer good selectivity, where 30/70% of ortho- and para-substituted alkylated products are obtained. Considering the acylation reaction, the selectivity is even higher, reaching 100% toward the para-substituted acylated product. The catalyst, due to its intrinsic monolithic character, can be easily extracted from the reactive media, recycled, and re-employed further.

Monolithic Catalysts Supported by Emulsion-Templated Porous Polydivinylbenzene for Continuous Reduction of 4-Nitrophenol

“…All samples exhibited chemical shifts at 28.7 and 40.7 ppm, belonging to methyl or methylene on the main chain, while chemical shifts at 128.4 and 145.2 ppm could be attributed to aromatic carbons on the pendant group. Chemical shifts of residual C=C at 112.5 and 137.7 ppm disappeared in the 13 C SSNMR spectrum for PH 40 -NO 2 and PH 40 -NH 2 , confirming the postpolymerization process.…”

“…PH 40 -NH 2 was obtained through a following amination, proved by the stretching oscillation peaks of C−N and N−H bonds at 1390 and 3410 cm −1 , respectively. 13 C SSNMR was employed to further confirm the modification process (Figure 3c). All samples exhibited chemical shifts at 28.7 and 40.7 ppm, belonging to methyl or methylene on the main chain, while chemical shifts at 128.4 and 145.2 ppm could be attributed to aromatic carbons on the pendant group.…”

“…Chemical structures of the porous monoliths were confirmed using a Fourier-transform infrared spectrometer (FTIR, Bruker Vertex 70v) in attenuated total reflectance (ATR) mode. Moreover, chemical structures were studied using solid-state 13 C nuclear magnetic resonance ( 13 C SSNMR, AVANCEIII/WB-400), and tested samples were ground into a fine powder. Porous morphologies of the porous monoliths were observed using a scanning electron microscope (SEM, FEI, Nova NanoSEM 450) at an accelerating voltage of 5 kV.…”

“…For a monolithic catalyst, the two main challenges are controlling of porous structures and loading of active components. A series of porous materials, including metal foams, − carbon materials, − ceramic foams, , porous polymers, − etc., have been successfully employed as support materials. Conventionally, active components were loaded onto porous carriers through solution impregnation, sol–gel process, or covering .…”

“…To achieve the catalytic application with these porous polymers, macropores are needed for a suitable flux of the feed liquid. Emulsion-templated polymers, usually synthesized from a high internal phase emulsion (HIPE, internal phase >74 vol %), showed excellent adaptability to form hierarchically porous structures. , Polymerized high internal phase emulsion (polyHIPE) possesses an interconnected macropore structure with connected channels, resulting in the flexible controlling of the overall mass transfer coefficient and micromixing efficiency. , Meanwhile, the active components on frameworks have been introduced through copolymerization of activated monomers, − loading of metal nanoparticles, ,,− and employment of activated Pickering stabilizers. , Moreover, for a better active component loading and higher catalytic activity, the frameworks were endowed with micro- or/and mesopores by postpolymerization modification, including hypercross-linking , and ex situ swelling …”