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

Taking advantage of tungsten oxide inherent Bronsted-Lewisacidity, the first series of WO3-SiO2(HIPE) monolithic (MUB-104(x) series) catalystsbearing multiscale porosity have been designed through integrativechemistry. At the microscopic length scale, beyond X-ray diffraction(XRD) revealing the WO3 monoclinic structure, local electronspin resonance (ESR) spectroscopy addresses g values clearly locatedat the frontier between extended WO3 phases and polyanionclusters, in agreement with scanning transmission electron microscopyhigh-angle annular dark field (STEM-HAADF) investigations. NH3-TPD shows that when the tungsten loading is increased from10 wt % for MUB-104(1) to 24 wt % for MUB-104(3), the amount of acidicsites significantly decreases from 0.35 to 0.08 mmol of NH3 g(-1), respectively, in agreement with the particlesizes. The MUB-104(x) series offers efficient cosolvent-lessheterogeneous cycling catalysis toward both Friedel-Craftsalkylation and acylation syntheses. MUB-104(1) carries the highestturnover number (TON) of 121 and turnover frequency (TOF) of 20 h(-1), while for acylation, MUB-104(1) carries the highestTON of 117 and TOF of 26 h(-1). Besides, we find outthat the catalysts offer good selectivity, where 30/70% of ortho-and para-substituted alkylated products are obtained. Consideringthe acylation reaction, the selectivity is even higher, reaching 100%toward the para-substituted acylated product. The catalyst, due toits intrinsic monolithic character, can be easily extracted from thereactive media, recycled, and re-employed further.