Metal–Acid Interface Engineering in Pd–WO_<i>x</i> Bifunctional Catalysts for the Hydroalkylation Tandem Reaction of Benzene

Abstract

The hydroalkylation tandem reaction of benzene to cyclohexylbenzene (CHB) provides an atom economy route for conversion and utilization of benzene; yet, it presents significant challenges in activity and selectivity control. In this work, we report a metal-support synergistic catalyst prepared via calcination of W-precursor-containing montmorillonite (MMT) followed by Pd loading (denoted as Pd– m WO x /MMT, m = 5, 15, and 25 wt %), which shows excellent catalytic performance for hydroalkylation of benzene. A combination study (X-ray diffraction (XRD), hydrogen-temperature programmed reduction (H 2 -TPR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis, Raman, and density functional theory (DFT) calculations) confirms the formation of interfacial sites Pd–(WO x )–H, whose concentration is dependent on the interaction between Pd and WO x . The optimized catalyst (Pd–15WO x /MMT) exhibits a CHB yield of up to 45.1% under a relatively low hydrogen pressure, which stands at the highest level among state-of-the-art catalysts. Investigations on the structure–property correlation based on in situ FT-IR and control experiments further verify that the Pd–(WO x )–H structure serves as the dual-active site: the interfacial Pd site accelerates benzene hydrogenation to cyclohexene (CHE), while the interfacial Bronsted (B) acid site in Pd–(WO x )–H boosts the alkylation of benzene and CHE to CHB. This study offers a new strategy for the design and preparation of metal–acid bifunctional catalysts, which shows potential application in the hydroalkylation reaction of benzene.