Metal–Acid Interface Engineering in Pd–WO_x 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 Wprecursor-containing montmorillonite (MMT) followed by Pd loading (denoted as Pd−mWO 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 stateof-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.