Tuning the selectivity of benzene hydroalkylation over PdZn/HBeta catalysts: identification of lattice contraction and electronic properties

One step hydroalkylation (HDA) of benzene to cyclohexylbenzene (CHB) is a tandem reaction with tremendous economic significance. Precisely regulating the density and diffusion of intermediate cyclohexene (CHE) is a key step but also a challenge. Herein, the lattice contraction and electron-rich surface of Pd were successfully regulated by the doping of low electronegative M (M = Zn, Ni, Co, or Cu). Pd14M/HBeta exhibited an improved CHB selectivity (39.0%) compared with Pd/HBeta (16.0%). Mechanism investigation demonstrates that PdZn promoted the asymmetric adsorption and activation of benzene to CHE and regulated the moderate adsorption of CHE. Thus, more CHE diffused to the acidic sites and was activated by Bronsted acid proton to C6H11, which led to the enhanced selectivity to CHB by electrophilic substitution with benzene. This work provides guidance and new insights into the intrinsic regulation of tandem reactions shared with one key intermediate.