Relating the performances of selective phenol hydrogenation with encapsulated palladium nanoparticles and surrounding distinct LTL-zeolite microenvironments

Cyclohexanone, as a significant raw material in the production of nylon 6 and nylon 66, is preferentially synthesized via selective phenol hydrogenation while the key point is to modulate the acidic/basic properties and metal dispersion of the catalytic system. Here, we report the fabrication of Pd@L core-shell catalysts via the insitu encapsulation of Pd nanoparticles within the L zeolite with a one-dimensional large-pore diffusion system for the selective hydrogenation of phenol to cyclohexanone. The different Pd amounts and acidic/basic properties of the L zeolite catalyst were modulated to study the effects of the microenvironment around the Pd centers in the Pd@L on the catalytic performances of selective phenol hydrogenation. The results show that the basicity of L zeolite greatly favors high selectivity to cyclohexanone. In contrast, modulating the microenvironment to weak or strong acid states can result in the dehydration product forming on the acid sites or even the suppression of phenol hydrogenation. The conversion of phenol increases from 14.0% to 99.9% and meanwhile the selectivity of cyclohexanone ranges from 67.5% to 93.8%. In the optimum condition, the obtained Pd@KL catalyst can demonstrate excellent catalytic performance with the phenol conversion of 99.9% and the cyclohexanone selectivity of around 93.8%. Our work presents a promising tactic to effectively control the target reaction pathway by means of maneuvering the microenvironment in the proximity of metal nanoparticles.