Mg-stabilized subnanometer Rh particles in zeolite Beta as highly efficient catalysts for selective hydrogenation

Nanoparticles are of interest in heterogeneous catalysis because of their excellent activity associated with atoms in a low coordination environment. However, their high reactivity becomes a drawback where selectivity is desired, compounded by their propensity towards agglomeration. Here, we show that stable subnanometric Rh particles can be prepared in a Mg-doped zeolite Beta based on the electrostatic interaction of the negatively charged zeolitic framework and the Rh³⁺ precursor. The Mg ions are incorporated into the zeolite framework whereas the Rh is located in the channels adjacent to the Mg. With only 0.27 and 0.5 wt% Mg and Rh, respectively, the Rh/Mg-Beta catalysts were highly active with > 94 % selectivity for the hydrogenation of phenol to cyclohexanone, an important intermediate for the production of Nylon. Key to the selectivity is the formation of the C=O double bond early in the reaction sequence, aided by the basicity of the Mg-Beta support.