Pd/MgAl-LDH nanocatalyst with vacancy-rich sandwich structure: Insight into interfacial effect for selective hydrogenation

Abstract

In this work, a Pd/MgAl-LDH catalyst was synthesized by the ion-exchange and liquid-reduction process (IE), with impregnation method (IM) as contrast, to study the difference in the interfacial structure induced by the preparation methods and the catalytic behavior for selective hydrogenation of 2-ethylanthraquinone. STEM-EDS measurement reveals that the IE-Pd/MgAl-LDH catalyst possesses an obvious sandwich structure of which Pd nanoparticles uniformly located in the LDH interlayer space, and therefore exhibits more Pd-LDH interface sites due to the high intimacy. More importantly, it was confirmed that the Pd-LDH interface structure was characterized by rich oxygen vacancies (Vo) due to the loss of surface hydroxyl groups on the LDH layer during the ion-exchange process. As expected, the IE-Pd/MgAl-LDH catalyst exhibited a 127% higher H2O2 yield than that of IM-Pd/MgAl-LDH catalyst. High activity was attributed to the facilitated hydrogen activation resulting from significantly enhanced hydrogen spillover over the Pd-LDH interface structure. Preferred selectivity was owing to the special adsorption mode of CO bond interacted with the Pd-Vo interfacial sites, which leads to the selective activation of CO bond. This work develops a feasible approach to fabricate the metal-hydroxide interface structure and provides a fundamental understanding on interfacial effect toward selective hydrogenation of CO bonds.