Tuning surface hydrophobicity of palladium catalysts via alkyl ligand functionalization for direct synthesis of hydrogen peroxide

Abstract

Hydrogen peroxide (H2O2), generating only water and oxygen as byproducts, is a highly desirable green oxidant widely used in environmental remediation, pharmaceuticals, and fine chemicals. Among various production routes, direct synthesis from H2 and O2 (DSHP) offers a sustainable alternative to the traditional process. However, its practical deployment is limited by poor selectivity and rapid H2O2 degradation, highlighting the need for advanced catalyst design. This study presents a surface engineering strategy to precisely tune the hydrophobicity of Pd/SiO2 catalysts via chemical grafting of octadecyltrimethoxysilane ligands. Unlike conventional hydrophobic carbon supports that suffer from weak metal–support interaction and site blockage, the functionalized catalysts exhibited improved structural stability. Stepwise enhancement of surface hydrophobicity facilitated the diffusion of nonpolar reactants (H2, O2) and accelerated the desorption of hydrophilic H2O2, effectively suppressing its decomposition. Notably, a catalyst with moderate ligand density (10C18-Pd/SiO2) achieved an optimal balance, delivering 84.5% selectivity and a productivity of 2,754 mmol gPd−1·h−1—approximately 52% higher than the unmodified Pd/SiO2 catalyst. Excessive ligand coverage hindered access of the H3PO4 stabilizer to Pd active sites, thereby delineating a critical hydrophobicity window necessary for effective DSHP catalysis.