Revealing the role of bromide in the H2O2 direct synthesis with the catalyst wet pretreatment method (CWPM)

 A tailor-made Pd⁰/K2621 catalyst was subjected to post synthesis modification via a wet treatment procedure. The aim was the understanding of the role of promoters and how—if any—improvements could be qualitatively related to the catalyst performance for the H₂O₂ direct synthesis. The Catalyst Wet Pretreatment Method was applied in different methanolic solutions containing H₂O₂, NaBr, and H₃PO₄, either as single modifiers or as a mixture. The catalyst was characterized by Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy. It was concluded that the modified catalysts give rise to higher selectivities compared to the pristine reference catalyst thus opening a possibility to exclude the addition of the undesirable selectivity enhancers in the reaction medium. This work provides original evidence on the role of promoters, especially bromide, allowing the formulation of a new reaction mechanism for one of the most challenging reactions recognized by the world.