Bromide and acids: a comprehensive study on their role on the hydrogen peroxide direct synthesis

Hydrogen peroxide direct synthesis was studied using different concentrations of NaBr and H3PO4 (promoters) with a commercial Pd/C catalyst. The aim of the study was to understand the role of the acids and bromide on the catalyst and thus the effect on the direct synthesis. The experimental work was done in a continuous trickle bed reactor (TBR) using different concentrations of promoters. The effect of the promoters on the catalyst (Pd leaching and bromide adsorption) was monitored by inductively coupled plasma (ICP) on the solution obtained from the reaction environment. ICP analysis coupled with the monitoring of conversion, selectivity, and productivity helped to understand the effect of the promoters and to check the possibility to discriminate better the reaction network mechanism with different reaction conditions. Pd leaching was correlated to catalyst activity and bromide/phosphoric acid ratio. This work provides new and original evidence on the role of promoters, allowing one to understand better how to push the direct synthesis and how to control the catalyst ability to produce H2O2 rather than H2O.