(90c) Direct Synthesis of H2O2 from H2/O2 Mixtures and Its Decomposition over Intermetallic Pd-Zn Catalysts | AIChE

(90c) Direct Synthesis of H2O2 from H2/O2 Mixtures and Its Decomposition over Intermetallic Pd-Zn Catalysts


Rioux, R. - Presenter, Pennsylvania State University
Dasgupta, A., Pennsylvania State University
Xie, T., Penn State University
Understanding the mechanism of H2O2 decomposition provides insight into the design of catalysts for the direct synthesis of H2O2 from H2 and O2, a promising and environmental-friendly reaction to replace the current the anthraquinone autoxidation (Riedl-Pfleiderer) process. Bimetallic catalysts developed by Hutchings and co-workers appear to be the state-of-the-art catalysts for direct synthesis, but these materials still demonstrate low apparent selectivity. The observed apparent selectivity are most likely influenced by decomposition reactions of hydrogen peroxide. Alkanol solvents or additives (mineral acids) increase H2O2 selectivity, but the impact of solvent, additives, and catalyst modification have been predominantly examined for apparent H2O2 selectivity. In this talk, we will focus on the impact of these variables on H2O2 decomposition and to a lesser extent on direct synthesis over phase-pure beta- and gamma-phase Pd-Zn nanoparticles supported on SiO2. The addition of Zn to Pd leads to increased rates of H2O2 decomposition even though supported Zn (or ZnSiO4) is completely inactive for this reaction. The turnover frequency based on the number of exposed Pd atoms was 2-10 times greater on the gamma-brass Pd-Zn/SiO2 at low temperature. Both monometallic Pd and Pd-Zn demonstrated Langmuir-Hinshelwood saturation kinetics, but the addition of Zn to Pd led to a reduction in the apparent activation energy for H2O2 decomposition. An interesting observation was the kinetically relevant role that solvent (water) played during decomposition of H2O2. The kH/kD ratio was far greater than a primary effect and differed between the monometallic and bimetallic catalysts. The impact of intermetallic stoichiometry and solvent was additionally examined for the direct synthesis of H2O2.