Catalytic reactions of hydrogen peroxide, H2O2, are actively studied in order to develop new energy-efficient and environmentally-friendly technologies for selective oxidation of hydrocarbons where the only byproduct is water. H2O2 can be synthesized directly from H2 and O2. The challenge, however, is that metal catalysts, such as supported Pd nanoparticles, which are effective in catalyzing H2O2 formation, also catalyze its decomposition. It is, therefore, important for both efficient production and utilization of H2O2 to understand effects of H2 and C3H6 presence on H2O2 decomposition. Kinetic measurements demonstrate that the rate of H2O2 decomposition over the Pd/SiO2 is significantly affected by the presence of H2 and C3H6. The decomposition rate is higher in the presence of H2 compared to that under inert N2 but is lower in the presence of C3H6. Results of DFT calculations in Figure 1 demonstrate that the decomposition of H2O2 on Pd can proceed through two pathways. The first decomposition pathway through O-O bond cleavage (Fig. 1b) is highly exothermic and, therefore, thermodynamically favorable. As a result, H2O2 decomposition in the presence of H2 is facile and can readily form water. In contrast, in the absence of H2, H2O2 decomposition must proceed through O-H cleavage (Fig. 1c,d). Since this pathway is thermodynamically unfavorable on Pd, the rate of decomposition in the absence of H2 (under N2) is lower. Additional DFT calculations show that C3H6 blocks Pd adsorption sites which decreases the rate of H2O2 decomposition. Undesirable H2O2 decomposition can be minimized by eliminating H2 from the reacting mixture and by introducing C3H6 that competes for adsorption sites with H2O2.

Effect of Hydrogen and Propylene Presence on Hydrogen Peroxide Decomposition over Pd

249th National Meeting (2015)

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