Hydrogenation and decomposition kinetic study of H2O2 over Pd/C catalyst in an aqueous medium at high CO2 pressure

Hydrogenation and decomposition of H2O2 cause an undesired decrease in selectivity when producing H2O2 over Pd/C catalysts via direct synthesis. Hydrogenation accounts for more than 70-85% of the decrease in selectivity itself, which means that the rate of hydrogenation is 3-4-fold the decomposition rate. In this study we have studied the operational interval for H2O2 concentration (1-10%, w/v), temperature (23-50 degrees C), pH (2-3.8), halide to active metal ratio (1.5-8.0), catalyst amount and palladium loading (1,3 and 5 wt% Pd/C) at 80 bar using CO2 as inert gas. A kinetic model coupling both decomposition and hydrogenation was fit to the results of a semicontinuous reactor achieving average deviations lower than 5% in most cases. Using the right proportion of promoters the activation energies obtained were E-ad = 18803.6 J mol(-1) (decomposition) and E-ah = 77462 J mol(-1) (hydrogenation). The order of reaction for decomposition respect to H2O2 was 1.031 and with hydrogenation -0.161. Turn over frequencies of decomposition and hydrogenation rates between 0.31 and 9.62 mol H2O2 h(-1) mol Pd-1 and 139 to 23.01 mol H2O2 h(-1) mol Pd-1 respectively have been observed in this study. (C) 2012 Elsevier B.V. All rights reserved.