Temperature Dependence of Heterogeneous Uptake of Hydrogen Peroxide on Silicon Dioxide and Calcium Carbonate

The heterogeneous kinetic processes of hydrogen peroxide on silicon dioxide (SiO2) and calcium carbonate (CaCO3) have been studied over the temperature range from 253 to 313 K using a Knudsen cell reactor, and the functions of temperature were obtained. The kinetic study indicates that the initial uptake coefficients increase evidently with a temperature decrease. They can be calculated by the equations gamma(BET)(SiO2) = [exp(934.5/T - 12.7)]/[1 + exp(934.5/T - 12.7)] and gamma(BET)(CaCO3) = [exp(1193.0/T - 11.9)]/[1 + exp(1193.0/T - 11.9)]. On the basis of the temperature dependence of uptake coefficients, the enthalpy (Delta H-obs) and entropy (Delta S-obs) of uptake progresses were determined to be -(7.77 +/- 1.55) KJ mol(-1) and -(105.8 +/- 21.2) J K mol(-1) for SiO2 and - (9.92 +/- 1.98) KJ mol(-1) and -(98.6 +/- 19.7) J K mol(-1) for CaCO3. The activation energies for desorption (E-des) of H2O2 on CaCO3 and SiO2 were calculated to be (5.9 +/- 0.9) KJ mol(-1) and (9.15 +/- 1.1) KJ mol(-1). The results suggest that hydrogen peroxide could mainly be adsorbed on SiO2 and CaCO3 reversibly in this temperature region, and the quick uptake on these mineral aerosols, especially at low temperature, provides an active surface for further complex reactions.