Ethylene Adsorption and Oxidation Kinetics in the Reactions with Pd(II)/SiO2 and Cr(VI)/SiO2: Consideration of Substrate Distribution between the Gas Phase,Silica Gel,and Reaction Centers

The kinetics of ethylene oxidation by PdCl₂ and CrO₃ complexes supported on silica gel (300 K, closed batch reactor) and the adsorption of C₂H₄ by silica gel and metal complex reaction centers (M ⁿ ) were studied. A new version of the kinetic distribution method was applied to determine the rate constants of ethylene reactions with metal complexes with consideration for the equilibrium distribution of C₂H₄ among the reactor gas phase, silica gel, and M ⁿ . The rate constant of a first-order reaction with respect to Cr(VI) (k _e) remained constant as M ⁿ ] was increased up to 0.15 mol % with the absence of detectable ethylene adsorption by chromium(VI). In the case of Pd(II)/SiO₂, strong ethylene adsorption by palladium(II) was found, and k _e was an exponential function of M ⁿ ]. This exponential function is indicative of an increase in the specific activity of Pd(II) with palladium concentration on SiO₂. Taking into account the adsorption of ethylene (physisorption on SiO₂ and chemisorption on Pd(II)), we found an analogy between the kinetic behaviors of Pd(II) in reactions with ethylene on silica gel and with ethylene and other hydrocarbons in solutions.