Deducing kinetic constants for the hydrodechlorination of 4-chlorophenol using high adsorption capacity catalysts

摘要

Employing high surface area supports for catalytic hydrodechlorination can result in pronounced adsorption of reactants, intermediates and products. The influence of these sorption processes on the activity and selectivity upon 4-chlorophenol (4-CP) hydrodechlorination in aqueous solution has been studied using four commercial Pd/Al2O3 and Pd/AC catalysts at ambient pressure within the temperature range of 20-40°C ([4-CP]0=0.78-2.90mmolL-1, [catalyst]=1gL-1, 50NmLH2min-1). The adsorption capacity of the catalysts was independently evaluated. The Al2O3-based catalyst did not show any significant adsorption of those species whereas the activated carbon materials presented in all cases high uptakes (e.g. up to 2.4mmol4-CPgcat -1). In order to deduce true kinetic constants also for these catalysts, a kinetic model was developed, which accounts for the consecutive reaction and sorption processes in parallel. This expanded model resulted in a reasonable fit, can thus be used for comparison of different catalysts regardless their sorption capacity and allows predicting successfully the selectivity to the reaction products