Prox kinetics over Pt-Sn/AC under fully realistic reaction conditions

Abstract

This experimental study comprises a kinetic study of preferential CO oxidation (PROX) in the presence of H2, CO2, H2O, and CH4 over HNO3-oxidized activated carbon supported 1wt.%Pt 0.25wt.%Sn/AC catalyst prepared by the sequential impregnation method. In this context, kinetic experiments were conducted at 383 K and atmospheric pressure, and different sets of CO and O2 concentrations, each at different space times and catalyst loadings, were used. Molar reactant concentrations in the feed were varied between 1-2.5 per cent CO and 1-1.5 per cent O2. The effects of CO flow rate, O2 flow rate, and λ (O:CO) on CO conversion were also investigated for various experiments ranging λ from 1 to 3. Experimental rate data were used to estimate kinetic parameters of the power-law kinetic model by using the method of initial rates. The investigation of power-law kinetics gave reaction orders of 0.29 and 0.17 with respect to carbon monoxide and oxygen, respectively, at 383 K. The variance of experimental error was found to be 0.1019 (μmol.mg-1.min-1)2 for this rate expression, which indicates that experimentally measured and model predicted rates was not perfectly fitted most probably due to the presence of a secondary mechanism through water activation involving surface OH- group, which has been confirmed by DRIFT studies in the production of surface oxygen; thus although H2, CH4, CO2, and H2O amounts in the feed is fixed, the surface mechanism may still be affected especially by CO/H2O and O2/H2O feed ratios. The activation energy was predicted as 42.3 kJ mol-1 and the frequency factor was calculated as 46.0115min1044.1kPamgmol . As the calculated orders with respect to CO and O2 in the current study are widely different from the previous one on the same catalyst with a feed having only CO and O2, which were 0.96 and (-0.31), respectively; the crucial importance of having a kinetic expression, which is valid for real feed, in the PROX reactor design has been confirmed.