Investigation of CO oxidation kinetics over gold catalysts

Abstract

This experimental study involves preliminary work conducted over 0.5wt%Au/Al2O3 and kinetic study of low-temperature CO oxidation over 1wt%Au/1.25-wt%MgO/Al2O3 prepared by the homogeneous deposition-precipitation method. Several sets of experiments were carried out to understand the fact that there is no interaction between chemical and physical phenomena. For this purpose, three different total flow rates, 100, 120 and 150 ml/min, were employed in the 90-130oC temperature range varying the catalyst weight to keep contact time constant in the absence and presence of hydrogen. Kinetic experiments were later conducted at 130oC and atmospheric pressure using different sets of CO and O2 concentrations at different catalyst loadings. Molar reactant concentrations in the feed were varied between 2-8 per cent CO and 1-6 per cent O2 in the absence of hydrogen. Experimental rate data were used to estimate the kinetic parameters of power law and proposed LHHW models using the method of initial rates. The investigation of power law kinetics gave reaction orders of 0.61 and 0.31 with respect to carbon monoxide and oxygen, respectively, and a reaction rate constant of 3.55 mol.g-1.h-1.atm-1 at 130oC. Both power law and LHHW models fit well to the experimental data. Finally, the effects of H2, CO2 and/or H2O addition to the feed on CO conversion in the low temperature oxidation of CO were also investigated. The addition of H2 or H2+H2O to the feed enhance CO conversion whereas the presence of CO2 has a negative effect.