Kinetic study of CO preferential oxidation over Pt–Rh/γ-Al2O3 catalyst in a micro-structured recycle reactor

A micro-structured recycle reactor was developed for studying the kinetics of heterogeneously catalysed gas phase reactions. The preferential CO oxidation reaction over Pt–Rh/γ-Al2O3 catalyst in reformate surrogate containing up to 60 vol.% H2 was investigated over a wide range of CO concentrations (0.5–2.0 vol.%) between one and four times O2 excess (λ = 1–4). Initial concentration of H2O and CO2 were 2.5 vol.% and up to 20 vol.%, respectively, and their influence on the reaction rate was investigated as well. Measurements in a microreactor showed that the optimum temperature for the preferential oxidation process (PROX) was ∼180 °C. Methanation and reverse water-gas shift reaction in this range were insignificant. The quantitative determination of CO oxidation rates as a function of CO, O2, H2 and CO2 concentration between 150 °C and 190 °C led to reaction orders of −0.58 for CO and +0.88 for O2, at an apparent activation energy of 92.9 kJ/mol. The addition of either H2 or CO2, decrease the CO oxidation rate.The study of H2 oxidation rate as a function of H2, O2 and CO revealed reaction orders of −0.26, 0.09 and −0.06, respectively.