Numerical simulation of CO oxidation using a Pt/Al₂O₃ catalyst under concentration and flowrate modulation

Chemical Engineering Department, Universitas Muhammadiyah Surakarta, Kartasura 57102, Indonesia

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Abstract

Carbon monoxide (CO) oxidation is a key reaction for controlling vehicle emissions and serves as a model for studying catalytic behavior. Fixed-bed reactor simulations are highly sensitive to kinetic parameters, where modulation of flow rate and feed concentration can influence conversion. However, comparative unsteady-state simulations of these modulations are still limited. This study numerically simulates high-temperature CO oxidation over a Pt/Al2O3 catalyst using FlexPDE 8.0 Lite under steady and unsteady conditions in a one-dimensional pseudo-homogeneous fixed-bed model. The effects of inlet CO concentration (0.020–0.125 mol/m³), gas velocity (0.48–0.90 m/s), and switch time (10– 30 s) were investigated at 900 K to eliminate light-off effects. As predicted by the Langmuir–Hinshelwood mechanism, steady-state conversion dropped sharply with increasing CO concentration, falling below 10% above 0.05 mol/m³. Unsteady-state operation enhanced conversion, with single-parameter modulation outperforming simultaneous modulation. Concentration modulation at a 15 s switch time achieved up to 35.24% conversion—twice that of steady state—while flow rate modulation at 10 s also doubled conversion (7.24% to 15.70%). Longer switch times reduced improvement. In simultaneous modulation, the best result occurred with a positive phase shift in CO concentration and a negative phase shift in velocity. These findings support future development of unsteady-state catalytic reactor models.