Abstract
In this study, α-Fe2O3 spherical particles with an average diameter of approximately 200 nm were synthesized by a solvothermal method for use as both a catalyst and medium for a Pd catalyst. The kinetics of CO oxidation over powders of α-Fe2O3 spherical particles and 14 wt % Pd/α-Fe2O3 spherical particles were measured in a static reactor by using a CO2 laser-based photoacoustic technique. The total pressure was fixed at 40 Torr for the CO/O2/N2 mixture for temperatures in the range of 225–350 °C. The variation in the CO2 photoacoustic signal with the CO2 concentration during CO oxidation was recorded as a function of time, and the CO2 photoacoustic data at the early reaction stage was used to estimate the rates of CO2 formation. Based on plots of ln(rate) vs. 1/T, apparent activation energies were calculated as 13.4 kcal/mol for the α-Fe2O3 submicron powder and 13.2 kcal/mol for the 14 wt % Pd/α-Fe2O3 submicron powder. Reaction orders with respect to CO and O2 were determined from the rates measured at various partial pressures of CO and O2 at 350 °C. The zero-order of the reaction with respect to Po2 was observed for CO oxidation over α-Fe2O3 submicron powder, while 0.48 order to Po2 was observed for CO oxidation over Pd/α-Fe2O3 submicron powder. The partial orders with respect to PCO were determined as 0.58 and 0.54 for the α-Fe2O3, and the Pd/α-Fe2O3 submicron powders, respectively. The kinetic results obtained from both catalysts were compared with those for the α-Fe2O3 fine powder catalysts and were used to understand the reaction mechanism.
Highlights
It is widely known that CO oxidation is one of the most important reactions in environmental research
Pd-loaded α-Fe2 O3 spherical submicron particles were prepared by using the impregnation method
In the catalytic oxidation of CO, the CO disproportion reaction (the Boudourd reaction corresponding to 2CO (g) (s) + CO2 (g)) is considered as a side reaction because it is thermodynamically feasible below 630 ◦ C based on the assumption of the standard free energy change
Summary
It is widely known that CO oxidation is one of the most important reactions in environmental research. Extant studies [1] indicate that transition metal oxides, including MnO2 , Fe2 O3 , Co2 O3 , NiO, and CuO, as well as noble metals, are highly active for CO oxidation. The catalytic performance of metal oxides is enhanced by increasing their surface area. Metal oxide catalysts were synthesized in the forms of nanoparticles to yield high surface areas. Nanostructured metal oxides are significantly active catalysts when compared with non-nanostructured metal oxides. It is not easy to utilize these oxides as a medium for noble metal catalysts due to their extremely small size
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