Factors affecting CO oxidation reaction over nanosized materials: A review

The high level of carbon monoxide (CO) in the atmosphere represents a serious health and environmental problem, thus many techniques were used to reduce CO concentration. The catalytic oxidation of CO proves to be one of the most effective techniques for removing this pollutant. In this paper, we review the factors that affect CO oxidation reaction, such as catalyst crystal size, pre-treatment and preparation technique, temperature including calcination and catalytic reaction temperature, catalyst mass, and water vapor on feedstock gas. The main findings of the present review are: (1) The catalyst used in the oxidation of CO to CO2 must have extraordinary CO oxidation activity, high selectivity, and respectable resistance toward deactivation by H2O and CO2; (2) Metal oxides nanoparticles are found to be favorable and effective catalysts for CO oxidation; (3) CO oxidation greatly affected by catalyst crystal size where it generally increases with reducing crystal size to a certain limit and after that the CO conversion % decrease; (4) Preparation methods affect the catalytic process as its effects on the surface area and the dispersion of the nanostructure prepared catalyst; (5) Temperature greatly affects CO oxidation catalysts. Thus, carbon monoxide catalytic materials have to work even at higher temperatures; (6) Increasing catalyst weight generally increases catalytic activity due to the increase in the total surface area and a number of active places on the surface of the catalyst; (7) H2O vapor on feedstock gas sometimes have positive effects and other time have negative effects on the catalytic oxidation of CO. Knowing the factors that affect CO oxidation over nanosized materials will help in optimizing the condition for CO oxidation over specific nanosized catalyst.