Development of wire-mesh supported impeller-structured V$_2$O$_5$/Al$_2$O$_3$ catalysts for selective catalytic reduction of NO with NH$_3$

Abstract

Humane society has become much better than in the past by the industrial revolution. However, overuse of fossil fuels during the development process has caused air pollution to reach serious levels, and it has a number of negative effects on society as a whole. PM$_{2.5}$, which is familiar to us as an ultrafine particle, is very small in size and goes into the body without any filtration, causing serious problems in the cardiovascular system. Most of the PM$_{2.5}$ is generated by secondary reaction of nitrogen oxides (NO$_X$) and sulfur oxides (SO$_X$). SO$_X$ which is mainly emitted by power plants can be treated by a wet-scrubber system because it has relatively high solubility to water. On the other hand, NO$_X$ cannot be removed easily due to its low solubility to water. NO$_X$ which is mostly emitted by diesel engines such as diesel vehicles and ships is now being removed by Selective Catalytic Reduction (SCR) because of the high efficiency. In this study, we were able to reduce NO$_X$ with high efficiency even with a smaller amount than conventional catalysts by developing a catalyst with a mesh-supported impeller structure. In order to develop the impeller-structured catalyst, coating technology was needed to make the catalyst be strongly adhered to the mesh without falling off even with the rotational force of the impeller. To achieve strong coating, an electrophoretic deposition (EPD) method was introduced, and alumina, a support for the catalyst, was uniformly and strongly coated on the mesh by EPD. Successful EPD coating is determined by the voltage, time and concentration of the materials in the suspension. In this study, the most effective coating conditions within 50~150V, 3~6min, 0.5~2.5x10$^{-6}$wt.% polyacrylic acid concentration were derived by response surface methodology (RSM), and the results are as follows: 112.54V, 6.67min, and 1.41x10$^{-6}$wt.% polyacrylic acid. The results of coating were analyzed by microscopic and SEM-EDS analysis. The surface which was deposited uniformly and the rough surface which is advantageous for supporting V$_2$O$_5$ catalyst were observed. A wet impregnation method was used to support the vanadium pentoxide catalyst on the mesh uniformly coated with alumina, and the results were confirmed through microscopic and SEM-EDS analysis. Nitrogen monoxide (NO) removal experiments were conducted by applying the catalysts supported mesh to the impeller. The removal efficiency at GHSV 10,000hr$^{-1}$ was 87.0% when the impeller system catalyst was applied, and 79.3% when the stationary system catalyst, which is similar to the honeycomb type catalyst, was applied. The impeller system efficiency at the same GHSV has higher efficiency than the honeycomb type catalyst. As a result, a higher removal efficiency can be obtained with the same amount of catalyst on the impeller system, and the amount of catalyst required to obtain the same removal efficiency can be reduced.