The catalytic removal of NOx must occur in the presence of what?

The correct answer emphasizes the essential role of a catalyst in the catalytic removal of nitrogen oxides (NOx). Catalysts are substances that accelerate chemical reactions without being consumed in the process. In the context of NOx removal, catalysts facilitate the conversion of nitrogen oxides into less harmful substances, such as nitrogen and oxygen, or nitrogen and water, depending on the specific catalytic process employed.

Without a catalyst, the reaction would proceed at much slower rates, making the removal of NOx inefficient and impractical for industrial applications. The presence of a catalyst allows the process to occur under milder conditions, which can lead to energy savings and reduced emissions in power plants and other combustion-related systems.

While other factors like temperature and moisture can influence the efficiency of the process, they are not the primary requirement compared to the necessity of a catalyst itself. The presence of high temperatures may enhance reaction rates, and excessive moisture can impact reaction efficiency, but neither can replace the function of the catalyst in this specific chemical transformation.