What type of compounds are typically used in NOx removal catalysts?

The correct answer is base metal compounds because they are commonly used in the formulation of catalysts designed for the removal of nitrogen oxides (NOx) from exhaust gases. These compounds often include metals such as copper, iron, and manganese, which are effective in facilitating the redox reactions necessary for breaking down NOx into harmless nitrogen and oxygen. Base metals can provide a balance of effectiveness and cost, making them a preferred choice in various catalytic converters for emissions control.

In contrast, alloy metals typically involve a combination of multiple metallic elements and may not be specific to the catalytic processes for NOx reduction. Non-metallic compounds are less effective in catalyzing these types of reactions due to their chemical properties. Organic compounds, while useful in some applications, do not play a significant role in NOx removal due to their tendency to combust rather than facilitate the necessary chemical reactions. Thus, base metal compounds are the most relevant and widely utilized in this context.