Reagents are substances or compounds added to a system to bring about a chemical reaction. In catalysis, reagents interact with catalysts to convert reactants into desired products. They can include: - Reactants: The starting materials that undergo transformation. - Promoters: Substances that enhance the effectiveness of the catalyst, without themselves being catalysts. - Inhibitors: Compounds that decrease the activity of catalysts, often used to control the rate of reaction. - Solvents: Mediums in which reactions occur, influencing the solubility and interaction of reactants and catalysts.