Catalysts and initiators start or promote chemical reactions that are used to produce organic chemicals, polymers and adhesives. A chemical catalyst is a substance that increases the rate at which a chemical reaction occurs; however, the catalyst itself does not undergo chemical change. An initiator is a chemical compound that helps start a chemical reaction such as polymerization. Unlike a catalyst, an initiator is usually consumed in the reaction. Substances such as organic peroxides are commonly used as initiators. According to some estimates, more than half of all petrochemical processes use catalysts and initiators. In heterogeneous catalysis, a chemical catalyst provides a surface on which reactants become adsorbed temporarily, and where chemical bonds in the reactants are weakened, allowing new bonds to be created. Because the bonds between the products and the catalyst are weaker, the products are released from the chemical catalyst. Continuous process catalysts (CPC) are used to process industrial chemicals such as solvents, plasticizers, monomers and intermediates. Catalytic solutions include a variety of specialized catalyst products.