Catalysts can either promote or inhibit combustion depending on their nature and the context in which they are used. For instance, platinum and palladium catalysts are used in catalytic converters to promote the complete combustion of unburned hydrocarbons and carbon monoxide in vehicle exhausts, thereby reducing harmful emissions. On the other hand, fire retardant materials often contain substances that act as negative catalysts, slowing down the combustion process and thus inhibiting fire spread.
