ADSORPTION OF HYDROCARBONS AND OTHER EXHAUST COMPONENTS ON SILICALITE

Temporary storage of vehicle emissions, in particular hydrocarbons (HC's), was evaluated by adsorption on silicalite. Silicalite, a zeolite consisting almost completely of silica, is characterized by a three-dimensional system of intersecting channels of molecular dimensions. The adsorption capacity of the zeolite for individual exhaust components was measured gravimetrically as a function of pressure, temperature, and time. Initial adsorption of a representative HC from simulated car exhaust was measured in a flow reactor. The requirements for practical storage of HC's during coldstart by adsorption are quantitatively evaluated, and the commanding influence of competitive water adsorption is examined. The volume of silicalite required for temporary adsorption of HC's emitted before the catalytic converter is hot and operational is found to be too large to be practical. A primary reason for insufficient HC storage is the competitive adsorption of the high concentration of water vapor present in automotive exhaust.