In-line hydrocarbon (HC) traps are not widely used to reduce HC emissions due to their limited durability, high platinum group metal (PGM) concentrations, complicated processing, and insufficient hydrocarbon (HC) retention temperatures required for efficient conversion by the three-way catalyst component. New trapping materials and system architectures were developed utilizing an engine dynamometer test equipped with dual Fourier Transform Infrared (FTIR) spectrometers for tracking the adsorption and desorption of various HC species during the light-off period. Parallel laboratory reactor studies were conducted which show that the new HC trap formulations extend the traditional adsorption processes (i.e., based on physic-sorption and/or adsorption at acid sites) to chemical reaction mechanisms resulting in oligomerized, dehydro-cyclization, and partial coke formation. This results in the initially adsorbed hydrocarbons being retained in the HC trap to sufficiently high temperatures for effective combustion via the three-way-catalyst (TWC) over-layer. Vehicle testing using a 2008 SULEV Ford Focus with E85 fuel and a 2007 BIN-8 1.6L GTDI Mini Cooper with gasoline confirmed an improved design. Additional vehicle work also showed that the HC trap performance may be enhanced with air/fuel calibration during the HC desorption phase. These new trap formulations not only improve HC storage and conversion efficiency, but substantially decrease the PGM requirement compared to previous designs.