Control of hydrocarbon cold-start emissions: A search for potential adsorbents

A principle of single-file diffusion has been successfully employed to control automotive hydrocarbon (HC) emissions particularly during the cold-start period. Temperature programmed desorption technique of toluene and ethylene, as probe sorbates, was employed to screen a series of as synthesized one-dimensional molecular sieves as potential HC traps. Ethylene was found to be trapped to varying degrees by the larger toluene molecules within the 1-D pores of the synthesized samples. In particular, ZSM-12 and SAPO-5 showed superior trapping performance for both sorbates. ZSM-12 was selected as a better candidate because of its higher temperature of desorption maximum for ethylene (150 °C), which is comparable to the light-off temperature of automotive catalytic converter. It was also found that this adsorbent was stable up to the desired temperature of operation i.e., 800 °C, however with some reduction in ethylene trapping capacity.