The role of oxidation catalyst in dual-catalyst bed for after-treatment of lean burn natural gas exhaust

A dual-catalyst bed composed of a reduction (Pd/SZ) and an oxidation (CoOx/CeO2) catalyst was investigated for selective catalytic reduction (SCR) of NO2 using hydrocarbons for lean-burn natural gas engines. The choice of a multifunctional oxidation catalyst was seen to play a crucial role to achieve the desirable NO2 reduction performance. A dual-catalyst bed optimization showed that different cobalt containing oxidation catalysts could be exploited to achieve desirable NOx and hydrocarbon conversions. Moreover, cyclic experiments in the presence of water vapor were conducted to understand its implications on dual catalyst bed performance. Finally, both kinetic and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies were undertaken to examine the behavior of the oxidation catalyst with respect to hydrocarbon oxidation which consequently affect the overall NOx reduction activity.