A model low temperature NOx adsorber (LTNA) consisting of Pd on a ceria/zirconia support was evaluated for NOx storage performance under lean conditions to assess its potential for adsorbing the cold-start NOx emissions on a diesel engine before the urea/SCR system becomes operational. A reactor-based transient test was performed with and without C2H4, CO/H2, and H2O in the feedgas to assess the effects of these gas species on the initial NOx storage performance. In the absence of C2H4 or CO/H2, H2O severely suppressed the NOx storage performance of the LTNA at temperatures below 100oC, presumably by blocking the storage sites. When C2H4 was included in the feedgas, H2O still suppressed the NOx storage below 100oC. However, the C2H4 significantly increased the NOx storage efficiency above 100oC, attributable to the formation of alkyl nitrites or alkyl nitrates on the catalyst. When the feedgas contained CO/H2, the NOx storage performance was greatly improved below 100oC, even in the presence of H2O. Tests with CO alone and H2 alone indicated that the CO was providing the improved NOx storage capability. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analysis on a Pd/ceria powder indicated that NO and CO react to form NCO at low temperatures, which could account for the improved NOx storage capability in the presence of CO. The formation of alkyl nitrites or nitrates with NO and C2H4 could not be confirmed because the spectra for these species occur in the same range as that of carbonates which form from the hydrocarbons.