## 3 Results  
Investigations began on the ceramic NSC catalyst. A preliminary screening was carried out to find the best technique for revealing morphologic variations of the substrate under the operative conditions. Firstly, the optical VMS--004D--400x USB Microscope was used to detect deposits on the metal support at the upstream and downstream of the catalytic converter (Figure 1). Deposits, collected by means of stickers coal, were analyzed via scanning electron microscopy--energy dispersed X-ray (SEM-EDS) techniques. Analyses of the upstream sample revealed the presence of magnesium, silicon, and aluminum, constituents of the ceramic monolith (Figure 2B). As expected, barium and cerium (as oxides) were also detected, which were added to improve the catalytic activity. The aluminum peak was due not only to the \(\gamma\)-alumina but also to the aluminum of the ceramic monolith. Since the exhaust gas entering the converter contains sulfur, the latter was also detected in the upstream sample. EDS analyses of the downstream sample revealed the absence of both sulfur and platinum elements (Figure 2D). In the case of the former, this was not a surprising result, because the ceramic monolith is expected to purify the exhaust gas from SOx compounds efficiently. In contrast, the lack of platinum in the downstream sample is an unexpected novelty and can be seen as a choice of the manufacturer, who decided that the presence of Pt in that section of device was an unnecessary cost, since much of the conversion process (including NOx reduction to N\({}_{2}\)) takes place at the start of converter. In contrast, SEM images provide only rough morphological information that is not sufficient to point out differences between the two samples (Figure 2A,C). Figure 1: (**A**) Upstream and (**B**) downstream samples of the ceramic support. Next, we turned our attention to the metallic catalytic converter, Diesel 2000 (Figure 3). In this case, sampling was carried out in a careful manner in order to obtain uniform and representative specimens, after which chemical composition throughout the catalyst was preliminarily investigated by EDS analyses, sampling both the upstream and downstream parts of NSC catalyst (Figure 4). Figure 3: NSC metallic catalytic converter: (**A**) the whole catalyst; (**B**) the metallic support; (**C**) longitudinal cuts; (**D**) a slice of the catalyst. Figure 2: NSC ceramic support: (**A**) SEM image and (**B**) EDS analysis of the upstream sample; (**C**) SEM image and (**D**) EDS analysis of the downstream sample. As EDS quantitative data showed a roughly uniform elemental composition along the entire NSC, with the exception of carbon percentage, which depends on sampling, specimens were obtained by cutting the catalyst first longitudinally (Figure 3C) and then transversally to produce slices among which the ones with unblocked pores were chosen (Figure 3D). Recent studies showed that some compounds in the exhaust feed can influence the NOx storage process, especially CO2 and water vapor, since these substances can be easily adsorbed on barium and alumina sites and can sterically block their active sites [10; 11; 12]. Therefore, when water vapor is present in the exhaust gas, the storage capacity of NOx on NSC is expected to be reduced. On these bases, with the aim of evaluating separately the contributions to the aging of the thermal treatment and the gaseous environment exposure, the samples listed in Table 1 were prepared, in which some slices of the catalyst were subjected to heating under argon atmosphere (namely **NSC_8_Ar** and **NSC_24_Ar**), to assess the sole thermal effect, while other ones where exposed, under the same thermic conditions, to a humid oxygen atmosphere (namely **NSC_8_O2** and **NSC_24_O2**) to evaluate the influence of a chemical oxidizing gaseous environment [7; 9; 10; 11; 12] at 800 \({}^{\circ}\)C, which is higher than the maximum temperature used for NSC catalysts. All samples were subjected to SEM-EDS and TEM analyses and compared with those of the pristine material.