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A series of Pt/Ce x Zr 1-x O 2-δ (x = 0.4–0.6) solids were synthesized and evaluated for the SCR of NO under lean burn conditions (2.5 vol% O 2 ) using C 3 H 6 and H 2 as reducing agents. SSITKA-Mass Spectrometry, SSITKA-DRIFTS and other in situ DRIFTS experiments were conducted for the first time to gather fundamental information in explaining the remarkable H 2 /C 3 H 6 synergy effect towards steady-state selective reduction of NO into N 2 at T > 400 °C. In particular, the chemical structure of adsorbed active and inactive (spectator) NO x species formed under C 3 H 6 -SCR, H 2 -SCR and H 2 /C 3 H 6 -SCR of NO and the surface coverage and site formation of active NO x were probed. The Pt/Ce 1-x Zr x O 2-δ catalysts present significant differences in their H 2 -SCR performance (NO conversion and N 2 -selectivity) in the low-temperature range of 120–180 °C but practically the same catalytic behavior at higher temperatures. It was proved that the active NO x of the H 2 -SCR path reside within a reactive zone around each Pt nanoparticle which extends to less than one lattice constant within the support surface. The chemical structure of the active intermediate was proved to be the chelating nitrite , whereas nitrosyl, monodentate and bidentate nitrates were considered as inactive species (spectators). It was illustrated for the first time that the presence of 15 vol% H 2 O in the H 2 -SCR feed stream applied over the 0.1 wt% Pt/Ce 0.5 Zr 0.5 O 2 catalyst results in a 25% decrease in the concentration of active NO x , thus partly explaining the drop in activity observed when compared to the H 2 -SCR in the absence of H 2 O. A remarkable activity and N 2 -selectivity enhancement was observed at T > 400 °C when both H 2 and C 3 H 6 reducing agents were used compared to H 2 -SCR or C 3 H 6 -SCR alone. This synergy effect was explained to arise mainly because of the increase of θ Η by the presence of –CH x species derived from adsorbed propylene decomposition on Pt, which block sites of oxygen chemisorption, and of the increase of surface oxygen vacant sites that promote the formation of a more active chelating nitrite (NO 2 − ) species compared to the case of H 2 -SCR. [ABSTRACT FROM AUTHOR]

Platinum nanoparticles (dPt = 1.0–1.2 nm) supported on single CeO2 and La2O3 metal oxides and Ce0.8La0.2O2−δ solid solution were prepared to investigate for the first time the effect of La3+-doping of ceria on important mechanistic and kinetic aspects of the water-gas shift (WGS) reaction, namely: (i) the concentration and chemical structure of active adsorbed reaction intermediates present in the C-path and H-path of WGS at 250 and 300 °C, () the chemical nature of inactive species formed during WGS, and () the prevailing mechanistic path among “redox” and “associative” both proposed in the literature. For this, steady-state isotopic transient kinetic analysis () experiments coupled with in situ DRIFTS and mass spectrometry were performed to follow the H-path (use of D2O) and C-path (use of 13CO) of the WGS. In addition, other transient isotopic experiments using methodology (use of and mass spectrometry) were designed to follow with time on stream the reactivity toward water of the various adsorbed species formed under WGS. It is proposed that on Pt/Ce1−xLaxO2−δ (x=0.0, 0.2 and 1.0) the WGS reaction follows both the “redox” and “associative” mechanisms but the extent of participation of each mechanism to the overall WGS reaction rate depends on the support chemical composition. The WGS kinetic rate (μmol CO g−1 s−1) increased by a factor of 2.0 and 2.8 at 300 °C on 0.5 wt% Pt supported on Ce0.8La0.2O2−δ compared to CeO2 and La2O3, respectively. This was explained by (i) the larger concentration of active surface intermediates formed around each Pt nanoparticle (larger extent of reactive zone) a(ii) the higher reactivity of sites (k, s−1) responsible for CO2 and H2 formation on Pt/Ce0.8La0.2O2−δ compared to Pt/CeO2 and Pt/La2O3. Active OH groups is suggested to be formed on defect sites (Ce3+□s) of Ce0.8La0.2O2−δ as a consequence of the introduction of La3+ into the ceria lattice, the latter enhancing the concentration of labile oxygen and its surface mobility, important characteristics of the “redox” mechanism. [Copyright &y& Elsevier]