Dissociative Adsorption Of NO Research Articles

Cerium-modified Pt/Al2O3 for NH3 synthesis by NO reduction with H2

The Haber–Bosch process is a mature and proven technology for the commercial production of NH3. However, with the increasing focus on achieving net-zero emissions, alternative technologies have gained interest. This paper proposes an effective catalytic system for synthesizing NH3 directly from NO and H2 at atmospheric pressures. Pt/CeOxAl2O3 synthesized via solvent-deficient precipitation (SDP) showed a much higher NH3 yield compared to conventional Pt/Al2O3 and other Pt/Ce-containing catalysts. Various characterization techniques demonstrated that achieving precise control of the electronic metal-support interaction (EMSI) is crucial for attaining the optimal electronic and geometric structure that balances the decisive factors, Pt oxidation state and Pt dispersion, to enable a high rate of NH3 production from NO and H2. Pt/CeOxAl2O3 possesses abundant metallic Pt nanoclusters that are well dispersed on CeOxAl2O3 due to the moderate Pt-Ce interactions. These small metallic Pt clusters in contact with CeOx turned out to play a critical role in the dissociative adsorption of NO and H2, leading to the formation of the reaction intermediates, the –NH2 species, which contribute to the improved NH3 productivity of Pt/CeOxAl2O3.

NO Bond Cleavage on Gas-Phase Irn+ Clusters Investigated by Infrared Multiple Photon Dissociation Spectroscopy.

The adsorption forms of NO on Irn+ (n = 3-6) clusters were investigated using infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory (DFT) calculations. Spectral features indicative both for molecular NO adsorption (the NO stretching vibration in the 1800-1900 cm-1 range) and for dissociative NO adsorption (the terminal Ir-O vibration around 940 cm-1) were observed, elucidating the co-existence of molecular and dissociative adsorption of NO. In all calculated structures for molecular adsorption, NO is adsorbed via the N atom on on-top sites. For dissociative adsorption, the O atom adsorbs exclusively on on-top sites (μ1) of the clusters, whereas the N atom is found on either a bridge (μ2) or a hollow (μ3) site. For Ir5+ and Ir6+, the N atom is also found on the on-top sites. The observed propensity for NO dissociation on Irn+ (n = 3-6) is higher than that for Rh6+, which can be explained by the higher metal-oxygen bond strengths for iridium.

Dissociative adsorption of NO introduces flexibility in gas phase Rh6+ clusters leading to a rich isomeric distribution

The adsorption of an NO molecule on a Rh6+ gas phase cluster was investigated based on a wide screening of the geometrical and spin isomers by density functional theory calculations. For molecular adsorption, several different on-top adsorption forms were found in a wider energy range. For dissociative adsorption, a characteristic adsorption form was found, which has many more geometrical and spin isomers than the other adsorption forms. These isomers can exist because of the relative flexible geometric structure, in which a Rh atom is connected to pyramidal Rh5 through two hinge-like connections formed by the N and O atoms.

Theoretical Study of NO Dissociative Adsorption onto 3d Metal Particles M55 (M = Fe, Co, Ni, and Cu): Relation between the Reactivity and Position of the Metal Element in the Periodic Table.

NO dissociative adsorption onto 3d metal particles M55 (M = Fe, Co, Ni, and Cu) was investigated theoretically using density functional theory computations. A transition state exists at higher energy in the Cu case but at lower energy in the Fe, Co, and Ni cases than the reactant (sum of M55 and NO), indicating that Cu55 is not reactive for NO dissociative adsorption because NO desorption occurs more easily than the N–O bond cleavage in this case, but Fe55, Co55, and Ni55 are reactive because NO desorption needs a larger destabilization energy than the N–O bond cleavage. This result agrees with the experimental findings. The energy of transition state E(TS) becomes higher in the order of Fe < Co < Ni ≪ Cu. Exothermicity Eexo (relative energy to the reactant) decreases in the order of Fe > Co > Ni ≫ Cu. These results indicate that the reactivity for NO dissociative adsorption decreases kinetically and thermodynamically in this order. In addition, the E(TS) and Eexo values show that 3d metal particles are more reactive than 4d metal particles when a comparison is made in the same group of the periodic table. Charge transfer (CT) from the metal particle to NO increases as the reaction proceeds. The CT quantity to NO at the TS increases in the order of Cu < Ni < Co < Fe, identical to the increasing order of reactivity. The negative charges of the N and O atoms of the product (N and O adsorbed M55) increase in the order of Ni < Co < Cu < Fe, identical to the increasing order of Eexo except for the Cu case; in the Cu case, the discrepancy between the order of Eexo and those of the N and O negative charges arises from the presence of valence 4s electron of Cu because it suppresses the CT from N and O to Cu55. From these results, one can infer that the d-valence band-top energy of M55 plays an important role in determining the reactivity for NO dissociative adsorption. Truly, the d valence orbital energy decreases in the order of Fe > Co > Ni ≫ Cu and the 3d metal > 4d metal in the same group of the periodic table, which reflects the dependence of reactivity on the metal element position in the periodic table.

Reaction Behavior of the NO Molecule on the Surface of an Mn Particle (M = Ru, Rh, Pd, and Ag; n = 13 and 55): Theoretical Study of Its Dependence on Transition-Metal Element.

Reaction of NO molecule on M13 and M55 clusters (M = Ru, Rh, Pd, and Ag) was theoretically investigated to elucidate why its reaction behavior depends on the position of metal element in the periodic table. DFT computations show that NO dissociative adsorption occurs on M = Ru and Rh, NO molecular adsorption occurs on M = Pd, and NO dimerization occurs on M = Ag, which agree with experimental findings. The d-band center and d-band top become lower in energy following the order Ru > Rh > Pd > Ag; this is one of the characteristic features of the periodic table. In the Ag cluster, the valence band-top consists of Ag 5s orbital and its energy is higher than the d-band top of Pd. For NO dissociative adsorption, the M-N and M-O bond strengths are crucially important at the transition state and the product, to which the metal d orbital contributes very much. Ru and Rh clusters have a high energy d-band center and d-valence band top, leading to the formation of strong M-N and M-O bonds. Pd and Ag clusters have a low energy d-band center and d-band top, leading to the formation of weak M-N and M-O bonds. Because the Ag cluster has a high energy 5s valence band that can overlap well with the π* + π* MO of ONNO (NO dimer) moiety due to the same symmetry, charge transfer (CT) occurs from the Ag cluster to the π* + π* MO, which is indispensable for NO dimerization. The 4d-valence band top of Ru and Rh clusters does not fit to the π* + π* MO because of the different symmetry. Though the d-valence band top of the Pd cluster can overlap with the π* + π* MO, its energy is low, which is not good for the CT. Thus, the reactivity of metal cluster for NO is determined by the energy and type (4d or 5s) of the valence band top, which both depend on the position of element in the periodic table; accordingly, Ru and Rh clusters are reactive for NO dissociative adsorption, the Ag cluster is reactive for NO dimerization, but the Pd cluster is not reactive for both and only NO molecular adsorption is possible.

Catalysis of Cu Cluster for NO Reduction by CO: Theoretical Insight into the Reaction Mechanism.

Density functional theory calculations here elucidated that Cu38-catalyzed NO reduction by CO occurred not through NO dissociative adsorption but through NO dimerization. NO is adsorbed to two Cu atoms in a bridging manner. NO adsorption energy is much larger than that of CO. N–O bond cleavage of the adsorbed NO molecule needs a very large activation energy (ΔG°‡). On the other hand, dimerization of two NO molecules occurs on the Cu38 surface with small ΔG°‡ and very negative Gibbs reaction energy (ΔG°) to form ONNO species adsorbed to Cu38. Then, a CO molecule is adsorbed at the neighboring position to the ONNO species and reacts with the ONNO to induce N–O bond cleavage with small ΔG°‡ and very negative ΔG°, leading to the formation of N2O adsorbed on Cu38 and CO2 molecule in the gas phase. N2O dissociates from Cu38, and then it is readsorbed to Cu38 in the most stable adsorption structure. N–O bond cleavage of N2O easily occurs with small ΔG°‡ and significantly negative ΔG° to form the N2 molecule and the O atom adsorbed on Cu38. The O atom reacts with the CO molecule to afford CO2 and regenerate Cu38, which is rate-determining. N2O species was experimentally observed in Cu/γ-Al2O3-catalyzed NO reduction by CO, which is consistent with this reaction mechanism. This mechanism differs from that proposed for the Rh catalyst, which occurs via N–O bond cleavage of the NO molecule. Electronic processes in the NO dimerization and the CO oxidation with the O atom adsorbed to Cu38 are discussed in terms of the charge-transfer interaction with Cu38 and Frontier orbital energy of Cu38.

A DFT Screening of M-HKUST-1 MOFs for Nitrogen-Containing Compounds Adsorption.

To develop promising adsorbent candidates for adsorptive denitrogenation, we screened the adsorption of NO, NO2, and NH3 in 19 M-HKUST-1 (M = Be, Fe, Ni, Cr, Co, Cu, V, Zn, Mo, Mn, W, Sn, Ti, Cd, Mg, Sc, Ca, Sr, and Ba) systematically using first-principle calculations. Of these, four variants of M-HKUST-1 (M = Ni, Co, V, and Sc) yield more negative adsorption Gibbs free energy ΔGads than the original Cu-HKUST-1 for three adsorbates, suggesting stronger adsorbate binding. Ti-HKUST-1, Sc-HKUST-1, and Be-HKUST-1 are predicted to have the largest NO, NO2, and NH3 adsorption energies within the screened M-HKUST-1 series, respectively. With the one exception of NO2 dissociation on V-HKUST-1, dissociative adsorption of NO, NO2, and NH3 molecules on the other considered M-HKUST-1 is energetically less favorable than molecular adsorption thermodynamically. The barrier calculations show that the dissociation is difficult to occur on Cu-HKUST-1 kinetically due to the very large dissociation barrier. Electronic analysis is provided to explain the bond nature between the adsorbates and M-HKUST-1. Note that the isostructural substitution of Cu to the other metals is a major simplification of the system, representing the ideal situation; however, the present study provides interesting targets for experimental synthesis and testing.

On the way of understanding the behavior of nanometer-scale metallic particles toward the adsorption of CO and NO molecules

Previously, we have proposed a relationship between the adsorption modes of a simple molecule (NO) and the behavior of the nanometer-scale monometallic clusters after this adsorption. More precisely, a set of experiments seems to show that dissociative adsorption of NO leads to the sintering of nanometer-scale metallic particles (NSMPs), whereas molecular adsorption is related to the oxidation. Although numerous investigations have been published on catalytic or electrocatalytic reactions where the interaction between carbon monoxide and NSMPs is involved, only a few studies have been dedicated to the adsorption of CO on NSMPs. This purely energetic approach is discussed through different results already published in the literature and through some recent theoretical calculations related to solid state physics. Although interesting and systematic results are gathered here and are partly explained, this adsorption process still remains a challenge.

A kinetic study for NO catalytic reduction on silica sub-micron diameter tubes with platinum nanoparticles

The selective catalytic reduction (SCR) of NOx with C3H6 in the presence of O2 on silica sub-microtubes with platinum nanoparticles was studied in order to establish a possible reaction mechanism at different experimental conditions. This catalyst showed a high NO conversion with very high selectivity to N2 at mild conditions in the presence of excess oxygen when using C3H6 as reducing agent.The influence of both NO and C3H6 concentrations on their conversions was analyzed at different space times. The obtained results suggest that the three reactants (C3H6, NO, and O2) are adsorbed on Pt sites. The kinetic model proposed considers that both dissociative adsorption of NO and activation of the hydrocarbon can take place simultaneously. Nevertheless, the value of the parameters obtained by the resolution of the model equations indicates that the first one presents a major relevance. These results are in concordance with the high selectivity to N2 observed, because the preponderance presence of dissociated NO avoids the formation of N2O by the reaction of molecular NO with N dissociated from NO. Furthermore, both NO reduction and C3H6 oxidation conversions are represented reasonably well by the model presented.

Effects of Second-Metal (Al, V, Co) Doping on the NO Reactivity of Small Rhodium Cluster Cations.

Reactions of pure and doped rhodium cluster cations, RhnX+ (n = 2-6; X = Al, V, Co, Rh), with NO molecules were investigated at near-thermal energy using a guided ion beam tandem mass spectrometer. We found that the doping with Al and V increases the total reaction cross section mostly. Under single-collision conditions, Rh2X+ reacts with NO to produce Rh2N+ with release of metal monoxide, XO, whereas RhnX+ (n = 3-6) adsorb NO. For the specific clusters RhnAl+ (n = 3 and 4) and RhnV+ (n = 4-6), the NO adsorption is often accompanied by the release of one Rh atom. In addition, we examined the reactions of Rh5X+ (X = Al, V, Co, Rh) with NO under multiple-collision conditions and observed the cluster dioxide formation and the N2 release, i.e., NO decomposition. Particularly, the V-doping is most effective for the NO decomposition. One possible explanation for the present results is that the formation of a stable dopant metal-oxygen bond directly leads to the increase of NO dissociative adsorption energy and the reduction of the energy barrier between the molecular and dissociative adsorption, thereby encouraging the NO decomposition on the small RhnX+ clusters studied.

Effect of Cu location and dispersion on carbon sphere supported Cu catalysts for oxidative carbonylation of methanol to dimethyl carbonate

A series of novel composite catalysts consisting of carbon spheres with encapsulated copper species were synthesized by incipient wetness impregnation. To improve catalytic activity, Cu location on the hollow carbon spheres was tuned by ultrasonic-assisted impregnation. The location, dispersion and chemical structure of copper species were characterized by X-ray diffraction, Temperature-programmed reduction, Transmission electron microscopy, N2-physisorption, Atomic absorption spectroscopy, X-ray photoelectron spectroscopy and dissociative N2O adsorption measurements. The results showed that hollow mesoporous carbon spheres have uniform mesopores, which were more favorable to the confinement and dispersion of the active species than solid carbon spheres. The catalyst with Cu species highly dispersed in the mesopores of hollow carbon spheres exhibited superior catalytic performance compared with those with Cu species located outside the support or inside the hollow interiors. The catalyst with ultrafine Cu particles of 2 nm in the mesopores of the 200 nm carbon sphere exhibited a dimethyl carbonate Space-Time Yield of 218.4 mg·g−1cat·h−1, much higher than traditional activated carbon and ordered mesoporous carbon supported Cu catalysts. Interestingly, copper species in the cavity showed high autoreduction ability in spite of poor dispersion after activation, and this catalyst is anticipated to achieve better activity by improving Cu dispersion.

Geometrical Structures of Partially Oxidized Rhodium Cluster Cations, Rh6Om+ (m = 4, 5, 6), Revealed by Infrared Multiple Photon Dissociation Spectroscopy.

Infrared multiple photon dissociation (IRMPD) spectra of Rh6Om+ (m = 4-10) are obtained in the 300-1000 cm-1 spectral range using the free electron laser for infrared experiments (FELIX) via dissociation of Rh6Om+ or Rh6Om+-Ar complexes. The spectra are compared with the calculated spectra of several stable geometries obtained by density functional theory (DFT) structural optimization. The spectrum for Rh6O4+ shows prominent bands at 620 and 690 cm-1 and is assigned to a capped-square pyramidal Rh atom geometry with three bridging O atoms and one O atom in a hollow site. Rh6O5+ displays bands at 460, 630, 690, and 860 cm-1 and has a prismatic Rh geometry with three bridging O atoms and two O atoms in a hollow site. Rh6O6+ shows three intense bands around 600-750 cm-1 and multiple weak bands in the range of 350-550 cm-1. This species has a prismatic Rh geometry with four bridging O atoms and two O atoms in a hollow site. Considering that Rh6Om+ (m ≤ 3) adopts tetragonal bipyramidal Rh6 structures, the change at m = 4 to capped bipyramidal and at m = 5 to prismatic geometries results in a reduction of the number of triangular hollow sites. Since NO preferentially binds on a triangular hollow site through the N atom, the geometry change lowers the possibility of NO dissociative adsorption.

Conversion of NO into N2 over γ-Mo2N

Cubic molybdenum nitride (γ-Mo2N) exhibits Pt-like catalytic behavior in many chemical applications, most notably as a potent catalyst for conversion of harmful NOx gases into N2. Guided by experimental profiles from adsorption of 15NO on γ-Mo214N, we map out plausible mechanisms for the formation of the three isotopologues of dinitrogen (14N2, 15N2, and 14N15N) in addition to 14N15NO. By deploying cluster models for the γ-Mo2N(100) and γ-Mo2N(111) surfaces, we demonstrate facile dissociative adsorption of NO on γ-Mo2N surfaces. Surfaces of γ-Mo2N clearly activate adsorbed 15NO molecules, as evidenced by high binding energies and the noticeable elongation of the N–O bonds. 15NO molecule dissociates through modest reaction barriers of 24.1 and 28.1 kcal/mol over γ-Mo2N(100) and γ-Mo2N(111) clusters; respectively. Dissociative adsorption of a second 15NO molecule produces the experimentally observed Mo2OxNy phase. Over the 100 surface, subsequent uptake of 15NO continues to occur until the dissociated O and...

Insight into the function of base-promoted Cu-containing catalysts for highly efficient hydrogenolysis of cellulose into polyols

The Cu-containing catalysts were synthesized via thermal treatment of the CuMgAl hydrotalcite with a fixed metal ratio at various calcination temperatures. The bi-functional solid base catalysts exhibited high activity for the hydrogenolysis of highly concentrated cellulose. The hydrotalcite precursors and the calcined samples were characterized by means of X-ray diffraction (XRD), thermogravimetric analysis (TG), N2 adsorption–desorption, temperature-programmed reduction of H2 (H2-TPR), temperature-programmed desorption of CO2 (CO2-TPD) and dissociative N2O adsorption. The characterization results indicated that the transformation of structure was caused by the increasing calcination temperature, which could further influence the numbers of the base sites and metal active sites in the CuMgAl catalysts. The hydrogenolysis of cellulose was systematically investigated over different catalytic systems. With the CuMgAl-600 catalyst, complete conversion of cellulose can be accomplished and the highest yield obtained is 81.4%, with total polyols yields obtained are 59.1% for the C2–C3 polyols. In addition, either the in-situ hydroxyl or the hydrated OH− due to the “memory effect” of hydrotalcite as Brønsted bases, was proved to exhibit promotional effect on the hydrogenolysis of cellulose, which could effectively substitute the effect of ionizing alkali. Furthermore, it is noteworthy that the conversion of cellulose could maintain up to 90.2% with unobvious formation of coke-like precipitates when the cellulose concentration reached a high level of 18%.

Catalytic CO–NO reaction over Cr–Cu embedded CeO2 surface structure

Deposition of a very small amount (0.14wt%) of Cr–Cu onto CeO2 accompanied by thermal aging at 900°C for 25h resulted in a high catalytic activity for stoichiometric CO–NO reaction. Although the catalyst was superior to Rh/CeO2 with the similar metal loading and thermal aging history, such a high activity could not be obtained by using other metal oxide supports (γ-Al2O3, TiO2, ZrO2, and CeO2–ZrO2). The active site that consists of Cu+ and Cr3+ embedded onto the CeO2 surface may be formed by thermal aging and its local structure is different from the bulk oxide of CuCrO2. A possible reaction mechanism of CO–NO reaction over the Cr–Cu embedded CeO2 surface was discussed from the results of kinetic analysis, isotopic reaction between C16O and N18O and in situ infrared spectroscopy. It is suggested to involve the dissociative adsorption of NO and subsequent oxygen exchange with the surface in parallel to CO oxidation by the surface oxygen species.

Low-temperature hydrogenation of maleic anhydride to succinic anhydride and γ-butyrolactone over pseudo-boehmite derived alumina supported metal (metal=Cu, Co and Ni) catalysts

Abstract The pseudo-boehmite derived alumina supported metal (Cu, Co and Ni) catalysts prepared by the impregnation method were investigated in hydrogenation of maleic anhydride (MA) to succinic anhydride (SA) and γ-butyrolactone. The catalysts were characterized by ICP-AES, N2 adsorption–desorption, XRD, H2-TPR, CO-TPD, dissociative N2O adsorption and TEM and the results showed that the alumina possessed mesoporous feature and the metal species were well dispersed on the support. Compared to Cu/Al2O3 and Co/Al2O3, Ni/Al2O3 exhibited higher catalytic activity in the MA hydrogenation with 92% selectivity to SA and nearly 100% conversion of MA at 140 °C under 0.5 MPa of H2 with a weighted hourly space velocity of 2 h−1 (MA). The stability of Ni/Al2O3 catalyst was also investigated.

Probing BaO Doping Effect on the Structure and Catalytic Performance of Pd/CexZr1–xO2 (x = 0.2–0.8) Catalysts for Automobile Emission Control

Pd/CeO2-ZrO2-BaO (Pd/CZB) catalysts with 5.0 wt % BaO and different CeO2/ZrO2 molar ratio were synthesized. The modification with BaO significantly promotes the catalytic activity of HC and NOx conversions when the molar ratio of CeO2 to ZrO2 is 2/1, because the substitution of Cex+/Zr4+ ions by Ba2+ promotes the formation of oxygen vacancy as revealed by XRD refinement analysis results and improves the mobility of active oxygen as a result of electronic and structural modifications. Among the Ba-doped catalysts, the crystalline form of the CZB supports gradually transform from cubic and pseudocubic to stable tetragonal phase as the increase of ZrO2 content. Meanwhile, the Raman results show that addition of moderate ZrO2 promotes the formation of structural defects, resulting in higher OSC and NOx storage efficiency. On the other hand, the introduction of moderate ZrO2 facilitates the dissociative adsorption of NO and promotes the deep oxidation of HC. Therefore, Pd/CZB catalysts with CeO2/ZrO2 molar ratio of 3/1–1/1, especially Pd/CZB21, show a much better catalytic activity of HC and NOx eliminations and a wider dynamic operation window. Zr-rich catalysts present worse catalytic activity of CO oxidation compared with Ce-rich catalysts, which is mainly arising from the decreased amount of active sites. After thermal aging treatment, Zr-rich catalysts (CeO2/ZrO2 < 1) undergo less severe deterioration of the catalytic activity compared with Ce-rich catalysts (CeO2/ZrO2 ≥ 1) as a result of better thermostability, and Pd/CZB11-a presents the best catalytic performance and widest dynamic operation window.

Adsorption and Reaction of CO and NO on Ir(111) Under Near Ambient Pressure Conditions

The adsorption and reaction of CO and NO on Ir(111) have been studied by near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) together with low-energy electron diffraction, scanning tunneling microscopy, and mass spectroscopy (MS). Under both ultrahigh vacuum (UHV) and NAP conditions CO molecules occupy on-top sites of the Ir(111) surface at room temperature (RT) by forming two-dimensional clusters. Exposure to NO under UHV conditions at RT induces partially dissociative adsorption, while NAP NO exposure leads to a Ir(111) surface that is covered by molecular NO. We conducted in-operando NAP-XPS/MS observation of the NO + 13CO reaction under a NAP condition as a function of temperature. Below 210 °C adsorption of NO is inhibited by CO, while above 210 °C the CO inhibition is released due to partial desorption of CO and dissociative adsorption of NO starts to occur leading to associative formation of N2. Under the most active condition studied here the Ir surface is covered by a dense co-adsorption layer consisting of on-top CO, atomic N and O, which suggests that this reaction is not a NO-dissociation-limited process but a N2/CO2 formation-limited process.

Reactions of Size-Selected Copper Cluster Cations and Anions with Nitric Oxide: Enhancement of Adsorption in Coadsorption with Oxygen

Reactions of size-selected Cu(n)(±) and Cu(n)O(m)(±) (n = 3-19, m ≤ 9) clusters with NO were investigated in the near-thermal energy region under single collision conditions using a tandem-type mass spectrometer with two ion-guided cells. Oxygen atoms preadsorbed on the cluster can significantly enhance the NO adsorption probability and cause additional reactions. NO adsorption is observed particularly for anionic copper cluster dioxides, Cu(n)O2(-) (n ≥ 8), followed by the release of a Cu atom from Cu(n)O2(-) (n = 8, 10, and 12), which suggests that NO adsorbs strongly, i.e., dissociatively on these clusters. Density functional theory calculations support that dissociative adsorption of NO occurs in the reaction of Cu8O2(-) under the present experimental conditions. On the other hand, NO oxidation proceeds in reactions of oxygen-rich cluster cations such as Cu4O3(+), Cu6O5(+), Cu9O7(+), and Cu11O8(+).

DRIFTS studies on CO and NO adsorption and NO + CO reaction over Pd2+-substituted CeO2 and Ce0.75Sn0.25O2 catalysts

Sequential adsorption of CO and NO as well as equimolar NO+CO reaction with variation of temperature over Pd2+ ion–substituted CeO2 and Ce0.75Sn0.25O2 supports has been studied by DRIFTS technique. The results are compared with 2at.% Pd/Al2O3 containing Pd0. Both linear and bridging Pd0–CO bands are observed over 2at.% Pd/Al2O3. But, band positions are shifted to higher frequencies in Ce0.98Pd0.02O2−δ and Ce0.73Sn0.25Pd0.02O2−δ catalysts that could be associated with Pdδ+–CO species. In contrast, a Pd2+–CO band at 2160cm−1 is observed upon CO adsorption over Ce0.98Pd0.02O2−δ and Ce0.73Sn0.25Pd0.02O2−δ catalysts pre-adsorbed with NO and a Pd+–CO band at 2120cm−1 is slowly developed on Ce0.73Sn0.25Pd0.02O2−δ over time. An intense linear Pd0–NO band at 1750cm−1 found upon NO exposure to CO pre-adsorbed 2at.% Pd/Al2O3 indicates molecular adsorption of NO. On the other hand, a weak Pd2+–NO band at 1850cm−1 is noticed after NO exposure to Ce0.98Pd0.02O2−δ catalyst pre-adsorbed with CO indicating dissociative adsorption of NO which is crucial for NO reduction. Pd0–NO band is initially formed over CO pre-adsorbed Ce0.73Sn0.25Pd0.02O2−δ which is red-shifted over time along with formation of Pd2+–NO band. Several intense bands related to nitrates and nitrites are observed after exposure of NO to fresh as well as CO pre-adsorbed Ce0.98Pd0.02O2−δ and Ce0.73Sn0.25Pd0.02O2−δ catalysts. Ramping the temperature in a DRIFTS cell upon NO and CO adsorption shows the formation of N2O and NCO surface species, and N2O-formation temperature is comparable with the reaction done in a reactor.