FTIR Of Adsorbed CO Research Articles

Upgrading biogas into syngas via bi-reforming of model biogas over ruthenium-based nano-catalysts synthesized via mechanochemical method

The upgrading of biogas to value-added syngas via reforming of biogas is of great significance from the perspective of green carbon science. A series of Ru based nano-catalysts (Ru/MgO, Ru/La2O2CO3, Ru/CeO2) with relatively low Ru loading and high dispersion were successfully prepared by mechanochemical method, and applied in the bi-reforming of model biogas reaction. The representative catalysts were comprehensively characterized by XRD, N2 physical adsorption, ICP-OES, SEM, XPS, H2-TPR, CO2-TPD, HRTEM, FTIR of CO adsorption, TPSR, TG, and Raman spectroscopy, etc. Ascribed to the appropriate basicity of MgO, homogeneous Ru dispersion with ultra-small particle size, and strong interaction between Ru ultra-small nano particles and MgO support, Ru/MgO exhibit higher CO2 adsorption and activation, higher CH4 activation and dissociation, compared with Ru/La2O2CO3, Ru/CeO2, which facilitate the formation of active oxygen species and intermediate coke removal, thus enhance the resistance to coke deposition and sintering. At reaction conditions of T = 750 °C and weight hourly space velocity = 32,400 mLgCat−1 h−1, 0.5Ru/MgO catalyst exhibit satisfying catalytic activity (initial CH4/CO2 conversation rate of 87/48%) and superior stability (stable for 150 h) with negligible deactivation rates.

Catalytic direct dehydrogenation of ethyl lactate to produce ethyl pyruvate over a synergetic Cu0/Cu+ interface

The direct dehydrogenation of ethyl lactate (EL) to produce ethyl pyruvate (EP) over non-precious heterogeneous catalysts is highly desirable, but challenging. Herein, we report a highly efficient silica-supported copper catalyst prepared via a hydrolysis-precipitation method (Cu/SiO2-HP) for the dehydrogenation of ethyl lactate, which exhibited an 85.4 % EL conversion with 91.1 % selectivity toward EP at 320 °C. XAFS, in situ XPS, and CO-adsorption FT-IR spectra revealed that the Cu/SiO2-HP catalyst had abundant Cu0/Cu+ interfaces. In situ FT-IR spectra, kinetic studies, and theoretical calculations also demonstrated that the Cu0/Cu+ interfaces synergistically activate the O−H and C−H bonds in the adsorbed EL for direct dehydrogenation into EP. The H/D kinetic isotope effect for model reaction confirmed that C−H bond activation is the key step in the dehydrogenation reaction. This study offers a new approach toward the selective conversion of EL into EP, which is of great significance for biomass conversion.

Geometrically embedding dispersive Pt nanoparticles within silicalite-1 framework for highly selective ɑ, β-unsaturated aldehydes hydrogenation via oriented C = O adsorption configuration

The issue for thermodynamically favored C = C hydrogenation needs to be overcome in the hydrogenation of ɑ, β-unsaturated aldehydes to unsaturated alcohols. Herein, we employ confinement effect in the catalyst-designing engineering to orient the C = O adsorption by the zeolitic microchannel, where highly dispersed Pt nanoparticles are homogeneously well-embedded within the silicalite-1 framework (Pt@S-1). Comprehensive characterizations, such as HAADF-STEM, H2-TPR, FT-IR of CO adsorption and XPS are carried out to demonstrate the geometric, confinement and electronic properties of metal species. In the hydrogenation of ɑ, β-unsaturated aldehydes with suitable molecular size, Pt@S-1 displays preferential C = O hydrogenation. For example, Pt@S-1 gives conversion of 99.8% and meanwhile the aiming cinnamal alcohol selectivity of 98.7% in the hydrogenation of cinnamaldehyde, outperforming larger Pt nanoparticles ill-suitedly embedded within silicalite-1 (Pt@S-1-is) and highly dispersed Pt nanoparticles supported on the silicalite-1 surface (Pt/S-1). For the hydrogenation of smaller 3-methyl-2-butenal, though the confinement effect boosts the C = O hydrogenation to some extent, the synergetic electronic effect via introducing Fe species effectively increases the unsaturated alcohol selectivity. Investigations on the adsorption configuration by in-situ FT-IR spectroscopy clearly indicate that the unsaturated aldehyde with suitable molecular size is preferentially adsorbed on Pt sites of Pt@S-1 via the oxygen atom of C = O with on-top η1 mode, thus favoring high unsaturated alcohol selectivities, while the di-σCOη2 and η4 adsorption modes on Pt@S-1-is and Pt/S-1 are relatively adverse for prioritized C = O hydrogenation.

Tuning the properties of the cobalt-zeolite nanocomposite catalyst by potassium: Switching between dehydration and dehydrogenation of ethanol

In this work, we offer an understanding of the potassium impact on the performance of the cobalt-zeolite catalysts in the ethanol steam reforming process (ESR) conditions. The catalytic behavior of the undoped and K-doped cobalt-containing materials (10 wt% of cobalt) is discussed concerning their structure and surface properties. The 2K/CoY and 4K/CoY samples, where potassium was introduced on the HY support together with cobalt phase upon incipient wetness impregnation (IWI method), were faced with the Co(K)Y sample with K+ in the ion-exchange positions (IE method), where cobalt was introduced on the surface of KY support by IWI method. The chemical and phase composition, texture, morphology, and reducibility of the catalysts were comprehensively evaluated by the ICP, XRD, low-temperature N2 adsorption, STEM/EDX, and H2-TPR methods, respectively. The catalysts’ active sites nature was assessed in the quantitative pyridine and CO adsorption FT-IR studies. A detailed description of the surface properties of the materials was faced with their catalytic interaction with the ethanol–water mixture at 500 °C. The in situ FT-IR reaction studies supported the catalytic results. Undoped CoY catalyst exhibited 100% ethanol conversion, whereas its selectivity to H2, CO2, CO, and C2H4, reached values in the range of 55–60%, 25–30%, 0–5%, and 65–70%, respectively, pointing the dehydration path as the main one. The presence of potassium altered the reaction mechanism, what reflected in the decrease of ethanol conversion to 75–80% for Co(K)Y sample and 15–30%, and 5–10%, respectively for 2K/CoY and 4K/CoY samples. Undesired C2H4 production was reduced to 40% for the potassium-exchanged sample and did not occur for both, 2K/CoY and 4K/CoY, IWI-prepared samples. The coke species of various chemical nature were identified over the deactivated catalysts with the use of Raman, UV–VIS, and XPS spectroscopic methods and thermogravimetric analysis method.

Direct methane conversion with oxygen and CO over hydrophobic dB-ZSM-5 supported Rh single-atom catalyst

Isolated Rh atoms are supported on hydrophobic dB-ZSM-5. Single-atom Rh on dB-ZSM-5 is characterized with Ac-HAADF/STEM and CO adsorption FTIR. Direct conversion of methane to oxygenates is carried out in an autoclave in water charged with CH4, O2 and CO at 150 °C. Hydrophobic Rh-dB-ZSM-5 is compared with hydrophilic Rh-ZSM-5 (Si/Al = 15) for its catalytic performance. Rh-dB-ZSM-5 catalyst exhibits higher CH3OH selectivity and lower CH3COOH and CO2 selectivity. The catalytic activity of Rh-dB-ZSM-5 is much higher than the activity of Rh-ZSM-5 when the reaction is carried out under low pressure.

Influence of ionic conductivity and dielectric constant of the catalyst on DBD plasma-assisted CO2 hydrogenation into methanol

Dielectric barrier discharge (DBD) plasma technology is a promising method for producing methanol from CO2 hydrogenation as the reaction can be run at atmospheric pressure and temperatures below 100 °C. The choice of the catalyst is crucial and has to be made not only according to its activity and selectivity towards the desired product, but its effect on plasma properties. In this work, the influence of several important catalytic properties of DBD plasma such as the dielectric constant of the catalyst and ionic conductivity is studied. The effects of the catalyst support and the addition of promoters on CO2 hydrogenation under DBD plasma are also studied. To this end, Cu and Cu–ZnO catalysts supported on γ-Al2O3 and a template-free seedless ZSM-5 (Si/Al molar ratio of 23) were prepared to study their catalytic performance on CO2 hydrogenation into methanol under DBD plasma. These catalysts were fully characterized by XRD, SEM, N2 physisorption, temperature programmed reduction and in situ FTIR CO adsorption. The relative complex permittivity of the catalysts was measured and the ionic conductivity was estimated using a modified Debye model. In this paper, the role of the ionic conductivity of the catalyst was identified as a crucial parameter in plasma-assisted CO2 hydrogenation. It was found that the lower the value of the ionic conductivity, the better the CO2 conversion. Indeed, high ionic conductivity reduces the density of the plasma and decreases the dissociation of CO2. The highest CO2 conversion value (34.0%) was observed for the nonconductive alumina support, whereas the highest methanol yield (0.5%) was observed for the zeolite-supported Cu–ZnO catalyst.

Uniformly sized Pt nanoparticles dispersed at high loading on Titania nanotubes

A range of Pt loadings (0.9–21.5 wt. %) on titania nanotubes (TNT) catalysts were prepared with a view to address metal-support interaction effects on Pt nanoparticles (size, dispersion, shape) and were prepared by a vapor-phase impregnation method using Pt(acac). The reduced catalysts were characterized by XRD, TEM, H2-TPD, CO adsorption FTIR and examined as catalysts in naphthalene hydrogenation. Pt nanoparticles have a very uniform size between 1.4–2.2 nm for Pt loadings 0.9–21.5 wt% as indicated by TEM, H2-TPD and CO-adsorption FTIR. A strong metal-support interaction between Pt and TNT support hinder Pt nanoparticles to agglomerate into larger particles, even at high Pt loadings. Both Pt edge sites and exposed surface total Pt sites are highest at 10.2 wt.% Pt loading and parallels naphthalene hydrogenation activity which peaks at this loading.

Efficient synthesis of the Cu-SAPO-44 zeolite with excellent activity for selective catalytic reduction of NOx by NH3

A small-pore Cu-chabazite zeolite, Cu-SAPO-44 was synthesized using a one-pot approach by combination of cyclohexylamine template and copper-amine complex. The Cu-SAPO-44 zeolite obtained exhibits excellent activity over a wide temperature window from 200 to 500 °C for the selective catalytic reduction of NOx with ammonia (NH3-SCR). The copper-amine complex allowed direct introduction as well as a high dispersion of extra-framework Cu species in the chabazite structure. In situ X-ray absorption fine structure (XAFS) confirmed the isolated Cu2+ ions and Cu2+ ↔ Cu+ cycle. Temperature-programmed reduction with H2 (H2-TPR) and in situ FTIR of CO adsorption demonstrated that a variety of isolated Cu2+ ions inside the large cages and in or near the six-membered rings of the chabazite structure are responsible for the wide temperature window of activity. Cu-SAPO-44 has shown to be a promising candidate as a SCR catalyst with great potential in after-treatment systems for either mobile or stationary sources.

Hydrogen production by methane decomposition on Pt/γ-alumina doped with neodymium catalysts and its kinetic study

Abstract This paper presents results for the catalytic decomposition of methane using Pt/γ-Al2O3 and Pt/γ-Al2O3-Nd2O3 catalysts for the hydrogen production. All catalysts were prepared by wet impregnation using Nd(NO3)3⋅6H2O and H2 PtCl6.6H2O as precursor salts. The concentrations of the catalysts were Pt, 1.0 wt%, and Nd, 1.0 and 10.0 wt%. The reaction was carried out from 400 to 750 °C. All the catalysts reduced methane decomposition temperature by 400–750 °C relative to noncatalytic thermal decomposition, which is carried out at 1300 °C. The Pt catalysts supported on γ-alumina doped with neodymium exhibited higher activity than Pt supported on alumina alone. All catalysts showed high activity and selectivity at 750 °C, with conversions around 57–80%vol and hydrogen productions of 0.29, 0.27 and 0.19 mmoles of H2/min*gcat for PtANd10, PtANd1 and PtA catalysts respectively also were observed in the output stream, traces of C2H4 y C2H6 (less than 1%) and unconverted methane. This work includes a kinetic study of methane cracking, for this purpose two experiments were carried out, the first one consisted of varying the amount of catalyst, keeping the feed flow constant, in the second experiment the flow rate was varied, keeping the mass of the catalyst constant. The activation energy of methane cracking is estimated at 35.5, 37.9 and 33 kJ/mol for the Pt/A, Pt/ANd1 and Pt/ANd10 catalysts, respectively. The characterization was done by X-ray diffraction, N2 adsorption-desorption, H2-TPR, FTIR of CO adsorption, FTIR of Pyridine adsorption, XPS, HRTEM, catalytic activity and TPO (Temperature programed Oxidation) analysis after reaction.

Cs2.5H0.5PW12O40 Encapsulated in Metal–Organic Framework UiO-66 as Heterogeneous Catalysts for Acidolysis of Soybean Oil

The Keggin-type Cs2.5H0.5PW12O40 was encapsulated in metal–organic framework UiO-66 by a simple solvothermal synthesis method. The characterization results showed that the morphology and crystal structure of UiO-66 were preserved, and the heteropolyanion structure remained unchanged after Cs2.5H0.5PW12O40 encapsulation. The prepared Cs2.5H0.5PW12O40@UiO-66 material has demonstrated to be an environmentally benign catalyst in the acidolysis of soybean oil with medium-chain fatty acids for the production of low-calorie structured lipids. The FT-IR CO adsorption experiments revealed that additional Lewis acid sites were formed in the solid acid catalyst, which were essential to catalyze the acidolysis reaction. The solid catalyst could be reused for several recycles without obvious deactivation due to hardly leaching of active components into the reaction mixture.

Pt and Pd Nanoparticles Immobilized on Amine-Functionalized Hypercrosslinked Porous Polymer Nanotubes as Selective Hydrogenation Catalyst for α,β-Unsaturated Aldehydes

Selective hydrogenation reaction over supported metal nanoparticles (NPs) through activation of molecular H2 is very demanding in the context of maintaining atom efficiency in chemical reactions. Although high selectivity is difficult to achieve in the reaction, but it is very challenging. In this research, we separately deposited Pd and Pt NPs on nanoporous hollow polymer tubes (PP-3) and studied their efficiency in hydrogenation of α,β-unsaturated aldehydes as substrates. We found hydrogenation selectivity over these two types of catalysts (Pd@PP-3 and Pt@PP-3) were entirely different. Pt@PP-3 shows high selectivity in the hydrogenation of C=O bonds, producing unsaturated alcohol in high yield, whereas Pd@PP-3 only hydrogenates C=C bonds and forms saturated aldehyde as the major product. Pd@PP-3 and Pt@PP-3 were thoroughly characterized by PXRD, N2 sorption, TEM, XPS, CO stripping experiment and in-situ CO adsorption FT-IR studies. Our research implies the utility of porous organic polymers as support for metal NPs mediated hydrogenation reactions.

Ultrasmall Platinum Stabilized on Triphenylphosphine-Modified Silica for Chemoselective Hydrogenation.

Chemoselective hydrogenation of substrates with more than one functional group that could be hydrogenated is quite challenging and is of fundamental importance. Here, the enhanced chemoselectivity of ultrasmall (<1 nm) platinum nanoparticles (NPs) stabilized on silica modified with triphenylphosphine (PSiO2 ) in hydrogenation reactions is reported. Platinum NPs on PSiO2 exhibit much higher selectivity than those on SiO2 in the hydrogenation of acetophenone to 1-phenylethanol (99.9 versus 36 %) and hydrogenation of phenylacetylene to styrene (85 versus 52 %). The results of NMR spectroscopy, X-ray photoelectron spectroscopy, and in situ CO adsorption FTIR spectroscopy indicate the existence of strong interactions between triphenylphosphine and Pt NPs. Consequently, Pt NPs on PSiO2 have smaller particle sizes and more positive Pt 4 f binding energy than those of Pt/SiO2 ; these are the main contributors to the superior chemoselectivity of Pt NPs. The organically modified silica could act as an efficient solid ligand for tuning the catalytic performance of metal NPs.

Photocatalytic hydrogen production over titania modified by gold – Metal (palladium, nickel and cobalt) catalysts

The photocatalytic production of hydrogen on modified Au/TiO2-based photocatalysts by using water/methanol mixtures was studied. The main goal was to study the effect of surface modification of Au/TiO2 with Pd, Ni and Co on H2 production under UV light irradiation (λ ca. 254 nm). Catalysts were produced by depositing Pd, Ni or Co precursors (nitrates hydrated salts) on TiO2 (Evonik, P25) by incipient wetness impregnation followed by thermal treatment under H2 (Pd and Co) or air (Ni). Thereafter, Au was incorporated by deposition-precipitation with urea (DPU method) and then the catalysts were thermally activated again under air flow. The photocatalysts were characterized by UV–Vis diffuse reflectance, HAADF-TEM, EDXS, FTIR CO adsorption, XPS and photoluminescence. In order to obtain detailed information about the composition of the nanoparticles, high-resolution elemental analyses (EDXS line scans) were performed. The Au-Pd, Au-Ni and Au-Co on TiO2 photocatalysts showed higher performance for H2 production (266, 256 and 171 mmol H2 mmolAu−1 h−1, respectively) compared to the Au/TiO2 material (106 mmol H2 mmolAu−1 h−1). PL results showed that the improved H2 production rate could be explained by an enhanced charge separation. The highest H2 production showed by the Au-Pd/TiO2 sample could be attributed to synergistic effects, derived from the interaction between Au and Pd particles. For the Au-Ni/TiO2 and Au-Co/TiO2 samples it is proposed that nickel or cobalt oxides worked as promoters (with additives effects) because of the formation of a p–n heterojunction.

Carbon dioxide reforming of methane over Ru catalysts supported on Mg-Al oxides: A highly dispersed and stable Ru/Mg(Al)O catalyst

Ru catalysts (2wt%) supported on Mg and/or Al oxides including γ-Al2O3, MgAl2O4, Mg3(Al)O, and MgO were prepared by incipient wetness impregnation and compared for the CH4-CO2 reforming to investigate the effect of support on the Ru dispersion and catalytic performance. The catalysts before and after reaction were well characterized by using N2 physical adsorption, ICP, SEM-EDX, XRD, H2-TPR, TEM, CO chemisorption, FTIR of CO adsorption, XPS, CO2-TPD, TG, and Raman spectroscopy. The characterization results revealed that Ru metal was very highly dispersed on the Mg3(Al)O mixed oxide obtained from Mg-Al layered double hydroxide, probably existing in very small nanoparticles and/or clusters. The order of Ru metal dispersion was Ru/Mg3(Al)O>Ru/MgO>Ru/MgAl2O4>Ru/γ-Al2O3. The catalytic activity and stability of the Ru catalysts were greatly dependent on the support. Both Ru/MgO and Ru/Mg3(Al)O showed higher activity than Ru/MgAl2O4 and Ru/γ-Al2O3, which might be related to the strong base intensity of support and more accessible surface Ru0 atoms, respectively. During 30h of reaction at 1023K, a significant deactivation occurred on Ru/γ-Al2O3, Ru/MgAl2O4, and Ru/MgO, which was mainly attributed to the sintering of Ru metal particles. In contrast, the Ru/Mg3(Al)O catalyst exhibited superior stability and no significant sintering of Ru metal was observed, suggesting that the highly dispersed Ru metal was stable. A 300h long-term test further demonstrated the excellent stability of Ru/Mg3(Al)O. These results highlight the significant effect of Mg(Al)O mixed oxide on the improvement of Ru dispersion and catalytic performance, and this might be related to the unique properties of Mg(Al)O mixed oxide including memory effect, low crystallinity, and its strong interaction with Ru.

Formation of Ru Shell on Co/Al2O3 by Galvanic Deposition Method and Its High Catalytic Performance for Three-Way Conversion

Abstract A supported Ru catalyst was prepared by a galvanic deposition (GD) of Ru on Co particles supported on Al2O3 (Ru/Co-GD). The structure and chemical state of Ru/Co-GD was characterized by using a pulsed CO chemisorption technique, STEM-EDS, XAFS, XPS, CO adsorption FT-IR spectroscopy, and temperature-programed reduction (TPR) method. It is indicated that Ru/Co-GD forms Ru shell on Co nanoparticles. Such a unique structure was not formed on Ru/Co/Al2O3 prepared by a conventional sequential impregnation method (Ru/Co-seq). The Ru shell of Ru/Co-GD showed higher reducibility than Ru species of Ru/Co-seq as well as higher than Ru/Al2O3. Owing to the Ru shell having high reducibility, Ru/Co-GD showed enhanced catalytic activity for NO–C3H6 reaction. In addition, Co oxide on Ru/Co-GD exhibited high catalytic activity for CO and C3H6 oxidation. As a result, Ru/Co-GD showed superior performance for NO–C3H6–CO–O2 reaction compared to the conventional catalysts. The Ru shell structure also contributed to the suppression of Ru vaporization.

Cooperative action of Brønsted and Lewis acid sites of niobium phosphate catalysts for cellobiose conversion in water

The lively acidic properties in water of niobium phosphate (NBP) catalyst and NBP modified samples by acidic treatments in HCl solutions at 0.1, 1.0, and 10M concentration (NBP01, NBP1, and NBP10, respectively) have been exploited for the direct conversion reaction of cellobiose to hydroxymethylfurfural (HMF) at temperature of 80–130°C. Acidity of the samples was determined by liquid-solid titrations working in a modified HPLC line with basic solutions of phenylethylamine (PEA), used as a base probe. As solvents, an apolar-aprotic one, cyclohexane, was used for determining the intrinsic acidity and water for the effective acidity. In addition, pyridine/water co-adsorption FT-IR experiments complemented the acidity study, and the results obtained confirmed the presence of both water-tolerant Lewis acid sites (LAS) and some residual Brønsted acid sites (BAS) on all the NBP samples. On NBP, the LAS to BAS ratio was 1.69, measured in cyclohexane, and only slightly decreased to 1.30, when measured in water. Catalytic activity was studied in a liquid-solid reaction line with fixed bed flow reactor working in complete recirculation. The reaction of HMF formation from cellobiose consists of three distinct catalytic actions: hydrolysis of the β-1,4-glycosidic bonds of cellobiose, isomerization of the formed glucose monomers to fructose, and cyclo-dehydration of fructose to HMF. Comparative catalytic results obtained with a sulfonic acid resin (Amberlite IR 120) showed that it was not able to form any HMF from cellobiose in the range of temperature studied, only cellobiose hydrolysis to glucose can be successfully achieved on the protonic acid resin.

Structural and electronic effects in bimetallic PdPt nanoparticles on TiO2 for improved photocatalytic oxidation of CO in the presence of humidity

Bimetallic PdxPt1−x/TiO2-P25 photocatalysts have been proven to maintain high activity for CO photocatalytic oxidation even under 50% relative humidity for 0.3<x<0.5 molar compositions, whereas humidity traces are highly detrimental when the reaction was performed over TiO2 supported monometallic particles. The catalysts were characterized by XPS, TEM, HAADF-STEM, TPR, CO-TPD and FTIR-CO adsorption characterization. The results suggested a random distribution of Pd and Pt atoms within the bimetallic nanoparticles, and in particular at their surface. It was proposed that the synergy observed in bimetallic PdxPt1−x/TiO2 may be explained by their modified electronic structure, playing a key role in overcoming the negative effects of humidity on the photocatalytic CO conversion. The behavior of PdxPt1−x/TiO2 under humid air was assumed to result from a preferential oxygen and water adsorption on surface Pt sites, leaving Pd sites free for CO adsorption, Pd being more resistant to oxidation than Pt in Pt-rich PtPd particles.

Effect of Pt cocatalyst in Pt/TiO2 studied by in situ FTIR of CO adsorption

In situ transmission infrared spectroscopy was used to study the role of Pt cocatalyst in Pt/TiO2 using CO as a probe molecule. An 11 cm−1 redshift of CO adsorbed on Pt/TiO2 was observed under irradiation in the absence of changes in the CO coverage or sample temperature. In contrast, no CO shift was detected on Pt/Al2O3. This indicates that the redshift of the CO adsorption peak is due to the photogenerated electron transfer from TiO2 to Pt, and this accounts for the increased photocatalytic activity by the loaded Pt cocatalyst.

Effect of steam addition on the structure and activity of Pt–Sn catalysts in propane dehydrogenation

To investigate the role of steam on the structure and activities of platinum-based catalyst, a tin modified Pt/γ-Al2O3 catalyst was prepared for propane dehydrogenation in the presence of steam. The propane conversion could be prominently elevated by nearly twofolds with only 1.0% loss of selectivity to propene when an optimum amount of H2O was added. The retarding effects of steam on the activities are also observed at higher H2O/C3H8 molar ratios (>1). Kinetic studies results show that the apparent activation energies for steam dehydrogenations are lower than those without steam addition. The fresh, spent and steam pretreated catalysts were characterized by TG, Raman, H2-chem, HAADF-STEM, XPS and CO adsorption FT-IR (CO-FTIR). It is observed that the platinum particles sizes are smaller in the samples subjected to certain period of steam pretreatment. The changes of platinum dispersion in steam conditions are related to the changes of tin oxidation states and the segregation of platinum from Pt–Sn alloys, as revealed by CO-FTIR and XPS results. More accessible Pt sites that are generated in the steam due to the phase transformation of Pt–Sn catalyst as well as the removal of coke accumulated on the catalyst surface would account for the increase of catalytic activities and the decrease of activation energies in steam atmosphere. Competitive adsorption of H2O and other reagent over Pt sites would lead to the retarding effects of steam on the activities at high H2O partial pressure.

Comparative surface analysis and TAP measurements to probe the NO adsorptive properties of natural gas vehicle Pd–Rh/Al2O3 catalyst

Thermal ageing has a significant detrimental effect on the behavior of bimetallic Pd–Rh natural gas fuelled vehicle (NGV) catalysts toward NO adsorption and its dissociation recognized as structure-sensitive. The ageing procedure at the lab-scale consisted of a thermal treatment under wet atmosphere (10vol.% H2O in air) at 980°C that would induce comparable surface reconstructions taking place under real exhaust conditions of Pd–Rh/Al2O3 catalysts. XPS and FTIR of CO adsorption highlight the occurrence of simultaneous particle sintering and preferential surface Rh enrichment. Temporal analysis of product (TAP) experiments have been implemented for in situ characterization that allows the elucidation of surface reactions and diffusion processes taking place at the surface of Pd–Rh/Al2O3 when single NO pulse is introduced. It was found that the relative rates of those processes are strongly affected by the dispersion and the Rh composition on freshly-prepared and aged catalysts. Interestingly, Rh recognized as the most suitable noble metal to convert NO to N2 would also slow down the agglomeration on Pd further protecting the metal/support interface.