CO Desorption Peak Research Articles

CO and H2 adsorption on Au-Ni bimetallic surfaces: a combined experimental and DFT theoretical study

Au-Ni bimetallic thin films were grown on refractory metal substrates. CO and H2 adsorption on Au-Ni bimetallic surfaces have been studied by a combination of in situ polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), temperature-programmed desorption (TPD), and density functional theory (DFT) calculations. It is found CO desorption peak shifts from 413 K on pure Ni surfaces to 293 K on the isolated Ni atoms formed by alloying with Au atoms. The sharp decrease of CO desorption temperature on Au-Ni surfaces with increasing Au coverage is caused by the change of the favored CO adsorption sites from bridge/hollow sites on pure Ni surfaces to Ni top sites on Au-Ni bimetallic surfaces. In situ PM-IRRAS shows two CO adsorption bands on Au sites at 2119 cm−1 and 2103 cm−1 on Au-Ni surfaces at 80 K, which are due to CO bound on under-coordinated Au atoms and electron negatively charged Au sites modified with nearby Ni atoms, respectively. Even with the Au-Ni surface temperature at as low as 100 K, CO adsorption induced Ni surface segregation has been observed by in situ PM-IRRAS. Furthermore, DFT calculation results discover the adsorption energy of CO on Ni top sites continues to decrease with increasing Au coverage due to the geometric ensemble effect and the lowered d-band center after Ni alloying with Au. H2 desorption temperature decreases from 363 K on pure Ni thin films to 302 K with increasing Au coverage to 0.6 ML. A new H2 peak appears at around 170 K on the Au-Ni surfaces with Au coverages between 0.6 ML and 0.9 ML. This new H2 TPD peak is assigned to H2 desorption from the totally isolated Ni sites. With Au coverage above 1.5 ML, there is no any H2 desorption detected. The combined surface science studies and DFT calculations provide new insights into the surface structure-activity correlation of Ni-base bimetallic surface alloys.

Efficient Electrochemical/Electroless Deposition Synthesis Routines for CO Tolerant Catalysts

Composite catalysts containing Pt and Mo-oxides are promising materials for anodic catalyst preparation in PEMFCs due to their high tolerance for CO-poisoning. The search for optimal preparation methods for these materials is an important task in modern electrochemical energetics.Two synthetic routines, namely electrodeposition and deposition under open-circuit conditions, were used for Pt-MoO x catalyst preparation. The prepared catalysts were characterized by a variety of modern physical methods (XRD, XPS, SEM, EDX); it was established that the material prepared by electroless deposition contains platinum shell upon platinum core. The materials obtained were tested in the reactions of CO adsorbate electrodeposition and dissolved CO-oxidation.It was found that molybdenum oxides in the composites prepared by electrodeposition broaden the major peak of CO-oxidation, but the peak maximum does not shift toward less positive values. Therefore, the CO monolayer is destabilized as a result of the contact with molybdenum oxides; however, only a small part of CO can be oxidized at these low potentials. Nevertheless, these catalysts are suitable for dissolved carbon monoxide oxidation. aPt·b(H x -2MoO3) composites were synthesized by the redox reaction of K2PtCl4 with reduced forms of hydrogen containing molybdenum bronzes. The CO desorption peak is broadened and shifted toward less positive potentials. aPt·b(H x -2MoO3) catalysts demonstrate high catalytic activity in the reaction of both adsorbed and dissolved CO oxidation. Therefore, one can conclude that both electrodeposition and electroless deposition are suitable methods for preparing PEMFC anode catalysts. Figure 1

Extending the basic function of lattice oxygen in lepidocrocite titanate – The conversion of intercalated fatty acid to liquid hydrocarbon fuels

We report herein the basicity of the external and internal lattice oxygen (OL) in lepidocrocite titanates with respect to CO2 and palmitic acid, respectively. Several compositions have been tested with different types of the metal M aliovalently (co)substituted for Ti, K0.8[MyTi2−y]O4 (M = Li, Mg, Fe, Co, Ni, Cu, Zn, Cu/Ni and Cu/Zn). The low CO2 desorption peak temperature (70–100°C) suggests that the external OL sites are weakly basic similar to TiO2. However, the internal OL sites are sufficiently basic to deprotonate palmitic acid, forming the intercalated potassium palmitate at the interlayer spaces. The latter serves as a two-dimensional (2D) molecular reactor for the production of liquid hydrocarbon fuels via deoxygenation under atmospheric N2. A relationship has been observed between the yield of the liquid products vs the partial charge of the lattice oxygen (δO). Since the deoxygenation pathway is highly dependent on the metal substitution, the redox-active sites might also play some roles. The co-substituted K0.8[Cu0.2Ni0.2]Ti1.6O4 produced ~68.0% yield of the liquid products, with ~ 51% saturated and ~ 15% unsaturated C15 hydrocarbons at 350°C.

Control of CO2 Adsorption and Desorption Using Polyethylene Glycol in a Tetraethylenepentamine Thin Film: An In Situ ATR and Theoretical Study

The reversible adsorption of CO2 on tetraethylenepentamine (TEPA) and the polyethylene glycol (PEG)-modified amine sites were investigated using attenuated total reflection infrared (ATR-IR) spectroscopy, mass spectrometry (MS), and density functional theory (DFT). The presence of PEG at the amine site increased the rate of formation of adsorbed CO2, enhanced the formation of weakly adsorbed CO2 which can be removed from flowing inert gas at room temperature, and decreased CO2 desorption peak (i.e., sorbent regeneration) temperature. The calculated CO2 binding energy (BE) and optimized structures suggest CO2 adsorbed on TEPA primarily in the form of ammonium carbamate. The presence of PEG promoted the formation of a species which exhibited an experimental IR spectrum resembling the simulated spectrum of a low BE zwitterion species. The observation suggests PEG controlled the formation of the adsorbed intermediate species. Modeling of the transient CO2 adsorption profiles further showed PEG accelerated the...

Promoting Effect of CeO2 on the Catalytic Activity of Ba–Y2O3 for Direct Decomposition of NO

Abstract The effect of CeO2 additive on the catalytic performance of Ba–Y2O3 prepared by coprecipitaion for the direct decomposition of NO was investigated. Although Ba–Y2O3 effectively catalyzed NO decomposition, its activity was clearly increased by addition of CeO2. The optimum CeO2 content was 10 mol %. CO2-TPD measurement revealed that the addition of CeO2 into Ba–Y2O3 caused an increase in the CO2 desorption peak in the temperature range of 473 and 723 K derived from highly dispersed Ba species. The predominant role of CeO2 additive was suspected to effectively create the highly dispersed Ba species as catalytically active sites. Kinetic studies of NO decomposition on Ba–CeO2(10)–Y2O3 suggested that coexisting O2 suppresses the NO decomposition reaction by competitive adsorption. Isotopic transient kinetic analysis suggested a reaction pathway in which the surface NOx adspecies act as reaction intermediates for the formation of N2 in NO decomposition over Ba–CeO2–Y2O3. We concluded that CeO2 additive does not directly participate in the NO decomposition reaction as catalytically active species.

Al (110) surface oxide thermal stability in ultrahigh vacuum

This research characterizes the stability of the Al2O3 surface oxide on Al (110) as a function of temperature and within an ultrahigh vacuum environment (p < 5 × 10−12 Torr). Auger electron spectroscopy and temperature desorption spectroscopy were used to correlate the change in oxygen and carbon surface concentration. The surface oxide was observed to remain stable up to 350–400 °C. Above this temperature, the oxide began to dissociate resulting in a CO desorption peak at 425 °C followed by extensive dissolution of the C and O into the Al bulk. A second and much smaller CO desorption peak was observed at 590 °C in concert with complete oxide breakdown and the virtual disappearance of surface carbon and oxygen. Extrapolation of the Auger electron spectral ratios of CKLL and OKLL peaks to the sum of the Al0LVV and Al3+LVV peak suggests that the surface concentration of each approaches zero at ~640 °C. The predominant mechanism for reduction of the surface oxide occurs by dissolution into the bulk instead of desorption. Copyright © 2013 John Wiley & Sons, Ltd.

Adsorption of SO2 and chlorobenzene on activated carbon

Activated carbon is very effective for simultaneous removal of multiple pollutants. The adsorption of SO2 and chlorobenzene modeling of VOCs on activated carbon was investigated in a fixed-bed reactor by four kinds of activated carbon. The results show that the SO2 adsorption is affected by the BET surface and basic functional groups as C=O and π–π* groups of the carbon, while the chlorobenzene adsorption is strongly affected by the carbon pore structure, with the micropore volume deciding the adsorption amount and larger pores increasing the adsorption rate. The chlorobenzene adsorption is little affected by the chemical properties of activated carbon as the O/C ratio detected by XPS. The effect of SO2 on the chlorobenzene adsorption was investigated, with the results showing the SO2 seriously restricts the individual chlorobenzene adsorption and this effect becomes smaller in the presence of O2. The adsorption products were analyzed by TPD-MS and the initial decomposition temperatures are 380 K for chlorobenzene and 500 K for SO2, showing that SO2 is much more stable adsorbed than chlorobenzene. The changes of the carbon functional groups that the CO2 desorption peak emerges at 700 K and decreases at 1000 K with the chlorobenzene adsorption, were observed by TPD-MS, indicating that the lactone and quinone groups on the carbon are likely to combine with the chlorobenzene and form weakly chemisorbed chlorobenzene.

ZnO–Al2O3–La2O3 layered double hydroxides as catalysts precursors for the esterification of oleic acid fatty grass at low temperature

ZnO–Al2O3–La2O3 layered double hydroxides were synthesized by the coprecipitation method and calcined at 400°C in order to obtain the corresponding mixed oxides. XRD patterns showed lamellar type materials in fresh solids (dried) while for calcined samples the characteristic mixed oxides and zincite peaks were observed. After calcination, high specific surface areas (180–130m2/g) were obtained in the mixed oxides. TPD-CO2 denotes a shift in the CO2 desorption peak to highest temperature in the samples containing La3+. In the oleic acid esterification with methanol, under soft reaction conditions (100°C and 6atm), ZnAlLa mixed oxides reached conversions of 75% to the ester after 15min and higher than 88% after 1h of reaction.

Oxidation of CO by NO on planar and faceted Ir(210)

Oxidation of CO by pre-adsorbed NO has been studied on planar Ir(210) and nanofaceted Ir(210) with average facet sizes of 5 nm and 14 nm by temperature programmed desorption (TPD). Both surfaces favor oxidation of CO to CO(2), which is accompanied by simultaneous reduction of NO with high selectivity to N(2). At low NO pre-coverage, the temperature (T(i)) for the onset of CO(2) desorption as well as CO(2) desorption peak temperature (T(p)) decreases with increasing CO exposure, and NO dissociation is affected by co-adsorbed CO. At high NO pre-coverage, T(i) and T(p) are independent of CO exposure, and co-adsorbed CO has no influence on dissociation of NO. Moreover, at low NO pre-coverage, planar Ir(210) is more active than faceted Ir(210) for oxidation of CO to CO(2): T(i) and T(p) are much lower on planar Ir(210) than that on faceted Ir(210). In addition, faceted Ir(210) with an average facet size of 5 nm is more active for oxidation of CO to CO(2) than faceted Ir(210) with an average facet size of 14 nm, i.e., oxidation of CO by pre-adsorbed NO on faceted Ir(210) exhibits size effects on the nanometer scale. In comparison, at low O pre-coverage planar Ir(210) is more active than faceted Ir(210) for oxidation of CO to CO(2) but no evidence has been found for size effects in oxidation of CO by pre-adsorbed oxygen on faceted Ir(210) for average facet sizes of 5 nm and 14 nm. The TPD data indicate the same reaction pathway for CO(2) formation from CO + NO and CO + O reactions on planar Ir(210). The adsorption sites of CO, NO, O, CO + O, and CO + NO on Ir are characterized by density functional theory.

Adsorption kinetics and dynamics of CO on silica supported Au nanoclusters—Utilizing physical vapor deposition and electron beam lithography

The adsorption kinetics and dynamics of CO on silica supported Au clusters have been studied by thermal desorption spectroscopy (TDS) and molecular beam scattering. Physical vapor deposition (PVD) and electron beam lithography (EBL) have been used to fabricate the samples. According to our prior study (Kadossov et al., in press [49]), a maximum in the initial adsorption probability, S 0, occurs for 3 nm Au clusters. Therefore, in the present study, we have focused on this cluster size for PVD samples. In addition, 12 nm EBL Au clusters have been studied. This is presently one of the smallest achievable cluster sizes using EBL for macroscopic samples. Auger electron spectroscopy and scanning electron microscopy have been used to further characterize the samples. TDS revealed well-known features for PVD samples; i.e., two peaks assigned to CO adsorption on different defect sites were present. Interestingly, TDS data of EBL samples were dominated solely by one CO desorption peak. The initial adsorption probability of CO, S 0, decreased as a function of impact energy, E i, and adsorption temperature, T s, for both samples, which is consistent with non-activated molecular adsorption. The coverage dependence of the adsorption probability and S 0 are discussed in the framework of the capture zone model.

Carbon monoxide adsorption on the metastable fcc-Co/Cu(1 0 0) surface

The adsorption properties of CO on the epitaxial five-monolayer Co/Cu(1 0 0) system, where the Co overlayer has stabilized in the metastable fcc-phase, are reported. This system is known to exhibit metallic quantum well (MQW) states at energies 1 eV or greater above the Fermi level, which may influence CO adsorption. The CO/fcc-Co/Cu(1 0 0) system was explored with low energy electron diffraction (LEED), inverse photoemission (IPE), reflection-absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD). Upon CO adsorption, a new feature is observed in IPE at 4.4 eV above E F and is interpreted as the CO 2 π ∗ level. When adsorbed at room temperature, TPD exhibits a CO desorption peak at ∼355 K, while low temperature adsorption reveals additional binding configurations with TPD features at ∼220 K and ∼265 K. These TPD peak temperatures are correlated with different C–O stretch vibrational frequencies observed in the IR spectra. The adsorption properties of this surface are compared to those of the surfaces of single crystal hcp-Co, as well as other metastable thin film systems.

Chemisorption of CO on Au/TiOx/Pt(111) Model Catalysts with Different Stoichiometry and Defectivity

Au/TiO(x)/Pt(111) model catalysts were prepared starting from well characterized TiO(x)/Pt(111) ultrathin films, according to an established procedure consisting in a reactive evaporation of Ti, subsequent thermal treatment in O2 or in UHV, and final deposition of submonolayer quantities of Au. Temperature Programmed Desorption measurements were performed to compare the interaction of CO in the case of two reduced TiO(x)/Pt(111) substrates (indicated as w-TiO(x) and w'-TiO(x), being the former characterized by an ordered array of defects that can act as template for the deposition of a stable array of Au nanoparticles), with the case of a stoichiometric rect'-TiO2/Pt(111) substrate. It was found that in all cases CO is molecularly adsorbed and two different desorption peaks are detected: one at approximately 140 K corresponding to CO desorption from less active adsorption sites (terraces) of the Au nanoparticles and one at approximately 200 K corresponding to CO desorption from Au nanoparticles step sites. After annealing at 770 K, the high temperature CO desorption peak is still present in the case of the defective reduced w-TiO(x) phase, supporting the good templating and stabilizing effect of such phase. On the rect'-TiO2 stoichiometric phase, the CO uptake decreases after annealing but only to a minor extent.

Enhancement effect of water on oxidation reactions over commercial three-way catalyst

The light-off temperature of the oxidations of CO and C3H6 over a commercial three-way catalyst (TWC) was shifted to a lower temperature by the addition of water to the feed stream. From FTIR analysis, the formation of carboxylate and carbonate by a reaction between adsorbed CO and OH on the catalyst surface was observed during the course of the reactions. In addition, the CO desorption peak of CO-TPD shifted to a lower temperature by water, which may be directly indicative of the reduction of the adsorption strength of CO on the catalyst surface. Detailed reaction kinetic models have been developed in view of the concept of microkinetics to describe the effect of water, particularly on the oxidation activity over a commercial TWC.

A temperature programmed desorption investigation on the interaction of Ba0.5Sr0.5Co0.8Fe0.2O3−δ perovskite oxides with CO2 in the absence and presence of H2O and O2

The adsorption of CO2 on Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) perovskite oxides in the absence and presence of O2 and H2O at various temperatures was investigated by temperature programmed desorption (TPD). XRD was used to characterize the phase of the samples before and after adsorption. No CO2 desorption peak was observed when CO2 was adsorbed on BSCF at room temperature. A CO2 desorption peak from the decomposition of surface Sr0.6Ba0.4CO3 appeared after CO2 was adsorbed at 400–700°C. The reactivity of CO2 with BSCF increased with increasing temperature, and the resulted carbonate became more stable. When CO2 and O2 were co-adsorbed, the CO2 desorption peak shifted to lower temperature and the peak area decreased compared with when only CO2 was adsorbed, which was due to the competitive adsorption of CO2 and O2. The adsorption of CO2 on BSCF was promoted in the presence of H2O. A CO2 desorption peak ranging from ca. 250 to 500°C, assigned to the decomposition of the bicarbonate, was observed when H2O was added. The amount of CO2 adsorbed on Ba1−xSrxCo0.8Fe0.2O3−δ increased when the barium doping level increased from 0.3 to 1.

Tetrahedral Aluminum Ions on High Purity Sub-Micron .ALPHA.-Alumina Powder Surfaces

The surface of six different grades of commercial sub-micron high purity α-Al2O3 powders produced by two different processes, in-situ chemical vapor deposition (“A” powders), and hydrolysis of aluminum alkoxide (“B” powders) methods, were evaluated by temperature programmed desorption mass spectrometry (TPDMS) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Desorption of CO2 molecules was detected for all the powders, but the quantity was greater for the “B” powders than the “A” powders. The maximum of the CO2 desorption peak was in the range of 230-270°C for all powders. The desorbed CO2 peak was considered to evolve from adsorbed CO2 molecules forming hydrogen carbonyl groups through interaction with the AlIV-OH groups on the α-Al2O3 surfaces. The DRIFT spectra of the powders heated at 700°C under vacuum confirmed a larger population of AlIV-OH groups on the surface of the “B” powders. The present study clearly demonstrates the presence and quality of the AlIV on the surface of α-Al2O3 powders and the effect of the type of manufacturing process on their proportion.

CO Oxidation, NO Decomposition, and NO + CO Reduction over Perovskite-like Oxides La2CuO4 and La2-xSrxCuO4: An MS−TPD Study

Perovskite-like oxides La2CuO4 and LaSrCuO4, prepared by the citrate combustion method, were studied and used as catalysts for CO oxidation, NO decomposition, and NO + CO reduction. The adsorption and desorption behaviors of the gases on catalyst surfaces were well characterized by mass spectrometric−temperature programmed desorption (MS−TPD) measurements. A large NO desorption peak was observed on LaSrCuO4, but only a small one was observed on La2CuO4, suggesting that the Sr addition or the existence of an oxygen vacancy is the necessary condition for NO adsorption. No CO desorption peak was observed on either LaSrCuO4 or La2CuO4, suggesting that the adsorbed CO was totally oxidized to CO2 before elution. The appearance of N2 desorption peak in the NO MS−TPD spectra of LaSrCuO4 (T = 400 °C) indicated that NO dissociation occurs easily and the crucial step of NO decomposition is O2 desorption. The activity of LaSrCuO4 was low for NO decomposition (34.3%, T = 850 °C), but high for CO oxidation (99%, T = 300 °C) and for NO + CO reduction (98.7%, T = 600 °C), suggesting that the desorption of oxygen, or the regeneration of active site, is difficult in NO decomposition but easy in CO oxidation and NO + CO reduction, due to the existence of CO. Finally, the mechanism of NO + CO reduction was investigated according to the ratio XNO/XCO; the variation of the ratio XNO/XCO suggests that the NO + CO reduction has different mechanisms over different catalysts and at different temperatures.

市販高純度α‐アルミナ粉末表面上における水和物，吸着物層の分析

The surface of six different grades of commercial sub-micron high purity alpha alumina powders produced by two different processes, in-situ chemical vapor deposition (AA powders) and hydrolysis of aluminum alkoxide (AKP powders) methods are evaluated by Temperature Programmed Desorption Mass Spectrometry (TPDMS). All AA powders show almost the same quantities of H2O and CO2 desorbed molecules. On the other hand, the different grades of AKP powders show different quantities of H2O and CO2 desorbed molecules. The AKP-3000 powder quantity of desorbed H2O molecules is similar to that of the AA powders. However, the AKP-3000 powder quantity of desorbed CO2 molecules is about seven times larger than that of the AA powders. The maximum of the CO2 desorption peak is the range 230-270°C for all powders. The desorbed CO2 peak is considered to evolve from the adsorbed CO2 molecules forming hydrogen carbonyl groups by interaction with AlIV-OH groups on the α-alumina surfaces. The amount of hydrogen carbonyl groups on surface of the AKP powders is larger than for the AA powders, indicating that on AKP powder surfaces the amount of AlIV-OH groups is larger. These results show that on the surface of commercial high purity alpha alumina powder a complex hydrated layer exists by interaction between surface hydroxyl groups and CO2 adsorbed molecules, unlike commonly accepted stable alpha alumina structure.

Structural and chemical properties of ac(2×2)−Ti/Pt(100)second-layer alloy: A probe of strong ligand effects on surface Pt atoms

We investigated the structure and chemisorption properties of a Ti/Pt(100) surface alloy using Auger electron spectroscopy (AES), low energy electron diffraction (LEED), scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), x-ray photoelectron diffraction (XPD), low-energy alkali ion scattering (ALISS), and temperature programed desorption (TPD). Samples were prepared by evaporating Ti onto a clean hex-Pt(100) reconstructed surface at 300 K. After annealing the sample to 800 K, a $c(2\ifmmode\times\else\texttimes\fi{}2)$ LEED pattern was observed that sharpened as the temperature was increased to 920 K. Further annealing to 1000 K caused this $(2\ifmmode\times\else\texttimes\fi{}2)$ LEED pattern to become diffuse because of the onset of disorder in the surface layers resulting from Ti diffusion into the bulk. Using XPD and ALISS, we determined that this LEED pattern is due to an ordered alloy structure that has Ti atoms present in the second layer of a $c(2\ifmmode\times\else\texttimes\fi{}2)\ensuremath{-}\mathrm{T}\mathrm{i}/\mathrm{P}\mathrm{t}(100)$ surface alloy, and not in the topmost layer. Thus, the surface layer of this alloy is pure Pt. XPS showed that the Ti $2p$ peak from the surface alloy is shifted by 1.4 eV to higher binding energy than that of a thick Ti film, and the Pt $4f$ peak is shifted by 0.1 eV higher from that of the clean hex-Pt(100) reconstructed surface, consistent with the formation of strong intermetallic bonds upon alloying. The chemisorption properties of the surface alloy were probed using CO and ${\mathrm{H}}_{2}$ adsorption. CO adsorbed reversibly on the alloy, desorbing in TPD in a broad peak with a maximum at 376 K. This is lower by 132 K from the CO desorption peak from a clean Pt(100) surface. Thermal desorption of ${\mathrm{H}}_{2}$ showed a similar peak shift to lower temperature, and much less hydrogen (20%) adsorbed on the $c(2\ifmmode\times\else\texttimes\fi{}2)\ensuremath{-}\mathrm{T}\mathrm{i}/\mathrm{P}\mathrm{t}(100)$ alloy than on Pt(100). These results show that second layer Ti atoms exert a strong ``ligand'' or electronic effect on Pt atoms at the surface. Thus, the $c(2\ifmmode\times\else\texttimes\fi{}2)\ensuremath{-}\mathrm{T}\mathrm{i}/\mathrm{P}\mathrm{t}(100)$ surface alloy represents an interesting model system for studying ligand effects on the chemistry of a bimetallic alloy surface.

Temperature-programmed desorption of methanol and oxidation of methanol on Pt–Sn/Al 2O 3 catalysts

The temperature-programmed desorption (TPD) of methanol, a widely used solvent contributing to industrial VOC emissions, was studied on two different series of Pt–Sn/Al 2O 3 catalysts that were prepared by coimpregnation and sequential impregnation with Sn first. TPD results showed that methanol decomposed primarily to hydrogen and carbon monoxide. Hydrogen desorbed first, followed by carbon monoxide at higher temperatures. Adding Sn to Pt shifted the desorption peaks of both H 2 and CO to higher temperatures. For the coimpregnated Pt–Sn catalysts, the temperature difference between the H 2 and CO desorption peak maxima increased systematically with increasing Sn content; for the sequentially impregnated catalysts, the temperature difference remained nearly constant. An exception was the catalyst containing 5 wt.% Sn, where the peaks shifted upward by 150 °C. In both catalyst series, the temperature difference between the hydrogen and the carbon monoxide desorption peak maxima increased with increasing Sn content. This study has demonstrated that the adsorption/desorption behavior of methanol on platinum is strongly modified by the presence of tin. The oxidation of methanol over the monometallic Pt and bimetallic Pt–Sn on alumina support was studied in the temperature range 35–300 °C and initial concentrations of methanol in the range 500–1200 ppm and excess oxygen (21% O 2). The experimental results showed that the monometallic Pt catalyst were much more active than the bimetallic catalysts. The coimpregnated catalysts were more active than the sequentially impregnated catalysts. CO 2 and methyl formate (CH 3OCHO) were the only carbon-containing products of methanol oxidation. Methyl formate was the principle product at low temperatures, while CO 2 was the principle product at high temperatures. The reaction order of methanol oxidation was 1.15±0.05. The apparent activation energy of the monometallic platinum catalyst was 14.4 kJ/mol. For the coimpregnated catalysts, addition of tin increased the apparent activation energy while in the sequentially impregnated Pt–Sn the apparent activation energy remained essentially constant over the range 0.6–1.5 wt.% Sn, then shifted to 66.8 kJ/mol for 5 wt.% Sn.

The interaction of ultrathin nickel films with yttria-stabilized zirconia ( [formula omitted

Increasing amounts of nickel, from 0.2 up to 5 equivalent monolayers, were vapour-deposited on a clean YSZ (1 0 0) surface at room temperature and then annealed at 600 K for up to 19 h. The nickel deposit was gradually oxidized at a rate depending on the deposited amount. For submonolayer coverages, it was completely converted into NiO within a few hours, whereas for multilayer quantities only a small fraction was oxidized. Carbon monoxide TPD experiments showed an intensity attenuation of the CO desorption peak, down to extinction for complete oxidation of the nickel surface, accompanied by a decrease in the TPD peak maximum temperature. This unexpected nickel oxidation upon prolonged heating was attributed to an interfacial interaction of the deposited Ni with mobile oxygen species present on YSZ at elevated temperature, due to its ionic conductor character.