Sensitive and selective chromogenic sensing of carbon monoxide via reversible axial CO coordination in binuclear rhodium complexes

The study of probes for CO sensing of a family of binuclear rhodium(II) compounds of general formula [Rh(2){(XC(6)H(3))P(XC(6)H(4))}(n)(O(2)CR)(4-n)]·L(2) containing one or two metalated phosphines (in a head-to-tail arrangement) and different axial ligands has been conducted. Chloroform solutions of these complexes underwent rapid color change, from purple to yellow, when air samples containing CO were bubbled through them. The binuclear rhodium complexes were also adsorbed on silica and used as colorimetric probes for "naked eye" CO detection in the gas phase. When the gray-purple colored silica solids containing the rhodium probes were exposed to air containing increasing concentrations of CO, two colors were observed, in agreement with the formation of two different products. The results are consistent with an axial coordination of the CO molecule in one axial position (pink-orange) or in both (yellow). The crystal structure of 3·(CO) ([Rh(2){(C(6)H(4))P(C(6)H(5))(2)}(2)(O(2)CCF(3))(2)]·CO) was solved by single X-ray diffraction techniques. In all cases, the binuclear rhodium complexes studied showed a high selective response to CO with a remarkable low detection limit. For instance, compound 5·(CH(3)CO(2)H)(2) ([Rh(2){(m-CH(3)C(6)H(3))P(m-CH(3)C(6)H(4))(2)}(2)(O(2)CCH(3))(2)]·(CH(3)CO(2)H)(2)) is capable of detection of CO to the "naked eye" at concentrations as low as 0.2 ppm in air. Furthermore, the binding of CO in these rhodium complexes was found to be fully reversible, and release studies of carbon monoxide via thermogravimetric measurements have also been carried out. The importance of the silica support for the maintenance of the CO-displaced L ligands in the vicinity of the probes in a noninnocent manner has been also proved.     

Chemical force microscopy investigation of phosphate adsorption on the surfaces of iron(III) oxyhydroxide particles

Phosphate-modified AFM tips were prepared by the deposition of self-assembled monolayers (SAMs) of bis(11-thioundecyl) phosphate on Au-coated silicon nitride cantilevers. The properties of the PO(2)H-terminated SAMs were investigated by studying the pH-dependent force interactions of the tips with phosphate- and carboxylic acid-terminated SAM control surfaces. The PO(2)H functional groups had a pK(a) of approximately 5.0. A chemical force microscopy (CFM) study was conducted on the interactions between the probes and the surfaces of hydrous ferric oxide particles prepared in our laboratory by hydrolytic precipitation from FeCl(3). The forces between PO(2)H probes and the hydrous ferric oxide surfaces were seen to exhibit a strong pH dependence, with maximum attractive forces occurring for pH values between 5 and 8. The effects of postprecipitation of the hydrous ferric oxide colloids with orthophosphate, H(2)PO(4)(-), dimethylphosphate, (CH(3)O)(2)PO(2)H (DMP), and tannic acid (TA) on the adhesive interactions between the PO(2)H tips and the solids were also investigated. Attenuated total reflectance infrared spectroscopy (ATR-IR) was used to verify the presence of surface-adsorbed species and zeta potentiometric measurements to determine surface charge on the colloids. We show that the method of chemical force titration using phosphate-terminated tips can differentiate between these various colloids and that it shows promise as a general method for studying this environmentally important class of compounds.     

Luminescence investigations of the adsorption properties of disperse Al2O3 surfaces by means of selective laser excitation

A new method for the determination of the adsorption activity of disperse materials by means of inorganic luminescent probes under selective laser excitation has been developed and tested for the investigation of the adsorption properties of disperse Al(2)O(3) surfaces. Water-uranyl complexes have been used as luminescent probes for these experiments, and the photoluminescence spectra of UO(2)(2+) molecular ions adsorbed on the disperse Al(2)O(3) surfaces were investigated. The luminescence properties of this adsorption system, as in the previously studied case of SiO(2), were determined by the type and structure of the adsorption complexes (AC) formed. Different ACs cause many (7 observed) "elementary" luminescence spectra. The water-uranyl-complex adsorption binding energies were obtained. The values of the binding energies and the electric field strength of the surface active centers support the validity of the water-uranyl model of AC and the electrostatic consideration used.     

Rh和Pt超薄层电极上的CO吸附行为(英文)

利用沉积在粗糙金电极上的过渡金属超薄层电极技术 ,我们获得了氢及一氧化碳在Rh和Pt表面上吸附的拉曼信号 ,并对两者之间的相互作用进行了分析 ..我们还进行了二氧化碳在这两种金属表面的还原行为的初步研究 ,以及对不同方式获得的一氧化碳吸附拉曼信号的特点进行了分析 .     

Fishing DNA targets in DNA solutions by using affinity microcontact printing

In this paper, we report the application of affinity microcontact printing (αCP) for "fishing" DNA targets in aqueous solutions and transferring them to solid surfaces for detection purposes. Affinity stamps used in this experiment were made of poly(dimethylsiloxane) (PDMS) with DNA probes covalently immobilized on their surface. When these stamps were immersed in DNA solutions, DNA targets with a perfect-match (PM) sequence to the probes can selectively hybridize to the stamp surfaces and then be transferred to solid surfaces. However, to distinguish PM DNA from single base-pair mismatch (1MM) DNA targets, 10 mM of NaCl must be added to the hybridization buffer. Under the optimized conditions, this αCP can lead to a surface density of PM which is 15 times higher than that of 1MM. The affinity stamp is also able to "fish" PM DNA targets from a mixture of PM/1MM DNA targets and transfer them to solid surfaces. Because DNA probes and targets are separated after printing, we also applied this technique for label-free detection of DNA targets by using liquid crystals.     

Carbon monoxide-assisted synthesis of single-crystalline Pd tetrapod nanocrystals through hydride formation

Carbon monoxide can adsorb specifically on Pd(111) to induce the formation of unique Pd nanostructures. In the copresence of CO and H(2), single-crystalline Pd tetrapod nanocrystals have now been successfully prepared. The Pd tetrapods are enclosed by (111) surfaces and are yielded through hydride formation. Density functional theory calculations revealed that the formation of PdH(x) in the presence of H(2) reduces the binding energy of CO on Pd and thus helps to decrease the CO coverage during the synthesis, which is essential to the formation of the PdH(x) tetrapod nanocrystals. In addition to tetrapod nanocrystals, tetrahedral nanocrystals were also produced in the copresence of CO and H(2) when the reaction temperature was ramped to further lower the CO coverage. Upon aging in air, the as-prepared PdH(x) nanocrystals exhibited a shape-dependent hydrogen releasing behavior. The conversion rate of PdH(x) tetrapod nanocrystals into metallic Pd was faster than that of tetrahedral nanocrystals.     

Vacuum ultraviolet (VUV) photodecomposition of urea isolated in cryogenic matrix: first detection of isourea

Vacuum ultraviolet (VUV) irradiation at wavelengths of lambda > 160 nm of urea-h4 (NH2CONH2) and urea-d4 (ND2COND2) has been monitored by Fourier transform infrared spectroscopy in argon and xenon matrixes. Several primary photoproducts, such as HNCO:NH3 (isocyanic acid:ammonia), CO:N2H4 (carbon monoxide:hydrazine) molecular complexes, and isourea (H2N(OH)C=NH), which is reported for the first time, were characterized. The assignment of complexes was achieved by co-depositing the pairs of respective species, whereas the isourea identification was based on the comparison between the experimental and theoretical (B3LYP) infrared spectra. Isourea is found in the argon matrix in its most stable (s-Z)-(E) configuration. It is an intermediate in the VUV decomposition process; its dehydration leads to the NH2CN:H2O complex. In the xenon matrix, the photochemistry of urea yields the HNCO:NH3 complex as a major product, whereas the CO:N2H4 complex is observed in trace amounts. The observed differences between the argon and xenon matrixes suggest the crossing between S1 and T1 potential surfaces of urea to be responsible for the formation of the HNCO:NH3 complex. A comparison is also performed with other carboxamides, such as formamide (HCONH2) or acetamide (CH3CONH2).     

γ-Alumina: The Essential and Unexpected Role of Water for the Structure, Stability, and Reactivity of "Defect" Sites

Combining experiments and DFT calculations, we show that tricoordinate Al(III) Lewis acid sites, which are present as metastable species exclusively on the major (110) termination of γ- and δ-Al(2)O(3) particles, correspond to the "defect" sites, which are held responsible for the unique properties of "activated" (thermally pretreated) alumina. These "defects" are, in fact, largely responsible for the adsorption of N(2) and the splitting of CH(4) and H(2). In contrast, five-coordinate Al surface sites of the minor (100) termination cannot account for the observed reactivity. The Al(III) sites, which are formed upon partial dehydroxylation of the surface (the optimal pretreatment temperature being 700 °C for all probes), can coordinate N(2) selectively. In combination with specific O atoms, they form extremely reactive Al,O Lewis acid-base pairs that trigger the low-temperature heterolytic splitting of CH(4) and H(2) to yield Al-CH(3) and Al-H species, respectively. H(2) is found overall more reactive than CH(4) because of its higher acidity, hence it also reacts on four-coordinate sites of the (110) termination. Water has the dual role of stabilizing the (110) termination and modifying (often increasing) both the Lewis acidity of the aluminum and the basicity of nearby oxygens, hence the high reactivity of partially dehyxdroxylated alumina surfaces. In addition, we demonstrate that the presence of water enhances the acidity of certain four-coordinate Al atoms, which leads to strong coordination of the CO molecule with a spectroscopic signature similar to that on Al(III) sites, thus showing the limits of this widely used probe for the acidity of oxides. Overall, the dual role of water translates into optimal water coverage, and this probably explains why in many catalyst preparations, optimal pretreatment temperatures are typically observed in the "activation" step of alumina.     

Hydrolytic stability of organic monolayers supported on TiO2 and ZrO2

The hydrolytic stability of C18 monolayers supported on TiO2 and ZrO2 was studied. Three types of monolayers were prepared from the following octadecyl modifiers: (1) octadecyldimethylchlorosilane (C18H37Si(CH3)2Cl); (2) octadecylsilane (C18H37SiH3); and (3) octadecylphosphonic acid (C18H37P(O)(OH)2). The hydrolysis of the surfaces prepared was studied under static conditions at 25 and 65 degrees C at pH 1-10. On the basis of the loss of grafted material, the stability of the monolayers fall in the following range: C18H37P(O)(OH)2 > or = C18H37SiH3 > C18H37Si(CH3)2Cl. At 25 degrees C, monolayers from C18H37P(O)(OH)2 showed only approximately 2-5% loss in grafting density after one week at pH 1-10. The high stability of these monolayers was explained because of the strong interactions of the phosphonic acids with the substrates. Monolayers from C18H37Si(CH3)2Cl showed poor hydrolytic stability at any pH, which was explained because of the low stability of Ti-O-Si and Zr-O-Si bonds. Unlike monofunctional silanes, trifunctional silane (C18H37SiH3) yielded surfaces that showed good hydrolytic stability. This suggests that the stability of the monolayers from trifunctional silanes is primarily due to "horizontal" bonding (Si-O-Si or Si-OH...HO-Si) rather than due to bondingwith the matrix (M-O-Si). At 65 degrees C, all C18 surfaces become more susceptible to hydrolysis; however, the trend observed for 25 degrees C remained unchanged. Low-temperature nitrogen adsorption was used to study the adsorption properties of the monolayers as a function of their grafting density. The energy of adsorption interactions showed a significant increase as the grafting density of the monolayers decreased. The order of the alkyl groups in the monolayers, as assessed from CH2 stretching, decreased as the grafting density of the monolayers decreased.     

The subtle effects of iron-containing metal surfaces on the reductive carbonylation of RuCl3

The use of iron-containing metal surfaces, Fe, Fe-Cr-alloy and stainless steel, for the synthesis of mixed metal Ru-Fe compounds has been studied. The studied process was reductive carbonylation of RuCl3 in the presence of a metal surface. Reactions were carried out in ethanol solutions under 10-50 bar carbon monoxide pressure at 125 degrees C using an autoclave. During the reaction the metal surface was oxidized, releasing iron into the solution and acting as a sacrificial source of iron. Under these conditions the corrosion of the metal surface was facile and produced a series of iron-containing species. In addition to the formation of most obvious iron(II) products, such as [Fe(H2O)6]2+ or [FeCl2(H2O)4] the use of the metal surface also provided a route to novel labile trinuclear [Ru2Cl2(mu-Cl)4(CO)6FeL2] (L = H2O, EtOH) complexes. The stability and reactivity of the [Ru2Cl2(mu-Cl)4(CO)6FeL2] complexes were further studied using computational DFT methods. Based on the computational results a reaction route has been suggested for the formation and decomposition of [Ru2Cl2(mu-Cl)4(CO)6FeL2].     

Competition between H and CO for Active Sites Governs Copper‐Mediated Electrosynthesis of Hydrocarbon Fuels

The dynamics of carbon monoxide on Cu surfaces was investigated during CO reduction, providing insight into the mechanism leading to the formation of hydrogen, methane, and ethylene, the three key products in the electrochemical reduction of CO₂. Reaction order experiments were conducted at low temperature in an ethanol medium affording high solubility and surface‐affinity for carbon monoxide. Surprisingly, the methane production rate is suppressed by increasing the pressure of CO, whereas ethylene production remains largely unaffected. The data show that CH₄ and H₂ production are linked through a common H intermediate and that methane is formed through reactions among adsorbed H and CO, which are in direct competition with each other for surface sites. The data exclude the participation of solution species in rate‐limiting steps, highlighting the importance of increasing surface recombination rates for efficient fuel synthesis.     

Effects of alloying on the chemistry of CO and H2S on Fe surfaces

Deleterious gases such as CO and H(2)S can cause degradation of steel by reacting with the metal surface. Here we consider whether alloying the steel surface might be able to inhibit these damaging surface reactions by raising the barriers to molecular dissociation. We employ first-principles density functional theory techniques to investigate the elementary reaction pathways and barriers for CO and H(2)S on FeAl and Fe(3)Si surfaces and compare them with pure Fe surfaces (as a model for steel). We find that H(2)S dissociates on iron surfaces much more easily than CO does. Although FeAl surfaces raise the barriers for H(2)S dissociation, they significantly lower the barriers for CO dissociation. On the other hand, Fe(3)Si surfaces raise the barriers for CO dissociation, but they are as vulnerable as Fe surfaces to H(2)S dissociation. Our findings suggest that alloying iron with Al or Si is unlikely to simultaneously increase its resistance to the initial stages of chemical degradation by CO and H(2)S.     

Transmission infrared spectroscopy of methyl- and ethyl-terminated silicon(111) surfaces

Transmission infrared spectroscopy (TIRS) has been used to investigate the surface-bound species formed in the two-step chlorination/alkylation reaction of crystalline (111)-oriented Si surfaces. Spectra were obtained after hydrogen termination, chlorine termination, and reaction of the Cl-Si(111) surface with CH(3)MgX or C(2)H(5)MgX (X = Cl, Br) to form methyl (CH(3))- or ethyl (C(2)H(5))-terminated Si(111) surfaces, respectively. Freshly etched H-terminated Si(111) surfaces that were subsequently chlorinated by immersion in a saturated solution of PCl(5) in chlorobenzene were characterized by complete loss of the Si-H stretching and bending modes at 2083 and 627 cm(-1)(,) respectively, and the appearance of Si-Cl modes at 583 and 528 cm(-1). TIRS of the CH(3)-terminated Si(111) surface exhibited a peak at 1257 cm(-1) polarized perpendicular to the surface assigned to the C-H symmetrical bending, or "umbrella" motion, of the methyl group. A peak observed at 757 cm(-1) polarized parallel to the surface was assigned to the C-H rocking motion. Alkyl C-H stretch modes on both the CH(3)- and C(2)H(5)-terminated surfaces were observed near 2900 cm(-1). The C(2)H(5)-terminated Si(111) surface additionally exhibited broad bands at 2068 and 2080 cm(-1), respectively, polarized perpendicular to the surface, as well as peaks at 620 and 627 cm(-1), respectively, polarized parallel to the surface. These modes were assigned to the Si-H stretching and bending motions, respectively, resulting from H-termination of surface atoms that did not form Si-C bonds during the ethylation reaction.     

Decomposition of CH2O by lanthanum: a theoretical study

This work aims to investigate the reaction mechanism of lanthanum atom with formaldehyde in the gas phase using density functional theory and coupled cluster calculations. The results indicate that the minimum energy pathway, similar to the reactions of its neighboring yttrium with formaldehyde, is the formation of the eta2-formaldehyde-metal complex followed by two C-H insertions which leads to metal dihydrides and carbon monoxide. The competing pathway producing a metal-carbonyl compound and hydrogen molecule favors a high-spin state and thus involves a spin conversion from doublet state to quartet state. The crossing region of the doublet and quartet potential energy surfaces (PES) has been estimated by a simple approach as proposed by Yoshizawa et al. Less favorable pathways leading to metal monoxide and carbene radical by C-O insertion as well as formyllanthanum by single C-H insertion are also studied. Compared with the CCSD(T) method, the BP86 method tends to overestimate the binding energies of the d-rich compounds, though the two methods qualitatively agree well on the reaction mechanism. Finally, the (n - 1)d1ns2 to (n - 1)d2ns1 promotion effect is proposed to account for the difference in the formation mechanism of the metal-carbonyl compounds LaCO and YCO, which may also extend to the reactions of formaldehyde with other "general" group III rare earth elements including Sc, Ce, Gd, and Lu.     

空间稳定的SERS标记金纳米棒探针用于免疫检测

报道了空间稳定的表面增强拉曼散射(SERS)标记的金纳米棒探针在免疫检测方面的应用.该探针是将拉曼活性分子4-巯基苯甲酸和生物亲和性高分子α-巯基-ω-羧基聚乙二醇共吸附于金纳米棒表面而制得.其中,聚乙二醇高分子链为探针提供保护作用和空间稳定,使之可以耐受较苛性的条件;其端位的羧基与抗体等靶向实体结合,从而赋予探针检测识别功能.当探针检测待测抗原时(通过固体基底上的捕获抗体、待测抗原和探针上的抗体之间的特异性结合,形成经典“三明治”夹心结构),探针上4-巯基苯甲酸的SERS信号就能示踪出这种识别.该探针对单组分抗原的检出浓度能低至1×10^-9mg·mL^-1.     

Theoretical study of the dynamics of AR collisions with C2H6 and C2F6 at hyperthermal energy

We present a classical-trajectory study of the dynamics of high-energy (5-12 eV) collisions between Ar atoms and the C2H6 and C2F6 molecules. We have constructed the potential-energy surfaces for these systems considering separately the Ar-molecule interactions (intermolecular potential) and the interactions within the molecule (intramolecular potential). The intermolecular surfaces consist of pairwise empirical potentials derived from high-accuracy ab initio calculations. The intramolecular potentials for C2H6 and C2F6 are described using specific-reaction-parameters semiempirical Hamiltonians and are calculated "on the fly", i.e., while the trajectories are evolving. Trajectory analysis shows that C2F6 absorbs more energy than C2H6 and is more susceptible to collision-induced dissociation (CID). C-C bond-breakage processes are more important than C-H or C-F bond breakage at the energies explored in this work. Analysis of the reaction mechanism for CID processes indicates that, although C-C breakage is mostly produced by side-on collisions, head-on collisions are more efficient in producing C-F or C-H dissociation. Our results suggest that high-energy collisions between closed-shell species of the natural low-Earth-orbit environment and spacecraft can contribute to the observed degradation of polymers that coat spacecraft surfaces.     

Inelastic scattering matrix elements for the nonadiabatic collision B(2P1/2)+H2(1Sigmag+,j)<-->B(2P3/2)+H2(1Sigmag+,j')

Inelastic scattering matrix elements for the nonadiabatic collision B(2P1/2)+H2(1Sigmag+,j)<-->B(2P3/2)+H2(1Sigmag+,j') are calculated using the time dependent channel packet method (CPM). The calculation employs 1 2A', 2 2A', and 1 2A" adiabatic electronic potential energy surfaces determined by numerical computation at the multireference configuration-interaction level [M. H. Alexander, J. Chem. Phys. 99, 6041 (1993)]. The 1 2A' and 2 2A', adiabatic electronic potential energy surfaces are transformed to yield diabatic electronic potential energy surfaces that, when combined with the total B+H2 rotational kinetic energy, yield a set of effective potential energy surfaces [M. H. Alexander et al., J. Chem. Phys. 103, 7956 (1995)]. Within the framework of the CPM, the number of effective potential energy surfaces used for the scattering matrix calculation is then determined by the size of the angular momentum basis used as a representation. Twenty basis vectors are employed for these calculations, and the corresponding effective potential energy surfaces are identified in the asymptotic limit by the H2 rotor quantum numbers j=0, 2, 4, 6 and B electronic states 2Pja, ja=1/2, 3/2. Scattering matrix elements are obtained from the Fourier transform of the correlation function between channel packets evolving in time on these effective potential energy surfaces. For these calculations the H2 bond length is constrained to a constant value of req=1.402 a.u. and state to state scattering matrix elements corresponding to a total angular momentum of J=1/2 are discussed for j=0<-->j'=0,2,4 and 2P1/2<-->2P1/2, 2P3/2 over a range of total energy between 0.0 and 0.01 a.u.     

Potential surfaces and dynamics of the O(3P)+H2O(X1A1)-->OH(X2pi)+OH(X2pi) reaction

We present global potential energy surfaces for the three lowest triplet states in O(3P)+H2O(X1A1) collisions and present results of classical dynamics calculations on the O(3P)+H2O(X1A1)-->OH(X2pi)+OH(X2pi) reaction using these surfaces. The surfaces are spline-based fits of approximately 20,000 fixed geometry ab initio calculations at the complete-active-space self-consistent field+second-order perturbation theory (CASSCF+MP2) level with a O(4s3p2d1f)/H(3s2p) one electron basis set. Computed rate constants compare well to measurements in the 1000-2500 K range using these surfaces. We also compute the total, rovibrationally resolved, and differential angular cross sections at fixed collision velocities from near threshold at approximately 4 km s(-1) (16.9 kcal mol(-1) collision energy) to 11 km s(-1) (122.5 kcal mol(-1) collision energy), and we compare these computed cross sections to available space-based and laboratory data. A major finding of the present work is that above approximately 40 kcal mol(-1) collision energy rovibrationally excited OH(X2pi) products are a significant and perhaps dominant contributor to the observed 1-5 micro spectral emission from O(3P)+H2O(X1A1) collisions. Another important result is that OH(X2pi) products are formed in two distinct rovibrational distributions. The "active" OH products are formed with the reagent O atom, and their rovibrational distributions are extremely hot. The remaining "spectator" OH is relatively rovibrationally cold. For the active OH, rotational energy is dominant at all collision velocities, but the opposite holds for the spectator OH. Summed over both OH products, below approximately 50 kcal mol(-1) collision energy, vibration dominates the OH internal energy, and above approximately 50 kcal mol(-1) rotation is greater than vibrational energy. As the collision energy increases, energy is diverted from vibration to mostly translational energy. We note that the present fitted surfaces can also be used to investigate direct collisional excitation of H2O(X1A1) by O(3P) and also OH(X2pi)+OH(X2pi) collisions.     

Hybrid thermochemical/biological processing

The conventional view of biorefineries is that lignocellulosic plant material will be fractionated into cellulose, hemicellulose, lignin, and terpenes before these components are biochemically converted into market products. Occasionally, these plants include a thermochemical step at the end of the process to convert recalcitrant plant components or mixed waste streams into heat to meet thermal energy demands elsewhere in the facility. However, another possibility for converting high-fiber plant materials is to start by thermochemically processing it into a uniform intermediate product that can be biologically converted into a bio-based product. This alternative route to bio-based products is known as hybrid thermochemical/biological processing. There are two distinct approaches to hybrid processing: (a) gasification followed by fermentation of the resulting gaseous mixture of carbon monoxide (CO), hydrogen (H(2)), and carbon dioxide (CO(2)) and (b) fast pyrolysis followed by hydrolysis and/or fermentation of the anhydrosugars found in the resulting bio-oil. This article explores this "cart before the horse" approach to biorefineries.     

Adsorption and co-adsorption of ethylene and carbon monoxide on silica-supported monodisperse Pt nanoparticles: volumetric adsorption and infrared spectroscopy studies

The adsorption of carbon monoxide and ethylene, and their sequential adsorption, was studied over a series of Pt/SBA-15 catalysts with monodisperse particle sizes ranging from 1.7 to 7.1 nm by diffuse-reflectance infrared spectroscopy and chemisorption. Gas adsorption was dependent on the Pt particle size, temperature, and sequence of gas exposure. Adsorption of CO at room temperature on Pt/SBA-15 gives rise to a spectroscopic feature assigned to the C-O stretch: nu(CO) = 2075 cm-1 (1.9 nm); 2079 cm-1 (2.9 nm); 2082 cm-1 (3.6 nm); and 2090 cm-1 (7.1 nm). The intensity of the signal decreased in a sigmoidal fashion with increasing temperature, thereby providing semiquantitative surface coverage information. Adsorption of ethylene on Pt/SBA-15 gave rise to spectroscopic features at approximately 1340, approximately 1420, and approximately 1500 cm-1 assigned to ethylidyne, di-sigma-bonded ethylene, and pi-bonded ethylene, respectively. The ratio of these surface species is highly dependent on the Pt particle size. At room temperature, Pt particles stabilize ethylidyne as well as di-sigma- and pi-bonded ethylene; however, ethylidyne predominated on the surfaces of larger particles. Ethylidyne was the only identifiable species at 403 K, with its formation being more facile on larger particles. Co-adsorption experiments reveal that the composition of the surface layer is dependent on the order of exposure to gases. Exposure of a C2H4-covered Pt surface to CO resulted in an approximately 50% decrease in chemisorbed CO compared to a fresh Pt surface. The nu(CO) appeared at 2050 cm-1 on Pt/SBA-15 pretreated with C2H4 at room temperature. The di-sigma-bonded and pi-bonded species are the most susceptible to displacement from the surface by CO. The formation of ethylidyne appeared to be less sensitive to the presence of adsorbed carbon monoxide, especially on larger particles. Upon exposure of C2H4 to a CO-covered Pt surface, little irreversible uptake occurred due to nearly 100% site blocking. These results demonstrate that carbon monoxide competes directly with ethylene for surface sites, which will have direct implications on the poisoning of the heterogeneously catalyzed conversion of hydrocarbons.