Adsorption of CO and O2 on W2C(0001)

CO, O(2), and H(2) adsorption on a clean W(2)C(0001)√13×√13 R ± 13.9° reconstructed surface at room temperature (RT) were investigated using high-resolution electron energy loss spectroscopy (HREELS). The W(2)C(0001) adsorbs CO molecularly and adsorbs O(2) dissociatively, but does not adsorb H(2) at RT. In the CO adsorption system, two C-O stretching (antisymmetric CCO stretching) modes were found at 242.3 meV (1954 cm(-1)) and at 253.0 meV (2041 cm(-1)). The low-frequency site is occupied at first with subsequent conversion to the high-frequency site with increasing coverage. Additionally, a small peak was apparent at 104.5 meV (843 cm(-1)), and a middle peak at 50-51 meV (400-410 cm(-1)), which are assignable to a symmetric stretching mode and a hindered translational mode, respectively, of a CCO (ketenylidene) species. These observations are consistent with the CO adsorption model on top of the surface carbon. For oxygen adsorption, two adsorption states were found at 65.2-68.1 meV (526-549 cm(-1)) and 73.6 meV (594 cm(-1)): typical frequencies to oxygen adsorption on metal surfaces. Results suggest that atomic oxygen adsorption occurred on a threefold hollow site of the second W layer.     

基于密度泛函理论计算的CO2在SrTiO3(100)表面的吸附

通过密度泛函理论的第一性原理,模拟了CO2分子在SrTiO3(100)表面TiO2-和SrO-位点上的吸附行为,获得了CO2在几种不同吸附模型下的结构参数及表面吸附能,进而研究了吸附机理和结构稳定性.计算结果表明,当CO2的C原子吸附在SrTiO3(100)表面SrO-及TiO2-位点的氧原子上时,吸附结构较稳定,尤其是C、O原子共吸附在TiO2-位点时最稳定,而其余吸附模型则不稳定.对吸附稳定模型的Mulliken布局数及态密度分析显示:CO2分子在SrTiO3(100)表面吸附主要是由于SrTiO3(100)面的电子跃迁至CO2分子,CO2分子得到电子形成弯曲的CO2-阴离子结构,并伴随着C-O键的伸长,从而达到吸附活化CO2的目的.     

Saturated adsorption of CO and coadsorption of CO and O2 on AuN- (N=2-7) clusters

A first-principles quantum chemistry method, based on the Kohn-Sham density-functional theory, is used to investigate the adsorption of CO and O2 on small gas-phase gold cluster anions. The saturated adsorption of carbon monoxide on gold cluster anions AuN- (N=2-7) is discussed. The adsorption ability of CO reduces with the increase of the number of CO molecules bound to gold cluster anions, resulting in saturated adsorption at a certain amount of absorbed CO molecules, which is determined by geometric and electronic properties of gold clusters cooperatively. The effect of CO preadsorption on the electronic properties of gold cluster anions depends on the cluster size and the number of adsorbed CO, and the vertical detachment energies of CO-adsorbed gold cluster anions show a few changes with respect to corresponding pure gold cluster anions. The results indicate that the impinging adsorption of CO molecules may lead to geometry structure transformation on Au3- cluster. For the coadsorption of CO and O2 on Au2-, Au3- isomers, Au4-, and Au6-, we describe the cooperative adsorption between CO and O2, and find that the O2 dissociation is difficult on gas-phase gold cluster anions even with the preadsorption of CO.     

CO2 capture by multivalent amino-functionalized calix[4]arenes: self-assembly, absorption, and QCM detection studies

The reactivity of CO(2) with polyamino substrates based on calix[4]arenes and on a difunctional, noncyclic model has been studied. All the compounds react with CO(2) in chloroform to form ammonium carbamate salts. However, the number, topology, and conformational features of the amino-functionalized arms present on the multivalent scaffold have a remarkable influence on the reaction efficiency and on the product composition. Tetraaminocalix[4]arenes 1-3 rapidly and efficiently react with 2 equiv of CO(2), yielding highly stable hydrogen-bonded dimers formed by the self-assembly of two bis-ammonium bis-carbamate intramolecular salts. 1,3-Diaminocalix[4]arene 4 absorbs 1 mol of CO(2), affording less stable zwitterionic ammonium carbamates. Gemini compound 5 reacts with CO(2) in a 1:1 stoichiometry, forming hydrogen-bonded dimers of ammonium carbamate derivatives of moderate stability. For upper rim 1,3-diaminocalix[4]arene 6, in addition to the labile intramolecular salt, the presence of a self-assembled polymer was also detected. These systems were fully characterized in solution by (1)H and (13)C NMR spectroscopy, whereas the corresponding gas-solid reactions were further investigated by QCM measurements. Interestingly, the high affinity and reversibility of CO(2) uptake shown by 1,3-diamino calix[4]arene 4 enabled us to attain a promising QCM device for carbon dioxide sensing.     

Adsorption and thermoresponsive behavior of poly(N-isopropylacrylamide-co-N,N'-cystaminebisacrylamide) thin films on gold

We describe the synthesis of thermoresponsive polymers made from N-isopropylacrylamide and varying amounts of a thiol-containing co-monomer, N,N'-cystaminebisacrylamide (P(NIPAm-co-CBAm)). Infrared spectroscopy revealed a backbone similar to that seen with pure PNIPAm. UV-vis spectroscopy showed that P(NIPAm-co-CBAm) undergoes a thermoresponsive phase transition around 32 degrees C in aqueous solution. The presence of the thiol groups enabled the polymer to adsorb onto gold surfaces. Following adsorption onto a gold surface, X-ray photoelectron spectroscopy showed a carbon/gold atomic ratio of 0.93 for a sample without CBAm and a ratio of 1.61 for a P(NIPAm-co-CBAm) sample with 0.20% CBAm. Quartz crystal microbalance (QCM) analysis showed increases in the mass of polymer adsorbed when the CBAm content in the polymer increased. The thermoresponsive behavior of the thin films on gold was investigated with contact angle and dissipative QCM analysis. Contact angles were measured for polymer films at both 25 and 60 degrees C. The largest temperature-induced alteration in the contact angle was seen with the 1.00% CBAm sample. Similarly, QCM-D results showed a significantly greater change in frequency and dissipation following a temperature change when CBAm was present than in pure NIPAm polymers.     

Kinetics of CO2 nanobubble formation at the solid/water interface

The kinetics of adsorption of CO(2) molecules dissolved in aqueous solution onto a hydrophobised silica surface were investigated using a quartz crystal microbalance (QCM). The results of this investigation were compared with those obtained earlier from tapping mode atomic force microscopy (TMAFM) under the same experimental conditions (J. Yang, J. Duan, D. Fornasiero, J. Ralston, J. Phys. Chem. B., 2003, 107(25), 6139-6147; ref. 1). The QCM results represent the early stage of CO(2) gas adsorption (<20 min), before CO(2) gas bubbles adsorbed on the surface can be directly observed by TMAFM. The QCM results confirmed our observation from TMAFM imaging: that CO(2) gas molecules present in solution only adsorb on silica when its surface is hydrophobic. More importantly, the results showed that gas adsorption/bubble growth undergoes two consecutive kinetic processes: a slow and a fast adsorption process.     

CO and methanol adsorption on (2 × 1)Pt(110) and ion‐eroded Pt(111) model catalysts

Methanol adsorption on ion‐sputtered Pt(111) surface exhibiting high concentration of vacancy islands and on (2 × 1)Pt(110) single crystal were investigated by means of photoelectron spectroscopy (PES) and thermal desorption spectroscopy. The measurements showed that methanol adsorbed at low temperature on sputtered Pt(111) and on (2 × 1)Pt(110) surfaces decomposed upon heating. The PES data of methanol adsorption were compared to the data of CO adsorbed on the same Pt single crystal surfaces. In the case of the sputtered Pt(111) surface, the dehydrogenation of H_xCO intermediates is followed by the CO bond breakage. On the (2 × 1)Pt(110) surface, carbon monoxide, as product of methanol decomposition, desorbed molecularly without appearance of any traces of atomic carbon. By comparing both platinum surfaces we conclude that methanol decomposition occurs at higher temperature on sputtered Pt(111) than on (2 × 1)Pt(110). Copyright © 2010 John Wiley & Sons, Ltd.     

Coadsorption of CO and O(2) on selected gold clusters: evidence for efficient room-temperature CO(2) generation

Spurred by the recent demonstrations of the size- and support-dependent reactivity of supported gold clusters, here we present results on the coadsorption of CO and O(2) on selected anionic gold clusters, Au(N)(-), in the gas phase. O(2) adsorbs in a binary (0,1) fashion as a one-electron acceptor on the Au(N)()(-) clusters, with even-N clusters showing varying reactivity toward O(2) adsorption, while odd-N clusters show no evidence of reactivity. CO shows a highly size-dependent reactivity for Au(N)(-) sizes from N = 4 to 19, but no adsorption on the gold dimer or trimer. When the gold clusters are exposed to both reactants, either simultaneously or sequentially, interesting effects have been observed. While the same rules pertaining to individual O(2) or CO adsorption continue to apply, the preadsorption of one reactant on a cluster may lead to the increased reactivity of the cluster to the other reactant. Thus, the adsorbates are not competing for bonding sites (competitive coadsorption), but, instead, aid in the adsorption of one another (cooperative coadsorption). New peaks also arise in the mass spectrum of Au(6)(-) under CO and O(2) coadsorption conditions, which can be attributed to the loss of a CO(2) molecule (or molecules). By studying the relative amount of reaction, and relating it to the reaction time, it is found that the gas-phase Au(6) anion is capable of oxidizing CO at a rate 100 times that reported for commercial or model gold catalysts.     

A versatile QCM matrix system for online and high-throughput bio-sensing

A 3 x 3 quartz crystal microbalance (QCM) sensor matrix, fabricated on an A-T cut quartz crystal, has the ability to detect online a variety of labeled DNA samples in a parallel and comparative fashion. The QCM matrix was equipped with a single oscillator circuit, which activated only one QCM at any given time, and was controlled by programmable time-shared electronic relays. The gold electrode had a diameter of 0.8 mm and operated at a fundamental resonating frequency of 40 MHz; the dimensions of the matrix were 1.2 cm x 1.2 cm. The sensitivity of an individual QCM was in the pictogram regime. Selected QCMs were coated with either streptavidin or the anti-DIG antibody; the specificity of their detections was monitored using various concentrations of samples of biotin- and DIG-labeled DNA. The basic design of the QCM matrix is readily expandable, without any conceivable difficulties, in both geometry and circuitry.     

Microcalorimetric investigation of high-surface-area mesoporous titania samples for CO2 adsorption

Mesoporous titania powders were synthesized using the triblock copolymer F127 (PEO(106)PPO(70)PEO(106)) as a surfactant template. Two different procedures (ammonia and/or low-temperature treatment at 393 K) were successfully applied to stabilize the mesoporous structure, resulting in significantly increased surface areas and pore volumes with respect to those of the untreated titania powders. Three of these samples were chosen for further investigation by adsorption microcalorimetry. These samples are characterized by high surface areas (varying between 340 and 141 m (2) g (-1)) and a varying degree of crystallization (anatase phase). The samples were compared to nanosized anatase particles treated to 873 K. The adsorption microcalorimetry was carried out using nitrogen and carbon dioxide at 77 and 303 K, respectively, to gain complementary information about the surfaces. Nitrogen at 77 K showed, for the three samples, adsorption enthalpies at low coverage of similar values, approximately -19 to -22 kJ mol (-1), indicating that the probe gas interacts with similar energetic surface sites. Two distinct energetic regions are observed, the first of which increases with increasing pretreatment temperature, which can be related to increased sample crystallinity. The adsorption of carbon dioxide at 303 K showed high adsorption enthalpies (up to approximately 65-80 kJ mol (-1)), highlighting strong interactions of the carbon dioxide with the titania surface at low pressures. Finally, the CO(2) adsorption properties of the titania samples (adsorbed amount and enthalpies of adsorption) are compared with those of other nanosized adsorbents. This comparison shows the potentiality of mesoporous titania powders for the adsorption of CO(2).     

Protein adsorption on surfaces: dynamic contact-angle (DCA) and quartz-crystal microbalance (QCM) measurements

Adsorption of the protein bovine serum albumin (BSA) on gold has been tested at various concentrations in aqueous solution by dynamic contact-angle analysis (DCA) and quartz-crystal microbalance (QCM) measurements. With the Wilhelmy plate technique advancing and receding contact angles and the corresponding hysteresis were measured and correlated with the hydrophilicity and the homogeneity of the surface. With electrical admittance measurements of a gold-coated piezoelectrical quartz crystal, layer mass and viscoelastic contributions to the resonator's frequency shift during adsorption could be separated. A correlation was found between the adsorbed mass and the homogeneity and hydrophilicity of the adsorbed film.     

Preparation and characterization of Cr(CO)(4)dpp (chromium tetracarbonyl 2,3-bis(2'-pyridyl)pyrazine) adsorbed on silver nanoparticles

A transition metal carbonyl species, Cr(CO)(4)dpp, has been successfully attached to bare silver nanoparticles prepared by laser ablation of a metal foil in ethanol. Transmission electron microscopy (TEM) images have shown that at least a portion of the silver nanoparticles have been capped by the chromium species, and ligand shells corresponding to Cr(CO)(4)dpp multilayer adsorption onto the silver nanoparticles of 30-50 nm diameter have been observed. The detection of the strongest Raman-active nu(CO) band of Cr(CO)(4)dpp at 2004 cm(-1) revealed that the species has been adsorbed without decomposition. The time-of-flight secondary ion mass spectrometry (TOF-SIMS) signals recorded of the chromium-capped silver nanoparticles were also consistent with the nondecomposition adsorption process. Density functional calculations have been used to reproduce the Raman spectrum using Ag(7)(+) as a model surface. A large binding energy of about 122 kJ/mol has also been computed between silver and nitrogen atoms thus lending support to Cr(CO)(4)dpp being chemisorbed onto the silver surface.     

X-ray emission spectroscopy of (2 square root of 3 x 2 square root of 3)R30 degrees CO/Ru(0001): comparison to c(2x2)CO/Ni(100) and c(2x2)CO/Cu(100)

The atom specific electronic structure of (2 square root of 3 x 2 square root of 3)R30 degrees CO on hcp Ru(0001) has been determined with resonantly excited x-ray emission spectroscopy. We find that the general features of the local adsorbate electronic structure are similar to the situation of CO adsorbed on the fcc metals Ni(100) and Cu(100). The interpretation of the surface chemical bond of (2 square root of 3 x 2 square root of 3)R30 degrees CO/Ru(0001) based on the direct application of the local, allylic model from on-top adsorption on the fcc(100) surfaces Ni(100) and Cu(100) explains many aspects of the surface chemical bond. However, also nonlocal contributions like adsorbate-adsorbate interaction and the deviation from upright on-top adsorption on the Ru(0001) surface influence observables like the heat of adsorption and the Me-CO bond strength.     

Communication: CO oxidation by silver and gold cluster cations: identification of different active oxygen species

The oxidation of carbon monoxide with nitrous oxide on mass-selected Au(3)(+) and Ag(3)(+) clusters has been investigated under multicollision conditions in an octopole ion trap experiment. The comparative study reveals that for both gold and silver cations carbon dioxide is formed on the clusters. However, whereas in the case of Au(3)(+) the cluster itself acts as reactive species that facilitates the formation of CO(2) from N(2)O and CO, for silver the oxidized clusters Ag(3)O(x)(+) (n=1-3) are identified as active in the CO oxidation reaction. Thus, in the case of the silver cluster cations N(2)O is dissociated and one oxygen atom is suggested to directly react with CO, whereas a second kind of oxygen strongly bound to silver is acting as a substrate for the reaction.     

Density functional theory study of CO catalytic oxidation on Co_2B_2/TiO_2（110） surface

Titanium dioxide with CoB amorphous alloys nanoparticles deposited on the surface is known to exhibit higher catalytic activity than the CoB amorphous. A study of the structure of such system is necessary to understand this effect. A quantum chemical study of Co2B2 on the TiO2 (110) surface was studied using periodic slab model within the framework of density functional theory (DFT). The results of geometry optimization indicated that the most stable model of adsorption was Co2B2 cluster adsorbed on the hollow site of TiO2.The adsorption energy calculated for Co2B2 on the hollow site was 439.3 kJ/mol.The adsorption of CO and O2 was further studied and the results indicated that CO and O2 are preferred to adsorb on the Co2 site. Co-adsorption of CO and O2 shows that Co2B2/TiO2 is a good catalyst for the oxidation of CO to carbon dioxide in the presence of oxygen.     

Molecular interactions and CO2-philicity in supercritical CO2. A high-pressure NMR and molecular modeling study of a perfluorinated polymer in scCO2

The carbon and fluorine chemical shifts of mixtures of carbon dioxide and Krytox, a carboxylic acid end-capped perfluorinated polyether used as stabilizer for the dispersion polymerization of methyl methacrylate, have been studied using high-pressure, high-resolution nuclear magnetic resonance. 13C and 19F spectra were measured in the density region between 0.54 and 0.73 g.cm(-3) at 334 K for different solutions of Krytox in scCO2 (0.22, 1.13 and 1.72 w/w %). An in-house developed high-pressure apparatus with the capability to change in situ the sample composition was used for this purpose using a 10 mm polyether ketone NMR tube. The nature of CO2-Krytox interaction was assessed both by comparing the CO2 deltaC variation of neat CO2 with that of mixtures with increasing surfactant composition and by the analysis of Krytox 19F corrected chemical shifts in terms of medium magnetic susceptibility. Ab initio calculations, at the second-order M?ller-Plesset level of theory to include the effects of electron correlation, were performed to access and compare the nature of the interactions between CO2 and perfluorinated and nonfluorinated analogue model molecules. Both experimental 13C and 19F HP-NMR results and molecular modeling studies support a F...CO2 site-specific Lewis acid-Lewis base interaction model. A positive entropic variation for the formation of CO2-fluorinated solute complex is advanced as an explanation for the higher solubility of perfluorinated molecules when compared to the nonfluorinated analogues.     

Modeling of the adsorption and desorption of CO2 on Cu/ZrO2 and ZrO2 catalysts

The interaction between carbon dioxide and two zirconia catalysts-a Cu/ZrO2 catalyst containing 34% copper and a pure ZrO2 catalyst-was studied by pulse adsorption and temperature-programmed desorption methods. Kinetic modeling by nonlinear regression was applied to acquire information on the adsorption and desorption of CO2 relevant in the synthesis of methanol from carbon dioxide. A model that included three types of adsorption sites described well the experimental data for both Cu/ZrO2 and ZrO2. The model assumed first-order kinetics and a Freundlich-type logarithmic dependence of adsorption enthalpy on surface coverage. The parameters of the model were well identified and were in the physically meaningful range. The results indicate that, at 30 degrees C, on both catalysts, carbon dioxide adsorbs reversibly on one type of site and irreversibly on two other types of sites.     

Ab initio study of the reaction of propionyl (C2H5CO) radical with oxygen (O2)

The reaction of propionyl radical with oxygen has been studied using the full coupled cluster theory with the complete basis set. This is the first time to gain a conclusive insight into the reaction mechanism and kinetics for this important reaction in detail. The reaction takes place via a chemical activation mechanism. The barrierless association of propionyl with oxygen produces the propionylperoxy radical, which decomposes to form the hydroxyl radical and the three-center alpha-lactone predominantly or the four-center beta-propiolactone. The oxidation of propionyl radical to carbon monoxide or carbon dioxide is not straightforward rather via the secondary decomposition of alpha-lactone and beta-propiolactone. Kinetically, the overall rate constant is almost pressure independent and it approaches the high-pressure limit around tens of torr of helium. At temperatures below 600 K, the rate constant shows negative temperature dependence. The experimental yields of the hydroxyl radical can be well reproduced, with the average energy transferred per collision -DeltaE=20-25 cm(-1) at 213 and 295 K (helium bath gas). At low pressures, together with the hydroxy radical, alpha-lactone is the major product, while beta-propiolactone only accounts for about one-fifth of alpha-lactone. At the high-pressure limit, the production of the propionylperoxy radical is dominant together with a fraction of the isomers. The infrared spectroscopy or the mass spectroscopy techniques are suggested to be employed in the future experimental study of the C2H5CO+O2 reaction.     

Electrooxidation of CO on Ru（0001） and RuO2（ 100） Electrode Surfaces

The electrooxidation of CO on Ru(0001) and RuO2(100) electrode surfaces were characterized by cyclic voltammetry,AES and RHEED,The CO adlayer was first partially oxidized at 0.8 V, which is controlled by the attack of oxygen species toward the Ru(0001) surface. The remaining CO aldayer oxidation at 0.55 V is related to the combination of CO molecules with oxygen species already located on the surface,In contrast,successive peaks on RuO2(100) at 0.4 V and 0.72 V are observed ,which shows that CO molecules can directly react with two different lattice-oxygen on the surface to carbon dioxide.     

Immobilization of RNase S-Peptide on a single-stranded DNA-fixed gold surface and effective masking of its surface by an acridinyl poly(ethylene glycol)

Oligonucleotide-peptide conjugate was synthesized by coupling of RNase S-peptide to a 24-mer single-stranded DNA (ssDNA) oligonucleotide to be immobilized on its complementary ssDNA oligonucleotide-fixed gold surface of sensor chip or electrode. Immobilization of on the ssDNA-fixed gold surface through DNA duplex formation was confirmed by quartz crystal microbalance (QCM) and electrochemical measurements. After treating with a synthetic acridinyl poly(ethylene glycol) (APEG), specific interaction of S-protein with the S-peptide immobilized on the gold surface was demonstrated by QCM without nonspecific adsorption of unrelated proteins such as BSA and RNase A at the surfaces. This result suggested that the acridine parts of APEG could bind to the DNA duplex on the gold surface and the poly(ethylene glycol) parts were fastened on the surface to resist the adsorption of proteins. Thus, the combination of oligonucleotide-peptide conjugate, ssDNA-fixed chip and APEG with effective masking property provides a new tool for the analysis of specific peptide-protein interactions without disturbance by other unrelated proteins.