High resolution infrared spectroscopy of carbon dioxide clusters up to (CO2)13

Thirteen specific infrared bands in the 2350 cm(-1) region are assigned to carbon dioxide clusters, (CO(2))(N), with N = 6, 7, 9, 10, 11, 12 and 13. The spectra are observed in direct absorption using a tuneable infrared laser to probe a pulsed supersonic jet expansion of a dilute mixture of CO(2) in He carrier gas. Assignments are aided by cluster structure calculations made using two reliable CO(2) intermolecular potential functions. For (CO(2))(6), two highly symmetric isomers are observed, one with S(6) symmetry (probably the more stable form), and the other with S(4) symmetry. (CO(2))(13) is also symmetric (S(6)), but the remaining clusters are asymmetric tops with no symmetry elements. The observed rotational constants tend to be slightly (≈2%) smaller than those from the predicted structures. The bands have increasing vibrational blueshifts with increasing cluster size, similar to those predicted by the resonant dipole-dipole interaction model but significantly larger in magnitude.     

The electrochemical reduction of carbon dioxide (CO2) to methanol in the presence of pyridoxine (vitamin B6)

Experiments aimed at ameliorating carbon dioxide (CO₂) into methanol were explored using pyridoxine, a member of the vitamin B₆ family, to enhance the reduction process. At a platinum electrode, an aqueous solution (pH ≈ 5) of pyridoxine showed a quasi-reversible redox couple with the cathodic peak detected at ca. − 0.55 V vs. Ag/AgCl (3 M KCl) in the presence of CO₂ and argon. An increase in the corresponding cathodic peak current was observed following saturation of the solution with CO₂ using a Pt electrode, but with no detectable reduction current recorded at a glassy carbon electrode for the same system. Confirmation of methanol formation during the pyridoxine-assisted CO₂ reduction was conducted by using gas chromatography analysis of the electrolyzed solutions and faradic yields of ca. 5% were afforded. A combination of the results from the cyclic voltammetry and constant current chronopotentiometry experiments revealed an overpotential of ≤ 200 mV was required. The results indicate a potential utility of pyridoxine as an alternative reagent to the more toxic pyridine during the electrochemical reduction of CO₂.     

Spectroscopic identification of the mixed hydrogen and carbon dioxide clathrate hydrate

In this contribution, we first found the novel clathrate hydrate containing two gaseous guests of hydrogen and carbon dioxide by spectroscopic analysis. X-ray powder diffraction and NMR spectroscopy were used to identify structure and guest distribution of the mixed H2 + CO2 hydrate. X-ray diffraction result confirmed that the unit cell parameter was 11.8602 +/- 0.0010 A, and the formed hydrate was identified as structure I hydrate. 1H magic angle spinning (MAS) NMR and 13C cross-polarization (CP) NMR spectroscopy were used to examine the distribution of hydrogen and carbon dioxide molecules in the cages of structure I, respectively. These NMR spectra showed that carbon dioxide molecules occupied both small 512 cages and large 51262 cages, and hydrogen molecules only were occluded in small 512 cages of structure I. The new finding of the mixed hydrogen hydrate is expected to contribute toward the development of hydrogen production technology and, particularly, inclusion chemistry.     

Quartz crystal microbalance (QCM) in high-pressure carbon dioxide (CO2): experimental aspects of QCM theory and CO2 adsorption

The quartz crystal microbalance (QCM) technique has been developed into a powerful tool for the study of solid-fluid interfaces. This study focuses on the applications of QCM in high-pressure carbon dioxide (CO2) systems. Frequency responses of six QCM crystals with different electrode materials (silver or gold) and roughness values were determined in helium, nitrogen, and carbon dioxide at 35-40 degrees C and at elevated pressures up to 3200 psi. The goal is to experimentally examine the applicability of the traditional QCM theory in high-pressure systems and determine the adsorption of CO2 on the metal surfaces. A new QCM calculation approach was formulated to consider the surface roughness contribution to the frequency shift. It was found that the frequency-roughness correlation factor, Cr, in the new model was critical to the accurate calculation of mass changes on the crystal surface. Experiments and calculations demonstrated that the adsorption (or condensation) of gaseous and supercritical CO2 onto the silver and gold surfaces was as high as 3.6 microg cm(-2) at 40 degrees C when the CO2 densities are lower than 0.85 g cm(-3). The utilization of QCM crystals with different roughness in determining the adsorption of CO2 is also discussed.     

Geometry optimization of carbon dioxide clusters (CO2)n for 4 < or = n < or = 40

Geometry optimization of carbon dioxide clusters (CO2)n with the size of 4 < or = n < or = 40 is performed by a heuristic and unbiased method combined with geometrical perturbations. Comparison with the global minima reported in the literature shows that the present method reproduces the global minima for clusters with n = 6, 8, 13, 19, 28, 30, and 32 and yields new global minima for (CO2)23, (CO2)25, and (CO2)35. For the other clusters under investigation, global minima are first reported in this article. Structural features of CO2 clusters and efficiency of the optimization method are discussed.     

Spectroscopic characterization of N(2)O aggregates: from clusters to the particulate state

Collisional cooling is used to generate N(2)O particles with radii ranging from the subnanometer to the submicrometer region. The vibrational dynamics of the aggregates is studied by Fourier transform infrared spectroscopy. In the region of the stretching fundamentals and combination bands, the infrared spectra of the particles exhibit characteristic size-dependent features. For the very small particles, the results obtained from collisional cooling are compared for the first time with corresponding results from supersonic jet expansions. It turns out that with both methods very similar clusters are generated. A pronounced temperature dependence of a combination band maximum in the collisional cooling cell spectra is found. This correlation is exploited to estimate cluster temperatures in supersonic jet spectra.     

Density functional study of CO adsorption on Sc(n) (n=2-13) clusters

The adsorption properties of a single CO molecule on Sc(n) (n=2-13) clusters are studied by means of a density functional theory with the generalized gradient approximation. Two adsorption patterns are identified. Pattern a (n=3, 4, 6, 8, 11, and 12), CO binds to hollow site while Pattern b (n=5, 7, 9, 10, and 13), CO binds to bridge site accompanied by significantly lengthening of the Sc-Sc bond. The adsorption energy exhibits clear size-dependent variation and odd-even oscillation for n<10 and reach the peak at n=5, 7, and 9, implying their high chemical reactivity. Similar variations are noted in C-O bond length, vibrational frequency, and charge transferred between CO and the clusters. This can be understood in light of the adsorption pattern, the atomic motif, and the relative stability of the bare Sc clusters. Compared with the free Sc clusters, the magnetic nature remains upon adsorption except n=2, 4, 12, and 13. Particularly, the moments of n=13 reduce significantly from 19 to 5 micro(B), implying the adsorption plays an attenuation influence on the magnetism of the cluster.     

(μ-RS)(μ-XMgS)Fe2(CO)6亲核性能的研究:铁硫配合物(μ-RS)[μ-Cp(CO)2FeS]Fe2(CO)6

研究了(μ-RS)(μ-XMgS)Fe2(CO)6与π-环戊二烯二羰基碘化铁的反应.首次制得(μ-RS)[(μ-CpFe(CO)2S]Fe2(CO)6的一系列含有机铁硫桥的非对称配合物.它们的核磁氢谱表明每个络合物只是以一类构象体存在.它们的甲基络合物的单晶结构分析证实了这一结论.     

Coarse-grained potential models for structural prediction of carbon dioxide (CO2) in confined environments

In this paper, we propose coarse-grained single-site (CGSS), wall-CO(2), and CO(2)-CO(2) interaction potential models to study the structure of carbon dioxide under confinement. The CGSS potentials are used in an empirical potential based quasi-continuum theory, EQT, to compute the center-of-mass density and potential profiles of CO(2) confined inside different size graphite slit pores. Results obtained from EQT are compared with those obtained from all-atom molecular dynamics (AA-MD) simulations, and are found to be in good agreement with each other. Though these CGSS interaction potentials are primarily developed and parameterized for EQT, they are also used to perform coarse-grained molecular dynamics (CG-MD) simulations. The results obtained from CG-MD simulations are also found to be in reasonable agreement with AA-MD simulation results.     

Novel diethanolamine based deep eutectic mixtures for carbon dioxide (CO2) capture: synthesis and characterisation

In this work, diethanolamine was successfully used as a hydrogen bond donor to prepare three different deep eutectic solvents (DESs) using three quaternary ammonium salts at different molar ratios. Important physical properties of the prepared DESs including melting point, glass transition, crystallisation temperature, density, refractive index and viscosity were measured in temperature ranging from (298.15 to 358.15 K). Moreover, in order to explore the changes in chemical structures of the DESs, FTIR analysis was performed. The developed DESs have melting points lower than 293.15 K, and of significantly low density (close to water) and comparable viscosity. The effect of temperature and molar ratio on physical properties were also discussed. Empirical models were used to correlate the density, refractive index and viscosity data of the DESs as a function of temperature and molar ratio. A quantitative analysis, also called as ANOVA analysis, was conducted to investigate the significance of the experimental physical properties data. The new DESs prepared in this work have a potential to be used in numerous applications including CO₂ capture.     

Synthesis of nonanuclear heterometallic carbide clusters. Unexpected formation of the [Ru6(CO)16]2-[Pt2(CO)2(dppm)2]2+ ion pair on the way to [Ru6C(CO)16Pt3(dppm)2

A novel trimetallic cluster [Ru5CRh2Pt2(CO)16(dppm)2] was synthesized via coupling of two neutral clusters-[Ru5C(CO)15] and [Rh2Pt2(CO)6(dppm)2]. The structure of this mixed metal complex was established using X-ray crystallography and 31P NMR spectroscopy. It was found that the reaction between [Ru6C(CO)17] and [Pt2(CO)3(dppm)2] leads to spontaneous electron transfer between these polynuclear complexes and results in the formation of an unusually stable cluster "salt" {[Ru6(CO)16]2-[Pt2(CO)2(dppm)2]2+}, which was characterized by crystallographic and spectroscopic methods. Heating of the Ru6-Pt2 ion pair in an autoclave (145 degrees C, 15 atm N2) results in fusion of the metal frameworks to give a nonanuclear mixed metal [Ru6C(CO)16Pt3(dppm)2] cluster in a good yield. The latter complex was obtained earlier as a minor product of another thermal reaction and now has been additionally characterized by 31P NMR spectroscopy.     

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.     

Remarkable carbon dioxide catalytic capture (CDCC) leading to solid-form carbon material via a new CVD integrated process (CVD-IP): An alternative route for CO2 sequestration

Through our newly-developed “chemical vapor deposition integrated process (CVD-IP)” using carbon dioxide (CO₂) as the raw material and only carbon source introduced, CO₂ could be catalytically activated and converted to a new solid-form product, i.e., carbon nanotubes (CO₂-derived) at a quite high yield (the single-pass carbon yield in the solid-form carbon-product produced from CO₂ catalytic capture and conversion was more than 30% at a single-pass carbon-base). For comparison, when only pure carbon dioxide was introduced using the conventional CVD method without integrated process, no solid-form carbon-material product could be formed. In the addition of saturated steam at room temperature in the feed for CVD, there were much more end-opening carbon nano-tubes produced, at a slightly higher carbon yield. These inspiring works opened a remarkable and alternative new approach for carbon dioxide catalytic capture to solid-form product, comparing with that of CO₂ sequestration (CCS) or CO₂ mineralization (solidification), etc. As a result, there was much less body volume and almost no greenhouse effect for this solid-form carbon-material than those of primitive carbon dioxide.     

An ab initio investigation on (CO2)n and CO2(Ar)m clusters: geometries and IR spectra

An ab initio investigation on CO(2) homoclusters is done at MPWB1K6-31++G(2d) level of theory. Electrostatic guidelines are found to be useful for generating initial structures of (CO(2))(n) clusters. The ab initio minimum energy geometries of (CO(2))(n) with n=2-8 are T shaped, cyclic, trigonal pyramidal, tetragonal pyramidal, tetragonal bipyramidal, pentagonal bipyramidal, and pentagonal bipyramid with one CO(2) molecule attached to it. A test calculation on (CO(2))(20) cluster is also reported. The geometric parameters of the energetically most favored (CO(2))(n) clusters match quite well their experimental counterparts (wherever available) as well as those derived from molecular dynamics studies. The effect of clustering is quantified through the asymmetric C-O stretching frequency shift relative to the single CO(2) molecule. (CO(2))(n) clusters show an increasing blueshift from 1.8 to 9.6 cm(-1) on increasing number of CO(2) molecules from n=2 to 8. The energetics and geometries of CO(2)(Ar)(m) clusters have also been explored at the same level of theory. The geometries for m=1-6 show a predominant T type of the argon-CO(2) molecule interaction. Higher clusters with m=7-12 show that the argon atoms cluster around the oxygen atom after the saturation of the central carbon atom. The CO(2)(Ar)(m) clusters exhibit an increasing redshift in the C-O asymmetric stretch relative to CO(2) molecule of 0.7-5.6 cm(-1) with increasing number of argon atoms through m=1-8.     

Structure and dynamic properties of substituted carbonylhydride clusters H2RuOs3(CO)13 and H4Ru4(CO)12 containing functionalized phosphines

The derivatives of the H₂RuOs₃(CO)₁₃ and H₄Ru₄(CO)₁₂ carbonylhydride clusters containing functionalized (including chiral) phosphines were synthesized. The solid-state structure of H₂RuOs₃(CO)₁₂(Ph₂P(C₄H₃S)) was determined by X-ray diffraction analysis. The structures of other compounds in solution were determined using IR and ¹H and ³¹P NMR spectroscopy. A study of the temperature dependences of the ¹H NMR spectra of the phosphine-substituted tetrahedral clusters along with the analysis of literature data for their analogs showed that compounds of this type exist in solution as an equilibrium mixture of isomers, which differ in arrangement of the hydride ligands at the cluster skeleton. Interconversion of the isomeric forms is due to migration of the hydride ligands over the cluster skeleton. A general model for this dynamic process was proposed. The model is consistent with both our data and earlier results of other authors. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1294–1301, July, 2007.     

Comparative ab initio study of CO adsorption on Sc(n) and Sc(n)O (n = 2-13) clusters

Using a cluster model, we investigated the similarities and differences in chemical activity and the magnetic properties of Sc(n) clusters (n = 2-13) and their oxides, Sc(n)O, toward CO molecule adsorption via a spin-polarized density functional theory approach. The Sc(n) and Sc(n)O clusters have similar chemical activity at small sizes of n = 2-10, whereas remarkable differences are observed at large sizes of n = 11-13. More interestingly, different magnetic responses are found in the Sc(n) and Sc(n)O clusters with the presence of CO molecule: The magnetic moment is attenuated significantly for Sc(n) with n = 2, 4, 12, and 13, whereas for Sc(n)O, it is enhanced at n = 4 and 13 and is reduced for n = 7, 8, 10, and 11. In particular, the magnetic moment remarkably increases from 7 μ(B) of Sc(13)O to 13 μ(B) of Sc(13)OCO, whereas it reduces from 19 μ(B) of Sc(13) to 5 μ(B) of Sc(13)CO.     

Collision induced fragmentation of mass-selected (CO2) n + clusters

The collisional velocity dependence of the cross sections for fragmentation of mass-selected (CO₂) _n ⁺ (n+2...7) clusters in collisions with Ar atoms is presented. Interesting structure can be observed in the cross sections which indicate that the collision occurs between the Ar atom and one CO₂ molecule within the cluster. The results may be explained by assuming that the collision leads to either vibrational excitation of a loosely bound CO₂ monomer which then leaves the cluster or excitation of the entire cluster to a dissociative state.     

Formation and characterization of gaseous adducts of carbon dioxide to magnesium, (CO2)MgX- (X=OH, Cl, Br)

A good fix: the structure and chemical reactivity of a reduced form of CO(2) bonded to magnesium, XMg(η(2)-O(2)C)(-), is reported. Upon reaction with water it loses CO, while it adds CH(3) upon reaction with alkyl halides, thereby signifying nucleophilicity of the carbon atom in XMg(η(2)-O(2)C)(-) in S(N)2 reactions.     

Infrared spectra of CO2-doped hydrogen clusters, (H2)N-CO2

Clusters of para-H(2) and/or ortho-H(2) containing a single carbon dioxide molecule are studied by high resolution infrared spectroscopy in the 2300 cm(-1) region of the CO(2) ν(3) fundamental band. The (H(2))(N)-CO(2) clusters are formed in a pulsed supersonic jet expansion from a cooled nozzle and probed using a rapid scan tunable diode laser. Simple symmetric rotor type spectra are observed with little or no resolved K-structure, and prominent Q-branch features for ortho-H(2) but not para-H(2). Observed rotational constants and vibrational shifts are reported for ortho-H(2) up to N = 7 and para-H(2) up to N = 15, with the N > 7 assignments only made possible with the help of theoretical simulations. The para-H(2) cluster with N = 12 shows clear evidence for superfluid effects, in good agreement with theory. The presence of larger clusters with N > 15 is evident in the spectra, but specific assignments are not possible. Mixed para- + ortho-H(2) cluster transitions are well predicted by linear interpolation between corresponding pure cluster line positions.