Adsorption Of Styrene Research Articles

Cooperative Chiral Adsorption of Styrene Molecules on the Si(001)-c(2 × 4) Surface: First-Principles Investigation of Reaction Mechanisms

Detailed reaction mechanisms for the chiral adsorption of styrene molecules on the reconstructed Si(001)-c(2 × 4) surface are investigated using first principles calculations based on density functional theory. The most stable configuration corresponds to the R chirality on the so-called “on-top” site, where the molecule is adsorbed on a single silicon dimer. The on-top styrene adsorption does not encounter reaction barriers, but there is a small energy barrier following an intermediate metastable state associated with the styrene adsorption on bridge sites between two Si dimers (the “single-end-bridge” site, or SEB). Our calculations show that when the first styrene molecule is adsorbed in the SEB configuration, there is no energy barrier associated with the adsorption of the second molecule. This cooperative effect leads to the experimentally observed “paired end-bridge” configuration.

Separation of Styrene and Ethylbenzene on Metal−Organic Frameworks: Analogous Structures with Different Adsorption Mechanisms

The metal-organic frameworks MIL-47 (V(IV)O{O(2)C-C(6)H(4)-CO(2)}) and MIL-53(Al) (Al(III)(OH)·{O(2)C-C(6)H(4)-CO(2)}) are capable of separating ethylbenzene and styrene. Both materials adsorb up to 20-24 wt % of both compounds. Despite the fact that they have identical building schemes, the reason for preferential adsorption of styrene compared to ethylbenzene is very different for the two frameworks. For MIL-47, diffraction experiments reveal that styrene is packed inside the pores in a unique, pairwise fashion, resulting in separation factors as high as 4 in favor of styrene. These separation factors are independent of the total amount of adsorbate offered. This is due to co-adsorption of ethylbenzene in the space left available between the packed styrene pairs. The separation is of a non-enthalpic nature. On MIL-53, the origin of the preferential adsorption of styrene is related to differences in enthalpy of adsorption, which are based on different degrees of framework relaxation. The proposed adsorption mechanisms are in line with the influence of temperature on the separation factors derived from pulse chromatography: separation factors are independent of temperature for MIL-47 but vary with temperature for MIL-53. Finally, MIL-53 is also capable of removing typical impurities like o-xylene or toluene from styrene-ethylbenzene mixtures.

Molecular modeling studies of interactions between styrene–butadiene latex and sodium polyacrylate polymer surface

The interaction between two important paper coating ingredients, sodium polyacrylate polymer dispersing agent and styrene–butadiene latex binder, was studied using classical force field and quantum chemical methods. The objective was to understand the adsorption of styrene–butadiene latex on the sodium polyacrylate polymer model surfaces at 300 K using molecular dynamics simulations. A quantum mechanical ab initio Hartree–Fock method was also used to obtain detailed information about the above interactions. In addition, the effect of moisture was investigated. Calculations showed that the conformation and orientation of styrene–butadiene latex, the number of carboxylate groups in the latex, and the characteristics of different sodium polyacrylate polymer surfaces affected the interplay between the styrene–butadiene latex and the surfaces. The force field applied and water molecules also had an effect on the adsorption process. Electrostatic interactions were observed to be important in the systems containing styrene–butadiene latex and the model surfaces. In addition, Hartree–Fock calculations suggested that the aromatic ring of styrene–butadiene latex was able to coordinate to the carboxylate group of sodium polyacrylate polymer via the sodium atom.

First Principle Study on the Adsorption of Styrene on Si(100)2 × 1

The chemisorption of styrene on Si(100)2 × 1 is modeled by density functional theory using a slab model, providing the adsorption structures, intermediates, adsorption energies, and reaction barrie...

Chiral Adsorption Structures of Styrene on Ge(001): A First-Principles Study

We investigated the chiral adsorption structures of styrene on the Ge(001) surface by first-principles density functional calculations within the generalized gradient approximation. Our calculated energy profile for the reaction pathways shows that styrene adsorbs not only on top of a single dimer but also across the ends of two adjacent dimers in the same dimer row. In the latter adsorption configuration (termed the configuration), we predict the existence of two different structures where two unsaturated Ge atoms within the two adjacent dimers are differently displaced up and down or down and up. Additional styrene adsorption on these two different end-bridge structures proceeds to formation of the cis- and trans-paired end-bridge (PEB) structures. The relative stability of the two different end-bridge structures provides an explanation for a recent scanning tunneling microscopy observation that the populations of the cis-PEB and trans-PEB structures are different from each other.

Extraordinary Atomic Mobility of Au{111} at 80 Kelvin: Effect of Styrene Adsorption

We describe how the presence of styrene, a weakly adsorbed molecule, dramatically restructures the Au{111} surface at temperatures as low as 80 K. The restructuring manifests itself both in mobility of step-edge atoms, as well as changes in the position of the herringbone reconstruction over time. These effects are explained in terms of the preferential adsorption sites of styrene allowing it to assist in atom detachment from step edges, as well as lowering of the energetic barrier for movement of the herringbone reconstruction. This work has important consequences for studies in which Au is used as a support for or as an electrical contact to molecules.

Surface nanopatterning through styrene adsorption on Si(100)

We present an ab initio study of the electronic properties of styrene molecules adsorbed on the dimerized Si(100) surface, ranging from the single molecule to the full monolayer (ML). The adsorption mechanism primarily involves the vinyl group via a $[2+2]$ cycloaddition process that leads to the formation of covalent $\mathrm{Si}\mathrm{C}$ bonds and a local surface derelaxation, while it leaves the phenyl group almost unperturbed. The investigation of the functionalized surface as a function of the coverage (e.g., 0.5--1 ML) and of the substrate reconstruction reveals two major effects. The first results from Si dimer-vinyl interaction and concerns the controlled variation of the energy band gap of the interface. The second is associated to phenyl-phenyl interactions, which give rise to a regular pattern of electronic wires at surface, stemming from the $\ensuremath{\pi}\text{\ensuremath{-}}\ensuremath{\pi}$ coupling. These findings suggest a rationale for tailoring the nanopatterning of the surface in a controlled way.

Chiral Attachment of Styrene Mediated by Surface Dimers on Ge(100)

We have investigated the chiral adsorption configurations of styrene on Ge(100) using scanning tunneling microscopy at 300 K. The chemisorbed styrene on a single Ge dimer reduces the symmetry of the molecule, which produces a chiral center, and leads to the (S) or (R) chiral on-top configuration. We have found that the dimeric adsorption of styrene induced by the Ge surface dimer structure forms the enantiomeric and diastereomeric paired end-bridge configurations. We determine the absolute chirality of adsorbed styrene on Ge(100) and demonstrate a novel method for the achiral molecule to produce dimeric enantiomers and diastereomers attached to the semiconductor surface.

Adsorption of styrene on Ag(1 1 1)

Temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) have been used to investigate the adsorption, desorption and molecular conformation of styrene adsorbed on Ag(1 1 1) at 100 K. Styrene adsorbs and desorbs molecularly. Three peaks are resolvable in TPD—257 K (α 1), 187 K (α 2) and 167 K (α 3)—depending on the coverage. RAIRS indicates that the α 1 and α 2 adsorption states are in contact with silver surface. For α 1, the aromatic ring lies parallel to the Ag(1 1 1) surface and for α 2, nearly parallel. Although the α 3 state in TPD is ascribed to the bulk-like multilayer desorption, RAIRS indicates that, as-dosed, this coverage region is separable into two components—a second layer and subsequent layers. In the second layer, the principle axis of styrene lies between 5° and 8° away from the surface normal, making a T-like configuration with the first layer. For subsequent layers, the RAIRS data are consistent with a mixture of orientations.

FTIR and Reaction Studies of Styrene and Toluene over Silica–Zirconia-Supported Heteropoly Acid Catalysts

The interactions of styrene and toluene with a sol–gel-prepared SiO 2–ZrO 2 mixed oxide and with two supported heteropolytungstic acid samples have been studied by FTIR. The results of the IR study of styrene adsorption and toluene/styrene coadsorption indicate that the oligomerization of styrene, which proceeds through a carbenium intermediate, takes place over the support and the supported catalysts. The alkylation of toluene by styrene, which also proceeds via the formation of a carbenium ion from styrene, is only detected for the supported heteropoly acid catalysts. These spectroscopic observations, which are in good agreement with the product distribution obtained for reaction experiments conducted in the liquid phase, suggest that the reaction of the adsorbed, activated styrene with toluene or with a second molecule of styrene depends on the relative coverage of the two competing reagents. The incorporation of the HPA to the silica–zirconia support increased the density and strength of the acid sites favoring the retention of a higher fraction of toluene and consequently the production of higher yields of alkylated products. Differences between the two supported HPA catalysts could be ascribed to the nature of the supported heteropoly acid species and the modification of the acid characteristics due to the interaction with the silica–zirconia support.

Adsorption of styrene on micron-sized, monodisperse, cross-linked polymer particles in a snowman-shaped state by utilizing the dynamic swelling method

Polystyrene/styrene–divinylbenzene copolymer composite particles with different cross-linking densities were produced by seeded copolymerization for (styrene/divinylbenzene)-swollen polystyrene particles prepared by utilizing the dynamic swelling method (DSM) which was proposed by the authors in 1991. Using the cross-linked, composite particles as seeds, styrene-adsorbed (swollen) composite particles having snowman shapes were prepared by the DSM. With a decrease in the cross-linking density in the composite particles, the volume of the composite particle which was embedded in a spherical styrene phase in the snowman-shaped, styrene-adsorbed particle increased and the contact angle of the styrene phase on the composite particle decreased. In the DSM process, the absorption stage of styrene in the composite particles and the adsorption stage thereon were clearly observed. This suggests that the cross-linking density of the composite particles greatly affects the morphology of the snowman-shaped particles.

Preliminary study on the TS-1 deactivation during styrene oxidation with H 2O 2

The deactivation of the TS-1 zeolite during styrene oxidation with H 2O 2 has been investigated by a series of kinetic experiments and further characterisation of the spent catalysts. A decline of the TS-1 activity with time has been observed, especially during the first hours of reaction. TG and TPD–MS analyses of the spent catalysts show that the main products occluded within the zeolite pores are styrene, phenylacetaldehyde and benzaldehyde. The presence of styrene oligomeric compounds has also been detected, although it is postulated they are formed mainly in the solution outside the zeolite pores. Diffusional hindrances due to the high degree of occupancy of the TS-1 pores, as well as, a strong adsorption of styrene, phenylacetaldehyde and benzaldehyde on the Ti sites are proposed as the main reasons for the TS-1 deactivation. These phenomena are enhanced at lower reaction temperatures, which cause a faster initial deactivation. Likewise, longer reaction times favour preferential chemisorption of aldehydes versus styrene.

The Electronic Structure and Orientation of Styrene Adsorbed on FeO(111) and Fe3O4(111)A Spectroscopic Investigation

The adsorption of styrene on (111)-oriented thin layers of FeO and Fe3O4 epitaxially grown on Pt(111) single-crystal surfaces has been investigated using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). High-resolution gas-phase measurements were recorded, and precise ab initio electronic structure calculations were performed in order to aid the assignment of the NEXAFS resonances. Whereas on Fe3O4 (magnetite), styrene forms a chemisorbed monolayer that is stable up to room temperature, on FeO (wustite), a significantly more weakly bound (physisorbed) species is observed that is stable only for temperatures below 200 K. A planar adsorption geometry is observed in the case of styrene on Fe3O4 in the low-coverage regime (ϑ < 0.5 ML); for higher coverages on the same surface and on FeO, the average tilt angle between the phenyl plane and the surface plane amounts to about 45°.

Ultra-selective epoxidation of styrene on pure Cu{111} and the effects of Cs promotion

Styrene undergoes efficient epoxidation to styrene epoxide on the Cu{111} surface. At the optimum condition (Θo = 0.03 ML) ∼20% of the styrene is converted to the epoxide with almost 100% selectivity. Comparison with Ag{111} shows that the epoxidation activity and selectivity of Cu greatly exceed those of Ag. Incipient oxidation of the Cu{111} surface does not suppress the adsorption of styrene, but the oxidised metal is catalytically inert. Submonolayer amounts of Cs enhance styrene uptake and increase conversion to the epoxide without adversely affecting epoxidation selectivity. This effect is due to inhibition of Cu oxidation by Cs. Our findings are discussed in the light of current understanding of Ag‐catalysed alkene epoxidation.

Bonding and reactivity of styrene on Cu(110): heterogeneous alkene epoxidation without the use of silver

Styrene adsorption on oxygenated Cu(110) has been studied by temperature programmed reaction, fast XPS and NEXAFS. When the molecule is adsorbed on Cu metal sites in the presence of co-adsorbed oxygen, it undergoes efficient epoxidation to styrene epoxide. This is the first demonstration of alkene epoxidation on the surface of a clean metal, other than silver. However, styrene adsorbed on the ‘oxidic’ p(2×1)-O surface is catalytically inert. The NEXAFS data indicate that the reactant molecule is oriented approximately parallel to the surface plane on both the clean and oxidic p(2×1)-O surfaces, so that the very different reactivity is unlikely to be due to geometrical effects. The implications of these findings for the mechanism of heterogeneous alkene epoxidation are discussed.

Selective Hydrogenation of Phenylacetylene on Pumice-Supported Palladium Catalysts

The liquid phase, selective hydrogenation of phenylacetylene on pumice-supported palladium catalysts has been studied for a large range of metallic dispersions (14% ≤ D x ≤ to 62%). The kinetics were analyzed by a five-parameter mathematical model. The mechanism was determined by the contribution of three basic routes involving only surface species in the rate-determining steps. The hydrogenation of phenylacetylene to styrene is "structure insensitive." The disappearance rate constant of styrene produced from phenylacetylene is slightly lower than that of phenylacetylene and does not change in the case of the direct hydrogenation of styrene on the same Pd/pumice catalyst. However, Q 3 (the ratio of adsorption constants K Eb/ K St, where Eb is ethylbenzene and St is styrene), which is typical of a zero order reaction ( Q 3 → 0) in the case of the direct hydrogenation, is practically constant ( Q 3 ≅ 2) in the case of hydrogenation of styrene produced from phenylacetylene. This is explained by the formation, in the latter case, of polymeric species or other species which are difficult to hydrogenate and by the consequent occupation of active sites so that the adsorption of styrene is inhibited. These species are also thought to be responsible for a flattening effect in the catalytic activity. Activity and selectivity data are critically analyzed and compared with those reported for other supported palladium catalysts. Since Pd/pumice catalysts also show high activity and selectivity at high metal dispersions, they could be of interest for industrial applications.

A theoretical model for respirator cartridge service life for binary systems: application to acetone/styrene mixtures.

A theoretical model, developed previously to assess respirator cartridge service life, was applied to various acetone/styrene binary assault systems. Experimental data, collected for several binary mixtures differing only with respect to the concentration of each of the two compounds, were interpreted in terms of the model. Styrene concentrations varied from 228 to 1578 ppm; the range of acetone concentrations was 92-985 ppm. The specific influence of the compound assault concentrations on respirator cartridge service life was carefully characterized, as break-through curves were generated for both acetone and styrene for each of several different binary systems. Specifically, experimental data for each system were used to determine values of the following theoretical parameters: k'1, tau 1, k'2, tau 2, and Am. These parameters were employed with the theory to generate complete theoretical breakthrough curves and to determine the time-dependence of the weight of each compound adsorbed by the respirator cartridge carbon bed. An interesting phenomenon observed for the acetone/styrene systems was the displacement (from the carbon) of previously adsorbed acetone molecules by styrene molecules. Acetone breakthrough was observed first in each of the systems studied. Following the onset of this breakthrough, the acetone breakthrough concentration was enhanced by the displacement of acetone from the carbon bed by the adsorption of styrene. The theoretical model accurately predicts both this enhancement and the associated breakthrough characteristics of styrene. In addition, the theory is capable of predicting the ratio of the number of displaced acetone molecules to the corresponding number of displacing styrene molecules. For these studies, this ratio ranged from 0.3 to 0.7. The service life of respirator cartridges exposed to acetone/styrene mixtures depends on the assault concentration of each compound and is significantly influenced (shortened) by the displacement phenomenon.

Use of a surface-acoustic-wave sensor to characterize the reaction of styrene vapor with a square-planar organoplatinum complex

A coated surface-acoustic-wave (SAW) sensor is used to probe the reaction of styrene vapor with the square-planar platinum-ethylene pi-complex, trans-PtCl2(ethylene)(pyridine). A dual-SAW delay-line oscillator configuration is employed: one oscillator is coated with a solvent-cast film of the solid platinum-ethylene complex dispersed in a poly(isobutylene) matrix, and the second oscillator is coated only with polymer. Absorbed styrene vapor displaces ethylene to form the stable styrene-substituted complex, trans-PtCl2(styrene)(pyridine), causing a decrease in the oscillator frequency from the increase of mass on the surface of the sensor. For short-term exposures, there is a linear relationship between the logarithm of the rate of frequency change and the logarithm of the styrene vapor concentration, consistent with a power-law kinetic model for the heterogeneous trapping reaction. Deviation from this relationship above 300 ppm at 25 degrees C is attributed to the onset of multilayer adsorption of styrene at the surface of the trapping reagent. The sensor response exhibits an Arrhenius temperature dependence permitting estimation of the thermal activation energy for the olefin-substitution reaction. Calculated detection limits of 3 and 0.6 ppm of styrene vapor are achieved for operation at 25 and 40 degrees C, respectively.

Alkylaromatic carbene ions on H-TsVK zeolites

The adsorption of styrene (298 K), triphenylcarbinol (298 K), and of propylene with toluene (473 K) on H-TsVK zeolite leads to the formation of alkylaromatic carbocations which are stable up to 473–573 K and are characterized by bands in DRS at 320–330 and 400–440 nm and in IR by vC=C of the aromatic ring in the regions 1500 and 1610–1620 cm−1. In the adsorption of benzene, toluene, isopropylbenzene, and 1,3-dimethylnaphthalene at 298 K, only weakly bonded surface complexes are formed.

Cyclic Adsorption of Styrene and of Plasticizer on BPL Carbon

The deactivation of BPL Carbon by styrene and by the plasticizer dimethyl phosphonate, which does not polymerize, was studied in cyclic adsorption-desorption. Breakthrough time for styrene at 323K over a 1 g bed was 225 min in the first cycle at 6900 mg/m3 inlet and 20 mg/m3 breakthrough concentrations. Breakthrough time fell to 140 min in the second cycle, to 101 min by the 40 th cycle. Desorption in vacuo was no more effective than atmospheric airflow at 423K. Similar results were had on plasticizer. Cyclic adsorber systems should be considered for inlet concentrations of these heavy materials above 1000 mg/m3. A non-cyclic adsorber is more economically effective below that concentration.