Diffuse-reflectance Fourier-transform Spectroscopy Research Articles

Revealing the gas sensitive stability of formate species during CO2 hydrogenation

Revisited a spectrokinetic approach.

Unique Chemistry and Structure of Pyrolyzed Bovine Bone for Enhanced Aqueous Metals Adsorption

Bone waste is a problematic slaughterhouse waste typically disposed of in landfills. The pyrolyzed product of this waste shows strong potential in mine and industrial waste water remediation and work is needed to identify chemical and structural parameters which drive performance. Diffuse Reflectance Fourier Transform Spectroscopy (DRIFTS) was used to probe carbonate (CO32−), phosphate (PO43−) and hydroxyl (OH−) environments of mineral phases and functional group chemistry in carbonaceous phase, revealing a potentially synergistic functionality between the two in bone char. CO32− and water substitutions in the mineral lattice were found to persist after pyrolysis to 750 °C, and more soluble non-apatite calcium phosphate phases were observed using second derivative analysis of the v3 PO43− band. Nitrogen-rich functional groups were found in the carbonaceous phase which are associated with complexation of aqueous metals, and ordered aromatic clusters identified by Raman spectroscopy indicate a porous carbon skeletal structure to promote metals adsorption and complexation. These results point to unique chemical and structural features of bone char which are not easily replicated by synthetic carbonated apatite or activated carbon and which contribute to the excellent aqueous metals removal power of bone char.Graphical

Interaction process between gaseous CH3I and NaCl particles: implication for iodine dispersion in the atmosphere.

Gaseous iodomethane (CH3I) is naturally emitted into the atmosphere by biological activity in oceans and during severe accidents (SAs) in nuclear power plants. In this latter case, a part of radioactive iodine such as 131I may be released. Improving the knowledge of CH3I transport and reactivity in the atmosphere is important since they are strongly linked to first the cycle of ozone and second to the dispersion of radioactive CH3I with potential radiological consequences on both the environment and human health. Here, the interaction process of CH3I with NaCl as a surrogate of atmospheric aerosols was investigated under ambient air conditions by using Diffuse Reflectance Fourier Transform Spectroscopy (DRIFTS). The DRIFTS spectra of NaCl clearly evidenced CH3I adsorption on the NaCl particle surface. A part of CH3I ((1.68 ± 0.85) × 1014 molecule per mgNaCl) was found to be strongly bonded to NaCl since no desorption was observed. The CH3I adsorption on the NaCl surface presented a 1st order kinetics relative to its gas phase concentration. The uptake coefficient was determined to be in the order of 10-11. These results show a low probability of CH3I to be taken up by halide-containing aerosols. These data are crucial for completing the iodine atmospheric chemical scheme.

In-situ incorporation of binder during sol-gel preparation of Pd-based sulfated zirconia for reduction of nitrogen oxides under lean-burn conditions: Effect on activity and wash-coating characteristics

We have developed a dual-catalyst aftertreatment system for reducing nitrogen oxides (NOx) in the exhaust stream of natural gas-fired lean-burn engines by utilizing the unburned hydrocarbons present in the engine exhaust. The dual-catalyst bed consists of a physical mixture of a reduction catalyst (Pd/SZ) and an oxidation catalyst (Co/CeO2). In order to make this dual-catalyst system viable for practical use in the real aftertreatment units, it is necessary to develop a catalytically active washcoat for loading it onto cordierite monolith cores. To be able to handle large throughputs of gases typical of aftertreatment units, irreversible loss of activity due to separation of the wash-coat from the monolith walls can be reduced by adding binders to improve the adhesive properties of the wash-coat. However, addition of such binders may affect the catalytic activity of the resulting dual-catalyst bed. In our study, we have incorporated binders such as alumina, boehmite, bentonite or silica to the Pd/SZ catalyst using a novel technique in which the binders were added in situ during the sol-gel synthesis rather than the conventional method of adding binders (ex-situ) in catalyst slurry. Surface area analysis, X-ray diffraction (XRD) and diffuse reflectance Fourier transform spectroscopy (DRIFTS) with pyridine show that in-situ addition of binder affects the textural properties, crystal phase of zirconia and the acidic properties of the resulting Pd/SZ catalyst respectively. Electron Paramagnetic Resonance (EPR) indicated the presence of Pd+, Pd3+ and Zr3+ species in the binder-free and in situ alumina-incorporated Pd/SZ catalysts. Furthermore, steady-state activity tests on the modified dual-catalyst bed with the alumina-incorporated Pd/SZ exhibit the best performance amongst the other binder-incorporated catalysts in the dual-catalyst bed. In-situ incorporation of binder during sol-gel synthesis yielded catalysts with far superior catalytic activity for NOx reduction than conventional ex-situ binder addition to the catalyst slurry for wash-coating. Time-on-stream experiments show that the alumina-incorporated Pd/SZ catalyst maintains the hydrothermal stability of the binder-free Pd/SZ in the mixed bed. Several parameters such as pH of the binder-incorporated catalyst slurry and calcination temperature of the wash-coat have also been optimized to develop a catalytically active wash-coat and its adhesivity and uniformity were tested using ultrasonication, cyclic thermal shock and SEM imaging.

Mechanistic investigations on dimethyl carbonate formation by oxidative carbonylation of methanol over a CuY zeolite: an operandoSSITKA/DRIFTS/MS study

The simultaneous combination of steady state isotopic transient kinetic analysis (SSITKA) with diffuse reflectance Fourier transform spectroscopy (DRIFTS) and mass spectrometric (MS) analysis was applied to study the oxidative carbonylation of methanol (MeOH) to dimethyl carbonate (DMC) on a CuY zeolite catalyst prepared by incipient-wetness impregnation of commercial zeolite NH(4)-Y. The interaction of the catalyst with different reactants and reactant mixtures (O(2), CO, CO/O(2), MeOH/O(2), MeOH/CO, and MeOH/CO/O(2)) was studied in detail using (16)O(2)/(18)O(2) as well as (12)CO/(13)CO containing gas mixtures. DMC is produced via a monodentate monomethyl carbonate (MMC) species as intermediate which is formed by the concerted action of adsorbed methoxide and CO with gas phase MeOH. Adsorbed bidentate MMC species were found to be inactive. Lattice oxygen supplied by CuO(x) species is involved in the formation of MMC. Gas phase oxygen is needed to re-oxidize the catalyst but favours also the oxidation of CO to CO(2) and unselective oxidation reactions of MeOH to methyl formate, dimethoxymethane, and CO(2). The appropriate choice of reaction temperature and of the oxygen content in the reactant gas mixture was found to be indispensable for reaching high DMC selectivities.

A Mechanistic Study of the Solid-State Reactions of H-Mordenite with Indium(0) and Indium(III)oxide

Solid-state reactions of In2O3/H-mordenite and In0/H-mordenite mixtures (Al/In = 3) were studied using an atmospheric flow-through microreactor, diffuse reflectance Fourier-transform spectroscopy (DRIFTS), and X-ray powder diffractometry (XRD). The indium(III)oxide/H-mordenite mixture was heated in a flow of 2% H2/N2 gas mixture or pure N2 to 873 and 973 K, respectively. The indium(0)/H-mordenite mixture was heated in a dry and wet N2 stream to 673−973 K. The reactions were monitored by analyzing the effluent gas, using mass spectroscopy (MS). The protons of H-mordenite were exchanged for In+ cations, indicating that In3+ was reduced and In0 was oxidized in the exchange processes. In the process of reductive solid-state ion exchange (RSSIE), the indium was reduced by H2. In the oxidative solid-state ion exchange (OSSIE) process, the indium was oxidized by H2O. Results substantiate that the ion exchange proceeds through a volatile InOH intermediate. Formation of InOH and its rapid transport within the zeolite crystals requires the presence of water vapor. The In+ in the zeolite lattice can be oxidized by O2 or H2O to indium oxycations, most probably to InO+, while the obtained oxycations can be reduced in hydrogen back to In+.

Quantitative analysis of the reactivity of formate species seen by DRIFTS over a Au/Ce(La)O 2 water–gas shift catalyst: First unambiguous evidence of the minority role of formates as reaction intermediates

The reactivity of the species formed at the surface of a Au/Ce(La)O 2 catalyst during the water–gas shift (WGS) reaction were investigated by operando diffuse reflectance Fourier transform spectroscopy (DRIFTS) at the chemical steady state during isotopic transient kinetic analyses (SSITKA). The exchanges of the reaction product CO 2 and of formate and carbonate surface species were followed during an isotopic exchange of the reactant CO using a DRIFTS cell as a single reactor. The DRIFTS cell was a modified commercial cell that yielded identical reaction rates to that measured over a quartz plug-flow reactor. The DRIFTS signal was used to quantify the relative concentrations of the surface species and CO 2. The analysis of the formate exchange curves between 428 and 493 K showed that at least two levels of reactivity were present. “Slow formates” displayed an exchange rate constant 10- to 20-fold slower than that of the reaction product CO 2. “Fast formates” were exchanged on a time scale similar to that of CO 2. Multiple nonreactive readsorption of CO 2 took place, accounting for the kinetics of the exchange of CO 2(g) and making it impossible to determine the number of active sites through the SSITKA technique. The concentration (in mol g −1) of formates on the catalyst was determined through a calibration curve and allowed calculation of the specific rate of formate decomposition. The rate of CO 2 formation was more than an order of magnitude higher than the rate of decomposition of formates (slow + fast species), indicating that all of the formates detected by DRIFTS could not be the main reaction intermediates in the production of CO 2. This work stresses the importance of full quantitative analyses (measuring both rate constants and adsorbate concentrations) when investigating the role of adsorbates as potential reaction intermediates, and illustrates how even reactive species seen by DRIFTS may be unimportant in the overall reaction scheme.

Thermal decomposition of bisphenol A-based polyetherurethanes blown with pentane: Part II—Influence of the novel NaH 2PO 4/NaHSO 4 flame retardant system

The thermal degradation process of ethoxylated bisphenol A (BPA) and oxyalkylenated 2,6-toluylenediamine-based polyurethane (PU) foams blown with pentane and flame retarded by novel NaH 2PO 4 and NaHSO 4 intumescent system (5:3, w/w) was studied by thermogravimetry coupled with mass spectrometry (TG–MS), thermogravimetry coupled with Fourier transform infrared spectroscopy (TG–FTIR), pyrolysis–gas chromatography coupled with mass spectrometry (Py/GC–MS) and diffuse reflectance Fourier transform spectroscopy (DRIFTS) methods. It has been found that NaH 2PO 4/NaHSO 4 system is active both at the initiation stage of PU decomposition as well as it catalyses cross-linking reactions that lead to enhanced char formation during degradation; both effects contribute to the overall flame retardation effect.

Quantitative analysis of less soluble form IV in commercial carbamazepine (form III) by diffuse reflectance fourier transform spectroscopy (DRIFTS) and lazy learning algorithm

Carbamazepine is a poorly soluble drug, with known bioavailability problems related to its polymorphism, and a form (C-monoclinic or form IV) less soluble than the pharmaceutically acceptable (P-monoclinic or form III) can be formed under various conditions, possible to occur during drug formulation. Therefore, quantitative analysis of form IV in form III is important to the drug formulators. In the present study, a fast and simple non-destructive method was developed for quantification of form IV in form III, by using DRIFTS spectral data subjected to the standard normal variate transformation (row centering and scaling) and to the lazy learning algorithm. Fast principal component (fast PCR) and partial least squares (PLS) regression methods of multivariate calibration were also used, which were compared with lazy learning. The lazy learning algorithm was performing better than the fast PCR and PLS methods (root mean squared error of cross-validation 1.318% versus 3.337 and 3.058%, respectively). Even with a small number of calibration samples it gave satisfactory predictive performance (root mean squared error of prediction <2.0% versus >3.3% of fast PCR and >2.6% of PLS), in the concentration range below 30% (w/w) of form IV. This is attributed to the capability of handling non-linearity in the relation of reflectance and concentration as well as to local modeling using a pre-selected number of nearest neighbor concentrations.

Surface characterisation of plasma-modified poly(ethylene terephthalate)

This paper reports the modifications produced by nitrogen and helium cold plasmas on the surface of PET. The changes have been studied by diffuse reflectance Fourier transform spectroscopy (DRIFTS), atomic force microscopy (AFM) and inverse gas–solid chromatography (IGSC). Nitrogen and oxygen atoms seem to appear on the surface of PET as a consequence of the exposure to the atmosphere after the treatments with plasmas. AFM shows that both plasmas altered in different extent the surface of PET as they break the polymer chains producing low molecular products which appear as bumps on the surface. The surface area and the porosity of PET does not change by plasma treatments even after 15 min. The dispersive component of the surface free energy, γ s d , decreases after long treatments with nitrogen plasma whereas it remains almost unchanged after long treatment with helium plasma.

Removal of PAH Compounds from Liquid Fuels by Pd Catalysts

Palladium catalysts supported on gamma-alumina (AN, AS), amorphous silica-alumina (ASA), and beta-zeolite (betaZ) were prepared with the aim to reduce the content of polycyclic aromatic hydrocarbons (PAHs) in diesel fuels. The removal of PAH compounds was evaluated with a model feed (toluene, naphthalene, and dibenzothiophene)that approached the composition of diesel fuel. The catalysts were characterized by N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, transmission electron microscopy, temperature-programmed reduction/temperature-programmed oxidation, Fourier transform (FT) IR of absorbed CO, and diffuse reflectance FT spectroscopy of adsorbed NH3. When palladium was supported on ASA instead of AN or betaZ, the intrinsic activity improved considerably. Such behavior is discussed in terms of larger Brønsted acidity and the degree of reduction of the Pd species on Pd/ASA. For the 2.2 Pd/betaZ catalyst, interaction of the Pd clusters with zeolite protons led to formation of Pddelta+ species, which are not active in the hydrogenation of aromatics. All catalysts were resistant to poisoning by S compounds.

Effect of MAO silica surface loading on ( nBuCp) 2ZrCl 2 anchoring, on catalyst activity and on polymer properties

Silica Grace 948 activated at 723 K was modified with MAO in aluminum contents comprised between 0.5 and 20.0 wt.% Al/SiO 2. Supported metallocene catalysts were prepared by grafting ( nBuCp) 2ZrCl 2 toluene solutions directly onto silica and onto MAO-modified silicas. The catalysts were characterized by a series of complementary techniques, namely, Rutherford backscattering spectrometry (RBS), Diffuse-reflectance Fourier transform spectroscopy (DRIFTS), ultraviolet-visible spectroscopy (UV-Vis) and electron probe microanalysis (EPMA). MAO-mediated systems presented higher Zr content comparing to directly silica supported system. For the MAO-modified silica systems, Zr content increases up to 2.0–4.0 wt.% Al/SiO 2 reaching 1.5 wt.% Zr/SiO 2. As the aluminum content increases, metal loading decreases achieving 0.6 wt.% Zr/SiO 2 for the supported catalyst having 20.0 wt.% Al/SiO 2. All the systems were shown to be active in ethylene polymerization having MAO as cocatalyst. Higher activity were achieved with MAO-mediated systems having 2.0–4.0 wt.% Al/SiO 2. The catalyst systems produced polyethylenes with high molecular weight and narrow molecular weight distribution. The preparative protocol was stepwisely monitored by DRIFTS. For lower MAO content (2.0 wt.% Al/SiO 2) residual isolated silanol groups were thoroughly consumed or perturbed after ( nBuCp) 2ZrCl 2 impregnation.

Compatibilization of nylon 6/liquid crystalline polymer blends with three types of compatibilizers

AbstractPolyblends of nylon 6 and liquid crystalline polymer (LCP) (Vectra A 950) are immiscible and highly incompatible, with resultant poor interfacial adhesion, large phase domains, and poor mechanical properties. In the present work, compatibilizing strategies are put forward for blends containing nylon and LCP. Effects of three types of compatibilizers, including ionomer Zn–sulfonated polystyrene (SPS), reactive copolymer styrene–maleic anhydride (SMA), functional grafted copolymers—polypropylene grafted glycidyl methacrylate (PP‐g‐GMA) and polypropylene grafted maleic anhydride (PP‐g‐MAH)—are studied in the aspects of morphology and dynamic mechanical behavior. The addition of compatibilizers decreases the domain size of the dispersed phase and results in improved interfacial adhesion between LCP and matrix. The compatibilization mechanism is discussed by way of diffuse reflectance Fourier transform spectroscopy (DRIFT), showing the reaction between compatibilizers and matrix nylon 6. Mechanical properties are improved by good interfacial adhesion. The contribution of SMA to mechanical properties is more obvious than that of Zn‐SPS and grafted PPs used. The blending procedure is correlated with the improvement of mechanical properties by the addition of compatibilizer. Two‐step blending is demonstrated as an optimum method to obtain composites with better mechanical properties as a result of a greater chance for LCP to contact the compatibilizer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1452–1461, 2003

DRIFTS studies of carbon monoxide coverage on highly dispersed bimetallic Pt-Cu and Pt-Au catalysts

Silica supported platinum-gold and platinum-copper catalysts prepared from organometallic cluster precursors were characterized with diffuse reflectance Fourier-transform spectroscopy (DRIFTS) of adsorbed CO. Because of the effects that dipole coupling of adsorbed carbon monoxide molecules can have on the infrared spectrum, coverage studies were employed to evaluate the interactions between CO and the catalyst surfaces. DRIFTS spectra of the catalysts prepared from bimetallic molecular cluster precursors showed significantly lower CO stretching frequencies relative to a traditionally prepared platinum catalyst. The lowering of the CO stretching frequency may be the result of the formation of unique alloys and particle morphologies. In the case of the catalyst prepared from the platinum-copper cluster, two peaks were identified in the PtCO stretching region, one of which is postulated to be a bridging or semi-bridging mode between Pt and Cu. Infrared spectroscopy results are also discussed in relation to kinetic data from the n-hexane conversion reaction. Differences in catalyst activities and selectivities are concluded to be primarily due to geometric (i.e. structural or morphological) effects.

Preparation and Characterization of Supported Bimetallic Pt–Au and Pt–Cu Catalysts from Bimetallic Molecular Precursors

Silica-supported bimetallic Pt–Cu and Pt–Au catalysts were prepared using bimetallic molecular cluster precursors as the metal source. The molecular precursors were adsorbed onto the support from an organic solvent, dried under vacuum, calcined under flowing oxygen, and reduced with hydrogen. The resulting catalysts were characterized with CO chemisorption, diffuse reflectance Fourier transform spectroscopy (DRIFTS) of adsorbed CO, transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). The new catalysts were also compared to traditionally prepared Pt and Pt–Cu catalysts (wetness impregnation or coimpregnation) that had been subjected to identical activation conditions. When the molecular cluster precursors were used as catalyst precursors, small and uniform bimetallic particles with high Pt dispersions were prepared. The DRIFTS spectrum of CO bound to the cluster-derived Pt–Cu catalyst was exceptionally broad and indicated a large red shift in ν(C≡O) relative to Pt. Catalytic performance was evaluated with the hexane conversion reaction. Both cluster-derived catalysts showed enhanced selectivity for light hydrocarbon production (cracking) and decreased activity for nondestructive alkane reforming and dehydrocyclization reactions. The cluster-derived catalysts had nearly identical distributions of light hydrocarbon; these distributions indicated a propensity for internal C–C bond cleavage. Despite the similarities of these fission patterns, the Pt–Au catalyst had greatly enhanced resistance to deactivation processes while the Pt–Cu had no superior deactivation performance over the traditional Pt catalyst.

Metal−Support Interactions in Co/Al2O3 Catalysts: A Comparative Study on Reactivity of Support

Co/Al2O3 catalysts have been prepared with conventional impregnation and sol−gel methods to vary the chemical reactivity of the alumina support. The material system has been investigated with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance Fourier transform spectroscopy (DRIFT), Brunauer−Emmett−Teller (BET) method, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) (with thermogravimetric analysis (TGA) and differential thermal analysis (DTA)), and gas chromotography (GC) for the catalytic oxidation of CO. It had been found that the reactivity of the support changes the surface structure and chemical composition of catalysts significantly. When the metal−support interaction is weak, Co3O4 is a predominant surface phase (which is interfaced by a “cobalt surface phase”). With an increase in support reactivity, CoO and CoAl2O4 are found to be present on the surface. The cobalt content on the surface decreases upon the increase in suppor...

NO x adsorption onto dehydroxylated or hydroxylated tin dioxide surface. Application to SnO 2-based sensors

SnO 2-based sensors present strong interactions with NO x -containing atmospheres. For this reason, it is fundamental to identify the nature of the adsorbed species resulting from the interaction of NO and NO 2 with the tin oxide surface. This aspect has been studied in literature by Temperature Programmed Desorption (TPD). To state more precisely structures of adsorbed species, we link TPD with Diffuse Reflectance Fourier Transform Spectroscopy (DRIFTS). Concerning NO 2 adsorption, DRIFTS experiments indicate the formation of monodentate nitrato species at room temperature. By increasing the temperature, a conversion of adsorbed species is observed. The nature of surface groups is discussed. In the presence of hydroxyl groups (two different OH groups are evidenced), the formation of hydrogeno nitrates is detected.

Microwave Treatment of Hazardous Wastes: Remediation of Soils Contaminated by Non-Volatile Organic Chemicals Like Dioxins

Dioxins are a class oforganic chemicalswhkhare insoluble, nonvolatile, chemically and physically non-reactive. Studies have been carried out on a surrogate, namely, 9,10-anthraquinone (anthraquinone), because it has similar chemical and physical properties but it is not toxic. It was found in microwave treatment studies that, at temperatures attainable in-situ, anthraquinone did not volatilize or diffuse but did become non-extractable. A model was then proposed which postulated that as water was removed from soil aggregates, anthraquinone adsorbed directly on the humus and clay fractions, and then reacted chemically. This led to spectroscopic studies to determine directly whether or not ant hraquinone did undergo a chemical reaction. Those studies were carried out using DRIFT (diffuse reflectance Fourier transform spectroscopy). Band shifts indicative of possible chemical reactions were found after microwave treatment of ant hraquinone adsorbed on humus and kaolin clay, respectively.

Thin-Layer Chromatographic-Diffuse Reflectance Infrared Fourier Transform Spectroscopic Analysis

Abstract Diffuse reflectance Fourier transform spectroscopy (DRIFTS) is used to gain abundant structural information about thin layer chromatographically (TLC) separated materials. Quantitative and qualitative in situ DRIFTS analysis can be accomplished considering the effect of the TLC chromatographic support on the optical measurement of the TLC spot. Methods for in situ FTIR analysis of TLC spots are reviewed along with techniques proposed to overcome spectral interferences associated with the in situ measurement.