Dataset Information

Multivariate Analysis of Coupled Operando EPR/XANES/EXAFS/UV-Vis/ATR-IR Spectroscopy: A New Dimension for Mechanistic Studies of Catalytic Gas-Liquid Phase Reactions.

ABSTRACT: Operando EPR, XANES/EXAFS, UV-Vis and ATR-IR spectroscopic methods have been coupled for the first time in the same experimental setup for investigation of unclear mechanistic aspects of selective aerobic oxidation of benzyl alcohol by a Cu/TEMPO catalytic system (TEMPO=2,2,6,6-tetramethylpiperidinyloxyl). By multivariate curve resolution with alternating least-squares fitting (MCR-ALS) of simultaneously recorded XAS and UV-Vis data sets, it was found that an initially formed (bpy)(NMI)CuI - complex (bpy=2,2'-bipyridine, NMI=N-methylimidazole ) is converted to two different CuII species, a mononuclear (bpy)(NMI)(CH3 CN)CuII -OOH species detectable by EPR and ESI-MS, and an EPR-silent dinuclear (CH3 CN)(bpy)(NMI)CuII (?-OH)2 ?CuII ?(bpy)(NMI) complex. The latter is cleaved in the further course of reaction into (bpy)(NMI)(HOO)CuII -TEMPO monomers that are also EPR-silent due to dipolar interaction with bound TEMPO. Both Cu monomers and the Cu dimer are catalytically active in the initial phase of the reaction, yet the dimer is definitely not a major active species nor a resting state since it is irreversibly cleaved in the course of the reaction while catalytic activity is maintained. Gradual formation of non-reducible CuII leads to slight deactivation at extended reaction times.

SUBMITTER: Rabeah J

PROVIDER: S-EPMC7317854 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Multivariate Analysis of Coupled Operando EPR/XANES/EXAFS/UV-Vis/ATR-IR Spectroscopy: A New Dimension for Mechanistic Studies of Catalytic Gas-Liquid Phase Reactions.

Rabeah Jabor J Briois Valérie V Adomeit Sven S La Fontaine Camille C Bentrup Ursula U Brückner Angelika A

Chemistry (Weinheim an der Bergstrasse, Germany) 20200514 33

Operando EPR, XANES/EXAFS, UV-Vis and ATR-IR spectroscopic methods have been coupled for the first time in the same experimental setup for investigation of unclear mechanistic aspects of selective aerobic oxidation of benzyl alcohol by a Cu/TEMPO catalytic system (TEMPO=2,2,6,6-tetramethylpiperidinyloxyl). By multivariate curve resolution with alternating least-squares fitting (MCR-ALS) of simultaneously recorded XAS and UV-Vis data sets, it was found that an initially formed (bpy)(NMI)Cu<sup>I< ...[more]

PMID: 32118340

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Project description:One of the most important issues in the wine sector and prevention of adulterations of wines are discrimination of grape varieties, geographical origin of wine, and year of vintage. In this experimental research study, UV-Vis and FT-IR spectroscopic screening analytical approaches together with chemometric pattern recognition techniques were applied and compared in addressing two wine authentication problems: discrimination of (i) varietal and (ii) year of vintage of red wines produced in the same oenological region. UV-Vis and FT-IR spectra of red wines were registered for all the samples and the principal features related to chemical composition of the samples were identified. Furthermore, for the discrimination and classification of red wines a multivariate data analysis was developed. Spectral UV-Vis and FT-IR data were reduced to a small number of principal components (PCs) using principal component analysis (PCA) and then partial least squares discriminant analysis (PLS-DA) and linear discriminant analysis (LDA) were performed in order to develop qualitative classification and regression models. The first three PCs used to build the models explained 89% of the total variance in the case of UV-Vis data and 98% of the total variance for FR-IR data. PLS-DA results show that acceptable linear regression fits were observed for the varietal classification of wines based on FT-IR data. According to the obtained LDA classification rates, it can be affirmed that UV-Vis spectroscopy works better than FT-IR spectroscopy for the discrimination of red wines according to the grape variety, while classification of wines according to year of vintage was better for the LDA based FT-IR data model. A clear discrimination of aged wines (over six years) was observed. The proposed methodologies can be used as accessible tools for the wine identity assurance without the need for costly and laborious chemical analysis, which makes them more accessible to many laboratories.

Project description:In small-pore zeolite catalysts, where the size of the pores is limited by eight-ring windows, aromatic hydrocarbon pool molecules that are formed inside the zeolite during the Methanol-to-Olefins (MTO) process cannot exit the pores and are retained inside the catalyst. Hydrocarbon species whose size is comparable to the size of the zeolite cage can cause the zeolite lattice to expand during the MTO process. In this work, the formation of retained hydrocarbon pool species during MTO at a reaction temperature of 400 °C was followed using operando UV-vis spectroscopy. During the same experiment, using operando X-ray Diffraction (XRD), the expansion of the zeolite framework was assessed, and the activity of the catalyst was measured using online gas chromatography (GC). Three different small-pore zeolite frameworks, i.e., CHA, DDR, and LEV, were compared. It was shown using operando XRD that the formation of retained aromatic species causes the zeolite lattice of all three frameworks to expand. Because of the differences in the zeolite framework dimensions, the nature of the retained hydrocarbons as measured by operando UV-vis spectroscopy is different for each of the three zeolite frameworks. Consequently, the magnitude and direction of the zeolite lattice expansion as measured by operando XRD also depends on the specific combination of the hydrocarbon species and the zeolite framework. The catalyst with the CHA framework, i.e., H-SSZ-13, showed the biggest expansion: 0.9% in the direction along the c-axis of the zeolite lattice. For all three zeolite frameworks, based on the combination of operando XRD and operando UV-vis spectroscopy, the hydrocarbon species that are likely to cause the expansion of the zeolite cages are presented; methylated naphthalene and pyrene in CHA, 1-methylnaphthalene and phenalene in DDR, and methylated benzene and naphthalene in LEV. Filling of the zeolite cages and, as a consequence, the zeolite lattice expansion causes the deactivation of these small-pore zeolite catalysts during the MTO process.

Dataset Information

Multivariate Analysis of Coupled Operando EPR/XANES/EXAFS/UV-Vis/ATR-IR Spectroscopy: A New Dimension for Mechanistic Studies of Catalytic Gas-Liquid Phase Reactions.

Publications

Multivariate Analysis of Coupled Operando EPR/XANES/EXAFS/UV-Vis/ATR-IR Spectroscopy: A New Dimension for Mechanistic Studies of Catalytic Gas-Liquid Phase Reactions.

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