Search

Temperature-programmed desorption mass spectrometry (TPD MS) was used to study the pyrolysis of p-coumaric acid (pCmA) on the nanoceria surface. The interaction of pCmA with the CeO2 surface was investigated by FT-IR spectroscopy. The obtained data indicated the formation on the nanoceria surface of bidentate carboxylate complexes with chelate (Δν = 62 cm−1) and bridge structure (Δν = 146 cm−1). The thermal decomposition of pCmA over nanoceria occurred in several stages, mainly by decarboxylation. The main decomposition product is 4-vinylphenol (m/z 120). The obtained data can be useful for studying the mechanisms of catalytic thermal transformations of lignin-containing raw materials using catalysts containing cerium oxide and the development of effective technologies for the isolation of pCmA from lignin.

Search for the “structure-reactivity” correlations of the thermally stimulated reactions of cinnamic acids on the surface of catalysts is important for the development of pyrolytic conversion methods of lignocellulosic biomass components into products with high added value, in particular, into styrene. Therefore, in this work, the kinetics of pyrolysis of the reaction series of para-substituted derivatives of trans-cinnamic acid (Н, -СН 3 , -С(СН 3 ) 3 , -ОСН 3 , -F) on the surface of nanosized silica by the method of thermoprogrammed desorption mass spectrometry (TPD MS) was investigated. The products of pyrolytic reactions on the surface are identified ‒ the corresponding, para-substituted vinylbenzenes, phenylacetylenes, and phenylketenes. The kinetic parameters of the decarboxylation, ketenization, and decarbonylation reactions were calculated. The correlations "structure-reactivity" between the kinetic parameters (activation energy) and thermodynamic parameters (Hammett substituents constants) have been obtained, which indicate that electron-donor substituents reduce the activation energy of these three reactions while the electron-acceptor substituents increase it. That is, in the transitional state of the rate-limiting step, a decrease in the electron density is observed at the reaction center. The calculated values of the reaction constants ρ show that the studied reactions dependent on the sensitivity to the effect of the substituents are placed in a sequence: decarbonylation> decarboxylation> ketenization. The formation of phenylacetylenes is the most sensitive to structural changes in the molecule and proceeds through the most polar transition state.

Fourier transform infrared spectroscopy (FT-IR) and temperature programmed desorption mass spectrometry (TPD-MS) data of O-glycoside MDP in pristine and immobilized on silica surface states indicate that O-glycoside MDP binds to the silica surface by means of carboxylic and NH moieties of isoglutamine. Moreover, pyrolysis of O-glycoside MDP on the silica surface proceeds through formation of additional product 3-iminopyridine-2(3H)-one, which identified in mass spectra as molecular ion with m/z 108 and its fragment ions with m/z 79, 77, 51. FTIR and TPD-MS data confirm existence of a MDP first β-turn on the silica surface resulting from the formation of a hydrogen bond between the NAc carbonyl and the L-Ala NH for MDP and its analogs, as reported previously.

Valeric acid is an important renewable platform chemical that can be produced efficiently from lignocellulosic biomass. Upgrading of valeric acid by catalytic pyrolysis has the potential to produce value added biofuels and chemicals on an industrial scale. Understanding the different mechanisms involved in the thermal transformations of valeric acid on the surface of nanometer-sized oxides is important for the development of efficient heterogeneously catalyzed pyrolytic conversion techniques. In this work, the thermal decomposition of valeric acid on the surface of nanoscale SiO2 , γ-Al2 O3 , CeO2 /SiO2 , Al2 O3 /SiO2 and TiO2 /SiO2 has been investigated by temperature-programmed desorption mass spectrometry (TPD MS). Fourier transform infrared spectroscopy (FTIR) has also been used to investigate the structure of valeric acid complexes on the oxide surfaces. Two main products of pyrolytic conversion were observed to be formed depending on the nano-catalyst used-dibutylketone and propylketene. Mechanisms of ketene and ketone formation from chemisorbed fragments of valeric acid are proposed and the kinetic parameters of the corresponding reactions were calculated. It was found that the activation energy of ketenization decreases in the order SiO2 >γ-Al2 O3 >TiO2 /SiO2 >Al2 O3 /SiO2 , and the activation energy of ketonization decreases in the order γ-Al2 O3 >CeO2 /SiO2 . Nano-oxide CeO2 /SiO2 was found to selectively catalyze the ketonization reaction.

Lignin processing products have an extensive using range. Because products properties depend on lignin precursor quality it was interesting to study lignin isolated from rice husk being a large tonnage waste of rice production and its structural transformations during carbonization. Lignin isolated by the thermal hydrolysis method with H2SO4 1 wt % solution and its carbonized products prepared under different carbonization conditions were characterized using elemental analysis, IR, TPD-MS, XRD, TEM, and EPR. It was shown lignin degradation takes place over the wide (220&ndash, 520 &deg, C) temperature range. Silica presenting in lignin affects the thermal destruction of this polymer. Due to the strong chemical bond with phenolic hydroxylic group it decreases an evaporation of volatile compounds and as a result increases the temperature range of the lignin degradation. Rice husk hydrolytic lignin transformations during carbonization occur with generation of free radicals. Their concentration is decreased after condensation of aromatic rings with carbon polycycles formation, i.e., the graphite-like structure. Quantity and X-ray diffraction characteristics of the graphite-like phase depend on carbonization conditions. Morphology of the lignin-based carbonized products is represented by carbon fibers, carbon and silica nanoparticles, and together with another structure characteristics provides prospective performance properties of lignin-based end products.

Thermochemical studies of hydroxycinnamic acid derivatives and their surface complexes are important for the pharmaceutical industry, medicine and for the development of technologies of heterogeneous biomass pyrolysis. In this study, structural and thermal transformations of caffeic acid complexes on silica surfaces were studied by UV-Vis spectroscopy, thermogravimetric analysis, temperature programmed desorption mass spectrometry (TPD MS) and quantum chemical methods. Two types of caffeic acid surface complexes are found to form through phenolic or carboxyl groups. The kinetic parameters of the chemical reactions of caffeic acid on silica surface are calculated. The mechanisms of thermal transformations of the caffeic chemisorbed surface complexes are proposed. Thermal decomposition of caffeic acid complex chemisorbed through grafted ester group proceeds via three parallel reactions, producing ketene, vinyl and acetylene derivatives of 1,2-dihydroxybenzene. Immobilization of phenolic acids on the silica surface improves greatly their thermal stability.

Compositions of polydimethylsiloxane (PDMS) polymer with nanosized silica and ceria/silica were prepared. The influence of these nano-fillers on the thermal stability and degradation mechanism of silicone polymer was investigated using Thermogravimetric Analysis (TGA) and Temperature Programmed Desorption Mass Spectrometry (TPD MS). The results showed that thermal decomposition of pure and adsorbed PDMS differs significantly. The three main stages of the PDMS thermal transformations in the adsorbed state were determined to be: 1) chemisorption of PDMS chains involving the terminal trimethylsilyl groups of the polymer and silanol groups of the silica surface; 2) formation and desorption of cyclic oligomers; 3) high temperature radical degradation of the polymer accompanied by the formation of methane and ethylene. The kinetic parameters of the corresponding reactions were calculated from the TPD MS data. It was found that nanoparticles of cerium dioxide strongly influence the degradation pattern, lower the decomposition temperature and catalyze the formation of methane.

Aliphatic carboxylic acids in the form of triglycerides are promising renewable raw materials for the development of green nanotechnology of biomass catalytic pyrolysis with the use of silica-supported catalysts. Therefore, the research of hydrolytic stability and thermal transformations of carboxylic acids on the silica surface is of practical importance. Since such investigations for carboxylic acid grafted ester groups have not been carried out, the hydrolytic stability of chemisorbed carboxylic acid fragment ≡Si–O–CO–R was studied using the high-vacuum TPD-MS system. It was found that only ~46 % of grafted ester groups of carboxylic acids are hydrolyzed in saturated water vapors at room temperature during an hour.

The research focuses on the synthesis of novel organic–inorganic hybrid materials based on polysaccharide chitosan and nanosilicas (SiO2, TiO2/SiO2 and Al2O3/SiO2). The chitosan modified nanooxides were obtained by the equilibrium adsorption method. The chitosan adsorption capacities of silica/titania and silica/alumina are higher than of the plain silica due to the additional active sites present on the surfaces of the mixed oxides. The hybrid materials were characterized by low-temperature nitrogen adsorption/desorption, photon correlation spectroscopy (PCS), scanning electron microscopy (SEM), thermogravimetry (TG/DTG) and temperature-programmed desorption with mass spectrometry control (TPD MS) methods. The chitosan treatment only modestly influences the surface area SBET of the nanooxides but the rearrangement of the secondary and tertiary structures (aggregates and agglomerates) results in an enhancement of the mesoporosity and affects the size of the aggregates. The more severe thermodestruction of the polysaccharide desorbing from the modified mixed silicas indicates a stronger interaction between the chitosan and the mixed oxides compared to the silanol groups of the plain silica surface.

The studies of pyrolysis of caffeic acid (CA) and its surface complexes is important for the development of technologies of heterogeneous catalytic pyrolysis of plant- and wood- based renewable biomass components. In this work, the structure and thermal transformations of the surface complexes of CA on the surface of nanoceria were investigated using Fourier transform&ndash, infrared (FT&ndash, IR) spectroscopy, thermogravimetric analysis (TGA) and temperature-programmed desorption mass spectrometry (TPD MS). It was found that CA on the surface of cerium dioxide forms several types of complexes: bidentate carboxylates, monodentate carboxylates and complexes formed as a result of interaction with phenolic hydroxyl groups. This is due to the ability of nanosized cerium dioxide to generate basic hydroxyl groups that can deprotonate phenolic groups to form phenolates on the surface. The main pyrolysis products were identified. The possible ways of forming 3,4-dihydroxyphenylethylene, acetylene carboxylic acid, pyrocatechol and phenol from surface complexes of CA were suggested. It was established that on the nanoceria surface effectively occur the decarboxylation, decarbonylation, and dehydration reactions of the CA, which are the desirable processes in biomass conversion technologies.

The interaction of acetic, propionic, butyric, isobutyric, valeric, nonanoic, decanoic, and pivalic acids with the surface of fumed silica was investigated by temperature-programmed desorption mass spectrometry (TPD–MS). Mechanisms of the formation of ketenes from chemisorbed fragments of carboxylic acids on the surface of fumed silica were proposed and the kinetic parameters of the reaction were calculated. The Taft correlation equation and the reaction parameter ρ could be obtained by application of the linear free energy relationship (LFER) principle for this reaction series. The applicability of the LFER method to the study of reactions of adsorbed organic molecules on mineral surfaces occurring during TPD–MS experiments was demonstrated using a series of acids.

Temperature-programmed desorption mass spectrometry was used to study the reaction of a series of primary amines (isobutylamine, isopentylamine, 1-pentylamine, 1-hexylamine, and 1-heptylamine) with a fumed silica surface. A mechanism was proposed and the kinetic parameters of the formation of alkenes from the chemisorbed aliphatic amine fragments on the silica surface were determined. A linear correlation was found between the activation energy and Taft constants for the substituents at the reaction site.

Pyrolysis of biologically active cinnamic acid derivatives: cinnamic, coumaric, ferulic and caffeic acids was studied by the method of thermal programmed desorption mass spectrometry. It was found that pyrolysis of coumaric and caffeic acid proceeds as a thermal decarboxylation reaction of the first order. Kinetic parameters of the reaction of decarboxylation including its order, the activation energy and pre-exponential factor were calculated. Under conditions of TPD MS experiment cinnamic acid sublimates at temperatures above 200 °C. Thermal decomposition of ferulic acid proceeds in several stages.

Curves representing the dependence of the pressure of volatile products formed in the destruction of chitin or chitosan on the thermolysis temperature were analyzed. The curves were obtained using temperature programmed desorption mass spectrometry. It was shown that the shape and positions of the maxima in the curves depend on the ratio of the numbers of pyranose rings bearing amine and acetamide groups in the polymer chain. A new approach was proposed for determining the deacetylation degree of chitin or chitosan based on the data of temperature programmed desorption mass spectrometry.

N-Acetylmuramyl- l -alanyl- d -isoglutamine or muramyl dipeptide is a cleavage product of peptidoglycan by lysozyme. This study explored the use of the temperature-programmed desorption mass spectrometry (TPDMS) in analysis of glycoside of muramyl dipeptide: O-{(4-tert-butylcyclohexyl)-2-acetamido-2,3-dideoxy-β- d -glucopyranoside-3-yl}- d -lactoyl- l -alanyl- d -isoglutamine (MDP) on the surface of fumed silica. Stages of pyrolysis of MDP in condensed state and on the silica surface have been determined. Three stages have been clear identified under pyrolysis of MDP on the silica surface. Kinetic parameters of thermal reactions on the fumed silica surface and in the condensed state have been calculated.

The interactions of bioactive ferulic acid with fumed silica were studied by UV/vis spectroscopy, FT-IR, TPD MS techniques and quantum chemical methods. It was found that surface complexes may form through phenol or carboxyl group of ferulic acid depending on its coverage value. The structure of surface complexes and mechanisms of the ferulic acid chemosorption on the silica surface are discussed. The kinetic parameters of the chemical reactions on silica surface are calculated. The mechanisms of thermal transformations of the ferulic chemosorbed surface complexes are proposed.

Several carbon adsorbents characterised by different matrix-confined microporosity and textural meso- and macroporosity were prepared by heat-treatment of porous phenolic resins. These were investigated using adsorption, one-pass temperature-programmed desorption (OPTPD) with mass-spectrometry (MS) control (300–850 K), 1 H NMR spectroscopy (190–280 K) and thermally stimulated depolarisation current (TSDC, 90–260 K) methods. Variations in resin composition and carbon preparation conditions allow us to control microporosity and/or textural porosity as well as adsorptive properties (energy of adsorption, adsorption potential and Gibbs free energy of adsorption) of the carbon adsorbents. According to the NMR and TSDC data, a portion of water (small clusters) in aqueous suspensions of the carbon adsorbents has the same structure as in bulk water. However, extended water structures undergo significant changes in the presence of carbon or carbon/nanosilica. TSDC-cryoporometry gives pore size distributions for carbons similar to those obtained using standard adsorption methods.

Polydimethylsiloxane (PDMS) is a widely used organosilicon polymer often employed in formulations with fine oxide particles for various high temperature applications. Although PDMS is considered to be thermally stable and chemically inert, it is not always clear how the oxide filler influences its thermoresistance, decomposition chemistry and what reactive products are formed in the underlying thermal reactions. In this work we use temperature programmed desorption mass spectrometry (TPD MS) to study the pyrolysis of PDMS and its composites with nanosized silica and ceria/silica. Our results suggest that the elusive organosilicon compound - dimethylsilanone is generated from PDMS over a broad temperature range (in some cases starting at 70${\deg}$C). The presence of nano-oxides catalyzed this process. Ions characteristic of the fragmentation of dimethylsilanone under electron ionization were assigned with the aid of DFT structure calculations. Possible reaction mechanisms for generating dimethylsilanone were discussed in the context of the calculated kinetic parameters. Observed accompanying products of PDMS pyrolysis, such as tetramethylcyclodisiloxane and hexamethylcyclotrisiloxane, indicate that multiple channels are involved in the dimethylsilanone release., Comment: 24 pages, 9 figures, 1 table

Polydimethylsiloxane (PDMS)/fumed silica A-300 and PDMS/ZrO2/A-300 were studied using adsorption, thermogravimetry, temperature-programmed desorption (TPD) mass-spectrometry, infrared spectroscopy, XRD, and broadband dielectric relaxation spectroscopy. ZrO2 was synthesized on fumed silica with zirconium acetylacetonate in CCl4 at 350 K for 1 h and calcinated at 773 K for 1 h (1–4 reaction cycles). PDMS (5–40 wt.%) was adsorbed onto silica and zirconia/silica from hexane solution and then dried. Grafted zirconia changes the chemistry of the surface (because of its catalytic capability) and the topology of secondary particles (because of occupation of voids in aggregates of primary silica particles by zirconia nanoparticles) responsible for the textural porosity of the powders. Therefore, many properties (such as structural characteristics of the composites, reactions on heating in air and vacuum, interfacial relaxation phenomena, hydrophobicity as a function of treatment temperature, etc.) of PDMS/zirconia/silica strongly differ from those of PDMS/A-300. Broadening of the α-relaxation of PDMS at the interfaces of disperse oxides suggests both weakening of the PDMS–PDMS interaction and strengthening of the PDMS–oxide interaction.

The interaction of cinnamic acid with the surface of highly dispersed silica is studied. The mechanisms of adsorption, chemisorption, and thermal transformations of cinnamic acid on the silica surface are proposed. The kinetic parameters of the chemical reactions on the surface of silica are calculated.

Several series of fumed silicas and mixed fumed oxides produced and treated under different conditions were studied in gaseous and liquid media using nitrogen and water adsorption-desorption, mass spectrometry, FTIR, NMR, thermally stimulated depolarization current (TSDC), photon correlation spectroscopy (PCS), zeta potential, potentiometric titration, and Auger electron spectroscopy methods. Aggregation of primary particles and adsorption capacity (Vp) decrease and hysteresis loops of nitrogen adsorption-desorption isotherms becomes shorter with decreasing specific surface area (S(BET)). However, the shape of nitrogen adsorption-desorption isotherms can be assigned to the same type independent of S(BET) value. The main maximum of pore size distribution (gaps between primary nonporous particles in aggregates and agglomerates) shifts toward larger pore size and its intensity decreases with decreasing S(BET) value. The water adsorption increases with increasing S(BET) value; however, the opposite effect is observed for the content of surface hydroxyls (in mmol/m2). Associative desorption of water (2(SiOH)-->SiOSi+H2O) depends on both the morphology and synthesis conditions of fumed silica. The silica dissolution rate increases with increasing S(BET) and pH values. However, surface charge density and the modulus of zeta-potential increase with decreasing S(BET) value. The PCS, 1H NMR, and TSDC spectra demonstrate rearrangement of the fumed silica dispersion depending on the S(BET) value and the silica concentration (C(SiO2)) in the aqueous suspensions. A specific state of the dispersion is observed at the C(SiO2) values corresponding to the bulk density of the initial silica powder.

In this study, chemical transformations of benzyl ester of О-(phenyl-2-acetamido-2,3-dideoxy-1-thio-β-d-glucopyranoside-3-yl)-d-lactoyl-l-alanyl-d-isoglutamine (SPhMDPOBn) on the fumed silica surface were examined, and the surface complex structure was characterized by temperature-programmed desorption mass spectrometry (TPD-MS), infrared spectroscopy (FTIR) and electrospray ion trap mass spectrometry (ES IT MS). Stages of pyrolysis of SPhMDPOBn in pristine state and on the silica surface have been determined. Probably, hydrogen-bonded complex forms between silanol surface groups and the C = O group of the acetamide moiety NH-(CH3)-C = O…H-O-Si≡. The thermal transformations of such hydrogen-bonded complex result in pyrolysis of SPhMDPOBn immobilized on the silica surface under TPD-MS conditions. The shifts ∆ν of amide I band (measured from 1,626 to 1,639 cm(-l) for SPhMDPOBn in pristine state) of 33 and 35 cm(-l) which occurred when SPhMDPOBn was immobilized on the silica surface may be caused by a weakening of the intramolecular hydrogen bonding of the SPhMDPOBn because the interaction with the silica surface as hydrogen bond with silanol groups is weaker than that in associates.

The investigation of thermal transformations of lignin samples have been carried out using temperature programmed desorption mass spectrometry method (TPD-MS). Main stages and products of lignin pyrolysis have been identified. The first stages (Tmax = 230 °C and Tmax = 300 °C) are attributed to thermal transformations of lignin peripheral polysaccharide fragments such as hemicellulose and cellulose respectively. The second stage (Tmax = 335 °C) is associated with desorption of lignin structural elements in the molecular forms as a result of depolymerization processes of polymeric blocks of lignin. The third stage (Tmax = 370 °C) correspond to a deeper decomposition of lignin and characterized by desorption of smaller structural fragments in molecular forms (m/z = 110, pyrocatechol). Pressure–temperature curves of pyrolysis of lignin samples have been analyzed.

The change in acid-base properties of pyrogenic, both in its original (chlorine-containing) and dechlorinated forms, has been studied as a function of the temperature of surface pretreatment. It has been found that some the base sites were substituted by chlorine atoms. During heating in vacuo at up to 600°C, values of both acidity and basicity of the sample surface increase; with further temperature increase the acidity decreases but basicity continues to increase.

Morphological, structural, adsorption, and catalytic properties of highly disperse titania prepared using sulfate and pyrogenic methods, and fumed titania-containing mixed oxides, were studied using XRD, TG/DTA, nitrogen adsorption, 1 H NMR, FTIR, microcalorimetry on immersion of oxides in water and decane, thermally stimulated depolarization current (TSDC) and catalytic photodecomposition of methylene blue (MB). Phase composition and aggregation characteristics of nanoparticles (pore size distribution) of sulfate and pyrogenically prepared titania are very different; temperature dependent structural properties are thus very different. Catalytic activity for the photodecomposition of MB is greatest (per gram of TiO 2 for the pure oxide materials) for non-treated ultrafine titania PC-500, which has the largest S BET value and smallest particle size of the materials studied. However, this activity calculated per m 2 is higher for PC-105, possessing a much smaller S BET value than PC-500. The activity per unit surface area of titania is greatest for the fumed silica–titania mixed oxide ST20. Calcination of PC-500 at 650 °C leads to enhancement of anatase content and catalytic activity, but heating at 800 and 900 °C lowers the anatase content (since rutile appears) and diminishes catalytic activity, as well as the specific surface area because of nanoparticle sintering.

The structural and adsorption characteristics of polymer adsorbent LiChrolut EN and the behavior of adsorbed water and water/organic mixtures were studied using adsorption, microcalorimetry, transmission and scanning electron microscopy, mass spectrometry, infrared spectroscopy, 1 H NMR spectroscopy with layer-by-layer freezing-out of liquids (190–273 K), and thermally stimulated depolarization current method (90–265 K). This adsorbent is characterized by large specific surface area (∼1500 m 2 /g) and pore volume (0.83 cm 3 /g) with a major contribution of narrow pores ( R 10 nm ) of a complicated shape (long hysteresis loop is in nitrogen adsorption–desorption isotherm). The adsorbent includes aromatic and aliphatic structures and oxygen-containing functionalities and can effectively adsorb organics and water/organic mixtures. On co-adsorption of water and organics (dimethyl sulfoxide, chloroform, methane), there is a weak influence of one on another adsorbate due to their poor mixing in pores. Weakly polar chloroform displaces a fraction of water from narrow pores. These effects can explain high efficiency of the adsorbent in solid-phase extraction of organics from aqueous solutions. The influence of structural features of several carbon and polymer adsorbents on adsorbed nitrogen, water and water/organics is compared on the basis of the adsorption and 1 H NMR data.