Showing papers on "Chemical decomposition published in 2022"

Efficient nickel and copper-based catalysts supported on modified graphite materials for the hydrogen production from formic acid decomposition

Abstract: Ni, Cu and Ni-Cu catalysts supported on high surface area graphite were synthesized by incipient wet impregnation. Also, the effect of doping the graphite support with alkali oxides (Li, Na and K) was studied. The catalysts were tested in the formic acid decomposition reaction to produce hydrogen. The bimetallic Ni-Cu catalyst doped with K showed the best catalytic performance with 100% conversion of formic acid at 130 °C and a 95% of selectivity to hydrogen. The turnover frequency (TOF) of the catalysts follows the order: Ni-Cu/K > NiCu/Na > Ni-Cu > Ni-Cu/Li. While the order for the apparent activation energy values is: Ni-Cu > Ni-Cu/Li > Ni-Cu/Na > Ni-Cu/K. The mechanism of the reaction is approached by programmed temperature surface reaction (TPSR) experiments and attenuated total reflectance (ATR). The greater catalytic activity of the Ni-Cu catalyst doped with potassium is ascribed to the lower stability of the formate, bicarbonate and carbonate species on its surface.

Effects of Biological and Chemical Degradation on the Properties of Scots Pine Wood—Part I: Chemical Composition and Microstructure of the Cell Wall

Abstract: Research on new conservation treatment for archaeological wood requires large amounts of wooden material. For this purpose, artificial wood degradation (biological—using brown-rot fungus Coniophora puteana, and chemical—using NaOH solution) under laboratory conditions was conducted to obtain an abundance of similar samples that mimic naturally degraded wood and can serve for comparative studies. However, knowledge about its properties is necessary to use this material for further study. In this study, the chemical composition and microstructure of degraded cell walls were investigated using FT-IR, XRD, helium pycnometry and nitrogen absorption methods. The results show that biological degradation caused the loss of hemicelluloses and celluloses, including the reduction in cellulose crystallinity, and led to lignin modification, while chemical degradation mainly depleted the amount of hemicelluloses and lignin, but also affected crystalline cellulose. These changes affected the cell wall microstructure, increasing both surface area and total pore volume. However, the chemical degradation produced a greater number of mesopores of smaller size compared to fungal decomposition. Both degradation processes weakened the cell wall’s mechanical strength, resulting in high shrinkage of degraded wood during air-drying. The results of the study suggest that degraded wood obtained under laboratory conditions can be a useful material for studies on new consolidants for archaeological wood.

Accelerated and Natural Aging of Cellulose-Based Paper: Py-GC/MS Method

Abstract: Samples of papers artificially (2 to 60 days) and naturally (10, 45, and 56 years) aged were studied by the Py-GC/MS method to identify decomposition products. Possible reaction scenarios for cellulose degradation were developed. One of the degradation products is acetic acid, which can (auto)catalyze the cleavage of cellulose β(1→4)-glycosidic bonds of cellulose polymer chains. However, during 20 s of Py-GC/MS analysis, temperatures of up to 300 °C did not significantly increase or modify the formation of decomposition products of paper components. At 300 °C, the amount of several cellulose decomposition products increased regularly depending on the number of days of artificial aging and natural aging, demonstrated mainly by the generation of 2-furancarboxaldehyde, 5-hydroxymethylfurfural, and levoglucosan and its consecutive dehydration products. No correlation between the amount of lignin decomposition products and the time of aging was found when the pyrolysis was performed at 300 °C and 500 °C. Compounds present in the products of decomposition at 500 °C bear the imprint of the chemical composition of the sampled paper. Pyrograms taken at 300 °C using the Py-GC/MS method can give additional information on the changes in the chemical structure of paper during natural or artificial aging, mainly about the cleavage of β(1→4)-glycosidic bonds during aging.

Modelling of tribo-chemical reactions in HiPIMS W-C:H coatings during friction in different environments

Abstract: The modelling of simultaneous chemical reactions in complex systems was successfully applied to mechano(tribo)chemical reactions during friction between steel ball and High Power Impulse Magnetron Sputtered (HiPIMS) W-C:H coatings in humid air, dry nitrogen, hydrogen and in vacuum. The main mechano(tribo)chemical reactions leading to transfer layer formation in humid air - oxidation of WC and Fe, water vapor decomposition and carbon hydrogenation - were confirmed. In nitrogen, the decomposition of WC producing carbon was predicted. The prediction in hydrogen was only the formation of methane. In vacuum, the decomposition of WC and FeOWO3 into W and Fe and CO formation were dominant. Thus, the friction is controlled via amount of hydrogenated carbon resulting from the dominant mechano(tribo)chemical reactions.

Numerical investigation of ozone decomposition by self-excited oscillation cavitation jet

Abstract: Abstract Extreme environmental changes caused by the cavitation bubble collapse, such as high pressure, high temperature and the microjet, will cause pyrolysis reaction at the gas and liquid interface inside the bubble. Self-excited pulsed cavitation jet has an instantaneous strong pulse pressure, which leads to local hot spots surrounding the cavitation bubbles. The generation of strong oxidizing free radicals promotes easy ozone conversion into oxygen. Numerical simulations were conducted for ozone decomposition by cavitation jet. Three groups of different collision angles were applied to compare and analyze the ozone degradation reaction. Results showed that the collision angle has a certain influence on the chemical reaction intensity, the degradation of ozone, and oxygen production. At the collision angle of 180°, the chemical reaction was the most violent, with ozone degradation and oxygen production at the highest level, followed by 120° and lowest at 90°.

Issues Affecting Interpretation

Abstract: The stability of analytes in a biological sample has been recognized as a key requirement in drug analysis. Artifacts are not naturally present in body fluids or in a corpse but can arise from drug degradation or formation and can also occur as a result of the preparative or investigative procedure. Instability or artifactual formation can commonly be caused by enzyme degradation, deconjugation, chemical reactivity, autoxidation (catechols, morphine), lactone, and hydroxyl carboxylic acid interconversion and N-oxide decomposition. Urine is generally free from protein, lipids, and enzymatic activities such as esterases but has a wide variation in its composition and a wide range of pH values. Chromatography has been the mainstay of drug analysis for many years. One should be aware that instability and formation of new entities primarily depends on the sample, the matrix, and the particular analyte.

Changes in chemical composition of cover crops residue during decomposition

Abstract: ABSTRACT: Crop residues decomposition are controlled by chemical tissue components. This study evaluated changes on plant tissue components, separated by the Van Soest partitioning method, during cover crop decomposition. The Van Soest soluble fraction was the first to be released from the crop residues, followed by cellulose and hemicellulose. Lignin was the crop residue component that suffered the least degradation, and for certain crop residue types, lignin degradation was not detected. The degradation of the main components of crop residues (soluble fraction, cellulose, hemicellulose and lignin) is determined by the chemical and structural composition of each fraction.

Special issue - Emerging Trends in Thermocatalytic, Photocatalytic, Electrocatalytic, Photoeletrocatalytic and Biological Conversion of Harmful Gases into Benign Compounds for Environmental Protection

Abstract: Considering the problems of high temperature and large reagent consumption in the current alkali decomposition processes, phosphate and fluoride were adopted to extract tungsten from scheelite. The results indicated that tungsten could be efficiently extracted with a decomposition rate of> 98.0% under moderate decomposition conditions, forming fluorapatite in the decomposition residue. The decomposition yield is influenced by the calcium fluoride dosage, decomposition temperature, liquid-to-solid ratio, and holding time. Furthermore, the decomposition reaction followed the surface chemical reaction controlling step. Additionally, the phosphorus concentration in the decomposition solution was lower than 0.2 g/L. This work may provide an alternative for the efficient tungsten extraction from scheelite, especially fluorite bearing scheelite under relatively low reagent costs and temperature.

Impact of chemical ageing on static mechanical behavior of elastomers

Abstract: In service, elastomers can be subjected to a combination of mechanical loads and chemical degradations depending on the environment in which they are used. We propose here to study static mechanical properties changes of two elastomers during ageing. A crosslinked PU based on polyester and a natural rubber have been chosen in order to study two different kind of degradation: a chain scission process induced by hydrolysis and a combination of crosslinking and chain scissions during thermo-oxidation. These chemical degradation mechanisms lead to a gradual decrease in average crosslinking density and stress at break. To study the coupling between mechanical loading and chemical degradation, relaxation tests under hydrolysis for PU or thermo-oxidation for NR were performed. Based on crosslinking density measurements after the relaxation/degradation tests, the impact of the applied strain on the degradation kinetics is discussed.

Effects of Two Common Binders on Decomposition Mechanism of HMX Molecule Under Linear Temperature Rise

Abstract: The effects of two common binders (BR and F binder) on the thermal decomposition of HMX molecules during linear heating were studied by molecular dynamics simulation. It was found that both binders can induce the decomposition reaction of HMX molecules earlier, promote the conversion of intermediate products to stable products, and reduce the activation energy and potential energy barrier of the system. The induction of the binder in the composite system makes the initial decomposition of HMX molecules appear at the interface between the binder and the HMX molecules, and the binder’s higher heat absorption rate absorbs a large amount of energy released by the hot spots. The promoting effect of binder on the conversion of intermediate products to stable products and the interaction between binder and HMX intermediate products consume excessive active particles, which inhibits the further decomposition of macromolecular intermediate products. The results show that both BR and F binders prolonged the decomposition duration of HMX, and F rubber with better thermal stability has the longest HMX decomposition duration in the composite system. Our simulation revealed the action mechanism of BR and F rubber in HMX thermal decomposition, which provided a new idea for studying the action mechanism of binders on the thermal properties of high explosives.

Decomposition of Irganox 1010 in plastic bonded explosives

Abstract: Degradation pathways of Irganox 1010 in aged plastic bonded explosive (PBX) 9501 were investigated using ultrahigh performance liquid chromatography coupled to quadrupole time of flight mass spectrometry (UHPLC-QTOF). Using a targeted approach, a total of 44 Irganox 1010 decomposition products were discovered. These decomposition products were formed through hydrolysis, scission, and/or oxidation of Irganox 1010. The hydrolytic decomposition of Irganox is a straightforward process resulting in the cleavage of the ester group(s) while oxidation and scission are more complicated and can happen at multiple locations on the Irganox 1010 molecule. Moreover, due to the symmetric nature of Irganox 1010, multiple decomposition reactions can occur. Indeed some decomposition products exhibited hydrolysis, oxidation, and scission. In order to probe any trends in the aged PBX 9501 samples, principal component analysis (PCA) was implemented. The greatest chemical differences between the aged PBX samples was hydrolysis of the ester functional groups on Irganox 1010. Despite the negative connotations of hydrolysis, the Irganox 1010 decomposition products are still able to function as a radical scavenger in PBX 9501 as intended.

Microbial Degradation of Plastics

Abstract: Abstract Microbial degradation in the environment is initiated by abiotic (nonliving physical or chemical) processes. Mechanical weathering and other mechanical processes are the main drivers of the initial degradation. This article presents an overview of weathering and biodegradation. It summarizes the main synthetic polymers that are released and available for bacterial and fungal decomposition. The article also presents a detailed discussion on the enzymes that are involved in plastic degradation, and the measurement of polymer degradation.

Efficient decomposition of perfluorooctane sulfonate by hydrated electrons: Performance, mechanism, and carbon emission reduction

Abstract: Perfluorooctane sulfonate (PFOS) is a typical perfluorinated compound, and the presence of sulfonic groups makes it difficult to decompose. In this study, ultraviolet photolysis of iodide (UV/KI) was conducted to generate hydrated electrons for PFOS decomposition, the key factors affecting the decomposition efficiency were investigated and the possible decomposition pathways were hypothesized. These results imply that the UV/KI system can effectively promote the decomposition and defluorination of PFOS. When the PFOS and KI concentrations were 0.03 mmol L−1 and 0.3 mmol L−1, respectively, the decomposition and defluorination efficiencies of PFOS at pH 10 reached 99.5 % and 94.8 % after 12 h of reaction, respectively. With the increase in KI concentration from 0.1 to 0.5 mmol L−1, the decomposition and defluorination efficiencies of PFOS increased; however, a further increase in KI will lead to a decrease in the performance. Weak and strong alkaline conditions are more favorable for PFOS decomposition than acidic conditions. Compared with the UV/Sulfite system, this system can be conducted under a lower concentration of hydrated electron source chemicals and a wider pH range. Kinetic analysis implied that PFOS decomposition followed the pseudo-first-order model with a reaction rate constant of 1.004 h−1, which was higher than most PFOS decomposition processes. Intermediate analysis and mass balance indicated that there were three PFOS decomposition pathways: desulfonation, H/F exchange, and CC bond dissociation. The main products were environmentally friendly fluoride ions, formic acid, and acetic acid, suggesting that the UV/KI system for PFOS decomposition is a relatively mild and green process.

Preliminary Study on Decomposition of HFC143a: A Reactive Molecular Dynamic Study

Abstract: The fluoride organics will experience the decomposition under the high temperature and high incident energy, which would have an effect on the system and equipment. The preliminary decomposition of HFC143a is investigated via reactive molecular dynamics in the present work. The results indicate that incident energy will aggravate the decomposition of HFC143a. And the main product of the reaction is FH. Besides, the first-order kinetic analysis is employed to analysis the reaction and obtain the relationship between the decomposition rate, temperature and the incident energy.