Thermal Analysis Techniques Research Articles

Design and characterization of multicolor water-repellent coatings: Impact of alkyl chain length on surface properties

Fabrication of functional colored water-repellent surfaces is very important for many industrial applications. Here, various colorful surface coating materials having water repellent property, chemical, thermal and UV light resistance and self-cleaning property were prepared using activated halloysite nanotube loaded with dye (A-Hal/dye), different alkoxysilanes (methyltriethoxysilane (MTES), octyltriethoxysilane (OTES) and hexadecyltrimethoxysilane (HDTMS)), and tetraethoxysilane and their coatings were performed on various substrates to determine the effect of alkyl chain length of alkoxysilane compound used in the coating formulation on the surface properties of colorful surfaces. Characterization studies of the synthesized surfaces or coated materials were performed using electron microscopy (TEM and SEM), SEM-mapping, FTIR, XRD, XPS and thermal gravimetic analysis techniques. Water contact angle (WCA) of glass surfaces coated with A-Hal/MB/MTES, A-Hal/MB/OTES and A-Hal/MB/HDTMS materials was found to be 148.0, 156.2 and 159.3°, respectively. The use of an alkoxysilane compound with long functional alkyl chain group in the coating formulation improved the water-repellent property of surface, while it slightly weakened the mechanical stability of the colorful surface. Polydimethylsiloxane (PDMS) coating, which were applied on colorful surfaces, improved the mechanical, thermal, chemical and environmental stability of coating, but decreased the water-repellent property of coated colorful surfaces. Fabricated coating materials having different colors were successfully used to coat various substrates such as glass, filter paper, wood, and cotton fabric. The results of this study show that A-Hal/dye/HDTMS coating materials prepared here are of a great potential in the fabrication of functional surface coatings.

Thermal analysis of mortar based on crushed dune sand

This study investigates the thermal decomposition behavior of mortars formulated using crushed dune sand and thixotropic polyester resin. Thermal analysis techniques, including Differential Scanning Calorimetry (DSC), Differential Thermal Analysis (DTA), and Gravimetric Thermal Analysis (GTA), were employed to characterize the thermal transitions, decomposition stages, and stability of these mortars. Results indicate that crushed dune sand maintains consistent glass transition (Tg) and crystallization temperatures (Tc) when integrated into the mortar matrix, highlighting its thermal stability. However, the melting point (Tm) varies due to the presence of the resin, which significantly influences the composite’s thermal behavior. Decomposition analysis reveals two major weight loss stages: water evaporation between 200°C to 400°C and organic decomposition of the resin between 700°C to 800°C, with minimal weight change beyond 800°C, indicating thermal stability. The DTA results exhibit distinct endothermic reactions related to dehydration and dehydroxylation, along with a pronounced exothermic peak around 400°C, signifying resin decomposition. Elemental analysis confirms that the crushed dune sand is predominantly silica with minimal impurities, making it suitable for construction applications. This research contributes to a deeper understanding of the thermal behavior of polymer-modified mortars, with implications for enhancing thermal and mechanical properties in construction materials.

1,4-Bis(pyridin-1-ium)benzene trifluoroacetate coordinated to chloropropyl functionalized SiO2-nano-NiFe2O4 (BPBTCSF): as a novel and effectual mesoporous bi-functional magnetic catalyst for the synthesis pyrido[2,3-d:6,5-d']dipyrimidines

Here in, we report the synthesis of 1,4-Bis(pyridin-1-ium)benzene trifluoroacetate coordinated to chloropropyl functionalized SiO2-nano-NiFe2O4 (BPBTCSF). Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), elemental mapping analysis, Brunauer-Emmett-Teller (BET), thermal gravimetric analysis (TGA), vibrating-sample magnetometry (VSM) and X-ray diffraction (XRD) techniques characterized the framework of this catalyst. The catalytic activity of this nano-composite was then examined in the one-pot four-component reaction of 2-thiobarbituric acid, NH4OAc, and aldehyde for synthesis of pyrido[2,3-d:6,5-d']dipyrimidines under optimal conditions (5 mg of BPBTCSF, H2O, 25°C). BPBTCSF exhibits benefits as a heterogeneous catalyst, such as exciting performance in the production of derivatives (2 to 5 min, 90% to 98%), six times reproducibility with a slight decrease in catalytic activity, the simultaneous presence of acidic and basic sites (Hydrogen attached to the electronegative nitrogen atom and CF3COOˉ, respectively), convenient purification and separation from the reaction mixture.

Liquid-phase synthesis of a Li3PS4 solid electrolyte using ethyl isobutyrate as a synthetic medium

A β-Li3PS4 solid electrolyte was prepared via liquid-phase synthesis using ethyl isobutyrate as a synthetic medium. The precursor and solid electrolyte structures were characterized using thermogravimetry–differential thermal analysis and X-ray diffraction techniques. The dielectric relaxation analysis showed two relaxation regions, which revealed a bulk and grain boundary ionic migration process. At a temperature lower than 90°C, the frequency dependence of the dielectric constant of the prepared sample was different from that of glassy Li3PS4, indicating that the motion of the PS4 unit enhances the ionic conductivity of the Li3PS4 solid electrolyte. The ionic conductivities of the cold-pressed and warm-pressed pellets at 25°C were 6.8 × 10−5 Scm−1 and 3.6 × 10−4 Scm−1, respectively.

LES and RANS Modeling of an 84-Pin Hexagonal Rod Bundle with Spacer Grid and Experimental Validation

As part of an ongoing integrated research project (IRP), detailed investigations of the flow characteristics of an 84-pin hexagonal rod bundle representing a potential modular gas-cooled fast reactor design have been performed. The rod bundle features a pitch-to-diameter ratio of 1.5 and a large central guide tube, along with simple spacer grids and an outer enclosure. The primary focus of the current work is modeling and simulation of this geometry using multiple computational techniques. These include high-fidelity large eddy simulation (LES) and advanced Reynolds-averaged Navier-Stokes (RANS) approaches. The flow predictions are validated at a Reynolds number of 12 000 using matched index of refraction particle image velocimetry experimental data that were also generated by Texas A&M University as part of the IRP. The comparison data include velocity magnitude and turbulent kinetic energy (TKE) at different lateral locations and at multiple distances downstream of the spacer grid. Many characteristics of the experimental flow are replicated in the LES and RANS runs, and a general agreement between simulation and experiment is shown. Except for the immediate vicinity of the grid, LES is able to capture the velocity magnitude within a 10% error and the TKE to within the experimental uncertainty. The LES shows notably better agreement with the experimental data than RANS, particularly regarding the TKE decay behavior downstream of the grid. Both methods show significant departures from the experiment in their predictions close to the central guide tube. The experimental and high-fidelity data will be used to inform closures for novel multiscale methodologies. The long-term goal of the work is to use the high-fidelity data to yield improved multiscale thermal analysis techniques for solving fuel performance problems of direct relevance to industry.

Oleo-extraction of microplastics using flotation plus sol-gel technique to confine small particles in silicon dioxide gel.

Extracting microplastics from natural sources is challenging, especially microplastics with sizes smaller than 100μm. The flotation method is the most common microplastic extraction, but it struggles with fine particles due to the difficulty in collecting floating plastic particles from the liquid during the separation process. This study proposes a new floating media, tetraethyl orthosilicate (TEOS), that could separate microplastics using its hydrophobic-oleophilic properties. Most interestingly, TEOS transformed from a liquid state to a solid state (gel) by hydrolysis and condensation reactions, thus safely capturing the separated microplastic particles after flotation and mitigating particle loss from scooping since its gel acted as a particle holder. The average recovery rates obtained were in the range of 95-100% for polyethylene terephthalate, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polytetrafluoroethylene, and aged tyre rubber. The recovery rates were slightly reduced for finer particles (sizes down to 40μm) at 82-98%. TEOS-based extraction provided a higher recovery rate for non-polar plastics than for polar or hydrophilic plastics. The separated microplastics maintained their characteristics for polymer identification, as proven by spectroscopic and thermal analysis techniques. Therefore, TEOS-based extraction could be a new approach to microplastic extraction, especially for preventing fine particle loss.

Removal of Textile Dye Using a Low‑Cost Composite Film Based on PVA-Clay: Preparation, Characterization and RSM Optimization

The use of adsorbent materials in powder form presents significant challenges for industrial wastewater treatment due to their poor regeneration after use. Our research described here aimed to prepare a low-cost and eco-friendly film with excellent regeneration capabilities for the efficient removal of Telon Orange dye (TO) from water. The film was fabricated by incorporating a natural clay, DD3, into a poly (vinyl alcohol) (PVA) matrix using the solvent casting method. The prepared film was characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA) techniques. The characterization results confirmed that the DD3 interacts and disperses within the PVA matrix. The influence of film dose and composition, pH, contact time, and initial concentration were studied in batch adsorption. Response surface methodology (RSM) using the Box-Behnken design matrix was then used to find the best conditions for dye adsorption. An ANOVA analysis approved the proposed quadratic model with a high correlation coefficients (R2 = 0.98). The F-value of the model was 46.39, indicating that the model was significant. The PVA/DD3 composite film achieved a 93.45% efficiency in removing TO dye under optimal conditions. The recyclability studies showed a removal efficiency of 90.13% after five uses of the film, making it suitable for large-scale applications and adaptable for use in water purification systems.

Investigation of halloysite thermal decomposition through differential thermal analysis (DTA): Mechanism and kinetics assessment

The study focused on analysing the kinetics of halloysite decomposition using the differential thermal analysis (DTA) technique. Tests were carried out across a temperature span from ambient temperature to 1673 K, employing heating rates spanning from 5 to 20 °C.min−1. X-ray diffraction and Fourier transform infrared spectroscopy (FT-IR) were utilized to identify the phases formed at different temperatures. Activation energies for halloysite decomposition were determined through isothermal and non-isothermal treatments, yielding values of approximately 151.68 kJ mol−1 and 173.14 kJ mol−1, respectively. The Ligero method's Avrami constant parameter (n) and the Matusita method's numerical factor parameter (m), linked to crystal growth dimensions, were both around 1.5. These findings indicate that the degradation of halloysite is primarily governed by bulk nucleation, succeeded by the 3-dimensional growth of meta-halloysite characterized by polyhedron-like structure, regulated by diffusion from a consistent number of nuclei. The frequency factor for halloysite dehydroxylation was established at 8.48 × 10⁸ s⁻1.

Exploring Biomimetic Heat Pipes for Space Radiator Enhancement

This study investigates biomimetic heat pipes for space radiator applications, utilizing nature-inspired structures to potentially enhance heat transfer efficiency. The research addresses the imperative for improved heat dissipation mechanisms in nuclear space systems, crucial for effective thermal management. Heat pipes are passive heat transfer devices widely adopted for thermal control. The study aims to evaluate the effectiveness of a biomimetic heat pipe design in comparison to a traditional design while also validating the fabrication process through industry-made heat pipe comparisons. Innovative hot oil bath testing methods are employed to fabricate and test both heat pipe types, utilizing comprehensive thermal analysis, physical experiments, and validation techniques to assess heat transfer capabilities. Tests span varying temperature levels to analyze heat pipe behavior and performance. Findings suggest the potential for enhanced heat dissipation along the length of the biomimetic heat pipe, hinting at the biomimetic structure’s role in improving heat transfer. This study underscores the promise of biomimetic design principles and their potential for advancing heat pipe technology. Recommendations for further exploration include alternative materials, optimized testing procedures, and refined fabrication processes.

Enthalpy relaxation of sodium aluminosilicate glasses from thermal analysis

AbstractThe sodium aluminosilicate (NAS) glass family is important for many different industrial applications, but glass relaxation has not yet been thoroughly studied in this system. Thermal analysis techniques such as differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC) can provide insight into the enthalpy relaxation of glass by measuring the glass transition temperature (Tg), activation energy, and enthalpy of relaxation. MDSC is mostly used to study nonoxide and low Tg glasses, and there is much debate about whether the nonreversing heat flow analysis method is accurate. To the authors’ knowledge, this is the first paper using MDSC to study these NAS compositions, and one of few papers to report MDSC on high Tg oxide glasses. We report on one set of modulation conditions that obtain a linear response using Lissajous curves, as well as comparing the activation energy calculated from DSC with the enthalpy of relaxation obtained from MDSC. Our results show that the activation energy and enthalpy of relaxation do not give the same compositional minimum in relaxation, and therefore more work is needed to investigate the validity of the nonreversing heat flow approach for high Tg oxide glasses.

A Systematic Study of the Solid-State Pathway from Melamine via Melaminate to Carbodiimide under Evolution of Hydrogen.

Thermal analysis techniques, such as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), can provide valuable insights into thermal properties, intermediate phases, and phase transitions; sometimes even a whole series of compounds appears in a given system. The solid-state reaction pathway from melamine to carbodiimide, monitored by DSC, involves a sequence of chemical reactions and intermediate phases departing from the reaction of potassium hydride and melamine. The fully analyzed reaction cascade begins with the formation of potassium melaminate, K(C3N6H5), and progresses through several intermediate phases, each with distinct structures and properties, before ultimately yielding β-K2(CN2). All crystalline compounds appearing in this reaction sequence are identified using X-ray diffraction analyses. With a 6:1 ratio of potassium hydride and melamine, equal numbers of protic and hydridic hydrogen atoms in the starting materials favor the release of H2 until the formation of the final product K2(CN2), which appears with two modifications.

Solubility enhancement of etoricoxib using inclusion complexation with cyclodextrins: formulation of oro dispersible tablets by QbD approach

Background: The work was intended to enhance etoricoxib's solubility and dissolution rate and then develop oro-dispersible tablets for faster onset of action. Methodology: Inclusion complexes (ICs) of the drug were obtained with β-cyclodextrin (β-CD) and hydroxypropyl β-cyclodextrin (HP β-CD) at ratios of 1:0.125, 1:0.25, 1:0.5, 1:1, and 1:2 (w/w). The selected cyclodextrin at appropriate drug carrier proportion was used to develop oro-dispersible tablets (ODTs) by direct compression, adding crospovidone as a super disintegrant. Phase solubility studies of etoricoxib were carried out by using multiple concentrations of β-cyclodextrin and hydroxypropyl β-cyclodextrin, i.e., 1 %, 2 %, 3 % w/v in distilled water at 37±2°C. Spectroscopic (FT-IR) and thermal analysis (DSC) techniques were employed to identify the drug-carrier interactions. Result: It showed that etoricoxib solubility improves with increasing hydrophilic carrier concentration. The Gibbs free energy values (ΔG˚tr) are consistently negative, showing the solubility of etoricoxib. Significant drug carrier interaction in spectroscopic or thermal analysis was not found. Discussion: The ICs of drugs with β-CD and HP β-CD have successfully addressed the challenges of solubility enhancement and taste masking for etoricoxib. Conclusions: It is observed that the inclusion complexes formed by the kneading method using β-cyclodextrin (β-CD) at a 1:1 ratio and hydroxypropyl β-cyclodextrin (HP β-CD) at a 1:2 ratio can be used to improve dissolution. Hence β-CD (at a 1:1 ratio) is selected for the formulation of oro-dispersible tablets. ODTs offer more patient compliance and an alternative to available conventional tablets.

Experimental Exploration of Cellulose Material for Battery Separators and Artificial Neural Network-Driven Predictive Modeling for Enhanced Thermal Safety in Electric Vehicles

Abstract Lithium-ion batteries (LIBs) are the most reliable energy storage devices nowadays because of their high energy density, long life cycle, and low self-discharge rate. But still, the safety concern is a significant problem in the area. When talking about LIB safety, thermal effects come first; this leads to thermal runaway, fires, and explosions. The critical component of LIB that has a great role in safety is the separator, which serves the purpose of preventing direct contact between the positive and negative electrodes while enabling the movement of lithium ions. This work aimed to find naturally available cellulose material for the LIB separator and to predict the performance of the material by artificial neural network (ANN) for better control of thermal problems that happen with traditional polymer separator materials. The cellulose derived from banana peels is isolated and characterized for its potential use as a separator material. The study conducts the four selected characterization approaches, scanning electronics microscopy (SEM) with three different resolutions to assess the morphology of the extracted cellulose, differential scanning calorimetry (DSC) to measure the heat flow with temperature change on the cellulose and the value obtained 231.22 J/g at a maximum temperature of 323.18 °C, thermogravimetric analysis (TGA) was used to examine the weight loss of the cellulose with respect to temperature variation, which results in a weight loss of 59.37% when the temperature reaches 235 °C, which is considered favorable, and a differential thermal analysis (DTA) was used to know the temperature difference in the banana peel cellulose (BPC), which results in a temperature of 330.23 °C. This morphological and thermal analysis technique for the BPC is used to determine the heat-related properties of the BPC, including phase transitions, thermal stability, and reaction. In addition, these results show BPC as an alternative material for separators in comparison to the existing polymer-based materials. Furthermore, these experimental results are used to train an ANN to predict the performance of BPC material using a binary classification. Because of the training process, 97.58% accuracy was achieved.

A comparative study on the slow pyrolysis of Miscanthus (Miscanthus×giganteus Greef et Deu.) cultivated on agricultural and contaminated soils: Assessment of distribution of final products

This study aims to investigate the slow pyrolysis behavior of uncontaminated (MSC-I - reference) and heavy metals contaminated (MSC-R) samples with heavy metals from the tailings of a Pb-Zn-Cu flotation mine, consisting of whole stems of Miscanthus. Physicochemical properties of raw materials were investigated through instrumental characterization techniques (Atomic Absorption Spectrometry (AAS), Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy, and X-ray diffraction (XRD)), while the pyrolysis process was monitored by simultaneous thermal analysis techniques (thermogravimetry (TG) – derivative thermogravimetry (DTG)), coupled with Mass spectrometry (MS), for evolved gas analysis. After determination of the lignocellulose content (cellulose, hemicellulose, and lignin) and extractive of the MSC-I and MSC-R samples, it was found that Pb, Zn, Fe, and Mn in MSC-R lead to very fast decomposition of extractive fraction, which facilitates their distribution in formed bio-char, together with lignin char-participation, acting catalytically. It was established that a much greater fraction of extractives decomposition products and non-volatile heavy metals are incorporated in MSC-R bio-char increasing its yield (23 %), compared to MSC-I bio-char yield (21.5 %). It was identified that MSC-R has increased production of H2, CO, and CO2, while decreased production of CH4, influenced by Fe (Fe has a significant positive effect on CO2 evaluation during MSC-R pyrolysis, enhancing decarboxylation process). It was established that CH4 reforming reactions catalyzed by iron additionally affect methane reduction, and increase production of H2, compared to the reference sample. Isoconversional kinetic analysis showed that pyrolysis reactions profile was strongly conditioned by the presence of heavy metals, such as Cd, Pb, and Zn, because they affect the modification of biomass lignocellulosic structure. Also, it was found that small amounts of Cd present in MSC-R can increase pyrolysis activation energy of three pseudo-components, and inhibit their deoxygenation, thus increasing yield of bio-char.

Synthesis, Structural Characterization, Anticancer, Antimicrobial, Antioxidant, and Computational Assessments of Zinc(II), Iron(II), and Copper(II) Chelates Derived From Selenated Schiff Base

ABSTRACTNovel selenated azomethine ligand (MSeOH) and its Zn(II), Fe(II), and Cu(II) chelates were synthesized. Their chemical structures were confirmed by molar conductivity, thermal analysis, X‐ray diffraction, IR, NMR, and MS spectroscopic techniques. The antitumor and antimicrobial properties were evaluated against various mammalian cells and pathogenic strains. Furthermore, the antioxidant activities were also assessed using DPPH and SOD bioassays. To gain a deeper understanding of the molecular structure and electronic properties of these complexes, a density functional theory (DFT) study was conducted. The parameters examined in this study provide valuable insight into the bonding, electronic properties, reactivity, and polarity of the compounds under investigation. The biological and theoretical results point to promising activities of the selenated ligand and its complexes.

Thermal and Thermomechanical Analysis of Amorphous Metals: A Compact Review

Metallic glasses are amorphous metals that are supercooled to a frozen, glassy state and lack long-range order, in contrast to conventional metal structures. The lack of a well-ordered structure largely contributes to the unique properties exhibited by these materials. However, their synthesis and processability are defined and thereby constrained by a plethora of thermal and mechanical parameters. Therefore, their broader utilization in the scientific field and particularly in the related industry is somewhat hindered by the limitations related to preparing them in higher amounts. This may be overcome by changing the approach of metal glass formation to a bottom-up approach by utilizing solid-state plasma techniques, such as spark plasma ablation. Another important aspect of amorphous metals, inherently related to their non-equilibrium metastable nature, is the necessity to understand their thermal transformations, which requires unconventional thermal analysis methods. Therefore, this minute review aims to highlight the most important conceptual parameters behind configuring and performing conventional and advanced thermal analysis techniques. The importance of calorimetry methods (differential and fast scanning calorimetry) for the determination of key thermal properties (critical cooling rate, glass-forming ability, heat capacity, relaxation, and rejuvenation) is underscored. Moreover, the contributions of thermomechanical analysis and in situ temperature-dependent structural analysis are also mentioned. Namely, all of the mentioned temperature-dependent mechanical and structural analyses may give rise to the discovery of new glass systems with low critical cooling rates.

Double pseudo-polymeric complexes of [Au(S2CNBu2)2][AgCl2] and [Au(S2CNHm)2]3[AgCl2][Ag0.59Au0.41Cl2]2: Preparation, supramolecular self-assembly, thermal behaviour and anti-mycobacterial activity

Pseudo-polymeric double complexes of [Au{S2CN(C4H9)2}2][AgCl2] (1) and [Au{S2CN(CH2)6}2]3[AgCl2][Ag0.59Au0.41Cl2]2 have been obtained and chemically identified using solution (1H, 13C{1H}) NMR and FT-IR spectroscopy. According to XRD analysis, it was established that both of the above crystalline compounds form complicated supramolecular architectures. Self-assembly and structural stabilization of these supramolecular formations are achieved due to numerous secondary interactions: Ag⋯S, Cl⋯S (in 1, 2) and Au⋯Cl, Au⋯S (in 2), which arose between the ionic structural units of the complexes. The combined manifestation of these interionic secondary interactions leads to the construction of two types of pseudo-polymeric chains of (⋯[Au(S2CNBu2)2]⋯[AgCl2]⋯)n (1) and (⋯[Au2(S2CNHm)4]⋯ [AgCl2]⋯)n (2). To study the thermal behaviour of the prepared compounds, the simultaneous thermal analysis (STA) technique was used, which allowed us to determine the conditions for the quantitative recovery of bound metals. Moreover, a high in vitro biological activity for each of the prepared gold(III)-silver(I) compounds against the non-pathogenic strain Mycolicibacterium smegmatis was experimentally revealed.

Effect of crosslinker molecular weight on the characteristics of thermoelectric ionogels

Abstract The present study investigates an ionic thermoelectric gel with adjustable functionality through the manipulation of crosslinker molecular weight. The thermoelectric properties of 2-hydroxyethyl acrylate (2-HEA) ionogels, prepared using PEGDA200, PEGDA575, and PEGDA1000 as crosslinkers, were thoroughly examined. Furthermore, dynamic thermal mechanical analysis (DMA) and X-ray diffraction (XRD) techniques were employed to elucidate the underlying reasons for variations in the thermoelectric material properties resulting from changes in crosslinker molecular weight. Notably, the thermoelectric gel synthesized with PEGDA575 exhibited a remarkable thermal power output of 19.19 mV•K-1 along with a tensile capacity of 231%. Additionally, the developed ionic thermoelectric capacitor demonstrated an impressive energy density of 4.288 J•m−2, thereby showcasing its potential application in flexible low-grade heat energy recovery devices.

Pyrolysis kinetics of waste ryegrass under nitrogen and air atmosphere

To investigate the pyrolysis reaction of ryegrass, we conducted a simultaneous thermal analysis using thermogravimetric(TG) analyzers. This involved obtaining data through Thermogravimetry (TG), Derivative Thermogravimetry (DTG), and Differential thermal analysis (DTA) techniques. The experiments were conducted under dynamic nitrogen and air atmospheres at different heating rates. The kinetic parameters of ryegrass pyrolysis were determined using the Kissinger method, the Flynn-Wall-Ozawa (FWO) peak conversion rate approximate equivalence method, the Flynn-Wall-Ozawa (FWO) equal conversion rate method, and the Škvára-Šesták (S–S) method. It provides a theoretical basis for the reuse of ryegrass resources. The findings indicated that the pyrolysis temperature of ryegrass increased with the accelerated rate of temperature increase in both atmospheres. The average weight loss rate of pyrolysis of ryegrass in the air atmosphere (92.27 %) is higher than that compared to that in a nitrogen atmosphere (86.11 %). Additionally, the temperature required for complete decomposition is lower in the former case. The FWO peak conversion rate approximation equivalence approach and the FWO equal conversion rate method do not apply to the solution of the pyrolysis activation energy of ryegrass. The pyrolysis activation energy for the two decomposition stages, as calculated by the Kissinger method, is 165.73 and 185.86 kJ/mol−1 in the air atmosphere, and 219.99 and 277.02 kJ/mol−1 in a nitrogen atmosphere, respectively. The activation energy and mechanism function of ryegrass pyrolysis calculated by using the S–S method are as follows: [−ln(1−α)]2, 119.79, 104.31, 95.75, and 91.93 kJ/mol−1 in air atmosphere, (1−α)−1, 176.64, 67.89, 61.15, and 54.25 kJ/mol−1 in nitrogen atmosphere, respectively. The activation energy of ryegrass pyrolysis, as determined by both the Kissinger method and S–S method, was found to be higher under an air atmosphere compared to a nitrogen atmosphere.

Influence of support properties on the activity of 2Cr-Fe/MgO-MO2 catalysts (M = Ce, Zr, CeZr and Si) for the dehydrogenation of n-octane with CO2

The influence of the support on catalytic activity and stability of supported 2Cr-Fe bimetallic catalysts for the CO2-assisted dehydrogenation (DH) of n-octane has been investigated. Four MgO modified supports viz; MgO-CeO2 (MgCe), MgO-ZrO2 (MgZr), MgO-CeO2-ZrO2 (MgCeZr) and MgO-SiO2 (MgSi) were synthesized by the sol-gel combustion technique. The supported catalysts were in turn prepared by vacuum impregnation and thereafter tested for the CO2-assisted DH of n-octane. The catalysts were characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), N2-physisorption, Raman spectroscopy, transmission electron microscopy (TEM), electron dispersive x-ray (EDX), temperature programmed desorption of CO2 (CO2-TPD), temperature programmed reduction and oxidation (H2-TPR and CO2-TPO), electron paramagnetic resonance (EPR) and thermal gravimetric analysis (TGA) techniques. Raman results showed that the CrOx is stabilized as mono- and/or polynuclear Cr(VI) species over the 2Cr-Fe/MgCe catalyst, which are reduced to lower oxidation state species during the DH reaction. The 2Cr-Fe/MgZr, 2Cr-Fe/MgCeZr and 2Cr-Fe/MgSi catalysts stabilized the CrOx as polymerized species, forming the more active Cr-O-Fe polymer units on the catalysts’ surface. XRD, TEM and EDX results showed that the ZrO2-containing supports have smaller particles and stabilized the active metal oxides in a more dispersed amorphous state. The CO2-TPO of the pre-reduced catalysts and EPR of the used catalysts indicated that the 2Cr-Fe/MgCeZr undergoes significant re-oxidation by CO2 during the catalytic process. The 2Cr-Fe/MgCe was the least active, while the 2Cr-Fe/MgZr catalyst showed the best performance and stability over three regeneration cycles. Selectivity to C8 products (octenes and aromatics) was found to strongly depend on the surface basicity of the catalysts. Deactivation of the catalysts was found to follow first order kinetics and coke deposition was identified as the major cause.