Showing papers on "Thermal decomposition published in 2019"

Expediting in-Situ Electrochemical Activation of Two-DimensionalMetal–Organic Frameworks for Enhanced OER Intrinsic Activityby Iron Incorporation

Abstract: Electrochemical activation is an effective and simple method to obtain in-situ surface modification of MOF materials away from thermal decomposition However, the impact of the rate and related pha

The effect of CO on CO2 methanation over Ru/Al2O3 catalysts: a combined steady-state reactivity and transient DRIFT spectroscopy study

Abstract: The reactivity of Ru/Al2O3 catalysts in the hydrogenation of CO/CO2 gas stream is investigated in this work to assess the possibility of carrying out CO2 methanation even in the presence of CO in the feed stream. Such a goal is pursued by conducting reactivity studies at process conditions of industrial interest (i.e., at high COx per-pass conversion and with concentrated COx/H2 streams) and by monitoring the surface species on the catalyst through transient DRIFTS-MS analysis. The catalyst shows gradual deactivation when the methanation is carried out in the presence of CO in the gas feed at low temperatures (200–300 °C). However, stable performance is observed at higher temperatures, showing CH4 yields even higher than those observed during methanation of a pure CO2 feed. DRIFTS-MS experiments agree with a CO2 methanation pathway where CO2 is adsorbed as bicarbonate on Al2O3 and successively hydrogenated to methane on Ru, passing through formate and carbonyl intermediates. In the presence of CO at low temperature, the catalyst shows a higher CO coverage of the Ru sites, a larger formate coverage of the alumina sites and the presence of adsorbed carbonaceous species, identified as carboxylate and hydrocarbon species. By carrying out the CO2 hydrogenation on the deactivated catalyst, carboxylates remain on the surface, effectively blocking CO2 adsorption sites. However, the catalyst deactivation at low temperature is reversible as thermal treatment (>350 °C) is able to restore the catalytic activity. Notably, working above the carboxylate decomposition temperature ensures a clean catalyst surface without high CO coverage, resulting in stable and high performance in CO/CO2 methanation.

Thermodynamics and reaction mechanism of urea decomposition

Abstract: The selective catalytic reduction technique for automotive applications depends on ammonia production from a urea–water solution via thermolysis and hydrolysis. In this process, undesired liquid and solid by-products are formed in the exhaust pipe. The formation and decomposition of these by-products have been studied by thermogravimetric analysis and differential scanning calorimetry. A new reaction scheme is proposed that emphasizes the role of thermodynamic equilibrium of the reactants in liquid and solid phases. Thermodynamic data for triuret have been refined. The observed phenomenon of liquefaction and re-solidification of biuret in the temperature range of 193–230 °C is explained by formation of a eutectic mixture with urea.

Carbon Dots from Citric Acid and its Intermediates Formed by Thermal Decomposition

Abstract: Thermal decomposition of citric acid is one of the most common synthesis methods for fluorescent carbon dots; the reaction pathway is, however, quite complex and the details are still far from being understood. For instance, several intermediates form during the process and they also give rise to fluorescent species. In the present work, the formation of fluorescent C-dots from citric acid has been studied as a function of reaction time by coupling infrared analysis, X-ray photoelectron spectroscopy, liquid chromatography/mass spectroscopy (LC/MS) with the change of the optical properties, absorption and emission. The reaction intermediates, which have been identified at different stages, produce two main emissive species, in the green and blue, as also indicated by the decay time analysis. C-dots formed from the intermediates have also been synthesised by thermal decomposition, which gave an emission maximum around 450 nm. The citric acid C-dots in water show short temporal stability, but their functionalisation with 3-aminopropyltriethoxysilane reduces the quenching. The understanding of the citric acid thermal decomposition reaction is expected to improve the control and reproducibility of C-dots synthesis.

p-Toluenesulfonic Acid-Based Deep-Eutectic Solvents for Solubilizing Metal Oxides

Abstract: Combinations of p-toluenesulfonic acid monohydrate with different hydrogen-bond acceptors (i.e., choline chloride, tetraethylammonium chloride, tetrabutylammonium chloride, betaine hydrochloride, β-alanine, tetrabutylphosphonium chloride, ethylammonium chloride, methyltriphenylphosphonium bromide, and benzyltriphenylphosphonium chloride) were tested for deep-eutectic solvent (DES) formation. Only p-toluenesulfonic acid monohydrate:choline chloride, p-toluenesulfonic acid monohydrate:tetrabutylammonium chloride, and p-toluenesulfonic acid monohydrate:tetrabutylphosphonium chloride at a 1:1 molar ratio remained liquid at room temperature. The obtained deep-eutectic solvents were characterized by determining their density and viscosity as a function of temperature and their thermal operational window (i.e., decomposition temperature and melting point/glass transition temperature). Moreover, IR spectroscopy was used to elucidate the formation of hydrogen bonds. The solubility of different metal oxides in the ...

Temperature-Dependent Thermal Decomposition Pathway of Organic–Inorganic Halide Perovskite Materials

Abstract: The thermal decomposition products and kinetics of two typical organic–inorganic halide perovskites, CH3NH3PbI3 (MAPbI3) and HC(NH2)2PbI3 (FAPbI3), were investigated via simultaneous thermogravimet...

Thermally conductive, super flexible and flame-retardant BN-OH/PVA composite film reinforced by lignin nanoparticles

Abstract: The usage of thermally conductive materials is limited due to their low thermal conductivity, poor thermal stability and brittleness, particularly at high working temperatures. In this work, for the first time, lignin nanoparticles (LNPs) were utilized to enhance the thermal conductivity, stability, flame-retardancy, and flexibility of boron nitride (BN)-OH/polyvinyl alcohol (PVA) composite film, which played an important role as reinforcements. BN-OH/PVA/LNP composite film was fabricated through vacuum filtration in conjunction with chemical cross-linking. With the loading of LNPs at 2.5 vol%, the BN-OH/PVA/LNP composite film exhibited a higher through-plane thermal conductivity (up to 1.74 W m−1 K−1) than the one without LNPs (1.65 W m−1 K−1). After cross-linking with glutaraldehyde (GA), the elongation of the composite at break was 132%, an increase of 267% compared with the non-crosslinked one. The initial decomposition temperature of the BN-OH/PVA composite film was approximately 260 °C. However, in the presence of 7.1 vol% LNPs, the BN-OH/PVA/LNP composite film started to degrade at a much higher temperature, i.e., 310 °C, demonstrating improved thermal stability. Furthermore, the addition of LNPs enhanced the flame-retardancy of the composites according to the burn test and differential scanning calorimetry (DSC). The resulting composite film with multiple improved properties is highly promising as a thermal interface material (TIM) and packaging material for various applications.

Selective 2-Propanol Oxidation over Unsupported Co3O4 Spinel Nanoparticles: Mechanistic Insights into Aerobic Oxidation of Alcohols

Abstract: Crystalline Co3O4 nanoparticles with a uniform size of 9 nm as shown by X-ray diffraction (XRD) and transmission electron microscopy (TEM) were synthesized by thermal decomposition of cobalt acetyl...

Synergistic effects between Cu metal–organic framework (Cu-MOF) and carbon nanomaterials for the catalyzation of the thermal decomposition of ammonium perchlorate (AP)

Abstract: In this study, a novel Cu-MOF@Carbon nanomaterial composite was prepared to catalyze the thermal decomposition of ammonium perchlorate (AP). The structure was characterized by using scanning electron microscope (SEM), X-ray energy-dispersive spectrum (EDS), and X-ray diffraction (XRD); the specific surface area was estimated by Brunauer–Emmett–Teller (BET) method; and the pore volumes and pore size distributions were derived from the adsorption branches of isotherms using the Barrett–Joyner–Halenda (BJH) model. And the thermal decomposition behavior was investigated by using differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The results indicated that all products showed excellent catalytic activity. Among the samples investigated here, Cu-MOF@CNT-rGO exhibited the best catalytic activity, since the high-temperature decomposition peak of AP decreased to 313.8 °C, which is reduced nearly 100 °C than the raw material (409.7 °C). And this was attributed to the high thermal and electrical conductivities of carbon nanomaterials, and the large surface area of both Cu-MOF and carbon nanomaterials. This study provides a new choice to be used as the promising catalysts in modifying the burning performance of AP-based composite propellant.

Synthesis of Thermally Stable and Insensitive Energetic Materials by Incorporating the Tetrazole Functionality into a Fused-Ring 3,6-Dinitropyrazolo-[4,3-c]Pyrazole Framework.

Abstract: A series of fused-ring energetic materials, i.e., 3,6-dinitro-1,4-di(1H-tetrazol-5-yl)-pyrazolo[4,3-c]pyrazole (DNTPP, compound 2) and its ionic derivatives (compounds 3-8), were designed and synthesized in this study. The molecular structures of compounds 2, 3, 6, 7·2H2O, and 8 were confirmed using single-crystal X-ray diffraction. Their physicochemical and energetic properties, such as density, thermal stability, heat of formation, sensitivity, and detonation properties (e.g., detonation velocity and detonation pressure), were also evaluated. The results indicate that DNTPP and most of its ionic derivatives are extremely thermally stable and insensitive toward mechanical stimuli. In particular, the thermal decomposition temperature of compound 3 is up to 329 °C, while compounds 7 and 8 are very insensitive (impact sensitivity: >20 J; friction sensitivity: >360 N). Compounds 2, 3, and 6 possess good comprehensive properties, including excellent thermal stability, remarkable low sensitivities, and favorable detonation performance. These features show that DNTPP and its ionic derivatives have considerable promise as thermally stable and insensitive energetic materials.

A facile low-temperature synthesis of hierarchical porous Co3O4 micro/nano structures derived from ZIF-67 assisted by ammonium perchlorate

Abstract: The thermolysis of metal–organic frameworks (MOFs) opens a new window for the fabrication of oxide semiconductors due to its simplicity, low cost and large-area uniformity of the resulting material. However, this approach usually requires high annealing temperatures over 350 °C. In this work, sub-micro hierarchical porous Co3O4 dodecahedra were synthesized by the thermolysis of zeolitic imidazolate frameworks 67 (ZIF-67) at a low temperature of 268 °C assisted by ammonium perchlorate (AP), in which ZIF-67 was employed as a metal source and a sacrificial template. The formation mechanism was probably attributable to the generation of Co–O bonds between the Co atom of ZIF-67 and the O atom of AP at lower temperatures which can accelerate the weakening of Co–N bonds of ZIF-67 and thus lead to an abrupt decomposition of ZIF-67 at 268 °C. More importantly, the generation of the Co–O bond and the weakening of the Co–N bond were identified using the FTIR, Raman and XPS results. As confirmed by DFT results, ZIF-67 can be decomposed into Co3O4 at lower temperatures assisted by AP than that in air. In addition, the obtained sub-micro hierarchical porous Co3O4 dodecahedra showed a very large specific surface area of 106.11 m2 g−1, much larger than that in previous reports. Therefore, this work can provide a novel atomic insight into the formation mechanism of Co3O4 hierarchical porous structures derived from ZIF-67 with AP at lower temperatures and also an energy-efficient method to synthesize porous metal oxide structures.

Unveiling the thermolysis natures of ZIF-8 and ZIF-67 by employing in situ structural characterization studies

Abstract: The thermolysis routes of two isostructural metal–organic framework compounds (Zn-based ZIF-8 and Co-based ZIF-67) are investigated based on temperature-dependent and time-dependent in situ Fourier transform infrared (FTIR) spectroscopy and in situ X-ray diffraction data, as well as thermogravimetric-differential scanning calorimetry (TG-DSC) analyses and density functional theory (DFT) calculations. These data highlight thermolysis effects on different vibrations and dissociations within specific atomic moieties. The coordination differences between Zn–N and Co–N lead to the distinct thermolysis routes of ZIF-8 and ZIF-67. ZIF-8 is easily deformed during heating while decomposes at a higher temperature due to the saturated Zn–N coordination. ZIF-67, however, does not deform during heating due to the stronger Co–N bonds, but easily reacts with oxygen due to the unsaturated Co–N bonds. Our results demonstrate that in situ FTIR paired with in situ XRD is a powerful technique for MOF thermolysis investigation, and we suggest that the thermolysis mechanisms of MOFs may be unveiled by investigating a series of MOFs having different coordination types using in situ characterisation methods.