High-temperature Gas-phase Reactions Research Articles

Investigation on supported AlCl3 catalyst in the isomerization of E-1-chloro-3,3,3-trifluoropropene

By negative pressure sublimation, various supported AlCl3 catalysts were prepared and further applied in the gas-phase isomerization of (E)-1‑chloro-3,3,3-trifluoropropene at higher temperatures ranging from 250 °C to 330 °C. Among these, the 2.0 wt%AlCl3 supported on active carbon catalyst exhibited high catalytic activity within 44 h but was significantly deactivated from 44 h to 100 h. And the possible deactivation reasons of the AlCl3 catalyst were first revealed as the following aspects: 1) The loss of AlCl3; 2) The covering of active sites by fluorinated olefin polymerization; 3) The conversion of AlCl3 to AlClxF3-x (0 ≤ x ≤ 3) leading to the significant enhancement of strong acid sites. This work will pave the way for the subsequent development of AlCl3 catalyst suitable for high-temperature gas-phase reaction system.

Catalytic Organic Reactions in Liquid Phase by Perovskite Oxides: A Review

The structural flexibility and controllable physico-chemical characters of perovskite oxides have drawn major attention of researchers for catalytic reactions. Perovskite oxide are mainly used as catalysts for electrochemical, high temperature gas-phase and photocatalytic reactions but their uses for catalytic organic reactions in liquid phase are limited. Various porous and nano-perovskite oxides have been prepared by different methods are effectively used as catalyst for different types of organic reactions in liquid phase. The liquid-phase catalytic organic reactions over perovskite oxides have been classified mainly into three groups: (i) acid/base catalyzed, (ii) selective oxidation and (iii) cross-coupling reactions. This review article mainly emphases on different examples of perovskite oxides catalyzed organic reactions in liquid phase along with the relationships among the unique catalytic performance with the structural and the physico-chemical properties of perovskites.

Flexible energy conversion and storage via high-temperature gas-phase reactions: The piston engine as a polygeneration reactor

Piston engines are typically considered devices converting chemical energy into mechanical power via internal combustion. But more generally, their ability to provide high-pressure and high-temperature conditions for a limited time means they can be used as chemical reactors where reactions are initiated by compression heating and subsequently quenched by gas expansion. Thus, piston engines could be “polygeneration” reactors that can flexibly change from power generation to chemical synthesis, and even to chemical-energy storage. This may help mitigating one of the main challenges of future energy systems – accommodating fluctuations in electricity supply and demand. Investments in devices for grid stabilization could be more economical if they have a second use.This paper presents a systematic approach to polygeneration in piston engines, combining thermodynamics, kinetics, numerical optimization, engineering, and thermo-economics. A focus is on the fuel-rich conversion of methane as a fuel that is considered important for the foreseeable future. Starting from thermodynamic theory and kinetic modeling, promising systems are selected. Mathematical optimization and an array of experimental kinetic investigations are used for model improvement and development. To evaluate technical feasibility, experiments are then performed in both a single-stroke rapid compression machine and a reciprocating engine. In both cases, chemical conversion is initiated by homogeneous-charge compression-ignition. A thermodynamic and thermo-economic assessment of the results is positive. Examples that illustrate how the piston engine can be used in polygeneration processes to convert methane to higher-value chemicals or to take up carbon dioxide are presented. Open issues for future research are addressed.

Preparation and catalytic evaluation of Au/γ-Al2O3nanoparticles for the conversion of 4-nitrophenol to 4-aminophenol by spectrophotometric method

A set of catalysts having gold nanoparticles deposited on γ -Al2O3 ( Au/ γ -Al2O3) with lowest effective amount of gold content were prepared by successive impregnation and hydrogen reduction method. The structural features of prepared catalysts were analysed by X-ray diffraction (XRD), N2 physisorption, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR). The catalytic activity was evaluated for the reduction of an organic pollutant 4-nitrophenol (4NP) to 4-aminophenol (4AP) by spectrophotometric analysis. Supported catalyst presented excellent catalytic ability to convert 4NP to 4AP in the presence of sodium borohydride (SBH) due to synergistic effect of Au NPs and mesoporous γ -Al2O3 support. The reduction reaction was also performed at a range of temperatures to calculate kinetic parameters. The development of highly stable Au/γ -Al2O3 catalysts with lowest noble metal content and recyclability made the process cost effective and may promote their applications in various fields including removal of organic pollutants in industrial waste water and high-temperature gas-phase reactions.

Fabrication of high-silica Cu/ZSM-5 with confinement encapsulated Cu-based active species for NH3-SCR

For high-temperature gas-phase reactions in the presence of steam such as the selective catalytic conversion of NOx from mobile sources, the deactivation of catalysts often occur because of their poor hydrothermal stability. Herein, we successfully prepared a high-silica Cu/ZSM-5-PAD catalyst based on an effectively induced polymer (polyacrylamide) assisted deposition (PAD) strategy. The obtained catalyst exhibited excellent catalytic performance for NH3-SCR in terms of activity, anti-hydrothermal aging and poison-resistant abilities. This excellent catalytic performance could be correlated with the encapsulation and confinement dispersion of Cu-based active species within the ZSM-5 molecular sieve channels, which dramatically optimized the catalytic properties and structural stability of the solid.

Tuning catalytic selectivity of propane oxidative dehydrogenation via surface polymeric phosphate modification on nickel oxide nanoparticles

Thermal stability has long been recognized as a major limitation for the application of ligand modification in high-temperature reactions. Herein, we demonstrate polymeric phosphate as an efficient and stable ligand to tune the selectivity of propane oxidative dehydrogenation. Beneficial from the weakened affinity of propene, NiO modified with polymeric phosphate shows a selectivity 2–3 times higher than NiO towards the production of propene. The success of this regulation verifies the feasibility of ligand modification in high-temperature gas-phase reactions and shines a light on its applications in other important industrial reactions.

Thermal stability of oxide-supported gold nanoparticles

In this study, we report on the influence of support and gas atmosphere on the thermal stability of Au nanoparticles on oxidic supports. All samples were prepared with a modified impregnation method and have initial Au particle sizes in the range of 3–4 nm. We observed that in air, Au nanoparticles on SiO2 and Al2O3 are thermally much more stable than Au nanoparticles on TiO2. For instance, upon treatment up to 700 °C, on SiO2, Au particles grew from 4 to 6 nm while on TiO2 from 3 to 13 nm. For Au nanoparticles on TiO2, growth is accelerated by oxidizing atmospheres and the presence of water and/or chloride. On non-reducible supports and in non-oxidizing atmosphere, the supported Au nanoparticles were remarkably stable. The insight into the growth of oxide-supported Au nanoparticles in reactive atmosphere offers an additional tool for a rational choice of a support for high-temperature gas-phase reactions involving gold nanocatalysts.

Acousto-optically modulated quantum cascade laser for high-temperature reacting systems thermometry.

We demonstrate time-resolved temperature measurements in shock-heated mixtures of carbon monoxide over a temperature range of 1000-1800K for two pressure ranges, 2.0-2.9atm and 7.6-10.7atm, at rates up to 250kHz using a single acousto-optically modulated quantum cascade laser with mid-infrared output spanning from 1975 to 2260 cm-1. Measured temperatures were in excellent agreement with values determined by ideal shock relations, and the temperature profile after the passage of the reflected shock wave was found to be well-modeled by an isentropic compression assumption. Temperature measurements made with this setup are largely immune to effects of emissions and beam steering, making the diagnostic system well-suited for studying high-temperature gas-phase reactions of energetic materials such as octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine and hexahydro-1,3,5-trinitro-1,3,5-triazine.

Synthesis of well-defined functional crystals by high temperature gas-phase reactions

Over the past decades, there have been many synthesis methods on producing well-defined crystals, due to their enormous application potentials in industrial field. Among them, high temperature gas-phase reactions (HTGR) approach may be one of the most promising processes for fabrication of well-defined crystals with controllable structure, size, shape, and composition. This review is focused on the recent progresses in synthesizing well-defined crystalline TiO2 dominated with, respectively, {001} facets and {105} facets, one-dimensional ZnO and SnO2 nanorods/nanowires, MoS2 nanosheets as well as GaP, InP, and GaAs nanowires via HTGR approach. Although these research works were currently carried out on experimental scale, it is worth to note that the industrial importance of this HTGR approach for design and fabrication of well-defined crystals in the future owing to its advantages of continuous and scalable production with controlled dimensions and low cost.

Single-Step Gas-Phase Polyperfluoroalkylation of Naphthalene Leads to Thermodynamic Products

High-temperature gas-phase, solvent- and catalyst-free reaction of naphthalene with an excess of RF I reagent (RF CF3 , C2 F5 , n-C3 F7 , and n-C4 F9 ) was used for the first time to produce a series of highly perfluoroalkylated naphthalene products NAPH(RF )n with n=2-5. Four 95+ % pure 1,3,5,7-NAPH(RF )4 with RF CF3 , C2 F5 , n-C3 F7 , and n-C4 F9 were isolated using a simple chromatography-free procedure. These new compounds were fully characterized by (19) F and (1) H NMR spectroscopy, X-ray crystallography (for RF CF3 and C2 F5 ), atmospheric-pressure chemical ionization mass spectrometry, and cyclic and square-wave voltammetry. DFT calculations confirm that the proposed synthesis yields the most stable isomers that have not been accessed by alternative preparation techniques.

Highly reactive {001} facets of TiO2-based composites: synthesis, formation mechanism and characterization

Titanium dioxide (TiO2) is one of the most widely investigated metal oxides due to its extraordinary surface, electronic and catalytic properties. However, the large band gap of TiO2 and massive recombination of photogenerated electron-hole pairs limit its photocatalytic and photovoltaic efficiency. Therefore, increasing research attention is now being directed towards engineering the surface structure of TiO2 at the most fundamental and atomic level namely morphological control of {001} facets in the range of microscale and nanoscale to fine-tune its physicochemical properties, which could ultimately lead to the optimization of its selectivity and reactivity. The synthesis of {001}-faceted TiO2 is currently one of the most active interdisciplinary research areas and demonstrations of catalytic enhancement are abundant. Modifications such as metal and non-metal doping have also been extensively studied to extend its band gap to the visible light region. This steady progress has demonstrated that TiO2-based composites with {001} facets are playing and will continue to play an indispensable role in the environmental remediation and in the search for clean and renewable energy technologies. This review encompasses the state-of-the-art research activities and latest advancements in the design of highly reactive {001} facet-dominated TiO2via various strategies, including hydrothermal/solvothermal, high temperature gas phase reactions and non-hydrolytic alcoholysis methods. The stabilization of {001} facets using fluorine-containing species and fluorine-free capping agents is also critically discussed in this review. To overcome the large band gap of TiO2 and rapid recombination of photogenerated charge carriers, modifications are carried out to manipulate its electronic band structure, including transition metal doping, noble metal doping, non-metal doping and incorporating graphene as a two-dimensional (2D) catalyst support. The advancements made in these aspects are thoroughly examined, with additional insights related to the charge transfer events for each strategy of the modified-TiO2 composites. Finally, we offer a summary and some invigorating perspectives on the major challenges and new research directions for future exploitation in this emerging frontier, which we hope will advance us to rationally harness the outstanding structural and electronic properties of {001} facets for various environmental and energy-related applications.

Radical detection in harsh environments by means of laser-induced fluorescence using a single bidirectional optical fiber

A new experimental method is described enabling detection of hydroxyl radicals (OH) by laser-induced fluorescence in high-temperature gas-phase reactions. This is accomplished by means of a bidirectional optical fiber probe, which is of interest for applications where optical access is limited. An optical setup that allows simultaneous excitation and detection of fluorescence using one and the same fiber has been developed. Complications resulting from coupling as well as laser-induced scattering are addressed, and different fibers are compared with regard to core material composition and geometric collection efficiency. On this basis, a suitable fiber is identified, and OH detection and profile measurements are demonstrated in a premixed laminar flame as reference experiment.

11C]Carbon Disulfide: A Versatile Reagent for PET Radiolabelling

Quick as a flash! 11CS2 can now be produced rapidly and with high radiochemical yields and specific radioactivities by the high temperature gas-phase reaction of 11CH3I with the thionating agent P2S5 (see figure). 11CS2 was found to be a highly reactive labelling reagent forming a range of [11C]dithiocarbamate compounds within extremely short reaction times.

Synthetic approaches to borocarbonitrides, BC xN ( x=1–2)

In order to synthesize borocarbonitrides of the general formula BC x N where x varies between 1 and 2, we have carried out high-temperature gas phase reaction of BBr 3 with a mixture of ethylene and ammonia. The composition of the product was close to BC 1.6N as shown by x-ray photon spectroscopy (XPS) and electron energy loss spectroscopy (EELS). The products were further characterized by infra-red, Raman and other spectroscopic techniques. The borocarbonitrides obtained from the gas phase reaction have low surface areas, in contrast to those of similar compositions prepared by the urea method. First principles calculations show that the most stable structures of the compositions BCN and BC 2N contain BN-rich and carbon-rich domains where BN 3 and NB 3 units are present.

Synthesis Pathway of Dioxins in Iron Ore Sintering Process

Dioxins are a kind of extremely toxic and Persistent Organic Pollutants (POPs). Sintering process has become one of the most dominant unintentional discharge sources. The dioxins synthesis pathway and mechanism being described, related research indicate that: in the low temperature sector (200-500ºС), chlorobenzene and chlorphenol are the representation precursors of dioxin’s precursor catalytic reaction, the dioxins formed in this temperature sector cased by the “de novo” under catalyst (like Cu2+) on the surface of smoke particles; high-temperature gas phase reaction mechanism of dioxins satisfied the first-order kinetic model, the formation of gas related with suitable precursors, it is the result of chlorinated precursors’ pyrolytic rearrangement like chlorobenzene and chlorophenol in the temperature sector 500-800ºС in the gas.

Synthesis of high-reactive facets dominated anatase TiO2

As an important metal oxide, anatase titanium dioxide has been widely investigated because of its many promising properties for catalysis and photocatalysis. The properties of anatase TiO2 crystals are largely determined by external surfaces exposed. Many efforts have been made to improve the percentage of high-reactive facets like {001} facets of anatase TiO2 to enhance its catalytic properties. This review reports the recent progress in designing and fabricating high-reactive facets dominated anatase TiO2via various strategies including traditional vapor phase epitaxial processes, hydrothermal/solvothermal methods, nonhydrolytic alcoholysis methods and high temperature gas phase reactions. Furthermore, focusing on the (001) surface, the article also covers advances in the theoretic simulations of various high-reactive facets of anatase TiO2 crystals. Finally, we offer a summary and some perspectives on the challenges and new directions for future research in this emerging frontier.

Theoretical Formation Model of Dioxin in Iron Ore Sintering Process

Dioxin is the unintentional synthesized extreme toxic Persistent Organic Pollutants (POPs) in the sintering process. The process of dioxin’s formation and decomposition in the sintering bed layer, as well as the reaction mechanism and related theoretical model of different temperature sector were expounded in this paper. The correlated research indicated that: in the low temperature sector (200-500°C), chlorobenzene and chlorphenol are the representation precursors of dioxin’s precursors catalytic reaction, the dioxin formed in this temperature sector cased by the “de novo” under catalyst (like Cu2+) on the surface of smoke particles, its catalytic mechanism of the same phases and heterogeneous all satisfied the four-step reaction model; high-temperature gas phase reaction mechanism of dioxin satisfied the first-order kinetic model, the formation of gas related with suitable precursors, it is the result of chlorinated precursors’ pyrolytic rearrangement like chlorobenzene and chlorophenol in the temperature sector 500-800°C in the gas.

The continuous self stirred tank reactor: measurement of the cracking kinetics of biomass pyrolysis vapours

The continuous self stirred tank reactor is a well known suitable device for studying the kinetics of high-temperature gas phase reactions. Temperature and composition are uniform at any point of the reactor, and for a given residence time, it is easy to calculate the values of kinetic constants from a very simple mathematical model. The aim of the present paper is to report the first experimental results obtained on the thermal cracking of vapours produced by the pyrolysis of biomass. The experiments are carried out between 836 and 1303 K and under mean residence times ranging from 0.3 to 0.5 s. The calculated activation energy ( 59 kJ mol - 1 ) and preexponential factor ( 1930 s - 1 ) are in good agreement with those obtained by other authors operating in more usual devices, but needing the solving of more sophisticated models.

High Temperature Gas Phase Reaction of SnOg with O2.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The Use of Ultrasound for the Degradation of Pollutants in Water: Aquasonolysis – A Review

AbstractThe degradation of organic compounds in water is the subject of a number of fundamental and applied investigations. Aquasonolysis of organic compounds is an advanced technology for the purification of contaminated water. The process is based on the phenomenon of acoustic cavitation. Dominant reactions of volatile compounds are: cavitative high‐temperature gas‐phase reactions and thermal‐oxidative decay in bubbles. Nonvolatile compounds are mainly decomposed by OH radicals in the aqueous solution (sonolytical cleavage of water). This article reviews mechanisms and kinetics of pollutant decomposition in water and discusses the influence of different experimental parameters. An overview of the application spectrum of aquasonolysis is provided, analyzing results gathered in experiments completed in our group as well as results reported in the literature.