全氟三乙胺热解机理的实验与理论研究

氟胺类物质是最有希望作为哈龙替代品的含氮化合物之一,全氟三乙胺作为典型的氟胺类物质具有良好的灭火效果。为研究全氟三乙胺热解机理,在管式加热炉内对全氟三乙胺进行热分解,通过GC-MS分析全氟三乙胺在不同温度条件下的热解产物,并用Gaussian软件对其热解反应路径进行理论计算。结果表明：保持停留时间为10 s,全氟三乙胺的初始热解温度为600℃,750℃完全热解,热解产物有C₄F₉N、C₃F₇N、C₂F₆和C₃F₈,热解温度较低时C₄F₉N体积分数最大,热解温度较高时C₃F₇N体积分数最大。在全氟三乙胺热解反应路径计算中,全氟三乙胺分子中的C—C键断裂后存在1条反应路径,可生成实验产物中的C₃F₈;全氟三乙胺分子的C—N键断裂后存在3条反应路径,可生成实验产物中的C₃F₇N、 C₄F₉N和C₂F₆。全氟三乙胺热解后产生的CF₃自由基可与H、OH自由基发生反应,从而产生灭火作用。此外,其热解产物C₄F₉N和C₃F₇N具有CN双键,更容易与燃烧活泼自由基·OH、·H发生化学作用,对研究全氟三乙胺的灭火机理具有十分重要的意义。     

全氟三乙胺热解机理的实验与理论研究

氟胺类物质是最有希望作为哈龙替代品的含氮化合物之一,全氟三乙胺作为典型的氟胺类物质具有良好的灭火效果。为研究全氟三乙胺热解机理,在管式加热炉内对全氟三乙胺进行热分解,通过GC-MS分析全氟三乙胺在不同温度条件下的热解产物,并用Gaussian软件对其热解反应路径进行理论计算。结果表明：保持停留时间为10 s,全氟三乙胺的初始热解温度为600℃,750℃完全热解,热解产物有C₄F₉N、C₃F₇N、C₂F₆和C₃F₈,热解温度较低时C₄F₉N体积分数最大,热解温度较高时C₃F₇N体积分数最大。在全氟三乙胺热解反应路径计算中,全氟三乙胺分子中的C—C键断裂后存在1条反应路径,可生成实验产物中的C₃F₈;全氟三乙胺分子的C—N键断裂后存在3条反应路径,可生成实验产物中的C₃F₇N、 C₄F₉N和C₂F₆。全氟三乙胺热解后产生的CF₃自由基可与H、OH自由基发生反应,从而产生灭火作用。此外,其热解产物C₄F₉N和C₃F₇N具有CN双键,更容易与燃烧活泼自由基·OH、·H发生化学作用,对研究全氟三乙胺的灭火机理具有十分重要的意义。     

Hydration reactions in pastes C3S+C3A+CaSO4.2aq+H2O at 25°C.I

A characteristic retardation of the hydration of C₃A is found in pastes C₃S+C₃A+CaSO₄.2aq+H₂O of weight ratios 1:3:z:4 at certain values of z, when sulphate concentration becomes insufficient for monosulphate formation. This retardation is ascribed to precipitation of amorphous Al(OH)₃, when C₃A dissolves in a limited amount of the aqueous phase shielded from the rest by C₄AH₁₃ or C₄AH₁₉. Evidence for the conversion of C₃AH₆ into C₄AH_n in supersaturated Ca(OH)₂ solution is found.     

Hydrodeoxygenation of aliphatic esters on sulphided NiMo/γ-Al2O3 and CoMo/γ-Al2O3 catalyst: The effect of water

Water formed during hydrotreating of oxygen-containing feeds has been found to affect the performance of sulphided catalysts in different ways. The effect of water on the activity of sulphided NiMo/γ-Al₂O₃ and CoMo/γ-Al₂O₃ catalysts in hydrodeoxygenation (HDO) of aliphatic esters was investigated in a tubular reactor by varying the amount of water in the feed. In additional experiments, H₂S was added to the feed, alone and simultaneously with water.

Under the same conditions, the NiMo catalyst exhibited a higher activity than the CoMo catalyst. The ester conversions decreased with increase in the amount of added water. When H₂S and water were added simultaneously, the conversion increased to the same level as without water addition on the NiMo catalyst and reached a higher value on the CoMo catalyst. The conversions were highest, however, when only H₂S was added. Unfortunately, the conversions decreased with time under all conditions. On both catalysts, the total yield of the C₇ and C₆ hydrocarbons decreased with the amount of added water, while the concentrations of the oxygen-containing intermediates increased. The presence of H₂S improved the total hydrocarbon yield and shifted the main products towards the C₆ hydrocarbons. Thus, the addition of H₂S effectively compensated the inhibition by water.     

The effect of oxygen concentration on the reduction of NO with propylene over CuO/γ-Al2O3

The effect of oxygen concentration on the pulse and steady-state selective catalytic reduction (SCR) of NO with C₃H₆ over CuO/γ-Al₂O₃ has been studied by infrared spectroscopy (IR) coupled with mass spectroscopy studies. IR studies revealed that the pulse SCR occurred via (i) the oxidation of Cu⁰/Cu⁺ to Cu²⁺ by NO and O₂, (ii) the co-adsorption of NO/NO₂/O₂ to produce Cu²⁺(NO₃⁻)₂, and (iii) the reaction of Cu²⁺(NO₃⁻)₂ with C₃H₆ to produce N₂, CO₂, and H₂O. Increasing the O₂/NO ratio from 25.0 to 83.4 promotes the formation of NO₂ from gas phase oxidation of NO, resulting in a reactant mixture of NO/NO₂/O₂. This reactant mixture allows the formation of Cu²⁺(NO₃⁻)₂ and its reaction with the C₃H₆ to occur at a higher rate with a higher selectivity toward N₂ than the low O₂/NO flow. Both the high and low O₂/NO steady-state SCR reactions follow the same pathway, proceeding via adsorbed C₃H₇---NO₂, C₃H₇---ONO, CH₃COO⁻, Cu⁰---CN, and Cu⁺---NCO intermediates toward N₂, CO₂, and H₂O products. High O₂ concentration in the high O₂/NO SCR accelerates both the formation and destruction of adsorbates, resulting in their intensities similar to the low O₂/NO SCR at 523–698 K. High O₂ concentration in the reactant mixture resulted in a higher rate of destruction of the intermediates than low O₂ concentration at temperatures above 723 K.     

全氟三乙胺和全氟己酮混合气体的灭火效果研究

全氟己酮是一种新型的哈龙替代灭火介质,但是研究人员发现全氟己酮在低浓度时具有助燃效果,未通过美国联邦航空局气溶胶爆炸实验(FAA-ACT)。为抑制全氟己酮的助燃效果,采用混合气体的方法,引入全氟三乙胺作为全氟己酮的协同灭火介质。首先利用杯式燃烧器研究不同浓度全氟己酮作用下的火焰高度、火焰宽度,并获取其临界灭火浓度;以火焰高度和火焰宽度作为助燃现象的判据,实验结果表明全氟己酮浓度为3.00%(占氧化剂体积分数,下同)左右时助燃现象最为显著,临界灭火浓度为5.80%。为研究全氟三乙胺抑制全氟己酮助燃现象的效果,在保持全氟己酮浓度3.00%不变的条件下,逐渐增加全氟三乙胺的浓度,获取火焰高度、火焰脉动频率和混合气体的临界灭火浓度变化趋势;结果表明全氟三乙胺对全氟己酮的助燃现象有抑制作用,且预测全氟三乙胺单独作用下的临界灭火浓度约为4.86%。全氟己酮和全氟三乙胺的混合灭火气体中,全氟三乙胺占灭火剂体积分数超过10.00%后,全氟己酮和全氟三乙胺具有较好的协同灭火效果。     

The influence of VTES on the hydration process of C3S

This paper investigated the hydration process of tricalcium silicate (C₃S) in which a small amount of vinyltriethoxysilane (VTES) was added by using the techniques of ¹H NMR, ²⁹Si MAS-NMR and XRD. In comparison with the hydration process of C₃S without adding any additives, not only the average molecular weight of hydrated calcium silicate in C₃S paste, but also the ordering of the silicon nuclei in it increased. This indicates that the VTES has joined effectively into the real hydration process of C₃S. These results imply some possible reasons why the intrinsic properties of low porosity hardened cement paste (HCP) in which a small amount of VTES was added could be improved. Besides, it has been found that in early stage hydration of C₃S with or without VTES, Ca(OH)₂ crystal in the paste appears earlier than Q₁ which shows that in the first several hours of hydration, there only exists Si(OH)₄ and other basic salts and no dimer and polymer of silicate anion when Ca(OH)₂ crystal begins to form.     

Synthesis of bulk and alumina-supported γ-Mo2N catalysts by a single-step complex decomposition method

A single-step complex decomposition method for the synthesis of bulk and alumina-supported γ-Mo₂N catalysts is described. The complex precursor (HMT)₂(NH₄)₄Mo₇O₂₄·2H₂O (HMT: hexamethylenetetramine) is converted to γ-Mo₂N under a flow of Ar in a temperature range of 823–1023 K. Furthermore, decomposition of the precursor in a NH₃ flow forms γ-Mo₂N in a temperature range of 723–923 K. Compared with direct decomposition of the precursor in Ar, the reaction in NH₃ shows obvious advantages that the nitride forms at a lower temperature. In addition, alumina-supported γ-Mo₂N catalysts with different nitride loadings can be prepared from the alumina-supported complex precursor in the Ar or NH₃ flow. The resultant catalysts exhibit good dibenzothiophene HDS activities, which are similar to the γ-Mo₂N/γ-Al₂O₃ prepared by traditional TPR method. The catalyst prepared by decomposition in an Ar flow exhibits highest activity. It proves that such a single-step complex decomposition method possesses the potential to be a general route for the preparation of molybdenum nitride catalysts.     

Water vapor sensitivity of nanosized La(Co, Mn, Fe)1−x(Cu, Pd)xO3 perovskites during NO reduction by C3H6 in the presence of oxygen

A series of La(Co, Mn, Fe)_1−x(Cu, Pd)_xO₃ perovskites having high specific surface areas and nanosized crystal domains was prepared by reactive grinding. The solids were characterized by N₂ adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed desorption (TPD) of O₂, NO + O₂, C₃H₆, in the absence or presence of 5% H₂O, Fourier transform infrared (FTIR) spectroscopy, as well as activity tests towards NO reduction by propene under the conditions of 3000 ppm NO, 3000 ppm C₃H₆, 1% O₂, 0 or 10% H₂O, and 50,000 h⁻¹ space velocity. The objective was to investigate the influence of H₂O addition on catalytic behavior. A good performance (100% NO conversion, 77% N₂ yield, and 90% C₃H₆ conversion) was achieved at 600 °C over LaFe_0.8Cu_0.2O₃ under a dry feed stream. With the exposure of LaFe_0.8Cu_0.2O₃ to a humid atmosphere containing 10% water vapor, the catalytic activity was slightly decreased yielding 91% NO conversion, 51% N₂ yield, and 86% C₃H₆ conversion. A competitive adsorption between H₂O vapor with O₂ and NO molecules at anion vacancies over LaFe_0.8Cu_0.2O₃ was found by means of TPD studies here. A deactivation mechanism was therefore proposed involving the occupation of available active sites by water vapor, resulting in an inhibition of catalytic activity in C₃H₆ + NO + O₂ reaction. This H₂O deactivation was also verified to be strictly reversible by removing steam from the feed.     

Hydrothermal transformation of the calcium aluminum oxide hydrates CaAl2O4·10H2O and Ca2Al2O5·8H2O to Ca3Al2(OH)12 investigated by in situ synchrotron X-ray powder diffraction

The hydrothermal transformation of calcium aluminate hydrates were investigated by in situ synchrotron X-ray powder diffraction in the temperature range 25 to 170 °C. This technique allowed the study of the detailed reaction mechanism and identification of intermediate phases. The material CaAl₂O₄·10H₂O converted to Ca₃Al₂(OH)₁₂ and amorphous aluminum hydroxide. Ca₂Al₂O₅·8H₂O transformed via the intermediate phase Ca₄Al₂O₇·13H₂O to Ca₃Al₂(OH)₁₂ and gibbsite, Al(OH)₃. The phase Ca₄Al₂O₇·19H₂O reacted via the same intermediate phase to Ca₃Al₂(OH)₁₂ and mainly amorphous aluminum hydroxide. The powder pattern of the intermediate phase is reported.     

Solubility properties of ternary and quaternary compounds in the CaO--- Al2O3--- SO3---H2O system

Solubility measurements are reported for four hydrated cement phases. A technique employing repeated dispersion and filtration is described which enabled the solubility (activity) products of ettringite (C₆A ₃H₃₂) and hydrogarnet (C₃AH₆) to be calculated with confidence. Free energies of formation are also given. These phases dissolve congruently, whereas monosulphate (C₄A H₂) and tetra-calcium aluminate hydrate (C₄AH₁₃) exhibit incongruent dissolution, and can therefore not be described by a conventional solubility product. The results represent additional data for inclusion in thermodynamic databases currently being applied to the modelling of cement systems.     

Enhanced activity of metal oxide-doped Ga2O3–Al2O3 for NO reduction by propene

Effect of additives, In₂O₃, SnO₂, CoO, CuO and Ag, on the catalytic performance of Ga₂O₃–Al₂O₃ prepared by sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. As for the reaction in the absence of H₂O, CoO, CuO and Ag showed good additive effect. When H₂O was added to the reaction gas, the activity of CoO-, CuO- and Ag-doped Ga₂O₃–Al₂O₃ was depressed considerably, while an intensifying effect of H₂O was observed for In₂O₃- and SnO₂-doped Ga₂O₃–Al₂O₃. Of several metal oxide additives, In₂O₃-doped Ga₂O₃–Al₂O₃ showed the highest activity for NO reduction by propene in the presence of H₂O. Kinetic studies on NO reduction over In₂O₃–Ga₂O₃–Al₂O₃ revealed that the rate-determining step in the absence of H₂O is the reaction of NO₂ formed on Ga₂O₃–Al₂O₃ with C₃H₆-derived species, whereas that in the presence of H₂O is the formation of C₃H₆-derived species. We presumed the reason for the promotional effect of H₂O as follows: the rate for the formation of C₃H₆-derived species in the presence of H₂O is sufficiently fast compared with that for the reaction of NO₂ with C₃H₆-derived species in the absence of H₂O. Although the retarding effect of SO₂ on the activity was observed for all of the catalysts, SnO₂–Ga₂O₃–Al₂O₃ showed still relatively high activity in the lower temperature region.     

The influence of CaCl2 on the crystallization of calcium silicates in autoclave hydration of C3S

The influence of CaCl₂ on the autoclave hydration C₃S (5 hours at 190°C) after different precuring times (0–16 hours) at room temperature has been studied. The addition of calcium chloride retards the autoclave hydration of C₃S and prevents completely the formation of the crystalline hydrated silicates (-C₂SH and C₃SH_1.5). This result has been compared with that observed in the ball-mill hydration of C₃S in the presence of CaCl₂, i.e., the complete absence of crystalline afwillite.

Abstract

On a étudié l'influence du CaCl₂ sur l'hydratation en autoclave du C₃S (5 heures à 190°C) après différents temps de conservation (0–16 heures à température ambiante. L'addition de chlorure de calcium retarde l'hydratation en autoclave du C₃S et empêche complétement la formation des silicates cristallins hydratés -C₂SH et C₃SH_1.5. Ce résultat a été comparé avec le phenomene observé en étudiant l'hydration du C₃S dans un moulin à boulets en presence de CaCl₂, c'est à dire la disparition complète du composé crystallin afwillite.     

Zeolite synthesis in the presence of flexible diquaternary alkylammonium ions (C2H5)3N(CH2)nN(C2H5)3 with n=3–10 as structure-directing agents

The use of flexible diquaternary alkylammonium ions (C₂H₅)₃N⁺(CH₂)_nN⁺(C₂H₅)₃ (Et₆-diquat-n with n=3–10) as structure-directing agents for zeolite synthesis in the presence of alkali metal cation is described. Among the organic structure-directing agents studied here, a considerable diversity in the phase selectivity was observed only for the Et₆-diquat-5 ion: this cation can produce five different zeolite structures (i.e., P1, SSZ-16, SUZ-4, ZSM-57, and mordenite), depending on the oxide composition of synthesis mixtures. Analysis of the variable-temperature ¹H CRAMPS NMR spectra obtained from the Et₆-diquat-5 molecules in these five zeolites reveals that the host–guest interactions occurring within the respective materials maintain in a manner different from one another even at 160 °C at which the zeolite hosts crystallize.     

Pt/TiO_2催化二甲醚部分氧化重整制氢

二甲醚是一种理想的氢载体,可用于解决氢的储存和运输。以Pt/TiO_2为部分氧化催化剂,结合Ni/Al_2O_3重整催化剂,考察钛前驱体和焙烧温度对二甲醚部分氧化重整制氢反应的影响。结果表明,以Ti(C4H9O)4为原料制备的TiO_2为金红石相,Ti(SO4)2或Ti O(OH)2为原料制备的TiO_2为锐钛矿相;以Ti(C4H9O)4为原料制备的Pt/TiO_2-E催化剂催化性能略好,转化率接近100%,H2收率约90%,表明金红石相TiO_2负载的Pt催化剂略佳;以Ti(SO4)2为原料制备的Pt/TiO_2-S催化剂500℃焙烧可获得金红石相TiO_2。与Pt/Al_2O_3催化剂相比,Pt/TiO_2催化剂具有更好的催化性能,H2收率超过90%,而Pt/Al_2O_3催化剂H2收率约80%。     

Designing the activity/selectivity of surface acidic, basic and redox active sites in the supported K2O–V2O5/Al2O3 catalytic system

The supported K₂O–V₂O₅/Al₂O₃ catalytic system was designed to create surfaces that were 100% acidic, 100% basic, 100% redox, mixed redox-acidic and mixed redox-basic. The resulting nature of the surface sites was controlled by the impregnation of the specific additives (K-basic or V-redox/acidic), their order of impregnation and their surface coverage. The exact locations of the surface methoxy intermediates (AlOCH₃, KOCH₃ or VOCH₃) on the mixed oxide catalyst surfaces during methanol oxidation were determined with in situ Raman spectroscopy. The surface chemistry of the various surface sites and their surface reaction intermediates were chemically probed by CH₃OH oxidation steady-state and temperature programmed surface reaction (TPSR) spectroscopy studies. The specific reactivity order and the product selectivity of the various surface sites were found to be: VOCH₃ (HCHO) AlOCH₃ (CH₃OCH₃) KOCH₃ (primarily CO₂ and minor amounts of HCHO). Formation of dimethoxy methane, (CH₃O)₂CH₂, required the presence of dual surface redox-acidic sites surface redox sites to yield H₂CO and surface acidic sites to insert the surface methoxy into H₂CO to form dimethoxy methane, (CH₃O)₂CH₂. The addition of basic surface potassium oxide to Al₂O₃ possessing surface acid sites completely suppressed reactions from the surface acidic sites and formed a surface with only basic characteristics. The addition of redox surface vanadia to the supported K₂O/Al₂O₃ catalyst was able to completely suppress reactions from surface basic sites and formed a surface with only redox characteristics. These studies demonstrate that it is possible to determine the specific surface site requirements for each reaction pathway for methanol oxidation to products, and that this informative approach should also be applicable to other reactant molecules.     

Phase transitions in R2 SnCl6-type crystals (R = NH3 C2H3, NH3C2H5 and N(CH3)4)

The thermal dilatation in (NH₃ ·CH₃) SnCl₆, (NH₃ · C₂H₅) SnCl₆ and [N(CH₃)] SnCl₆ was measured, and as the results it has turned out that (NH₃ ⁶·C₂H₅) SnCl₆ and [N(CH₃)₄]₂ SnCl₆ undergo the first order transitions at 128 K and 158 K, respectively. The low temperature phases of (NH · C₂H₅) SnCl₆ and [N(CH₃)₄]₂ SnC1₆ are found to be monoclinic and tetragonal, respectively, No phase transition was observed in (NH₃ ·CH₃)₂ SnCl₆ down to 77 K.     

氟化钙对共沉淀法硅酸三钙中游离氧化钙含量的影响

以硝酸钙、硅酸钠、碳酸钠、氟化铵为原料,采用共沉淀反应法制备掺杂氟化钙的硅酸三钙。研究不同氟化钙掺杂量对合成硅酸三钙中游离氧化钙含量的影响。用甘油无水乙醇法测定游离氧化钙的含量,扫描电子显微镜（SEM）和X射线分析（XRD）对硅酸三钙的微观形貌和晶相组成进行表征。结果表明,氟化钙的加入使得样品在煅烧过程中形成了低共融化合物,明显降低了游离氧化钙的含量,缩短了反应时间,降低了煅烧温度,氟化钙掺杂量为0.6%（质量分数）时,在1 350 ℃下保温4 h可以得到游离氧化钙含量很低的硅酸三钙。     

Lean reduction of NO by C3H6 over Ag/alumina derived from Al2O3, AlOOH and Al(OH)3

The effectiveness of Ag/Al₂O₃ catalyst depends greatly on the alumina source used for preparation. A series of alumina-supported catalysts derived from AlOOH, Al₂O₃, and Al(OH)₃ was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible (UV–vis) spectroscopy, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, O₂, NO + O₂-temperature programmed desorption (TPD), H₂-temperature programmed reduction (TPR), thermal gravimetric analysis (TGA) and activity test, with a focus on the correlation between their redox properties and catalytic behavior towards C₃H₆-selective catalytic reduction (SCR) of NO reaction. The best SCR activity along with a moderated C₃H₆ conversion was achieved over Ag/Al₂O₃ (I) employing AlOOH source. The high density of Ag–O–Al species in Ag/Al₂O₃ (I) is deemed to be crucial for NO selective reduction into N₂. By contrast, a high C₃H₆ conversion simultaneously with a moderate N₂ yield was observed over Ag/Al₂O₃ (II) prepared from a γ-Al₂O₃ source. The larger particles of Ag_mO (m > 2) crystallites were believed to facilitate the propene oxidation therefore leading to a scarcity of reductant for SCR of NO. An amorphous Ag/Al₂O₃ (III) was obtained via employing a Al(OH)₃ source and 500 °C calcination exhibiting a poor SCR performance similar to that for Ag-free Al₂O₃ (I). A subsequent calcination of Ag/Al₂O₃ (III) at 800 °C led to the generation of Ag/Al₂O₃ (IV) catalyst yielding a significant enhancement in both N₂ yield and C₃H₆ conversion, which was attributed to the appearance of γ-phase structure and an increase in surface area. Further thermo treatment at 950 °C for the preparation of Ag/Al₂O₃ (V) accelerated the sintering of Ag clusters resulting in a severe unselective combustion, which competes with SCR of NO reaction. In view of the transient studies, the redox properties of the prepared catalysts were investigated showing an oxidation capability of Ag/Al₂O₃ (II and V) > Ag/Al₂O₃ (IV) > Ag/Al₂O₃ (I) > Ag/Al₂O₃ (III) and Al₂O₃ (I). The formation of nitrate species is an important step for the deNO_x process, which can be promoted by increasing O₂ feed concentration as evidenced by NO + O₂-TPD study for Ag/Al₂O₃ (I), achieving a better catalytic performance.     

Reaction network of indole hydrodenitrogenation over NiMoS/γ-Al2O3 catalysts

The reaction network of indole hydrodenitrogenation (HDN) was investigated over γ-Al₂O₃ supported NiMo sulfide catalysts in an effort to acquire a fundamental understanding of the different reaction pathways in the mechanism. Experiments were performed primarily at 1000 psig, using a wide range of temperatures and feed concentrations. The effect of H₂S on different reaction steps of the network was also investigated. Two major pathways were proposed to account for the formation of ethylcyclohexane (ECH) and ethylbenzene (EB) which are the two main HDN products from indole. One route occurs from the hydrogenolysis of indoline to o-ethylaniline (OEA) and the other from the hydrogenation of indoline to octahydro-indole. Also included in the proposed mechanism is a secondary route from o-ethylcyclohexylamine (OECHA) to ethylcyclohexene (ECHE), that occurs through a nucleophilic substitution reaction. The product distribution was a strong function of temperature and H₂S concentration. H₂S enhanced the hydrogenolysis reactions but inhibited the hydrogenation reactions.