硫化氢热分解制氢过程的化学动力学研究

采用化学热平衡分析方法研究了硫化氢热分解制氢过程，研究了硫化氢在不同温度和体积分数下的分解过程，并与试验数据进行了比较。结果表明，基元反应机理能较好地模拟硫化氢热分解制氢过程。硫化氢的热分解率依赖于反应温度，高温下能获得较好的分解制氢效果；温度较低时，时间是硫化氢趋于平衡的主要影响因素，随着温度的提高，温度成为影响硫化氢趋于平衡的主要影响因素。硫化氢初始体积分数对热分解制氢反应具有较大的影响，采用较低体积分数的硫化氢混合气有利于获得高的硫化氢热分解制氢率。     

Thermal decomposition of poly(vinylidene chloride) prepared in presence of oxygen

The thermal decomposition of poly(vinylidene chloride) was studied for samples prepared in the presence of oxygen. The products from both mass and aqueous suspension polymerizations show two modes of thermal decomposition. A rapid initial mode varies in rate and extent with the amount of oxygen present. A slower mode is unaffected by oxygen and in similar in rate to the polymer made in the absence of oxygen. The chief volatile products are phosgene and formaldehyde for the rapid decomposition and hydrogen chloride for the slow decomposition. The rapid decomposition is interpreted to be an unzipping reaction of a vinylidene chloride–oxygen alternating copolymer initiated by homolysis of a peroxide bond. The absence of significant amounts of hydrogen chloride during this stage of decomposition shows that none of the free radicals generated are capable of initiating a chain reaction that would unzip hydrogen chloride from the poly(vinylidene chloride) backbone. The presence of oxygen during the aqueous suspension polymerization correlates with the generation of hydrochloric acid in the aqueous phase. By analogy with the high temperature decomposition, the hydrochloric acid is believed to result primarily from the hydrolysis of phosgene produced by partial decomposition of the polyperoxide. Initiation of the decomposition is believed due to a reaction of the chain propagating radical.     

双金属催化剂体系催化过氧化氢分解反应

研究了双金属催化剂体系催化过氧化氢分解反应,测量了不同催化剂体系的活化能.结果表明,双金属催化剂对过氧化氢分解反应具有良好的催化性能,且双金属催化剂存在协同催化作用;而酸性环境对过氧化氢催化分解有明显的抑制作用.     

镁铜合金储氢材料的制备及对高氯酸铵热分解过程的影响

采用置换-扩散法制备了镁铜合金储氢材料(Mg2Cu-H), 并对其结构进行了表征. 结果表明, Mg2Cu经过氢化得到的镁铜合金储氢材料不是单一晶相, 而是MgCu2和MgH2的混合物. 用热分析法(DSC)研究了镁铜合金储氢材料对固体火箭推进剂常用氧化剂——高氯酸铵(AP)热分解过程的影响. 结果表明, 镁铜合金储氢材料可以显著促进AP的热分解过程, 加快热分解速率, 降低高温热分解温度, 使DSC表观分解热明显增大. Mg2Cu-H对AP热分解过程的促进作用明显强于Mg2Cu. 随着加入量增加, 镁铜合金储氢材料对AP热分解的催化促进作用增强. 探讨了镁铜合金储氢材料促进AP热分解过程的作用机制.     

Isothermal decomposition of hydrogen peroxide dihydrate

We present a new method of growing pure solid hydrogen peroxide in an ultra high vacuum environment and apply it to determine thermal stability of the dihydrate compound that forms when water and hydrogen peroxide are mixed at low temperatures. Using infrared spectroscopy and thermogravimetric analysis, we quantified the isothermal decomposition of the metastable dihydrate at 151.6 K. This decomposition occurs by fractional distillation through the preferential sublimation of water, which leads to the formation of pure hydrogen peroxide. The results imply that in an astronomical environment where condensed mixtures of H(2)O(2) and H(2)O are shielded from radiolytic decomposition and warmed to temperatures where sublimation is significant, highly concentrated or even pure hydrogen peroxide may form.     

Co/Fe催化剂乙醇裂解和部分氧化制氢研究

采用共沉淀法制备的Co/Fe催化剂催化乙醇裂解和部分氧化制氢反应，考察了反应温度对两种途径反应的影响。结果发现，Co/Fe催化剂对乙醇部分氧化制氢显示出较高的氢选择性，且稳定性较好；该催化剂对乙醇裂解制氢也具有较高的氢选择性，但其稳定性很很差。XRD表征结果表明，在催化乙醇部分氧化反应后，Co70Fe30催化剂中存在CoFe合金和CoO相；而催化乙醇裂解反应后，Co70Fe30催化剂中仅存在CoFe合金，即CoFe合金可能是裂解反应的活性组分。     

原位漫反射新方法研究煤中氢键的分解动力学

采用一种新的原位漫反射红外技术研究了干燥脱灰褐煤中氢键的分解动力学,同时介绍并应用了一种防止高温下挥发分冷凝的原位漫反射红外实验方法。基于两条假设,当煤加热至560℃时,单一反应模型可以用于除OH－π键以外氢键分解动力学参数的求解。结果表明,煤中羧酸二聚体、OH－N 和SH－N三种氢键的分解动力学遵循二级反应;OH－OR₂,紧密结合的羟基四聚体和自缔合的羟基多聚体则遵循一级反应。计算所得的几种氢键分解活化能与文献中采用其他 方法所得结果基本一致。在所考察的六种氢键中,羧酸二聚体、OH－N 、SH－N和紧密结合的羟基四聚体的分解可以分为两个阶段（230℃~380℃和 380℃~500℃）,而OH－OR₂和自缔合的羟基多聚体的分解可以按照一段来处理。另外,通过比较自缔合的羟基多聚体的分解活化能和文献中的氢键键能,获得了其分解机理。
     

A first-principles study of methanol decomposition on Pt(111)

A periodic, self-consistent, Density Functional Theory study of methanol decomposition on Pt(111) is presented. The thermochemistry and activation energy barriers for all the elementary steps, starting with O[bond]H scission and proceeding via sequential hydrogen abstraction from the resulting methoxy intermediate, are presented here. The minimum energy path is represented by a one-dimensional potential energy surface connecting methanol with its final decomposition products, CO and hydrogen gas. It is found that the rate-limiting step for this decomposition pathway is the abstraction of hydroxyl hydrogen from methanol. CO is clearly identified as a strong thermodynamic sink in the reaction pathway while the methoxy, formaldehyde, and formyl intermediates are found to have low barriers to decomposition, leading to very short lifetimes for these intermediates. Stable intermediates and transition states are found to obey gas-phase coordination and bond order rules on the Pt(111) surface.     

Catalytic activity of Cu(II)–poly(vinyl alcohol) complex for decomposition of hydrogen peroxide

Decomposition of hydrogen peroxide was examined was examined by using Cu(II)–poly(vinyl alcohol) (PVA) as catalyst. The rates of decomposition were measured. Electronic spectra and infrared spectra of Cu(II)–PVA complex systems were determined at various stages of decomposition. Effect of addition of various amines to the Cu(II)–PVA system on catalytic action was considered. The relation between the initial rate and the initial concentration of hydrogen peroxide varied in accordance with the rate expression of Michaelis-Menten type. Cu(II)–PVA complex was found to have a large catalytic activity, while the polymeric PVA ligand and copper(II) ion exhibited less activity than Cu(II)–PVA complex. For hydrogen peroxide decomposition, Cu(II)–PVA complex showed catalytic activity when a stable complex of planar structure formed, while many other polymer complexes reported by other authors showed the catalytic activity when they were in unstable complex forms. An amine substituent has a critical influence on the rate of hydrogen peroxide decomposition. The mechanism in the first step of reaction for hydrogen peroxide decomposition is discussed.     

Investigations of changes in the oxidation state of the catalyst during the OsO4-catalysed decomposition of hydrogen peroxide

By using different methods, such as spectrophotometry, potentiometric titration, polarography and extraction, it was found that at pH 8.5 osmium (VIII) is reduced by hydrogen peroxide to osmium(VI) to various extents. At pH 10.6, where the rate of the OsO₄-catalysed decomposition of hydrogen peroxide reaches its maximum, the concentration ratio of osmium (VIII) and osmium (VI) was found to be nearly one. This favours the explanation that the maximum rate of hydrogen peroxide decomposition is found at the pH where the rate of reduction of osmium (VIII) by hydrogen peroxide just becomes equal to the rate of oxidation of osmium (VI) by hydrogen peroxide.     

Hydrogen sulfide as a source of hydrogen production

Potentialities and perspectives of using the known processes of hydrogen sulfide decomposition (thermal, plasmochemical, electrochemical, and photochemical) to produce hydrogen are examined. The results of theoretical and experimental studies of hydrogen sulfide dissociation on the surface of single crystals are presented. The data on the low-temperature decomposition of H₂S on the sulfide and metal catalysts are discussed. The electronic structure of diatomic sulfur and thermodynamics of its formation in the processes of H₂S decomposition are considered. The decomposition of hydrogen sulfide on the heterogeneous catalysts placed under the solvent layer is shown to be promising. The mechanism of assimilation of hydrogen sulfide by colorless sulfur bacteria is proposed.     

氢化物原子吸收机理的研究 Ⅰ.H_2和空气在氢化物原子化中的作用

研究了氢气和空气在氢化物原子化过程中的作用,观察到H_2的存在下不仅引发自由基过程,而且抑制氢化物的热分解.空气的存在,使一些元素氢化物的最佳原子化温度降低,其增感作用只有在H_2共存时才表现出来.在没有H_2共存时,空气可能与氢化物反应生成氧化物,对吸收信号产生抑制.     

NO在碳纳米管(CNTs),Rh/CNTs,Rh/Al_2O_3上的分解(英文)

甲烷在预还原的ＬａＣｏＯ３催化剂上分解生成碳纳米管（ＣＮＴｓ）。研究了稳态下ＮＯ在ＣＮＴｓ,Ｒｈ／ＣＮＴｓ,Ｒｈ／Ａ１２Ｏ３上的分解,温度区间为５７３Ｋ～９７３Ｋ,原料气为６０００ｐｐｍ的ＮＯ,Ｈｅ为平衡气。程序升温还原结果表明：（１）Ｒｈ的负载显著降低了ＣＮＴｓ的氢吸收量;（２）负载于ＣＮＴｓ上的Ｒｈ比负载于Ａ１２Ｏ３上的Ｒｈ更易还原。在５７３Ｋ时ＮＯ即能与预还原后的ＣＮＴｓ,Ｒｈ／ＣＮＴＳ,Ｒｈ／Ａｌ２Ｏ３中存储的氢反应;随着氢的消耗,反应活性逐渐降低,当储存的氢消耗完后,ＮＯ的直接催化反应发生。在８７３ Ｋ及以上,Ｒｈ／ＣＮＴｓ中的ＣＮＴｓ能彼ＮＯ分解产生的氧氧化为ＣＯ。在９７３Ｋ时,ＮＯ在ＣＮＴｓ上几乎能１００％分解,连续反应１５０ｍｉｎ后其反应活性不降低,且未观察到ＣＯ或ＣＯ２的生成。在９７３Ｋ时ＣＮＴｓ本身可作为ＮＯ分解的催化剂,这是一个非常有意义的结果。     

Spectroscopic studies of dehydrogenation of ammonia borane in carbon cryogel

Ammonia borane (AB) is of great interest for storing hydrogen, an important issue in the growing field of hydrogen technology. The reaction pathways leading to the thermal decomposition of solid-state AB incorporated in carbon cryogels (CC) have been studied by spectroscopic methods. The time-dependent thermal decomposition was followed by in situ 11B nuclear magnetic resonance (NMR) and showed a significant increase in hydrogen release kinetics for AB in CC compared to neat AB. Both 11B NMR and Fourier transform infrared spectroscopy show a new reaction product, formed in the thermal decomposition of AB in CC scaffold (CC-AB) that is assigned to reactions with surface oxygen groups. The results indicate that incorporation of AB in CC enhances kinetics because of the reactions with residual surface-bound oxygen functional groups. The formation of new products with surface -O-B bonds is consistent with the greater reaction exothermicity observed when hydrogen is released from CC-AB materials. Scanning electron microscopy shows different morphology of AB in CC-AB nanocomposite as compared to neat AB.     

甲醇在CeO2担载Pd催化剂上分解机理的研究

采用原位红外(in-situFTIR)技术对甲醇在CeO₂和Pd/CeO₂催化剂上的吸附和反应进行了研究,提出一个新的甲醇分解反应机理模型.甲醇在CeO₂上容易吸附并结合其晶格氧生成甲酸盐物种,而甲醇分解的产物氢被Pd活化后,溢流到CeO₂上促进了甲酸盐物种的分解.Cl^-的存在加强了Pd/CeO₂催化剂与氢的相互作用,Pd和CeO₂通过对氢和氧物种的作用对甲醇分解反应的过程表现出协同效应.     

Hydrogen Halide-Catalyzed Thermal Decomposition of Poly(vinyl Chloride)

The thermal decomposition of solid PVC was studied in the presence of added hydrogen chloride and hydrogen bromide over the temperature range 170–210°C. Under certain conditions the decomposition was shown to be dependent in a first-order manner on the hydrogen halide pressure. These gases acted as catalysts, increasing the rate of HCl evolution and the degree of discoloration but not producing longer polyene sequences. Activation energy for the HCl-catalyzed process was found to be similar to that of the uncatalyzed decomposition of PVC. A unified mechanism is presented for an overall process consisting of three steps: random generation of a single carbon-carbon double bond in the cis configuration; 1,4-elimination of HCl via a six-centered transition state yielding a polyene; HCl- or HBr-catalyzed isomerization of the polyene formed by HC1 elimination to regenerate the initial structure. Hydrogen chloride catalysis is seen as an integral part of the overall process.     

Ni/SiO2催化剂上甲烷催化裂解制氢

研究了固定床反应器上甲烷在Ni/SiO2催化剂上的裂解反应，并分别用O2、H2O进行催化剂失活/活化循环实验，并对催化剂用XRD进行分析。结果表明,Ni/SiO2催化剂具有良好的催化性能,甲烷转化率～40%，并能在150 min的时间内保持其活性，无论是用空气氧化还是水蒸气汽化，都能有效地活化已失活的催化剂。XRD实验显示，多次裂解－再生循环过程，对催化剂结构没有明显破坏。     

ESR study of the xenon-photosensitized decomposition of gaseous hydrogen

The gas-phase ESR technique has been used to study the xenon-photosensitization of hydrogen. The ESR spectrum of atomic hydrogen was observed when the mixtures of xenon and hydrogen were irradiated by the xenon resonance line (147 nm). The results show that photosensitized decomposition of hydrogen takes place due to the chemical quenching of the excited xenon by hydrogen molecules.     

Physico-chemical aspects of polyethylene processing in an open mixer. Part 19: Mechanisms and kinetics of vinyl and vinylidene group formation

Vinyl and vinylidene group formation is detected in the initial stages of polyethylene processing. In the high temperature range (170-200 °C) the amount formed is small but significant. Formation of these double bonds is usually obscured by their rapid consumption. Bimolecular hydroperoxide decomposition does not seem to be an important source for these products in the early stages of processing. Vinyl and vinylidene group formation can be attributed mainly to intramolecular decomposition of special hydroperoxide groups. The data suggest vinyl groups to arise from secondary hydroperoxide groups formed in α-position to methyl branching. Intramolecular hydroperoxide decomposition involving a primary hydrogen atom from the methyl group yields a vinyl group and an aldehyde. Vinylidene groups seem to arise from secondary hydroperoxide groups formed in α-position to quaternary structures that necessarily include one methyl group. Intramolecular hydrogen abstraction of a primary hydrogen atom from the methyl group yields a vinylidene group and an aldehyde. The calculated rate parameters are in agreement with the thermochemical estimations relative to intramolecular abstraction of primary hydrogen atoms for both reactions. Vinyl groups are also formed on bimolecular hydroperoxide decomposition. The yield of vinylidene groups from the last reaction is negligible.     

The thermal decomposition of fluorinated esters. III. Esters without β hydrogen atoms

The kinetics of the gas-phase decomposition of methyl trifluoroacetate and 2,2,2-trifluoroethyl trifluoroacetate, two esters without β hydrogen atoms, have been investigated, and a comparative study was carried out on methyl acetate. All these compounds are thermally much more stable than fluorinated esters with β hydrogens, decomposing at temperatures some 150°C above the latter by a completely different mechanism involving partly heterogeneous radical chains. The marked difference in behavior between the two types of fluorinated ester confirms that none of them decomposes by hydrogen fluoride elimination, but that those with β hydrogen atoms follow the normal ester decomposition route. The fluorinated esters examined here decompose in a manner generally similar to methyl acetate, but the presence of fluorine in the molecule brings about an extreme sensitivity to surface conditions.