共查询到20条相似文献,搜索用时 25 毫秒
1.
采用水热沉积法制备Ni-Al 2O 3催化剂,用于CO 2-CH 4重整反应;基于程序升温氢化(TPH)表征,研究了反应时间、温度、原料气CO 2/CH 4比例和空速等因素对CO 2-CH 4重整反应过程中Ni-Al 2O 3催化剂上表面积炭行为的影响。结果表明,表面积炭是导致催化剂重整反应失活的重要原因。随反应时间的延长,催化剂表面积炭量增多,虽未成比例增加,但其TPH峰温有向高温方向移动的趋势,表明所积之炭的石墨化程度增加。反应温度和空速对催化剂表面积炭也有一定影响,且空速的影响更大。另外,由于CO 2消炭反应(CO 2+C=2CO)的存在,CO 2/CH 4比例对表面积炭的影响也很大。CO 2/CH 4比例太低,不能明显抑制积炭;随着CO 2/CH 4比例增加,积炭将得到有效抑制,但CO 2/CH 4比例过高,CO 2在产物中的分离和回收再利用将使成本增加。 相似文献
2.
在密度泛函理论B3LYP/6-31G *水平上,研究了ClONO 2+Cl( 2P 3/2)Cl 2+NO 3和ClONO 2+Cl( 2P 3/2)ClO+ClONO(cis)及ClONO 2+Cl( 2P 3/2)ClOCl+NO 2的反应机理.计算得到各可能反应途径的过渡态,并经过内禀反应坐标(IRC)分析加以证实.反应ClONO 2+Cl( 2P 3/2)Cl 2+NO 3反应活化能垒最低,为4.5kJ/mol,是反应主通道. 相似文献
3.
The reaction between SiCl 4 and O 2 at 1 atm between 25 and 1200°C has been followed by mass spectrometry. Below 600°C no reaction with O 2 is noted. Above 600°C the reaction proceeds in two steps. Between 800 and 1000°C the 28Si/ 32O 2 peak height ratio is constant with no evolution of Cl 2. It is suggested that silicon oxychlorides are being formed in this temperature regime. Above 1000°C the reaction between SiCl 4 and O 2 intensifies with concomitant production of Cl 2. It is suggested that above 1000°C the reaction SiCl 4 + O 2 → SiO 2 + Cl 2 becomes important. At low temperatures (<800°C) adsorbed H2O and OH groups from the surface of the fused silica tube react with SiCl4 to form HCl. The importance of this reaction decreases with increasing temperature. The increased production of HCl above 1000°C is ascribed to H2O and H2 diffusing from the tube. 相似文献
4.
采用量子化学密度泛函理论(DFT)对NO与NH i自由基的反应机理进行了研究,并结合经典过渡态理论对各反应速率常数进行了计算。结果表明,NO与NH 2自由基的反应体系可通过六个反应通道形成N 2+H 2O、N 2O+H 2和N 2H+OH。从能量变化和反应速率两方面考虑,产物N 2+H 2O最容易生成,其最佳反应通道为NO+NH 2→→N 2+H 2O;NO与NH自由基的反应体系可通过七个反应通道形成N 2+OH、N 2O+H和N 2H+O;其中,N 2+OH最容易生成,最佳反应通道为NO+NH→→N 2+OH。比较发现, NH比NH 2自由基更易与NO发生反应生成N 2。因此,在实际运行中改变操作条件,实现NH 2等向NH方向转化,有利于NO x的还原。 相似文献
5.
用密度泛函理论(DFT)的B3LYP方法,在6-311G、6-311+G( d)、6-311++G( d, p) 基组水平上研究了CH 3CF 2O 2与HO 2自由基反应机理. 结果表明, CH3CF 2O 2与HO 2自由基反应存在两条可行的通道. 通道CH3CF 2O 2+HO 2→IM1→TS1→CH 3CF 2OOH+O 2的活化能为77.21 kJ•mol -1,活化能较低,为主要反应通道,其产物是O 2和CH 3CF 2OOH. 这与实验结果是一致的;而通道CH 3CF 2O 2+HO 2→IM2→TS2→IM3→TS3→IM4+IM5→IM4+TS4→IM4+OH+O 2→TS5+OH+O 2→CH 3+CF 2O+OH+O 2→CH 3OH+CF 2O+O 2的控制步骤活化能为93.42 kJ•mol -1,其产物是CH 3OH、CF 2O和O 2. 结果表明这条通道也能发生,这与前人的实验结果一致. 相似文献
6.
利用热天平对比研究了大同煤及煤焦在O 2/N 2、O 2/CO 2和O 2/H 2O/CO 2中的燃烧行为,探讨CO 2和H 2O气化反应对其富氧燃烧特性的影响。结果表明,在5%氧气浓度下,煤粉在O 2/N 2、O 2/CO 2和O 2/H 2O/CO 2中的燃烧速率按顺序依次降低。氧气浓度降低到2%,由于CO 2和H 2O气化反应的作用,煤粉在高温区的整体反应速率按顺序依次增大。当氧气浓度为5%时,煤焦在O 2/CO 2中的燃烧速率要低于O 2/N 2中的燃烧速率,但燃烧反应推迟后气化反应的参与使得煤焦在O 2/H 2O/CO 2中的整体反应速率显著升高。当氧气浓度降低到2%后,随着温度的升高,在CO 2气化反应的作用下,煤焦在O 2/CO 2中的整体反应速率逐渐高于O 2/N 2中的燃烧速率。在O 2/H 2O/CO 2中,由于H 2O在共气化中起主要作用,煤焦在O 2/H 2O/CO 2高温区的整体反应速率进一步升高。动力学分析表明,在5%氧浓度时,煤焦在O 2/N 2、O 2/CO 2和O 2/H 2O/CO 2中的表观活化能依次升高。随着氧气浓度的降低,在不同反应气氛中的表观活化能均有所下降。 相似文献
7.
在φ80×3 000mm耐高温不锈钢管气流床反应器中,以150-180μm胜利褐煤为气化原料,考察了800和900℃时添加氧气前后褐煤转化率的变化,研究了氧化反应对水蒸气气化反应影响的宏观特征。结果表明,添加氧气后褐煤转化率明显大于O_2和H_2O气氛下褐煤转化率之和,即向水蒸气气氛添加氧气后褐煤转化率的增幅大于氧气氧化作用导致的褐煤转化率的增幅,随着H_2O含量增大以及温度的升高此现象愈加明显。该协同作用主要是氧化反应对水蒸气气化反应的促进作用造成的。利用φ40×200 mm石英圆筒流化床反应器进行了类似的实验,也发现了该协同作用。同时,借鉴收缩核模型并结合气流床气化实验条件推导了水蒸气气化宏观动力学方程,得到的速率方程(Z-(1-x))~(1/3)=(tβk_(H_2O)/Rρ_C)φ_(H_2O)=K_(H_2Oφ_(H_2O))与实验值吻合较好,添加氧气后水蒸气气化反应速率和水蒸气气化反应表观速率常数K_(H_2O)明显增大,这是氧气对水蒸气气化反应促进作用的动力学特征。 相似文献
8.
Rate constants for the tunneling reaction (HD + D → h + D 2) in solid HD increase steeply with increasing temperature above 5 K, while they are almost constant below 4.2 K. The apparent activation energy for the tunneling reaction above 5 K is 95 K, which is consistent with the energy (91–112 K) for vacancy formation in solid hydrogen. The results above 5 K were explained by the model that the tunneling reaction was accelerated by a local motion of hydrogen molecules and hydrogen atoms. The model of the tunneling reaction assisted by the local motion of the reactans and products was applied to the temperature dependence of the proton-transfer tunneling reaction (C 6H 6− + C 2H 5OH → C 6H 7 + C 2H 5O −) in solid ethanol, the tunneling elimination of H 2 molecule of H 2 molecule ((CH 3) 2 CHCH(CH 3) 2+ → (CH 3) 2 C = C(CH 3) 2+ + H 2) in solid 2,3-dimethylbutane, and the selective tunneling reaction of H atoms in solid neo-C 5H 12-alkane mixtures. 相似文献
9.
共沉淀法制备CeZrYLa+LaAl 复合氧化物载体, 等体积浸渍法制备了Pt 催化剂, 用于研究理论空燃比天然气汽车(NGVs)尾气净化反应中CH 4与NO的反应规律. 并考察了10% (体积分数, φ)H 2O和计量比O 2对CO 2存在时的CH 4+NO反应的影响. 结果表明: 对于不同条件下的NO+CH 4反应, 主要生成N 2和CO 2, 高温区有CO生成. 低温区无O 2时可以生成N 2O, 有O 2时可以生成NO 2; 添加10% (φ)的H 2O后, CH 4 转化活性降低, NO转化活性基本不变, 这是由于H 2O减弱了CH 4与CO 2的重整反应, 但是对CH 4与NO的反应基本没有影响; 添加计量比的O 2后, CH 4转化活性提高, 而NO转化活性降低, 这是由于O 2和NO之间存在竞争吸附, CH 4被O 2氧化为主要反应, 从而减弱了NO的转化; 同时添加计量比的O 2和10% (φ) H 2O, CH 4与CO 2的重整反应受到抑制,CH 4与NO的反应、甲烷蒸汽重整反应和甲烷被O 2氧化反应同时发生, CH 4和NO的转化活性均提高. 相似文献
10.
The reaction of singlet oxygen with a variety of allyltin compounds CH 2=CHCH 2SnR 3 (R 3 = Me 3, Bu 3, allyl 3, (cyclo-C 6H 113, Ph 3, allylBu 2, Bu 2Cl, Bu 2OAc, allylCl 2, allylCl 2bipy) has been investigated, and the allylperoxytin compounds, 3-stannylallyl hydroperoxides, and 4-stannyl-1,2-dioxolanes which result from M-ene, H-ene and cycloaddition processes, respectively, have been identified by NMR spectroscopy. As the tin centre becomes more electropositive, as indicated by the 13C NMR shift of the allylic CH 2 group, the proportion of the M-ene reaction increases, and when δCH 2 is above about 23.7, the allylperoxytin compound is the only product. An exception to this rule is tetraallyltin, δCH 2 16.13, which similarly shows only the M-ene reaction. This is tentatively ascribed to the special effect of hyperconjugation between the C---Sn σ-bond and the remaining π-systems. A polar solvent favours the M-ene reaction. The cycloaddition reaction is favoured by low temperature, and at − 70°C in a non-polar solvent it may become the major route. Diallylmercury and allylmercury chloride react with singlet oxygen to show only the M-ene reaction, but also undergo extensive photosensitized decomposition. With 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD), allylmercury chloride shows only the M-ene reaction. 相似文献
11.
以邻甲酚和二氧化碳为原料,以磷酸钾为中和剂一步羧化合成邻甲基水杨酸及相关产物。探讨了反应条件对产率的影响。实验结果表明,当磷酸钾与邻甲酚物料比为2.5∶1,反应温度150 ℃,反应压力3.0 MPa时,羧化反应产物总收率达到95.4%,同时邻甲基水杨酸收率也达到最大。与传统碳酸钾中和法相比,磷酸钾中和法产物在后处理过程中无二氧化碳放出,后处理过程中的磷酸根可制备为磷酸钾使用,新工艺是一条绿色化工路线。 相似文献
12.
The solid state formation of lithium manganese oxides has been studied from the thermal decomposition of mixtures Li 2CO 3–Mn 3O 4 with XLi (lithium cationic fraction)=0.33 (LiMn 2O 4), 0.50 (LiMnO 2) and 0.66 (Li 2MnO 3). The analysis of the reactivity has been performed mainly by thermoanalytical (TG/DSC) and diffractometric (XRPD) techniques either on physical mixtures and on mixtures subjected to mechanical activation by high energy milling. At XLi=0.33, the cubic lithium manganese spinel oxide (LiMn 2O 4) forms in air. TG measurements showed that the reaction starts at a considerably lower temperature in the activated mixture. By variable temperature X-ray diffraction it has been assessed that, upon mechanical activation, LiMn 2O 4 forms directly and its formation is completed within 700 °C whereas, starting from a physical mixture, the formation goes through Mn 2O 3 and is complete only at 800 °C. At T>820 °C LiMn 2O 4 reversibly decomposes to LiMnO 2 and Mn 3O 4 with an enthalpy of 30.05 kJ mol −1 of LiMn 2O 4. At XLi=0.50, by annealing under nitrogen flow for 6 h at 650 °C the activated mixture, the orthorhombic LiMnO 2 is formed. Such a formation goes through a mixture of LiMnO 2 and LiMn 2O 4. The enthalpy of LiMnO 2 solid state formation from the activated mixture has been determined to be 57.4 kJ mol −1 of LiMnO 2. At XLi=0.66 in air the mechanical activation considerably lowers the temperature within the monoclinic phase Li 2MnO 3 forms. Besides the reaction enthalpy could be determined as 40.13 kJ mol −1 of Li 2MnO 3. The reaction, when performed under nitrogen flow, goes through the formation of LiMnO 2. Such a first stage of the reaction is affected by the temperature of reaction rather than by mechanical activation. The activation greatly enhances the second stage of the reaction leading from LiMnO 2 to Li 2MnO 3. 相似文献
13.
采用高温固相反应法、Pechini合成方法和柠檬酸配位法,制备了系列锂锰复合氧化物LiMn2O4催化剂,应用于NH3-SCR反应,并与固相反应法合成的MnO2进行了比较。采用N2吸附-脱附、扫描电镜、X射线衍射、H2程序升温还原、NH3程序升温脱附、NO程序升温脱附和X射线光电子能谱对LiMn2O4催化剂进行表征。结果表明,引入Li有利于提高锰基催化剂的SCR活性和抗硫性。Pechini法制备LiMn2O4的NO转化率可在130~260℃达到90%以上;固相反应法制备LiMn2O4的NO转化率大于90%的温度为90~310℃;MnO2的温度窗口则仅为140~280℃。与MnO2相比,引入Li可形成LiMn2O4结构,因此,催化剂中更多的锰离子保持在相对较低的价态Mn3+,并调整表面活性氧含量;同时,Li的存在调变了LiMn2O4表面的酸位,从而减少高温下MnO2表面容易发生的NH3非选择性氧化,改善其催化NH3-SCR反应的温度窗口,也增强了抗硫性。 相似文献
14.
自1991年Ohzuku[1] 、 Tarascon[2]等成功地将LiMn2O4用于锂离子电池正极以来, 人们对尖晶石LiMn2O4的电化学性质进行了广泛的研究[3]. 尖晶石LiMn2O4的一个缺点是充放电过程中, 特别在较高温度(如50 ℃)下, 其容量下降明显. Zhou等[4]详细研究了该过程, 发现造成容量下降的主要原因是充电状况下正极LiMn2O4的溶解, 由于Jahn-Taller效应生成不稳定的两相结构以及电解液的分解等. 为了提高LiMn2O4的充放电循环稳定性, 人们除了优化合成条件和溶液组分外, 主要采用添加少量掺杂元素(M), 部分替代LiMn2O4中的Mn, 制得LiMxMn2-xO4, 以抑制溶解和Jahn-Taller效应引起的结构变化. 相似文献
15.
The complexes (O---O)Rh(CH 2CH 2) 2 ((O---OH) = FcC(O)CH 2C(O)CH 3, PhC(O)CH 2C(O)CH 3, 1,2-(CH 3CO)(OH)C 6H 4, 3-benzoyl-(+)-camphor) are catalysts for the hydrosilylation of PhMeCO with Ph 2SiH 2. The optical yield from the reaction catalyzed by the camphor derivative is too low to measure. Only low optical yields (max 8.7% e.e.) are obtained from the same reaction by using similar in situ catalysts with ligands prepared from (+)-PhCH(Me)NH 2. Bases such as H − and PhCH(Me)NH − catalyze the hydrosilylation reaction in the absence of rhodium salts, but only low optical yields are obtained. Ph 2SiH 2 reacts with 2-cyclohexen-1-one under these conditions and the mode of reaction depends on the reaction conditions. 相似文献
16.
The solvent-free interaction of 2-phenylpyrrole with bromobenzoylacetylene (room temperature) upon their grinding with solid metal oxides (MgO, CaO, ZnO, BaO, Al 2O 3, TiO 2, ZrO 2) and salts (CaCO 3, ZrSiO 4) leads to either the cross-coupling product or the adduct of pyrrole addition to the riple bond of acetylene. The ethynylation is accompanied by the formation of intermediate and side products: E-2-(1-bromo-2-benzoylethenyl)-5-phenylpyrrole and 1,1-di(5-phenylpyrrol-2-yl)-2-benzoylethene. The activity of the metal oxides in the ethynylation reaction falls in the order (in the brackets, the content of 2-benzoylethynyl-5-phenylpyrrole in the reaction mixture is given): ZnO (81%), BaO (73%), Al 2O 3 (71%), MgO (69%), CaO (50%). The oxides, SiO 2, TiO 2, ZrO 2, and the salts, CaCO 3 and ZrSiO 4, are inactive in the ethynylation reaction affording only the intermediate adduct, with ZrO 2 the isolated yield of the bromoethenylpyrrole reaching 60%. ESR monitoring shows the reaction to start from one electron transfer from pyrrole to acetylene mediated by the oxide surface. The adduct is readily converted on Al 2O 3 to 2-(benzoylethynyl)-5-phenylpyrrole crystallized mostly as cis-rotamer (X-ray data). 相似文献
17.
Partial oxidation of methane (POM) to make syngas has been largely studied in recent years because of its potential to reduce the cost of syngas. Two reaction schemes have been proposed for the reaction:one is the sequence of combustion of CH 4 followed by reforming of unconverted CH 4 with CO 2 and H 2O,and the other is the direct partial oxidation of CH 4 to CO and H 2 without the experience of CO 2 and H 2O as reaction intermediates. In the industrial process, if the combustion-reforming mechanism predominantly contributes to the conversion of methane to syngas, severe heat management problems have to be taken into account. Therefore, the elucidation of the reaction pathway is of vital importance. In this paper, in situ time-resolved FTIR (in situ TR-FTIR) spectroscopy was used to study the POM reaction over lwt%Pd/SiO 2. The results of catalytic performance evaluation on the POM reaction over lwt%Pd/SiO 2 under different space velocity are also presented. It is expected that the additional proof can be presented to interpret POM mechanism. 相似文献
18.
采用固相反应法制备了具有尖晶石结构的LiMn_2O_4/TiO_2系列催化剂,探讨了TiO_2、Li/TiO_2、Mn/TiO_2、LiMn_2O_4及LiMn_2O_4/TiO_2等不同组成催化剂的甲烷氧化偶联反应性能,采用XRD、XPS、CO_2-TPD和H_2-TPR等表征方法对该系列催化剂进行了分析。结果表明,具有尖晶石结构的LiMn_2O_4化合物具有较高的甲烷氧化偶联催化活性,在775℃、0.1MPa、7200mL/(h·g),CH_4∶O_2(体积比)为2.5的条件下,甲烷转化率可达25.8%,C2选择性可达43.2%。TiO_2的存在不仅进一步提高了甲烷转化率和C2选择性,还有效抑制了甲烷完全氧化形成CO_2的过程。负载8%LiMn_2O_4的LiMn_2O_4/TiO_2催化剂性能达到最优,此时甲烷转化率达到31.6%,C2选择性为52.4%,CO_2选择性降低到26.3%。考察了不同焙烧温度对催化剂活性的影响,850℃为LiMn_2O_4/TiO_2催化剂的最佳焙烧温度。 相似文献
19.
The replacement of Ln site with different rare earth cations alters the crystalline phases of Ln 2Zr 2O 7, which in turn influences the surface active oxygen and alkaline sites significantly. The abundance and the interaction of the two types of sites determine the OCM reaction performance. 相似文献
20.
Only trace of quinhydrone, a urease-inhibitor, can inhibit enzymatically promoting hydrolytic reaction of urea [1]. A new enzymatic inhibition kinetic spectrophotometry method [2] for determination of trace quinhydrone was obtained by urea and P-dimethylamino-benzadehyde (color reagent) developing action. In this reaction, maximal absorptive wavelength is 420 nm. The enzymatic promoting reaction rate, log (A 0/A 1),enzymatic inhibition reaction rate, log (A 0/A 2,and their difference, log (A 2/A 1), are measured by detecting the remains of urea. All factors (urease, urea and color reagent dosage; reaction temperature; heating time), effecting log (A 2/A 1) were investigated. 相似文献
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