Ca对Cu/B/Ca/Al_2O_3结构及其催化醋酸仲丁酯加氢反应性能的影响

以γ-Al2O3为载体采用分步浸渍法制备了不同Ca O含量的Cu/B/Ca/Al2O3催化剂,并测试了其催化醋酸仲丁酯加氢制备仲丁醇的反应性能.Ca O含量对催化剂的结构、氧化还原性能、酸碱性和金属铜分散度的影响分别采用XRD、H2-TPR、XPS、NH3-TPD和N2O-H2氧化还原滴定实验进行分析.结果表明,适量氧化钙的引入对金属铜的分散度无明显影响,过量的氧化钙(20%)降低催化剂的比表面积,进而导致金属铜分散度的降低;但钙作为给电子助剂能够补偿电子从铜向氧化硼之间的迁移,提高催化剂的酯加氢活性.同时,氧化钙的引入能够有效消除Cu/B/Ca/Al2O3催化剂表面的强酸性位点并降低催化剂的酸量,减少醋酸仲丁酯加氢反应中酸催化副产物以及催化剂表面积碳的生成.     

(Ag/Al2O3+Cu/Ce(x)/Al2O3)组合催化剂催化乙醇选择性还原NOx及其副产物的消除

制备了Cu/Ce(x)/Al2O3(x为Ce与Al的摩尔比)系列氧化催化剂,并考察了(Ag/Al2O3 Cu/Ce(x)/Al2O3)组合体系催化乙醇还原NOx以及氧化去除反应副产物(CO和未完全燃烧的碳氢化合物)的活性.在200～350℃温度区间,组合催化剂具有与Ag/Al2O3相似的NOx去除效率.随着Ce/Al比增加,氧化催化剂去除CO的活性逐渐提高.Cu/CeO2催化剂具有最好的氧化活性,但其对NOx的去除有较大影响.综合考虑NOx转化率以及CO和HC的去除效果,(Ag/Al2O3 Cu/Ce(0·15)/Al2O3)是最佳的催化剂组合体系.通过对此系列氧化催化剂的BET比表面积、XRD、H2-TPR以及XPS等表征结果的分析,发现Cu和Ce之间的相互作用是催化剂氧化CO能力提高的主要原因.     

CeO2改性Cu/Al2O3催化剂上甲醇水蒸气重整制氢

研究CeO2改性Cu/Al2O3催化剂上甲醇水蒸气重整制氢反应过程,得到低温活性、氢选择性和稳定性较好的催化剂.Cu/Al2O3催化剂中添加CeO2提高了催化剂的活性和稳定性,当CeO2质量分数为20％时,催化剂活性表现最佳.在反应温度250 ℃,水醇摩尔比为1.0,液体空速为3.28 h －1条件下,甲醇转化率为95.5％,氢气选择性为100％.此外,CeO2通过促进水气转化反应降低了重整气中CO的含量.Cu/CeO2/Al2O3催化剂在200 h的寿命实验中,活性仍保持在90.0％以上,而Cu/Al2O3催化剂在100 h的寿命实验中,活性已很快下降.XRD和TPR分析及表面元素分布结果表明,铜和铈相互作用促进了铜在催化剂表面的高度分散,阻止了铜晶粒团聚、烧结,促使铜晶粒细小化,促进了铜的还原,改善了Cu/CeO2/Al2O3催化剂的性能.     

氢气对Ag/Al2O3和Cu/Al2O3催化剂选择性催化C3H6还原NOx反应的影响

 添加H2对Ag/Al2O3和Cu/Al2O3催化剂选择性催化C3H6还原NOx反应具有不同的影响. 原位漫反射红外光谱分析表明,在Ag/Al2O3催化剂上, H2的存在促进了C3H6部分氧化产物烯醇式物种(RCH=CH-O-)和乙酸盐等的形成,烯醇式物种和硝酸盐为主要反应中间体,二者间的相互反应性能很强,能形成高浓度的反应关键中间体异氰酸酯(-NCO)表面吸附物种,因此NOx的去除活性提高; 而在Cu/Al2O3催化剂上, H2的存在并没有促进C3H6部分氧化产物的形成,而且抑制了硝酸盐的形成,进而抑制了C3H6部分氧化产物与硝酸盐反应形成表面-NCO 物种,导致NOx的去除活性降低.     

H2S对NiW/Al2O3和CoMo/Al2O3上二苯并噻吩和4,6-二甲基二苯并噻吩加氢脱硫反应的影响

 考察了H2S对NiW/Al2O3和CoMo/Al2O3上二苯并噻吩(DBT)和4,6-二甲基二苯并噻吩(DMDBT)加氢脱硫反应的影响. 结果表明,H2S同时抑制DBT和DMDBT两种硫化物的加氢脱硫反应,并且对DBT的抑制作用更为明显. 对于NiW/Al2O3和CoMo/Al2O3两种催化剂,H2S抑制了DBT和DMDBT的直接脱硫路径活性; 对于CoMo/Al2O3催化剂上DBT转化中的加氢反应也有抑制作用,但促进了DMDBT转化中加氢反应的进行. NiW/Al2O3催化剂更易受H2S的影响.     

CeO2改性Cu/Al2O3催化剂上甲醇水蒸气重整制氢

研究CeO2改性Cu/Al2O3催化剂上甲醇水蒸气重整制氢反应过程,得到低温活性、氢选择性和稳定性较好的催化剂.Cu/A12O3催化剂中添加CeO2提高了催化剂的活性和稳定性,当CeO2质量分数为20%时,催化剂活性表现最佳.在反应温度250℃,水醇摩尔比为1.0,液体空速为3.28 h-1条件下,甲醇转化率为95.5%,氢气选择性为100%.此外,CeO2通过促进水气转化反应降低了重整气中CO的含量.Cu/CeO2/Al2O3催化剂在200 h的寿命实验中,活性仍保持在90.0%以上,而Cu/Al2O3催化剂在100 h的寿命实验中,活性已很快下降.XRD和TPR分析及表面元素分布结果表明,铜和铈相互作用促进了铜在催化剂表面的高度分散,阻止了铜晶粒团聚、烧结,促使铜晶粒细小化,促进了铜的还原,改善了Cu/CeO2/Al2O3催化剂的性能.     

纳米ZrO2/Al2O3复合载体及Ni/ZrO2/Al2O3催化剂的性能研究

 采用溶胶-凝胶法在经过扩孔处理的Al2O3基载体上制备了纳米ZrO2/Al2O3复合载体,并通过浸渍法制备了NiO/ZrO2/Al2O3催化剂. 用XRD,TPR,TPD和N2吸附等技术分别考察了载体和催化剂的结构及表面性能,研究了复合载体对Ni/ZrO2/Al2O3催化CO2重整CH4反应性能的影响. 结果表明,纳米ZrO2/Al2O3复合载体具有较大的比表面积、适宜的孔径分布及稳定的t-ZrO2结构,Ni/ZrO2/Al2O3催化剂具有较好的CO2重整CH4反应活性和稳定性.     

富氧条件下Cu/Al2O3催化剂上C3H6选择性还原NO的研究

以Cu/Al2O3为催化剂,对富氧条件下C3H6为还原剂选择性催化还原NO反应进行了研究.活性评价结果表明,与高活性的Ag/Al2O3催化剂相比,Cu/Al2O3催化剂选择性还原NO的活性较低,NO的最高转化率仅为40%.在所考察的温度范围(473～723K)内,红外谱图中不存在有机含氮化合物(R—ONO和R—NO2)的特征振动吸收峰.作为反应中间体—NCO的前驱体,有机含氮化合物在Cu/Al2O3催化剂表面难以生成是造成催化剂选择性还原NO活性低的直接原因.在Cu/Al2O3催化剂上,NO2吸附能够优先发生,并以NO3-物种的形式覆盖在大部分催化剂表面.动态原位红外光谱实验发现,这种NO3-表面物种与C3H6的反应性较差,使生成有机含氮化合物的关键反应难以发生,但此时的催化剂表面有利于C3H6和O2的完全氧化反应,这是导致Cu/Al2O3催化剂选择性较低的根本原因.     

沉淀温度对CuO/ZnO/Al2O3催化剂前驱体物相及催化水煤气变换反应活性的影响

 用X射线衍射、差热热重测定、程序升温还原、N2吸附、N2O滴定和常压微反活性评价技术考察了沉淀温度对CuO/ZnO/Al2O3系催化剂及其前驱体的物相和催化水煤气变换反应活性的影响. 结果表明,在沉淀温度为60～90 ℃时,催化剂前驱体中主要存在Cu2CO3(OH)2,(Cu,Zn)2CO3(OH)2和(Cu,Zn)6Al2(OH)16CO3·4H2O三种物相. 焙烧后的催化剂样品中形成了较多的CuO-ZnO固溶体,沉淀温度升高有利于CuO-ZnO固溶体的形成及催化剂活性的提高. 水煤气变换反应是一个非结构敏感型反应.     

富氧条件下Ag/Al2O3-Cu/Al2O3组合催化剂催化乙醇选择性还原NOx

 在富氧条件下,以乙醇为还原剂,考察了不同金属负载量的Ag/Al2O3和Cu/Al2O3催化剂选择性还原NOx的活性. 结果表明,4%Ag/Al2O3和10%Cu/Al2O3分别为各自体系中的最佳催化剂. 4%Ag/Al2O3具有很高的选择性催化还原NOx的活性,但同时会产生一定量的副产物CO. 10%Cu/Al2O3选择性催化还原NOx的活性不高,但却具有很好的消除CO的活性. 将4%Ag/Al2O3和10%Cu/Al2O3以不同方式组合,其评价结果表明,4%Ag/Al2O3-10%Cu/Al2O3组合催化剂具有与单纯4%Ag/Al2O3相似的NOx脱除活性,同时能够完全消除反应过程中产生的CO,并且能大大降低尾气中乙醇和乙醛的浓度.     

Crystallization of MgFe2O4 from a glass in the system K2O/B2O3/MgO/P2O5/Fe2O3

Spherical magnetic Mg-Fe-O nanoparticles were successfully prepared by the crystallization of glass in the system K₂O/B₂O₃/MgO/P₂O₅/Fe₂O₃. The magnetic glass ceramics were prepared by melting the raw materials using the conventional melt quenching technique followed by a thermal treatment at temperatures in the range 560–700 °C for a time ranging from 2 to 8 h. The studies of the X-ray diffraction, electron microscopy and FTIR spectra confirmed the precipitation of finely dispersed spherical (Mg, Fe) based spinel nanoparticles with a minor quantity of hematite (α-Fe₂O₃) in the glass matrix. The average size of the magnetic nano crystals increases slightly with temperature and time from 9 to 15 nm as determined by the line broadening from the XRD patterns. XRD studies show that annealing the glass samples for long periods of time at temperature ≥604 °C results in an increase of the precipitated hematite concentration, dissolution of the spinel phase and the formation of magnesium di-borate phase (Mg₂B₂O₅). For electron microscopy, the particles were extracted by two methods; (i) replica extraction technique and (ii) dissolution of the glass matrix by diluted acetic acid. An agglomeration of the nano crystals to larger particles (25–35 nm) was observed.     

High-precision measurements of 17O/16O and 18O/16O of O2 and O2/Ar ratio in air

A method for high-precision and high-accuracy mass spectrometric measurements of the ratios among the three oxygen isotopes, and of the O(2)/Ar ratio, is presented. It involves separation of the O(2)-Ar mixture from air and includes a fully automated system that ensures highly reliable sample processing. Repeated measurements of atmospheric oxygen yield the repeatability (+/-SE x t, standard error of the mean (n = 12) multiplied by Student's t-factor for a 95% confidence limit) of 0.004, 0.003 and 0.2 per thousand for delta(18)O, delta(17)O and delta O(2)/Ar, respectively.     

乙烷/H2O/O2/N2体系中光致过氧化物的产生

采用长光路Fourier红外光谱(LP-FTIR)和高压液相色谱(HPLC)技术研究了乙烷/H2O/O2/N2光化学体系中过氧化物的产生，证实乙烷降解产物中有过氧化氢、乙基过氧化氢(CH3CH2OOH,EHP)和过氧乙酸[CH3C(O)OOH,PAA]，并首次发现了甲基过氧化氢(CH3OOH,MHP)、羟甲基过氧化氢(HOCH2OOH,HMHP)和过氧甲醚(CH3OOCH3,DMP).H2O2,MHP和EHP的最大计算产率分别为6.8%，6.4%和6.7%，是乙烷降解生成的主要过氧化产物。MHP主要来自乙烷降解过程中的中间物乙醛的光解。HMHP的检出表明乙烷降解过程中可能有Criegee中间体.CH2OO.产生。OH自由基引发的乙烷降解反应可能是对流层大气H2O2，MHP及EHP的重要来源之一。     

苯对Pt/Ga2O3/WO3/ZrO2和Pd/Al2O3/WO2/ZrO2催化剂上正己烷异构化反应的影响

研究了苯对Pt/Ga2O3/WO3/ZrO2(PtGWZ)和Pd/Al2O3/WO3/ZrO2(PdAWZ)催化剂上正己烷异构化反应的影响.结果表明,苯可影响PtGWZ和PdAWZ上正己烷异构化反应性能,苯含量越高影响越显著.与PdAWZ相比较,苯对PtGWZ上正己烷异构化反应的影响相对较小;苯对PtGWZ上正己烷异构化反应活性的影响是可逆的,撤除苯后PtGWZ对正己烷异构化的催化性能可完全恢复;苯对PtGWZ上正己烷异构化反应的稳定性没有影响.苯对PdAWZ上正己烷异构化反应活性的影响足不可逆的,PdAWZ用于含苯正己烷异构化反应催化剂会逐渐失活.热失重法积炭分析结果表明,相同条件下,含苯正己烷异构化反应后,PtGWZ上的积炭量较PdAWZ上的积炭量少.分析讨论了苯对PtGWZ和PdAWZ上正己烷异构化反应影响差异性的原因.     

Synthetic architectures of TiO2/H2Ti5O11.H2O, ZnO/H2Ti5O11.H2O, ZnO/TiO2/H2Ti5O11.H2O, and ZnO/TiO2 nanocomposites

Although synthetic investigations of inorganic nanomaterials had been carried out extensively over the past decade, few of them have been devoted to fabrication of complex nanostructures that comprise multicomponents/phases (i.e., composite nanobuilding blocks), especially in the area of structural/morphological architecture. In this work, nanobelts of a protonated pentatitanate (H(2)Ti(5)O(11).H(2)O) were synthesized hydrothermally for the first time. Two technologically important transition-metal-oxides TiO(2) and ZnO were then grown respectively or sequentially onto the surface of the as-prepared nanobelts in aqueous mediums. With a main emphasis on organizational manipulation, the present investigation examines general issues of morphological complexity, synthetic interconvertibility, and material combinability related to fabrication of inorganic nanocomposites. Using this model material system, we demonstrate that complex binary and tertiary composite building blocks of TiO(2)/H(2)Ti(5)O(11).H(2)O, ZnO/H(2)Ti(5)O(11).H(2)O, ZnO/TiO(2)/H(2)Ti(5)O(11).H(2)O, and ZnO/TiO(2) can be architected stepwise in solution. Structural features of these nanocomposites have also been addressed.     

Oxidative dehydrogenation of propane over V2O5/MoO3/Al2O3 and V2O5/Cr2O3/Al2O3: structural characterization and catalytic function

The structure and catalytic properties of binary dispersed oxide structures prepared by sequential deposition of VO(x) and MoO(x) or VO(x) and CrO(x) on Al(2)O(3) were examined using Raman and UV-visible spectroscopies, the dynamics of stoichiometric reduction in H(2), and the oxidative dehydrogenation of propane. VO(x) domains on Al(2)O(3) modified by an equivalent MoO(x) monolayer led to dispersed binary structures at all surface densities. MoO(x) layers led to higher reactivity for VO(x) domains present at low VO(x) surface densities by replacing V-O-Al structures with more reactive V-O-Mo species. At higher surface densities, V-O-V structures in prevalent polyvanadates were replaced with less reactive V-O-Mo, leading to lower reducibility and oxidative dehydrogenation rates. Raman, reduction, and UV-visible data indicate that polyvanadates predominant on Al(2)O(3) convert to dispersed binary oxide structures when MoO(x) is deposited before or after VO(x) deposition; these structures are less reducible and show higher UV-visible absorption energies than polyvanadate structures on Al(2)O(3). The deposition sequence in binary Mo-V catalysts did not lead to significant differences in structure or catalytic rates, suggesting that the two active oxide components become intimately mixed. The deposition of CrO(x) on Al(2)O(3) led to more reactive VO(x) domains than those deposited on pure Al(2)O(3) at similar VO(x) surface densities. At all surface densities, the replacement of V-O-Al or V-O-V structures with V-O-Cr increased the reducibility and catalytic reactivity of VO(x) domains; it also led to higher propene selectivities via the selective inhibition of secondary C(3)H(6) combustion pathways, prevalent in VO(x)-Al(2)O(3), and of C(3)H(8) combustion routes that lead to low alkene selectivities on CrO(x)-Al(2)O(3). VO(x) and CrO(x) mix significantly during synthesis or thermal treatment to form CrVO(4) domains. The deposition sequence, however, influences catalytic selectivities and reduction rates, suggesting the retention of some of the component deposited last as unmixed domains exposed at catalyst surfaces. These findings suggest that the reduction and catalytic properties of active VO(x) domains can be modified significantly by the formation of binary dispersed structures. VO(x)-CrO(x) structures, in particular, lead to higher oxidative dehydrogenation rates and selectivities than do VO(x) domains present at similar surface densities on pure Al(2)O(3) supports.     

Thermochemische Untersuchungen im System V/Nb/O. II Zum chemischen Transportverhalten im Bereich V2O5/Nb2O5/VO2/NbO2

Thermochemical Investigations in the System V/Nb/O. II. Chemical Transport in the Region V₂O₅/Nb₂O₅/VO₂/NbO₂ Transport experiments were used to support the phase relationships of the V₂O₅/Nb₂O₅/VO₂/NbO₂ system, which were established by annealing experiments of powder mixtures. The phase relations were studied in the NbO₂-rich region of the system by means of X-ray and ESMA methods. The NbO₂-rich section is characterized by the following two phase and three phase regions: Two phase region: V₃Nb₉O₂₉/rutile mixed crystal V_1?xNb_xO₂ Two phase region: BI-mixed crystal/V_xNb_1?xO₂ Three phase region: V₃Nb₉O₂₉/solubility limit LG1 (V_1?xNb_xO₂)/BI-mixed crystal Three phase region: solubility limit LG1 (V_1?xNb_xO₂)/BI-mixed crystal/solubility limit LG2 (V_xNb_1?xO₂). The composition of the solubility limits LG1 and LG2 was ascertained by means of ESMA-investigation: LG1: 57.5 ± 5 mol% NbO₂/43.5 ± 5 mol% VO₂ LG2: 22.5 ± 5 mol% NbO₂/78.5 ± 5 mol% VO_2?     

Identification of corona discharge-induced SF6 oxidation mechanisms using SF6/18O2/H2 16O and SF6/16O2/H2 18O gas mixtures

The absolute yields of gaseous oxyfluorides SOF₂, SO₂F₂, and SOF₄ from negative, point-plane corona discharges in pressurized gas mixtures of SF₆ with O₂ and H₂O enriched with¹⁸O₂ and H₂ ¹⁸O have been measured using a gas chromatograph-mass spectrometer. The predominant SF₆ oxidation mechanisms have been revealed from a determination of the relative¹⁸O and¹⁶O isotope content of the observed oxyfluoride by-product. The results are consistent with previously proposed production mechanisms and indicate that SOF₂ and SO₂F₂ derive oxygen predominantly from H₂O and O₂, respectively, in slow, gas-phase reactions involving SF₄, SF₃, and SF₂ that occur outside of the discharge region. The species SOF₄ derives oxygen from both H₂O and O₂ through fast reactions in the active discharge region involving free radicals or ions such as OH and O, with SF₅ and SF₄.     

Zur Kenntnis der Systeme Li2O/CoO und Li2O/ZnO

On the Systems Li₂O/CoO and Li₂O/ZnO According to powder photographs the systems Li₂O/CoO and Li₂O/ZnO are so far similar as the Li-richest phase in near ?Li₄MO₃”?. Single crystal investigations lead to a pseudocubic, trigonal unit cell; a = 13.14, c = 7.99 Å (Zn); a = 13.10, c = 7.98 Å (Co). The oxygen form a cubic closest packing. Surprisingly there is obviously no completely ordered arrangement of cations. In spite of single crystal data the extent of the phases is still unknown.     

Shock tube studies of the N2O/Ar and N2O/H2/Ar systems

N₂O decay has been monitored via infrared emission for a series of mixtures containing N₂O/Ar and N₂O/H₂/Ar. These mixtures were studied behind reflected shock waves in the temperature interval of 1950–3075°K with total concentrations ranging from 1.2 to 2.5 × 10¹⁸ molec/cm³. In all cases the N₂O decayed exponentially, and a rate constant k_obs was obtained. Runs without added H₂ could be described by the following Arrhenius parameters: log A = ?9.72 ± 0.08 (in units of cm³/molec · sec) and E_A = 203.5 ± 3.6 kJ/mole. Addition of 0.01% and 0.1% H₂ was observed to increase the decay rate; the largest increase occurred between 2250 and 2500°K with 0.1% H₂, where k_obs doubled. Mixtures with no added H₂ were analyzed by numerical integration of the following reactions: Quantitative agreement between calculations and observations were obtained with both high and low choices for k₂ and k₃. The additional reactions were included in the analysis of the mixtures containing H₂. Here agreement was obtained only when low values were assigned to k₂ and k₃. The combinations of k₁ ← k₃ which agreed with all the data were k₁ = 3.25 × 10^?10 exp (?215 kJ/RT) and k₂ = k₃ = 1.91 × 10^?11 exp (-105 kJ/RT).