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91.
Ag/Al2O3选择性催化丙烯还原氮氧化物表面反应机理的原位红外光谱研究 总被引:2,自引:0,他引:2
在富氧条件下Ag/Al2O3对以丙烯为还原剂选择性催化还原NOx的反应有很高的催化活性.本实验成功地利用原位红外光谱分析手段,在真实的催化反应条件下,探讨了丙烯选择性还原NOx的反应机理,证实了催化剂表面反应中间体Al-NCO和Ag-NCO虽在真空中稳定,但在实际反应条件下极为活泼.催化剂表面上R-ONO和R-NO2分解成NCO是整个反应的速度控制步骤.这一结论与在真空系统条件下对其反应机理的研究结果一致,证明了在这一反应体系中两种研究方法的相关性.同时本实验还从反应机理上探讨了催化剂的水蒸气中毒现象.水蒸气的存在阻碍了催化剂表面R-ONO和R-NO2的生成,并进一步阻碍了反应的速度控
制步骤,即R-ONO和R-NO2向Al-NCO和Ag-NCO的转化,但这是一种完全可逆的暂时中毒现象.结合相应的催化剂活性评价结果对表面反应机理进行了讨论. 相似文献
92.
Cu-Mg/Al复合氧化物催化碳颗粒物燃烧性能的研究 总被引:5,自引:0,他引:5
恒定二价与三价阳离子比为3(nM2+/nM3+=3),采用共沉淀法制备不同Cu含量的系列水滑石前驱物, 800 ℃焙烧4 h形成复合氧化物(CuO质量百分数分别为0%、5%、10%、15%、20%、30%、40%)用作柴油车排放碳颗粒物燃烧的催化剂,并采用XRD、BET、TG-DSC、FT-IR、TPR等表征手段研究了Cu、Mg含量对材料前驱物物化性能的影响及对其衍生复合氧化物催化碳颗粒物燃烧性能的影响.结果表明,Cu、Mg含量对材料的热稳定性、比表面和催化氧化活性有显著的影响. Mg有助于提高催化剂的热稳定性; Cu含量增加,催化剂比表面下降,但比表面不是影响催化剂活性的主要因素. CuO含量为15%时,催化剂具有最好的催化活性和稳定性,碳颗粒物的起燃温度(T10)和半转化温度(T50)分别为336 ℃和409 ℃.在CuO含量≤30%时可以形成结构完整的水滑石前驱物, CuO含量为40%时出现Cu(OH)2杂相; CuO含量< 20%时,经高温焙烧可得到均匀的复合氧化物, CuO含量≥20%时出现CuO偏析. TPR结果表明焙烧温度和复合氧化物的组成决定了材料的可还原性能. 相似文献
93.
In 1959, Horner showed that metalated alkyldiphenylphosphane oxides react with aldehydes or ketones to give alkenes. With this reaction, the diphenylphosphoryl (Ph2PO) group made its entrance into synthetic organic chemistry. In the thirty-six years since that date, extensive research has shown that this olefination, the Horner–Wittig reaction, has unique properties that make it much more than simply the phosphane oxide cousin of the more famous phosphorus-based olefinations—the Wittig reaction (based on phosphonium salts) and the Wadsworth–Emmons reaction (based on phosphonate esters). Early work on the Horner–Wittig reaction concentrated on the reactivity of phosphane oxides and the regioselectivity of their reactions, but more recently the power of the Ph2PO group to control the stereochemistry of alkenes, and to produce “on demand” either stereoisomer in high stereochemical purity, has emerged. From the study of these stereocontrolled Horner–Wittig reactions arose the realization that the Ph2PO group is useful not only for the control of the two-dimensional stereochemistry of alkenes, but also of three-dimensional stereochemistry in general. After a brief introduction to phosphane oxide chemistry, this review will examine the Horner–Wittig reaction, in both its original and “stereocontrolled” varieties. From there, we will move on to an account of the stereoselective construction of molecules containing the Ph2PO group, concentrating on the stereochemical directing effects of the Ph2PO group and on the role of its unique combination of attributes—steric bulk, electronegativity, and Lewis basicity—in controlling these reactions. Finally, we will present what is intended as a practical guide to this chemistry, covering the type of functionalized alkenes that have been made with the help of the Ph2PO group and giving guidelines that we hope will help the organic chemist to make the most of the chemistry the Ph2PO group has to offer. 相似文献
94.
L. Ya. Gavrilova T. V. Aksenova L. A. Bannykh Ya. V. Teslenko V. A. Cherepanov 《Journal of Structural Chemistry》2003,44(2):248-251
Phase equilibria in the La–Sr–Co–Ni–O system were studied in air at 1100°. The samples for the study were synthesized by the standard ceramic and citrate processes. The limiting solubility and structure of La1-xSrxCo1-yNiyO3- and (La1-xSrx)2Co1-yNiyO4 solid solutions were determined by Xray powder diffraction analysis. La1-xSrxCo1-yNiyO3- solid solutions with 0 x 0.5 have a distorted rhombohedral perovskitelike structure (R
c space group). An increase in the strontium concentration reduces the rhombohedral distortions, and the compounds with x < 0.5 have an ideal cubic structure (Pm3m space group). (La1-xSrx)2Co1-yNiyO4 crystals have a tetragonal K2NiF4 type unit cell (I4/mmm space group). The relationships between unit cell parameters and compositions were obtained for singlephase La1-xSrxCo1-yNiyO3- and (La1-xSrx)2Co1-yNiyO4 samples. The existence regions of La1-xSrxCo1-yNiyO3- and La1-xSrx)2Co1-yNiyO4 solid solutions were distinguished on P–T phase diagrams. 相似文献
95.
用水合五氧化二锑分离放射性母子体的研究─—一个新的~(201)Pb—~(201)T1发生器的制备 总被引:1,自引:0,他引:1
本文研究了无机离子交换剂—水合五氧化二锑(Sb2O5·nH2O)的制备,并用它分离了放射性母子体,制备了一个新的201Pb—201Tl放射性发生器。结果表明,末发生器具有高效、快速、简便的特点,此外还讨论了离子交换反应的机理。 相似文献
96.
T.?GrygarEmail author T.?Rojka P.?Bezdi?ka E.?Ve?erníková F.?Kovanda 《Journal of Solid State Electrochemistry》2004,8(4):252-259
Mixed Cu,Mn, Cu,Mn,Al, Cu,Mg,Mn, and Cu,Mg,Mn,Al oxides were obtained by calcination of amorphous basic carbonate (Cu,Mn oxides) or hydrotalcite-like precursors at 300–800 °C. The product composition was characterized by chemical analysis, XRD, and voltammetry of the microparticles. The XRD amorphous portion was detected indirectly by XRD and directly by voltammetry. Tenorite (CuO) and spinels were the main crystalline components of the oxide mixtures. The presence of Al shifted the onset of the crystallization of XRD-detectable tenorite and spinel to temperatures higher by 100–200 °C, and the presence of Mg shifted tenorite crystallization by 100 °C, but voltammetry was able to detect these phases even in XRD-amorphous or nanocrystalline calcines. Voltammetry is hence suitable for analysis of poorly crystalline oxides that can be used in heterogeneous catalysis. 相似文献
97.
H. N. Altshuler L. P. Abramova N. V. Malyshenko G. Yu. Shkurenko E. V. Ostapova 《Russian Chemical Bulletin》2005,54(8):1978-1981
The ion-exchange equilibrium in network polymers obtained from cis-2,8,14,20-tetraphenyl-4,6,10,12,16,18,22,24-octahydroxycalix[4]arene by template synthesis on cations Na+, K+, and Ba2+ as matrices was studied. The selectivity coefficients of ion exchanges Ba2+-H+, Na+-H+, K+-H+, Na+-K+, and Na+-NH4
+ were determined. The template synthesis enhanced the affinity of the polymers to matrix-forming cations by 6–8 kJ mol−1.
__________
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1919–1922, August, 2005. 相似文献
98.
99.
The reaction of dibenzylphosphine oxide with O-methyloximes of some ,-unsaturated ketones results in the phosphorylation at the -carbon atom to form methoxyiminophosphine oxides, whereas the reaction of dibenzylphosphine oxide with O-methyloximes of ,-unsaturated aldehydes affords aminodihydrophosphole oxides. 相似文献
100.
p-tert-Butylcalix[8]arene bonded capillaries for open-tubular capillary electrochromatography were prepared with γ-glycidoxypropyltrimethoxysilane as a bridge. The bonded capillary displayed low and steady electroosmotic flow (EOF) values over the pH range from 4 to 9. Detection limits for direct spectrophotometric detection at 277 nm for benzenediols (at a signal to noise ratio of 2) were 0.96 mg l−1 for the unbonded capillary and 1.48 mg l−1 for the bonded capillary, showing that the bonded layer did not show significant absorbance and hence decreased sensitivity. The bonded capillaries showed good separation selectivity for o-, m- and p-benzenediols, α- and β-naphthols, and α- and β-naphthylamines. This selectivity was attributed to significant interactions between the analytes and the bonded p-tert-butylcalix[8]arene, which contributed to the electrochromatographic separation mechanism. The bonded capillaries gave high stability and reproducibility. 相似文献