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排序方式: 共有441条查询结果,搜索用时 31 毫秒
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醋酸甲酯在Cs_(1.5)PW/SiO_2催化剂上的水解反应 总被引:1,自引:0,他引:1
通过改变阳离子的种类与配比,制备了一系列SiO2负载的磷钨酸盐催化剂,考察了制备方法对催化剂性能的影响,采用傅里叶变换红外光谱、X射线衍射、X射线荧光光谱、环境扫描电子显微镜等方法对催化剂进行了表征,并考察了该系列催化剂对醋酸甲酯水解反应的活性。实验结果表明,Cs1.5PW/SiO2催化剂的活性最好,当Cs1.5PW负载量(质量分数)为30%时,Cs1.5PW的Keggin结构保持完好,没有硅钨酸阴离子形成,Cs1.5PW在SiO2载体上高度分散;在反应温度55℃、反应时间2h的条件下,醋酸甲酯的转化率为35.79%,约为均相磷钨酸催化剂的1.3倍。该催化剂重复使用4次后,醋酸甲酯的转化率稳定在25%;80℃下反应2h,与NKC-9磺酸树脂催化剂相比,醋酸甲酯的转化率提高了5.17%。 相似文献
4.
The interaction of alkali metal with surfaces has been of great interest to the community of catalysis since alkali metal can play an important role as a promoter. On alkali-doped MoS2, such a promotion effect of alkali metal has been exemplified in the direct synthesis of linear alcohols from CO and H2, where the alkali-doping switches the catalyst selectivity from methanation to alcohol synthesis. This paper reviews recent high-resolution X-ray photoelectron spectroscopy experiments that have provided direct
observation of electron transfer from alkali metals to a model single crystal MoS2 and the capture of the supra-valence electrons in the subsequent oxidation reactions. 相似文献
5.
Hongwu Xu Alexandra Navrotsky M. Lou Balmer Yali Su 《Journal of the American Ceramic Society》2002,85(5):1235-1242
The crystal structures for a suite of substituted pollucites with the compositions CsTi x Al1– x Si2 O6+0.5 x , 0 ≤ x ≤ 1, have been determined from Rietveld analysis of powder synchrotron XRD data. Our results indicate that the pollucite end member (CsAlSi2 O6 ) has a tetragonal structure (space group I 41 / a ), whereas all other compositions are cubic (space group Ia 3 d ). The increased symmetry for the titanium-substituted structures is presumably due to the incorporation of additional O2− anions (needed for compensating the charge imbalance between Ti4+ and Al3+ ), which effectively holds open the expanded cubic framework. In situ cooling experiments of the substituted phase CsTi0.1 Al0.9 Si2 O6.05 reveal a displacive transformation to the tetragonal structure at ∼230 K. This transformation is tricritical in nature and is analogous to the tetragonal-to-cubic transition in pollucite on heating. 相似文献
6.
Carbon dioxide and carbon monoxide undergo reactive chemisorption with cesium modified Cu(110) and Cu(110)-O surfaces and via the anionic intermediate CO
2
–
(a) form a surface carbonate. The CO
2
–
(a) species was characterised by VEELS and XPS at low temperature (80 K) and the surface carbonate at 295 K. For cesium modified Cu(110) surfaces chemisorption of carbon monoxide gives rise to electron energy loss peaks (v
co) as low as 1450 cm–1 at 295 K. 相似文献
7.
采用粉冶法制备了添加Y2O3/CeO2(≤0.6w%)的复合强化钼合金(MYC)丝。用XRD标定合金相组成,用SEM观察合金的显微组织,用万能电子拉伸机测定合金丝的力学性能并将测定结果与纯钼丝进行了对比研究。研究结果表明:添加Y2O3/CeO2复合强化钼合金的相组成为Mo,YMoO4和CeO2;MYC合金断口具有典型的塑性断裂特征,MYC合金丝在1600℃退火后仍然表现明显的纤维状织构组织形态。 相似文献
8.
Xiaoxia Wang Hong Zhou Shuangping Yuan Weihao Zheng Ying Jiang Xiujuan Zhuang Hongjun Liu Qinglin Zhang Xiaoli Zhu Xiao Wang Anlian Pan 《Nano Research》2017,10(10):3385-3395
High-performance multiphoton-pumped lasers based on cesium lead halide perovskite nanostructures are promising for nonlinear optics and practical frequency upconversion devices in integrated photonics.However,the performance of such lasers is highly dependent on the quality of the material and cavity,which makes their fabrication challenging.Herein,we demonstrate that cesium lead halide perovskite triangular nanorods fabricated via vapor methods can serve as gain media and effective cavities for multiphoton-pumped lasers.We observed blue-shifts of the lasing modes in the excitation fluence-dependent lasing spectra at increased excitation powers,which fits well with the dynamics of Burstein-Moss shifts caused by the band filling effect.Moreover,efficient multiphoton lasing in CsPbBr3 nanorods can be realized in a wide excitation wavelength range (700-1,400 nm).The dynamics of multiphoton lasing were investigated by time-resolved photoluminescence spectroscopy,which indicated that an electron-hole plasma is responsible for the multiphoton-pumped lasing.This work could lead to new opportunities and applications for cesium lead halide perovskite nanostructures in frequency upconversion lasing devices and optical interconnect systems. 相似文献
9.
Thang Phan Nguyen Abdullah Ozturk Jongee Park Woonbae Sohn Tae Hyung Lee 《Science and Technology of Advanced Materials》2018,19(1):10-17
In this work, CsPbBr3 and PbSe nanocomposites were synthesized to protect perovskite material from self-enlargement during reaction. UV absorption and photoluminescence (PL) spectra indicate that the addition of Se into CsPbBr3 quantum dots modified the electronic structure of CsPbBr3, increasing the band gap from 2.38 to 2.48 eV as the Cs:Se ratio increased to 1:3. Thus, the emission color of CsPbBr3 perovskite quantum dots was modified from green to blue by increasing the Se ratio in composites. According to X-ray diffraction patterns, the structure of CsPbBr3 quantum dots changed from cubic to orthorhombic due to the introduction of PbSe at the surface. Transmission electron microscopy and X-ray photoemission spectroscopy confirmed that the atomic distribution in CsPbBr3/PbSe composite clusters is uniform and the composite materials were well formed. The PL intensity of a CsPbBr3/PbSe sample with a 1:1 Cs:Se ratio maintained 50% of its initial intensity after keeping the sample for 81 h in air, while the PL intensity of CsPbBr3 reduced to 20% of its initial intensity. Therefore, it is considered that low amounts of Se could improve the stability of CsPbBr3 quantum dots. 相似文献
10.
摘要: 用K4Fe(CN)6·3H2O和FeCl3·6H2O制备纯普鲁士蓝(PB)和负载量为55%普鲁士蓝/二氧化硅(PB/SiO2),考察了不同因素条件下(吸附时间、起始离子含量、c(H+)浓度、干扰阳离子K+和NH4+),纯PB对Rb+、Cs+混合模拟液的静态吸附情况.结果表明:随着吸附时间的增加,Kd(Rb+)和Kd(Cs+)增大,随着起始离子含量、c(H+)浓度、干扰阳离子K+和NH4+浓度的增大,Kd(Rb+)和Kd(Cs+)整体来说稍有下降,但变化不大.由于纯PB在水中易分散,不利于柱操作,故选取负载量为55% PB/SiO2进行柱实验,结果表明此柱对Rb+、Cs+显示出好的离子交换性能. 相似文献