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1.
采用浸渍法制备了Nb改性的Pd/Al2O3催化剂,考察了该催化剂催化苯燃烧反应性能,并研究了催化剂的稳定性. 结果表明,Nb的添加明显提高了Pd/Al2O3催化剂性能,在195 ℃时苯转化率达到90%,苯的完全燃烧温度降低了40 ℃. 采用X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、H2 程序升温还原(H2-TPR)、NH3程序升温脱附(NH3-TPD)和氮气吸附等手段对催化剂进行了表征,结果表明,Nb的加入不仅提高了Pd物种的分散度,同时改变了部分Pd的价态,形成适宜反应的PdO-Pd物种,并促进了催化剂表面氧浓度的增加,使氧物种氧化能力增强,从而提高了催化性能. 1%Pd-5%Nb/Al2O3催化剂的催化活性高于2.0%Pd/Al2O3催化剂.  相似文献   

2.
The temperature-programmed desorption of hydrogen from a Pt/TiO2 catalyst reduced in a wide temperature range (RT-773 K) has been studied. It is found that the presence of labile surface oxygen species increases the amount of hydrogen species formed at room temperature, and greatly decreases the quantities of adsorbed hydrogen species at medium temperatures. After the catalyst was reduced at high temperature, it is observed that two strong hydrogen desorption peaks appear at 450–600 K and above 600 K, which are ascribed to surface titanium hydride and the hydrogen species stored in the sublayer and bulk of the support, respectively.  相似文献   

3.
CeO2 promoted palladium catalysts supported on Al2O3 were prepared using the impregnation (IM) and the deposition-precipitation (DP) methods. The activities and sulfur tolerance of the catalysts for hydrodesulfurization (HDS) were detected with thiophene HDS as probe reaction. H2 adsorption, XRD, FTIR, NH3-TPD, XPS were used to characterize the catalysts. The Pd-CeO2/Al2O3 (IM) catalyst was highly active for the HDS reaction, and it had much stronger sulfur tolerance than the Pd/Al2O3 catalyst. Pd-CeO2/Al2O3 (DP) showed excellent sulfur tolerance while its initial activity decreased. It was observed that with the chlorine bridge, the interfacial structure of Pd-Cl−1-Ce3+ was responsible for the high activity of the Pd-CeO2/Al2O3 (IM) catalyst, at the same time the interaction of Pd with Ce was weakened by Cl−1 ions. The enhanced sulfur tolerance over the Pd-CeO2/Al2O3 (IM) catalyst was attributed to the weakened Pd-S bond caused by the competitive adsorption of H2S on Ce3+ ions. As to the Pd-CeO2/Al2O3 (DP) catalyst, a strong interaction of Pd with Ce put Pd at an electron-deficient state, the creation of sulfided palladium was therefore inhibited.  相似文献   

4.
Pd/Al2O3 catalysts were prepared by the impregnation method and were used for the direct formation of hydrogen peroxide from H2 and O2. The H2O2 concentration and selectivity were strongly dependent on the solubility of hydrogen in the reaction medium. The modification of the support by halogenate has a beneficial effect on the selectivity. The state of the active Pd on Pd/Al2O3 catalysts was studied using X-ray photoelectron spectroscopy, and Pd(0) was found to be active.  相似文献   

5.
During an initial stage of the reaction of CCl2F2 with hydrogen on alumina-supported Pd and Pd-Au catalysts, an extensive defluorination occurs. However, at steady state, this undesired defluorination is greatly reduced; CH4 and CH2F2 constitute the only major reaction products. A temperature programmed hydrogen treatment study shows retention of fluorine (and carbon) in used catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

6.
唐紫蓉  尹霞  张燕辉  张楠  徐艺军 《催化学报》2013,34(6):1123-1127
用一维CeO2纳米管替代非一维结构的商用CeO2, 用于负载Pd而制得的催化剂在空气气氛下高温煅烧过程中Pd纳米粒子的团聚受到明显抑制, 在选择性有氧氧化苯甲醇生成苯甲醛反应中, 所制CeO2纳米管负载的Pd催化剂表现出更高的催化活性. 可见, 一维金属氧化物材料有望用作载体以抑制贵金属纳米粒子的团聚, 从而提高其催化性能.  相似文献   

7.
A series of 1%Pd/WO3-ZrO2 catalysts with different W/Zr ratios and calcination temperatures of WO3-ZrO2 were prepared by an impregnation method. Their crystal structure, surface state, and acidity were determined using X-ray diffraction, N2 adsorption, NH3 temperature-programmed desorption, pyridine infrared spectroscopy, and temperature-programmed reduction. Special attention was paid to the surface states of tungsten and palladium under different preparation conditions. The results revealed that WOx surface species underwent a transformation from polytungstate species to coexistent polytungstate/crystalline WO3 and further to crystalline WO3 particles with increase of W/Zr ratio and calcination temperature. The W/Zr = 0.2 sample calcined at 1 073 K showed the maximum amount of polytungstates, which were responsible for the excellent activity. Moreover, the state of palladium was only dependent on the calcination temperature. Well-dispersed Pd species were responsible for high selectivity to acetic acid, and large metallic Pd particles were favorable for ethylene combustion.  相似文献   

8.
利用等体积浸渍法制备了M-Pd/TS-1(M=Ce,La,Pt,Fe,Co,Ni,Cr,Mn,Zn,Cd,Cu)系列催化剂,并将制得的催化剂用于常压下氢、氧直接合成过氧化氢的反应。考察了M的类型及负载量对M-Pd/TS-1催化剂催化性能的影响。结果表明,M选Ce时,催化剂的性能最好。Ce的最佳掺入量,n_(Ce)/(n_(Ce)+n_(Pd))=0.5%。对Ce改性与未改性的催化剂进行了TEM及静态化学吸附分析,结果表明,掺入Ce可使Pd在TS-1分子筛表面的粒度及分散度得到改善。考察了n_(O_2)/n_(H_2)比,气体流量,反应时间等反应条件对H_2转化率、H_2O_2选择性及收率的影响。在相对优化的工艺条件下,即n_(O_2)/n_(H_2)=3,气体流量为25 mL·min~(-1),反应时间为3 h时,H_2O_2,的收率可达到25.7%,TOF值为18.7 mol·mol~(-1)·h~(-1),此时溶液中H_2O_2的质量百分数为0.8%。  相似文献   

9.
Composite supports Zr0.5Al0.5O1.75 modified by metal oxides,such as La2O3,ZnO,Y2O3 or BaO,were prepared by co-precipitation method,and palladium catalysts supported on the modified composite supports were prepared by impregnation method.Their properties were characterized by X-ray diffraction(XRD),NH3 temperature-programmed desorption(NH3-TPD),H2 temperature-programmed reduction(H2-TPR),N2 adsorption/desorption,and CO-chemisorption.The catalytic activity and the resistance to water poisoning of the prepared Pd catalysts were tested in a simulated exhaust gas from lean-burn natural gas vehicles with and without water vapor.The results demonstrated that the modified supports had an apparent effect on the performance of Pd catalysts,compared with the Pd catalyst supported on the unmodified ZrAl.The addition of ZnO or Y2O3 promoted the conversion of CH4.In the absence of water vapor,Pd/ZnZrAl exhibited the best activity for CH4 conversion with the light-off temperature(T50) of 275℃ and the complete conversion temperature(T90) of 314℃,respectively.However,in the presence of water vapor,Pd/YZrAl was the best one over which the light-off temperature(T50) of methane was 339℃ and the complete conversion temperature(T90) was 371℃.These results indicated that Pd catalyst supported on the modified composite ZrAl support showed excellent catalytic activity at low temperature and high resistance to H2O poisoning for the exhaust purification of lean-burn natural gas vehicles.  相似文献   

10.
An X-ray photoelectron spectroscopy study of Mo/Al2O3 catalysts prepared via [MoV 2O4(C2O4)2(H2O)2]2- complexes showed that after heating the catalysts with hydrogen in the spectrometer chamber, the position of the Mo3d line shifted to higher values of binding energy. This shift is interpreted as oxidative addition of hydrogen to the surface Mo species. A similar phenomenon was observed for a CO treated catalyst. A temperature-programmed desorption study has shown that hydrogen is strongly bounded to Mo and can only be removed from the catalysts at temperatures as high as 500°C. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

11.
以经过浓硝酸和等离子体放电预处理后的多壁碳纳米管(MWCNTs)为载体, 锰氧化物(MnOx)为活性组分, 采用等体积浸渍法制备MnOx/MWCNTs 催化剂. 利用热重分析(TGA)、扫描电子显微镜(SEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、程序升温还原/脱附(TPR/TPD)以及傅里叶变换红外(FTIR)光谱对催化剂进行表征, 探讨SO2对催化剂低温氨选择性催化还原(SCR)NOx活性的影响及SO2中毒机理. 结果表明, 低温下SO2对MnOx/MWCNTs 催化剂活性有明显毒化作用. 反应温度越高, SO2浓度越大, 催化剂SCR活性下降越快. 活性中心Mn原子硫酸化是催化剂失活的主要原因. 另外, 催化剂表面生成硫酸铵盐以及SO2对NO吸附的抑制作用也一定程度上造成了催化剂的失活.  相似文献   

12.
钴基费-托合成催化剂上CO、H2的吸附行为   总被引:2,自引:0,他引:2  
采用程序升温脱附及FT IR技术考察了CO、H2在钴基催化剂上的吸附行为.H2 TPD表明,Co/SiO2催化剂有两类脱附氢,引入锆助剂后,低温脱附氢量明显增加,高温吸附氢量下降.CO TPD及吸附态CO的红外光谱表明锆助剂使CO在钴催化剂上的吸附强度减弱,但其吸附量增大.钴基催化剂的费 托合成反应性能可以用吸附态物种的变化来解释.  相似文献   

13.
Palladium supported by Ce0.7Sn0.3O2 has been prepared by an impregnation method, and used for low temperature carbon monoxide oxidation. They were characterized by means of XRD and H2-TPR techniques. For PdO/Ce0.7Sn0.3O2 catalyst, three reduction peaks (α, β and γ) are observed. The β peak contributes to the reduction of PdO species and Sn4+ species on the surface of Ce0.7Sn0.3O2; β peak to the reduction of bulk SnO2 and surface Ce4+and the γ peak to the reduction of bulk CeO2. The increase of Pd loading from 0 to 0.75% enhances oxidation of CO, further increase of the Pd content affects the catalytic activity but slightly. XRD and TPR results show that highly dispersed Pd on the surface of the support is the active species for CO oxidation. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

14.
A series of Pd and Pd‐Ga bimetallic catalysts were prepared by a co‐impregnation method for 2‐ethylanthraquinone (EAQ) hydrogenation to produce hydrogen peroxide. Compared with 0.6Pd catalyst, the hydrogenation efficiency of 0.6Pd1.2Ga catalyst (11.9 g L?1) increases by 32.2%, and the stability of 0.6Pd1.2Ga catalyst is also higher than that of 0.6Pd catalyst. The structures of the samples were determined by N2 adsorption–desorption, ICP, XRD, CO chemisorption, TEM, H2‐TPR, in situ CO‐DRIFTS and XPS. The results suggest that incorporation of Ga species improves Pd dispersion and generates a strong interaction between Ga2O3 and Pd interface or between Pd and support. DFT calculation results indicate that the strong adsorption of carbonyl group on Ga2O3/Pd interface facilitates the activation of EAQ and promotes the hydrogenation efficiency.  相似文献   

15.
Peng Wu 《Acta Physico》2008,24(3):369-374
It was found that Si-MCM-41 mesoporous molecular sieves as a support of noble metal Pt could be used for the selective catalytic reduction of NO by hydrogen (H2-SCR) under lean-burn conditions. Pt/Si-MCM-41, together with Pt/Si-ZSM-5 and Pt/SiO2, was characterized by X-ray diffraction analysis (XRD), nitrogen adsorption/desorption, hydrogen adsorption, and transmission electron microscopy (TEM). The results indicated that Pt/Si-MCM-41 had the best H2-SCR activity in comparison with Pt/Si-ZSM-5 and Pt/SiO2 catalysts and that the maximum conversion of NO was up to 60.1% at 100 °C and a gas hourly space velocity (GHSV) of 80000 h-1 under lean-burn conditions. Characterization showed that the large surface area and pore volume of MCM-41 favored the dispersion of Pt. The maximum NO conversion of Pt/Si-MCM-41 catalyst decreased obviously to 15% at 120 °C when the pore structure of Si-MCM-41 support was destroyed. The reaction mechanism over Pt/Si-MCM-41 was investigated using in situ diffuse reflectance infrared spectroscopy (DRIFTS), which revealed that the main reaction intermediates should be nitrate species during NO reduction.  相似文献   

16.
The effects of palladium precursors (PdCl2, (NH4)2PdCl4, Pd(NH3)2Cl2, Pd(NO3)2 and Pd(CH3COO)2) on the catalytic properties in the selective oxidation of ethylene to acetic acid have been investigated for 1.0 wt% Pd–30 wt% H4SiW12O40/SiO2. The structures of the catalysts were characterized using X-ray diffraction, N2 adsorption, H2-pulse chemical adsorption, infrared spectrometry of the adsorbed pyridine, H2 temperature-programmed reduction and X-ray photoelectron spectroscopy. The present study demonstrates that the different palladium precursors can lead to the significant changes in the dispersion of palladium. It is found that Pd dispersion decreases as follows: PdCl2 > (NH4)2PdCl4 > Pd(NO3)2 > Pd(NH3)2Cl2 > Pd(C2H3O2)2, which is nearly identical to the catalytic activity. This indicates that the dispersion of palladium plays an important role in the catalytic activity. Furthermore, density of Lewis (L) and Brönsted (B) acid sites are also strongly dependent on the palladium precursors. It is also demonstrated that an effective catalyst should possess a well combination of Brönsted acid sites with dispersion of palladium.  相似文献   

17.
Under atmospheric pressure, methanol was produced from CO2–H2 over Pd/ZnO and from CO–H2 over Pd/MgO catalyst. Similar support effects were observed over Cu catalysts.  相似文献   

18.
Selectivity of product formation has been tested in hydrogenation of acetylene over 0.3 wt.% Pd/-alumina and 0.5 wt.% Pd/TiO2catalysts. Non-steady-state regime of catalyst operation was tested in pulse-flow experiments. Significant carbon poisoning appears to be a necessaryrequisite for selective formation of ethylene. The effect of hydrogen and acetylene partial pressure has been tested on the selectivity of C4products. At 273–298 K the catalysts showed 26–35% selectivity for C4 hydrocarbons and <2.5% for ethane production at conversionsof 30–40%. Deuterium distribution in ethylene and 1,3-butadiene and the deuterium content of the surface hydrogen pool have been compared and mechanismof diene formation has been discussed.  相似文献   

19.
以基于借氢策略的苯甲醇和苯胺一步合成N-苯基苄胺为模型反应,研究了三种不同表面结构的氧化铝对其负载的Pt-Sn催化剂上N-烷基化合成仲胺反应性能的影响.采用N2吸附-脱附法、压汞法、X射线衍射、透射电镜、扫描电镜、CO脉冲吸附、H2-程序升温还原及NH3-程序升温脱附等技术对载体和Pt-Sn/Al2O3催化剂进行了表征.结果表明,与Al2O3相互作用较弱且高度分散的Pt颗粒具有很高的催化活性,Al2O3载体较大的孔体积和大孔分布的孔结构有助于反应物扩散和吸附到催化剂表面并提高反应活性.同时也有利于反应产物从催化剂表面离开,从而提高催化剂的稳定性.然而Al2O3较强的酸性及酸性分布降低了产物仲胺的选择性和催化剂稳定性.  相似文献   

20.
The effect of temperature on the adsorption/desorption of ammonia from the air mixture on the surface of commercial binary V/Al and ternary Pd/V/Al, V(0.65 wt.%) /W(6.73 wt.%) /Ti and V(1.8 wt.%) /W(7.3 wt.%) /Ti de-NOx catalysts has been investigated by temperature-programmed desorption (TPD) method. The ability of the commercial catalysts to adsorb ammonia in the most stable surface species was shown to correlate well with their suppression of the NH3 oxidation.  相似文献   

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