共查询到19条相似文献,搜索用时 125 毫秒
1.
超声波振动在Ce-Zr-La/Al2O3及负载型Pd三效催化剂制备中的应用 总被引:1,自引:0,他引:1
制备了CeO2-ZrO2-La2O3/Al2O3材料,在制备过程中使用超声波振动对材料进行处理,并以此材料为载体制备了单Pd三效催化剂.对所制备的载体进行了织构性能分析(BET)和X射线衍射(XRD)表征.对催化剂进行了NO程序升温脱附(NO-TPD)及H2程序升温还原(H2-TPR)表征,并对催化剂进行了活性测试.BET结果表明,900 ℃焙烧后,超声波振动处理的载体比表面积为130 m2·g-1,而没有进行处理的载体比表面积为117 m2·g-1.超声波处理的CeO2-ZrO2-La2O3/Al2O3材料介孔直径为11.4 nm,相对较大,载体更加稳定.XRD测试结果表明,超声波处理的载体在1150 ℃焙烧5 h后仍然只有Ce0.5Zr0.5O2一个单一物相,而未经过超声波处理的载体此时出现相分离,体相中有θ-Al2O3出现.以超声波处理材料为载体的Pd催化剂新鲜和老化后NO-TPD测试结果变化很小.H2-TPR测试中,超声波振动处理的材料制备的催化剂中活性组分和载体的还原峰温较未超声处理材料制备的催化剂稍高,而峰面积远大于未超声处理材料制备的催化剂.活性测试结果说明,由超声波振动处理过的载体制备的三效催化剂对汽车尾气中的三种污染物的起燃温度更低,有更好的活性以及温度特性. 相似文献
2.
催化消除汽车尾气中氮氧化物(NOx)物种在大气环境保护方面有着重要意义.随着环保法规的越来越严格,研制活性更高,稳定性更好的 NOx催化剂势在必行.贵金属 Pt、Pd、Rh三效催化剂(TWC)能够同时去除 NOxs、CO、HxCy三种污染物,生产工艺比较成熟.其中Rh是公认的促使NOx还原为N2的最有效组分,但Rh的价格较高且资源贫乏,限制了其实际应用.所以人们一直尝试采用一种廉价的替代品.单Pd的三效催化剂,由于其相对低廉的价格,较好的耐高温性能,有可能是合适的选择[1-2].此外,以NH3为还… 相似文献
3.
Ce-Zr-La-Al2O3的制备及负载的单Pd三效催化剂 总被引:6,自引:0,他引:6
采用共沉淀和浸渍两种方法制备了Ce-Zr-La-Al2O3(CZLA),对其进行了N2吸附和X射线衍射分析.以CZLA为载体制备了2%Pd/CZLA三效催化剂,并对催化剂进行了程序升温还原和活性测试.结果表明,两种方法制备的CZLA均具有较好的结构、织构和储氧性能,共沉淀法制备的CZLA具有更好的抗老化性能.以CZLA为载体所制备的单Pd三效催化剂表现出低的起燃温度、优异的三效性能,特别是优异的转化NO性能及抗老化性能. 相似文献
4.
5.
采用了一种由氨水和碳酸铵组成的复合沉淀剂来制备CeO2-ZrO2-Al2O3 (CZA)复合氧化物。作为对比,分别采用氨水和碳酸铵为沉淀剂制备了另外两个CZA复合氧化物。系统地研究了各CZA材料在织构、结构、氧化还原性能、热老化行为之间的区别,以及其负载的单Pd三效催化剂的催化性能。结果表明,不同的沉淀剂制得的材料中其CeO2-ZrO2 (CZ)和Al2O3之间的相互作用不同。用氨水做沉淀剂时,得到的材料中CZ和Al2O3之间的相互作用很小,导致其热稳定性较差。在碳酸铵做沉淀剂的情况下,CZ和Al2O3之间具有很强的相互作用,可以提高材料的热稳定性,但同时,CZ固溶体的均一性被严重破坏,使得材料的氧化还原性能不理想。而复合沉淀剂的使用可以有效地平衡CZ和Al2O3之间的相互作用,导致得到的CZA材料具有优异的织构、结构性能及良好的热稳定性。因此,其负载的单Pd催化剂表现出最为优异的氧化还原性能和三效催化活性。 相似文献
6.
采用共沉淀法制备了耐高温高比表面的La2O3-Al2O3(LA)以及铈含量分别为15%、33%和47%的储氧材料CeO2-ZrO2-La2O3-Al2O3(CZLA)、CeO2-ZrO2-La2O3+La2O3-Al2O3(CZL+LA)和CeO2-ZrO2-La2O3(CZL)4类载体材料,并用浸渍法制备了整体式Pd/LA、Pd/CZLA、Pd/CZL+LA和Pd/CZL汽油车尾气净化三效催化剂,考察了载体材料对单Pd三效催化剂的影响。采用低温N2吸附-脱附、H2-程序升温还原(H2-TPR)以及X射线光电子能谱(XPS)对载体材料及催化剂进行了表征,并考察了催化剂的空燃比性能和三效催化性能。结果表明,CZLA有效地结合了铈基和铝基载体材料的优点,表现出了优异的织构性能、热稳定性及还原性能。老化前后,其负载的单Pd三效催化剂在低温还原率、表面元素含量及Pd的电子结合能等性能方面表现出了最小的差异。催化剂活性测试结果表明,Pd/CZLA的三效窗口明显较宽,且拥有最低的起燃温度,尤其经1000℃老化处理后,其催化活性最高,C3H8、NOx和CO的起燃温度分别为370、257和223℃。可见,相较于其他3种载体材料,CZLA更适合于负载单Pd三效催化剂,从而满足更高标准的三效催化剂的性能要求。 相似文献
7.
The effect of pure and high silica Hβ zeolites on the catalytic performance of toluene combustion over Pd/H/3 catalyst was evaluated.Pure and high silica β zeolites were prepared by direct synthesis procedures,then 0.1 wt% of palladium was impregnated on different Hβ zeolites via incipient wetness technique using palladium nitrate as the Pd source.The Pd/Hβ catalysts were characterized by XRD,N2 adsorption/desorption,H2O adsorption,NH3-TPD,H2-TPR and XPS techniques.With increasing the SIO2/Al2O3 ratio of β zeolite,the activity of the Pd/Hβ catalysts for toluene combustion increased clearly and the pure silica β zeolite supported Pd catalyst showed the best catalytic activity.The superior catalytic performance of Pd/β catalyst prepared from pure silica β zeolite was attributed to its high hydrophobicity and the preserving ability for PdO active species. 相似文献
9.
Ce0.35Zr0.55La0.10O1.95对低贵金属Pt-Rh型三效催化剂性能的影响 总被引:1,自引:0,他引:1
采用共沉淀技术制备了Ce0.35Zr0.55La0.10O1.95固溶体, 其织构和结构性能以及氧化还原性能分别采用BET、XRD和程序升温(TP)技术进行了表征. 制备了低贵金属Pt-Rh型三效催化剂, 考察了Ce0.35Zr0.55La0.10O1.95对催化剂性能的影响. XRD和BET的结果表明, 经600 ℃焙烧5 h后, Ce0.35Zr0.55La0.10O1.95具有与Ce0.50Zr0.50O2相似的立方结构和高的比表面积;经1000 ℃焙烧5 h后, 仍能保持稳定的立方结构和47.25 m2•g−1的比表面积, 表现出优越的织构性能和高的热稳定性. H2-TPR和O2-TPO的结果表明, Ce0.35Zr0.55La0.10O1.95具有比Ce0.50Zr0.50O2更好的氧化还原性能. 和含Ce0.50Zr0.50O2的催化剂相比, 含Ce0.35Zr0.55La0.10O1.95的催化剂具有较宽的工作窗口, 优越的低温起燃性能, 较强的水气变换能力;催化剂经1000 ℃高温水热老化5 h后, 仍具有良好的催化活性, 表现出了优异的抗老化性能. 相似文献
10.
CeO2在Pd/γ-Al2O3催化剂中的助剂作用 总被引:11,自引:0,他引:11
用色谱微反流动法技术考察了富氧和贫氧条件下,添加CeO2对Pd/γAl2O3催化剂上CO氧化反应的影响,并运用TPR、TPDMS及SEM等技术研究了CeO2Pd/γAl2O3催化剂.结果表明:CeO2、Pd的共助作用使CeO2Pd/γAl2O3催化剂TPR还原峰温向低温方向移动;CeO2的存在使Pd/γAl2O3催化剂表面的吸附氧容易脱出,从而改善了催化剂的氧化活性;CeO2、Pd间的强相互作用使催化剂上Pd元素的分散程度增加. 相似文献
11.
Appropriate Na addition led to the formation of well-dispersed metallic Pd particles, which facilitated oxygen adsorption. Proper Na addition further promoted the transformation of absorbed water into liable surface oxygen species and improved the mobility of the lattice oxygen species, which contributed to enhanced catalytic activity and water resistance. 相似文献
12.
以丙烯酸铵为模板剂,由油柱成型法制备了系列球形Al2O3载体,采用XRD、BET等分析测试手段对其晶体结构、比表面积、孔容和孔径分布进行了表征,结果表明,600℃焙烧的球形γ-Al2O3载体具有介孔结构,并且比表面较不使用模板剂的样品有大幅度增加。焙烧温度升至960℃得到δ-Al2O3,介孔结构消失,但由于结构记忆效应,载体的大表面特性得以保持。以δ-Al2O3为载体制备Pd/Al2O3催化剂,采用氢-氧滴定(HOT)方法测定发现,比表面的增加显著提高了Pd金属的分散度,从而大幅度提高了催化剂的蒽醌加氢活性,氢化效率最高可达10.5 g.L-1。 相似文献
13.
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
14.
Reaction pathways for steam reforming of 2-propanol (isopropyl alcohol, IPA) on Rh/Al2O3, Ru/Al2O3 and Pd/Al2O3 have been studied by temperature-programmed reactions (TPRs) of IPA and acetone in the presence of steam. The results of
TPRs suggest that that of IPA on Rh/Al2O3 and Ru/Al2O3 proceeds via acetone, while the steam reforming of IPA on Pd/Al2O3 takes place via propene from acetone.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
Marta Legawiec-Jarzyna Anna Srebowata Zbigniew Karpinski 《Reaction Kinetics and Catalysis Letters》2003,79(1):157-163
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
16.
V.R. Choudhary C. Samanta T.V. Choudhary 《Journal of molecular catalysis. A, Chemical》2006,260(1-2):115-120
Since H2O2 decomposition can result in selectivity/yield loss in the direct H2O2 synthesis process from H2 and O2 over supported Pd catalysts, it is important to have an enhanced understanding about the factors affecting the H2O2 decomposition reaction. Herein, detailed studies have been undertaken to investigate the influence of different factors, such as (a) nature and concentration of acid in reaction medium, (b) nature and concentration of halide in presence and absence of acid in reaction medium, (c) pretreatment procedures and (d) catalyst modification by incorporation of different halides, on the H2O2 decomposition reaction over a 5% Pd/C catalyst in aqueous medium at 25 °C. This study has shown that the H2O2 decomposition activity is profoundly influenced by all the above factors. The effectiveness of the acids in suppressing the H2O2 decomposition activity decreased in the following order: hydroiodic acid > hydrobromic acid > hydrochloric acid acetic acid > phosphoric acid > sulfuric acid > perchloric acid. The ability of the acid to decrease the H2O2 decomposition activity was found to very strongly depend on the nature of its associated anion. Halides, such as iodide, bromide and chloride were particularly effective in suppressing the H2O2 decomposition activity. Oxidation pretreatment of the catalyst was found to strongly suppress its H2O2 decomposition activity, while a reduction treatment was found to promote its activity. A gradual decrease in the H2O2 decomposition activity of the catalyst was observed with each successive usage due to in situ sub-surface oxidation of Pd by H2O2. Halide incorporation either via the reaction medium or prior catalyst modification had a similar qualitative effect on the H2O2 decomposition activity. 相似文献
17.
Antal Sárkány 《Reaction Kinetics and Catalysis Letters》2001,74(2):299-307
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
18.
Shuhua Yuan 《Acta Physico》2008,24(3):364-368
The catalysts for the combustion of ethyl acetate were prepared using Fe, Co, Cu, Cr, and Mn metal oxide as active components supported on Al2O3-Ce0.5Zr0.5O2 mixed oxides and characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), oxygen storage capacity measurement, BET surface area, XPS measurement, and activity test. According to the results of characterization, it was found that Cu/Al2O3-Ce0.5Zr0.5O2 (1:2, mass ratio) and Mn/Al2O3-Ce0.5Zr0.5O2 (1:2) catalysts presented excellent activity for the catalytic combustion of ethyl acetate, because of the more reducible species and high reducibility of the catalysts. For ethyl acetate oxidation, more than 99% conversion was achieved at 245 °C over catalysts Cu/Al2O3-Ce0.5Zr0.5O2 (1:2) and Mn/Al2O3-Ce0.5Zr0.5O2 (1:2, mass ratio), indicating that the catalysts had great potential for wide use. 相似文献
19.
以活性氧化铝(γ-Al2O3)为载体,分别以Mn(NO3)2溶液和酸性氯化钯(PdCl2)溶液为修饰组分和活性组分前体,采用分步浸渍法制备了Mn修饰Al2O3载体负载钯催化剂。将催化剂应用于蒽醌加氢反应,考察了催化剂制备方法、活性组分负载量和催化剂还原温度对反应效果的影响。用XRD、BET、XPS和TPR对催化剂进行了表征。结果表明,催化剂活性受到制备方法的影响,在对Mn修饰Al2O3载体进行焙烧,Pd负载量0.2(wt)%、还原温度300℃的条件下,催化剂蒽醌加氢活性较高,较未修饰的催化剂提高了约16%。催化剂中Mn以MnO的形式存在,影响了γ-Al2O3的组织结构,使载体与活性组分之间的作用力增强,活性组分Pd高度分散在催化剂表面,从而提高了催化剂的活性。 相似文献