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1.
加氢脱氯Pd/C催化剂失活原因探讨 总被引:1,自引:0,他引:1
在自制的气-固连续固定床反应器上,在反应温度为145℃,氢气体积流速为140ml/min,空速为10g/(g·cat)的条件下,对采用传统浸渍方法制备的载钯量为1.25%(质量分数)的Pd/C催化剂的寿命进行评价。其实验结果表明,Pd/C催化剂是氯乙酸母液混酯选择性加氢脱氯制备氯乙酸甲酯优良的催化剂。为了找到催化剂失活的原因,分别对反应前后的催化剂进行了XRD,差示热分析(DTA)和X射线光电子光谱(XPS)分析。结果表明,催化剂表面炭化物沉积是催化剂失活的主要原因,积炭物中以物理吸附的非永久性积炭为主,并可以通过惰性气体吹扫而除掉。 相似文献
2.
在2-硝基-4-乙酰胺基苯甲醚(NMA)催化加氢合成2-氨基-4-乙酰胺基苯甲醚(AMA)反应中,规整纳米Pd/C催化剂表现出很好的催化活性和选择性。但Pd/C催化剂在反应的套用过程中表现出反应活性逐渐降低。通过XRD、BET、EDS、XPS等物性表征以及Na2S滴定法和原子吸收法测定Pd含量的研究表明,钯微晶的长大、钯流失、催化剂中毒等不是引起Pd/C催化剂失活的主要原因,而Pd/C催化剂表面金属钯活性位在反应后被2-氨基-4-乙酰胺基苯甲醚产物等有机物覆盖可能是导致其性能逐渐降低的关键。使用酸洗法可以去除反应后Pd/C催化剂表面覆盖的2-氨基-4-乙酰胺基苯甲醚等有机物,释放金属钯活性位,实现Pd/C催化剂的性能有较大程度的恢复;而其他方法对Pd/C催化剂活性恢复的效果不明显。 相似文献
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活性炭载体的杂质成分和表面含悦官能团对钯炭催化剂的性能有显著影响。从改性活性炭载体的杂质成分,增加或去除表面含悦官能团的角度综述了近年来活性炭载体的改性对钯炭催化剂性能的影响。文献分析表明:活性炭载体的杂质成分一般会对钯炭催化剂的性能产生负面影响,但在氢化脱氯反应中却起到积极的作用;活性炭载体在液相和气相中悦化,能够增加表面含悦官能团的种类和数量,而惰性气氛下的热处理常被用于恒择性的移去或去除一些官能团;表面官能团的数量和种类决定着贵金属钯前驱体的平衡吸附量,贵金属钯的分散度以及钯的粒径等,从而进一步影响所制备的催化剂的性能。 相似文献
4.
研究了在三效催化反应过程中热老化对Pd/Al_2O_3选择性催化NH_3反应性能的影响。在稀/富循环流中进行稳态实验,采用X射线衍射(XRD)、BET比表面积、X射线光电子能谱(XPS)、拉曼光谱(Raman)和透射电镜(TEM)对催化剂的物理化学性质进行表征。结果表明,高温热老化导致活性金属钯的分散度降低、颗粒尺寸增大、Pd~(2+)活性物种的相对比例下降,这些微结构变化促使催化剂的三效活性降低、氨选择性增加。热老化诱导催化剂表面活性钯颗粒明显增大,较大的钯颗粒有助于NO解离生成活性氮物种,进而与氢反应生成NH_3。 相似文献
5.
研究了模拟铸铁文物在加入乙二胺的2%NaOH脱氯溶液中的化学和电化学脱氯效果,用红外光谱(IR)和紫外光谱(UV)测试了采用加入乙二胺的碱性溶液处理后试片表面的成分,用动电位极化曲线和交流阻抗(EIS)技术研究了其耐腐蚀性能.结果表明,试片在该碱性脱氯溶液中化学和电化学脱氯速度和脱氯效果比传统的碱溶液脱氯方法有明显的提高;处理后的试片表面形成一层配合物膜,该表面膜明显提高了铁器的耐腐蚀性能. 相似文献
6.
曾利辉 《稀有金属材料与工程》2016,45(1):236-239
通过催化加氢合成茚虫威(indoxacarb)中间体反应用钯炭催化剂的性能对比,考察了钯炭催化剂的载体和载体预处理对催化剂性能的影响。实验结果表明:硝酸超声回流处理活性炭可以有效地去除活性炭中的杂质灰分,减小杂质对催化剂性能的影响;选择平均孔径大和比表面积高的活性炭为Pd/C催化剂载体可以获得较好的催化反应活性和选择性。 相似文献
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采用不同稀土La前驱体浸渍掺杂改性Pd/γ-Al2O3催化剂,利用多功能催化性能评价装置测试不同催化剂的C3H8催化氧化性能,并通过H2-TPR、XRD、XPS等手段对催化材料进行结构表征,结果表明:La能促进贵金属钯分散,增强钯与载体相互作用,稳定高活性Pd2+物种,从而提高了催化剂的C3H8催化氧化性能。在选用不同La前驱体改性的Pd/γ-Al2O3催化剂中,硝酸镧改性效果最佳,能更好地促进活性金属钯的分散和Pd2+高活性物种的稳定。相比Pd/γ-Al2O3,La改性催化剂均降低了C3H8和NO的反应转化温度。选用不同La前驱体对催化活性影响存在差异的主要原因是La前驱体添加而引起的金属-载体相互作用和活性贵金属钯的分散状态变化。 相似文献
9.
担载型钯催化剂对CO_2加H_2甲烷化反应的催化性能 总被引:4,自引:1,他引:3
采用水溶液浸渍法制备了一系列无机氧化物担载的钯催化剂,并对其在二氧化碳甲烷化反应中的催化性能作了研究。结果表明,不同载体担载的体系有如下的活性顺序:二氧化锆>二氧化钛>氧化铝>海泡石>二氧化硅;反应条件及第2组份VII族金属的添加对反应结果均有影响:氨配体的引入可改变催化剂制备的前体,进而影响到催化活性 相似文献
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This article is about the reaction of selective hydrogenation of 1,3-butadiene performed in an excess of alkenes (propene/butadiene
ratio = 100) over supported gold catalysts, so as to mimic the conditions of purification of light alkenes (C4 cuts) from
the presence of impurities (highly unsaturated compounds, 1–3%). Gold was found highly selective (close to 100%, no propane
or butane formation) for the hydrogenation of butadiene to butenes at 100% conversion of butadiene. The influence of the concentrations
of the various reactants, i.e. hydrogen, butadiene and propene, on the rates of butadiene and propene hydrogenation was investigated,
and the apparent reaction orders were deduced from the dependence of rate on partial pressure in the gas phase. The reason
for the high selectivity of gold catalysts is that the reaction of hydrogenation of alkenes occurs at much higher temperature
(0.1% conversion at 300°C) than that of selective hydrogenation of butadiene (100% at T <170°C). Moreover, the presence of
propene has only a limited influence on the reaction of butadiene hydrogenation, while butadiene has no influence on propene
hydrogenation; the two reactions of hydrogenation hardly influence each other. Hydrogen dissociation is the rate limiting
step of the reaction (partial order of 0.7 and 1 with respect to H2 for butadiene and propene hydrogenation, respectively), responsible for the low activity of gold. The catalytic properties
of gold were compared to those of palladium-based catalysts, and reasons for their different behaviour were discussed. 相似文献
12.
E. V. Efremov D. V. Filippov A. V. Barbov 《Protection of Metals and Physical Chemistry of Surfaces》2016,52(3):425-430
The structure and physicochemical properties of palladium catalysts used in liquid-phase hydrogenation processes were studied with the use of adsorption, calorimetric, thermogravimetry, and temperature-programmed reduction techniques. The specific surface areas and average sizes and volume of pores of the adsorbents were determined. The palladium on activated carbon catalysts was found to possess a complex porous structure, whereas palladium on combined alumina and coal carrier catalysts is an adsorbent with a nonporous structure. The concentration of the applied metal and the nature of a support have a significant impact on the physicochemical properties of palladium catalysts. 相似文献
13.
采用氢氧化钠和盐酸调节钯炭(Pd/C)催化剂制备过程中的浸渍液的pH,制备了相应的钯炭催化剂。对Pd/C催化剂的成分、形貌等性质进行表征分析,研究了不同浸渍条件下制备的Pd/C催化剂对苯甲醛和2-氰基吡啶加氢的催化性能。结果表明,酸/碱浸渍方法可有效控制钯颗粒的尺寸大小及分散度。在浸渍液的pH值为3的条件下制备出的Pd/C-1~#催化剂平均粒径为2.78 nm。当浸渍液的pH值为10时,制备的Pd/C-2~#催化剂平均粒径为3.75 nm。对于2-氰基吡啶加氢,采用酸性浸渍条件制备的Pd/C催化剂具有更好的催化效果;而采用碱性浸渍条件制备的Pd/C-2~#催化剂对苯甲醛加氢效果更好。 相似文献
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采用浸渍法以TiO2成型载体制备了Pd/TiO2催化剂,考察了浸渍液pH值、Pd负载量、焙烧温度以及还原温度等因素对粗对苯二甲酸(CTA)中的主要杂质对羧基苯甲醛(4-CBA)的加氢精制性能的影响,并采用BET、XPS、XRD、H2-TPR等手段对催化剂进行了表征。结果表明,浸渍液pH值的升高会造成催化剂表面Pd原子富集,导致催化剂比表面积降低。Pd负载量0.5%时,催化剂所提供的活性中心数目足以满足4-CBA加氢所需。适当提高催化剂焙烧温度,有利于含钯前驱体的分解,催化剂还原温度过高时,会造成Pd/TiO2催化剂活性的迅速降低。Pd/TiO2催化剂的适宜制备条件为:浸渍液pH=2.0、Pd负载量0.5%、催化剂焙烧温度400℃、还原温度低于200℃。 相似文献
16.
Arthur Mpela Diane Hildebrandt David Glasser Mike S Scurrell Graham J Hutchings 《Gold bulletin》2007,40(3):219-224
The hydrogenation of carbon monoxide over Au/ZnO catalysts has been re-examined and new data is presented on the way in which
the product distribution can be manipulated by choice of coadded solids such as alumina or zeolite-Y. This comparative study
reveals that while ZnO itself leads to a high selectivity to methanol, the incorporation of gold drastically alters the product
spectrum and leads to a very high selectivity to hydrocarbons. The hydrocarbon selectivity at a reaction temperature of 300oC
is in fact much higher than in the case where alumina or zeolite-Y is introduced into a composite catalyst comprising the
Au/ZnO and the acidic solid. In the latter case DME is a major product. Significant light hydrocarbon formation on gold-based
systems under these circumstances appears not to have been discussed before. The reactions taking place on these catalysts,
the selectivities and absolute activities are discussed and the role of gold highlighted. 相似文献
17.
《Synthetic Metals》2001,125(2):183-188
Molecular sieving carbon (MSC) catalysts were prepared from polyimide containing nickel nitrate, and the catalytic function of the nano-space structure was investigated. After heat-treatment at 650°C, the polyimide film containing nickel nitrate gave an MSC in which Ni particles with the size of 5–10 nm were homogeneously dispersed. The molecular sieve property of the MSC catalyst was comparable to that of zeolite 5A. High selectivity of the MSC catalyst was shown by the competitive hydrogenation reaction of butene isomers. The selectivity is considered to be due to a contribution of the shape selectivity of nano-space having the molecular sieve property, though the perfect shape selectivity was not attained by the catalyst prepared because of the coexistence of reaction sites without selectivity such as a surface of metal particle exposed out of MSC matrix. 相似文献
18.
以介孔碳材料CMK-3为载体,采用乙二醇还原的方法进行金属铂负载,制备了不同铂含量(1.5%、2.0%和3%)的催化剂。XRD、BET、TEM的表征结果表明,催化剂保持了CMK-3高度有序的介孔结构,铂粒子的平均粒径在5 nm左右,均匀地分散在CMK-3孔道内。用萘的加氢反应对此催化剂的性能进行评价,获得的最优条件为:使用Pt(2%)/CMK催化剂,在280℃、氢气压力3 MPa、氢油比500、质量空速2 h-1的条件下,萘的转化率和生成十氢萘的选择性均大于98%。此催化剂对降低石油产品中芳烃具有潜在应用价值。 相似文献
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Alireza Babaei Lan ZhangErjia Liu San Ping Jiang 《Journal of Alloys and Compounds》2011,509(14):4781-4787
The effect of catalyst loading, operation temperature and co-infiltration of the palladium-based catalysts on the performance and stability of La0.8Sr0.2MnO3 (LSM) cathode of solid oxide fuel cells (SOFCs) is investigated. The result shows that adding a small amount of Pd catalyst (0.08 mg cm−2) has a remarkable effect on the reduction of overpotential of LSM cathodes and high palladium loading is detrimental to the electrochemical activity of LSM cathodes. The performance and stability of the Pd-impregnated LSM cathodes can be enhanced significantly by co-infiltration of palladium with either 20 mol% of silver or 5 mol% of cobalt. Increased stability of the co-infiltrated catalyst materials is probably related to the enhanced resistance of the co-impregnated Pd0.95Co0.05 and Pd0.8Ag0.2 nanoparticles against agglomeration and sintering at SOFC operation temperatures. The results indicate the co-impregnation is effective not only to enhance the electrochemical activity but also to improve the stability of LSM cathodes for the O2 reduction reaction of SOFCs. 相似文献