原位红外光谱法研究Pd-Ag/Al2O3和Pd/ Al2O3乙炔加氢催化剂

以一氧化碳和乙炔为探针分子,采用原位红外光谱技术研究了Pd-Ag/ Al₂O₃和Pd/ Al₂O₃催化剂上乙炔加氢反应以及催化剂本身的表面形态,动态考察了乙炔加氢的气相反应行为、CO吸附以及催化剂表面吸附物种的变化。结果表明,在Pd-Ag/ Al₂O₃催化体系中,由于Ag的加入而受到几何效应和电子效应的共同影响,引起了催化剂表面形态的改变从而改变了催化剂的性能。另外,乙炔加氢反应会导致钯催化剂表面形成由长分子链的饱和烃组成的碳氢化合物层,该碳氢化合物层有可能是加氢反应形成的绿油。     

不同Pd/Ag配比Pd-Ag/Al2O3催化乙炔加氢微观反应动力学分析

乙炔加氢是乙烯工业中的重要精制反应。以α-Al₂O₃作为载体,采用分步等量浸渍法制备了不同Pd/Ag配比的加氢催化剂,使用N₂物理吸附、XRD、ICP、XPS、TEM和CO化学吸附等手段表征催化剂的结构和组成,根据正交实验设计方案进行动力学实验,建立了微观反应动力学模型,并根据动力学模拟结果和动力学参数值的变化分析了Ag助剂含量对乙炔加氢反应动力学的影响。研究结果表明,以Pd-Ag催化剂上碳二加氢的DFT计算结果为基础参数来源,经过吸脱附步骤活化能的优化,微观反应动力学模型可以很好地模拟不同Pd/Ag配比催化剂上的乙炔加氢反应动力学结果;在所研究范围内,各催化剂上加氢反应的表面最丰物种皆为C₂H₄^*,速率控制步骤为乙烯基加氢,不会随着Ag含量的不同发生变化;但是Ag含量的增加显著降低了氢气脱附活化能,提高了乙烯的选择性,这可能与Ag含量的提高增加了催化剂表面Ag和Pd之间的电子转移现象有关。     

CuNi/Al2O3催化剂上乙炔选择加氢的研究

采用浸渍法制备了CuNi/Al2O3催化剂,研究了Ni负载量、Cu负载量及n(Cu)/n(Ni)对催化剂上乙炔选择加氢活性和选择性的影响,以及催化剂的还原性能。结果表明:CuNi/Al2O3催化剂中Cu提高了Ni的还原性,使催化剂具有很高的活性及乙烯选择性。随Cu/Ni原子比的提高,催化剂的活性下降,选择性升高,当Ni的负载量为10%、n(Cu)/n(Ni)=0.5时,在反应温度为50℃、反应压力为0.2 MPa、原料气流量为45 mL/min及H2流量为1.5 mL/min的反应条件下,乙炔的转化率达88.98%,乙烯的选择性达74.01%,乙烯收率为65.86%。     

Kinetics of acetone hydrogenation over Pt/Al2O3 catalysts

The hydrogenation of acetone to isopropanol has been studied in the vapour phase over Pt/Al₂O₃ catalysts. The rate law obtained at a total pressure of 1 atm and temperatures between 303 and 363 K is of the form V=kP⁰_aP^1/2_H exp (-44 kJ mol^?1 RT^?1). The kinetic results are consistent with a Langmuir-Hinshelwood hydrogenation mechanism involving a half hydrogenated species and a non-competitive chemisorption of acetone and hydrogen on the platinum surface. The specific activity (calculated per platinum surface atom) has been found to be scarcely dependent on the platinum particle size. It is suggested that the chemisorption sites are made of a very small ensemble of platinum atoms.     

乙炔选择性加氢催化剂研究进展

乙烯是石化工业中最重要的工业原料之一,然而乙烯产品中少量乙炔杂质的存在会直接影响乙烯的下一步应用。乙炔选择性催化加氢被认为是脱除乙炔杂质最有效的方法之一。本文综述了乙炔选择性加氢催化剂近年来的研究进展,介绍了乙炔选择加氢的反应机理,归纳总结了活性组分、助剂、载体以及结构对乙炔加氢催化剂性能的影响。鉴于Pd基催化剂仍然是工业应用的主流催化剂,文中综述了Pd基催化剂的研究现状和目前存在的一些挑战,同时提出了催化性能优化的建议。最后,就如何进一步提高乙炔选择性加氢催化剂性能的发展趋势进行了归纳,主要从单原子合金催化剂、催化剂微观调控以及电化学炔烃加氢方面进行论述,为未来提高乙炔加氢催化剂的性能提供了指导方向。     

Al_2O_3焙烧温度对乙炔选择加氢催化剂性能的影响

采用浸渍法制备了NiCu/Al2O3乙炔选择加氢催化剂,研究了焙烧温度对Al2O3结构、酸性及催化剂催化性能的影响,结果表明：随着焙烧温度的提高,Al2O3的晶相结构由γ相逐渐转变为δ相和θ相,最后转化为α相,比表面积降低而孔径增大;酸强度逐渐降低最后直至消失。随Al2O3载体焙烧温度的提高,NiCu/Al2O3催化剂上乙炔的转化率和乙烯的选择性同时增加,当焙烧温度为1100℃时,乙炔的转化率和乙烯选择性分别为89.3%和77.5%。     

强静电吸附法制备PdZnx/Al2O3催化1,4-丁炔二醇选择加氢

针对1,4-丁炔二醇选择加氢反应特性,以强静电吸附法可控地制备了一系列Pd、Zn不同物质的量比的PdZnx/Al2O3双金属催化剂,并探究Zn的引入对催化加氢性能的影响.研究发现,少量Zn的添加能够保持催化剂在较高活性的情况下,大幅度改善其对中间产物1,4-丁烯二醇的选择性.其中,PdZn2/Al2O3催化剂表现出较高的催化活性和顺式-1,4-丁烯二醇的选择性.反应在50℃、1 MPa的条件下进行,1,4-丁炔二醇在接触时间为6 gcat·h/mol时的转化率为91％,顺式-1,4-丁烯二醇的选择性可达到86％.结合程序升温还原与X射线电子衍射光谱分析发现,前驱体经400℃焙烧和400℃还原处理后形成了PdZn双金属催化剂.Zn原子的掺入有效调变了Pd活性位点的几何效应和电子效应,抑制了中间产物的过渡加氢.     

The choice of an optimal composition and preparation method of non-promoted Pd/Al2O3 and promoted Pd-Co/Al2O3 catalysts for the selective hydrogenation of vinylacetylene

For the purpose of optimizing the chemical composition and technology of synthesis of the catalyst for the acetylene hydrocarbons hydrogenation in industrial streams of butadiene and ethyl-vinylacetylene fractions, the influence of the palladium initial compound nature, the active component concentration, the promotion by cobalt, the molar ratio of palladium to cobalt, the phase composition of the supporter on physical chemical properties, and the activity and selectivity to 1,3-butadiene of the catalysts was studied. The effect of acidic-base characteristics of the supporter on its ability to oligomerize unsaturated hydracarbons has been investigated. It has been established, than the δ-Al₂O₃ supporter is characterized by a low concentration of Bronsted and Lewis acidic sites, decreasing the quantity of oligomers formed on its surface. The optimal composition of the non-promoted KGV-07 catalyst, recommended for the raw butadiene fraction hydrogenation, is 0.5% of Pd deposited from palladium acetate on δ-Al₂O₃ with palladium particles of 16 nm in size, on which the vinylacetylene conversion of 100% and the selectivity to 1,3-butadiene of 69.9% are reached at a temperature of 20°C at the reactor input, hourly space velocity (HSV) of hydrocarbon raws of 700 h⁻¹, molar ratio of hydrogen to ethyl-vinylacetylenes of 4: 1, summary concentration of 49% of acetylene hydrocarbons, and 1.5% of 1,3-butadiene in hydrocarbon raws. The synthesis of the cobalt-promoted KGVP-07 catalyst with 0.5% of Pd deposited from palladium acetylacetonate on δ-Al₂O₃ and molar ratio of Pd: Co = 1: 1 has been developed for the hydrogenation of an ethyl-vinylacetylene fraction with a concentration of acetylene hydrocarbons to 6 wt %, with the vinylacetylene conversion of 100% and the selectivity to 1,3-butadiene of 61.3%, at HSV of the hydrocarbon stream of 700 h⁻¹, temperature of 6°C at the reactor input, and molar ratio of hydrogen to ethyl-vinylacetylene admixtures of 4: 1. Promotion by cobalt leads to the formation of palladium particles at the zero oxidation level and to an increase in their average size from 11 to 14 nm in comparison with the non-promoted Pd-catalyst. In the work, IR-spectroscopy, transmission electron microscopy (TEM), and physicochemical methods have been used to characterize the catalysts texture and supporter phase composition. Pilot tests of the KGV-07 and KGVP-07 catalysts on the Etilen plant unit have proven the correctness of the choice for the catalysts’ optimal chemical composition.     

钯基乙炔选择性加氢催化剂研究进展

催化选择加氢去除乙烯中微量乙炔是石化工业重要的反应过程,工业钯基催化剂选择性低、催化剂使用寿命较短。本文综述了近年来国内外乙炔选择性加氢钯基催化剂的研究进展。主要探讨了过渡金属、金属氧化物与非金属配体助剂能调变钯粒子空间结构,隔离分散钯粒子并与钯粒子产生电子效应;阐明了钯粒子尺寸与织构形貌的调控能改变钯的晶面结构,影响钯对乙烯的吸脱附和对氢气的活化与解离性能;评述了单一氧化物、复合金属氧化物、碳材料等载体为催化剂提供合适的表面酸碱性并加强了与活性中心之间的相互作用,稳定钯粒子抑制其发生迁移与团聚。提高乙烯选择性与催化剂稳定性是该研究的重点与难点,负载型钯基催化剂的发展方向是构建高分散钯粒子,并在反应过程中保持稳定。     

Performance and aging of catalysts for the selective hydrogenation of acetylene: a micropilot-plant study

Some catalysts for the “tail-end” selective hydrogenation of acetylene were tested in a micropilot plant. This was operated under conditions similar to those of industrial plants. The influence of temperature, carbon monoxide concentration and H₂/C₂H₂ ratio on the activity and selectivity were investigated. Three possible definitions for the calculation of the selectivity to ethylene were used and compared. Great differences in the physico-chemical properties and in catalytic performance were found among the catalysts examined. A decrease in the conversion of acetylene was found at high temperatures.In spite of the short duration of the tests (⩽350 h), aging phenomena were frequently observed, due to the formation of oligomers on the catalysts. Large amounts of carbon were measured in the unloaded catalysts. The formation of oligomers was favoured by higher acetylene concentrations and occurred only in the presence of the hydrogenation reaction. Deactivation was also correlated with 1) the concentration of carbon monoxide, 2) the hydrogen/acetylene ratio, 3) the use of constant or variable reaction conditions during the test and 4) the linear velocity. It was suggested that carbon monoxide is involved in the formation of the organic compounds that deactivate the catalysts. Aging was faster for fresh catalysts. It caused a loss of total surface area, of activity in acetylene hydrogenation and, often, of selectivity to ethylene.A set of tests, planned according to statistical criteria, was performed. Results were interpolated by second degree polynomials, yielding an empirical model which accounted for the influence of both time and reaction variables. This model was used to find conditions of high selectivity and to simulate some runs at constant conversion, maximum selectivity and minimum deactivation of the catalysts.     

Enantioselective hydrogenation of ethyl pyruvate on tin promoted Pt/Al2O3 catalysts

The enantioselective hydrogenation of ethyl pyruvate has been studied on a Pt/Al₂O₃-dihydrocinchonidine catalyst promoted with different amount of tin. The surface reaction between hydrogen adsorbed on Pt and tin tetraalkyls is used for the tin introduction. This reaction leads to the formation of surface organometallic complexes (I), with SnR_(4-x) moieties anchored to the platinum surface. The enantioselectivity of the Pt/Al₂O₃-dihydrocinchonidine catalyst is found to change only slightly upon promotion with tin, while the rate of ethyl pyruvate hydrogenation depends strongly on the amount and the form of tin introduced. The hydrogenation activity is suppressed completely at relatively low tin coverage (Sn/Pt_s < 0.06). The highest hydrogenation rate is measured over catalysts containing complex (I) (Sn/Pt_s = 0.025) on the platinum surface. On Sn-Pt alloy type active sites, which are formed after decomposition of (I) in hydrogen, the rate of hydrogation is considerably lower than on the unpromoted reference Pt/Al₂O₃ catalyst.On leave from the Central Research Institute for Chemistry of the Hungarian Academy of Sciences.     

Recent advances in selective acetylene hydrogenation using palladium containing catalysts

Recent advances with Pd containing catalysts for the selective hydrogenation of acetylene are described. The overview classifies enhancement of catalytic properties for monometallic and bimetallic Pd catalysts. Activity/selectivity of Pd catalysts can be modified by controlling particle shape/morphology or immobilisation on a support which interacts strongly with Pd particles. In both cases enhanced ethylene selectivity is generally associated with modifying ethylene adsorption strength and/or changes to hydride formation. Inorganic and organic selectivity modifiers (i.e., species adsorbed onto Pd particle surface) have also been shown to enhance ethylene selectivity. Inorganic modifiers such as TiO₂ change Pd ensemble size and modify ethylene adsorption strength whereas organic modifiers such as diphenylsulfide are thought to create a surface template effect which favours acetylene adsorption with respect to ethylene. A number of metals and synthetic approaches have been explored to prepare Pd bimetallic catalysts. Examples where enhanced selectivity is observed are generally associated with decreased Pd ensemble size and/or hindering of the ease with which an unselective hydride phase is formed for Pd. A final class of bimetallic catalysts are discussed where Pd is not thought to be the primary reaction site but merely acts as a site where hydrogen dissociation and spillover occurs onto a second metal (Cu or Au) where the reaction takes place more selectively.

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不同粒径Pd/Al2O3催化乙炔加氢反应微观动力学分析

采用等量浸渍法制备了α-Al₂O₃负载的系列Pd催化剂,运用BET、XRD、ICP-AES、CO化学吸附、TEM等手段对催化剂进行了表征;根据部分析因实验设计方案进行动力学实验,采用微观反应动力学方法模拟和分析了所获稳定期本征动力学实验结果。结果发现,制备所得催化剂Pd颗粒的平均粒径分别为1.6、3.4、5.5 nm,CO化学吸附所测定达到活性稳定期后的催化剂表面Pd原子数与Hardeveld模型计算的Pd（111）表面原子数一致;模拟结果表明该微观动力学模型可以很好地模拟不同粒径催化剂上的动力学结果,在所研究范围内表面最丰物种为C₂H₄^*和C₂H₃^*,通过微观与宏观动力学的特征判断3种催化剂上乙炔加氢的速率控制步骤为乙烯基加氢生成乙烯。     

Activation of acetylene selective hydrogenation catalysts using oxygen containing compounds

Hydrogenation of acetylene in the presence of a large excess of ethylene has been investigated on the Pd–Ag catalyst at 60°C with a space velocity of 2000 h⁻¹. It was found that an enhancement in the performance of Pd–Ag catalyst can be obtained by pretreatment with N₂O. It is suggested that a certain amount of N₂O added to the catalyst before use not only augments the sites associated with ethylene production from acetylene, but also depletes the sites responsible for direct ethane formation. Upon aging, the pretreated catalyst exhibited good stability.     

Effect of the support on the selective hydrogenation of benzeneover ruthenium catalysts. 1. Al2O3 and SiO2

The effect of the support on the liquid phase selective hydrogenation of benzene to cyclohexene over Ru catalysts was studied. Catalysts were prepared using RuCl₃ as precursor and characterized by hydrogen chemisorption, XPS and TPR. The reaction was carried out at 373 K and 2 MPa using a stirred tank reactor. It was found that the catalytic activity is not influenced by the Ru dispersion. More electron-deficient Ru species are present on Al₂O₃ than on SiO₂. The electronic state of Ru affects the selectivity to cyclohexene.     

还原条件对镍/氧化铝油脂加氢催化剂的影响研究

采用沉淀法制备了镍/氧化铝催化剂前驱体,前驱体经焙烧、还原、包油成型制得镍/氧化铝油脂加氢催化剂。通过对催化剂进行TPR、氮吸附测定以及棕榈油加氢评价实验,考察了还原条件（还原温度、还原时间和氢气流速等）对催化剂孔结构和加氢活性的影响。结果表明,还原温度对催化剂孔结构和加氢活性影响最明显;催化剂前驱体最适宜的还原条件为还原温度500 ℃、还原时间3.0 h、氢气流速150 mL/min。在此条件下制备的催化剂用于棕榈油加氢反应,能够使每100 g棕榈油碘值由56.0 g降到0.81 g。     

Pd/Al2O3催化剂用于连续重整汽油全馏分加氢的失活分析

研究了负载在氧化铝载体上的贵金属Pd基催化剂在重整生成油选择性加氢脱烯烃反应中的性能。结果表明,在连续重整生成油全馏分的选择性加氢实验中，采用现有工业常用的工艺条件，单使用Pd作活性组分的Pd/Al₂O₃催化剂不能满足产品质量要求。探讨了切割馏分油加氢反应中催化剂失活原因，并对失活前后的催化剂采用XRD、SEM和FTIR等手段进行分析表征。结果表明，造成催化剂失活原因是催化剂表面油品中重组分等热敏类物质强吸附或聚合作用的结果。改进后的双金属Pd基催化剂UDO-01可用于重整生成油全馏分的选择性加氢脱烯烃反应，加氢后产品的溴价小于200 mg Br·(100 g-油)^-1,芳烃损失小于0.5%，且表现出好的稳定性。     

Deactivation of the Pd-Ag-Al2O3 catalyst and Ag-Al2O3 chemisorbent at joint operation in the process of selective acetylene hydrogenation

The deactivation of the commercial Al-Pd catalyst promoted with silver and Ag-containing chemisorbent in selective acetylene hydrogenation in an ethane-ethylene mixture was studied. It was found that carbonaceous deposits are formed on dispersed silver particles of the Pd-Ag-Al₂O₃ catalyst and on large silver crystallites of the Ag-Al₂O₃ chemisorbent. The lightest rapidly burning hydrocarbons of composition CH_2.5m with a low degree of aromaticity are sorbed on the silver particles or in the nearest neighborhood of them. Slowly burning hydrocarbons of composition CH_1.5–1.8m with high a degree of aromaticity are fixed on the alumina support. It was suggested to replace the Pd-Ag-Al₂O₃ catalyst currently used at the Nizhnekamskneftekhim plant in the process of selective acetylene hydrogenation by a system with a lower content of silver or without it.     

Pd-Ag/Al2O3催化剂上丁二烯的加氢反应性能

对Pd-Ag/Al2O3催化剂在裂解混合碳四选择加氢制丁烯反应中的性能进行了研究。实验结果表明,1,3-丁二烯加氢生成1-丁烯的选择性与反应器入口1,3-丁二烯浓度和氢/丁二烯比密切相关,在反应器入口温度40℃、反应压力1.0 MPa、液空速40 h 1的条件下,当入口丁二烯摩尔分数大于2.6%,1-丁烯选择性维持在66%以上;当入口丁二烯摩尔分数降至2.6%以下时,1-丁烯选择性开始下降;当反应器入口1,3-丁二烯摩尔分数小于1.0%时,出口1,3-丁二烯摩尔分数可降至小于1.0×10-5。当反应器入口1,3-丁二烯摩尔分数为0.50%～0.85%时,1-丁烯选择性随着氢/丁二烯摩尔比的增加呈现线性下降趋势,表明过量的氢气是发生丁烯的异构化和加氢反应的重要原因。H2-TPR和XPS表征结果显示,Pd-Ag/Al2O3中的Pd和Ag还原过程中形成了Pd-Ag合金。