Towards the insights into the deactivation behavior of acetylene hydrogenation catalyst

A series of model catalysts were obtained by treating commercial fresh and spent catalysts unloaded from the factory with different methods, including green oil dipping, extraction and high-temperature regeneration;finally, the deactivation behavior of the commercial catalyst for acetylene hydrogenation were studied. The influence of various possible deactivation factors on the catalytic performance was elucidated via detailed structural characterization, surface composition analysis, and activity evaluation.The results showed that green oil, carbon deposit and sintering of active metal were the main reasons for deactivation, among which green oil and carbon deposit led to rapid deactivation, while the activity could be recovered after regeneration by high-temperature calcination. The sintering of active metal components was attributed to the high-temperature regeneration in hydrothermal conditions, which was slow but irreversible and accounted for permanent deactivation. Thus, optimizing the regeneration is expected to extend the service life of the commercial catalyst.

MOF-assisted Synthesis of Dual-atom Palladium Catalysts for Acetylene Semi-hydrogenation

The selective removal of trace acetylene in ethylene feed gas is of great significance in the petrochemicalindustry;however, there are still challenges in designing and developing high-performance catalysts. Here, a MOFassistedencapsulation strategy was adopted for the precise synthesis of diatomic Pd2 sites on a ZnO support. When usedfor the acetylene semi-hydrogenation reaction, the dual-atom Pd2-ZnO catalyst exhibited improved catalytic performance,achieving complete conversion of acetylene at 125 °C with an 89% selectivity to ethene, as compared to Pd single-atom andnanoparticles. This enhancement was mainly attributed to the catalyst’s ability to dissociate H2 and facilitate the desorptionof intermediate C2H4. Moreover, the strong interaction between the support and the diatomic Pd sites was responsible for thecatalyst’s excellent stability during the long-term reaction.

Selective hydrogenation of acetylene on SiO_2-supported Ni-Ga alloy and intermetallic compound

Ni/Si O_2 and bimetallic Ni_xGa/SiO_2 catalysts with different Ni/Ga atomic ratios(x = 10～2) were investigated for the selective hydrogenation of acetylene.It was found that Ni_xGa/SiO_2 showed higher selectivity to ethylene than Ni/Si O_2.This is attributed to the formation Ni-Ga alloy and Ni3 Ga intermetallic compound(IMC) where there was a charge transfer from Ga to Ni,which is favorable for reducing the adsorption strength and amount of ethylene on Ni atoms.As a result,the over-hydrogenation,the C–C bond hydrogenolysis and the polymerization were suppressed,and subsequently the selectivity to ethylene was enhanced.With the decrease of Ni/Ga atomic ratio,the activity and stability of the Ni_xGa/SiO_2 catalysts increased first and then decreased,while the ethylene selectivity tended to increase.Ni_5 Ga/SiO_2 exhibited the best performance.Under the conditions of 180 °C,0.1 MPa,and a reactant(1.0 vol% acetylene,5.0 vol% H_2 and 94 vol% N_2) with the space velocity of 36,000 m L h^(-1) g^(-1),the acetylene conversion maintained at 100% on Ni_5 Ga/SiO_2 during 120 h time on stream and the selectivity to ethylene was 75%～81%after reaction for 68 h.It was also found that the formation of Ni-Ga alloy and Ni_3 Ga IMC suppressed the incorporation of carbon to form NiCx,subsequently enhancing the catalyst stability.Additionally,with increasing the Ga content,the catalyst acid amount and strength tended to increase,which promoted the polymerization and carbon deposition and so the catalyst deactivation.

Effect of IB-metal on Ni/SiO2 catalyst for selective hydrogenation of acetylene

The IB metal(Au,Ag and Cu)alloyed Pd single atom catalysts had been proved to be efficient in promoting the selectivity for hydrogenation of acetylene to ethylene.As a base metal in the same group as Pd,the Ni-based catalysts are also active for hydrogenation reactions.Herein,the effects of the IB metals on the Ni/SiO2 catalyst for the selective hydrogenation of acetylene were systematically studied.Different from the Pd/SiO2 catalyst,the monometallic Ni/SiO2 catalyst is not active at low temperatures.The addition of the IB metals to the Ni/SiO2 catalysts can greatly enhance the activity.Besides,the catalytic activity of the AuNix/SiO2 and CuNix/SiO2 catalysts increase with the reduction temperature,while the AgNix/SiO2 catalysts are not sensitive to the pretreatment temperature.The origin of the effect of the different IB metals on the Ni-based catalysts for selective hydrogenation of acetylene is discussed based on the characterizations by XRD,TPR and microcalorimetric measurements.

Catalytic Performance of Carbon Materials Supported Pd Nanoparticles in Selective Hydrogenation of Acetylene

Pd/C catalysts were prepared by deposited Pd nanoparticles （NPs） on different carbon supports including activated carbon （AC）, graphite oxide （GO）, and reduced graphite oxide （rGO） using sol-immobilization method. Through transmission electron microscopy, powder X-ray di raction, and X-ray photoelectron spectroscopy, the role of the carbon supports for the catalytic performances of Pd/C catalysts was examined in selective hydrogenation of acetylene. The results indicate that Pd/AC exhibited higher activity and selectivity than Pd/GO and Pd/rGO in the gas phase selective hydrogenation of acetylene. Thermal and chemical treatment of AC supports also have some effect on the catalytic performance of Pd/AC catalysts. The differences in the activity and selectivity of various Pd/C catalysts were partly attributed to the metal-support interaction.

SiO_2-supported Au-Ni bimetallic catalyst for the selective hydrogenation of acetylene

Supported Au catalysts have been reported to exhibit high ethylene selectivity in the hydrogenation of acetylene,but the conversion is relatively low.Adding a second metal to Au has proven to be a promising approach to enhance its catalytic performance in acetylene hydrogenation.In this work,SiO2‐supported Au‐Ni bimetallic catalysts were synthesized and investigated in the selective hydrogenation of acetylene.The Au‐Ni bimetallic catalysts exhibited much higher catalytic performance than that of the corresponding monometallic Au or Ni catalysts.By tuning the reduction temperature and/or Ni loading,we obtained an Au‐Ni/SiO2catalyst with optimal performance.The results of transmission electron microscopy imaging revealed that the Au‐Ni bimetallic particles were highly dispersed on the SiO2support.Meanwhile,analysis of the bimetallic catalyst by energy‐dispersive X‐ray spectroscopy,high‐resolution transmission electron microscopy,and in situ diffuse reflectance infrared Fourier transform spectroscopy demonstrated the formation of Au‐Ni alloy,which contributed to the synergistic effect between Au and Ni in the hydrogenation of acetylene.

Reverse Microemulsion Synthesis and Characterization of Pd-Ag Bimetallic Alloy Catalysts Supported on Al_2O_3 for Acetylene Hydrogenation

Pd-Ag bimetallic alloy nanoparticles were synthesized by the reverse microemulsion method, and then deposited on A1203 to form the supported catalyst. The nanoparticles of Pd-Ag and Pd-Ag/AI203 samples were characterized by UV/ Vis, HRTEM, EDX, XRD, and XPS. The test results indicated that Pd-Ag bimetallic alloy nanoparticles with a size of about 2 nm and a face-centered cubic （fcc） structure were formed in the measured area of microemulsion. The growth of nanopar- ticles was effectively limited within the droplet of micoremulsion. TEM image exhibited that the Pd-Ag alloy nanoparticles were well-dispersed on the A1203 support. The catalytic performance of various catalysts for selective hydrogenation of acetylene showed that a higher acetylene conversion and selectivity to ethylene upon acetylene hydrogenation was achieved on a nano-sized Pd-Ag bimetallic catalyst with a Pd/Ag alloy supported molar ratio of 1：1.5.

Catalytic Performance and Characterization of Anatase TiO_(2) Supported Pd Catalysts for the Selective Hydrogenation of Acetylene

Anatase TiO_(2)nanospindles containing 89%exposed{101}facets(TIO_(2)-101)and nanosheets with 77%exposed{001}facets(TiO_(2)-001)were hydrothermally synthesized and used as supports for Pd catalysts.The effects of the TiO_(2)materials on the catalytic performance of Pd/TiO_(2)-101 and Pd/TiO_(2)-001 catalysts were investigated in the selective hydrogenation of acetylene to polymer-grade ethylene.The PdfTiO_(2)-101 catalyst exhibited enhanced performance in terms of acetylene conversion and ethylene yield.To understand these effects,the catalysts were characterized by H_(2)temperature-programmed desorption(H_(2)-TPD),H_(2)temperature-programmed reduction(H=-TPR),transmission electron microscopy(TEM),pulse CO chemisorption,X-ray photoelectron spectroscopy(XPS),and thermogravimetric analysis(TGA).The TEM and CO chemisorption results confirmed that Pd nanoparticles(NPs)on the TiO_(2)-101 support had a smaller average particle size(1.53 nm)and a higher dispersion(15.95%)than those on the TiO_(2)-001 support(average particle size of 4.36 nm and dispersion of 9.06%).The smaller particle size and higher dispersion of Pd on the Pd/TiO_(2)-101 catalyst provided more reaction active sites,which contributed to the improved catalytic activity of this supported catalyst.

Isolation of Pd atoms by Cu for semi-hydrogenation of acetylene: Effects of Cu loading

Cu‐alloyed Pd single‐atom catalysts exhibit excellent catalytic performance for the semi‐hydrogenation of acetylene;however,the limit of the Cu/Pd atomic ratio for forming the alloyed Pd single‐atom catalyst is ambiguous.Herein,silica‐supported Cu-Pd bimetallic catalysts with fixed Pd content and varied Cu loadings were synthesized using an incipient wetness co‐impregnation method.The X‐ray absorption spectroscopy results indicated that Pd formed an alloy with Cu after reduction at250°C and that the Pd atoms were completely isolated by Cu for Cu/Pd atomic ratios≥40/1.Notably,increasing the reduction temperature from250to400°C hardly affected the catalytic performances of the Cu-Pd/SiO2catalysts.This finding can be attributed to the similar chemical environments of Pd demonstrated by the X‐ray absorption spectroscopy results.

Size-controlled Pd Nanoparticles Supported on α-Al_2O_3 as Heterogeneous Catalyst for Selective Hydrogenation of Acetylene

Size-controlled Pd nanoparticles （PdNPs） were synthesized in aqueous solution, using sodium car-boxymethyl cellulose as the stabilizer. Size-controlled PdNPs were supported onα-Al2O3 by the incipient wetness impregnation method. The PdNPs onα-Al2O3 support were in a narrow particle size distribution in the range of 1-6 nm. A series of PdNPs/α-Al2O3 catalysts were used for the selective hydrogenation of acetylene in ethylene-rich stream. The results show that PdNPs/α-Al2O3 catalyst with 0.03%（by mass） Pd loading is a very effective and sta-ble catalyst. With promoter Ag added, ethylene selectivity is increased from 41.0%to 63.8%at 100 ＆#176;C. Comparing with conventional Pd-Ag/α-Al2O3 catalyst, PdNPs-Ag/α-Al2O3 catalyst has better catalytic performance in acety-lene hydrogenation and shows good prospects for industrial application.

Preparation of Uniform Ni-B Amorphous Alloy Catalyst on CNTs and its Performance for Acetylene Selective Hydrogenation

Uniform Ni-B amorphous alloys about 14 nm have been prepared on CNTs-A support,named Ni-B/CNTs-A. In comparison with the Ni-B/CNTs amorphous catalyst, Ni-B/CNTs-A showed higher nickel loading, determined by ICP and better catalytic activity and ethylene selectivity in the acetylene hydrogenation reaction.

Acetylene hydrochlorination over supported ionic liquid phase(SILP)gold-based catalyst:Stabilization of cationic Au species via chemical activation of hydrogen chloride and corresponding mechanisms

The activation of HCl by cationic Au in the presence of C2H2 is important for the construction of active Au sites and in acetylene hydrochlorination.Here,we report a strategy for activating HCl by the Au-based supported ionic liquid phase(Au–SILP)technology with the[N(CN)2^–]anion.This strategy enables HCl to accept electrons from[N(CN)2^–]anions in Au–[N(CN)2^–]complexes rather than from pure[Bmim][N(CN)2],leading to notable improvement in both the reaction path and the stability of the catalyst without changing the reaction triggered by acetylene adsorption.Furthermore,the induction period of the Au–SILP catalyst was shown to be absent in the reaction process due to the high Au(III)content in the Au(Ⅲ)/Au(Ⅰ)site and the high substrate diffusion rate in the ionic liquid layer.This work provides a facile method to improve the stability of Au-based catalysts for acetylene hydrochlorination.

Exergy Analysis and Retrofitting of Natural Gas-based Acetylene Process

This article presents an acetylene production process by partial oxidation/combustion of natural gas. The thermodynamic performance and exergy analysis in the process are investigated using the flow-sheeting program Aspen Plus. The results indicate that the most important destruction of exergy is found to occur in the reactor and water quenching scrubber, amounting to 8.23% and 10.39%, respectively, of the entire system. Based on the results of thermodynamic and exergy analysis, the acetylene reactor has been retrofitted. The improvement ratios of molar 02 to CH4 and molar CO to CN4 are 0.65 and 0.20, respectively. An improvement of the acetylene production system is proposed. Adopting the improvement operation conditions and using oil to realize the reaction heat recovery, the feedstock of natural gas is reduced by 9.88% and the exergy loss in the retrofitting process is decreased by 19.71% compared to the original process.

用于MTO装置中的乙炔选择加氢催化剂研究

在MTO工艺装置生产乙烯的过程中,乙烯中常含有50~200μL/L左右的微量乙炔,现有的石油烃蒸汽裂解制乙烯装置中常用的碳二加氢催化剂或适用于微量乙炔选择加氢的乙烯精制催化剂并不是MTO工艺中乙炔选择加氢的最好选择。通过研究Pd含量变化对催化剂性能的影响,发现降低Pd含量能够提高催化剂的乙烯选择性,降低催化剂的乙炔合格温度,在保证乙炔加氢合格的情况下,通过控制较低的氢炔比还能获得更好的乙烯选择性。通过添加适当的助剂,控制助剂的用量也能够提高催化剂的乙烯选择性。和商业碳二加氢催化剂BC2相比,采用浸渍法制备的BC2-MTO催化剂活性组分Pd含量降低了50%以上,活性金属Pd的分散度提高了69%,能够在较低的反应温度和氢炔比条件下使用,具有更好的催化活性和乙烯选择性。

乙炔黑包覆的铅及其氧化物复合材料对铅酸电池负极性能的影响

铅酸电池负极析氢问题和硫酸盐化问题是限制铅酸电池性能的主要因素,大量的研究集中在负极的添加剂上。本文以乙炔黑包覆的铅及其氧化物形成的复合材料作为铅酸电池负极添加剂,研究其对铅酸电池性能的影响。实验结果表明,加入复合材料的电极,有效抑制了析氢问题,并降低了硫酸盐化现象,延长了其寿命。

含碳Cu-Zn-Al乙炔选择性加氢催化剂制备及性能

采用共沉淀法制备不同Cu/Zn摩尔比铜-锌-铝水滑石前体,焙烧后经过乙炔预处理和H_(2)还原得到Cu_(m)Zn_(3-m)Al-LDO(T140-R150)催化剂(m取值为1、1.5、2、3)。对上述含碳铜-锌-铝催化剂进行N_(2)物理吸附、X射线衍射、扫描电子显微镜和透射电镜表征,研究其在大量乙烯存在时乙炔选择性加氢反应中的催化性能。结果表明:在铜-铝水滑石中引入锌,可提高前体中铜的分散度,有利于碳化铜(Cu_(x)C)加氢活性相的生成,提高乙炔选择性加氢反应的性能。催化剂最佳制备条件为:Cu/Zn摩尔比1,乙炔处理温度140℃,乙炔处理时间2 h,氢气还原温度150℃,氢气还原时间3 h。在温度100℃和压力0.1 MPa条件下,Cu_(1.5)Zn_(1.5)Al-LDO(T140-R150)催化乙炔选择性加氢反应的乙炔转化率达100%,乙烯选择性为53.9%,C4选择性为15.5%,乙烷选择性为30.6%。

乙炔选择加氢反应中碳化钯的动态精细调控: 气氛和氧化锌助剂的作用

碳化钯通常被认为是乙炔选择加氢反应中原位生成的活性相,其生成有助于抑制次表面非选择性的氢化钯物种,从而实现高选择性乙炔加氢制乙烯的目标.次表面上碳化钯和氢化钯物种之间的竞争很大程度上决定了乙炔加氢反应的选择性.然而,由于实际反应环境的复杂性,反应环境下的两种物种之间的动态转化过程和竞争关系尚不清晰.特别是,反应环境(比如氢气组分)对碳化钯物种的调控机制仍不明确,也使得对碳化钯活性物种的精准调控变得困难.此外,氧化锌助剂作为乙炔选择加氢反应中最常用的助剂之一,存在典型的金属-氧化物界面相互作用,也会对渗碳过程产生重要影响.因此,从动态视角理解碳化钯物种的原位形成过程,对于精准设计和合成高性能乙炔选择加氢钯基催化剂具有重要的科学意义.近年来,先进原位表征光谱技术的不断发展使得从原子、分子层面理解原位过程机制成为可能.本文旨在通过先进的原位表征技术揭示乙炔选择加氢反应中碳化钯物种的动态生成过程,并进一步探究气氛环境、温度、助催化剂等参数对碳化钯物种的动态调控机制,从而为高性能乙炔选择加氢催化剂的精准设计和合成提供有力支撑.原位研究结果表明,在氢气升温还原条件下,空气焙烧后新鲜催化剂中氧化钯相首先转变为氢化钯相;随着还原温度升高,氢化钯相的含氢量逐渐降低.当切换至乙炔选择加氢反应原料气时,氢化钯相迅速分解为金属钯,并随着恒温碳化时间的延长,烃类裂解产生的碳原子逐渐渗入钯的体相,最终形成稳定的碳化钯活性相.通过移除乙炔加氢反应原料气氛中的氢气,考察了反应气中的氢气组分对碳化钯形成的调控机制.实验发现,在仅有乙炔和乙烯存在时,碳化过程仍能发生;而引入少量氢气(体积分数2.2%)后,碳化程度显著增强,C/Pd原子比从0.136提升至0.154.相变机理研究表明,氢气的引入促进了氢化钯物种的形成,并通过晶格扩张作用促进渗碳过程.此外,还研究了氧化锌助剂对原位渗碳过程的影响,揭示了氧化锌助剂对碳化钯的抑制作用.结合原位CO吸附漫反射红外光谱、准原位X射线光电子能谱分析发现,低温氢气还原下Pd-ZnO界面作用促进了微量表面PdZn合金的生成,从而抑制了碳的渗入.这种现象在不含氢气的碳化气氛中尤为显著,碳含量降低一个数量级(C/Pd原子比仅为0.019).在此基础上,通过调节反应条件,实现了对碳化钯物种碳含量的精准调控,并与反应活性关联,揭示了碳化钯含量与乙炔选择加氢反应活性之间的线性关系.电子结构表征和同位素实验进一步表明,Pd-C的电子相互作用促进了向Pd中心原子的电子转移,从而提高了氢气的活化解离能力和乙炔加氢反应活性.综上,本工作原位解析了碳化钯的动态形成过程,阐明了氢气辅助插碳和ZnO抑制插碳的微观机制,实现了碳化钯活性物种的精准调控,揭示了碳化程度与反应活性的线性关系,为高性能乙炔选择加氢催化剂设计提供了参考.

水热法制备Ni/CeO_(2)-Al_(2)O_(3)及催化乙炔选择性加氢

首先,采用水热法制备了不同CeO_(2)质量分数(x%)的xCeO_(2)-Al_(2)O_(3)载体;然后,采用初湿浸渍法制备了Ni质量分数为2%的Ni/xCeO_(2)-Al_(2)O_(3),以乙炔选择性加氢制乙烯反应为探针反应,结合XRD、SEM、H_(2)-TPR、BET、XPS、NH_(3)-TPD、TG评价了Ni/xCeO_(2)-Al_(2)O_(3)催化性能。结果表明,Ni/5CeO_(2)-Al_(2)O_(3)表现出最佳的催化性能,在280℃下,乙炔转化率为99.7%,乙烯选择性为94.9%。Ni/5CeO_(2)-Al_(2)O_(3)具有最大的比表面积(164.2 m^(2)/g)和孔径(7.2 nm),适当的氧空位含量〔9.2%,即Ce^(3+)峰面积/(Ce^(3+)峰面积+Ce^(4+)峰面积),下同〕。CeO_(2)的添加减弱了Ni/Al的强相互作用,减少了惰性NiAl2O4尖晶石相的生成,有效提升了催化剂的活性、选择性和稳定性。在30 h的反应时间内,乙炔转化率降至90.0%,原因在于反应过程中造成的炭沉积降低了Ni/5CeO_(2)-Al_(2)O_(3)的比表面积(151.5 m^(2)/g)和孔径(6.6 nm)。

颗粒分辨的乙炔选择性加氢固定床反应器数值模拟

乙烯产量是反映国家石油化工发展水平的关键指标。构建了颗粒分辨的乙炔选择性加氢固定床反应器模型,分析圆柱形颗粒堆积结构对传递过程以及操作条件对其反应性能的影响。结果表明,床层压降主要集中在反应器入口段,该段乙炔加氢反应速率最高,但在后半段催化剂颗粒未被充分利用,而且反应器内存在明显的径向温度梯度。入口压力的增加和空速的降低均有利于提升乙炔转化率,但同时会降低乙烯选择性,其中乙烯选择性对压力更敏感,而乙炔转化率对空速更敏感;反应温度和氢炔比的提高均有利于促进乙炔生成乙烯的速率,但会导致乙烯富集在催化剂颗粒的外表面,其进一步向颗粒内部扩散时过度加氢生成乙烷,使乙烯选择性降低。

乙炔加氢反应器长周期运行的瓶颈原因分析及对策

独山子石化公司220 kt/a乙烯装置乙炔加氢反应器,设有2个并联反应床层,采用“1开1备”模式。R-401A/B反应器延用的是原厂家A型催化剂,运行周期小于10个月,未达到技术要求的12个月;R-401C/D更换新催化剂后,发现新投用的催化剂在运行期间绿油生产量较之前明显增多,初次运行周期仅为3个月,未达到技术要求的6个月。反应器运行周期短不仅影响乙烯增量,且反应器运行到末期进行切换,系统需要排火炬造成物料损失,因此反应器的长周期运行对装置提质增效及节能降耗有着非常重要的意义。