钾改性氧化铝基羰基硫水解催化剂及其失活机理.pdf

物 理 化 学 学 报 Acta Phys.-Chim.Sin.2023,39(9),2210038(1 of 10)Received:October 27,2022;Revised:November 9,2022;Accepted:November 11,2022;Published online:November 16,2022.*Corresponding authors.Emails:(L.S.);(Y.Z.);(L.J.)The project was supported by the National Natural Science Foundation of China(21825801,22208053,22178057,21878053,22278073,22208055,22078063)and the Natural Science Foundation of Fujian Province(2020H6007,2022J05131).国家自然科学基金(21825801,22208053,22178057,21878053,22278073,22208055,22078063)及福建省自然科学基金(2020H6007,2022J05131)资助项目 Editorial office of Acta Physico-Chimica Sinica Article doi:10.3866/PKU.WHXB202210038 Deactivation Mechanism of COS Hydrolysis over Potassium Modified Alumina Ganchang Lei 1,2,Yong Zheng 1,2,Yanning Cao 1,2,Lijuan Shen 1,3,*,Shiping Wang 1,2,Shijing Liang 1,2,Yingying Zhan 1,2,*,Lilong Jiang 1,2,*1 National Engineering Research Center of Chemical Fertilizer Catalyst,School of Chemical Engineering,Fuzhou University,Fuzhou 350002,China.2 China Fujian Innovation Laboratory of Chemical Engineering,Qingyuan Innovation Laboratory,Quanzhou 302801,Fujian Province,China.3 College of Environmental Science and Engineering,College of Carbon Neutral Modern Industry,Fujian Key Laboratory of Pollution Control&Resource Reuse,Fujian Normal University,Fuzhou 350007,China.Abstract:Carbonyl sulfide(COS)is commonly found in conventional fossil fuels,such as nature gas,oil-associated gas,and blast-furnace gas,and its untreated emission not only corrodes pipelines and poisons catalysts but will also inevitably pollute the environment and endanger human health.Catalytic hydrolysis is recognized as the most promising strategy to eliminate COS because it can be performed under mild reaction conditions with a high removal efficiency.Notably,alkali metals promote catalytic COS hydrolysis over Al2O3 owing to their electron donor properties,basicity,and electrostatic adsorption.However,despite the significant attraction of using potassium-promoted Al2O3(K2CO3/Al2O3)as conventional catalysts for COS hydrolysis,the mechanism of COS hydrolysis over K2CO3/Al2O3 remains unclear and is controversial owing to the complex composition of the K species.In this study,commercial Al2O3 modified with potassium and sodium salts were synthesized using the wet impregnation method and characterized by various techniques.Based on the results of the activity measurements,the K2CO3-,K2C2O4-,NaHCO3-,Na2CO3-,and NaC2O4-modified catalysts had a positive effect on COS hydrolysis.Among them,the K2CO3/Al2O3 catalyst exhibited the highest COS conversion.Notably,the K2CO3/Al2O3 catalyst exhibited an excellent catalytic performance(93%,20 h),which is significantly better than that of pristine Al2O3(58%).Furthermore,this study provides strong evidence for the role of H2O during catalytic hydrolysis over K2CO3/Al2O3 using in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS)and X-ray photoelectron spectroscopy(XPS).The in situ DRIFTS analysis revealed that hydrogen thiocarbonate formed as an intermediate during COS hydrolysis over K2CO3/Al2O3.Meanwhile,the XPS findings suggested that sulfates and elemental sulfur accumulated on the catalyst surface,which may have contributed to catalyst poisoning.Additionally,the effect of water vapor content in the reaction pathway of COS hydrolysis over K2CO3/Al2O3 was investigated.The presence of excess water resulted in a reduction in catalytic activity owing to competitive adsorption between H2O and COS molecules on the catalyst surface.The enhancement in the catalytic activity over K2CO3/Al2O3 may be attributed to the formation of HO-Al-O-K interfacial sites.More importantly,all the catalysts were used under industrially relevant conditions,which provides valuable theoretical guidance for practical applications in the future.Thus,this detailed mechanistic study reveals new insights into the roles of the interfacial K co-catalyst,which provides a new opportunity for the rational design of stable and efficient catalysts for COS hydrolysis.Key Words:Carbonyl sulfide;Catalytic hydrolysis;HO-Al-O-K interface site;Deactivation mechanism;Industrial-relevant condition物理化学学报 Acta Phys.-Chim.Sin.2023,39(9),2210038(2 of 10)钾改性氧化铝基羰基硫水解催化剂及其失活机理 钾改性氧化铝基羰基硫水解催化剂及其失活机理 雷淦昌1,2，郑勇1,2，曹彦宁1,2，沈丽娟1,3,*，王世萍1,2，梁诗景1,2，詹瑛瑛1,2,*，江莉龙1,2,*1福州大学石油化工学院，化肥催化剂国家工程研究中心，福州 350002 2中国福建化学工程科学与技术创新实验室，清源创新实验室，福建 泉州 302801 3福建师范大学环境与资源学院、碳中和现代产业学院，福建省污染控制与资源循环利用重点实验室，福州 350007 摘要：摘要：天然气、油田伴生气、高炉煤气等化工生产过程中伴生COS气体，不仅会腐蚀管道和毒害催化剂，还会严重污染环境并危害人类健康。COS催化水解反应可在温和条件下高效的将COS脱除，是最具应用前景的COS脱除技术之一。碱金属元素因其具有独特的电子供体性质、表面碱性和静电吸附等特性，常被用作助催化剂以提高Al2O3的COS催化水解性能。近年来，以钾为助剂改性的Al2O3催化剂(K2CO3/Al2O3)在COS催化水解反应中得到广泛的应用，但由于负载在Al2O3上的K物种的组成复杂，目前研究者对K2CO3/Al2O3催化剂上COS水解机理的理解仍存在一定的困惑和争议。本论文通过湿法浸渍法合成出一系列钾盐和钠盐改性的Al2O3催化剂，并利用各类先进的表征技术对这些催化剂进行分析。活性测试表明，以K2CO3、K2C2O4、NaHCO3、Na2CO3和NaC2O4改性Al2O3催化剂均有助于COS的水解。其中K2CO3/Al2O3拥有最佳的COS水解性能，连续运行20 h后其COS转化率仍高于93%，远远优于未改性的Al2O3(58%)。我们利用原位红外光谱和X射线光电子能谱探明了反应过程中催化剂的化学结构特征，阐明了H2O分子在K2CO3/Al2O3上的水解作用机制。原位红外表明COS在K2CO3/Al2O3上的水解过程中形成了硫代碳酸氢盐中间产物。X射线光电子能谱表征证明催化剂的失活主要是因为催化剂表面积累了硫酸盐和单质硫。此外，我们还研究了水蒸气含量对COS水解性能的影响，研究发现，由于H2O和COS分子在催化剂表面存在竞争吸附，过量的H2O会引起催化活性的下降。上述研究表明，K2CO3/Al2O3催化剂上COS水解性能的提高主要是形成了HO-Al-O-K界面活性位。更为重要的是，所制备的催化剂都是在模拟工业工况条件下进行的，这为后续的工业应用提供了宝贵理论指导。本工作为理解助剂钾在Al2O3催化剂上COS水解活性的增强提供了新的见解，这为未来设计稳定高效的COS水解催化剂打开了新的发展方向。关键词：关键词：羰基硫；催化水解；HO-Al-O-K界面活性位点；失活机理；工业工况条件 中图分类号：中图分类号：O643 1 Introduction Carbonyl sulfide(COS),exists in petroleum gas,water gas,natural gas,and industrial tail gas,is usually considered as highly toxic substance that can cause the deactivation of the industrial catalysts 13.Even worse,when COS is directly released into the atmosphere,it will yield fog,haze,and acid raid,which is harmful to the environment and human health 4,5.With the rigorous environmental standards,it is crucial to develop efficient technologies for the elimination of COS.Among the strategies,the hydrolysis of COS was regarded as the most promising process due to the higher removal efficiency and mild reaction condition(COS+H2O H2S+CO2)68.Alumina(Al2O3)and/or alumina supported materials have been served as desulfurizers at ambient conditions for several decades 912.Owing to good thermal stability and hydrophobicity as well as ample surface chemistry,the alumina-based catalysts display higher reactivity and durability compared with other metal-based materials at relatively low temperature.In this system,the catalytic activity of COS hydrolysis is ascribed to the admirable surface acid-base properties of alumina.In previous studies,it has been reported that catalytic activity of alumina-based materials can be improved by introducing transition metals.In the work of Huang et al.and West et al.,transition metals modified alumina catalysts(e.g.,Zn,Cu,Ni,Co and Fe)were synthesized by the incipient wetness impregnation approach 13,14.The superior activity of these modified catalysts could be assignable to the enhanced basicity and polarity of the catalyst induced as a result of transition metals introduction.Nonetheless,the performances of these catalysts are still not satisfactory.In recent years,the alkali metal potassium(K)species as a promoter to modify a catalyst has attracted considerable attention 1517.K species can promote the catalytic hydrolysis of COS on Al2O3 owing to its electron donor properties,basicity and electrostatic adsorption of K+and O in oxygen-containing species.For example,Thomas et al.reported that in the hydrolysis of COS over Al2O3,the catalytic performance can be enhanced by adding K promoter 15.However,not all aspects of the catalytic hydrolysis reaction have been explored in sufficient depth,and several key issues are still being discussed:(i)what is the nature of the active sites?(ii)what are the roles that H2O plays in COS hydrolysis?(iii)what kinds of intermediates are involved?Therefore,it is of great significance to verify whether K species can promote the hydrolysis activity of Al2O3,and how about its sulfur resistance.In the present work,we have prepared a series of Al2O3 物理化学学报 Acta Phys.-Chim.Sin.2023,39(9),2210038(3 of 10)catalysts modified with K and Na species by a facile wet impregnation method.We have investigated their catalytic performance for the catalytic hydrolysis of COS.It has been found that K2CO3/Al2O3 catalyst displays highest activity compared with other K and Na species modified catalysts.Based on this,our study aimed to elucidate the influence of K2CO3 impregnation on Al2O3 and the mechanism of COS hydrolysis enhancement by K2CO3 impregnation.Furthermore,we provide strong evidence for deeper understanding of the role of H2O during catalytic hydrolysis mechanism over K2CO3/Al2O3 by using in situ DRIFTS(diffuse reflection infrared Fourier transform spectroscopy)spectroscopy.Importantly,the effect of water vapor content in the reaction pathway of COS hydrolysis on K2CO3/Al2O3 is also investigated.2 Experimental 2.1 Materials and reagents Potassium carbonate(K2CO3),potassium oxalate monohydrate(K2C2O4H2O),tripotassium citrate monohydrate(K3C6H5O7),potassium acetate(KC2H3O2),sodium carbonate(Na2CO3),sodium hydrogen carbonate(NaHCO3),sodium oxalate(Na2C2O4),trisodium citrate dihydrate(Na3C6H5O72H2O)and sodium acetate(NaC2H3O2)were purchased from Sinopharm Chemical Reagents,China.Deionized water was obtained from local sources.All the materials were used as received without further purification.2.2 Preparation Impregnated K2CO3/Al2O3 catalyst was prepared by using commercial Al2O3(Sumitomo,GO-12,BET surface area and pore volume are 216.1 m2g1 and 0.45 cm3g1,respectively).In detail,the catalysts were prepared by the wet impregnation technique using carbonate as active component.The preparation process was as follows:Initially,5 g of K2CO3 was dissolved in a 35 mL of deionized water.Then the completely dissolved K2CO3 solution was added in the 50 g of Al2O3 carrier and stirred 4 h at ambient temperature.After that,the mixture was slowly heated to 60 C to remove the deionized water.Finally,the as-prepared sample was calcined at 150 C for 12 h in the air to afford the K2CO3/Al2O3 catalyst.The particle size used for the experiment was in the range of 4060 mesh.The other K and Na species modified Al2O3 catalysts were prepared using the same method as that for the K2CO3/Al2O3 catalyst.2.3 Characterization of sample Powder X-ray diffraction(XRD)measurements were carried out on an XPertPro diffractometer with Cu-K1 radiation(=0.154 nm).Raman profiles were obtained on a Renishaw in Via Raman Microscope with a 532 nm laser excitation.X-ray photoelectron spectroscopy(XPS)data were collected on a Thermo ESCALAB 250 instrument with Al K radiation(200 W).Nitrogen adsorption-desorption isotherms were acquired using a Micromeritics ASAP 2020 surface area and porosity analyzer.The morphologies and microstructures of samples were studied by scanning electron microscope(SEM)analysis(S-4800,Hitachi,Japan).TEM images were collected on a Tecnai G2 F20(200 kV).In situ DRIFTS characterization.DRIFTS were recorded using a Nicolet Nexus FT-IR spectrometer in the range of 4000650 cm1 with 64 scans at a resolution of 2 cm1.First,20 mg of catalyst was placed in a sample cup and set inside a DRIFT cell.The cell was purged with a stream of He at 150 C for 1 h to eliminate adsorbed impurities and then cooled to 100 C.The background profile was collected under He and automatically subtracted from the catalyst spectrum.Then 1100 mgm3 COS gas with N2 balance was introduced to the chamber at 100 C with a flow rate of 20 mLmin1,and then DRIFTS profiles were collected.Subsequently,a certain amount of water vapor(the temperature of the water bath was set in the range from room temperature to 70 C)was fed to the chamber at 100 C,and DRIFTS spectra were collected.2.4 Evaluation of catalytic activity A fix-bed glass reactor apparatus was applied in this study.The schematic of the reactor set-up is displayed in Fig.1.The reactor was a 200 mm long quartz tube with an inner diameter of 8 mm and a wall thickness of 1 mm,which was placed in the Fig.1 Schematic of the reactor for the catalytic hydrolysis of COS.物理化学学报 Acta Phys.-Chim.Sin.2023,39(9),2210038(4 of 10)heating block.Detailly,400 mg of catalyst(4060 mesh)was placed in the reactor(inner diameter 8 mm).A flow of feed gas(COS 224 mgm3,CO2 11.01%,CO 18.594%,H2 1.487%,O2 1.667%,(w,mass fraction)balance N2)was fed into the reactor at a total flow rate of 20 mLmin1(WHSV=9000 mLg1h1).H2O was injected into the reactor from a thermostatic water bath via a controlled saturator.The relative humidity(water vapor contents were ca.6%,ca.9%,ca.12%and ca.15%,respectively)by adjusting the temperatures of the water bath(40,50,60,70 C).The content of COS in the reactor effluent was detected online with a FULI GC-9790 II gas chromatograph equipped with a flame photometric detector.Equation(1)was used to calculate the COS conversion:COS conversion=inoutinCOSCOSCOS-100%(1)3 Results and discussion 3.1 Synthesis and Structure characterization of catalyst The K2CO3/Al2O3 catalyst is synthesized by a one-step impregnation as illustrated in Fig.2a.First,the bulk K2CO3 can be decomposed at low temperature due to their interaction with the support.Then the hydroxyl groups and/or unsaturated oxygen on the Al2O3 surface was then reacted with the impregnated K+ions,creating K-O-Al active sites.The XRD patterns of the K and Na species modified Al2O3 samples are displayed in Fig.2a and Fig.S1(Supporting Information),respectively.All of the K species modified Al2O3 samples exhibit six base peaks at 25.4,37.7,45.8,48.0,54.8 and 66.9,which are assignable to the mixed phases of-Al2O3,-Al2O3,Al(OH)3,respectively(Fig.2b)1820.No diffraction peaks attributable to K-containing phases over all modified samples are detected,suggesting the high dispersion of K species.As for Na species modified Al2O3 samples(Fig.S1),no peaks assignable to impurities can be detected for NaC2H3O2/Al2O3,Na3C6H5O7/Al2O3 samples.The detection of the other phases over NaC2O4/Al2O3,NaHCO3/Al2O3 and Na2CO3/Al2O3 suggests rich existence of Na species on the Al2O3 surface 21.Fig.2c depicts the Raman spectra of Al2O3 and K2CO3/Al2O3.The peaks at around 148 and 399 cm1 are assigned to deformation modes whereas the peaks at around 517 and 642 cm1 are attributable to AlO stretching mode 22.For K2CO3/Al2O3,two new peaks at 1061 and 1096 cm1 assignable to the presence of potassium species are observed 23.Overall,these result indicates that the K species are successfully introduced to Al2O3 structure.3.2 Textural properties of catalyst The surface morphology of Al2O3 and K2CO3/Al2O3 samples was characterized by SEM images(Fig.S2,Supporting Information).Compared with pure Al2O3,there is significant change in morphology on K2CO3/Al2O3 sample.As shown in Fig.S2ab,the pure Al2O3 displays structure of stacked-sheet.After K2CO3 doping,some needle-like species are clearly Fig.2 (a)Illustration of the process for the synthesis of K2CO3/Al2O3 catalyst;(b