甲苯、丙酮和乙酸乙酯在新型铂-钯不锈钢丝网催化剂上的催化氧化.pdf

物理化学学报(Wuli Huaxue Xuebao)Acta Phys.鄄Chim.Sin.,2008,24(7)：1132-1136Received:January 7,2008;Revised:March 19,2008;Published on Web:May 7,2008.English edition available online at 鄢Corresponding author.Email:,;Tel:+86571鄄88273495;Fax:+86571鄄88273283.国家自然科学基金(20577042)及浙江省自然科学基金(Y505285)资助项目鬁 Editorial office of Acta Physico鄄Chimica SinicaAJuly甲苯、丙酮和乙酸乙酯在新型铂鄄钯/不锈钢丝网催化剂上的催化氧化马莹陈敏鄢宋萃郑小明(浙江大学(西溪校区)催化研究所,杭州310028)摘要：采用阳极氧化法制备了一种用于催化氧化处理挥发性有机化合物(VOCs)的 0.1%Pt鄄0.5%Pd/不锈钢丝网(SSWM)催化剂.活性测试结果表明,0.1%Pt鄄0.5%Pd/不锈钢丝网催化剂具有较高的催化活性和热稳定性.该催化剂上甲苯、丙酮和乙酸乙酯的完全氧化温度分别为 220、260 和 280 益.通过扫描电镜(SEM)、X 射线光电子能谱(XPS)和超声波等手段对催化剂和不锈钢丝网进行了表征.SEM 结果表明,经阳极氧化工艺处理过的不锈钢金属丝网载体表面形成了一层沟壑形态的复合氧化膜.该阳极氧化膜有利于活性组分 Pd、Pt 的分散.关键词：催化氧化;不锈钢丝网;阳极氧化;X 射线光电子能谱中图分类号：O643Catalytic Oxidation of Toluene,Acetone and Ethyl Acetate ona New Pt鄄Pd/Stainless Steel Wire Mesh CatalystMA YingCHEN Min鄢SONG CuiZHENG Xiao鄄Ming(Institute of Catalysis,Zhejiang University(Xixi Campus),Hangzhou310028,P.R.China)Abstract：A new volatile organic compound(VOC)combustion catalyst of 0.1%Pt鄄0.5%Pd/stainless steel wire mesh(SSWM)was prepared via anodic oxidation treatment.The result of activity tests for complete oxidation of toluene,acetone,and ethyl acetate showed that 0.1%Pt鄄0.5%Pd/steel wire mesh catalyst had good catalytic activity and thermalstability.The total oxidation temperature for toluene,acetone,and ethyl acetate was at 220,260,and 280 益 for thecatalyst calcined at 500 益,respectively.The catalyst and stainless steel wire mesh support were characterized bymeans of scanning electron microscopy(SEM),X鄄ray photoelectron spectrum(XPS),and ultrasonic vibration tests.TheSEM results indicated that a typical donga structure layer appeared on the surface of stainless steel wire mesh supportafter anodic oxidation procedure.This typical anodic oxidation film was favorable for dispersing Pd and Ptcomponents.Key Words：Catalytic oxidation;Stainless steel wire mesh;Anodic oxidation;X鄄ray photoelectron spectraNowadays,the volatile organic compounds(VOCs),fromchemical and petrochemical plants,have given rise to compre-hensive attention as they are hazardous to the environment andhuman health1.There are many different techniques used for theremoval of VOCs,such as adsorption,absorption,biofiltration,thermal incineration,and catalyst combustion2-6.Among them,catalytic deep oxidation that converts VOCs into carbon dioxideand water has been recognized as one of the most promisingmethods7-9.Noble metal catalysts like Pt or Pd on a suitable support havegenerally been used as the most active catalysts for VOCs oxida-tion10,11.As previously reported,Pt and Pd supported on aluminawas the most active catalyst12-14.However,it is frequently re-ported that alumina phase from 酌 to 琢 transition would cause adrastic decrease in the surface area,and the sintering of the no-ble metals would also lead to the thermal deactivation of the cat-alysts.Therefore,to find a new series of catalysts,which are lessexpensive,higher temperature鄄resistance,and more efficient in1132No.7MA Ying et al.：Catalytic Oxidation of Toluene,Acetone and Ethyl Acetate on a New Pt鄄Pd/Stainless Steellow temperature for volatile organic compound combustion isneeded.The stainless steel wire mesh(SSWM)is regarded as an attrac-tive replacement of conventional support in catalysts because ofits high anticorrosion,high thermal conductivity,and fictileproperty.Our previous work15reported that a 0.01%Pt鄄0.02%Pd/stainless steel catalyst showed high catalytic activity fortoluene,acetone,and ethyl acetate oxidation.This work is acontinuation of the previous work,in which 0.1%Pt鄄05%Pdsupported on a new kind of stainless steel wire mesh was pre-pared and reported.The aim of this work is to investigate anoth-er kind of stainless steel used as support and extend its applica-tion.1Experimental1.1Preparation of catalystThe stainless steel wire mesh(400 mm伊40 mm伊0.3 mm)wasmachined into a typical shape as needed.The anodic oxidationtreatment was carried out in the subsequent process:the stainlesssteel wire mesh was put into an isolated electrochemical cell,inwhich 10%(w)sulphuric acid aqueous solution was used as elec-trolyte.Then at a constant stirring rate,keeping the constantvoltages of 3-5 V and electric current density of 1 A dm-2,theanodized oxidation film appeared on the stainless steel wiremesh support surface.Finally,the stainless steel wire mesh sup-port was dried at 110 益 for 1 h in the air atmosphere.The sup-ported platinum and palladium catalyst was prepared by impreg-nation method.The aqueous solutions,H2PtCl6and H2PdCl4,were used as precursors for Pt and Pd,respectively.Finally,thecatalyst was dried at 110 益 for 1 h and then calcined at 500 益for 1 h.The obtained catalyst was denoted as 0.1%Pt鄄0.5%Pd/SSWM in the following sections.1.2Measurement of activityCatalytic activity tests were carried out at atmospheric pres-sure in a fixed bed flow鄄reactor system(length=600 mm,i.d.=28mm).The typical VOCs substance of toluene,acetone,and ethylacetate was introduced into the reactor by a carrying gas of airflow through a saturator maintained.The reactions were per-formed at temperature range of 180-400 益,and the gas hourlyspace velocity(GHSV)is 10000 h-1.The concentrations oftoluene,acetone,and ethyl acetate in the feed were 0.10%-0.16%,0.17%-0.25%,and 0.11%-0.17%,respectively.The catalystwas placed at the center of the reactor supported by quartz wooland a thermocouple was positioned to monitor the reaction tem-perature.The analysis of the concentration of VOCs in the inletand outlet gas was performed on a GC鄄1690 chromatographwith a FID attachment.The GC column was 3 mm伊0.3 滋m伊3 mstainless steel tubing packed with quartzite.The analysis condi-tions were as follows:the temperatures of injector,detector,andcolumn chamber were 170,140,and 150 益,respectively.Theflow rate of carrier gas(N2)was 20 cm3 min-1.The catalytic ac-tivities are characterized by parameter of T98,which indicates thetemperature at which acetone,ethyl acetate,toluene conversionreaches 98%.1.3Catalyst characterizationThe morphologies of the stainless steel wire mesh support and0.1%Pt鄄0.5%Pd/SSWM were characterized by scanning electronmicroscopy(SEM,Instrument JEM鄄T20).X鄄ray photoelectronspectrum(XPS)experiment was carried out on a RBD upgradedPHI鄄5000C ESCA system(Perkin Elmer)with Mg K琢radiation(h淄=1253.6 eV).Binding energies were calibrated using the con-tainment carbon(C 1s,284.6 eV).According to the method described in the published work16,the fastness of the obtained anodic oxidation film support wastested in an ultrasonic bath with water for 10-60 min to measurethe mass loss of the sample.2Results and discussion2.1Activity measurementCatalytic activities of acetone,toluene,and ethyl acetate com-plete oxidation over the sample of 0.1%Pt鄄0.5%Pd/SSWM cal-cined at 500 益 are shown in Fig.1.As seen from Fig.1,the totaloxidation temperature(T98)for toluene,acetone,and ethyl acetateis at 220,260,and 280 益,respectively.This indicates that thecatalyst shows a higher catalytic activity compared with the cat-alyst of Pd/Al2O3/cordierite(the corresponding T98is 230,280,and 320 益)17,and the T98is 10,20,and 40 益 lower for toluene,acetone,and ethyl acetate,respectively.Moreover,after the cat-alyst calcined at 700 益,the total oxidation temperature fortoluene,acetone,and ethyl acetate is 250,300,and 320 益,re-spectively.Compared with that of catalyst calcined at 500 益,the T98only increases by 30,40,and 40 益(not shown in Fig.1),indicating that the catalyst has a better temperature鄄resistantproperty.2.2SEM resultsThe SEM images of stainless steel wire mesh before and afteranodic oxidation treatment are shown in Fig.2,and obvious dif-ferences appear on the stainless steel wire mesh after anodic oxi-dation treatment(Fig.2(B).Meanwhile,compared with the blankstainless steel wire mesh(Fig.2(A),a film with donga structurelayer visibly appears over the stainless steel wire mesh surfaceafter anodizing oxidation procedure(Fig.2(C).The enlargementFig.1Light鄄off curves for toluene,acetone,and ethylacetate combustion over 0.1%Pt鄄0.5%Pd/SSWM catalyst1133Acta Phys.鄄Chim.Sin.,2008Vol.24of SSWM after anodizing oxidation treatment shown in Fig.2(C)suggests that this typical donga structure layer is favorable fordispersing platinum and palladium active phases.Thus,we thinkthat the presence of anodizing oxidation film seems to be impor-tant to offer a synergistic interaction between the support and ac-tive composion;this is responsible for favoring the active phasesof platinum and palladium that are easily dispersed on the sur-face of the stainless steel wire mesh support.Fig.3(A)shows the representative SEM image of 0.1%Pt/SS-WM catalyst,and an enlargement of this catalyst is displayed inFig.3(C).Similarly,the SEM image of Fig.3(B)gives the mi-crostructure of 0.1%Pt鄄0.5%Pd/SSWM catalyst and Fig.3(D)isan enlarged photograph of the catalyst.It is generally observedthat the active phases,whether Pt or Pt鄄Pd,are well dispersed onthe surface of stainless steel wire mesh support.In contrast,Fig.4 gives the comparison of catalytic activity of0.1%Pt/SSWM and 0.1%Pt鄄0.5%Pd/SSWM catalysts.It can befound that 0.1%Pt鄄0.5%Pd/SSWM catalyst shows better activitythan0.1%Pt/SSWMcatalyst.Asdescribedin published works18,19,bimetallic catalysts can enhance catalytic stabilities and activi-ties for their markedly different properties from either of theconstituent metals.The result indicated in Fig.4 is consistentwith this conclusion.2.3XPS resultsChemical states of surface atoms in the catalysts were investi-gated by XPS.The spectra of the specific positions of Pd 3d peaks,Pt 4fpeaks,and O 1s peaks of 0.1%Pt鄄0.5%Pd/SSWM catalyst beforeand after reaction are presented in Figs.5-7,respectively.From Fig.5,it can be found that there is a shift from 337.1 eVto a lower position of 336.0 eV in the binding energy of Pd 3d5/2in the sample after reaction.Here,Pd 3d5/2of 336.0 eV can beassigned to the binding energies of PdO.However,Pd 3d5/2of337.1 eV can be ascribed to PdO2species20.It indicates that avalence change of palladium onto the catalyst surface acts as anFig.2SEM images of SSWM before and after anodic oxidation procedure(A)SSWM,(B)SSWM after anodizing oxidation treatment,(C)the enlargement of SSWM after anodizing oxidation treatmentFig.3SEM images of different samples(A)0.1%Pt/SSWM,(B)0.1%Pt鄄0.5%Pd/SSWM,(C)the enlargement of 0.1%Pt/SSWM,(D)the enlargement of 0.1%Pt鄄0.5%Pd/SSWMFig.4T98of VOCs on different catalysts0.1%Pt/SSWM,0.1%Pt鄄0.5%Pd/SSWMFig.5Pd 3d region of 0.1%Pt鄄0.5%Pd/SSWM catalystbefore(A)and after(B)reaction1134No.7MA Ying et al.：Catalytic Oxidation of Toluene,Acetone and Ethyl Acetate on a New Pt鄄Pd/Stainless Steelactive redox site during the oxidation reaction.Additionally,some Pd4+ions were formed during the sample calcination pro-cess and then the adsorbed oxygen species got into the PdOcrystal lattice and resulted in the change of binding energy21.XPS results of Fig.6 indicate that there are obvious changes inthe positions of Pt 4f7/2peaks on the spectra of 0.1%Pt鄄0.5%Pd/SSWM catalyst before and after reaction.It demonstrates thatthe environment around Pt 4f7/2was changed.As far as we know,the surface oxygen species of the catalystis another important factor for catalytic activity.Fig.7 shows theXPS of O 1s analysis of the catalyst before and after reaction.Clearly,the O 1s peak located near 532.0 eV is attributed to ad-sorbed oxygen22and it can be found that the binding energy ofO 1s peak decreases in the sample after reaction.This can be ex-plained as the amount of adsorbed oxygen species transformedinto lattice oxygen during reaction.Therefore,we suppose thatthe adsorbed oxygen species has participated and played an im-portant role in the oxidation reaction.The XPS result revealsthat the adsorbed oxygen is the main contributor in this oxida-tion reaction,which is in agreement with the result reported byTitkov et al.23.2.4Adherence test of anodizing oxidation filmIn order to investigate the fastness of anodizing oxidation filmover SSWM,the ultrasonic vibrate test was carried out.As canbe seen from Fig.8,a mass loss-time curve of the anodizing oxi-dation film over SSWM reveals some interesting facts.The massloss on SSWM by anodizing oxidation treatment is 0.32%(w)after 10 min ultrasonic treatment,then after testing for 60 min amass loss of 0.34%(w)appeared,indicating that there are nearlyno significant changes on the sample.Meanwhile,the mass losstends to hold a fixed value after exposure to ultrasonic for 50min.This suggested that the anodizing oxidation film on SSWMshowed a good adherence state even at a long time breakage.This also indicated that a good synergistic interaction was in ex-istence between SSWM support and anodizing oxidation film.3ConclusionsIn this work,a new support and the 0.1%Pt鄄0.5%Pd/SSWMcatalyst were prepared and characterized by SEM and XPS tech-niques.The research revealed that the new support of SSWMpretreated by an anodic oxidation process favored dispersing thepalladium and platinum particles on the surface of SSWM sup-port.From catalytic activity tests,it can be found that 0.1%Pt鄄0.5%Pd/SSWM catalyst shows optimum catalysis for toluene,acetone,and ethyl acetate.Using stainless steel wire mesh ascatalyst support can overcome the shortcoming of 酌-Al2O3sup-port.To sum up,the 0.1%Pt鄄0.5%Pd/SSWM catalyst is a promis-ing catalyst for control of 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