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
物理化学学报(Wuli Huaxue Xuebao )
Acta Phys.鄄Chim.Sin .,2008,24(7)：1132-1136
Received:January 7,2008;Revised:March 19,2008;Published on Web:May 7,2008.English edition available online at https://www.wendangku.net/doc/a114930217.html,
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Corresponding author.Email:chenmin@https://www.wendangku.net/doc/a114930217.html,,yingmy@https://www.wendangku.net/doc/a114930217.html,;Tel:+86571?88273495;Fax:+86571?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
?Editorial office of Acta Physico ?Chimica Sinica
[Article]
https://www.wendangku.net/doc/a114930217.html,
July
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
马
莹
陈
敏?
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 ?0.5%Pd/不锈钢丝网(SSWM)催化剂.活性测试结果表明,0.1%Pt ?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℃.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：O643
Catalytic Oxidation of Toluene,Acetone and Ethyl Acetate on
a New Pt ?Pd/Stainless Steel Wire Mesh Catalyst
MA Ying CHEN Min ?SONG Cui ZHENG Xiao ?Ming
(Institute of Catalysis,Zhejiang University (Xixi Campus),Hangzhou
310028,P.R.China )
Abstract ：A new volatile organic compound (VOC)combustion catalyst of 0.1%Pt ?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 ?0.5%Pd/steel wire mesh catalyst had good catalytic activity and thermal stability.The total oxidation temperature for toluene,acetone,and ethyl acetate was at 220,260,and 280℃for the catalyst calcined at 500℃,respectively.The catalyst and stainless steel wire mesh support were characterized by means of scanning electron microscopy (SEM),X ?ray photoelectron spectrum (XPS),and ultrasonic vibration tests.The SEM results indicated that a typical donga structure layer appeared on the surface of stainless steel wire mesh support after anodic oxidation procedure.This typical anodic oxidation film was favorable for dispersing Pd and Pt components.
Key Words ：Catalytic oxidation;
Stainless steel wire mesh;
Anodic oxidation;X ?ray photoelectron spectra
Nowadays,the volatile organic compounds (VOCs),from chemical and petrochemical plants,have given rise to compre-hensive attention as they are hazardous to the environment and human health [1].There are many different techniques used for the removal of VOCs,such as adsorption,absorption,biofiltration,thermal incineration,and catalyst combustion [2-6].Among them,catalytic deep oxidation that converts VOCs into carbon dioxide and water has been recognized as one of the most promising methods [7-9].Noble metal catalysts like Pt or Pd on a suitable support have generally been used as the most active catalysts for VOCs oxida-tion [10,11].As previously reported,Pt and Pd supported on alumina was the most active catalyst [12-14].However,it is frequently re-ported that alumina phase from γto αtransition would cause a drastic 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 less expensive,higher temperature ?resistance,and more efficient in
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No.7MA Ying et al.：Catalytic Oxidation of Toluene,Acetone and Ethyl Acetate on a New Pt?Pd/Stainless Steel
low temperature for volatile organic compound combustion is needed.
The stainless steel wire mesh(SSWM)is regarded as an attrac-tive replacement of conventional support in catalysts because of its high anticorrosion,high thermal conductivity,and fictile property.Our previous work[15]reported that a0.01%Pt?0.02% Pd/stainless steel catalyst showed high catalytic activity for toluene,acetone,and ethyl acetate oxidation.This work is a continuation of the previous work,in which0.1%Pt?0.5%Pd supported 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.
1Experimental
1.1Preparation of catalyst
The stainless steel wire mesh(400mm×40mm×0.3mm)was machined into a typical shape as needed.The anodic oxidation treatment was carried out in the subsequent process:the stainless steel wire mesh was put into an isolated electrochemical cell,in which10%(w)sulphuric acid aqueous solution was used as elec-trolyte.Then at a constant stirring rate,keeping the constant voltages of3-5V and electric current density of1A·dm-2,the anodized oxidation film appeared on the stainless steel wire mesh support surface.Finally,the stainless steel wire mesh sup-port was dried at110℃for1h 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,the catalyst was dried at110℃for1h and then calcined at500℃for1h.The obtained catalyst was denoted as0.1%Pt?0.5%Pd/ SSWM in the following sections.
1.2Measurement of activity
Catalytic activity tests were carried out at atmospheric pres-sure in a fixed bed flow?reactor system(length=600mm,i.d.=28 mm).The typical VOCs substance of toluene,acetone,and ethyl acetate was introduced into the reactor by a carrying gas of air flow through a saturator maintained.The reactions were per-formed at temperature range of180-400℃,and the gas hourly space velocity(GHSV)is10000h-1.The concentrations of toluene,acetone,and ethyl acetate in the feed were0.10%-0.16%, 0.17%-0.25%,and0.11%-0.17%,respectively.The catalyst was placed at the center of the reactor supported by quartz wool and a thermocouple was positioned to monitor the reaction tem-perature.The analysis of the concentration of VOCs in the inlet and outlet gas was performed on a GC?1690chromatograph with a FID attachment.The GC column was3mm×0.3μm×3m stainless steel tubing packed with quartzite.The analysis condi-tions were as follows:the temperatures of injector,detector,and column chamber were170,140,and150℃,respectively.The flow rate of carrier gas(N2)was20cm3·min-1.The catalytic ac-tivities are characterized by parameter of T98,which indicates the temperature at which acetone,ethyl acetate,toluene conversion reaches98%.
1.3Catalyst characterization
The morphologies of the stainless steel wire mesh support and 0.1%Pt?0.5%Pd/SSWM were characterized by scanning electron microscopy(SEM,Instrument JEM?T20).X?ray photoelectron spectrum(XPS)experiment was carried out on a RBD upgraded PHI?5000C ESCA system(Perkin Elmer)with Mg Kαradiation (hν=1253.6eV).Binding energies were calibrated using the con-tainment carbon(C1s,284.6eV).
According to the method described in the published work[16], the fastness of the obtained anodic oxidation film support was tested in an ultrasonic bath with water for10-60min to measure the mass loss of the sample.
2Results and discussion
2.1Activity measurement
Catalytic activities of acetone,toluene,and ethyl acetate com-plete oxidation over the sample of0.1%Pt?0.5%Pd/SSWM cal-cined at500℃are shown in Fig.1.As seen from Fig.1,the total oxidation temperature(T98)for toluene,acetone,and ethyl acetate is at220,260,and280℃,respectively.This indicates that the catalyst shows a higher catalytic activity compared with the cat-alyst of Pd/Al2O3/cordierite(the corresponding T98is230,280, and320℃)[17],and the T98is10,20,and40℃lower for toluene, acetone,and ethyl acetate,respectively.Moreover,after the cat-alyst calcined at700℃,the total oxidation temperature for toluene,acetone,and ethyl acetate is250,300,and320℃,https://www.wendangku.net/doc/a114930217.html,pared with that of catalyst calcined at500℃, the T98only increases by30,40,and40℃(not shown in Fig.
1),indicating that the catalyst has a better temperature?resistant property.
2.2SEM results
The SEM images of stainless steel wire mesh before and after anodic 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 blank stainless steel wire mesh(Fig.2(A)),a film with donga structure layer visibly appears over the stainless steel wire mesh surface after anodizing oxidation procedure(Fig.2(C)).The
enlargement
Fig.1Light?off curves for toluene,acetone,and ethyl acetate combustion over0.1%Pt?0.5%Pd/SSWM catalyst
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Acta Phys.鄄Chim.Sin.,2008
Vol.24
of SSWM after anodizing oxidation treatment shown in Fig.2(C)suggests that this typical donga structure layer is favorable for dispersing platinum and palladium active phases.Thus,we think that 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 phases of 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 in Fig.3(C).Similarly,the SEM image of Fig.3(B)gives the mi-crostructure of 0.1%Pt ?0.5%Pd/SSWM catalyst and Fig.3(D)is an enlarged photograph of the catalyst.It is generally observed that the active phases,whether Pt or Pt ?Pd,are well dispersed on the surface of stainless steel wire mesh support.
In contrast,Fig.4gives the comparison of catalytic activity of 0.1%Pt/SSWM and 0.1%Pt ?0.5%Pd/SSWM catalysts.It can be found that 0.1%Pt ?0.5%Pd/SSWM catalyst shows better activity
than 0.1%Pt/SSWM catalyst.As described in published works [18,19],bimetallic catalysts can enhance catalytic stabilities and activi-ties for their markedly different properties from either of the constituent metals.The result indicated in Fig.4is consistent with this conclusion.2.3XPS results
Chemical states of surface atoms in the catalysts were investi-gated by XPS.
The spectra of the specific positions of Pd 3d peaks,Pt 4f peaks,and O 1s peaks of 0.1%Pt ?0.5%Pd/SSWM catalyst before and after reaction are presented in Figs.5-7,respectively.
From Fig.5,it can be found that there is a shift from 337.1eV to a lower position of 336.0eV in the binding energy of Pd 3d 5/2in the sample after reaction.Here,Pd 3d 5/2of 336.0eV can be assigned to the binding energies of PdO.However,Pd 3d 5/2of 337.1eV can be ascribed to PdO 2species [20].It indicates that a valence change of palladium onto the catalyst surface acts as an
Fig.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
treatment
Fig.3SEM images of different samples
(A)0.1%Pt/SSWM,(B)0.1%Pt ?0.5%Pd/SSWM,(C)the enlargement of 0.1%Pt/SSWM,(D)the enlargement of 0.1%Pt ?
0.5%Pd/SSWM
Fig.4T 98of VOCs on different catalysts
0.1%Pt/SSWM,
0.1%Pt ?
0.5%Pd/SSWM
Fig.5
Pd 3d region of 0.1%Pt 鄄0.5%Pd/SSWM catalyst
before (A)and after (B)
reaction
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No.7MA Ying et al .：Catalytic Oxidation of Toluene,Acetone and Ethyl Acetate on a New Pt ?Pd/Stainless Steel active redox site during the oxidation reaction.Additionally,some Pd 4+ions were formed during the sample calcination pro-cess and then the adsorbed oxygen species got into the PdO crystal lattice and resulted in the change of binding energy [21].XPS results of Fig.6indicate that there are obvious changes in the positions of Pt 4f 7/2peaks on the spectra of 0.1%Pt ?0.5%Pd/SSWM catalyst before and after reaction.It demonstrates that the environment around Pt 4f 7/2was changed.
As far as we know,the surface oxygen species of the catalyst is another important factor for catalytic activity.Fig.7shows the XPS of O 1s analysis of the catalyst before and after reaction.Clearly,the O 1s peak located near 532.0eV is attributed to ad-sorbed oxygen [22]and it can be found that the binding energy of O 1s peak decreases in the sample after reaction.This can be ex-plained as the amount of adsorbed oxygen species transformed into lattice oxygen during reaction.Therefore,we suppose that the adsorbed oxygen species has participated and played an im-portant role in the oxidation reaction.The XPS result reveals that the adsorbed oxygen is the main contributor in this oxida-tion reaction,which is in agreement with the result reported by Titkov et al .[23].
2.4Adherence test of anodizing oxidation film
In order to investigate the fastness of anodizing oxidation film over SSWM,the ultrasonic vibrate test was carried out.As can be seen from Fig.8,a mass loss -time curve of the anodizing oxi-dation film over SSWM reveals some interesting facts.The mass
loss on SSWM by anodizing oxidation treatment is 0.32%(w )after 10min ultrasonic treatment,then after testing for 60min a mass loss of 0.34%(w )appeared,indicating that there are nearly no significant changes on the sample.Meanwhile,the mass loss tends to hold a fixed value after exposure to ultrasonic for 50min.This suggested that the anodizing oxidation film on SSWM showed 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.
3Conclusions
In this work,a new support and the 0.1%Pt ?0.5%Pd/SSWM catalyst were prepared and characterized by SEM and XPS tech-niques.The research revealed that the new support of SSWM pretreated by an anodic oxidation process favored dispersing the palladium and platinum particles on the surface of SSWM sup-port.From catalytic activity tests,it can be found that 0.1%Pt ?0.5%Pd/SSWM catalyst shows optimum catalysis for toluene,acetone,and ethyl https://www.wendangku.net/doc/a114930217.html,ing stainless steel wire mesh as catalyst support can overcome the shortcoming of 酌-Al 2O 3sup-port.To sum up,the 0.1%Pt ?0.5%Pd/SSWM catalyst is a promis-ing catalyst for control of VOCs.References
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