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1.
直接乙醇燃料电池因其优异的性能备受关注。乙醇的电催化氧化并非简单的燃烧,涉及多种催化反应过程。乙醇的C-C键断裂选择性低,以及乙醇氧化中间产物C1分子由于没有及时氧化离开催化剂表面而造成的催化剂中毒,是制约其应用的瓶颈问题。电化学原位红外光谱是在电化学反应的同时,原位采集反应物种特定官能团的振动信息,可在分子水平揭示反应过程,推测反应机理。不同温度条件下乙醇电氧化过程的研究,有助于合理的设计高性能乙醇燃料电池催化剂。选用高性能的PtRh/RGO催化剂,结合同位素示踪法和电化学原位红外光谱技术,研究了不同温度下乙醇的电氧化过程。循环伏安研究表明,乙醇电氧化性能及其C-C键断裂的程度为PtRh/RGO (45℃)>PtRh/RGO (25℃)>商业Pt/C。电化学原位红外光谱从分子水平跟踪了乙醇的电氧化过程,观察到随着电位的增加, CO2, CO,-CH3,-C-O特征峰的强度逐渐增加。CO2和CH3COOH分别归属于乙醇完全氧化和不完全氧化的终产物,因此红外光谱中两种物质特征峰积分面积的比值[CO2]/[CH3COOH]可做为CO2选择性的量度。用来定量标定CH3COOH的特征峰是位于1 280 cm-1的-C-O振动峰,但对于PtRh/RGO催化剂的红外光谱而言,它的乙酸特征峰振动峰位1 280 cm-1附近出现1 214 cm-1甲醇衍生物的振动峰,通过一种反射红外光谱与标样透射红外光谱差减扣除叠加峰方法,定量计算了叠加峰中1 280 cm-1特征峰的积分强度,从而计算出PtRh/RGO的CO2选择性。结果表明对比25℃时, 45℃下PtRh/RGO具有更高的选择性, 0.3 V时提高48.1%, 0.5和0.6 V时略有提高, 0.4 V时降低,这可能是乙醇中β-C和水中OH竞争吸附所致。在两种反应温度条件下, CO2选择性都在电位高于0.4 V时呈现下降趋势。为了进一步研究CO2来源于α-C或β-C的完全氧化,使用同位素标记的13CH312CH2OH做为探针分子,通过电化学原位红外光谱研究了25和45℃下PtRh/RGO电极上乙醇电氧化过程。结果表明,β-C完全氧化为CO2的起始电位与温度无关,都为0.3 V。通过用13CO2/12CO2积分面积的比值定量分析,发现45℃下,该比值在电位0.3~0.5 V时相比于25℃下分别增加0.11, 0.18和0.22,表明随着温度或电位的增加,β-C完全氧化的选择性增加。  相似文献   

2.
采用电化学原位傅里叶变换红外反射光谱(electrochemical in situ fourier transform infrared reflec-tion spectroscopy,in situFTIRS)研究了草酸在铅电极上电催化还原过程。多步电位阶跃FTIRS(MSFTIRS)和时间分辨FTIRS(TRFTIRS)的结果表明:当研究电位为-0·70V(vs·SCE)时,即可明显检测到乙醛酸生成;研究电位为-0·85V时,电极表面累积生成乙醛酸的量达到最大值。随着电位的负移,生成的乙醛酸的量减少。同时在-0·95V时即可明显检测到乙醛酸进一步被还原,生成的乙醇酸在1093cm-1附近为—CH2OH的CO伸缩振动吸收。当研究电位为-1·50V时,电极表面的乙醛酸几乎都被还原成乙醇酸。另外,随着电位的负移,并没有检测到其他新物种的出现,表明乙醇酸在电极表面不会进一步发生还原反应。研究电位为-0·75V的原位时间分辨红外反射光谱显示反应产物乙醛酸在1750cm-1左右CO的伸缩振动吸收谱峰的左右积分强度随时间线性增加;而研究电位在-1·60V原位时间分辨红外反射光谱还观察到乙醇酸在1093cm-1附近—CH2OH的C—O伸缩振动吸收。电化学原位红外反射光谱技术有利于对反应中各物种官能团振动吸收的检测,为草酸电催化还原反应机理提供直接实验依据。  相似文献   

3.
CuO-CeO2系列催化剂是高效的CO选择性氧化反应的催化剂,通过原位漫反射红外光谱对掺杂碱金属和碱土金属氧化物的CuO-CeO2催化剂表面的吸附物种进行了研究。结果表明CuO-CeO2系列催化剂上,2 106 cm-1处出现CO的红外吸附峰。在反应气氛中,此峰的强度随着温度先升高后降低,说明Cu+是CO主要的活性吸附中心。低温下催化剂表面吸附的CO主要以可逆形式脱附出来,而高温下CO则以不可逆的形式脱附出来。催化剂表面在3 660 cm-1处出现尖锐的红外峰,归属于CeO2经还原产生的Ce-(OH)2偕式基团。在1 568,2 838和2 948 cm-1附近处出现甲酸根的红外谱峰,以及1 257和1 633 cm-1处出现碳酸根物种的红外峰。甲酸根物种是气相的CO与表面的羟基反应生成的产物,该物种的C—H键断裂生成碳酸根物种,这两物种均会降低催化剂的高温活性。Cu1Li1Ce9Oδ催化剂出现较强的CO2和甲酸根的红外峰,温度高于180℃时,该催化剂上还能看到微弱的CO红外峰,说明锂离子的给电子性质有利于提高Cu1Li1Ce9Oδ催化剂上CO的不可逆脱附,抑制氢的活化吸附,同时促进了甲酸根物种的生成。低温下Cu1Mg1Ce9Oδ和Cu1Ba1Ce9Oδ催化剂上CO的吸附量较多,但主要以可逆脱附形式脱附出来,对CO选择性氧化没有贡献。  相似文献   

4.
通过多元醇还原法制备了石墨烯(GN)负载的Pt及Pt基多元催化剂:Pt/GN,PtRh/GN,PtSn/GN,PtRhSn/GN。循环伏安研究表明,Rh的加入提升了Pt基催化剂的甲醇电催化氧化活性,而Sn的加入明显降低了甲醇在Pt基催化剂上的过电位,起始氧化电位负移106mV。电化学原位红外光谱研究进一步表明,Rh和Sn的加入使得Pt基催化剂对甲醇氧化的起始氧化电位负移;Rh的加入使得CO谱峰强度增大,而Sn的加入明显降低了CO谱峰强度。三元催化剂PtRhSn/GN很好的综合了Rh和Sn的电子效应及协同效应特点,相比于Pt/GN催化剂,起始氧化电位负移60mV,且活性达到其1.57倍。  相似文献   

5.
运用电化学循环伏安和原位FTIR反射光谱研究了碱性介质中乙醇在nm-Pt/GC电极上的氧化。结果表明,主要产物是CH3COO^-,仅存在少量乙醛,未检测到CO谱峰。与酸性介质中乙醇氧化的双途径机理不同,碱性介质中乙醇的氧化未经过解离吸附的中间步骤。  相似文献   

6.
表面合金电催化剂上甲酸氧化的原位FTIR反射光谱研究   总被引:1,自引:0,他引:1  
运用原位红外反射光谱(FTIRS)和电化学循环伏安法(CV)研究了甲酸在三种不同电极上的电催化特性。结果表明甲酸在碳载铂电极(Pt/GC)上的电催化氧化机理与本体铂电极(Pt)相类似,即可以通过活性中间体或毒性中间体氧化至CO_2。Pt/GC对甲酸的氧化比Pt具有更高的电催化活性。Pt/GC表面以Sb吸附原子修饰的电极(Sb-Pt/GC)上,甲酸氧化的起始电位(E;)提前至-0.10V,氧化电流峰电位(Ep)提前至0.34V,氧化峰电流(jp)值增加了7.28倍,半峰宽(FWHM)为0.30V。同样,Surface al-loy/GC电极上,E_I为-0.12V,E_p为0.32V和j_p为7.25mA·cm~(-2),相对Pt/GC分别负移了0.22,0.02V和增大了8.15倍,半峰宽(FWHM)为0.5V。表明Sb-Pt/GC和Surface alloy/GC电极不仅能够有效地抑制毒性中间体CO的生成,而且还可以显著地提高其对活性中间体的氧化的电催化活性。  相似文献   

7.
采用共沉淀法制备了Cu1Zr1Ce9Oδ催化剂,用于富氢气体中CO的选择性氧化反应,利用原位漫反射红外光谱技术考察了Cu1Zr1Ce9Oδ催化剂表面上的吸附物种和反应中间产物。研究发现,H2,O2和CO物种竞争吸附于Cu1Zr1Ce9Oδ表面相同的吸附位上。氢气预处理会引起Cu1Zr1Ce9Oδ催化剂上Cu+物种的深度还原,降低了CO的吸附量。氧气预处理为催化剂提供了较多的活性氧物种,同时抑制了Cu+物种的深度还原。氦气预处理仅起到净化催化剂表面的作用。180℃时Cu1Zr1Ce9Oδ催化剂在2938.7和2843.8cm-1处出现桥式和双齿型甲酸根物种的红外吸收峰。Cu1Zr1Ce9Oδ催化剂上活性较高的氧阴离子在常温下即可将催化剂表面上吸附的CO氧化成表面碳酸根。甲酸根和碳酸根物种占据Cu1Zr1Ce9Oδ催化剂的吸附中心,导致催化剂活性降低。300℃下用氦气吹扫Cu1Zr1Ce9Oδ催化剂表面,双齿型的甲酸根物种分解生成碳酸根物种,碳酸根物种再继续分解生成CO2,释放出催化剂表面的吸附位,恢复了Cu1Zr1Ce9Oδ催化剂的活性。  相似文献   

8.
本文研究了CO在不同温度氢处理的Pt/TiO_2上的红外吸附态。发现CO的红外吸收峰强度随氢预处理温度的增高而有规律地逐渐变小,CO在Pt上的主要红外吸收峰逐渐向低波数位移。观察到CO在174℃和374℃氢预处理的Pt/TiO_2上的红外吸收峰随时间的加长向高波数位移。当CO和H_2在Pt/TiO_2上共吸附时,上述位移的速度加快,反映了结构氢或表面氢的溢流或解离过程。  相似文献   

9.
臭氧在SnO2表面吸附的红外光谱研究   总被引:1,自引:0,他引:1  
以SnO2催化臭氧化降解高浓度糖蜜酒精废水为探针反应,研究SnO2催化臭氧化降解糖蜜酒精废水的活性,并采用红外光谱研究臭氧在SnO2及金属氧化物改性的SnO2催化剂表面的吸附行为。结果表明:由纯氧源制得的O3在SnO2表面吸附的红外光谱上的1 027和1 055 cm-1及2 099和2 122 cm-1处存在两处明显的吸收双峰,而空气制备的O3在SnO2表面与CO及CO2等存在竞争吸附,使得O3的吸附减少,催化臭氧化降解糖蜜废水的降解率下降。催化剂助剂对SnO2催化臭氧化降解糖蜜酒精废水有较大的影响。采用Fe2O3,NiO,CuO,ZnO,MgO,SrO及BaO等金属氧化物为助剂改性的SnO2在2 236和2 213 cm-1,1628和1 599 cm-1出现强度相似的吸收峰,但是几种催化剂对CO2和CO的吸附差别较大,过渡金属改性的SnO2在1 580~1 070 cm-1处出现较宽的吸收峰,碱土金属氧化物改性的SnO2催化剂在1 580~1 070 cm-1之间,出现了1 298和1 274 cm-1两个新的峰,从而引起了不同助剂催化臭氧化的活性差别,碱土金属改性的SnO2对糖蜜酒精废水的催化臭氧化脱色效果明显优于过渡金属改性的SnO2,其中BaO改性的SnO2催化剂的活性最好。  相似文献   

10.
原位DRIFTS研究CH4部分氧化和CO2重整的耦合   总被引:3,自引:0,他引:3  
8%Ru-5?/γ-Al2O3催化剂对于甲烷的低温活化具有较好的催化活性,在500℃下甲烷、二氧化碳和氧气的耦合反应中,吸热反应二氧化碳重整和放热反应甲烷部分氧化进行耦合强化,使得耦合反应中的甲烷转化率为38.8%。用原位漫反射傅里叶红外光谱法对钌系催化剂耦合甲烷部分氧化和二氧化碳重整反应体系机理进行研究。CO在8%Ru-5?/γ-Al2O3上吸附,表明CO在催化剂表面上波数为2 167 cm-1(2 118 cm-1)和2031 cm-1(2 034 cm-1)处形成孪生态Ru(CO)2和Ce(CO)2吸附物种,而且高温下CO吸附物种很容易从催化剂表面脱附出来。原位漫反射红外实验结果表明甲烷部分氧化反应时催化剂表面上有吸附物种碳酸根、甲酰基(甲酸盐)和一氧化碳的形成,其中表面的甲酰基和甲酸盐物种是甲烷部分氧化反应的主要活性中间物,这些中间活性中间体由甲烷吸附态CHx和催化剂表面的氧吸附态结合而形成的,随后这种中间物种再分解为CO产物;甲烷和二氧化碳重整反应时没有新的吸附物种产生,由此提出重整反应的机理是吸附态的甲烷和二氧化碳在催化剂活性中心上进行活化解离而生成合成气;甲烷、二氧化碳和氧气耦合反应过程中出现新的羟基物种(桥式羟基Ru-(OH)2),耦合反应机理复杂可能是由部分氧化和重整两类反应机理的复合,其中桥式羟基Ru-(OH)2参与了反应的进行。  相似文献   

11.
PtSn/C electrocatalysts (Pt:Sn atomic ratios of 50:50 and 60:40) were prepared using citric acid as reducing agent, and the pH of the reaction medium was varied by the addition of OH ions. The obtained electrocatalysts were characterized by energy dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy. The electrocatalysts were tested on the direct ethanol fuel cell (DEFC) at 90 °C. The obtained PtSn/C electrocatalysts showed the presence of a face-centered cubic, Pt, and SnO2 phases. In DEFC studies, the PtSn/C electrocatalysts showed a superior performance compared to a commercial PtSn/C and Pt/C electrocatalysts from E-TEK.  相似文献   

12.
The PtBi-modified Pt/C catalyst was prepared by liquid chemical reduction method. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) were used to characterize PtBi-modified Pt/C catalyst. The electrochemical behaviors for the 2-propanol electrooxidation reaction in alkaline medium were measured by cyclic voltammetry, line sweep voltammetry, and electrochemical impedance spectra (EIS). The results showed that the prepared PtBi is ordered intermediate compound. Compared with the spectrum obtained from Pt/C catalyst, the XPS peak of PtBi-modified Pt/C catalyst is obviously moving toward the low Pt 4f biding energy. The Bi0 and Bi2O3 coexist on the surface of PtBi/C catalyst. In alkaline medium, the electrochemical activity of 2-propanol electrooxidation of PtBi/C catalyst is higher than that of commercial Pt/C catalyst. EIS result shows that the reaction mechanism of 2-propanol electrooxidation for both catalysts is similar.  相似文献   

13.
PtRh/C (90:10), PtRh/C (50:50), PtSn/C (50:50), and PtSnRh/C (50:40:10) electrocatalysts were prepared by an alcohol-reduction process using ethylene glycol as solvent and reduction agent and Vulcan Carbon XC72 as supports. The electrocatalysts were characterized by energy-dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy. The electro-oxidation of ethanol was studied by cyclic voltammetry chronoamperometry at room temperature and on a single cell of a direct ethanol fuel cell at 100 °C. Cyclic voltammetry and chronoamperometry experiments showed that PtSnRh/C and PtSn/C electrocatalysts have similar performance for ethanol oxidation at room temperature, while the activity of PtRh/C electrocatalysts was very low. At 100 °C on a single cell, PtSnRh/C showed superior performance compared to PtSn/C and PtRh/C electrocatalysts.  相似文献   

14.
To improve the electrocatalytic properties of PtRu/C in methanol electrooxidation, nanoparticulate TiO2-promoted PtRu/C catalysts were prepared by directly mixing TiO2 nanoparticles with PtRu/C. Using cyclic voltammetry, it was found that the addition of 10 wt% TiO2 nanoparticles can effectively improve the electrocatalytic activity and stability of the catalyst during methanol electrooxidation. The value of the apparent activation energy (E a) for TiO2-PtRu/C was lower than that for pure PtRu/C at a potential range from 0.45 to 0.60 V. A synergistic effect between PtRu and TiO2 nanoparticles is likely to facilitate the removal of CO-like intermediates from the surface of PtRu catalyst and reduce the poisoning of the PtRu catalysts during methanol electrooxidation. Therefore, we conclude that the direct introduction of TiO2 nanoparticles into PtRu/C catalysts offers an improved facile method to enhance the electrocatalytic performance of PtRu/C catalyst in methanol electrooxidation.  相似文献   

15.
PtSn/C and PtSnSb/C electrocatalysts (20 wt.% metal loading) were prepared by an alcohol reduction process using H2PtCl6.6H2O, SnCl2.2H2O, and Sb(OOCCH3) as metal sources, ethylene glycol as solvent and reducing agent, and Vulcan XC72 as carbon support. The electrocatalysts were characterized by energy dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy, while that the performance for ethanol oxidation was investigated by cyclic voltammetry and chronoamperommetry (chrono) at room temperature. The diffractograms of the PtSn/C and PtSnSb/C electrocatalysts showed four peaks associated to Pt face-centered cubic structure and two peaks that were related to a SnO2 phase. For PtSb/C and PtSnSb/C electrocatalysts, no Sb (antimony) peaks corresponding to a metallic antimony or antimony oxide phases were observed. Transmission electron microscopy images showed that the metal particles were homogeneously distributed over the support. The PtSnSb/C (50:45:05) electrocatalyst showed an increase of performance for ethanol oxidation in relation to PtSn/C electrocatalyst at room temperature. In the tests at 100 °C on a single cell of a direct ethanol fuel cell, the maximum power density of PtSnSb/C (50:45:05) electrocatalyst was slightly higher than that of PtSn/C electrocatalyst.  相似文献   

16.
A highly dispersed and ultrafine carbon supported Pd nanoparticles (Pd/C) catalyst is synthesized by a facile homogeneous precipitation-reduction reaction method. Under the appropriate pH conditions, [PdCl4]2− species in PdCl2 solution are slowly transformed into the insoluble palladium oxide hydrate (PdO·H2O) precipitation by heat treatment due to a slow hydrolysis reaction, which results in the generation of carbon supported PdO·H2O nanoparticles (PdO·H2O/C) sample with the high dispersion and small particle size. Consequently, a highly dispersed and ultrafine Pd/C catalyst can be synthesized by PdO·H2O → Pd0 in situ reduction reaction path in the presence of NaBH4. As a result, the resulting Pd/C catalyst possesses a significantly electrocatalytic performance for formic acid electrooxidation, which is attributed to the uniformly sized and highly dispersed nanostructure.  相似文献   

17.
Ultrasound effect on the Pd(0) catalysed reaction of arylboronic acid with halobenzenes was investigated. The effect of catalyst, base as well as solvent was tested. Heterogenous reaction of iodoarenes with different arylboronic acids, catalysed by Pd/C and KF as the base in methanol:water mixture resulted in good yields of cross-coupling products. Reaction time of sonochemical reaction was 1 h, while 4 h of reflux was necessary to achieve comparable results. Bromobenzenes gave best results using aqueous solution of PdCl2 as the catalyst, potassium carbonate as the base in toluene:water two phase system using TEBA (benzyltriethylammonium chloride) as PT catalyst. Chlorobenzenes gave just feeble yields of cross-coupling products.  相似文献   

18.
This paper repots a highly catalytic palladium nanoparticle catalyst dispersed on the purified multi-walled carbon nanotubes (P-MWCNTs) for the electrooxidation of formic acid, in which sodium oxalate is employed as both a dispersant and a coordination agent. The nanostructured catalysts have been characterized by X-ray diffraction technique and transmission electron microscopy. It is found that the as-prepared face-centered cubic crystal Pd nanoparticles are uniformly dispersed on the surface of MWCNTs with an average particle size of 5.6 nm. Fourier transform infrared spectroscopy and thermogravimetric analysis revel that sodium oxalate is a tractable ligand with the aid of a suitable solution. Cyclic voltammetry and chronoamperometry tests demonstrate that the obtained Pd/P-MWCNT catalyst from typical experiment has better catalytic activity and stability for formic acid electrooxidation than acid-oxidation treatment MWCNT (AO-MWCNT)-supported Pd catalyst from the control experiment. Therefore, the as-prepared Pd/P-MWCNTs would be a potential candidate as an anode electrocatalyst in direct formic acid fuel cells.  相似文献   

19.
Pt rare earth–C electrocatalysts (rare earth = La, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, and Lu) were prepared by an alcohol reduction process using ethylene glycol as reduction agent and solvent and Vulcan XC 72 as support. The electrocatalysts were characterized by energy-dispersive X-ray analysis, X-ray diffraction (XRD), and cyclic voltammetry. The electrooxidation of ethanol was studied in acid medium by cyclic voltammetry and chronoamperometry using thin porous coating technique. The XRD patterns indicate that all electrocatalysts present the face-centered cubic structure of Pt and the presence of rare earth hydroxides. All electrocatalysts prepared by this methodology showed superior performance for ethanol electrooxidation at room temperature compared to Pt–C.  相似文献   

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