Influence of catalyst pretreatments on the catalytic oxidation of toluene over nanostructured platinum based spent catalyst

In this study, we regenerated a nano-structured platinum based spent catalyst by applying thermal gas and acid pretreatment and examined the influence of treatment on the catalytic oxidation of toluene. The spent catalysts were pretreated with air, hydrogen and six different acid aqueous solutions (HCl, H2SO4, HNO3, H3PO4, CH3COOH and C2H2O4). The physicochemical properties of the parent and its modified catalysts were characterized by XRD, BET, TEM, and ICP. The results of light-off curves showed that air and hydrogen treated catalysts were more active than the parent catalyst. In addition, the catalytic activities of toluene oxidation for acid aqueous treated samples were identical with the order of Pt/Al ratio.     

Influence of physicochemical treatments on spent palladium based catalyst for catalytic oxidation of VOCs

To recycle the spent catalyst for the removal of VOCs, the benzene, toluene, and xylene (BTX) complete oxidations were studied over pretreated palladium based spent catalyst in a fixed bed flow reactor system at atmospheric pressure. Two different pretreatment methods with gas (air and hydrogen) and acid aqueous solution (HCl, H(2)SO(4), HNO(3), H(3)PO(4) and CH(3)COOH) were used to investigate the catalytic activity of spent catalyst. The properties of the spent and pretreated Pd based catalyst were characterized by XRD, BET, TEM, ICP, and XPS. The results of light-off curves indicate that the catalytic activity of toluene oxidation for pretreated samples is in the order of hydrogen>air>HNO(3)>CH(3)COOH>H(2)SO(4)>H(3)PO(4)>HCl. In addition, the air and the acid aqueous pretreated catalyst activities were significantly decreased compared to that of the spent (or parent) catalyst. Moreover, hydrogen pretreated (or reduced) catalysts having mainly metallic form show the best performance in removing the toluene vapours compared to other pretreated samples. The reduction temperature made a significant difference in the catalytic performance of the spent catalyst pretreated with hydrogen. XPS results clearly supported that the palladium state of the spent catalysts pretreated at 300 degrees C was shifted more toward metallic form than other reduced catalysts. Furthermore, the results of a long-term test and catalytic activity of aromatic hydrocarbons also supported that the hydrogen pretreated spent catalyst was a good candidate for removing toxic compounds.     

Effect of pretreatment conditions on particle size of bimetallic pt-au catalysts supported on ZnO/Al2O3 and its activity for toluene oxidation

Bimetallic Pt-Au catalysts supported on ZnO/Al2O3 were prepared by incipient wetness impregnation (IW-IMP) method with different pretreatment conditions such as flow velocity, calcination temperature, and heating rate under H2 during the calcination procedure, and characterized by X-ray diffraction (XRD), CO chemisorption, and scanning transmission electron microscopy (STEM) equipped energy dispersive spectroscopy (EDS). Furthermore, catalytic activity for complete oxidation of toluene was measured using a flow reactor under atmospheric pressure. Finally, relationship between the particle sizes with pretreatment conditions and catalytic activity for toluene on the bimetallic Pt-Au catalysts was discussed. In these results, nanosized bimetallic Pt-Au particles on ZnO/Al2O3 could be prepared by IW-IMP method. Relationship between the Pt and Au particle size and activity for toluene oxidation was clearly observed.     

Influence of physicochemical treatments on iron-based spent catalyst for catalytic oxidation of toluene

The catalytic oxidation of toluene was studied over an iron-based spent and regenerated catalysts. Air, hydrogen, or four different acid solutions (oxalic acid (C2H2O4), citric acid (C6H8O7), acetic acid (CH3COOH), and nitric acid (HNO3)) were employed to regenerate the spent catalyst. The properties of pretreated spent catalyst were characterized by the Brunauer Emmett Teller (BET), inductively coupled plasma (ICP), temperature programmed reduction (TPR), and X-ray diffraction (XRD) analyses. The air pretreatment significantly enhanced the catalytic activity of the spent catalyst in the pretreatment temperature range of 200-400 degrees C, but its catalytic activity diminished at the pretreatment temperature of 600 degrees C. The catalytic activity sequence with respect to the air pretreatment temperatures was 400 degrees C>200 degrees C>parent>600 degrees C. The TPR results indicated that the catalytic activity was correlated with both the oxygen mobility and the amount of available oxygen on the catalyst. In contrast, the hydrogen pretreatment had a negative effect on the catalytic activity, and toluene conversion decreased with increasing pretreatment temperatures (200-600 degrees C). The XRD and TPR results confirmed the formation of metallic iron which had a negative effect on the catalytic activity with increasing pretreatment temperature. The acid pretreatment improved the catalytic activity of the spent catalyst. The catalytic activity sequence with respect to different acids pretreatment was found to be oxalic acid>citric acid>acetic acid>or=nitric acid>parent. The TPR results of acid pretreated samples showed an increased amount of available oxygen which gave a positive effect on the catalytic activity. Accordingly, air or acid pretreatments were more promising methods of regenerating the iron-based spent catalyst. In particular, the oxalic acid pretreatment was found to be most effective in the formation of FeC2O4 species which contributed highly to the catalytic combustion of toluene.     

掺磷非晶氧化钛负载铂用于高效催化氧化挥发性有机化合物

高活性催化剂是挥发性有机化合物(VOCs)催化氧化消除的关键因素。本研究通过简单的共沉淀法成功制备了具有高比表面积的非晶介孔磷掺杂氧化钛负载铂催化剂(Pt/ATO-P)。通过P掺杂, 既可获得非晶介孔结构, 又可获得高ATO-P比表面积(可达278.9 m²·g^-1)。非晶介孔Pt/ATO-P催化剂显示出优异的VOCs催化氧化性能和良好的热稳定性。Pt/ATO-P样品在空速为36000 mL·h^-1·g^-1、甲苯浓度为10000 mL·m^-3的反应条件下, 对甲苯催化氧化的T₅₀和T₉₀(实现50%和90%转化率所需的温度)分别为130 ℃和140 ℃, 明显优于无磷催化剂Pt/TiO₂。这些发现可以为拓展非晶介孔磷化材料在环境净化和能源转化等领域的应用提供重要参考。     

Pt/C催化剂制备及CO催化氧化性能研究

采用大气压介质阻挡放电辅助氢气热还原方法和氢气热还原方法制备Pt/C催化剂,考察了制备方法及Pt负载量对Pt/C催化性能的影响。采用X-射线衍射(XRD)、循环伏安法、CO催化氧化反应研究Pt/C催化剂的晶相结构、电催化性能和CO催化氧化活性。结果表明:大气压介质阻挡放电辅助氢气热还原所制备的样品具有更高的电化学活性和CO催化氧化活性。当Pt负载量在2%到10%之间变化时,Pt/C-PC催化活性随负载量增加而增加。XRD测试结果显示当Pt负载量为2%,5%和10%时,Pt粒径分别为:10.6 nm,9.1 nm和6.4 nm,说明采用等离子体辅助氢气热还原方法制备的Pt/C-PC催化剂,Pt负载量越大,Pt粒径越小,CO催化氧化活性更高。     

Preparation of platinum nanoparticle and its catalytic activity for toluene oxidation

Colloidal Pt nanoparticles are prepared using H2PtCl6 as a precursor, polyvinylpyrrolidone (PVP: molecular weight = 10,000 and 40,000) and hydrogen as a stabilizing agent and a reducing agent, respectively. The amounts of the precursor and the stabilizing agent and the molecular weight of PVP have an effect on the formation of Pt nanoparticles. Supported Pt catalyst (CSPt) is prepared from colloidal Pt nanoparticles and y-Al2O3. Another supported Pt catalyst (ISPt) is prepared by using the conventional incipient wetness impregnation method with an aqueous H2PtCl6 solution and gamma-Al2O3. The catalytic activities of CSPt and ISPt catalysts are compared for VOC (toluene) oxidation. Transmission Electron Microscopy (TEM), UV-vis, X-ray diffraction (XRD) and temperature programmed reduction (TPR) are used to characterize CSPt and ISPt catalysts. The experimental results reveal that the catalytic activity of CSPt is superior to that of ISPT.     

Atomic Carbon Layers Supported Pt Nanoparticles for Minimized CO Poisoning and Maximized Methanol Oxidation

Maximizing activity of Pt catalysts toward methanol oxidation reaction (MOR) together with minimized poisoning of adsorbed CO during MOR still remains a big challenge. In the present work, uniform and well‐distributed Pt nanoparticles (NPs) grown on an atomic carbon layer, that is in situ formed by means of dry‐etching of silicon carbide nanoparticles (SiC NPs) with CCl₄ gas, are explored as potential catalysts for MOR. Significantly, as‐synthesized catalysts exhibit remarkably higher MOR catalytic activity (e.g., 647.63 mA mg^?1 at a peak potential of 0.85 V vs RHE) and much improved anti‐CO poisoning ability than the commercial Pt/C catalysts, Pt/carbon nanotubes, and Pt/graphene catalysts. Moreover, the amount of expensive Pt is a few times lower than that of the commercial and reported catalyst systems. As confirmed from density functional theory (DFT) calculations and X‐ray absorption fine structure (XAFS) measurements, such high performance is due to reduced adsorption energy of CO on the Pt NPs and an increased amount of adsorbed energy OH species that remove adsorbed CO fast and efficiently. Therefore, these catalysts can be utilized for the development of large‐scale and industry‐orientated direct methanol fuel cells.     

Mn、Fe和Cu氧化物在低温等离子体催化氧化甲苯体系中的活性比较

采用等体积浸渍法制备了MnOx/γ-Al2O3、FeOx/γ-Al2O3和CuOx/γ-Al2O3催化剂,测定了不同催化剂在低温等离子体场内分解甲苯的活性,用X射线衍射(XRD)、氢气程序升温还原(H2-TPR)技术对催化剂进行表征。结果表明催化剂分解甲苯的活性的顺序是MnOx/γ-Al2O3>FeOx/γ-Al2O3>CuOx/γ-Al2O3。催化剂分解臭氧的实验表明,不同催化活性组分对臭氧的催化分解性能顺序与对甲苯的分解性能顺序是一致的。MnOx/γ-Al2O3催化剂的Mn负载量对其催化活性有明显影响,Mn的含量为1%(质量分数)时,催化剂的活性最高,当能量密度为19J/L时,其对甲苯催化氧化的转化率接近100%。催化剂表征结果表明当Mn含量为1%(质量分数)时,氧化锰在载体γ-Al2O3上最接近单层分散量,此时活性组分与载体表面的相互结合力最强,在载体上有很好的分散性,从而表现出对甲苯分解的最好性能。     

熔盐电解制备Zr基低价金属氧化物担载铂催化剂催化氧化甲醇和CO

通过在700℃下的CaCl_2和NaCl混合熔盐中电化学还原ZrO_2制备得到了Zr的低价金属氧化物ZrO0.35,该低价金属氧化物作为铂催化剂载体催化甲醇显示了很高的催化活性和稳定性。分析了该催化剂的组成结构和电化学行为。结果显示,在酸性介质中该载体能够有效地提高铂纳米颗粒对甲醇和CO的催化活性。有两种机制可以解释其表现:一是电子协同效应,即Zr原子的电子转移到Pt原子,Pt与CO的相互作用力减弱,从而抑制了Pt中毒;另外一方面是Pt和金属载体的协同效应,它可以有效地移除和氧化CO的中间体。     

堇青石蜂窝陶瓷载体酸处理对整体式La0.8Sr0.2MnO3催化剂催化甲苯燃烧性能的影响

整体式催化剂是一种常用的催化剂,蜂窝陶瓷载体是其重要组成部分。酸处理可以改进其结构上的不足。使用不同质量分数、种类的酸溶液对堇青石蜂窝陶瓷载体进行了预处理,考察了酸处理对整体式催化剂的基本性质及甲苯催化活性的影响,并采用XRD、BET等表征手段进行分析。结果表明,蜂窝陶瓷载体经质量分数为30%硝酸溶液处理后可达最佳效果,负载率提高48%以上,比表面积扩大20倍以上,由其制得的催化剂催化甲苯燃烧的起燃温度为219℃,降低了19℃,完全转化温度为281℃。表征结果说明酸洗过程未改变载体组成,而是使载体比表面积增加20倍以上,从而提高了整体催化剂的催化活性。     

Characteristics of porous carbon nano-fibers synthesized by selective catalytic gasification

Carbon nanofibers (CNFs) with uniquely oriented channels were prepared via selective catalytic gasification in air at 450 and 500 degrees C, using Pt or Ru nano particles as catalysts. Catalytic gasification was chosen because it can selectively generate channels in the vicinity of the catalyst particles at relatively low temperatures, where thermal oxidation does not intensively occur. The structures and surface properties of the CNFs were examined via X-ray diffraction, analysis of the nitrogen adsorption-desorption isotherms, and high-resolution transmission electron microscopy. The effects of the catalyst species and loading amount on the formation of pores (channels) were investigated. The gasification mechanism, especially the channeling direction, throught the selection of the gasification catalysts, is discussed based on the results. This process can be effectively utilized for preparation of porous carbons, which have a well-aligned graphitic structure, and also channel-type pores can be designed by selection of gasification catalysts and conditions. The present porous CNF can be applied for catalyst support in fuel cells, without further treatment (e.g., acid treatment for the removal of metallic components).     

Catalytic performance of nanosized Pt-Au alloy catalyst in oxidation of methanol and toluene

The alloy formed between a group-VII metal such as platinum and a group-IB metal such as gold changes the catalytic behavior compared to the monometallic phase, increasing the selectivity toward certain products and also decreasing the deactivation rate. Pt-Au alloy nanoparticles coated on alumina support were found to be catalytically very active for complete oxidation of methanol and toluene. Furthermore, the nanosized Pt-Au particles were added to ZnO/Al2O3 on monolith catalyst. Also, effect of various parameters such as concentration of methanol and toluene and feed flow rate was investigated. Au particles were sized in 20 approximately 30 nm and Pt particles were well dispersed. In case of alumina supported powder catalyst, complete oxidation of methanol occurred at a temperature lower than that of toluene. From oxidation activity of monolithic honeycomb with Pt and Au particles, the conversion of methanol was increased with increasing the concentration of methanol, but conversion of toluene showed a decreasing tendency as the concentration of toluene increased. Also, conversion of methanol over honeycomb catalyst was not largely affected by feed flow rate, while conversion in toluene oxidation was decreased rapidly as feed flow rate was increased. As a result, the Pt-Au/ZnO/Al2O3/M catalyst used is likely to efficiently treat a large volume of exhaust gas containing VOCs.     

羟基锡酸盐载铂复合催化剂Pt/(Co,Zn)Sn(OH)6的合成及其甲醇电催化氧化性能

以羟基锡酸盐CoSn（OH）₆和ZnSn（OH）₆纳米空心立方体为前体,采用抗坏血酸作为弱还原剂,经过超声过程分别合成了羟基锡酸钴载Pt/CoSn（OH）₆和羟基锡酸锌载Pt/ZnSn（OH）₆复合催化剂,并在甲醇氧化反应（MOR）中表现出良好的性能。Pt/CoSn（OH）₆和Pt/ZnSn（OH）₆催化剂的单位质量活性分别为1 095.6 mA/mg和699.5 mA/mg,高于C载Pt（Pt/C）的594.6 mA/mg。利用XRD、SEM、TEM、XPS和电化学测试对催化剂晶体结构和性能间的关系进行了探索。CO溶出实验结果表明,羟基锡酸盐载体有利于Pt表面CO的去除,载体与Pt间的强相互作用和载体表面的大量羟基基团增强了催化剂的催化活性和CO抗毒性。此外,Pt/（Co,Zn）Sn（OH）₆催化剂中单质Pt高的相对含量也有利于提高MOR活性。通过研究载铂羟基锡酸盐电催化氧化甲醇性能,能够揭示载体结构对催化性能的影响,有助于羟基锡酸盐载铂复合催化剂在直接甲醇燃料电池（DMFCs）领域的应用。     

Effect of ceria on carbon supported platinum catalysts for methanol electrooxidation

Pt–CeO₂/C catalysts were synthesized by a one-step microwave polyol process and compared with Pt/C (E-TEK) catalyst in terms of the electrochemical activity for methanol oxidation using the cyclic voltammetry and chronoamperometry. The results demonstrated that Pt–CeO₂/C catalysts exhibited lower onset potential, higher current peak and better stability for methanol electrooxidation than Pt/C (E-TEK) catalyst. The effect of ceria on the catalytic activity was investigated by electrochemical measurements and the highest electrochemical activity was obtained at the molar ratio of Pt to Ce by 2:1. The preliminary mechanism of the enhanced electrocatalytic performance for methanol oxidation was discussed.     

Effect of controlling nano-sized copper by silver in copper-based catalyst on catalytic oxidation of toluene

Catalytic oxidation of VOC (toluene) over a copper based catalyst was carried out to assess its properties and performance. The Brunauer Emmett Teller (BET) method, X-ray diffraction (XRD), temperature programmed reduction (TPR), N2O pulse titration and energy dispersive spectroscopy (EDS) were used to characterize a series of 5 wt% Cu/gamma-Al2O3 catalysts modified with silver. The experimental results revealed that the addition of silver to 5 wt% Cu/gamma-Al2O3 catalyst highly enhanced its catalytic activity. With increasing addition amount of silver, the light-off curve for complete oxidation of toluene shifted to lower temperature. In addition, the increase of the addition amount of silver caused the copper particle size of 5 wt% Cu/gamma-Al2O3 catalyst to gradually increase. Subsequently, it demonstrated that the increase in the copper particle size is closely associated with the increase in catalytic activity.     

Preparation of nanosized Pt-Au alloy catalyst and its activity in methanol oxidation

The alloy catalyst has been widely used because it will be able to improve the activity and selectivity of the single metal catalyst in a given chemical reaction. In this study, the preparation and characteristics of nanosized Pt and Au particles on alumina and their catalytic activity were described. Nanosized Pt-Au catalysts were prepared by impregnation (IMP) method and deposition (DP) method using alumina or ZnO/Al2O3 as support. The size of Pt and Au particles were observed by transmission electron microscopy (TEM), energy dispersive spectroscope (EDS), and X-ray diffraction (XRD). Catalytic activity for oxidation of methanol was measured using a flow reactor. It could be seen that the Pt particle size and dispersion in the alloy catalysts was rarely influenced by preparation methods and Au particles coated by deposition method were well dispersed. TEM images showed that Au particles were well dispersed in the Pt/Au/ZnO/Al2O3 catalyst of which Au particles was supported by deposition method. The catalytic activity for methanol are given in the order of Pt-Au[IMP]/ZnO/Al2O3 > Pt[IMP]/Au[DP]/ZnO/Al2O3 > Au[DP]/Pt[IMP]/ZnO/Al2O3 > Pt-Au[DP]/ZnO/Al2O3. Therefore, Au particle size was doing not play an important role in increasing the oxidation activity, but the Au particles may promote the methanol oxidation.     

Synthesis of ordered macroporous Pt/Ru nanocomposites for the electrooxidation of methanol

Highly catalytic PtRu catalysts with different molar ratios of Pt to Ru have been synthesized by using the inverted colloidal crystals template technique. Three-dimensional ordered Pt/Ru alloys with pore size of 320 nm could be conveniently obtained by electrochemical codeposition of metal precursors inside the voids of the template. The structural and chemical properties of the macroporous catalysts were studied by using SEM, XPS and XRD methods. The decomposition and oxidation of methanol on the macroporous catalyst surfaces with different Pt and Ru molar ratios (Pt100Ru0, Pt90Ru10, Pt80Ru20, Pt70Ru30 and Pt56Ru44) were systemically discussed. Potentiostatic experiments showed that the special structure characteristics (e.g., interconnected pore framework and the flexible curvature) lead to enhanced methanol oxidation efficiency on the macroporous materials as compared to the directly deposited catalyst. These results demonstrate that the three-dimensional ordered porous bimetallic catalysts are promising alternatives for developing high performance DMFC anodic catalysts, especially for the fabrication of microfuel cells.     

Pt/C doped TiO2/SWNTs as catalyst for methanol oxidation

Platinum/carbon doped titanium dioxide/single-walled carbon nanotubes (Pt/C/TiO2/SWNTs) were successfully prepared by blending method. These composite catalysts were found to exhibit an anatase TiO2 structure with uniform Pt/C and the existence of SWNTs can be confirmed by transmission electron microscopy (TEM). The composite of Pt/C with TiO2/SWNTs could improve an enhancement in catalytic properties upon applying TiO2/SWNTs as catalyst support. The catalytic oxidation of methanol of Pt/C doped TiO2/SWNTs is found to be higher as compared to the undoped and Pt/C doped materials.     

Catalytic reduction of U(VI) in H2SO4 solutions with hydrazine and formic acid in the presence of bimetallic platinum-ruthenium catalysts

The structure of bimetallic platinum-ruthenium catalysts was studied by X-ray phase analysis and X-ray absorption spectroscopy. The effects of strong electronic interaction of Pt and Ru atoms in formation of the binary catalyst were revealed. The kinetics of catalytic reduction of U(VI) with hydrazine and formic acid in sulfuric acid solutions on 5% (Pt-Ru)/SiO₂ was studied. The mechanisms of these reactions with platinum and bimetallic platinum-ruthenium catalysts are similar. A catalytic synergistic effect is observed in heterogeneouscatalytic reactions of U(VI) reduction with hydrazine and formic acid in H₂SO₄ solutions.