Tuning of catalytic CO oxidation by changing composition of Rh-Pt bimetallic nanoparticles

Recent breakthroughs in synthesis in nanoscience have achieved control of size and composition of nanoparticles that are relevant for catalyst design. Here, we show that the catalytic activity of CO oxidation by Rh/Pt bimetallic nanoparticles can be changed by varying the composition at a constant size (9+/-1 nm). Two-dimensional Rh/Pt bimetallic nanoparticle arrays were formed on a silicon surface via the Langmuir-Blodgett technique. Composition analysis with X-ray photoelectron spectroscopy agrees with the reaction stoichiometry of Rh/(Pt+Rh). CO oxidation rates that exhibit a 20-fold increase from pure Pt to pure Rh show a nonlinear increase with surface composition of the bimetallic nanoparticles that is consistent with the surface segregation of Pt. The results demonstrate the possibility of controlling catalytic activity in metal nanoparticle-oxide systems via tuning the composition of nanoparticles with potential applications for nanoscale design of industrial catalysts.     

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.     

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.     

Ethylene glycol oxidation on Pt and Pt-Ru nanoparticle decorated polythiophene/multiwalled carbon nanotube composites for fuel cell applications

A novel supporting material containing polythiophene (PTh) and multiwalled carbon nanotubes (MWCNTs) (PTh-CNTs) is prepared by in?situ polymerization of thiophene on carbon nanotubes using FeCl(3) as oxidizing agent under sonication. The prepared polythiophene/CNT composites are further decorated with Pt and Pt-Ru nanoparticles by chemical reduction of the corresponding metal salts using HCHO as reducing agent at pH = 11 (Pt/PTh-CNT and Pt-Ru/PTh-CNT). The fabricated composite films decorated with nanoparticles were investigated towards the electrochemical oxidation of ethylene glycol (EG). The presence of carbon nanotubes in conjugation with a conducting polymer produces a good catalytic effect, which might be due to the higher electrochemically accessible surface areas, electronic conductivity and easier charge-transfer at polymer/electrolyte interfaces, which allows higher dispersion of Pt and Pt-Ru nanoparticles. Such nanoparticle modified PTh-CNT electrodes exhibit better catalytic behavior towards ethylene glycol oxidation. Results show that Pt/PTh-CNT and Pt-Ru/PTh-CNT modified electrodes show enhanced electrocatalytic activity and stability towards the electro-oxidation of ethylene glycol than the Pt/PTh electrodes, which shows that the composite film is more promising for applications in fuel cells.     

Nanosized Pt-Co catalysts for the preferential CO oxidation

The preferential CO oxidation in the presence of excess hydrogen was studied over Pt-Co/gamma-Al2O3. CO chemisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDX) and temperature programmed reduction (TPR) were conducted to characterize active catalysts. The catalytic activity for CO oxidation and methanation at low temperatures increased with the amounts of cobalt in Pt-Co/gamma-Al2O3. This accompanied the TPR peak shift to lower temperatures. The optimum molar ratio between Co and Pt was determined to be 10. The co-impregnated Pt-Co/gamma-Al2O3 appeared to be superior to Pt/Co/gamma-Al2O3 and Co/Pt/gamma-Al2O3. The reductive pretreatment at high temperature such as 773 K increased the CO2 selectivity over a wide reaction temperature. The bimetallic phase of Pt-Co seems to give rise to high catalytic activity in selective oxidation of CO in H2-rich stream.     

Pt nanoparticles inside the mesopores of TiO<Subscript>2</Subscript>–MCM-48: synthesis,characterization and catalytic activity for CO oxidation

TiO₂ and Pt nanoparticles were deposited in the channels of siliceous MCM-48 via a sequential incipient wetness-impregnation method employing (NH₄)₂PtCl₄ as platinum source. The resulting composite Pt/TiO₂–MCM-48 (1 wt% Pt, ca. 3 wt% Ti) was characterized using XRD, TEM, nitrogen physisorption, hydrogen chemisorption, UV–vis spectroscopy, and XPS; its catalytic activity for CO oxidation was also explored. These data were compared with those of Pt/MCM-48 prepared via an analogous route. The results reveal that the platinum was deposited inside the intact pore system in both cases. It remains inside upon mild reduction but tends to segregate out of the pore system at higher reduction temperatures or during CO oxidation. Both composites were found to be highly active in CO oxidation, with 50% conversion at 460–475 K after activation of the unreduced catalysts in the (net oxidizing) feed. Striking differences in this activation process between Pt/MCM-48 and Pt/TiO₂–MCM-48 suggest that the precursor reduction is influenced by an interaction with the TiO₂ component in the latter.     

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。     

Ultralow loading Pt nanocatalysts prepared by atomic layer deposition on carbon aerogels

Using atomic layer deposition (ALD), we show that Pt nanoparticles can be deposited on the inner surfaces of carbon aerogels (CA). The resultant Pt-loaded materials exhibit high catalytic activity for the oxidation of CO even at loading levels as low as approximately 0.05 mg Pt/cm2. We observe a conversion efficiency of nearly 100% in the 150-250 degrees C temperatures range, and the total conversion rate seems to be limited only by the thermal stability of the CA support in ambient oxygen. The ALD approach described here is universal in nature, and can be applied to the design of new catalytic materials for a variety of applications, including fuel cells, hydrogen storage, pollution control, green chemistry, and liquid fuel production.     

WO3-Assisted Synergetic Effect Catalyzes Efficient and CO-Tolerant Hydrogen Oxidation for PEMFCs

Developing anode catalysts with substantially enhanced activity for hydrogen oxidation reaction (HOR) and CO tolerance performance is of great importance for the commercial applications of proton exchange membrane fuel cells (PEMFCs). Herein, an excellent CO-tolerant catalyst (Pd-WO₃/C) has been fabricated by loading Pd nanoparticles on WO₃ via an immersion-reduction route. A remarkably high power density of 1.33 W cm⁻² at 80 °C is obtained by using the optimized 3Pd-WO₃/C as the anode catalyst of PEMFCs, and the moderately reduced power density (73% remained) in CO/H₂ mixed gas can quickly recover after removal of CO-contamination from hydrogen fuel, which is not possible by using Pt/C or Pd/C as anode catalyst. The prominent HOR activity of 3Pd-WO₃/C is attributed to the optimized interfacial electron interaction, in which the activated H* adsorbed on Pd species can be effectively transferred to WO₃ species through hydrogen spillover effect and then oxidized through the H species insert/output effect during the formation of H_xWO₃ in acid electrolyte. More importantly, a novel synergetic catalytic mechanism about excellent CO tolerance is proposed, in which Pd and WO₃ respectively absorbs/activates CO and H₂O, thus achieving the CO electrooxidation and re-exposure of Pd active sites for CO-tolerant HOR.     

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。     

Oxidizing catalysts supported on nanostructured TiO<Subscript>2</Subscript>

This paper compares the catalytic performance of platinum catalysts supported on different forms of TiO₂. A composite material in the form of Pt supported on titanium dioxide nanotubes is shown to possess the highest catalytic performance for CO oxidation. It exhibits stable catalytic activity at temperatures from 65 to 300°C.     

Pt/TiO2 composite nanoparticles synthesized by electron beam irradiation for preferential CO oxidation

This paper describes a novel synthesis method of stabilizer-free Pt/TiO₂ composite nanoparticles using electron beam irradiation. The chemical compositions were analyzed by inductively coupled plasma-atomic emission spectroscopy. The microstructures of the samples were observed by using transmission electron microscope. Pt nanoparticles with the sizes of 2–4 nm were deposited on TiO₂ without any use of stabilizers. The concentrations of Pt ions and 2-propanol notably affected the size and shape of Pt nanoparticles. Their reactions of preferential CO oxidation were measured in temperature region from 60 to 140 °C. The Pt/TiO₂ catalyst with spherical Pt nanoparticles exhibited a 67% of CO conversion rate and 100% of selectivity at a low temperature of 60 °C.     

The operating performance and products distribution of the catalytic oxidation of methyl-isobutyl-ketone over a Pt/gamma-Al2O3 catalyst

Catalytic oxidation is one of the cost-effective technologies to solve the troublesome volatile organic compounds. This study treated methyl-isobutyl-ketone (MIBK) by a commercial catalyst, Pt/gamma-Al(2)O(3), in a fixed-bed reactor. The effects of operating factors, such as operating temperature, MIBK concentration, space velocity, and O(2) concentration, on the performance of the catalyst were investigated. The products and reactants distributions from the oxidation of MIBK over Pt/gamma-Al(2)O(3) were observed. The results show that the products containing carbon atoms are CO, CO(2), and C(3)H(6)O. Two catalyst life-tests were also carried out to characterize the deactivation effect of MIBK. The result shows that the deactivation effect may be due to the coke on the catalyst surface at 423 K. From the statistical analysis, the operating temperature is the most effective factor on the conversion of MIBK. The catalysts were also characterized by surface area analysis and elemental analysis before and after the test. The results show that the catalytic deactivation may be due to carbon coating. At low temperature (423 K), the phenomenon of carbon coating was more obvious than that at high temperature (573 K). The product distributions from the oxidation of MIBK over Pt/gamma-Al(2)O(3) were analyzed by GC. The results indicate that the C(3)H(6)O is formed from the beginning, presenting a peak at 423 K, 6.54 ppm. The CO concentration also peaked at the same temperature, 6.84 ppm.     

Pt Single Atoms on CrN Nanoparticles Deliver Outstanding Activity and CO Tolerance in the Hydrogen Oxidation Reaction

The large-scale application of proton exchange membrane fuel cells is currently hampered by high cost of commercial Pt catalysts and their susceptibility to poisoning by CO impurities in H₂ feed. In this context, the development of CO-tolerant electrocatalysts with high Pt atom utilization efficiency for hydrogen oxidation reaction (HOR) is of critical importance. Herein, Pt single atoms are successfully immobilized on chromium nitride nanoparticles by atomic layer deposition method, denoted as Pt SACs/CrN. Electrochemical tests establish Pt SACs/CrN to be a very efficient HOR catalyst, with a mass activity that is 5.7 times higher than commercial PtRu/C. Strikingly, the excellent performance of Pt SACs/CrN is maintained after introducing 1000 ppm of CO in H₂ feed. The excellent CO-tolerance of Pt SACs/CrN is related to weaker CO adsorption on Pt single atoms. This work provides guidelines for the design and construction of active and CO-tolerant catalysts for HOR.     

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.     

薄壳层核壳型Ni/Pt纳米粒子的制备及电催化性能

通过胶体-化学镀法制备不同厚度薄壳层核壳型Ni/Pt纳米粒子, 采用HRTEM、EDS、XPS和XRD手段对粒子的形貌、晶型和组成进行物理表征. 采用动电位、循环伏安法对其氧电还原和甲醇电氧化活性进行测试. 实验结果表明, 核壳结构Ni/Pt纳米颗粒基本为球形, 其中Ni₁-Pt_0.067平均直径为7 nm左右, 壳层厚度约1 nm. 与Pt/C相比, 核壳型Ni/Pt纳米粒子对氧电还原和甲醇电氧化的催化活性显著提高. 在所制备的不同壳层厚度催化剂中, Ni₁-Pt_0.067/C在0.5 mol/L H₂SO₄中氧电还原的最大峰电流密度可达到143.06 mA/mg, 是相同反应条件Pt/C峰电流密度的1.4倍; 而Ni₁-Pt_0.067/C在0.5 mol/L H₂SO₄+1.0 mol/L CH₃OH溶液中甲醇电氧化峰电流密度可达538.3 mA/mg, 是Pt/C峰电流密度的5.2倍. 若以1 mg贵金属Pt为基准, Ni₁-Pt_0.067/C的比质量活性相对Pt/C的提高了30倍.     

Dendrimer templated synthesis of one nanometer Rh and Pt particles supported on mesoporous silica: catalytic activity for ethylene and pyrrole hydrogenation

Monodisperse rhodium (Rh) and platinum (Pt) nanoparticles as small as approximately 1 nm were synthesized within a fourth generation polyaminoamide (PAMAM) dendrimer, a hyperbranched polymer, in aqueous solution and immobilized by depositing onto a high-surface-area SBA-15 mesoporous support. X-ray photoelectron spectroscopy indicated that the as-synthesized Rh and Pt nanoparticles were mostly oxidized. Catalytic activity of the SBA-15 supported Rh and Pt nanoparticles was studied with ethylene hydrogenation at 273 and 293 K in 10 torr of ethylene and 100 torr of H 2 after reduction (76 torr of H 2 mixed with 690 torr of He) at different temperatures. Catalysts were active without removing the dendrimer capping but reached their highest activity after hydrogen reduction at a moderate temperature (423 K). When treated at a higher temperature (473, 573, and 673 K) in hydrogen, catalytic activity decreased. By using the same treatment that led to maximum ethylene hydrogenation activity, catalytic activity was also evaluated for pyrrole hydrogenation.     

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.     

Nanofence Stabilized Platinum Nanoparticles Catalyst via Facet‐Selective Atomic Layer Deposition

A facet‐selective atomic layer deposition method is developed to fabricate oxide nanofence structure to stabilize Pt nanoparticles. CeO_x is selectively deposited on Pt nanoparticles' (111) facets and naturally exposes Pt (100) facets. The facet selectivity is realized through different binding energies of Ce precursor fragments chemisorbed on Pt (111) and Pt (100), which is supported by in situ mass gain experiment and corroborated by density functional theory simulations. Such nanofence structure not only has exposed Pt active facets for carbon monoxide oxidation but also forms ceria–metal interfaces that are beneficial for activity enhancement. The composite catalysts show excellent sintering resistance up to 700 °C calcination. CeO_x anchors Pt nanoparticles with a strong metal oxide interaction, and nanofence structure around Pt nanoparticles provides physical blocking that suppresses particles migration. The study reveals that forming oxide nanofence structure to encapsulate precious metal nanoparticles is an effective way to simultaneously enhance catalytic activity and thermal stability.     

Preparation and characterization of PtRu nanoparticles supported on nitrogen-doped porous carbon for electrooxidation of methanol

N-doped porous carbon nanospheres (PCNs) were prepared by chemical activation of nonporous carbon nanospheres (CNs), which were obtained via carbonization of polypyrrole nanospheres (PNs). The catalysts, PtRu and Pt nanoparticles supported on PCNs and Vulcan XC-72 carbon black, were prepared by ethylene glycol chemical reduction. Transmission electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy were employed to characterize samples. It was found that PCNs containing N function groups possess a large number of micropores. Uniform and well-dispersed Pt and PtRu particles with narrow particle size distribution were observed. The electrooxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). The results showed that alloy catalyst (Pt(1)Ru(1)/PCN) possessed the highest catalytic activity and better CO tolerance than the other PtRu and Pt-only catalysts; PtRu nanoparticles supported on PCN showed a higher catalytic activity and more stable sustained current than on carbon black XC-72. Compared to commercial Alfa Aesar PtRu catalyst, Pt(1)Ru(1)/PCN reveals an enhanced and durable catalytic activity in methanol oxidation because of the high dispersion of small PtRu nanoparticles and the presence of N species of support PCNs.