Platinum Particle Size Research Articles

Cataluminescence Performance on Catalysts of Graphene Supported Platinum

Platinum nanoparticles supported by graphene were prepared by the colloid deposition process. The effects of particle size and loading amount of platinum particles on the cataluminescence (CTL) properties of CO have been investigated. The CTL properties and some analysis characteristics of the catalyst on other gas phase systems were explored. The results show that the Pt nanoparticles are well distributed on graphene and a faster catalytic reaction rate is apparent. The smaller particles lead to a higher CTL intensity. When the volume concentration of CO in air is below 40% (φ, volume fraction) the CTL intensity is proportional to the concentration of CO for all the catalysts (0.4%-1.6% (w, mass fraction) Pt). Among them, the catalyst containing 0.8% Pt was found to be the best. However, by increasing the CO concentration the CTL intensity of the catalysts with a low Pt loading (0.4%, 0.8%) decreased while the highly loaded (1.2%, 1.6%) catalysts continued to increase their intensity. Moreover, a higher Pt loading led to a higher CTL intensity. Under certain conditions the catalyst shows good CTL performance for CO oxidation, and ether, methanol as well as toluene show different degrees of response. No response was obtained for carbon dioxide, formaldehyde, glutaraldehyde, acetone, ethyl acetate, chloroform, and water vapor.

Enantioselective hydrogenation of ethyl pyruvate and 1-phenyl-1,2-propanedione on catalysts prepared by impregnation of colloidal platinum on SiO2

The enantioselective hydrogenation of ethyl pyruvate and 1-phenyl-1,2-propanedione was studied at 298 K and 40 bar of H2 over colloidal Pt stabilized with cinchonidine (CD) and supported on silica. The catalysts were prepared by impregnation of colloidal Pt on SiO2, leading to a metal load close to 1 wt.%. The colloid was prepared from an aqueous solution of H2PtCl6 and stabilized with different quantities of CD. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, XPS, XRD and TEM techniques. The reactions were carried out in a stainless steel batch reactor using cyclohexane as solvent and cinchonidine as chiral modifier. The addition of CD to the catalysts allows the stabilization and control of the platinum particle size and also affects the enantiomeric excess (ee) of the system, affording a higher proportion of the (R)-product. The relationship between the enantioselectivity and the CD concentration (added in situ) exhibits a bell type curve for both reactions, this being indicative of the importance of a competitive adsorption of the modifier and substrate on the catalyst surface.

Dispersed platinum supported by hydrogen molybdenum bronze-modified carbon as electrocatalyst for methanol oxidation

A new electrocatalyst, Pt/HxMoO3-C, for methanol oxidation, was prepared by dispersing platinum nano-particles on Vulcan XC-72 modified by hydrogen molybdenum bronze (HxMoO3, 0 ≤ x ≤ 2). The modification of Vulcan XC-72 with HxMoO3 on was accomplished by reducing the adsorbed molybdic acid and the platinum nano-particles were dispersed on the modified carbon by reducing chloroplatinic acid, with formaldehyde as the reductant. The prepared Pt/HxMoO3-C was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersion spectrometer, cyclic voltammetry (CV), chronoamperometry (CA), and single-cell test, with a comparison of the electrocatalyst, carbon-supported platinum (Pt/C) prepared under the same condition but without the modification. The results obtained from XRD and SEM showed that the modification of Vulcan XC-72 with HxMoO3 reduced the platinum particle size and improved distribution uniformity of platinum on carbon. The results, obtained from CV, CA, and the single-cell test, showed that Pt/HxMoO3-C exhibited better electrocatalytic activity toward methanol oxidation than Pt/C.

Platinum nanoparticle size effect on specific catalytic activity in n-alkane deep oxidation: Dependence on the chain length of the paraffin

The specific activity of 0.8% Pt/Al2O3 catalysts in the deep oxidation of C1–C6n-alkanes increases with an increase in the Pt particle size from 1 to 3–4 nm. Further coarsening of the particles insignificantly changes the specific activity. The size effect was studied for a series of catalysts containing platinum nanoparticles 1 to 11 nm in diameter. The specific catalytic activity variation range depends on the size of the reacting hydrocarbon molecules. As the platinum particle size increases, the specific catalytic activity increases 3–4 times for the oxidation of CH4 and C2H6 and by a factor of 20–30 for the oxidation of n-C4H10 and n-C6H14.

Pt/TiO<SUB>2</SUB>/Poly(vinyl sulfonic acid) Layer-by-Layer Films for Methanol Electrocatalytic Oxidation

One major challenge for the widespread application of direct methanol fuel cells (DMFCs) is to decrease the amount of platinum used in the electrodes, which has motivated a search for novel electrodes containing platinum nanoparticles. In this study, platinum nanoparticles were electrodeposited on layer-by-layer (LbL) films from TiO2 and poly(vinyl sulfonic) (PVS), by immersing the films into a H2PtCl6 solution and applying a 100 microA current during different electrodeposition times. Scanning tunnel microscopy (STM) and atomic force microscopy (AFM) images showed increased platinum particle size and electrode roughness for increasing electrodeposition times. The potentiodynamic profile of the electrodes indicated that oxygen-like species in 0.5 mol L(-1) H2SO4 were formed at less positive potentials for the smallest platinum particles. Electrochemical impedance spectroscopy measurements confirmed the high reactivity for the water dissociation and the large amount of oxygen-like species adsorbed on the smallest platinum nanoparticles. This high oxophilicity of the smallest nanoparticles was responsible for the electrocatalytic activity of Pt-TiO2/PVS systems for methanol electrooxidation, according to the Langmuir-Hinshelwood bifunctional mechanism. Significantly, the approach used here combining platinum electrodeposition and LbL matrices allows one to both control the particle size and optimize methanol electrooxidation, being therefore promising for producing membrane-electrode assemblies of DMFCs.

Platinum nanoparticles on fullerene black as effective catalysts of hydrogenation

Fixation of platinum from H2PtCl6 on fullerene black through non-conjugate double bonds or hydroxyl groups created on their base in the presence of an organic base with postreduction by formate ions allows platinum particles of size 3–4 nm to be obtained. These compositions catalyze 1-decene and nitrobenzene hydrogenation and exceed in activity the traditional catalyst Pt/C with platinum particle size of 70–80 nm. The average size of the fixed platinum particles affects the catalytic activity stronger than the specific surface area and the electron conduction of the carrying agent.

Platinum nanoparticles on carbon nanomaterials with graphene structure as hydrogenation catalysts

Carbon nanomaterials with graphene structure (single- and multiwall nanotubes and nanofibers) after oxidizing by a mixture of sulfuric and nitric acids and presumable introducing of carboxyl groups can be used as carrying agents of hydrogenation catalysts. Platinum in a concentration which should not exceed 10 wt % can be fixed using H2PtCl6 as a precursor in presence of an organic base. Catalysts based on these nanomaterials with the average size of platinum particles 6–8 nm exceed in activity the Pt/C catalyst with the size of platinum particles 65–70 nm, but are inferior to catalysts based on fullerene black with the average size of platinum particles 3–4 nm.

Synchronization between Kinetic Oscillations Occurring on Neighboring Nanoscaled Supported Platinum Clusters via Thermal Conduction

Monte Carlo technique is applied to simulate the synchronization between neighboring kinetic oscillators of nanoscaled supported platinum particles. Non-isothermal kinetics caused by local overheating provides an extra thermal conduction channel for synchronization between oscillators. Kinetic oscillation is produced when fast carbon monoxide oxidation is accompanied with slow subsurface oxygen formation and removal. Different effects are investigated on synchronization, including thermal conduction efficiency, heat dissipation efficiency, and distance between the two oscillators. Decreasing thermal conduction efficiency isolates each kinetically oscillating catalyst and results in complicated oscillation patterns. Heat dissipation has the opposite influence on synchronization comparing to thermal conduction. Low heat dissipation from the substrate to the environment maintains the temperature of the system and thus promotes synchronization. In addition, synchronization is destroyed when the distance between two oscillating particles becomes several-fold longer than the platinum particle size.

Reducibility of Platinum Supported on Nanostructured Carbons

The nanostructure of graphite like carbon, i.e. carbon nanofibers (CNF), carbon nanotubes (CNT) and carbon nanoplatelets (CNP), displayed a significant influence on the reducibility of platinum deposited on these carbons. The onset temperature for reduction increased from 461 K for Pt/CNF to 466 K for Pt/CNP and 487 K for Pt/CNT. The retarded reduction for Pt/CNT was related to the higher amount of acidic oxygen surface groups on this support resulting in a strong stabilization of the cationic platinum species. A higher reduction temperature for that sample increased the amount of metallic platinum, however the platinum particle size was larger (2–11 nm) compared to that of Pt/CNF and Pt/CNP (both 1–3 nm). The orientation of the graphene sheets had a significant influence on the selectivity for cinnamaldehyde hydrogenation: Pt/CNP resulted in a higher selectivity towards cinnamyl alcohol compared to Pt/CNF.

Mechanisms involved in the platinization of sol–gel-derived TiO 2 thin films

Sol–gel TiO 2 thin films have been loaded with platinum nano-particles via their immersion within a Pt 4+ precursor liquid solution exposed to UV light. Mechanisms involved in the photo-induced formation of platinum particles have been studied by UV/visible spectroscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray analysis, scanning electron microscopy, and transmission electron microscopy. According to studied mechanisms, it is shown that the amount, size, and structural state of photo-generated platinum particles dispersed at a solid surface can flexibly be monitored.

연료전지 촉매의 입자크기가 내구성에 미치는 영향

본 연구에서는 백금의 입자크기가 내구성과 활성에 미치는 영향을 고찰하였다. 상용 Pt/C의 열처리를 통해 백금 입자 크기를 <TEX>$3.5{\sim}9\;nm$</TEX>로 조절하였고, XRD와 TEM을 통해 이를 확인하였다. 촉매의 내구성 분석을 위해 가속 실험을 실시하였고, 촉매 활성 측정을 위해 산소환원반응 실험을 하였다. 백금의 입자크기를 증가시킬수록 내구성은 향상되었으나 촉매의 활성이 저하되었다. 즉 촉매의 내구성과 활성은 반비례관계가 성립된다는 것을 확인하였다. 그리고 저하된 촉매 활성과 내구성을 향상시키기 위해, 합금 촉매를 사용하였다.상용 Pt/C의 최대 전력 밀도는 약 <TEX>$507.6\;mV/cm^2$</TEX> 이고, PtCo/C 합금촉매는 <TEX>$585.8\;mV/cm^2$</TEX>이었다. 전기화학적 표면적은 상용 Pt/C는 약 60%정도 감소하였고, PtCo/C 합금촉매는 약 24%정도의 감소율을 나타냈다. 따라서 백금의 입자 크기 조절과 합금화를 통해 백금의 내구성과 활성을 동시에 높일 수 있었다. The influence of the particle size of platinum(Pt) on the stability and activity was studied. The particle size of platinum was controlled in the range of <TEX>$3.5{\sim}9\;nm$</TEX> by heat treatment of commercial Pt/C and confirmed by XRD and TEM. An accelerated degradation test was performed to evaluate the stability of platinum catalysts. Oxygen reduction reaction was monitored for the measurement of activity. As increasing the Pt particle size, the stability of Pt/C electrode was enhanced and the activity was reduced. It was confirmed that the stability of Pt/C electrode was in inverse proportion to the activity. PtCo/C alloy catalyst was used to improve the activity and stability of large-sized platinum particle. The maximum power density of commercial Pt/C was <TEX>$507.6\;mV/cm^2$</TEX> and PtCo/C alloy catalyst was <TEX>$585.8\;mV/cm^2$</TEX>. The decrement of electrochemical surface area showed Pt/C(60%) and PtCo/C alloy catalyst(24%). It was possible to enhance both of stability and activity of catalyst by the combination of particle size control and alloying.

Platinum Nanoparticles Stabilized by Polyvinylpyrrolidone for Hydrogenation

Abstract Nanosized colloidal platinum was prepared by reduction of H2PtCl6 in methanol-water mixture by refluxing. The particle size and morphology were characterized by transmission electron microscopy and electron diffraction. The influence of polyvinylpyrrolidone (PVP) molecular mass (MM), PVP concentration, and reduction time on platinum particle size was investigated. Small (1–2 nm) Pt particles are formed in the case of PVP with MM = 1.2×104. With increasing polymer MM and decreasing polymer concentration, large aggregates from small particles appear. High catalytic activity of the obtained colloidal platinum in hydrogenation of acetylene compounds is shown. The effect of Pt particle size on the catalytic activity was studied.

Platinum–Phosphorus Nanoparticles on Carbon Supports for Oxygen-Reduction Catalysts

Highly dispersed platinum nanoparticles on carbon supports were synthesized by electrochemical reducing platinum ions in an aqueous solution containing hypophosphite . Adding during the synthesis of the catalyst was effective for reducing platinum particle size, and the platinum particles with a mean size of were obtained at a high platinum loading amount of over . The oxygen-reduction activity of the catalysts that added was higher than that of the catalyst that did not add , which was due to the large surface area of the platinum in the former catalyst. According to the results of scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analysis, the phosphorus in the catalysts bonded with the surface of platinum particles as an oxide. The growth suppression of platinum particles was therefore attributed to the existence of a phosphorus oxide on the surface of platinum particles. But, adding excessively reduced the platinum surface area.

Syngas Production from Catalytic Partial Oxidation ofn-Butane: Comparison between Incipient Wetness and Sol−gel Prepared Pt/Al2O3

Catalytic partial oxidation (CPO) of n-butane under autothermal condition was studied over both incipient wetness (IW) and sol−gel (SG) prepared Pt/Al2O3 catalysts. These catalysts gave different results, with SG Pt/Al2O3 producing more H2 and CO than IW Pt/Al2O3 under the same reaction conditions. The difference between these two may be attributed to the particle size of platinum: the observed Pt particle sizes on both freshly prepared and used SG Pt/Al2O3 was 50% smaller than those on IW Pt/Al2O3.

Formation of layered Al2O3 and its inhibitory effect on the sintering of supported platinum particles

Layered Al 2 O 3 was prepared by calcination of a commercially available aluminum hydroxide with gibbsite structure. Platinum particles resided in the pore when the layered-Al 2 O 3 was used as a support, and the sintering of the Pt particles supported on the Al 2 O 3 was suppressed even in an oxidizing atmosphere at above 1000 °C. The sintering behavior of Pt particles on layered Al 2 O 3 was investigated. Layered Al 2 O 3 was prepared by calcination of a commercially available aluminum hydroxide. The growth of Pt particles on layered Al 2 O 3 was suppressed even in an oxidizing atmosphere at above 1000 °C, and the particle size was greatly affected by the pore diameter of the layered Al 2 O 3 . On the other hand, the particle size of platinum on γ-Al 2 O 3 was drastically increased. The diameters and the supported states of Pt particles were evaluated by transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), and chemisorption of carbon monoxide. The platinum particles in a highly dispersed state were captured in the pores of layered Al 2 O 3 , so the space for the particles for aggregation or migration was limited.

Uniformly dispersed platinum nanoparticles loading on porous carbons without using reduction agents

Platinum nanoparticles loading on carbon nanotube, activated carbon, and activated carbon fiber was carried out by impregnation of hexachloro palatinate ion(IV) from hydrogen hexachloro platinate hydrate [H 2PtCl 6·5.7H 2O] dissolved solution without using reduction agents, and heating the hexachloro platinate(IV) impregnated carbons up to 800 °C. When the initial platinum content was controlled to 1000 ppm in the solution, the adsorption capacities of hexachloro platinate(IV) on carbon nanotube, activated carbon and activated carbon fiber were 24%, 47%, and 76%, respectively at the equilibrium state. The adsorption isotherm type of hexachloro platinate(IV) on carbon nanotube was two-step linear and quite different from Langmuir model of activated carbon fiber due to the uniformly developed cylindrical pore structure and size distribution. The average platinum particle size on porous carbons was under 2 nm by heating the hexachloro platinate(IV) up to 400 °C in spite of non-using reduction agents, while the average size increased due to the agglomeration of some particles by heating them up to 800 °C. Therefore, uniformly distributed platinum nanoparticles loading on porous carbons can be obtained from simple impregnation of hexachloro palatinate ion(IV) from solution and heating it up to 400 °C.

Low Pt Thin Cathode Layer Catalyst Layer by Reactive Spray Deposition Technology

National Research Council Canada's Institute for Fuel Cell Innovation, NRC-IFCI, has been developing the Reactive Spray Deposition Technology (RSDT) process to optimize composite electrode layer formation and develop novel electrocatalysts and catalyst layers. The RSDT process provides the means necessary to develop the next generation of thin, low platinum or alloy catalyst layers for PEM MEA's. In order to best manage water distribution, mass transport and conductivity, the structure should be a gradient with controlled porosity and controlled distribution of both platinum and ionomer across the catalyst layer. The RSDT process allows good control of the platinum particle size as they are created directly from metal vapors, which prevents agglomeration in the catalyst layer. Additionally, it has the flexibility to build a gradient layer structure across a very thin film catalyst layer (<1 um). In our design, a platinum sub-layer (100 nm) was deposited directly on a Nafion® 117 membrane as a columnar structure. After the sub-layer, the platinum loading was reduced in a co-deposited layer of Pt-Nafion (ionomer)-carbon with the lowest loading closest to the GDL. The combined loading of both layers was <0.05mg/cm2 Pt with this approach. The manufactured catalyst layer has a performance of 0.65V at 1 A/cm2 with 0.05mg/cm2 Pt loading using pure oxygen .

MWCNT activation and its influence on the catalytic performance of Pt/MWCNT catalysts for selective hydrogenation

Multi-walled carbon nanotubes were submitted to three activation procedures: nitric acid oxidation, ball-milling and air oxidation. The influence of these treatments on nanotubes surface chemistry and morphology was evaluated by XPS, Raman and infrared spectroscopy, TGA, TPD, nitrogen adsorption and TEM. The three activated materials were used to prepare Pt supported catalysts from the organometallic precursor [Pt(CH 3) 2(COD)]. The influence of the activation treatments, together with that of a post-reduction thermal treatment, on the performances of the catalytic systems in the selective hydrogenation of cinnamaldehyde was investigated. It was shown that the best compromise between catalyst activity and selectivity requires a low amount of oxygenated groups on the support surface of the final catalyst, typically less than 700 μmol/g CO + CO 2 evolved during TPD experiments, together with an optimized platinum particle size ranging between 10 and 20 nm.

Modeling of single catalyst particle in cathode of PEM fuel cells

A microscopic catalyst model is proposed for predicting the local mass diffusion of a single catalyst particle in the cathode catalyst layer. The numerical model is employed to obtain a geometric description of the active layer. The cathode catalyst particle model proposed here is based on the microstructure of the catalyst layer. The catalyst particle is treated as many small platinum particles (1–10.0 nm) embedded in the larger carbon particle support (30–100 nm). This assembly is surrounded by an ionomer film with thickness ranging from 0.5 nm to 10.0 nm. The modeling results confirm that the platinum particle size, platinum loading and ionomer thickness can each play an important role on local mass and charge transport in the PEM fuel cell catalyst particle agglomerate. The local spherical diffusion, reactant distribution and electrochemical kinetics are strongly influenced by particle size, platinum loading and ionomer thickness.

Effect of sintering on the catalytic activity of a Pt based catalyst for CO oxidation: Experiments and modeling

The goal of this paper was to make the link between sintering of a 1.6% Pt/Al2O3 catalyst and its activity for CO oxidation reaction. Thermal aging of this catalyst for different durations ranging from 15min to 16h, at 600 and 700°C, under 7% O2, led to a shift of the platinum particle size distributions towards larger diameters, due to sintering. These distributions were studied by transmission electron microscopy. The number and the surface average diameters of platinum particles increase from 1.3 to 8.9nm and 2.1 to 12.8nm, respectively, after 16h aging at 600°C. The catalytic activity for CO oxidation under different CO and O2 inlet concentrations decreases after aging the catalyst. The light-off temperature increased by 48°C when the catalyst was aged for 16h at 600°C. The CO oxidation reaction is structure sensitive with a catalytic activity increasing with the platinum particle size. To account for this size effect, two intrinsic kinetic constants, related either to platinum atoms on planar faces or atoms on edges and corners were defined. A platinum site located on a planar face was found to be 2.5 more active than a platinum site on edges or corners, whatever the temperature. The global kinetic law {r (molm−2s−1)=103×exp(−64,500/RT)[O2]0.74[CO]−0.5)} related to a reaction occurring on a platinum atom located on planar faces allows a simulation of the CO conversion curves during a temperature ramp. Modeling of the catalytic CO conversion during a temperature ramp, using the different aged catalysts, allows prediction of the CO conversion curves over a wide range of experimental conditions.