Size Of Pt Particles Research Articles

A Theoretical Consideration on the Surface Structure and Nanoparticle Size Effects of Pt in Hydrogen Electrocatalysis

Microkinetic modeling and density functional theory (DFT) calculations are combined to understand the surface structure and nanoparticle size effects of Pt on the kinetics of hydrogen electrode reactions (HERs). The microkinetic modeling leads to a mechanism-free volcano relation between the exchange current density of HERs (j0) and the surface coverage of the reactive H adatoms at the equilibrium potential (θ0), making the activity trend of various catalytic surfaces for HERs predictable with θ0. It is shown that catalytic surfaces with θ0 values closer to 0.5 monolayer will have higher j0. A DFT calculation scheme is developed to determine the nature of the reactive H atoms and the corresponding θ0 values. The calculated results on Pt single crystal electrodes predict that j0 follows a trend that Pt(110) ≈ Pt(100) > Pt(111), whereas for Pt nanoparticles the j0 follows a trend that (100) facets > (111) facets ≈ edge rows, which in turn suggests a decrease of j0 with the decreasing particle size of Pt. It...

Complete elimination of indoor formaldehyde over supported Pt catalysts with extremely low Pt content at ambient temperature

A series of highly active supported Pt catalysts, developed by sodium borohydride reduction under mild preparation conditions, were used to eliminate indoor formaldehyde (HCHO) at ambient temperature. The influences of oxidation state, support and size of Pt particles, and the operating parameters were investigated. The reduced Pt nanoparticles with different supports are highly active for catalytic oxidation of HCHO. For example, nearly 100% HCHO conversion was obtained on the reduced Pt/TiO 2 catalysts (denoted as Pt–TiO 2) even with 0.1% Pt loading while it was less than 25% on the oxidized ones. Negatively charged metallic Pt nanoparticles, which probably facilitate the electron transfer and formation of active oxygen, provide the active sites for HCHO oxidation. The turnover frequencies (TOFs) of HCHO oxidation on Pt nanoparticles with different supports are not sensitive to the reducibility of support but somewhat affected by the Pt particle sizes. A maximum TOF of 2.87 s −1 was obtained on the 1% Pt–MgO with Pt particle size of about 3 nm. The 0.1% Pt–TiO 2 catalyst remained highly active and stable in humid air with a wide gas hourly space velocity range between 40,000 and 240,000 h −1 and initial HCHO concentration range between 5 and 30 ppm.

Graphene Role as Platinum Support for CO and Formic Acid Electrooxidation

AbstractThe direct methanol fuel cell (DMFC) is a promising power source for electronic applications due to its high efficiency and compactness. To improve the efficiency, many support materials have been developed. We investigated uniform graphene nanoflake films as a support for catalytic Pt nanoparticles in direct carbon monooxide and formic acid electro-oxidation. Pt nanoparticles were deposited on the surface of graphene films with chemical reduction method. Chemical functionalization of graphene with ethylenediamine enables Pt nanoparticles mobilize on graphene uniformly. By simply changing the loading amount of Pt precursor, various particle sizes were achieved. The particle size of Pt plays prominent role in fuel cell test. The electrochemically active surface area of different sample are 6.3 (5 wt% Pt/G), 4.1 (20 wt% Pt/G), and 3.0 (50 wt% Pt/G) cm2mg-1 corresponding to the particle size 3±1nm, 10±2nm, 20±2nm respectively. The results obtained are ascribed to a uniform network made of 2-4 nm Pt monolayer nanopaticles on the surface of graphene flakes. Graphene will play significant role in developing next-generation advanced Pt based fuel cells and their relevant electrodes in the field of energy.

10.2478/s11814-009-0320-6

Highly loaded and dispersed Pt/C catalysts, used as cathodic electrocatalysts in low temperature fuel cells, were prepared using a new method involving the slow addition of a Pt precursor to a solution containing dispersed carbon powder and a reducing agent. During this process, the added Pt precursor was reduced instantaneously into fine particles and adsorbed onto the carbon surface in the solution. A Pt loading of 55 wt% was obtained, which was close to the nominal amount of Pt, 60 wt%, added in the preparation step. The average particle size of Pt was about 4.2 nm, according to X-ray diffraction. The surface area of the Pt measured by cyclic voltammetry was about 61.4 m2/(g of Pt). The activity of the prepared Pt/C, as an electrode of polymer electrolyte membrane fuel cell, was increased by 34.8% and 15.0%, according to the half- and single-cell tests, respectively, compared to the activity of one prepared using a conventional precipitation method.

Methanol-Tolerant Oxygen Reduction Reaction at Pt–Pd/C Alloy Nanocatalysts

Carbon-supported platinum and Pt–Pd alloy electrocatalysts with different Pt/Pd atomic ratios were synthesized by a microemulsion method at room temperature (metal loading is 10 wt %). The Pt–Pd/C bimetallic catalysts showed a single-phase fcc structure and the mean particle size of Pt–Pd/C catalysts was found to be lower than that of Pt/C. The methanol-tolerant studies of the catalysts were carried out by activity evaluation of oxygen reduction reaction (ORR) on Pt–Pd catalysts using a rotating disk electrode (RDE). The studies indicated that the order of methanol tolerance was found to be PtPd3/C>PtPd/C>Pt3Pd/C. The oxygen reduction activities of all Pt–Pd/C were considerably larger than that of Pt/C with respect to onset and overpotential values. The Pd-loaded catalysts shift the onset potential of ORR by 125 mVMSE, 53 mVMSE, and 41 mVMSE to less cathodic potentials for Pt3Pd/C, PtPd/C, and PtPd3/C, respectively, with reference to Pt/C and the Pt3Pd/C catalyst showed greater shift in the onset value than the other PtPd catalysts reported in literature. Moreover, the Pt–Pd/C catalysts exhibited much higher methanol tolerance during ORR than the Pt/C, assessing that these catalysts may function as a methanol-tolerant cathode catalysts in a direct methanol fuel cell.

Development of Supported Bifunctional Oxygen Electrocatalysts with High Performance for Unitized Regenerative Fuel Cell Applications

Titania supported platinum and iridium electrocatalysts (Pt/TiO2 and Ir/TiO2) were synthesized and investigated as bifunctional oxygen electrode (BOE) catalysts for unitized regenerative fuel cells (URFCs). TEM images revealed uniform distribution of Pt and Ir nanoparticles on the TiO2 support. Histogram analysis showed particle sizes of Pt and Ir to be 4.5 and 2.0 nm, respectively, which was also confirmed by the XRD characterization. Among the various Pt-Ir compositions prepared, Pt85Ir15 (with a Pt/Ir weight ratio of 85/15) showed the highest catalyst efficiency towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The URFC testing results showed that the round-trip energy conversion efficiency (εRT) of supported Pt-Ir/TiO2 (42%) was significantly higher than that of unsupported PtIr black (30%). The TiO2 support provided high surface area for uniform dispersion of the catalyst particles. The URFC performance increase was ascribed to the uniform dispersion and better utilization of noble metal catalysts.

Enhancement of CO Tolerance on Electrodeposited Pt Anode for Micro‐PEM Fuel Cells

AbstractElectrodeposited and sprayed Pt anode catalysts were electrochemically characterised by CO stripping voltammetry as well as their activity to CO tolerance in micro‐PEMFCs was demonstrated using polarisation measurements. While the onset and peak potentials of CO oxidation on the sprayed Pt/C varied with the CO coverage, these were lower (∼50 mV) with the electrodeposited Pt anode. This difference is attributed to the varying properties of the Pt–OH on either rough or smooth surface mainly created from different sizes of Pt particles. In fuel cell performance test, the electrodeposited Pt anode showed maximum power density of 360 mW cm–2 and it was markedly (∼110 mW cm–2) higher than the sprayed Pt/C anode. The enhanced activity of the electrodeposited Pt anode is also reflected by the fact that the entire amount of adsorbed CO becomes almost desorbed during the first three polarisation scans, while with the Pt/C anode at least five cycles are required.

Microwave-assisted Pt–Co–Cr/C ternary compound preparation applied as a cathode catalyst for PEMFC

The present study describes the preparation of catalyst nanocomposites comprised of 20 wt.% Pt–Co–Cr (2:1:1) particles attached on the surface of carbon Vulcan XC-72R by microwave radiation; cases of carbon being chemically treated and untreated are considered. Ethylene glycol was used as the solvent and electron source for the microwave-assisted reduction reaction, whereas H2PtCl6⋅xH2O, Co(NO3)3⋅6H2O and Cr(NO3)3⋅9H2O were used as metal precursors. The C powder surface was chemically modified by stirring the C in 8N H2O2 for 48 h. For the nanocomposite in which C was not treated, EDS analysis showed a content of 4.9 wt.% Pt and 1.2 wt.% Cr with only a trace amount of Co. Higher Pt and Cr contents were observed in the catalyst sample prepared from treated carbon (5.6% Pt and 2.2% Cr), but no Co was detected. Chromium appeared as Cr3O4 in both samples confirmed by the XAS spectrum. The obtained phase was therefore Pt–Cr3O4 /C for both samples. The TEM results indicated that the average particle size of Pt–Cr3O4 was 2.22 ±0.41 nm on treated C and 1.93 ±0.34 nm on untreated C. By the CV technique, it was observed that the catalytic activity of the treated carbon Pt–Cr3O4 catalyst was not only higher than that of the untreated carbon Pt– Cr3O4 catalyst, but also higher than that of the standard platinum catalyst.

Development of Durable Platinum Nanocatalyst on Carbon Nanotubes for Proton Exchange Membrane Fuel Cells

Platinum nanocatalyst on multiwalled carbon nanotubes (MWCNTs) functionalized with citric acid (CA) was synthesized by a two-phase approach to transfer from aqueous to organic phase. Pt-thiol ligand-based Pt/MWCNTs were fabricated with the presence of dodecanethiol (DDT). A homogeneous distribution as well as a uniform particle size of Pt particle was achieved by optimizing the CA and DDT contents. Pt/MWCNTs were examined by a high resolution transmission electron microscope for particle size and distribution. The Pt/MWCNT-based electrodes were characterized by electrochemical impedance spectroscopy for cell resistance and cyclic voltammetry (CV) for durability evaluation using humidified and gases at . The single-cell fuel cell performance with 0.2 (anode) and 0.4 mg (cathode) evaluated using Nafion 212 electrolyte showed a power density of about with and gases. The electrochemically active surface area, as measured by CV between 0.1 and 1.2 V, showed no degradation up to 1500 cycles for Pt/MWCNTs, showing exceptional durability.

Effect of ultrasonic irradiation on the catalytic performance of PtSnNa/ZSM-5 catalyst for propane dehydrogenation

Effects of ultrasonic irradiation on the catalytic performance of PtSnNa/ZSM-5 catalyst for propane dehydrogenation were studied. XRD, TEM and TPDA were used to characterize the catalysts. From the results of XRD, the structure of ZSM-5 was not destroyed by the ultrasound. Ultrasound promoted the dispersion of Pt on the surface of the carrier during impregnation and decreased the size of Pt particles. Compared with the catalyst prepared by conventional impregnation, the supported catalyst prepared by ultrasonic irradiation showed better catalytic activity in propane dehydrogenation.

Thermal deactivation of Pt/Rh commercial automotive catalysts

The influence of thermal ageing effects on catalytic activity was analyzed for a Pt/Rh three-way catalyst. Characterization techniques such as X-ray fluorescence (XRF), N 2 physisorption, X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption of H 2 (H 2-TPD) and scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDX) revealed deep textural, structural and physicochemical changes in the catalyst washcoat caused by exposure to high temperatures (900 °C and 1200 °C). The catalytic activity was evaluated in terms of CO and propane oxidation and the reduction of NO by CO. In general, the conversions were lower after the ageing. The exception was the catalyst aged at 900 °C for 12 h. This catalyst presented a better propane conversion than the fresh Pt/Rh catalyst. It is likely that the well-dispersed Pt in the fresh catalyst was more susceptible to oxidation. A short-time ageing would increase the size of Pt particles, which are harder to oxidize, contributing to an improved activity. On the other hand, the NO reduction showed lower conversions after ageing, probably related the rhodium to being the most sensitive metal towards sintering at high temperatures under exhaust gas conditions.

Control of Particle Size of Pt and Pt Alloy Electrocatalysts Supported on Carbon Black by the Nanocapsule Method

Monodisperse Pt and Pt-M (M = Co, Ru) alloy nanoparticles supported on carbon black (Pt/CB, Pt(2)Ru(3)/CB, Pt(3)Co/CB) were prepared by the nanocapsule method. We have succeeded in controlling the particle size simply by changing the molar ratio of metal precursor(s) to surfactant (M/S) in the preparation, with the other conditions being identical. The particle size was well-controlled between 2.0 and 4.5 nm with a metal loading level of 50 wt % for all catalysts. The compositions of the alloy particles were close to the projected values, with a small standard deviation, i.e., <3.1 atom % for Pt(2)Ru(3) and 1.4 atom % for Pt(3)Co. It was also found that these alloys were in the form of the corresponding solid solutions with the fcc structure.

The activity of Pt/Al 2O 3 diesel oxidation catalyst after sulphur and calcium treatments

A fresh powder-like Pt/Al 2O 3 diesel oxidation catalyst was treated with sulphur (S–), sulphur–water (SW–), calcium–water (Ca–), sulphur–calcium–water (SCa–), and water (W–). BET, TEM–EDS, XPS, ICP-OES, AAS analyses and catalytic activity tests were used to find the effect of sulphur, calcium and water on the Pt/Al 2O 3 catalyst and its performance. Based on the ICP-OES and EDS results, sulphur was found to accumulate on the surface, whenever it was used in the pretreatments. Calcium was found in a very small amount on the Ca- and SCa-treated Pt/Al 2O 3 catalysts according to AAS and EDS results. For all the cases, the specific surface area was decreased after pretreatment. As expected, for the S- and SW-treated Pt/Al 2O 3 catalysts the light-off temperatures for CO and propene were higher compared to the corresponding fresh catalyst. Ca-, SCa-, and W-treated Pt/Al 2O 3 catalysts had almost the same light-off temperatures of CO and C 3H 6 than the fresh catalyst, instead. Based on the TEM–EDS results, the particle size of Pt and alumina washcoat microstructure was found to be unchanged after all the pretreatments. The pronounced deactivation is explained with sulphates formation on the active sites and with a decrease in the specific surface area.

Catalytic oxidation of heavy hydrocarbons over Pt/Al2O3. Influence of the structure of the molecule on its reactivity

Deep oxidation of 48 hydrocarbons (HCs), from 6 to 20 carbon atoms, was studied over a 1%Pt/Al2O3 catalyst (105m2g−1; mean particle size of Pt: 1nm). The oxidation reaction (1500ppm C of HC in air) was carried out by increasing the temperature by step of 5°C from 100 to 400°C. The reactivity of HCs was characterized by their T50 (temperature at 50% conversion). The reactivity of n-alkanes increases with the chain length, following the same evolution with n as the ionization potential of the molecule. Isoalkanes are more difficult to oxidize than the corresponding n-alkanes. Hydrocarbon reactivity depends on the nature of carbon in the molecule. The ability to be oxidized is greater with CII and CIII carbons while CI and CIV carbons, still more than CI, are refractory to oxidation. The reactivity of n-alkenes depends relatively little on the number of carbons in the molecule. Light alkenes are much more reactive than light alkanes while the reverse can be observed with long-chain hydrocarbons. Contrary to branched alkanes, isoalkenes or cyclenic hydrocarbons are generally more reactive than the corresponding n-alkenes. Short side-chain alkylbenzenes (toluene, ethylbenzene, …) and polymethylbenzenes are more difficult to oxidize than benzene. When the length of the alkyl group is increased, the behaviour of the hydrocarbon in oxidation resembles more and more to long-chain alkanes with a better oxidability. Polyalkylbenzenes with hindered heavy alkyl groups are quite easy to oxidize. The behaviour of bicyclic or tricyclic hydrocarbons is much more complex. Partial or complete hydrogenation increases their reactivity. For instance, oxidability of bicyclic hydrocarbons is in the order: decaline>tetraline>naphthalene. The reactivity of heavier aromatics also depends on their ability to form partial oxidation intermediates (for instance: fluorene to fluorenone) or to possess extremely rigid internal CC bonds (for instance: acenaphthylene and acenaphthene). These results were discussed in the light of several factors which can affect the reactivity in oxidation: (i) an electron transfer between adsorbed hydrocarbon and adsorbed oxygen species via the surface metal atoms; (ii) the mean C–H bond strength in the molecule and hindrance effects in branched hydrocarbons; (iii) the relative adsorption strength of oxygen and hydrocarbons; (iv) the relative reactivity of hydrocarbons and partially oxidized molecules, intermediates in total oxidation.

Preparation of Pt/C electrocatalysts using an incipient precipitation method

Highly loaded and dispersed Pt/C catalysts, used as cathodic electrocatalysts in low temperature fuel cells, were prepared using a new method involving the slow addition of a Pt precursor to a solution containing dispersed carbon powder and a reducing agent. During this process, the added Pt precursor was reduced instantaneously into fine particles and adsorbed onto the carbon surface in the solution. A Pt loading of 55 wt% was obtained, which was close to the nominal amount of Pt, 60 wt%, added in the preparation step. The average particle size of Pt was about 4.2 nm, according to X-ray diffraction. The surface area of the Pt measured by cyclic voltammetry was about 61.4 m 2 /(g of Pt). The activity of the prepared Pt/C, as an electrode of polymer electrolyte membrane fuel cell, was increased by 34.8% and 15.0%, according to the half- and single-cell tests, respectively, compared to the activity of one prepared using a conventional precipitation method.

Effect of pore diameter of wormholelike mesoporous carbon supports on the activity of Pt nanoparticles towards hydrogen electrooxidation

Pt nanoparticles are successfully deposited on wormholelike mesoporous carbons (WMCs) using a pulse microwave-assisted polyol method. WMCs with two different pore diameters are used. The particle size of Pt on both supports is identical, about 3 nm. It has been found that Pt utilization efficiency is very low when the pore diameter of WMCs ( D p) is equal to the diameter of Pt nanoparticles ( D Pt). However, in the case that D p is more than twice D Pt, the electrochemical surface area and Pt utilization efficiency are dramatically enhanced, and in turn, hydrogen electrooxidation activity is greatly improved.

Complete oxidation of toluene over bimetallic Pt–Au catalysts supported on ZnO/Al2O3

Bimetallic Pt–Au catalysts supported on ZnO/Al2O3 were prepared by the impregnation (IMP) and incipient wetness impregnation (IW-IMP) methods in air or H2 and compared with a monometallic Pt/ZnO/Al2O3 catalyst. The catalysts were characterized by ultraviolet–visible spectroscopy (UV–vis), X-ray diffraction (XRD), CO chemisorption, temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM) in conjunction with energy dispersive spectroscopy (EDS). The catalytic activity for the complete oxidation of toluene was measured using a flow reactor under atmospheric pressure. The relationship between the particle size and catalytic activity for toluene over bimetallic Pt–Au catalysts is discussed. In the results, generally, the Pt particles prepared by IW-IMP in H2 were larger than those prepared by IMP in air. On the other hand, the Au particles prepared by IW-IMP in H2 were smaller than those prepared by IMP in air, namely when using IW-IMP in H2 the Au particle size was decreased and the Pt particle size was increased. Also, the particle sizes of Pt and Au increased with increasing calcination temperature. The STEM and XRD results show that Pt and Au were simultaneously deposited as metallic particles on the ZnO/Al2O3 without forming an alloy with the Pt and Au. From the TPR results, it was found that the nanosized Au particles might promote the reduction of the surface oxygen and that the complete oxidation of toluene shows higher activity at lower temperature over the bimetallic Pt–Au catalysts as compared to the Pt/ZnO/Al2O3 catalyst. The bimetallic Pt–Au catalysts prepared by IW-IMP in H2 calcined at 400°C showed higher activity for complete toluene oxidation.

The influence of pore geometry of Pt containing ZSM-5, Beta and SBA-15 catalysts on dehydrogenation of propane

The influence of the pore geometry of the catalyst supports on dehydrogenation of propane (DHP) activity, selectivity to propylene and the degree of coke formation was evaluated over micro-(Pt-ZSM-5 and Pt-Beta) and meso-(Pt-SBA-15) porous materials in a tapered element oscillating microbalance (TEOM) reactor by analyzing reaction products and mass changes simultaneously. The catalysts were prepared by incipient wetness impregnation and were characterized by N 2-physisorption, X-ray diffraction (XRD) and H 2-chemisorption. The characterization results indicate that catalysts contain Pt within the pores and Pt nanoparticles of more or less similar sizes however stabilized on markedly different pore geometries (structure and size). This allowed to (i) largely marginalize the effect of the sizes of Pt particles on DHP and (ii) evaluate exclusively the vital role of pore geometry of the supports, where a fraction of Pt is located within the pores, on the catalytic performance. Pt-ZSM-5 presents the highest propane conversion followed by Pt-Beta and Pt-SBA-15 indicating that the activity decreases with increasing pore size (ZSM-5 < Beta < SBA-15) of the support. TEOM results evidence that the amount of coke formed during DHP is the highest on Pt-ZSM-5 and is the lowest on Pt-Beta thus, the latter exhibits better catalytic stability than the former and Pt-SBA-15. Among Pt-ZSM-5 and Pt-SBA-15, the former shows better selectivity and stability than the latter despite higher coke content. These observations demonstrate that the three dimensional microporous materials are better catalytic supports for DHP than the mesoporous SBA-15 because of their intrinsic nature that may induce optimum catalytic properties of Pt sites.

Pt/Solid-Base: A Predominant Catalyst for Glycerol Hydrogenolysis in a Base-Free Aqueous Solution

A series of HBeta, HZSM-5, Al2O3, MgO and hydrotalcite precursor supported Pt catalysts were prepared and used for glycerol hydrogenolysis to 1,2-propanediol (1,2-TPD) in a base-free aqueous solution. XRD, TEM, CO2-TPD and H2-TPD characterizations concluded that the activity for glycerol hydrogenolysis of the tested catalysts depends mainly on their alkalinity and particle size of Pt. A hydrotalcite precursor supported Pt catalyst with strong alkalinity and highly dispersed Pt particles exhibited the predominant performance for the desired reaction (with a 93.0% selectivity of 1,2-PDO at a conversion of 92.1%) in a base-free aqueous solution at lower pressure, and can be recycled simply by filtration.

Effect of W on activity of Pt–Ru/C catalyst for methanol electrooxidation in acidic medium

The effect of W on the activity of Pt–Ru/C catalyst was investigated. The Pt–Ru–W/C and Pt–Ru/C-TR catalysts were prepared by thermal reduction method. Comparison was made to a homemade Pt–Ru/C-CR catalyst prepared by chemical reduction. Their performances were tested by using a glassy carbon thin film electrode through cyclic voltammetric and chronoamperometric curves. The particle size, structure, composition, and surface state of homemade catalyst were determined by means of X-ray diffraction (XRD), energy dispersive analysis of X-ray (EDAX), transmission electron microscopy (TEM), and X-ray photoelectron spectrometry (XPS). The result of XRD analysis shows that the homemade ternary catalyst exhibits face-centered cubic structure and has smaller lattice parameter than Pt-alone and homemade Pt–Ru/C catalysts. The particle size of Pt–Ru–W/C catalyst is relatively large of 6.5 nm. Its electrochemically active specific area is 20 m 2 g −1 less than that of Pt–Ru/C-CR, and much twice as big as that of Pt–Ru/C-TR. But, XPS analysis shows that the addition of W changes the surface state of Pt components in the alloy and can clean Pt surface active sites which are adsorbed by hydrogen. The electrocatalytic activity and tolerance performance to CO ads of Pt–Ru–W/C catalyst for methanol electrooxidation is the best due to the promoting function of W in comparison with homemade Pt–Ru/C ones.