Binding Energy Of Pt Research Articles

Effect of molybdenum addition on supported platinum catalysts for the water–gas shift reaction

The effect of molybdenum on water–gas shift (CO+H2O↔CO2+H2) turnover frequencies was investigated for 2wt% platinum, up to 11wt% molybdenum, alumina and silica supported catalysts. The maximum PtMo turnover frequencies were observed for Mo weight loadings of 1.4% and 1.2% when supported on Al2O3 and SiO2, respectively. Above these loadings, the exposed Pt surface area as measured by hydrogen chemisorption was reduced. The hydrogen chemisorption values and X-ray absorption spectroscopy of the reduced catalysts indicate the formation of PtMo bimetallic particles that are surface rich in Mo, yet increases in Pt–Mo coordination do not correlate with changes in turnover frequency, and most of the Mo is present in the form of Mo-oxide. The decrease in TOF from the optimum Mo loading is attributed to differences in surface coverages of intermediates that are observed in the changing reaction orders and ascribed to the interplay between the PtMo alloy metal function and the promotion of water activation by MoOx promotion of the support. The decreased Pt dispersion and CO binding energy of Pt–Mo catalysts result in CO reaction orders as high as 0.8 at 300°C, and Mo addition resulted in apparent activation energies which were 20–40kJ/mol lower than the Mo free samples. The promoted catalysts achieved higher TOF than Pt/CeO2 when calculated at or below 250°C with 6.8% CO, 8.5% CO2, 21.9% H2O, 37.4% H2, and balance Ar at 1atm total pressure.

Performance Effect of Pt/MO<sub><em>x</em></sub>-SiO<sub>2</sub> (M=Ce, Zr, Al) Catalysts for CO and C<sub>3</sub>H<sub>8</sub> Oxidation

MOx-SiO2(M=Ce,Zr,Al) mixed oxides with a MOx:SiO2 mass ratio of 1:1 were prepared by co-precipitation.Pt-only diesel oxidation catalysts supported on these mixed oxides were obtained by the incipient wetness method.The catalytic activities in simplified diesel exhaust gas before and after SO2 treatment were analyzed.The catalysts were characterized by X-ray diffraction,N2 adsorption-desorption,NH3/O2/CO2 temperature programmed desorption(NH3/O2/CO2-TPD) and X-ray photoelectron spectroscopy(XPS).The results of NH3-TPD suggested that the surface of the catalysts had multiple acidic sites,and the number of medium-strength acidic sites increased following treatment with SO2.The results of O2-TPD revealed that there were α and β oxygen species in the catalysts,and the amount of O2 desorption decreased for the SO2-treated catalysts.The Pt/Al2O3-SiO2 catalyst exhibited the lowest surface acidity and the largest amount of oxygen desorption.XPS indicated that the binding energy of Pt 4f5/2 decreased when the catalysts were treated with SO2.All the catalysts showed excellent activity for CO and C3H8,and the Pt/ZrO2-SiO2 catalyst exhibited the best SO2 poisoning resistance,showing the potential for these catalysts to be applied in diesel oxidation.

Preparation and Activity of Nb2O5·nH2O-PtRu/C for Methanol Oxidation

10%Nb2O5•nH2O-20%Pt10%Ru/C electro-catalyst for methanol oxidation was prepared by deposition method, followed with heat treatment in Ar atmosphere. The effect of heat treatment on morphology, structure and electrochemistry performance of the product was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry and chronoamperograms. No diffraction peaks of Ru were observed in the XRD patterns, while all the peaks of Pt were in accordance with the face centered cubic crystal structure. The binding energy of Pt was not affected by Nb2O5•nH2O. Compared with 20%Pt10%Ru/C, in 10%Nb2O5•nH2O-20%Pt10%Ru/C samples, the activated particles were uniformly dispersed, and the performances of methanol oxidation and resistance to “CO” were better. The results indicated that the introduction of Nb2O5•nH2O inhibited the growth of active particles, and decreased the alloying degree of Pt-Ru during heat treatment. Besides, Nb2O5•nH2O also provided active “-OH” and improved H+ transfer, leading to easier adsorption-desorption of methanol and its oxidation intermediates.

Theoretical Study of Pt(PR3)2(AlCl3) (R = H, Me, Ph, or Cy) Including an Unsupported Bond between Transition Metal and Non-transition Metal Elements: Geometry, Bond Strength, and Prediction

The molecular structure and the binding energy of Pt(PR(3))(2)(AlCl(3)) (R = H, Me, Ph, or Cy) were investigated by DFT, MP2 to MP4(SDTQ), and CCSD(T) methods. The optimized structure of Pt(PCy(3))(2)(AlCl(3)) (Cy = cyclohexyl) by the DFT method with M06-2X and LC-BLYP functionals agrees well with the experimental one. The MP4(SDTQ) and CCSD(T) methods present similar binding energies (BE) of Pt(PH(3))(2)(AlCl(3)), indicating that these methods provide reliable BE value. The DFT(M06-2X)-calculated BE value is close to the MP4(SDTQ) and CCSD(T)-calculated values, while the other functionals present BE values considerably different from the MP4(SDTQ) and CCSD(T)-calculated values. All computational methods employed here indicate that the BE values of Pt(PMe(3))(2)(AlCl(3)) and Pt(PPh(3))(2)(AlCl(3)) are considerably larger than those of the ethylene analogues. The coordinate bond of AlCl(3) with Pt(PR(3))(2) is characterized to be the σ charge transfer (CT) from Pt to AlCl(3). This complex has a T-shaped structure unlike the well-known Y-shaped structure of Pt(PMe(3))(2)(C(2)H(4)), although both are three-coordinate Pt(0) complex. This T-shaped structure results from important participation of the Pt d(σ) orbital in the σ-CT; because the Pt d(σ) orbital energy becomes lower as the P-Pt-P angle decreases, the T-shaped structure is more favorable for the σ-CT than is the Y-shaped structure. [Co(alcn)(2)(AlCl(3))](-) (alcn = acetylacetoneiminate) is theoretically predicted here as a good candidate for the metal complex, which has an unsupported M-Al bond because its binding energy is calculated to be much larger than that of Pt(PCy(3))(2)(AlCl(3)).

Cluster size dependence of Pt core-level shifts for mass-selected Pt clusters on TiO2(110) surfaces

In order to examine cluster size dependence, mass-selected platinum clusters, Ptn (n=2–5, 7, 8, 10, 15), were deposited on TiO2(110) surfaces at room temperature under soft landing conditions, and their core levels were investigated by x-ray photoelectron spectroscopy. Pt core-level shifts with cluster size are observed. The binding energies of Pt 4f7/2 decrease steeply with increasing cluster size up to n=7 for Ptn and decrease gradually for n≥8. This inflection point (n=8) agrees well with the cluster size at a geometric transition (planar-to-three-dimensional) seen with scanning tunneling microscopy (STM) [N. Isomura, X. Wu, and Y. Watanabe, J. Chem. Phys. 131, 164707 (2009)]. It was found that the core-level shifts of mass-selected Pt clusters deposited on TiO2 are closely correlated with cluster geometries determined directly by atomic-resolution STM imaging.

Density Functional Study of Interaction of Atomic Pt with Pristine and Stone−Wales-Defective Single-Walled Boron Nitride Nanotubes

Interactions between atomic Pt and pristine or Stone−Wales-defective (5,5) single-walled boron nitride nanotubes (BNNTs) were studied using density functional theory (DFT) with truncated nanotube models. The binding energy of Pt on a pristine BNNT is about 20 kcal/mol with little dependency on the binding site. On the other hand, when the Stone−Wales (SW) defect is presented, the atomic Pt is preferentially inserted between the B−B bond in the SW defect region with a large binding energy of 58 kcal/mol. On an SW-defective BNNT, the atomic Pt, even placed away from the defect site, may eventually (thermodynamically) move toward the defect area until being trapped between the B−B bond, and the final adduct has decreased reactivity toward both electrophiles and nucleophiles compared with Pt adsorption to pristine BNNTs. Pt adsorption on pure or SW-defective BNNTs makes the hosting nanotube wide-gap semiconductive by introducing the valence states of the absorbed Pt into the band gap of the nanotube. In compa...

Methanol oxidation enhanced by the presence of O2 at novel Pt–C co-sputtered electrode

In this paper, we describe a novel electrode that exhibits sensitized methanol electrooxidation in an oxygen atmosphere. A binary Pt-C electrode has been developed for use as the anode catalyst of a direct methanol fuel cell using a co-sputtering technique. Characterizations of the electrodes revealed that the sputtered Pt-C forms nanosize and phase-separated Pt and C domains, in which the Pt particle size decreases and its crystallinity gradually becomes amorphous with increasing C content. The current density of methanol oxidation in deaerated conditions exhibited a maximum value at a C content of 23 at%. The result can be well explained from the viewpoints of the morphology and binding energy of Pt. The methanol oxidation current is sensitized by O(2) when the Pt-C electrode contains >23 at% C, and the extent of sensitization increases monotonically with C content. This phenomenon is not observed at a Pt electrode. The sensitization mechanism was investigated by considering the reduction reaction of O(2); it was clarified that the amount of adsorbed species created by O(2) reduction increases with increasing C content. It was deduced that the Pt-OH produced by O(2) reduction participates in oxidation of Pt-CO, which is believed to be the rate-determining step of the methanol electrooxidation.

Pt, PtCo and PtNi electrocatalysts prepared by mechanical alloying for the oxygen reduction reaction in 0.5 M H 2SO 4

Electrocatalysts of Pt, PtCo and PtNi powders for the oxygen reduction reaction (ORR) were processed by Mechanical Alloying. Physical characterization was made by X-ray diffraction, scanning electron microscopy and scanning transmission electron microscopy. It was found that milled powders formed agglomerates in the range of 0.2–20 μm formed by nanometric size crystallites. The synthesized powders were alloys of PtFe, PtCoFe and PtNiFe due to iron incorporation during the milling process. The binding energies of Pt in the alloys were determined by XPS. Polarization curves were obtained by Rotating Disk Electrode technique in 0.5 M H 2SO 4 to determine the electrocatalytic activity of the mechanically alloyed powders. Tafel curves were plotted and kinetic parameters for the ORR were calculated. The PtFe alloy showed the highest electrocatalytic activity for the ORR. However, the lowest overpotential was found for the PtCoFe alloy and it also showed a higher current exchange density. A linear relationship was found between the Pt-binding energy in the alloys and the overpotential at the same current density independent of the Pt alloy composition.

Selective hydrogenation of cinnamaldehyde over Pt-supported multi-walled carbon nanotubes: Insights into the tube-size effects

Abstract The multi-walled carbon nanotubes (MWCNTs) having different outer diameters but similar inner diameters were loaded with 3.0 wt.% Pt via the reduction of H2PtCl6 by formaldehyde in the solution of ethanol and water. For both the MWCNT supports and catalysts, the BET surface areas and pore size distributions determined by N2 adsorption and desorption were varied significantly although type II adsorption isotherms with closed hysteresis loops were observed. The 3.0 wt.% Pt/MWCNT catalysts were investigated for the selective hydrogenation of cinnamaldehyde (CALD) in a batch reactor under the conditions of 80 °C and 2.0 MPa of hydrogen. All the catalysts showed reasonably high catalytic activity but significantly different product selectivities. The highly selective hydrogenation of C C bonds into hydrocinnamaldehyde (88% selectivity at 100% conversion) occurred over Pt-supported MWCNT4 with the biggest outer diameters (>50 nm). In the case of the other three catalysts, however, C O bonds were selectively hydrogenated showing about 60–80% selectivities to cinnamyl alcohol (CA) depending on the catalysts and CALD conversions. Irrespective of the catalysts, the results of X-ray diffraction and high-resolution transmission electron microscopy indicated that the metallic Pt particles with an average size of about 11 nm were overwhelmingly deposited on the outer surface of the MWCNTs. The binding energies of Pt and the surface atomic ratios of oxygen to carbon determined by X-ray photoelectron spectroscopy were slightly varied for different catalysts. Based on these characterization results together with the hydrogenation results of CA, the different selective behaviors of the Pt/MWCNTs catalysts were discussed. Besides other factors, the electronic effects induced by the significantly varied tube diameters of the MWCNTs played the major role in determining the selective behaviors of different catalysts.

Different Sized Platinum Nanoparticles Supported on Carbon: An XPS Study on These Methanol Oxidation Catalysts

Different sized platinum nanoparticles on carbon supports have been prepared using PtCl4 (catalyst Ia) and H2PtCl6 (catalyst IIa) as starting materials and 1-hexanethiol as a surfactant and then heated to 200 °C (catalyst Ib and catalysts IIb), 300 °C (catalyst Ic and catalysts IIc), and 400 °C (catalyst Id and catalysts IId) for 4 h under argon gas. All the catalysts showed a face-centered cubic (fcc) crystal structure as determined by X-ray diffraction. X-ray diffractograms and transmission electron microscopy results reveal that the platinum nanoparticles are homogeneously dispersed on the carbon support, exhibit narrow particle size distribution, and show no appreciable aggregation. The average platinum particle size as determined from XRD data was found to be ∼2.00, ∼2.56, ∼4.23, ∼4.52, ∼2.13, ∼2.77, ∼4.29, and ∼4.62 nm for catalysts Ia−d and IIa−d, respectively. X-ray photoelectron spectra of all the catalysts indicated that most (>70%) of the platinum nanoparticles have an oxidation state of zero and a small amount (<30%) have a +4 oxidation state with binding energies of 71.2−72.2 (Pt 4f7/2) and 74.3−75.5 eV (Pt 4f7/2), respectively. Increasing the temperature during the heat treatment process results in an enlargement of platinum particle size, a positive shift in the binding energies of Pt(0) and Pt(IV), and a decrease in catalytic activity in the methanol oxidation reaction.

Stabilization of Platinum Clusters by Substitutional Boron Dopants in Carbon Supports

To stabilize platinum clusters on carbon supports, carbon substituted boron dopants were introduced in graphite and fullerene models, and the binding energies of Pt(1) to Pt(6) clusters on the carbon supports were investigated using first-principles density functional theory (DFT) calculations. The adsorption energies of the Pt clusters increased significantly in the presence of boron. The adsorption energies of Ru(1) and Au(1) were also found to dramatically increase in the presence of boron.

Theoretical Study of M(PH3)2Complexes of C60, Corannulene (C20H10), and Sumanene (C21H12) (M = Pd or Pt). Unexpectedly Large Binding Energy of M(PH3)2(C60)

DFT and MP2 to MP4(SDQ) methods were applied to M(PH3)2(C60), Pt(PH3)2(C20H10), and Pt(PH3)2(C21H12) (M = Pd or Pt, C20H10 = corannulene, and C21H12 = sumanene). The binding energy considerably fluctuates around MP2 and MP3 levels but much less upon going from MP3 to MP4(SDQ) in Pt(PH3)2(C2H4), Pt(PH3)2(C20H10), and Pt(PH3)2(C21H12). Also, the MP4(SDQ) method presents a binding energy similar to that of the CCSD(T) method in Pt(PH3)2(C2H4). Thus, it is likely that the MP4(SDQ) method is useful to evaluate binding energies of these complexes. The binding energies of Pt(PH3)2(C20H10) and Pt(PH3)2(C21H12) are evaluated to be 24.9 and 26.1 kcal/mol, respectively, by the MP4(SDQ) method and only +5.8 and -2.6 kcal/mol, respectively, by the DFT(B3LYP) method. These MP4(SDQ)-calculated binding energies of Pt(PH3)2(C20H10) and Pt(PH3)2(C21H12) are similar to that of Pt(PH3)2(C2H4), which strongly suggests that these complexes can be successfully synthesized. The binding energy of Pt(PH3)2(C60) is evaluated to be 44.8 and 45.5 kcal/mol with the ONIOM(MP4(SDQ):UFF) and ONIOM(MP4(SDQ):B3LYP) methods, respectively, and that of the Pd analogue is evaluated to be 39.9 kcal/mol with the ONIOM(MP4(SDQ):UFF) method, whereas the DFT(B3LYP), DFT(BVP86), and DFT(BPW91) methods provide much smaller binding energies. It is noted that these binding energies are much larger than those of the ethylene, corannulene, and sumanene analogues. This difference is reasonably interpreted in terms that the LUMO of C60 is at much lower energy than those of ethylene, corannulene, and sumanene. We investigated also how to separate the high level and the low level regions in the ONIOM calculation of M(PH3)2(C60) and proposed here the reasonable way to evaluate the binding energy of transition-metal complexes of C60.

Electrochemical oxidation of CO over tin oxide supported platinum catalysts

Tin oxide supported platinum catalysts (Pt/SnO x ) for use in polymer electrolyte fuel cells were prepared, and their electrochemical oxidation of CO was investigated. From the XPS measurements of Pt/SnO x catalysts, it was found that the binding energy of Pt showed no change compared to bulk Pt, regardless of tin oxide addition. In accordance with this result, CO-stripping voltammograms for Pt/SnO x catalysts revealed that the peak potential for the pre-adsorbed CO oxidation was almost the same value of Pt/C catalyst. However, the onset potential of CO oxidation shifted negatively compared to PtRu/C catalyst, indicating an enhancement of CO tolerance of Pt/SnO x catalysts.

Nature of the Metal−Support Interaction in Bifunctional Catalytic Pt/H-ZSM-5 Zeolite

The metal-support interaction of a dispersed Pt atom on H-ZSM-5 zeolite has been investigated by using an embedded cluster and cluster models with the density functional theory/B3LYP functional method. We found that the Pt atom interacts with a Brønsted proton and a nearby framework oxygen. Interaction with the framework oxygen causes electron transfer from the zeolite to the Pt atom. Concurrently, a Brønsted proton stabilizes the Pt atom on the zeolite surface by withdrawing excess electron density from the Pt atom. These charge transfers result in a zero net charge on the Pt atom while changing its orbital occupation. The binding energy of Pt on the Brønsted acid was 15 kcal/mol. Inclusion of the Madelung potential by Surface Charge Representation of the Electrostatic Embedded Potential method (SCREEP) had small effects on structure and charge density of Pt/H-ZSM-5 but it shifted the stretching mode of CO toward a higher frequency by almost 40 cm(-1). The frequency shift of absorbed CO calculated with embedded cluster models was from 8 to 11 cm(-1) red shift, compared to 20 cm(-1) red shift from experiment. This implies that not only the electronic state of the Pt atom but also the Madelung potential of the support is responsible for the observed small red shift of CO on the Pt-H-ZSM-5.

Support effects in Pt/TiO2–ZrO2 catalysts for NO reduction with CH4

ZrO2–TiO2 mixed oxides, prepared using the sol–gel method, were used as supports for platinum catalysts. The effects of catalyst pre-reduction and surface acidity on the performance of Pt/ZT catalysts for the reduction of NO with CH4 were studied. The diffuse reflectance infrared Fourier transformed (DRIFT) spectra of CO adsorbed on the Pt/ZT catalysts, and also on the Pt/T and Pt/Z references, pre-reduced at 773K in hydrogen, revealed that an SMSI state is developed in the Ti-rich oxide-supported platinum catalysts. However, no shift in the binding energy of Pt 4f7/2 level for Pt/T and Pt deposited on Ti-rich support counterparts pre-reduced at 773K was found by photoelectron spectroscopy. The DRIFT spectra of the catalysts under the NO+O2 co-adsorption revealed the appearance of nitrite/nitrate species on the surface of the Zr-containing catalysts, which displayed acidic properties, but were almost absent in the Pt/T catalyst. The intensity of these bands reached a maximum for the Pt/ZT(1:1) catalyst, which in turn exhibited a larger specific area. In the absence of oxygen in the feed stream, the NO+CH4 reaction showed DRIFT spectra assigned to surface isocyano species. Since the intensity of this band is higher for the Pt/ZT (9:1) catalyst, it seems that such species are developed at the Pt–support interface.

Photodesorption of carbonyl from Pt 3(CO) n− (n = 1–6)

The photodesorption of CO from Pt 3(CO) n − (n = 1–6) has been studied in laser excitation experiments. Loss of CO is the major product channel for each species. The time-resolved profiles of photodesorption product ions are measured following excitation with visible laser radiation, 420–800 nm. Slow fragmentation on the 10 μs–1 ms time scale is observed for n = 2, 3, and 6. The binding energies of carbonyl in Pt 3(CO) n − (n = 2, 3, 6) are derived by fitting these time profiles using a statistical unimolecular dissociation model. The recommended CO binding energies of Pt 3(CO) 3 − and Pt 3(CO) 6 − are 206 ± 14 and 166 ± 14 kJ/mol, respectively, in good agreement with previous results from threshold collision-induced dissociation measurements. For Pt 3(CO) 2 −, a minor second product channel Pt 2CO − + PtCO is observed in addition to CO photodesorption. Experimental evidence suggests that there is more than one isomer for Pt 3(CO) 2 − species.

Measurement of the binding energy of kink-site atoms of metals and alloys.

The binding energies of kink-site atoms of several metals and alloys have been measured from a kinetic-energy analysis of low-temperature field-evaporated ions using a high-resolution pulsed-laser time-of-flight atom-probe field ion microscope. Data are collected from atomically well-defined surfaces. The binding energies of metal atoms in kink sites obtained by this low-temperature and high-field method are found to agree with the cohesive energies of these metals, derived by thermodynamic methods, to -0.03\ifmmode\pm\else\textpm\fi{}0.19 eV. The binding energy of Co atoms in ${\mathrm{Pt}}_{3}$Co alloys, either in ordered state or in disordered state, is 0.65\ifmmode\pm\else\textpm\fi{}0.17 eV higher than that in Co metal whereas the binding energy of Pt in the alloy is about 0.1 eV lower than that in Pt metal. We present details of the experimental method and indicate other problems which can be studied with this method.