Vapor Deposition Of Pt Research Articles

Pt–Ga Model SCALMS on Modified HOPG: Thermal Behavior and Stability in UHV and under Near-Ambient Conditions

We have prepared model systems for Pt–Ga supported catalytically active liquid metal solutions (SCALMS) by physical vapor deposition of Pt and Ga onto highly oriented pyrolytic graphite (HOPG). Pri...

Understanding Active Sites in the Water–Gas Shift Reaction for Pt–Re Catalysts on Titania

Pt–Re clusters supported on titania have shown promise as catalysts for the low temperature water–gas shift reaction. However, the enhanced activity of the bimetallic Pt–Re catalyst versus pure Pt is not well understood. In this work, exclusively bimetallic clusters were grown on TiO2(110) by vapor-deposition of Pt on 2 ML Re clusters and Re on 2 ML Pt clusters. Temperature programmed desorption experiments with CO were used to determine the concentration of Re at the surface, given that CO dissociates on Re but not on Pt. Deposition of 2 ML Pt on 2 ML Re resulted in Re core–Pt shell structures, whereas deposition of low coverages (<0.5 ML) of Re on 2 ML Pt resulted in complete diffusion of Re into the Pt clusters. Both of these Pt on Re bimetallic clusters are thermodynamically favored by the lower surface free energy of Pt compared to Re, and both are also more active than pure Pt clusters in the WGS reaction. Postreaction XPS experiments indicate that Re in the Pt on Re clusters is not oxidized under W...

Atomic Scale Surface Structure of Pt/Cu(111) Surface Alloys

Pt–Cu bimetallic alloys are a key component in many heterogeneous catalysts that have the potential to be used in a range of industrially important reactions. Given the catalytic differences between Pt and Cu, the surface composition and geometry of Pt–Cu alloys can have a large influence on their chemistry. Extensive characterization of bulk Pt–Cu alloys has been performed; however, only a few studies have addressed surface and subsurface alloying of Pt with Cu, and none have examined the atomic scale surface structure of Pt–Cu. In this study, scanning tunneling microscopy was used to determine the local structure of surface alloys formed by physical vapor deposition of Pt onto Cu(111) over a range of alloying temperatures (315–550 K). Our results indicated that Pt and Cu were capable of intermixing at 315 K and forming multiple metastable states. Increasing the temperature of the Cu surface during the deposition of Pt altered the surface geometry and further enhanced the dispersion of Pt. The results ar...

Catalytic surface development of novel nickel plate catalyst with combined thermally annealed platinum and alumina coatings for steam methane reforming

Catalytically active surface of small nickel (min 99 wt%) plates for steam methane reforming was enhanced by successive temperature programmed oxidation−reduction (TPO−TPR) pretreatment and combined physical vapor deposition of Pt and Al2O3. The effect of annealing time, temperature, order and number of coatings on the catalytic activity was investigated by means of a pulse technique at the reaction temperature of 760 °C. The most active and stable surface phases resulted after the successively deposited layers of Pt, Al2O3, and Pt had been annealed for 12 h onto 2-cycle TPO−TPR pretreated nickel plate at the temperature of 700 °C in a circulating atmosphere of N2. The durability performance of the so-prepared surface phases on a specifically structured plate catalyst element (diameter 43 mm and length 42 mm) was tested in a tubular reactor for some 70 h in temperature range 500−650 °C. Deactivation was mainly caused by carbon surface deposition.

Platinum vapor deposition surface‐assisted laser desorption/ionization for imaging mass spectrometry of small molecules

Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) allows for the simultaneous detection and imaging of several molecules in a sample. However, when using an organic matrix in the MALDI-IMS of small molecules, inhomogeneous matrix crystallization may yield poorly reproducible peaks in the mass spectra. We describe a solvent-free approach that employs a homogeneously deposited metal nanoparticle layer (or film) for small-molecule detection. Platinum vapor deposition surface-assisted laser desorption/ionization imaging mass spectrometry (Pt vapor deposition SALDI-IMS) of small molecules was performed as a solvent-free and organic-matrix-free method. A commercially available magnetron sputtering device was used for Pt deposition. Vapor deposition of Pt produced a homogenous layer of nanoparticles over the surface of the target imaging sample. The effectiveness of Pt vapor deposition SALDI-IMS was demonstrated for the direct detection of small analytes of inkjet ink on printed paper as well as for various other analytes (saccharides, pigments, and drugs) separated by thin-layer chromatography (TLC), without the need for extraction or concentration processes. The advantage of choosing Pt instead of Au in SALDI-IMS was also shown. A solvent-free approach involving the direct deposition of Pt on samples (SALDI-IMS) is effective for the analysis of inkjet-printed papers and various analytes separated by TLC. This method would be useful in imaging analyses of various insulating materials such as polymers and biological materials.

In situ laser processing in a scanning electron microscope

Laser delivery probes using multimode fiber optic delivery and bulk focusing optics have been constructed and used for performing materials processing experiments within scanning electron microscope/focused ion beam instruments. Controlling the current driving a 915-nm semiconductor diode laser module enables continuous or pulsed operation down to sub-microsecond durations, and with spot sizes on the order of 50 μm diameter, achieving irradiances at a sample surface exceeding 1 MW/cm2. Localized laser heating has been used to demonstrate laser chemical vapor deposition of Pt, surface melting of silicon, enhanced purity, and resistivity via laser annealing of Au deposits formed by electron beam induced deposition, and in situ secondary electron imaging of laser induced dewetting of Au metal films on SiOx.

Molecular-dynamics investigation of early film growth of Pt/Au(100) and Au/Pt(100) and an interdiffusive growth mode.

We simulate the early vapor deposition of Pt on reconstructed Au(100), and also Au on reconstructed Pt(100), with surface-embedded-atom-method potentials and the molecular-dynamics code DAMSEL utilizing simulated annealing. The early growth of Pt/Au(100) exhibits a type of interdiffusive growth where the Pt burrows into the Au substrate, forming a bumpy, mounded surface. The predicted growth is a consequence of the pliable nature of the reconstructed Au(100) substrate, and the ease with which it accommodates interlayer replacement diffusion. For Au/Pt(100), in agreement with low-energy electron-diffraction analyses, Au loses its quasihexagonal reconstruction at about 0.5-ML coverage, whereupon it grows layer by layer on Pt(100), pseudomorphic with the Pt(100) bulklike substrate, until a quasihexagonal reconstruction reappears at 2 ML.

N-butane hydrogenolysis on planar and faceted Pt/W(111) surfaces

The Relationship between surface structure and reactivity is investigated by means ofn-butane hydrogenolysis, a known structure sensitive reaction, for planar and faceted Pt/ W(111) surfaces. The W(111) surface reconstructs to form pyramidal facets with [211] orientation upon vapor deposition of Pt (>1.3 ML) and annealing above 750 K. The hydrogenolysis kinetics over the planar and the faceted surface are found to be quite different. The planar surface has a higher selectivity towards ethane formation and a higher reaction rate. The apparent activation energies are found to be 33 ± 4 kJ/mol for the planar surface and 76 ± 6 kJ/mol for a surface covered with ∼ 20 nm facets. There appears to be a correlation between the concentration of fourfold coordination (C4) sites on the surface and the amount of ethane produced. The C4 concentration is altered by changing the facet size (annealing temperature). The results indicate the presence of a different intermediate on the C4 sites as evidenced by the differences in the apparent activation energy, the reaction rate and the overall selectivity.

CO Oxidation on Pt/α-Al2O3(0001): Evidence for Structure Sensitivity

The oxidation of CO by O2 has been studied over model catalysts prepared by vapor deposition of Pt onto an α-Al2O3(0001) crystal. Reaction rates were measured for two particle sizes, 14 and 1.7 nm, in order to determine whether this reaction is structure sensitive and how the rates were affected by changes in the desorption kinetics of CO on small and large particles which had been observed previously (E. I. Altman and R. J. Gorte. J. Catal.110, 191 (1988)). For 10 Torr each of CO and O2, between 560 and 680 K, the turnover frequencies on the 14-nm particles were much higher than on the 1.7-nm particles, and the activation energy, 30 ± 3 kcal/mol, was much lower than that found on the smaller particles, 41 ± 4 kcal/mol. A simple model of the reaction demonstrates that changes in the desorption kinetics of CO with particle size can explain the observed structure sensitivity found in the reaction rates. The results indicate that adsorption studies on model catalysts can be used to understand the properties of real catalysts.

A study of CO, NO, and H 2 adsorption on model Pt/CeO 2 catalysts

Model catalysts consisting of Pt particles on an amorphous CeO 2 film have been investigated to determine the effect of ceria on the adsorption properties of Pt for CO, NO, and H 2. The catalysts were prepared by vapor deposition of Pt and the film growth was characterized by Auger electron spectroscopy. Film growth for Pt is the same on both ceria and an oxidized Al foil and appears to be three-dimensional at room temperature on both substrates. Temperature programmed desorption (TPD) results show strong variations in the adsorption properties for CO, NO, and H 2 as a function of particle size; however, the results for the model Pt/ceria catalysts were found to be identical to results for Pt on both oxidized Al or α-Al 3O 2(0001) when particles of the same size are compared. The results suggest that interactions between Pt and ceria are relatively weak within the temperature and pretreatment conditions studied and that the presence of ceria does not substantially affect the adsorption properties of Pt.

A study of CO, NO, and H 2 adsorption on model Pt/CeO 2 catalysts

Abstract Model catalysts consisting of Pt particles on an amorphous CeO 2 film have been investigated to determine the effect of ceria on the adsorption properties of Pt for CO, NO, and H 2 . The catalysts were prepared by vapor deposition of Pt and the film growth was characterized by Auger electron spectroscopy. Film growth for Pt is the same on both ceria and an oxidized Al foil and appears to be three-dimensional at room temperature on both substrates. Temperature programmed desorption (TPD) results show strong variations in the adsorption properties for CO, NO, and H 2 as a function of particle size; however, the results for the model Pt/ceria catalysts were found to be identical to results for Pt on both oxidized Al or α-Al 3 O 2 (0001) when particles of the same size are compared. The results suggest that interactions between Pt and ceria are relatively weak within the temperature and pretreatment conditions studied and that the presence of ceria does not substantially affect the adsorption properties of Pt.

A comparison of Pt overlayers on α-Al2O3(0001), ZnO(0001)Zn, and ZnO(0001̄)O

The growth of Pt films on ZnO(0001)Zn and ZnO(0001̄)O and their adsorption properties for CO have been studied and compared to results obtained for Pt on α-Al2O3(0001). Samples were prepared by vapor deposition of Pt onto flat substrates in ultra high vacuum, and metal coverages were measured using a quartz-crystal, film thickness monitor. On both ZnO surfaces, Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) indicate that Pt grows in as a 2D film at 300 K, in contrast to results for Pt on α-Al2O3(0001) where 3D particles are formed under these conditions. Furthermore, transmission electron diffraction (TED) showed that the Pt grew as an ordered overlayer on the ZnO crystals. Heating the Pt/ZnO surfaces resulted in the formation of Pt particles starting at ∼650 K, but the Pt particles were still oriented with the ZnO. On both ZnO surfaces, temperature programmed desorption (TPD) curves for CO from high Pt coverages (&amp;gt;one monolayer) and from Pt particles formed by heating thinner films were identical to TPD curves for CO from Pt on α-Al2O3(0001). The main desorption features were observed at 400 and 510 K and are interpreted as being due to different site geometries on the Pt by comparison to results from Pt single crystals. However, for Pt at submonolayer coverages prior to particle formation, the TPD curves for CO from Pt on ZnO(0001)Zn were shifted down in temperature by ∼60 K compared to results for Pt on ZnO(0001̄)O. These results are interpreted as indicating a chemical interaction between Pt and the Zn+2 ions which are in direct contact.

ChemInform Abstract: Interaction of Pt with Ceria and Silica.

AbstractPt is deposited on oxidized Ce foils, high surface area CeO2 powder, and on a sputtered SiO2 thin film.

The desorption of CO from small Pt particles on Al 2O 3

The adsorption of CO on small Pt particles supported on alumina was studied using temperature programmed desorption (TPD). Samples were prepared by vapor deposition of Pt onto a flat substrate in ultra high vacuum. Metal coverages were reproducibly obtained using a film thickness monitor which was calibrated with Auger electron spectroscopy (AES). AES results indicated that Pt grew in a layer-by-layer manner on alumina at both 90 and 300 K and that these metal films aggregated into particles when heated above 650 K in vacuum. The average particle size could be estimated from the amount of CO desorbing in TPD and from the metal coverage and could be varied from 1.1 nm up to a continuous film. For the smallest particles, CO desorbed in a single state at 510 K. For larger particles, a second desorption state at 400 K was also observed. Since the desorption of CO occurs at similar temperatures on single crystals of Pt, these results indicate that the adsorption properties for CO on small particles of Pt on alumina are very similar to those for CO on bulk Pt. The change in the relative populations of the two desorption states with increasing particle size is interpreted as evidence for the formation of (111)-type facets on the larger particles.