Download or read book Pyrrole Hydrogenation Over Rh 111 and Pt 111 Single Crystal Surfaces and Hydrogenation Promotion Mediated by 1 Methylpyrrole written by and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Sum-frequency generation (SFG) surface vibrational spectroscopy and kinetic measurements using gas chromatography have been used to study the adsorption and hydrogenation of pyrrole over both Pt(111) and Rh(111) single-crystal surfaces at Torr pressures (3 Torr pyrrole, 30 Torr H2) to form pyrrolidine and the minor product butylamine. Over Pt(111) at 298 K it was found that pyrrole adsorbs in an upright geometry cleaving the N-H bond to bind through the nitrogen evidenced by SFG data. Over Rh(111) at 298 K pyrrole adsorbs in a tilted geometry relative to the surface through the p-aromatic system. A pyrroline surface reaction intermediate, which was not detected in the gas phase, was seen by SFG during the hydrogenation over both surfaces. Significant enhancement of the reaction rate was achieved over both metal surfaces by adsorbing 1-methylpyrrole before reaction. SFG vibrational spectroscopic results indicate that reaction promotion is achieved by weakening the bonding between the N-containing products and the metal surface because of lateral interactions on the surface between 1-methylpyrrole and the reaction species, reducing the desorption energy of the products. It was found that the ring-opening product butylamine was a reaction poison over both surfaces, but this effect can be minimized by treating the catalyst surfaces with 1-methylpyrrole before reaction. The reaction rate was not enhanced with elevated temperatures, and SFG suggests desorption of pyrrole at elevated temperatures.

Download or read book Morphological Compositional and Shape Control of Materials for Catalysis written by Paolo Fornasiero and published by Elsevier. This book was released on 2017-05-23 with total page 712 pages. Available in PDF, EPUB and Kindle. Book excerpt: Morphological, Compositional, and Shape Control of Materials for Catalysis, Volume 177, the latest in the Studies in Surface Science and Catalysis series, documents the fast-growing developments in the synthesis, characterization, and utilization of nanostructures for catalysis. The book provides essential background on using well-defined materials for catalysis and presents exciting new paradigms in the preparation and application of catalytic materials, with an emphasis on how structure determines catalytic properties. In addition, the book uniquely features discussions on the future of the field, with ample space for future directions detailed in each chapter. - Presents the latest paradigms in the preparation and application of catalytic materials - Provides essential background on using well-defined materials for catalysis - Features discussion of future directions at the end of each chapter

Download or read book Structural Sensitivity Studies of Ethylene Hydrogenation on Platinum and Rhodium Surfaces written by and published by . This book was released on 1996 with total page 106 pages. Available in PDF, EPUB and Kindle. Book excerpt: The catalytic hydrogenation of ethylene and hydrogen on the well characterized surfaces of the noble metals platinum and rhodium has been studied for the purposes of determining the relative activity of these two substrates as well as the degree of structure sensitivity. The Pt(111) and the Rh(755) single crystal surfaces, as well as Pt and Rh foils, were employed as substrates to study the effect of surface step structure on reactivity. In addition, vibrational spectroscopy studies were performed for ethylene adsorption on the stepped Rh(755) surface. The catalytic reaction were obtained using a combined ultrahigh vacuum chamber coupled with an atmospheric pressure reaction chamber that functioned as a batch reactor. Samples could be prepared using standard surface science techniques and characterized for surface composition and geometry using Auger Electron Spectroscopy and Low Energy Electron Diffraction. A comparison of the reactivity of Rh(111) with the results from this study on Rh(755) allows a direct determination of the effect of step structure on ethylene hydrogenation activity. Structure sensitivity is expected to exhibit orders of magnitude differences in rate as surface orientation is varied. In this case, no significant differences were found, confirming the structure insensitivity of this reaction over this metal. The turnover frequency of the Rh(111) surface, 5 x 101 s−1, is in relatively good agreement with the turnover frequency of 9 x 101 s−1 measured for the Rh(755) surface. Rate measurements made on the Pt(111) surface and the Pt foil are in excellent agreement, both measuring 3 x 102 s−1. Likewise, it is concluded that no strong structure sensitivity for the platinum surfaces exists. High Resolution Electron Energy Loss Spectroscopy studies of adsorbed ethylene on the Rh(755) surface compare favorably with the ethylidyne spectra obtained on the Rh(111) and Rh(100) surfaces.

Download or read book The Hydrogenation and Dehydrogenation of C2 c4 Hydrocarbons on Pt 111 Monitored in Situ Over 13 Orders of Magnitude in Pressure with Infrared visible Sum Frequency Generation written by Paul Samuel Cremer and published by . This book was released on 1996 with total page 452 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Atmospheric Pressure Ethylene Hydrogenation Over Pt 111 and Pt 210 Single Crystals written by Robert Vaughn Wheeler and published by . This book was released on 1994 with total page 376 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Catalytic Hydrogenation over Platinum Metals written by Paul Rylander and published by Elsevier. This book was released on 2012-12-02 with total page 565 pages. Available in PDF, EPUB and Kindle. Book excerpt: Catalytic Hydrogenation over Platinum Metals focuses on catalytic hydrogenation as an effective process in attaining controlled transformations of organic compounds. Composed of contributions of various authors, the book first provides information on catalysts, equipment, and conditions. Catalyst stability and reuse; types of catalyst; platinum metals; and synergism are covered. The text proceeds with discussions on hydrogenation reactors. Topics include atmospheric pressure reactors; low pressure reactors; microreactors; and high pressure reactors. The book also covers hydrogenation of carbon-carbon unsaturation. Catalytic metal; modified catalyst systems; stereochemistry; diacetylenes; and hydrogenolysis are discussed. The text also looks at the hydrogenation of aromatics, nitrogen and carbonyl compounds, and hydrogenolysis. Numerical representations and analysis, diagrams, and reactions of compounds when exposed to different laboratory conditions are considered. The selection is a great source of data for readers interested in studying the process of catalytic hydrogenation.

Download or read book The Hydrogenation and Dehydrogenation of C2 C4 Hydrocarbons on Pt 111 Monitored in Situ Over 13 Orders of Magnitude in Pressure with Infrared visible Sum Frequency Generation written by and published by . This book was released on 1996 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt: The hydrogenation and dehydrogenation of ethylene, propylene, and isobutene were monitored in situ during heterogeneous catalysis over Pt(111) between 10−1° Torr and 1000 Torr with infrared-visible sum frequency generation (SFG). SFG is a surface specific vibrational spectroscopy capable of achieving submonolayer sensitivity under reaction conditions in the presence of hundreds of Toff of reactants and products. Olefin dehydrogenation experiments were carried out with SFG under ultra high vacuum (UHV) conditions on the (111) crystal face of platinum Ethylene chemisorbed on Pt(111) below 230 K in the di-[sigma] bonded conformation (Pt-CH2CH2-Pt). Upon annealing the system to form the dehydrogenation product, ethylidyne (M=CCH3), evidence was found for an ethylidene intermediate (M=CHCH3) from its characteristic v{sub as}(CH3) near 2960 cm−1. Hydrogenation of ethylene was carried out between 1 Toff and 700 Torr of H2 while the vibrational spectrum of surface species was monitored with SFG. Simultaneously, gas chromatography was used to obtain the turnover rate for the catalytic reaction, which could be correlated with the adsorbed intermediate concentration to determine the reaction rate per surface intermediate. Di-[sigma] bonded ethylene, [pi]-bonded ethylene, ethyl groups and ethylidyne resided on the surface during reaction. The mechanistic pathway for ethylene hydrogenation involved the stepwise hydrogenation of [pi]-bonded ethylene through an ethyl intermediate to ethane. The hydrogenation of propylene was carried out under the same conditions as ethylene. It was found that propylene hydrogenates from [pi]-bonded propylene through a 2-propyl intermediate to propane on Pt(111). The rate of reaction was approximately 50% slower than that of ethylene hydrogenation. Isobutene, however, was found to hydrogenate almost two order of magnitude slower than propylene on Pt(111).

Download or read book Sum Frequency Generation Studies of Hydrogenation Reactions on Platinum Nanoparticles written by James Michael Krier and published by . This book was released on 2013 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt: Sum frequency generation (SFG) vibrational spectroscopy is used to characterize intermediate species of hydrogenation reactions on the surface of platinum nanoparticle catalysts. In contrast to other spectroscopy techniques which operate in ultra-high vacuum or probe surface species after reaction, SFG collects information under normal conditions as the reaction is taking place. Several systems have been studied previously using SFG on single crystals, notably alkene hydrogenation on Pt(111). In this thesis, many aspects of SFG experiments on colloidal nanoparticles are explored for the first time. To address spectral interference by the capping agent (PVP), three procedures are proposed: UV cleaning, H2 induced disordering and calcination (core-shell nanoparticles). UV cleaning and calcination physically destroy organic capping while disordering reduces SFG signal through a reversible structural change by PVP. Disordering is a dynamic and powerful way to perform SFG experiments on colloidal nanoparticles. Simply adding H2 (a reactant) to Pt-PVP reduces signal of PVP by>90%, making it possible to resolve intermediates. The selection rules of SFG indicate intensity may be reduced by a decrease in concentration or an increase in disorder. As H2 dissociates on Pt, the bond between PVP and Pt is weakened and PVP is able to rearrange into an unstructured geometry. Disordering makes size-controlled SFG studies possible for the first time because with PVP left intact, the nanoparticles are much less likely to aggregate. As evidence that a chemisorbed reaction intermediate is can be monitored, cyclohexene hydrogenation is performed. When PVP is disordered and the particles are "solvent-cleaned," the distinct C-H stretch of adsorbed 1,4-cyclohexadiene (1,4-CHD) appears at 2765 cm-1. In addition, the mechanism of hydrogenation of 1,3-butadiene (1,3-BD) at 75 °C is characterized using the disordering procedure. For larger Pt-PVP nanoparticles (4.6-6.7 nm), one major pathway is preferred (2-buten-1-yl). However, using smaller nanoparticles (0.9-1.8 nm), two major pathways exist (1-buten-4-yl and 2-buten-1-yl) and coincide with preference for full hydrogenation. Growth in the aliphatic stretch range following H2 dosing shows UV treatment is not able to produce "naked" nanoparticles. Although outer layers removed quickly, persistent C fragments remain near the Pt surface. The properties of residual fragments of PVP following UV treatment are very mystifying. PVP is known to block active sites on Pt and reduce turnover frequency for ethylene hydrogenation. (After three hours of UV treatment, ethylene hydrogenation increases tenfold.) However, it is shown that for methanol oxidation, residual fragments become impermeable and actually reduce the turnover rate. Under oxidation conditions, the regular capped Pt-PVP nanoparticles are more active than the same particles following PVP removal with UV treatment. As further evidence of this effect, cyclohexene hydrogenation is performed with different level of H2. Residual fragments are permeable with H2 and the 1,4-CHD intermediate appears in the SFG spectrum. However, once H2 is removed, chemisorbed 1,4-CHD completely disappears in favor of molecular (physisorbed) cyclohexene (not bonded to Pt). Even for a strongly bound dehydrogenated intermediate like 1,4-CHD, access to Pt is only possible with H2. Under varying amounts of UV treatment (PVP removal), the mechanism of cyclohexene hydrogenation varies widely among 1,4-CHD, 1,3-cyclohexadiene and pi-allyl. Removing PVP does not simply open equivalent sites but shifts the reaction mechanism in this case. Using Stöber encapsulation, a variety of PVP-capped catalysts can be coated in a thin porous SiO2 shell (5-10 nm) and used for in situ characterization. Surrounding the catalyst with SiO2 allows PVP to be thoroughly removed without compromising morphology. It is shown that alloying Pt with Sn (with SiO2 shell) allows a new reaction mechanism of CO oxidation to take place which is not limited by surface O2 concentration (as on pure Pt). In addition, 1,3-BD hydrogenation on 4 nm Pt@SiO2, Pd@SiO2 and Rh@SiO2 is studied with SFG. Previous work shows Pd makes only partially hydrogenated products while Pt makes all products. SFG and kinetic experiments indicate multiple pathways (1-butene-4-yl, butan-1,3-diyl and 2-buten-1-yl) are possible on Pt@SiO2 while only one (2-buten-1-yl) is favored on Pd@SiO2. This work is the first SFG reaction selectivity study on core-shell nanoparticles. Using catalysts inside SiO2 shells in dense 2-D films, it may become possible to assess industrial 3-D catalysts at a molecular level.

Download or read book The Hydrogenation and Dehydrogenation of C sub 2 C sub 4 Hydrocarbons on Pt 111 Monitored in Situ Over 13 Orders of Magnitude in Pressure with Infrared visible Sum Frequency Generation written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The hydrogenation and dehydrogenation of ethylene, propylene, and isobutene were monitored in situ during heterogeneous catalysis over Pt(111) between 10[sup -10] Torr and 1000 Torr with infrared-visible sum frequency generation (SFG). SFG is a surface specific vibrational spectroscopy capable of achieving submonolayer sensitivity under reaction conditions in the presence of hundreds of Toff of reactants and products. Olefin dehydrogenation experiments were carried out with SFG under ultra high vacuum (UHV) conditions on the (111) crystal face of platinum Ethylene chemisorbed on Pt(111) below 230 K in the di-[sigma] bonded conformation (Pt-CH[sub 2]CH[sub 2]-Pt). Upon annealing the system to form the dehydrogenation product, ethylidyne (M=CCH[sub 3]), evidence was found for an ethylidene intermediate (M=CHCH[sub 3]) from its characteristic v[sub as](CH[sub 3]) near 2960 cm[sup -1]. Hydrogenation of ethylene was carried out between 1 Toff and 700 Torr of H[sub 2] while the vibrational spectrum of surface species was monitored with SFG. Simultaneously, gas chromatography was used to obtain the turnover rate for the catalytic reaction, which could be correlated with the adsorbed intermediate concentration to determine the reaction rate per surface intermediate. Di-[sigma] bonded ethylene, [pi]-bonded ethylene, ethyl groups and ethylidyne resided on the surface during reaction. The mechanistic pathway for ethylene hydrogenation involved the stepwise hydrogenation of[pi]-bonded ethylene through an ethyl intermediate to ethane. The hydrogenation of propylene was carried out under the same conditions as ethylene. It was found that propylene hydrogenates from[pi]-bonded propylene through a 2-propyl intermediate to propane on Pt(111). The rate of reaction was approximately 50% slower than that of ethylene hydrogenation. Isobutene, however, was found to hydrogenate almost two order of magnitude slower than propylene on Pt(111).

Download or read book Hydrogenation of the Alpha Beta Unsaturated Aldehydes Acrolein Crotonaldehyde and Prenal Over Pt Single Crystals written by and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Sum-frequency generation vibrational spectroscopy (SFG-VS) and kinetic measurements using gas chromatography have been used to study the surface reaction intermediates during the hydrogenation of three?,?-unsaturated aldehydes, acrolein, crotonaldehyde, and prenal, over Pt(111) at Torr pressures (1 Torr aldehyde, 100 Torr hydrogen) in the temperature range of 295K to 415K. SFG-VS data showed that acrolein has mixed adsorption species of?2-di-?(CC)-trans,?2-di-?(CC)-cis as well as highly coordinated?3 or?4 species. Crotonaldehyde adsorbed to Pt(111) as?2 surface intermediates. SFG-VS during prenal hydrogenation also suggested the presence of the?2 adsorption species, and became more highly coordinated as the temperature was raised to 415K, in agreement with its enhanced C=O hydrogenation. The effect of catalyst surface structure was clarified by carrying out the hydrogenation of crotonaldehyde over both Pt(111) and Pt(100) single crystals while acquiring the SFG-VS spectra in situ. Both the kinetics and SFG-VS showed little structure sensitivity. Pt(100) generated more decarbonylation 'cracking' product while Pt(111) had a higher selectivity for the formation of the desired unsaturated alcohol, crotylalcohol.

Download or read book Hydrogenation and Dehydrogenation of Nitrogen Containing Species on the Pt 111 Surface written by Kumudu K. W Mudiyanselage and published by . This book was released on 2008 with total page 274 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Crotonaldehyde Hydrogenation on Pt 111 based Model Catalysts written by Dmitri I. Jerdev and published by . This book was released on 2001 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Hydrogenation of Ethylene Over Platinum Single Crystal Surfaces written by Arthur Leonard Backman and published by . This book was released on 1987 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Surface Science and Catalytic Studies of Hydrocarbon Skeletal Rearrangements written by David John Godbey and published by . This book was released on 1987 with total page 500 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Sum Frequency Generation Studies of Hydrogenation Reactions on Platinum Nanoparticles written by and published by . This book was released on 2013 with total page 195 pages. Available in PDF, EPUB and Kindle. Book excerpt: Sum Frequency Generation (SFG) vibrational spectroscopy is used to characterize intermediate species of hydrogenation reactions on the surface of platinum nanoparticle catalysts. In contrast to other spectroscopy techniques which operate in ultra-high vacuum or probe surface species after reaction, SFG collects information under normal conditions as the reaction is taking place. Several systems have been studied previously using SFG on single crystals, notably alkene hydrogenation on Pt(111). In this thesis, many aspects of SFG experiments on colloidal nanoparticles are explored for the first time. To address spectral interference by the capping agent (PVP), three procedures are proposed: UV cleaning, H2 induced disordering and calcination (core-shell nanoparticles). UV cleaning and calcination physically destroy organic capping while disordering reduces SFG signal through a reversible structural change by PVP.

Download or read book Structural Sensitivity Studies of Ethylene Hydrogenation on Platinum and Rhodium Surfaces written by Michael Andrew Quinlan and published by . This book was released on 1996 with total page 226 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Ethylene Decomposition and Hydrogenation on Platinum Single Crystal Surfaces written by Arthur Leonard Backman and published by . This book was released on 1990 with total page 612 pages. Available in PDF, EPUB and Kindle. Book excerpt: The adsorption and decomposition of ethylene on the Pt(210) crystal surface is examined using TPD and EELS. At 100 K, ethylene adsorbs molecularly to form a type 2 $pi$-bound complex. Upon heating to 250 K, some of the $pi$-bound complex desorbs and also reacts to form ethane. However, most of the $pi$-bound species is stable to room temperature. Further heating results in the decomposition of the $pi$-bound species to form a mixture of ethylylidyne, methyl groups, surface carbon and hydrogen. Ethylylidyne decomposes to form a mixture of ethynyl, methylidyne, hydrogen and adsorbed surface carbon while the methyl groups decompose to form methylene and methylidyne. Further decomposition of these intermediates results in hydrogen liberation as well as more surface carbon and a C$sb2$ species. At high ethylene exposures, a weakly $pi$-bonded species forms in addition to the $pi$-bonded complex at low temperatures. The weakly $pi$-bound species can also be formed at low temperatures by pre-exposing the Pt(210) crystal to hydrogen before ethylene exposure. This species is less stable than the $pi$-bound complex since around 195 K, it either desorbs or reacts to form ethane. A new high pressure/low pressure reaction system is developed to investigate ethylene hydrogenation on the Pt(111) and (5x20)Pt(100) crystal surfaces around atmospheric pressure. Two limiting reaction rates are observed for reactions initiated over an atomically clean surface. Both XPS and EELS results indicate a build up of a carbonaceous overlayer as a function of reaction time suggesting that the decrease in rate results from the increase of the carbonaceous overlayer. Both limiting reaction rates are larger for reactions over the Pt(111) than on the (5x20)Pt(100) implying that higher concentrations of the adsorbed overlayer are present on the (5x20)Pt(100) surface. On Pt(111), ethylidyne and an ethyl species are identified using EELS following atmospheric pressure hydrogenation experiments. Post reaction treatments with pure hydrogen indicate that the ethyl species can be reacted off the surface whereas ethylidyne is stable. In addition, carbon monoxide is found to adsorb only after the hydrogen treatment. These results suggest that the reaction occurs on the platinum surface and not on top of the ethylidyne layer.