Structure and Reactivity of Platinum−Copper Alloy Particles Supported on ZSM-5

Shpiro, E. S.; Ткаченко, О. П.; Jaeger, N. I.; Schulz‐Ekloff, G.; Grünert, Wolfgang

doi:10.1021/jp981029g

Cited by 23 publications

(40 citation statements)

References 52 publications

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“…CO is relatively unstable and easily removed from fully reduced Cu surfaces (i.e., during the He flush required to remove gas-phase CO) yet is stable at ambient temperatures when adsorbed on cationic Cu species. 43 Consequently, the lack of higher-energy stretching frequencies (ca. 2140-2110 cm -1 ) eliminates the possibility that cationic Cu surface species are present and indicates that Cu is fully reduced by the hydrogen treatment.…”

Section: Resultsmentioning

confidence: 99%

“…Cu surface enrichment in this system been postulated for a number of traditionally prepared supported Pt-Cu catalysts, particularly under reducing atmospheres. [36][37][38]43 Copper has a lower work function (heat of sublimation) than platinum, 34 indicating generally weaker interatomic bonding for the coinage metal. As a result, Pt is expected to cluster at the center of the nanoparticle to maximize the stronger Pt-Pt metal bonding, leaving Cu atoms more stable at the particle surface.…”

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confidence: 99%

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Tuning Supported Catalyst Reactivity with Dendrimer-Templated Pt−Cu Nanoparticles

2006

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The effects of particle composition on heterogeneous catalysis were studied using dendrimer-encapsulated nanoparticles (DENs) as precursors to supported Pt-Cu catalysts. Bimetallic Pt-Cu DENs with varying Pt/Cu ratios were prepared in an anaerobic aqueous solution and deposited onto a high-purity commercial alumina support. The dendrimer template was then thermally removed to yield supported nanoparticle catalysts, which were studied with toluene hydrogenation and CO oxidation catalysis as well as infrared spectroscopy of adsorbed CO. Incorporating Cu into Pt nanoparticles had opposite effects on the two test reactions. Cu acted as a mild promoter for CO oxidation catalysis, and the promoting effect was independent of the amount of Cu present. Conversely, Cu acted as a strong poison for toluene hydrogenation catalysis, and the normalized rate tracked inversely with Cu content. Infrared spectroscopy of the supported nanoparticles indicated that electronic effects (electron donation from Cu to Pt) were minimal for these materials. Consequently, the catalysis results are interpreted in terms of potential structural differences as a function of Cu incorporation and reaction conditions. IntroductionHighly dispersed supported metal nanoparticle catalysts are an important class of industrial materials, as one-third of material U. S. gross national product involves a catalytic process somewhere in the production chain. 1 State of the art heterogeneous catalysts often contain dopant metals, which are incorporated to promote a desired reaction, prevent undesirable side reactions, or enhance catalyst longevity. 2,3 Traditional preparative routes involve impregnating metal salts onto high-surfacearea supports, followed by various thermal activation steps. 3 Most important industrial supports can also be employed as separation media; consequently, chromatographic separation of salt precursors as they pass through the support pore structure is unavoidable. Further, nanoparticle preparation via traditional routes depends on the surface (and even gas phase) mobility of the species present during the thermal treatments. 4,5 These processes vary widely for different metals and are poorly understood, at best. 4,5 Consequently, bimetallic materials prepared by such methods are often complicated, have significant compositional inhomogenaity from one particle to the next, and are difficult to characterize.Recent advances in computational methods are beginning to shed light onto the fundamental properties of bimetallic catalyst systems, and predictive models are beginning to emerge. [6][7][8][9] The potential to controllably tune catalyst properties through the nanoscale design of bimetallic nanoparticles is becoming apparent, and designed bimetallic catalysts with novel behavior for important reactions already appear in the recent literature. [10][11][12] However, the utilization of traditional preparative techniques and the complicated materials that arise from these methods remain a significant hurdle to studying new catalysts, eva...

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Section: Resultsmentioning

confidence: 99%

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Tuning Supported Catalyst Reactivity with Dendrimer-Templated Pt−Cu Nanoparticles

2006

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“…Among the noble metals, Pt-loaded catalysts were widely used in the selectivity of C–O hydrogenolysis. , Mikhailov et al reported that Pt nanoparticles were regarded as active sites of C–C bond formation by the DFT calculations. Efim et al studied that the high fractional exposure of Pt–Cu alloys could be detected by FTIR of adsorbed CO. Kotobuki et al conducted a series of research studies on the preferential oxidation (PROX) over Fe, Pt, and Pt–Fe/mor to determine that Pt was the adsorption site for carbon monoxide. However, Pt–Cu bimetallic catalysts have not yet been explored for dimethyl ether carbonylation to ethanol.…”

Section: Introductionmentioning

confidence: 99%

Platinum–Copper Bimetallic-Modified Nanoprism Mordenite for Carbonylation of Dimethyl Ether

Sheng

Qian

et al. 2019

Energy Fuels

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Platinum–copper bimetallic-modified mordenite catalysts for the dimethyl ether (DME) carbonylation to methyl acetate (MA) were carried out using a laboratory-made nanoprism mordenite, which was synthesized by hydrothermal method and modified by ion exchange with Cu(NO3)2 and wet impregnation with H2PtCl6. The catalyst was characterized by X-ray diffraction, inductively coupled plasma atomic emission spectroscopy, N2O titration, NH3 temperature-programmed desorption, H2 temperature-programmed reduction, pyridine-infrared, Fourier transform infrared, Brunauer–Emmett–Teller, high-resolution transmission electron microscopy, energy-dispersive spectrometry mapping, scanning electron microscopy, X-ray photoelectron spectroscopy, and temperature-programmed oxidation. Bimetallic platinum–copper catalysts exhibited high catalytic activity for carbonylation of DME, which was attributed to the large quantity of the Brønsted acid sites in the eight-membered ring (8-MR). Moreover, the bimetallic catalyst with small copper particle size and bimetallic synergism promoted conversion of DME and MA selectivity. Over the 1Pt/Cu-mor catalyst (1 wt % Pt and 2 wt % Cu), DME conversion and MA selectivity reached 86.0% and 96.0%, respectively. What’s more, the addition of Pt reduced the acidity of the 12-membered ring (12-MR) in the Cu-mor catalyst, resulting in a suppression of hard coke formation.

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“…11- 14 The bi metallic catalysts often served as model systems to ob tain information on the electronic states and interactions between Pt and Cu. 11,12,15- 18 An analysis of the IR spectra of CO adsorbed on metals is widely used for investigation of the electronic and struc tural characteristics of the surface of bulky and supported metals. Information on the state of metals is obtained by examining vibrational frequencies of non interacting (iso lated) molecules of CO linearly adsorbed on the metals (singleton frequencies) and shifts of the frequencies of absorption band (AB) maxima, which appear due to the dipole dipole interaction between the neighboring CO molecules adsorbed on metals.…”

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The state of metals in the Pt/Al2O3 and (Pt-Cu)/Al2O3 catalysts as indicated by IR spectroscopy with isotope dilution of 12C16O with 13C18O molecules

et al. 2007

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Adsorptionof 13 С 18 О+ 12 С 16 О mixtures on the Pt(2.9%)/γ Al 2 O 3 , (Pt(2.6%)+Cu(2.7%))/γ Al 2 O 3 , and (Pt(2.6%)+Cu(5.1%))/γ Al 2 O 3 catalysts was studied by FTIR spectroscopy. On the metallic Pt surface at coverages close to saturation, CO is adsorbed both strongly and weakly to form linear species for which the vibrational frequencies of the isolated 13 С 18 О molecules adsorbed on Pt are ~1940 and ~1970 cm -1 , respectively. The redis tribution of intensities of the high and low frequency absorption bands in the spectra of adsorbed 13 С 18 О indicates that these linear forms are present on the adjacent metal sites. The weak adsorption is responsible for the fast isotope exchange between the gaseous CO and CO molecules adsorbed on metal. The Pt-Cu alloys, in which the electronic state of the surface Pt atoms characteristic of monometallic Pt remains unchanged, are formed on the surface of the reduced Pt-Cu bimetallic catalysts. The decrease in the vibrational frequencies of the isolated С=О bonds in the isolated Pt-СО complexes suggests that the CO molecules adsorbed on the Cu atoms affect the electronic properties of Pt.The monometallic platinum catalysts exhibit high ac tivity in various hydrocarbon conversions. 1 The addition of the second metal component to the catalyst can result in the formation of alloys and intermetallic compounds that strongly change the activity and selectivity of the bimetallic systems. 2 Similar changes were observed when studying the behavior of the Pt-Cu bimetallic catalysts in the reactions of hydrocarbon reforming, 3-5 paraffin dehydrogenation, 6-8 CO oxidation, 9,10 and hydrode chlorination of vicinal chlorohydrocarbons. 11-14 The bi metallic catalysts often served as model systems to ob tain information on the electronic states and interactions between Pt and Cu. 11,12,15-18 An analysis of the IR spectra of CO adsorbed on metals is widely used for investigation of the electronic and struc tural characteristics of the surface of bulky and supported metals. Information on the state of metals is obtained by examining vibrational frequencies of non interacting (iso lated) molecules of CO linearly adsorbed on the metals (singleton frequencies) and shifts of the frequencies of absorption band (AB) maxima, which appear due to the dipole dipole interaction between the neighboring CO molecules adsorbed on metals. 19-21 Under the condi tions when the dipole dipole interaction between the adsorbed molecules is absent, the frequency of the AB maximum defined as the singleton frequency depends on the electron density on the metal atom that forms an adsorption complex with a CO molecule. Thus, the single ton frequency characterizes the electronic donor accep tor properties of the adsorption sites on metals. 22 When the metal surface is covered with the adsorbed CO mol ecules, a dipole dipole shift is observed, the magnitude of which is determined by the number of interacting adja cent vibrating dipoles, 4 and for adsorption close to satura tion it characterizes the size of ensembles ...

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Structure and Reactivity of Platinum−Copper Alloy Particles Supported on ZSM-5

Cited by 23 publications

References 52 publications

Tuning Supported Catalyst Reactivity with Dendrimer-Templated Pt−Cu Nanoparticles

Tuning Supported Catalyst Reactivity with Dendrimer-Templated Pt−Cu Nanoparticles

Platinum–Copper Bimetallic-Modified Nanoprism Mordenite for Carbonylation of Dimethyl Ether

The state of metals in the Pt/Al2O3 and (Pt-Cu)/Al2O3 catalysts as indicated by IR spectroscopy with isotope dilution of 12C16O with 13C18O molecules

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