Structure and Reactivity of Small Metallic and Bimetallic Clusters Hosted in Molecular Sieves

Shpiro, E. S.; Jaeger, N. I.; Schulz‐Ekloff, G.

doi:10.1002/bbpc.199500078

Cited by 9 publications

(10 citation statements)

References 32 publications

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“…Upon thermodesorption up to 473 K the band of Pt-CO is shifted by only 9 cm -1 . 34 Oxidation and rereduction of the sample at 623 K gives spectra which, at first glance, look rather similar to those observed for the sample reduced at 523 K, i.e., two principal bands of Cu + -CO and Pt-CO at 2157 and 2068 cm -1 , respectively (Figure 8). High-pressure adsorption gives a better resolved structure around the band at 2157 cm -1 while the band at 2072 cm -1 became even broader and more asymmetrical (spectrum 2).…”

Section: Resultssupporting

confidence: 56%

“…The intensity of the latter band does not change during evacuation at room temperature. Upon thermodesorption up to 473 K the band of Pt−CO is shifted by only 9 cm -1 …”

Section: Resultsmentioning

confidence: 99%

“…The principal bands at 2157 and 2068 cm -1 gradually decreased upon thermodesorption (cf. ref ). The Cu + −CO band was shifted very slightly and vanished at 473 K while the Pt−CO band underwent a downward shift of 30 cm -1 and remained in the spectrum still at 623 K.

8 FTIR spectra of adsorbed CO at 300 K following reduction (523 K), reoxidation (523 K), and high-temperature reduction (623 K) of the 1% Pt−0.3% Cu/ZSM-5 sample: 1, 30 min (ca.…”

Section: Resultsmentioning

confidence: 99%

“…The most pronounced change upon thermodesorption was the large downward shift of the Pt−CO band from 2088 cm -1 at 300 K to 2062 cm -1 at 523 K (cf. ref ). On the other hand, the intensity decrease in this temperature region was only 2-fold.…”

Section: Resultsmentioning

confidence: 99%

“…49 This is in agreement with the results inferred from the EXAFS measurements for sample 2. 35 The further shift of the frequency of on-top adsorbed CO toward lower wavenumbers, i.e., 2055 cm -1 (sample 3 34 ) and 2049 cm -1 (sample 2,Figure 6b, spectrum 6), at 473 K can then be attributed to the temperature-dependent downward shift of the frequency of the stretching vibration. 50 An important observation in our samples is the observed tendency of a relative increase of CO adsorbed in the bridged position with increasing copper content.…”

Section: Xps Datamentioning

confidence: 99%

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

Shpiro¹,

Ткаченко²,

Jaeger³

et al. 1998

J. Phys. Chem. B

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Electronic and structural properties of highly dispersed Pt−Cu alloys supported on zeolite HZSM-5 with narrow particle size distribution (1−2 nm) were studied by transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy of chemisorbed carbon monoxide. FTIR of adsorbed CO proved to be the most sensitive tool for the detection of alloy formation. Dilution of the platinum surface with copper can be recognized by the absence of dipole−dipole interaction between the chemisorbed CO molecules (geometric effect). A strong red shift of the vibration frequency of linearly bonded CO in conjunction with an increase of the relative intensity of bridge-bonded CO is discussed in terms of an electronic effect. All spectroscopic methods demonstrate the ready reoxidation and redispersion of the copper component of the particles and the reversible formation of the alloy again by repeated reduction.

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Section: Resultssupporting

confidence: 56%

“…The intensity of the latter band does not change during evacuation at room temperature. Upon thermodesorption up to 473 K the band of Pt−CO is shifted by only 9 cm -1 …”

Section: Resultsmentioning

confidence: 99%

8 FTIR spectra of adsorbed CO at 300 K following reduction (523 K), reoxidation (523 K), and high-temperature reduction (623 K) of the 1% Pt−0.3% Cu/ZSM-5 sample: 1, 30 min (ca.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Xps Datamentioning

confidence: 99%

See 3 more Smart Citations

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

Shpiro¹,

Ткаченко²,

Jaeger³

et al. 1998

J. Phys. Chem. B

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Evidence for Monatomic Platinum Species in H-ZSM-5 from FTIR Spectroscopy of Chemisorbed CO

Stakheev

Shpiro

Ткаченко

et al. 1997

Journal of Catalysis

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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 Small Metallic and Bimetallic Clusters Hosted in Molecular Sieves

Cited by 9 publications

References 32 publications

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

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

Evidence for Monatomic Platinum Species in H-ZSM-5 from FTIR Spectroscopy of Chemisorbed CO

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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