Digital temperature programmer for isothermal and thermal desorption measurements

Muha, R. J.; Gates, S. M.; Yates, John T.; Basu, P.

doi:10.1063/1.1138298

Cited by 104 publications

(44 citation statements)

References 13 publications

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“…The grid was secured by nickel clamps and mounted on electrical feedthroughs mounted on the bottom of a reentrant Dewar. The sample was heated electrically using a digital temperature programmer/controller and cooled by filling the reentrant Dewar with liquid nitrogen. Sample temperatures were measured by a K-type thermocouple spot welded on the top center of the tungsten grid.…”

Section: Methodsmentioning

confidence: 99%

Nitrogen Chemisorption on the Coordinatively Unsaturated Rh Site on Al₂O₃

Wovchko

Yates

1996

J. Am. Chem. Soc.

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The UV (3.8 eV) photolysis of atomically-dispersed Rh I (CO) 2 species supported on an Al 2 O 3 surface in the presence of N 2 at 175 K caused the replacement of CO by N 2 ligands. Therefore dinitrogen chemisorption effectively probes the coordinatively unsaturated Rh(CO) species generated during photodecomposition of Rh I (CO) 2 / Al 2 O 3 . Two infrared bands, observed at 2234 and 2048 cm -1 , are attributed respectively to ν N2 and ν CO in Rh(N 2 )(CO), and a band at 2188 cm -1 is assigned to Rh(N 2 ) 2 surface species. The assignments are based on frequencies and the relative rates of spectral development for the two N 2 -containing species. The Rh(N 2 ) 2 species on Al 2 O 3 exhibits identical N-N stretching modes to a similar species produced by matrix isolation methods. It is shown that both the Rh-CO bond and the Rh-N 2 bond may be broken by photolysis.

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Section: Methodsmentioning

confidence: 99%

Nitrogen Chemisorption on the Coordinatively Unsaturated Rh Site on Al₂O₃

Wovchko

Yates

1996

J. Am. Chem. Soc.

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“…Using an electronic temperature controller, a constant sample temperature (from 150 to 1400 K, within ±1 K) can be maintained by passing electrical current and using liquid nitrogen coolant. 45 The IR cell is connected to a stainless steel vacuum system (base pressure < 1 x 10-s Torr) which is pumped by a 60 L s"1 turbomolecular pump and a 30 L s-1 ion pump. The system also contains a differentially pumped Dycor M100M quadrupole mass spectrometer and an MKS 116A Baratron capacitance manometer (range: 10-3 to 103 Torr).…”

Section: Methodsmentioning

confidence: 99%

“…After the sprayed powder deposit (RhCf/AhOd was mounted into the IR cell, the powder was outgassed in situ at 475 K for at least 12 h under vacuum before reduction. Reduction was carried out at 475 K with four exposures (15,30,45, and 60 min) of 200 Torr of hydrogen gas (Matheson 99.9995% pure); the cell was evacuated for 15 min after each exposure. Then the fully-reduced sample (Rh/ALO/) was allowed to outgas under vacuum at 475 K for another 12 h. Before the photo- reaction studies were carried out, the metallic Rh deposit was converted to Rh'fCO);) by CO adsorption.…”

Section: Methodsmentioning

confidence: 99%

Heterogeneous Photochemical Activation of Methane on a Rhodium Catalyst. Formation of an Acetyl Moiety on the Surface

Wong¹,

Yates²

1995

J. Phys. Chem.

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The photochemical activation of methane over a substrate containing Rh'(C0)z species has been studied using transmission infrared spectroscopy. At 233 K, methane activation is achieved by the oxidative addition of the C-H bond to a postulated 16-electron surface species, Rh'(CO), which is produced by UV (325 nm) photodecomposition of the Rh1(CO)2 on the surface. The oxidative addition product, Rh(CO)(H)(CH3), further undergoes a migratory-insertion reaction in the presence of CO to form a proposed Rh(CO)(H)(COCH3) surface species. Isotopic experiments using CI8O have been performed to confirm the product assignment.An IR spectroscopic study of acetaldehyde and acetone adsorption following the photoreaction suggests that other CH3CO-containing species may also be formed on the surface as a result of C-H bond activation followed by CH3 insertion into the Rh-CO bond region.

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“…The grid and sample could be heated electrically using a digital temperature programmer/controller. 28 Sample cooling was achieved by filling the reentrant Dewar with liquid nitrogen. A K-type thermocouple spot welded on the top center of the tungsten grid measured sample temperatures.…”

Section: Infrared Experimentsmentioning

confidence: 99%

Electronic Excitation of Rh^I(CO)₂ Species on Al₂O₃ Surfaces: Photodissociation of the Rh^I−CO Bond

1998

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The photoexcitation of Rh I (CO) 2 /Al 2 O 3 has been studied by infrared and ultraviolet absorption spectroscopy. A photodissociation energy threshold between 2.8 and 2.9 eV, for the Rh I -CO bond of the Rh I (CO) 2 species, has been determined by monitoring the depletion of the CO moiety, leading to the production of a highly active surface site. A Rh I -CO photodissociation cross section of 3.6 × 10 -20 cm 2 photon -1 and a quantum efficiency of 0.01 [Rh I -CO dissociation] photon -1 has been estimated for the initial stages of Rh I (CO) 2 photodepletion. Three absorption bands, observed at 3.3, 3.9, and 4.6 eV in the ultraviolet absorption spectra, are assigned to electronic transitions from filled Rh d-character molecular orbitals to d-character and/or ligandbased antibonding orbitals. Photodissociation of the Rh I -CO bond occurs from the direct excitation of Rh I -(CO) 2 species. During later stages of photolysis, the role of depletion of Rh I (CO) 2 decreases dramatically and this effect may be due to the slow diffusion of CO through the pores of the Al 2 O 3 support.

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Digital temperature programmer for isothermal and thermal desorption measurements

Cited by 104 publications

References 13 publications

Nitrogen Chemisorption on the Coordinatively Unsaturated Rh Site on Al₂O₃

Nitrogen Chemisorption on the Coordinatively Unsaturated Rh Site on Al₂O₃

Heterogeneous Photochemical Activation of Methane on a Rhodium Catalyst. Formation of an Acetyl Moiety on the Surface

Electronic Excitation of Rh^I(CO)₂ Species on Al₂O₃ Surfaces: Photodissociation of the Rh^I−CO Bond

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Digital temperature programmer for isothermal and thermal desorption measurements

Cited by 104 publications

References 13 publications

Nitrogen Chemisorption on the Coordinatively Unsaturated Rh Site on Al2O3

Nitrogen Chemisorption on the Coordinatively Unsaturated Rh Site on Al2O3

Heterogeneous Photochemical Activation of Methane on a Rhodium Catalyst. Formation of an Acetyl Moiety on the Surface

Electronic Excitation of RhI(CO)2 Species on Al2O3 Surfaces: Photodissociation of the RhI−CO Bond

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Product

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Nitrogen Chemisorption on the Coordinatively Unsaturated Rh Site on Al₂O₃

Nitrogen Chemisorption on the Coordinatively Unsaturated Rh Site on Al₂O₃

Electronic Excitation of Rh^I(CO)₂ Species on Al₂O₃ Surfaces: Photodissociation of the Rh^I−CO Bond