Infrared Study of the Dynamics of Adsorbed Species During Co Hydrogenation

Balakos, Michael W.; Chuang, Steven S. C.; Srinivas, Girish; Brundage, Mark A.

doi:10.1006/jcat.1995.1267

Cited by 36 publications

(14 citation statements)

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“…While a few recent studies of the CO−H 2 reaction have directly measured the rate at which CO adsorbs/desorbs on the catalyst surface at higher pressures, , there has been no systematic effort made to elucidate the mechanism by which this exchange occurs. One obstacle to monitoring this process at elevated pressures has been the challenge of acquiring high-quality vibrational spectra with a rapidity sufficient to follow the switching in real time.…”

Section: Resultsmentioning

confidence: 99%

“…A major focus has been placed on the factors that determine selectivity toward any one of the numerous possible reaction products. On polycrystalline, , single-crystal, and supported Rh surfaces, − methane is predominantly formed along with much smaller amounts of other hydrocarbons. However, oxygenate formation has been observed over some types of supported Rh − and on rhodium oxide surfaces. , These investigations reveal that selectivity is highly dependent on a number of experimental parameters, including support material, temperature, pressure, and the reactant ratio utilized.…”

Section: Introductionmentioning

confidence: 99%

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Adsorption and Hydrogenation of Carbon Monoxide on Polycrystalline Rhodium at High Gas Pressures

et al. 1997

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Surface-enhanced Raman spectroscopy (SERS) in conjunction with mass spectroscopy (MS) has been utilized to investigate the adsorption and hydrogenation of carbon monoxide on polycrystalline rhodium surfaces. The SERS-active Rh substrates were prepared by electrodeposition of ultrathin films on electrochemically roughened gold and display remarkably robust SERS activity over a wide range of temperatures (up to 400 °C) and pressures (here up to 1 atm). The SER spectra reveal that CO adsorbed primarily on atop sites (νRh - C = 470 cm-1) and desorbed by about 250−300 °C under all gas-phase conditions examined. Partial dissociation of the CO adlayer, however, was obtained at temperatures as low as 100 °C, most likely facilitated by the large number of steps and kinks present on these roughened surfaces. This was evidenced by a partial removal of CO at temperatures (ca 100 °C) well below those expected for thermal desorption (200−250 °C) and supported by the observed formation of surface carbonate (665 cm-1) under these conditions. The CO dissociation, however, is hampered at lower temperatures (<200 °C) when gas-phase H2 and/or CO are present, most likely due to blocking of site ensembles necessary for decomposition to proceed. Interestingly, heating a CO adlayer in pure H2 resulted in the formation of an adsorbed oxygen species (νRh - O = 295 cm-1) at temperatures above 250 °C. The CO hydrogenation reaction was examined over a wide range of gas-phase conditions (H2:CO = 99:1 to 4:1 at 1 atm), with methane being the only hydrocarbon product detectable with MS. In addition to the presence of adsorbed CO observed up to 250 °C under all H2/CO reaction ratios, the adsorbed oxygen species noted above was detected at higher temperatures (>250 °C) when a low percentage of CO (≤1%) in the feed reactant stream was used. The influence of the adsorbed species on the overall methanation rates is discussed in light of these findings. Utilizing the seconds time-scale resolution of SERS, the exchange between gas-phase and adsorbed CO was also studied. The results of such transient 13CO/12CO exchange experiments reveal that this desorption pathway is weakly activated (≈1 kcal mol-1), first order with respect to CO coverage, yet independent of CO partial pressure in the regime studied (8−760 Torr). This contrasts the first-order pressure dependence for much lower CO partial pressures (≤10-5 Torr) reported earlier in the literature. A rate law and mechanism are proposed which account for these differences and rationalize the observed behavior.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Adsorption and Hydrogenation of Carbon Monoxide on Polycrystalline Rhodium at High Gas Pressures

et al. 1997

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“…Ni [44], Ru [45], Rh [46], Co [37,47] and Fe [48,49]. As it has been found that synthesis of methane and higher hydrocarbons are closely related [13,37,43,47,50,51], so it can be concluded that similar two reaction paths mechanism may exist in FTS for all aforementioned active metals.…”

Section: -From Ssitka Studies Two Reaction Paths For Methanation Havmentioning

confidence: 92%

Generalized kinetic model for iron and cobalt based Fischer–Tropsch synthesis catalysts: Review and model evaluation

Mousavi

Zamaniyan

Irani

et al. 2015

Applied Catalysis A: General

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“…Different CO species bonded to the surface, such as linear and bridged molecules, were found on Ni/A1 2 O 3 , 201 Ni/SiO 2 29 and Rh/SiO 2 . 202 The results showed that CO dissociation mechanism prevailed over hydrogen-assisted CO activation because no reactive H−C− O species were detected on these catalysts. The nature of the CH x pool could be further investigated using these combined techniques.…”

Section: Ssitka Coupled With Spectroscopic Techniquesmentioning

confidence: 97%

Recent Approaches in Mechanistic and Kinetic Studies of Catalytic Reactions Using SSITKA Technique

et al. 2014

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One of the most useful techniques to obtain valuable information on catalyzed heterogeneous reactions at, or near to, molecular level is the Steady-State Isotopic Transient Kinetic Analysis (SSITKA). Kinetic parameters of catalyst-surface reaction intermediates, such as concentration, site coverage, reactivity, and rate constants can be obtained and processed to provide valuable information about the reaction mechanism. This technique has been extensively tested in a wide range of different surface-catalyzed reactions, where the influence of different parameters on the intermediates has been studied (i.e., supports, active phases, particle size, addition of promoters). Progresses in the coupling of spectroscopic techniques and advanced modeling could greatly improve the understanding of the surface reaction mechanism and provide more reliable kinetic models. This review compiles the main goals achieved up to date in heterogeneous catalytic systems using SSITKA and analyzes the perspectives of this technique in the near future.

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Infrared Study of the Dynamics of Adsorbed Species During Co Hydrogenation

Cited by 36 publications

References 0 publications

Adsorption and Hydrogenation of Carbon Monoxide on Polycrystalline Rhodium at High Gas Pressures

Adsorption and Hydrogenation of Carbon Monoxide on Polycrystalline Rhodium at High Gas Pressures

Generalized kinetic model for iron and cobalt based Fischer–Tropsch synthesis catalysts: Review and model evaluation

Recent Approaches in Mechanistic and Kinetic Studies of Catalytic Reactions Using SSITKA Technique

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