Empirical estimation of desorption energies from the maxima of thermal desorption curves

Knor, Z.

doi:10.1016/0039-6028(85)90032-9

Cited by 17 publications

(12 citation statements)

References 86 publications

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“…) and uses the Redhead equation, one obtains an adsorption energy of ∼10.6 kcal/mol, which corresponds to 0.45 eV.] The calculated adsorption energy of −0.45 eV corresponds to a desorption temperature of ∼180 K, after dividing this adsorption energy by a factor of 0.0025 eV/K, in good agreement with the experimental TPD data reported by Moon et al…”

Section: Resultssupporting

confidence: 85%

“…4) and uses the Redhead equation, one obtains an adsorption energy of ∼10.6 kcal/mol, which corresponds to 0.45 eV.] The calculated adsorption energy of -0.45 eV corresponds to a desorption temperature of ∼180 K, after dividing this adsorption energy by a factor of 0.0025 eV/K, 37 in good agreement with the experimental TPD data reported by Moon et al 4 Further, the metal-CO distance is enlarged whereas the C-O distance is shortened at both sites with respect to the same adsorption configuration on the sulfur-free Fe(100) surface. Vibrational frequency calculations show that only the adsorption at 4-fold hollow sites is a minimum in the PES, whereas the CO molecule adsorbed at top sites presents an imaginary frequency, and consequently, it is a transition state in the PES (Table 3).…”

Section: Adsorption Of Co On Fe(100)-s-c(2 × 2)mentioning

confidence: 99%

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A DFT Study of the Adsorption and Dissociation of CO on Sulfur-Precovered Fe(100)

et al. 2006

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Sulfur is known to be a poison to several catalytic reactions, e.g., the Fischer-Tropsch synthesis (FTS), in which it affects drastically the performance of both iron- and cobalt-based catalysts. However, despite the importance of this industrial process, little is known about what elementary steps are poisoned by sulfur. In the present article, we report, using density functional theory, the effect of sulfur on one of the most relevant reactions in the FTS: the dissociation of carbon monoxide over iron surfaces. We have studied the adsorption and dissociation of CO on Fe(100)-S-p(2 x 2) (theta(S) = 0.25 ML) and on Fe(100)-S-c(2 x 2) (theta(S) = 0.50 ML). We have found surface configurations that correlate well with the desorption features observed in temperature-programmed desorption mass spectroscopy. In addition, we have calculated the activation energy of CO dissociation on Fe(100)-S-p(2 x 2), which, interestingly, is very similar to the activation energy of CO dissociation on the sulfur-free Fe(100) surface. However, the sign of the reaction changes by the presence of sulfur; CO dissociation is highly exothermic on the sulfur-free Fe(100) surface, whereas on the Fe(100)-S-p(2 x 2) surface, it is slightly endothermic. Moreover, according to our results, the influence of sulfur in the CO dissociation seems to be short-ranged.

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Section: Resultssupporting

confidence: 85%

Section: Adsorption Of Co On Fe(100)-s-c(2 × 2)mentioning

confidence: 99%

A DFT Study of the Adsorption and Dissociation of CO on Sulfur-Precovered Fe(100)

et al. 2006

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“…650 K using the 0.0025 eV/K factor discussed above. 57 This temperature is significantly higher than that reported by several groups for CO(R 2 ), which lies between 360 and 450 K. 35,[37][38][39]71,72 This discrepancy contrasts with the excellent agreement obtained above for CO(β). The origin of this discrepancy might be that the 0.0025 eV/K conversion factor cannot be applied indistinctly to both CO adsorption states.…”

Section: Resultsmentioning

confidence: 79%

“…Moreover, it is worth mentioning that once a substantial fraction of CO has dissociated the adsorption energy of the remaining CO molecules decreases to -2.46 eV. This is around 0.55 eV lower for both the adsorption of CO molecules after pre-adsorption of 0.25 ML CO and the adsorption energy of CO at a surface coverage of 0.25 ML, and corresponds to a desorption temperature of around 980 K. 57 Comparison of CO Dissociation Calculations with Experiments. The calculated activation energy of CO dissociation on W(100) at a surface coverage of 0.25 ML is 0.31 eV, which corresponds to a temperature of around 120 K. This agrees quite nicely with experimental CO dissociation temperatures reported to be as low as 80 K. 38,40 On the other hand, the calculated apparent recombination energy is much smaller (196 kJ mol -1 ) than the values given in literature (347 kJ mol -1 ).…”

Section: Resultsmentioning

confidence: 94%

“…For tungsten, this value is 0.0025 eV K -1 . Thus, the desorption temperature ( T m ) corresponds to approximately 1200 K. For further details regarding the relation of desorption temperatures to adsorption energies, we refer to the article by Knor and references therein. According to Wang et al, the only desorption feature present at this surface coverage is the β 3 desorption peak.…”

Section: Resultsmentioning

confidence: 99%

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Adsorption, Desorption, and Dissociation of CO on Tungsten(100), a DFT Study

2008

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Density functional theory (DFT) calculations have been performed to investigate the adsorption of CO on W(100) for several adsorption sites at four different surface coverages. Dissociation of CO on W(100) has been explored for two surface concentrations: 0.25 and 0.5 monolayer (ML). To establish whether the calculated structures are stable adsorption states or transition states, a complete analysis of the vibrational frequencies of CO was carried out. For coverages up to 0.5 ML, the CO adsorbs molecularly on the W(100) surface at fourfold hollow sites with the molecular axis tilted away from the surface normal by 58°with an adsorption energy of -3.00 eV. The calculated C-O stretching frequency at 0.25 ML CO coverage is 926 cm -1 , in good agreement with experiments. Increasing CO coverage to 0.5 ML leads to a lower C-O stretching frequency of 847 cm -1 , which is extraordinary, since it is not expected from previous experimental observations. The CO is able to dissociate very easily with activation energies of only 0.25-0.31 eV, which results in an energy gain of 1.72 and 0.69 eV at 0.25 and 0.5 ML, after dissociation, respectively. In addition, calculations reveal that reported β CO desorption peaks in literature are due to molecular desorption of tilted CO at the fourfold hollow sites and are not limited by C + O recombination, as was concluded experimentally.

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FEM study of palladium and molybdenum clusters on an alumina covered field emitter

Šotola

Knor

1993

Czech J Phys

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Empirical estimation of desorption energies from the maxima of thermal desorption curves

Cited by 17 publications

References 86 publications

A DFT Study of the Adsorption and Dissociation of CO on Sulfur-Precovered Fe(100)

A DFT Study of the Adsorption and Dissociation of CO on Sulfur-Precovered Fe(100)

Adsorption, Desorption, and Dissociation of CO on Tungsten(100), a DFT Study

FEM study of palladium and molybdenum clusters on an alumina covered field emitter

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