Reactions of Methanol with Pristine and Defective Ceria (111) Surfaces: A Comparison of Density Functionals

Kropp, Thomas; Paier, Joachim

doi:10.1021/jp505088b

Cited by 34 publications

(98 citation statements)

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“…At the (111) surface, entropy contributions for this reaction amount to −TΔS = −0.56 eV (300 K, 0.1 MPa). 41 These two competitive pathways give rise to different products, but computation of their precise ratio is beyond the scope of the present work. This would require accurate desorption barriers that include temperature effects.…”

Section: Resultsmentioning

confidence: 99%

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Activity versus Selectivity of the Methanol Oxidation at Ceria Surfaces: A Comparative First-Principles Study

Kropp

Paier

2015

J. Phys. Chem. C

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Ceria nanoparticles may expose (100) and (111) facets depending on the preparation method. Motivated by that, we study the reactions of methanol with the CeO 2 (100) surface using dispersion-corrected PBE+U subject to periodic boundary conditions and compare with results for the CeO 2 (111) surface. At (100) facets, the oxidative dehydrogenation of methanol to formaldehyde occurs with an intrinsic barrier of only 0.94 eV (91 kJ/mol), which is significantly lower than the corresponding barrier of 1.23 eV (119 kJ/mol) at the (111) surface. The lower barrier maps to lower formaldehyde desorption temperatures as observed in temperature-programmed desorption spectroscopy. The higher activity is in accordance with predicted lower oxygen defect formation energy in the (100) surface. Thus, defect formation energies are valid reactivity descriptors for oxidation reactions following a Mars-van Krevelen mechanism. At both surfaces, formaldehyde either desorbs or forms a bridging dioxymethylene intermediate, which can be further oxidized into carbon oxides. However, formaldehyde desorption from the (100) surface is significantly more endothermic. Thus, methanol oxidation at the (100) surface is predicted to yield both formaldehyde and carbon oxides, whereas at the (111) surface, formaldehyde can easily desorb. Therefore, the desorption step appears to be the key to the selectivity of methanol oxidation to formaldehyde.

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Section: Resultsmentioning

confidence: 99%

“…65), which correlates with lower coordination numbers of the surface oxygen ions at the (100) surface (CN = 2 compared to CN = 3 at the (111) surface). At the (111) surface, two nextnearest neighbor Ce 3+ ions are favored, 41 but at the (100) surface two nearest neighbor Ce 3+ ions are favored (cf. Figure 3).…”

Section: Resultsmentioning

confidence: 99%

Activity versus Selectivity of the Methanol Oxidation at Ceria Surfaces: A Comparative First-Principles Study

Kropp

Paier

2015

J. Phys. Chem. C

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“…65,78 The resulting chemisorbed HCHO binds rather strongly, 1.23 eV, therefore allowing an eventual subsequent conversion to CO.…”

Section: Resultsmentioning

confidence: 99%

Descriptor Analysis in Methanol Conversion on Doped CeO₂(111): Guidelines for Selectivity Tuning

Capdevila‐Cortada

López

2015

ACS Catal.

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ABSTRACT:Descriptors are crucial to systematize and optimize activity, selectivity, and stability of catalysts. Adsorption energies have usually been taken as the main representative parameter that can summarize reaction energies and activation barriers for simple reactions on relatively simple reaction sites. However, more chemically sound terms, which can be directly mapped to experiments, would be more desirable.Besides, larger molecules with more than one potentially active position and complex sites, like the acid-base pairs present in oxides, are typically beyond the scope provided by common linear-scaling methods. In the present work, we have analyzed the selectivity of the conversion of a polyfunctional molecule on a complex oxide that presents both acid-base and redox chemistry. The conversion of methanol to formaldehyde or CO on isovalently doped ceria (111) has been taken as an example.The selectivity towards CO is triggered by the competition between formaldehyde desorption and C-H cleavage. Our results show that, by introducing dopant cations, the activation energy of the first H-stripping of formaldehyde can be decreased so that its conversion becomes favorable over desorption for Zr, Hf doped systems and expanded lattice ceria. More importantly, desorption is controlled by geometric and acid-base factors, whereas C-H cleavage is exclusively electronically governed through acid-base and redox factors. Thus, both geometric and electronic structure parameters are needed to optimize the performance of ceria to attain the desired selectivity. Selectivity is then estimated by a collective descriptor of the surface that incorporates the ensemble size, acid-base, and redox contributions that can be directly compared to experimental values. In addition, this scaling relationship reduces the error associated to more traditional energy-based descriptors. We can anticipate that the present scheme can be extended to metal oxides and other polyfunctionalized catalysts.2

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“…Despite all the above and other theoretical works reported in the literature [37][38][39][40][41][42], up to date there is no complete study assessing the selectivity of methanol dehydrogenation on the most representative ceria facets and proving their different behavior as experimentally observed. Herein, we present a thorough mechanistic study on the selective conversion of methanol to formaldehyde and its subsequent conversion to CO. To account for the particular morphology of the three common nanoshapes above, we have studied the three lowest index and energy surfaces (111), (110), and (100) (Fig.…”

Section: Introductionmentioning

confidence: 94%

Unraveling the structure sensitivity in methanol conversion on CeO2: A DFT+U study

Capdevila‐Cortada

García‐Melchor

López

2015

Journal of Catalysis

108

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Highlights:-Structure sensitivity correlates with the surface oxygen content in the methanol decomposition on ceria.-Methanol selectively converts to formaldehyde on ceria (111) and (110) facets.-The CeO 2 (100) facet traps formaldehyde and ultimately enables its oxidation to produce CO+H 2 .-Hydrogen evolution is permitted on (100) due to its ability to stabilize a hydrogen precursor.-Formaldehyde can easily exchange its oxygen with the lattice in all facets. 2 ABSTRACTMethanol decomposes on oxides, in particular CeO 2 , producing either formaldehyde or CO as main products. This reaction presents structure sensitivity to the point that the major product obtained depends on the facet exposed in the ceria nanostructures. Our Density Functional Theory (DFT) calculations illustrate how the control of the surface facet and its inherent stoichiometry determine the sole formation of formaldehyde on the closed surfaces or the more degraded byproducts on the open facets (CO and hydrogen). In addition, we found that the regular (100) termination is the only one that allows hydrogen evolution via a hydride-hydroxyl precursor. The fundamental insights presented for the differential catalytic reactivity of the different facets agree with the structure sensitivity found for ceria catalysts in several reactions and provide a better understanding on the need of shape control in selective processes.3

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Reactions of Methanol with Pristine and Defective Ceria (111) Surfaces: A Comparison of Density Functionals

Cited by 34 publications

References 100 publications

Activity versus Selectivity of the Methanol Oxidation at Ceria Surfaces: A Comparative First-Principles Study

Activity versus Selectivity of the Methanol Oxidation at Ceria Surfaces: A Comparative First-Principles Study

Descriptor Analysis in Methanol Conversion on Doped CeO₂(111): Guidelines for Selectivity Tuning

Unraveling the structure sensitivity in methanol conversion on CeO2: A DFT+U study

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Reactions of Methanol with Pristine and Defective Ceria (111) Surfaces: A Comparison of Density Functionals

Cited by 34 publications

References 100 publications

Activity versus Selectivity of the Methanol Oxidation at Ceria Surfaces: A Comparative First-Principles Study

Activity versus Selectivity of the Methanol Oxidation at Ceria Surfaces: A Comparative First-Principles Study

Descriptor Analysis in Methanol Conversion on Doped CeO2(111): Guidelines for Selectivity Tuning

Unraveling the structure sensitivity in methanol conversion on CeO2: A DFT+U study

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Descriptor Analysis in Methanol Conversion on Doped CeO₂(111): Guidelines for Selectivity Tuning