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1.
Sci Adv ; 6(1): eaay4289, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31922009

RESUMO

The free-standing Au20 cluster has a unique tetrahedral shape and a large HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gap of around 1.8 electron volts. The "magic" Au20 has been intensively used as a model system for understanding the catalytic and optical properties of gold nanoclusters. However, direct real-space ground-state characterization at the atomic scale is still lacking, and obtaining fundamental information about the corresponding structural, electronic, and dynamical properties, is challenging. Here, using cluster-beam deposition and low-temperature scanning tunneling microscopy, atom-resolved topographic images and electronic spectra of supported Au20 clusters are obtained. We demonstrate that individual size-selected Au20 on ultrathin NaCl films maintains its pyramidal structure and large HOMO-LUMO gap. At higher cluster coverages, we find sintering of the clusters via Smoluchowski ripening to Au20n agglomerates. The evolution of the electron density of states deduced from the spectra reveals gap reduction with increasing agglomerate size.

2.
J Chem Phys ; 151(22): 224705, 2019 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-31837688

RESUMO

The surface basicity of the alkaline-earth metal oxides has been investigated by studying the properties of 17O nuclear magnetic resonance (NMR). To this end, we performed density functional theory calculations and determined the 17O chemical shift and the quadrupolar coupling constants of the regular and stepped surfaces of MO (M = Mg, Ca, Sr, and Ba) oxides. The computed average chemical shift (δiso av) for 17O NMR of bulk MgO, CaO, SrO, and BaO is 46, 301, 394, and 636 ppm, respectively, in excellent agreement with the experiment. The 17O NMR chemical shifts correlate linearly with the Madelung potential in the four oxides. Next, we considered the changes in the 17O chemical shift due to the adsorption of BR3 (R = F and OCH3) and pyrrole as probe molecules. We found that the 17O NMR signal of the O ion directly bound to the probe molecule shifts considerably compared to the clean surface. This is due to a change in the polarization of the O charge distribution due to the molecular adsorption. This change is the largest for BaO, with the strongest bond and the shortest surface-adsorbate distance, and the smallest for MgO, thus showing a direct correlation between 17O NMR and surface basicity. The 17O chemical shift of the basic site correlates linearly also with several properties of the adsorbed molecules, providing a direct measure of the surface basicity.

3.
J Chem Phys ; 151(23): 234708, 2019 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-31864260

RESUMO

Calcium-molybdate ultrathin films were prepared on a Mo(001) crystal and characterized by means of scanning tunneling microscopy (STM), electron diffraction, photoelectron spectroscopy, and density functional theory (DFT). The films were grown via reactive Ca deposition, followed by a vacuum annealing step to trigger Mo diffusion from the support into the Ca-O ad-layer. A series of crystalline oxide configurations was revealed that evolves from a (3 × 3) to a (4 × 4) and (6 × 6) superstructure with increasing annealing temperature and finally decays to a binary MoOx phase. The stoichiometry of the initial (3 × 3) phase was estimated to CaMo3O6, yet with decreasing Ca concentration at higher temperature. In the search for a suitable structure model for DFT calculations, we have started with a bulk CaMo5O8 configuration that was iteratively modified to match the experimental data. The optimized structure is made of regular sequences of flat-lying and upright standing Mo octahedrons, being separated from each other by Ca2+ ion rows. With decreasing Ca content, the central Mo units grow in size, which explains the observed transition from (3 × 3) to (6 × 6) superstructures upon annealing. The proposed structure model rationalizes the periodicity and corrugation of the regular oxide surface as well as the characteristic domain patterns in the film. Its electronic properties, as deduced from STM conductance spectroscopy, can be correlated with an increasing metallicity of the ad-layer upon annealing. Our work presents a facile pathway to produce high-quality ternary oxide films via interdiffusion of atoms from a suitable metal support into a binary oxide layer.

4.
J Chem Theory Comput ; 15(11): 6294-6312, 2019 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-31614082

RESUMO

Reproduction of the band gaps of semiconductors and insulators represents a well-known problem for standard DFT approaches based on semilocal functionals. The problem can be partly solved using hybrid functionals, in which a given portion of exact exchange is mixed with the DFT exchange. Recently, a new class of dielectric-dependent functionals has been introduced in which the amount of exact exchange is derived from the static dielectric function of a given compound. In this study we considered in a systematic way on an equal footing a set of 24 nonmagnetic three-dimensional (3D) bulk metal oxides and 24 quasi-two-dimensional (quasi-2D) semiconductors (oxides, hydroxides, chlorides, oxyhalides, nitrides, and transition metal dichalcogenides) and computed the corresponding Kohn-Sham band gaps with three global hybrid functionals and four range-separated hybrid functionals. These in turn were divided into standard (PBE0, B3LYP, HSE06, SC-BLYP) and dielectric-dependent (DD-B3LYP, DD-SC-BLYP, DD-CAM-B3LYP) functionals. We also performed a statistical analysis of the DFT data set along with structural parameters of these 2D and 3D materials. The surprising result is that overall there is no real improvement with the use of dielectric-dependent functionals compared to PBE0, HSE06, and B3LYP. Short-range DD-SC-BLYP gives a minor improvement in the band gaps for bulk metal oxides compared with standard SC-BLYP, but the mean absolute error is still 0.12 eV higher than with B3LYP. The use of dielectric-dependent standard or short-range functionals such as DD-B3LYP or DD-HSE06 worsens the situation. However, the dielectric-dependent version of the long-range-separated functional implemented with the Coulomb attenuating method (CAM), DD-CAM-B3LYP, leads to a clear improvement for band gaps of quasi-2D materials. On the basis of this analysis, the conclusion is that the use of a standard hybrid functional such as B3LYP or HSE06 is recommended for nonmagnetic bulk 3D metal oxides. On the other hand, the treatment of layered materials such as MoO3 or V2O5 benefits from the use of dielectric-dependent range-separated functionals.

5.
Phys Chem Chem Phys ; 21(38): 21497-21505, 2019 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-31535113

RESUMO

In this work we study the effect of nitrogen (N)-doping on the structural and electronic properties of coexposed anatase (001)-(101) surfaces by means of Density Functional Theory (DFT). This work is motivated by recent experiments, showing that these materials are highly active for photocatalysis. The introduction of doping species such as N further improves their activity under visible light. Our results indicate a tendency toward dopant segregation at the interface at low N concentrations, while at larger concentrations also doping sites in the bulk regions are populated. N-Doping does not affect the reciprocal band alignment of TiO2(101) and (001), where the former stabilizes photogenerated electrons and the latter hosts the holes. However, N-doping enhances the visible light absorption of the composite material, due to the introduction of gap states. Moreover, N-doping strongly stabilizes oxygen vacancies, which in turn enhance the light absorption properties.

6.
J Phys Condens Matter ; 31(43): 434001, 2019 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-31282386

RESUMO

The valence and conduction band (CB) alignments and the nature of the WO3/BiVO4 heterojunction have been analysed in detail based on hybrid functionals density functional theory calculations. The WO3/BiVO4 junction is widely studied in photocatalysis for its capability to reduce electron-hole recombination and to improve efficiency. This is assumed to be due to a favourable band alignment of the junction's components, which generates a flow of negative charge carriers towards WO3, and positive ones towards BiVO4. This conclusion is often based on the properties of the two isolated, non-interacting units. Here, we propose an explicit interface model where the (0 0 1) surface of WO3 is put in contact with the (0 1 0) surface of BiVO4 rotated by about 45°, which leads to a small strain and a favourable cation-anion matching. The interface displays a moderate charge transfer and a small interface dipole. This leads to only moderate effects on the band alignment, which remains qualitatively similar to that obtained from the two independent oxides. We also considered in detail the role of the amount of exact exchange used in the description of the heterojunction, and in particular of the BiVO4 component, for which rather different hybrid functional approaches have been proposed in the literature.

7.
Angew Chem Int Ed Engl ; 58(32): 10903-10908, 2019 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-31050096

RESUMO

A new two-dimensional (2D) germanium dioxide film has been prepared. The film consists of interconnected germania tetrahedral units forming a bilayer structure, weakly coupled to the supporting Pt(111) metal-substrate. Density functional theory calculations predict a stable structure of 558-membered rings for germania films, while for silica films 6-membered rings are preferred. By varying the preparation conditions the degree of order in the germania films is tuned. Crystalline, intermediate ordered and purely amorphous film structures are resolved by analysing scanning tunnelling microscopy images.

8.
J Phys Chem Lett ; 10(10): 2372-2377, 2019 May 16.
Artigo em Inglês | MEDLINE | ID: mdl-31018090

RESUMO

A heterojunction made by coexposed anatase (001)-(101) surfaces is studied using an explicit atomistic model of the interface via density functional theory. High photoactivity for this system has been demonstrated recently. Usually, the nature of a semiconductor heterojunction is evaluated by looking at band edges of the separate, noninteracting units, thus neglecting interfacial effects. Our results show non-negligible structural and electronic effects occurring at the junction, but because of the canceling nature of these effects, the alignment of the bands is qualitatively similar for the real interface and for the separated, noninteracting fragments. We also show from first principles that upon light absorption and electron excitation, the junction promotes charge carrier separation via localization of holes at O ions of the (001) side and electrons at Ti ions of the (101) side of the junction. This hinders recombination and is most likely the reason for high photoactivity.

9.
Nat Mater ; 18(7): 746-751, 2019 07.
Artigo em Inglês | MEDLINE | ID: mdl-31011216

RESUMO

The use of oxide-supported isolated Pt-group metal atoms as catalytic active sites is of interest due to their unique reactivity and efficient metal utilization. However, relationships between the structure of these active sites, their dynamic response to environments and catalytic functionality have proved difficult to experimentally establish. Here, sinter-resistant catalysts where Pt was deposited uniformly as isolated atoms in well-defined locations on anatase TiO2 nanoparticle supports were used to develop such relationships. Through a combination of in situ atomic-resolution microscopy- and spectroscopy-based characterization supported by first-principles calculations it was demonstrated that isolated Pt species can adopt a range of local coordination environments and oxidation states, which evolve in response to varied environmental conditions. The variation in local coordination showed a strong influence on the chemical reactivity and could be exploited to control the catalytic performance.

10.
J Phys Condens Matter ; 31(14): 145503, 2019 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-30650395

RESUMO

CuWO4 is a semiconducting oxide with interesting applications in photocatalysis. In this paper we present an accurate study of the electronic properties of stoichiometric and oxygen deficient CuWO4 based on a dielectric dependent hybrid density functional. In CuWO4 the Cu ions (Cu2+) are in a 3d9 configuration, so that the material must be classified as a magnetic insulator. Various magnetic configurations of CuWO4 have been considered, the most stable configuration being anti-ferromagnetic. The band structure, described in terms of density of states (DOS), exhibit the presence of a wide band dominated by W 5d states, separated by about 5 eV from the top of the valence band (VB), consisting of O 2p states partly mixed with Cu 3d states. The empty component of the Cu 3d orbitals forms a narrow band 3.6 eV above the VB maximum. The electronic structure emerging from the DOS curves and the Kohn-Sham energies is hard to reconcile with an experimental band gap of 2.1-2.3 eV. This gap can be rationalized within the Mott-Hubbard model of magnetic insulators, and has been computed from the total energies of the system with one electron removed from the O 2p band and one electron added to the Cu 3d states. Computing the charge transition levels for CuWO4, we come to a theoretical band gap of 2.1 eV, in excellent agreement with the experimental observations. We also studied the nature of the oxygen vacancy in CuWO4 with particular attention to the electron redistribution following the oxygen removal. The excess electrons, in fact, can occupy the localized 3d states of Cu or the localized 5d states of W. The resulting solution depends on various factors, including the concentration of oxygen vacancies.

11.
Phys Chem Chem Phys ; 21(1): 369-377, 2018 Dec 19.
Artigo em Inglês | MEDLINE | ID: mdl-30525148

RESUMO

The effect of doping with group-III metals (Al, Ga and In) and Cu free standing and Cu(111) supported ZnO bilayer films has been investigated computationally by using the DFT+U method including dispersion contributions. The changes in the electronic properties of doped ZnO and ZnO/Cu(111) films have been tested by adsorbing CO probe molecules. The replacement of a lattice Zn ion in a free-standing ZnO bilayer by a group-III element generates an extra electron whose distribution depends on the dopant. In particular, while the excess electron is delocalized over the conduction band for Al or Ga doping, it is localized on the dopant in the case of In. The situation is different on the supported ZnO/Cu(111) film, where the extra electron is transferred to the underlying Cu support. While the CO adsorption energy at the doped sites in the ZnO bilayer is the same as in the ZnO/Cu(111) ultrathin films, CO exhibits a larger red-shift in the unsupported ZnO bilayer. The oxidation state of Cu replacing Zn in the unsupported ZnO films is 2+, Cu(3d9) state, while it is 1+, Cu(3d10) state, in the ZnO/Cu(111) supported films where a charge transfer from the supporting Cu metal to the Cu impurity occurs. Cu doping results in a stronger interaction with CO and a large red-shift of the CO stretching frequency. In this respect, Cu doping of ZnO/Cu(111) bilayer films could have interesting consequences in gas adsorption while doping with group-III elements does not lead to major changes of the adsorption properties when the free-standing ZnO films are compared to the supported ZnO/Cu(111) counterparts.

12.
Chem Soc Rev ; 47(22): 8474-8502, 2018 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-29697127

RESUMO

Model systems are very important to identify the working principles of real catalysts, and to develop concepts that can be used in the design of new catalytic materials. In this review we report examples of the use of model systems to better understand and control the occurrence of charge transfer at the interface between supported metal nanoparticles and oxide surfaces. In the first part of this article we concentrate on the nature of the support, and on the basic difference in metal/oxide bonding going from a wide-gap non-reducible oxide material to reducible oxide semiconductors. The roles of oxide nanostructuring, bulk and surface defectiveness, and doping with hetero-atoms are also addressed, as they are all aspects that severely affect the metal/oxide interaction. Particular attention is given to the experimental measures of the occurrence of charge transfer at the metal/oxide interface. In this respect, systems based on oxide ultrathin films are particularly important as they allow the use of scanning probe spectroscopies which, often in combination with other measurements and with first principles theoretical simulations, allow full characterization of small supported nanoparticles and their charge state. In a few selected cases, a precise count of the electrons transferred between the oxide and the supported nanoparticle has been possible. Charge transfer can occur through thin, two-dimensional oxide layers also thanks to their structural flexibility. The flow of charge through the oxide film and the formation of charged adsorbates are accompanied in fact by a substantial polaronic relaxation of the film surface which can be rationalized based on electrostatic arguments. In the final part of this review the relationships between model systems and real catalysts are addressed by discussing some examples of how lessons learned from model systems have helped in rationalizing the behavior of real catalysts under working conditions.

13.
Nanoscale ; 10(5): 2363-2370, 2018 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-29328339

RESUMO

Au nanoparticles represent the most remarkable example of a size effect in heterogeneous catalysis. However, a major issue hindering the use of Au nanoparticles in technological applications is their rapid sintering. We explore the potential of stabilizing Au nanoclusters on SiO2 by alloying them with a reactive metal, Ti. Mass-selected Au/Ti clusters (400 000 amu) and Au2057 clusters (405 229 amu) were produced with a magnetron sputtering, gas condensation cluster beam source in conjunction with a lateral time-of-flight mass filter, deposited onto a silica support and characterised by XPS and LEIS. The sintering dynamics of mass-selected Au and Au/Ti alloy nanoclusters were investigated in real space and real time with atomic resolution aberration-corrected HAADF-STEM imaging, supported by model DFT calculations. A strong anchoring effect was revealed in the case of the Au/Ti clusters, because of a much increased local interaction with the support (by a factor 5 in the simulations), which strongly inhibits sintering, especially when the clusters are more than ∼0.60 nm apart. Heating the clusters at 100 °C for 1 h in a mixture of O2 and CO, to simulate CO oxidation conditions, led to some segregation in the Au/Ti clusters, but in line with the model computational investigation, Au atoms were still present on the surface. Thus size-selected, deposited nanoalloy Au/Ti clusters appear to be promising candidates for sustainable gold-based nanocatalysis.

14.
ACS Omega ; 3(5): 5301-5307, 2018 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-31458739

RESUMO

Bulk ZrO2 is both nonreducible and nonmagnetic. Recent experimental results show that dopant-free, oxygen-deficient ZrO2-x nanostructures exhibit a ferromagnetic behavior at room temperature (RT). Here, we provide a comprehensive theoretical foundation for the observed RT ferromagnetism of zirconia nanostructures. ZrO2 nanoparticles containing up to 700 atoms (3 nm) have been studied with the help of density functional theory. Oxygen vacancies in ZrO2 nanoparticles form more easily than in bulk zirconia and result in electrons trapped in 4d levels of low-coordinated Zr ions. Provided the number of these sites exceeds that of excess electrons, the resulting ground state is high spin and the ordering is ferromagnetic. The work provides a general basis to explain magnetism in intrinsically nonmagnetic oxides without the help of dopants.

15.
Philos Trans A Math Phys Eng Sci ; 376(2110)2018 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-29175816

RESUMO

Biomass refers to plant-based materials that are not used for food or feed. As an energy source, lignocellulosic biomass (lignin, cellulose and hemicellulose) can be converted into various forms of biofuel using thermal, chemical and biochemical methods. Chemical conversion implies the use of solid catalysts, usually oxide materials. In this context, reducible oxides are considered to be more active than non-reducible oxides. But why? Using density functional theory DFT + U calculations with the inclusion of dispersion forces, we describe the properties of anatase TiO2, a reducible oxide, and tetragonal ZrO2, a non-reducible oxide, the (101) surfaces in this context. In particular, we focus on the role of surface reduction, either by direct creation of oxygen vacancies via O2 desorption, or by treatment in hydrogen. We show that the presence of reduced centres on the surface of titania or zirconia (either Ti3+ or Zr3+ ions, or oxygen vacancies) results in lower barriers and more stable intermediates in two key reactions in biomass catalytic conversion: ketonization of acetic acid (studied on ZrO2) and deoxygenation of phenol (studied on TiO2). We discuss the role of Ru nanoparticles in these processes, and in particular in favouring H2 dissociation and hydrogen spillover, which results in hydroxylated surfaces. We suggest that H2O desorption from the hydroxylated surfaces may be a relevant mechanism for the regeneration of oxygen vacancies, in particular on low-coordinated sites of oxide nanoparticles. Finally, we discuss the role of nanostructuring in favouring oxide reduction, by discussing the properties of ZrO2 nanoparticles of diameter of about 2 nm.This article is part of a discussion meeting issue 'Providing sustainable catalytic solutions for a rapidly changing world'.

16.
ACS Appl Mater Interfaces ; 9(27): 23212-23221, 2017 Jul 12.
Artigo em Inglês | MEDLINE | ID: mdl-28622467

RESUMO

The nature of the interaction of water with the WO3 surface is of crucial importance for the use of this semiconductor oxide in photocatalysis. In this work, we investigate water adsorption and dissociation on both clean and O-deficient (001) WO3 surfaces by means of an accurate DFT approach. The O vacancy formation energy (computed with respect to O2) has been evaluated for all possible surface configurations, and the removal of the terminal O atom along the c axis is found to be preferred, costing about half the corresponding energy in the bulk. The presence of oxygen vacancies leads to a semiconductor to metal transition, confirming the experimental evidence of n-type conductivity in defective WO3 films. H2O preferably adsorbs on WO3 in a molecular undissociated form, due to the presence of W ions at the surface that act as Lewis acid sites. This interaction, about -1 eV per H2O molecule, is not very strong. Contrary to what is usually expected, the presence of oxygen vacancies does not significantly affect H2O adsorption. Finally, we investigated the H2O desorption from a hydroxylated surface. This suggests that the exposure of WO3 to H2 directly results in a hydroxylated surface and the corresponding H2O desorption turns out to be a very efficient mechanism to generate a reduced oxide surface, with important consequences on the electronic structure of this oxide.

17.
Nanoscale ; 9(20): 6866-6876, 2017 May 25.
Artigo em Inglês | MEDLINE | ID: mdl-28497820

RESUMO

Oxide reducibility is an important property that determines the chemical and physical behavior of the materials under working conditions. Zirconia is a non-reducible oxide that exhibits high resistance to the loss of oxygen and low reactivity towards hydrogen, two typical processes involved in oxide reduction. Oxide reducibility can change substantially by nanostructuring (e.g. formation of nanoparticles). In this study, we investigate theoretically by means of DFT+U calculations including dispersion interactions the properties of 2D zirconia films supported on a Pt3Zr alloy and Pt metal surfaces, two systems recently prepared experimentally. The results show that the supported ZrO2 ultrathin films behave very differently from the corresponding bulk oxide, with a low formation energy of oxygen vacancies, and a clear tendency to split the H2 molecule homolytically with direct reduction of the oxide. The comparison of free-standing and supported ZrO2 films shows that these peculiar properties are not due to the formation of a 2D nanostructure, but rather to the presence of the metal support and of a metal/oxide interface. The results provide evidence for the uncommon properties of supported 2D oxides.

18.
Angew Chem Int Ed Engl ; 56(10): 2604-2607, 2017 03 01.
Artigo em Inglês | MEDLINE | ID: mdl-28128485

RESUMO

We report direct evidence for quintuplet spin states in a particular kind of reduced TiO2 anatase obtained by the mild oxidation of TiB2 under hydrothermal conditions. Continuous-wave and pulse EPR spectroscopy at X and Q band frequencies provide compelling evidence for the presence of S=2 states, stable in a wide range of temperatures up to room temperature. A tentative model, corroborated by spin-polarized DFT calculations, is proposed, which consists of four ferromagnetically interacting Ti3+ ions with distances ranging from 0.5 nm to 0.8 nm and tetrahedral arrangement.

19.
Phys Chem Chem Phys ; 19(4): 3279-3286, 2017 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-28085160

RESUMO

The nature of isolated nitrogen-dopants in bulk BaO (N-BaO) and their magnetic interaction have been investigated by means of density functional theory calculations based on hybrid, self-interaction corrected functionals. A thermodynamic analysis shows that N is preferably incorporated into interstitial sites. Only at very high temperatures and under oxygen poor-conditions the formation of N dopants substitutional to O is preferred. The spin density is rather localized in both cases, as proven by the calculation of the hyperfine coupling constants of the electron spin with the nuclear spin of nitrogen. The magnetic interaction of two N defects in various configurations has been considered as a function of their distance. Different behaviors have been observed, depending on the position of the N defects and on the nature of the dominating magnetic mechanism. In any case, the computed Curie temperature is below room temperature, suggesting that RT ferromagnetism cannot be attained for this kind of doping in BaO. Finally, the interplay of oxygen vacancies with the N dopants has been studied. The inclusion of nitrogen has the effect of drastically reducing the cost to create oxygen vacancies. These in turn quench the magnetic moment of N-dopants, contributing to reducing the concentration of magnetic impurities.

20.
ACS Omega ; 2(7): 3878-3885, 2017 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-31457694

RESUMO

Reduction of zirconia by water desorption from a hydrogenated surface is the topic of this study. The focus is on the role of nanostructuring the oxide reducibility measured by the cost of formation of oxygen vacancies by water desorption. We have performed density functional theory calculations using the Perdew-Burke-Ernzerhof + U approach and including dispersion forces on the adsorption, dissociation, diffusion of hydrogen on the ZrO2 (101) surface and on Zr16O32, Zr40O80, and Zr80O160 nanoparticles (NPs). The process involves the formation of a precursor state via diffusion of hydrogen on the surface of zirconia. The results show that O vacancy formation via H2O desorption is more convenient than via direct O2 desorption. The formation of an OsH2 surface precursor state to water desorption is the rate-determining step. This step is highly unfavorable on the ZrO2 (101) surface both thermodynamically and kinetically. On the contrary, on zirconia NPs, characterized by the presence of low coordinated ions, water desorption becomes accessible such that even at temperatures close to 450 K the reaction becomes exergonic. The study shows the role of nanostructuring on the chemical and electronic properties of an oxide.

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