The Effect of Metal–Cation Vacancies on Vanadium Antimonate Surface Properties. A Theoretical Study

Abstract

In this work, we studied the distribution of V and Sb vacancies in the rutile-type vanadium antimonate phase and the influence of these cationic defects on the VSbO4(110) surface properties. We performed density functional theory (DFT) calculations to compute the energy stability of bulk supercells with different geometrical arrangements of the metal-cation-deficient sites. Then, we built a model of the nonstoichiometric VSbO4(110) surface, which exhibited an extra O layer and isolated V cationsV atoms surrounded by Sb ionsthat could act as Lewis acid sites. The density of states (DOS) plot of this surface showed contributions of O(2p) states, coming from surface O atoms nearest-neighbor of a V vacancy, and V(3d) states near the Fermi level. We also studied the influence of cation-vacancies in the formation of Brønsted acid sites.

Electronic and Dielectric Properties of MoV-Oxide (M1 Phase) under Alkane Oxidation Conditions

“…Under the assumption of a homogeneous sample, the disagreement might point to the involvement of oxygen 2p states in the valence band near the Fermi level and suggests substantial covalent bonding contributions of the corresponding V–O bonds, which are affected by the chemical changes taking place on the surface in the presence of steam. For defective VSbO 4 , it has been shown that 2p states of oxygen atoms located near a vanadium vacancy present a sharp peak at 1 eV …”

“…For defective VSbO 4 , it has been shown that 2p states of oxygen atoms located near a vanadium vacancy present a sharp peak at 1 eV. 44 The work function decreased clearly by 200 meV between the dry C 3 H 8 /O 2 and wet C 3 H 8 /O 2 /H 2 O feed (Figure S13). The valence band onset (Figures 6b, S15, and S16) and the core-level binding energies (Figures S9 and S15) shift to a much smaller extent, but consistently to higher energies by 50 meV, suggesting a change in band bending (eΔV s ) induced by the wet propane oxidation feed.…”

Electronic and Dielectric Properties of MoV-Oxide (M1 Phase) under Alkane Oxidation Conditions

“…Under the assumption of a homogeneous sample, the disagreement might point to the involvement of oxygen 2p states in the valence band near the Fermi level and suggests substantial covalent bonding contributions of the corresponding V–O bonds, which are affected by the chemical changes taking place on the surface in the presence of steam. For defective VSbO 4 , it has been shown that 2p states of oxygen atoms located near a vanadium vacancy present a sharp peak at 1 eV …”

“…For defective VSbO 4 , it has been shown that 2p states of oxygen atoms located near a vanadium vacancy present a sharp peak at 1 eV. 44 The work function decreased clearly by 200 meV between the dry C 3 H 8 /O 2 and wet C 3 H 8 /O 2 /H 2 O feed (Figure S13). The valence band onset (Figures 6b, S15, and S16) and the core-level binding energies (Figures S9 and S15) shift to a much smaller extent, but consistently to higher energies by 50 meV, suggesting a change in band bending (eΔV s ) induced by the wet propane oxidation feed.…”

Propylene Adsorption On a Nonstoichiometric VSbO4(110) Surface

“…39 The calculations were performed using a surface supercell formed by 22 V cations, 22 Sb cations, and 96 oxygen atoms derived from the trirutile-type conventional cell (Figure 1a), which represents the geometric optimization of the VSbO 4 (110) surface with 16% cationic vacancies. 27 There are relevant experimental reasons to choose this exposed surface and this vacancy concentration. The VSbO 4 oxide was synthesized by Birchall and Sleight, who reported a rutile-type crystal structure.…”

“…31,44 In a previous study, we modeled the 16% cation-defective VSbO 4 introducing two metal cations (Sb and V) obtaining the V 0.292 3+ V 0.625 4+ Sb 0.916 5+ □ 0.167 O 4 2− composition for the nonstoichiometric slab. 27 This composition is in good agreement w i t h t h a t c o r r e s p o n d i n g t o t h e e x p e r i m e n t a l V 0.28 41 In our calculations, we have selected the (110) plane because it appears to be one of the most stable crystal faces of rutile oxides 45 and results from breaking the smallest number of M− O bonds. This plane has been recently used to represent the active surface of vanadium antimonate catalysts and calculate ammonia adsorption, 33 and light hydrocarbon ammoxidation and oxidative dehydrogenation processes, 31 uncovering the involved reaction mechanism.…”

“…The comparison of the structural, surface, and reactivity characteristics for different samples of rutile Sb–V oxides, in the propane to acrylonitrile ammoxidation reaction, has allowed us to establish a correlation between the nonstoichiometry of the catalyst and its reactivity . Metal-cation defects also facilitate the formation of redox couples V 4+ /V 3+ , enhancing the catalytic activity of antimonate in hydrocarbon selective oxidation reactions. , In a previous study, we modeled the 16% cation-defective VSbO 4 introducing two metal cations (Sb and V) obtaining the V 0.292 3+ V 0.625 4+ Sb 0.916 5+ □ 0.167 O 4 2– composition for the nonstoichiometric slab . This composition is in good agreement with that corresponding to the experimental V 0.28 3+ V 0.64 4+ Sb 0.92 5+ □ 0.16 O 4 formula …”

Electronic and Dielectric Properties of MoV-Oxide (M1 Phase) under Alkane Oxidation Conditions

“…Under the assumption of a homogeneous sample, the disagreement might point to the involvement of oxygen 2p states in the valence band near the Fermi level and suggests substantial covalent bonding contributions of the corresponding V–O bonds, which are affected by the chemical changes taking place on the surface in the presence of steam. For defective VSbO 4 , it has been shown that 2p states of oxygen atoms located near a vanadium vacancy present a sharp peak at 1 eV …”

“…For defective VSbO 4 , it has been shown that 2p states of oxygen atoms located near a vanadium vacancy present a sharp peak at 1 eV. 44 The work function decreased clearly by 200 meV between the dry C 3 H 8 /O 2 and wet C 3 H 8 /O 2 /H 2 O feed (Figure S13). The valence band onset (Figures 6b, S15, and S16) and the core-level binding energies (Figures S9 and S15) shift to a much smaller extent, but consistently to higher energies by 50 meV, suggesting a change in band bending (eΔV s ) induced by the wet propane oxidation feed.…”

Propylene Adsorption On a Nonstoichiometric VSbO4(110) Surface

“…39 The calculations were performed using a surface supercell formed by 22 V cations, 22 Sb cations, and 96 oxygen atoms derived from the trirutile-type conventional cell (Figure 1a), which represents the geometric optimization of the VSbO 4 (110) surface with 16% cationic vacancies. 27 There are relevant experimental reasons to choose this exposed surface and this vacancy concentration. The VSbO 4 oxide was synthesized by Birchall and Sleight, who reported a rutile-type crystal structure.…”

“…31,44 In a previous study, we modeled the 16% cation-defective VSbO 4 introducing two metal cations (Sb and V) obtaining the V 0.292 3+ V 0.625 4+ Sb 0.916 5+ □ 0.167 O 4 2− composition for the nonstoichiometric slab. 27 This composition is in good agreement w i t h t h a t c o r r e s p o n d i n g t o t h e e x p e r i m e n t a l V 0.28 41 In our calculations, we have selected the (110) plane because it appears to be one of the most stable crystal faces of rutile oxides 45 and results from breaking the smallest number of M− O bonds. This plane has been recently used to represent the active surface of vanadium antimonate catalysts and calculate ammonia adsorption, 33 and light hydrocarbon ammoxidation and oxidative dehydrogenation processes, 31 uncovering the involved reaction mechanism.…”

“…The comparison of the structural, surface, and reactivity characteristics for different samples of rutile Sb–V oxides, in the propane to acrylonitrile ammoxidation reaction, has allowed us to establish a correlation between the nonstoichiometry of the catalyst and its reactivity . Metal-cation defects also facilitate the formation of redox couples V 4+ /V 3+ , enhancing the catalytic activity of antimonate in hydrocarbon selective oxidation reactions. , In a previous study, we modeled the 16% cation-defective VSbO 4 introducing two metal cations (Sb and V) obtaining the V 0.292 3+ V 0.625 4+ Sb 0.916 5+ □ 0.167 O 4 2– composition for the nonstoichiometric slab . This composition is in good agreement with that corresponding to the experimental V 0.28 3+ V 0.64 4+ Sb 0.92 5+ □ 0.16 O 4 formula …”

Electronic and Dielectric Properties of MoV-Oxide (M1 Phase) under Alkane Oxidation Conditions

“…Under the assumption of a homogeneous sample, the disagreement might point to the involvement of oxygen 2p states in the valence band near the Fermi level and suggests substantial covalent bonding contributions of the corresponding V–O bonds, which are affected by the chemical changes taking place on the surface in the presence of steam. For defective VSbO 4 , it has been shown that 2p states of oxygen atoms located near a vanadium vacancy present a sharp peak at 1 eV …”

“…For defective VSbO 4 , it has been shown that 2p states of oxygen atoms located near a vanadium vacancy present a sharp peak at 1 eV. 44 The work function decreased clearly by 200 meV between the dry C 3 H 8 /O 2 and wet C 3 H 8 /O 2 /H 2 O feed (Figure S13). The valence band onset (Figures 6b, S15, and S16) and the core-level binding energies (Figures S9 and S15) shift to a much smaller extent, but consistently to higher energies by 50 meV, suggesting a change in band bending (eΔV s ) induced by the wet propane oxidation feed.…”

Propylene Adsorption On a Nonstoichiometric VSbO4(110) Surface

“…39 The calculations were performed using a surface supercell formed by 22 V cations, 22 Sb cations, and 96 oxygen atoms derived from the trirutile-type conventional cell (Figure 1a), which represents the geometric optimization of the VSbO 4 (110) surface with 16% cationic vacancies. 27 There are relevant experimental reasons to choose this exposed surface and this vacancy concentration. The VSbO 4 oxide was synthesized by Birchall and Sleight, who reported a rutile-type crystal structure.…”

“…31,44 In a previous study, we modeled the 16% cation-defective VSbO 4 introducing two metal cations (Sb and V) obtaining the V 0.292 3+ V 0.625 4+ Sb 0.916 5+ □ 0.167 O 4 2− composition for the nonstoichiometric slab. 27 This composition is in good agreement w i t h t h a t c o r r e s p o n d i n g t o t h e e x p e r i m e n t a l V 0.28 41 In our calculations, we have selected the (110) plane because it appears to be one of the most stable crystal faces of rutile oxides 45 and results from breaking the smallest number of M− O bonds. This plane has been recently used to represent the active surface of vanadium antimonate catalysts and calculate ammonia adsorption, 33 and light hydrocarbon ammoxidation and oxidative dehydrogenation processes, 31 uncovering the involved reaction mechanism.…”

“…The comparison of the structural, surface, and reactivity characteristics for different samples of rutile Sb–V oxides, in the propane to acrylonitrile ammoxidation reaction, has allowed us to establish a correlation between the nonstoichiometry of the catalyst and its reactivity . Metal-cation defects also facilitate the formation of redox couples V 4+ /V 3+ , enhancing the catalytic activity of antimonate in hydrocarbon selective oxidation reactions. , In a previous study, we modeled the 16% cation-defective VSbO 4 introducing two metal cations (Sb and V) obtaining the V 0.292 3+ V 0.625 4+ Sb 0.916 5+ □ 0.167 O 4 2– composition for the nonstoichiometric slab . This composition is in good agreement with that corresponding to the experimental V 0.28 3+ V 0.64 4+ Sb 0.92 5+ □ 0.16 O 4 formula …”