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Adsorption and oxidation of NO on various SnO2(1 1 0) surfaces: A density functional theory study
Sensors and Actuators B 221 (2015) 717–722
Contents lists available at ScienceDirect
Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
Adsorption and oxidation of NO on various SnO2 (1 1 0) surfaces: A density functional theory study Guoliang Xu a , Lin Zhang a , Chaozheng He b,∗ , Dongwei Ma c , Zhansheng Lu a,∗ a b c
College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, China Physics and Electronic Engineering College, Nanyang Normal University, Nanyang 473061, China School of Physics, Anyang Normal University, Anyang 455000, China
a r t i c l e
i n f o
Article history: Received 18 December 2014 Received in revised form 10 June 2015 Accepted 30 June 2015 Available online 3 July 2015 Keywords: NO adsorption NO oxidation SnO2 (1 1 0) Gas sensor
a b s t r a c t Density functional theory (DFT) calculation was employed to study the adsorption of NO molecules on SnO2 (1 1 0) surface. For comparison, the adsorption of NO on SnO2 , SnO2−x and O2 + SnO2−x surfaces are considered. The most stable configurations were found for NO adsorption on various SnO2 (1 1 0) surfaces, respectively, and NO is preferentially adsorbed on the oxygen vacancy site through an N-down orientation. A further exploration was made about the oxidation of NO molecules. The results show that the highly reactive O2 + SnO2−x (1 1 0) surface can oxidize the NO molecule into a NO2 species easily. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The performance of gas sensor strongly depends on the surface chemical activity of the active materials. The theoretical study of surface–adsorbate interactions, especially by using the density functional theory calculations, provides a valuable tool for understanding the chemistry of gas sensors, which can present accurate energetic and electronic properties of materials. There are many stages involved in the chemical transduction, including the adsorption of the target species and charge transfer from the compound to the sensing material. As a broadband-based metal oxide semiconductor material (E = 3.6 eV) [1,2], SnO2 have been widely exploited as gas sensors [3,4], with its good electrical conductivity, thermal stability, and good surface reactivity for reducing and oxidizing gases. With the development of the industry, the air pollution is getting heavier due to the emission of nitrogen oxide (NOx ) [5,6]. Especially NO, which is mainly produced by automobile exhaust and coal combustion, leads to the formation of acid rain and photochemical smog [7], so it is crucial to remove NO [8,9]. There are several methods for this purpose, such as direct decomposition, catalytic oxidation of NO on molecular sieve and reduction of NO on metal-oxide. The last method recently attracted a great attention and SnO2 has
∗ Corresponding author. E-mail addresses: [email protected] (C. He), [email protected] (Z. Lu). http://dx.doi.org/10.1016/j.snb.2015.06.143 0925-4005/© 2015 Elsevier B.V. All rights reserved.
been often used as a metal oxide catalyst [10–12]. The interaction between nitrous oxides, i.e., NO and NO2 , and SnO2 surfaces has been widely investigated experimentally [13–16]. The experimental studies, which explored the gas-kinetic interaction of nitrous oxides with SnO2 surfaces, presented that NO2 can be converted into different nitrogen-containing species on SnO2 surface, and the properties of interaction depend on the availability of the surface oxygen ions. As the most stable surface with the lowest surface energy, SnO2 (1 1 0) surfaces received a widespread attention [17,18], and several studies on the adsorption of NO on SnO2 (1 1 0) surface have been done [19,20]. It was found that the interaction strength of NO with the SnO2 (1 1 0) surface is significantly increased by the presence of oxygen defects compared with perfect SnO2 (1 1 0) surfaces [21]. Moreover, NO molecules cannot be trapped efficiently on the SnO2 (1 1 0) surface, unless the SnO2 (1 1 0) surface has some modifications, such as deposition, defects and hydrogenation. The oxygen defect could be introduced through CO oxidation on SnO2 (1 1 0) surface, and the trapped O2 on the oxygen defect can promote the activity of the surface [22–24], enhancing the efficiency of the oxidation of NO. Summarily, the SnO2 based catalyst can be recycled: SnO2 + CO → SnO2−x + CO2 ; SnO2−x + O2 + NO → SnO2 + NO2 . Given the importance of oxygen contents to NO adsorption properties on various SnO2 (1 1 0) surfaces, our current study presents the adsorption of NO on various SnO2 (1 1 0) surfaces with different oxygen contents, and the NO conversion mechanism is focused. Here, three SnO2 (1 1 0) surfaces, perfect SnO2 (1 1 0)
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Fig. 1. The structure of SnO2 (1 1 0) surface (a), the substrates selected in this article SnO2 (1 1 0), SnO2−x (1 1 0) and O2 + SnO2−x (1 1 0) (b).
surface, the partially reduced SnO2 (1 1 0) surface, and the partially reduced SnO2 (1 1 0) surface with O2 trapped into the oxygen vacancy are marked as “SnO2 ”, “SnO2−x ”, “O2 + SnO2−x ”, respectively (see Fig. 1). The study of the systems would shed light on the understanding of the sensing mechanism of the SnO2 based gas sensor. 2. Computational details 2.1. Computational method All the spin-polarized density functional theory (DFT) calculations were performed using DMol3 in Material Studio [25,26] with the GGA-PBE exchange-correlation functional [27] and the basic set of double-numeric-quality (DNP). The ion–electron interaction was described using DFT semi core pseudopotentials (DSPPs) [28]. Complete LST/QST calculations were performed to locate transition states (TS). The geometries were considered to be converged until the energy dropped below 1.0 × 10−5 Ha/atom, the force dropped below 0.002 Ha/A˚ and the max displacement dropped ˚ The thickness of the vacuum layer was 15 A˚ and the below 0.005 A. Fermi smearing parameter of 0.005 Ha was used in the calculations. 2.2. Models used As expected for GGA-PBE calculations with the relaxing of the ˚ c = 3.264 A, ˚ which SnO2 unit cell, we obtained values a = 4.838 A, are in good agreement with the previous GGA calculation [29]. The SnO2 (1 1 0) surfaces were simulated by the periodic (2 × 1) slab models with four O Sn O layers, as shown in Fig. 1. During the geometric optimization processes, the Monkhorst-Pack [30] k-point meshes of 2 × 2 × 1 were adopted for the surface. The bottom two trilayers were fixed in the relaxed bulk positions to mimic
the bulk, while the rest atoms were allowed to relax freely. And a 10 × 10 × 10 A˚ 3 unit cell was used for NO molecule. There were four adsorption sites on the (1 1 0) surface (see Fig. 1), including five-fold and six-fold coordinated Sn (denoted as Sn5c and Sn6c ), two-fold and three-fold coordinated O (denoted as O2c and O3c ). Under coordinated atoms were active sites and O2c was more active than O3c which located in the In-plane site. The adsorption energy Eads was calculated as follows: Eads = ENO + Esurface − ENO/surface where ENO is the total energy of an isolated NO molecule, Esurface and ENO/surface are the total energy of the various SnO2 (1 1 0) surfaces without and with NO adsorption, respectively. With this definition, a positive value indicates an exothermic adsorption. 3. Results and discussion This section is organized as follows: firstly, the different adsorption configurations of NO on various SnO2 surfaces (SnO2 , SnO2−x and O2 + SnO2−x ) will be examined in order to find out the most stable adsorption configurations. Secondly, the process of the NO oxidation on these surfaces will be investigated. When N atom of NO molecule interacts with the O2c atom of the surface, it is denoted as ON O2c . Other cases are denoted in the same way hereafter. The calculated parameters of the NO molecule adsorption on SnO2 are listed in Table 1. 3.1. Adsorption of NO on various SnO2 (1 1 0) surfaces 3.1.1. Adsorption of NO on perfect SnO2 (1 1 0) surface Three configurations were found for NO molecules adsorption on the perfect SnO2 (1 1 0) surface, marked as “ON O2c , “ON Sn5c and “NO Sn5c (see Fig. 2a–c, respectively). As the atoms on
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Table 1 Adsorption energy (Eads in kcal/mol) of the various species in Fig.2, and Mulliken charges of NO before and after adsorption (q in |e|). Configuration
Eads (eV)
Before q (|e|)
After q (|e|)
SnO2 (1 1 0)
a b c
ON O2c ON Sn5c NO Sn5c
0.94 0.85 0.64
0 (O: −0.03; N: 0.03) – –
0.221 (O: 0.025; N: 0.196) 0.143 (O: 0.068; N: 0.075) 0.157 (O: 0.027; N: 0.130)
SnO2−x (1 1 0)
d e f
ON O2c NO O2c ON Sn5c
1.20 0.56 0.73
– – –
−0.251 (O: −0.064; N: −0.187) 0.055 (O: −0.033; N: 0.088) 0.015 (O: −0.009; N: 0.026)
O2 + SnO2−x (1 1 0)
g h i
O3c NO O3c ON Ob NO
0.66 0.70 0.87
– – –
0.203 (O: 0.053; N: 0.150) 0.200 (O: 0.068; N: 0.132) 0.236 (O: 0.061; N: 0.175)
Surface
the outer surface are more active than the atoms in-plane, the NO prefers to adsorb on O2c and Sn5c sites of the SnO2 surface, which agrees well with the NO molecules adsorbed on TiO2 surface [31–33], because the similar surface configurations of the SnO2 (1 1 0) surface and TiO2 (1 1 0) surface. The Eads of ON O2c configuration is 0.94 eV, which is close to the previous reports [21]. In the ON O2c configuration, NO adsorbs on the O2c site through an N-down orientation with the O2c N ˚ slight decrease in the length of N O bond bond length of 1.93 A, ˚ and slight elongation of the adjacent Sn6c O2c from 1.16 A˚ to 1.15 A, bond from 2.04 A˚ to 2.11 A˚ (Fig. 2a). The Eads values of the ON Sn5c and NO Sn5c configurations are 0.85 eV and 0.64 eV, respectively. The adsorption of NO induces slight perturbation of the (1 1 0) sur˚ face, and the lengths of N Sn5c and O Sn5c are 2.56 A˚ and 3.05 A, respectively (see Fig. 2b and c). To further understand the electronic properties, the below panel of Fig. 2 presents the Mulliken population analysis of the adsorption configurations. For the ON O2c configuration, comparing to the free NO molecule, the charge of the N atom in the NO molecule changes from 0.03 |e| to 0.20 |e|, losing 0.19 |e|, and the charge of the O atom in the NO molecule changes from −0.03 |e| to 0.025 |e|, losing 0.025 |e|. It indicates that the NO molecule loses 0.22 e due to the
adsorption. The other two configurations (ON Sn5c and NO Sn5c ) show that the NO molecules transfer 0.143 e and 0.157 e to the surfaces, respectively. The smaller charge transfers and adsorption energies and larger heights of the adsorbed NO to the supports indicate that the interaction between the NO molecule and the in-plane Sn5c site is weak. Summarily, ON O2c is most stable for adsorption of NO molecules on the perfect SnO2 (1 1 0) surface. 3.1.2. Adsorption of NO on SnO2−x (1 1 0) surface The defect of bridge oxygen O2c is more stable than the defect of oxygen O3c which located in-plane site [34–36], so only partially reduced SnO2 surface with the defect of bridge oxygen O2c was considered, marked as “SnO2−x (1 1 0) surface”. The calculated three stable configurations of the NO on SnO2−x (1 1 0) surface are presented in Fig. 2d–f. The N atom of the NO molecule interacts with the two Sn6c atoms beside the oxygen vacancy healing the vacancy. The two N Sn6c bond lengths are both ∼2.28 A˚ and the N O bond is slightly ˚ The adsorption energy of this elongated from 1.16 A˚ to 1.20 A. configuration is 1.20 eV (see Table 1). In contrast, the N-up configuration of NO molecule on the oxygen vacancy is weak with the Eads of 0.56 eV, and the O Sn6c distance of 3.262/3.264 A˚ and the
Fig. 2. Three adsorption configurations for NO on perfect SnO2 (1 1 0) surface, (a), (b) and (c), respectively. Three adsorption configurations for NO on SnO2−x (1 1 0) surface, (d), (e) and (f), respectively. Three adsorption configurations for NO on O2 + SnO2−x (1 1 0) surface, (g), (h) and (i), respectively.
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Fig. 3. The catalytic oxidation products for NO on perfect SnO2 (1 1 0), SnO2−x (1 1 0) and O2 + SnO2−x (1 1 0) surfaces.
˚ The ON Sn5c configuralength of N O bond decreased to 1.162 A. tion (see Fig. 2f) shows that NO locates at the top site of the in-plane Sn5c with the N-down adsorption model. The N Sn5c bond length is 2.52 A˚ and the length of N O bond is slightly enlarged from 1.16 A˚ to 1.17 A˚ due to the adsorption. The adsorption energy of this configuration is 0.73 eV which is much lower than that at bridging O2c site on perfect SnO2 (1 1 0) surface. The Mulliken charges analysis showed that NO molecule of the N Sn6c adsorption configuration gains 0.25 |e| from the surface, while the NO molecule in the NO Sn6c and ON Sn5c configurations are negatively charged about 0.06 |e| and 0.02 |e|, respectively. The result of charge analysis matches the change of NO bond length i.e., the bond order weakens when the NO molecule gets electrons, and the bond length will get longer as a result. Summarily, NO molecules prefer to adsorbed on the oxygen vacancy site of the SnO2−x (1 1 0) surface through an N-down adsorption model.
In addition, NO molecule can adsorb on in-plane O2c Sn5C site in both the O-down and N-down adsorption modes. The lengths of Oa Sn6C and Ob Sn5C bonds are almost unchanged upon NO adsorption, however, the Oa Ob bond of the O2 molecule ˚ The NO molecule is negatively charged by is enlarged to 1.44 A. 0.20 |e|, (N, 0.13; O, 0.07) in O-down adsorption model, resulting ˚ and the calculated Eads in a reduced N O bond length (1.14 A), is 0.66 eV. The adsorption properties of the N-down adsorption model are similar to those of the N-up adsorption model. The calculated Eads is 0.701 eV, slightly larger than that of N-up adsorption model (0.66 eV). The adsorbed NO molecule is negatively charged ˚ Sumby 0.20 |e|, and the N O bond length is reduced to 1.14 A. marily, NO molecule prefers to adsorbed on the in-plane O3c site on the O2 + SnO2−x (1 1 0) surface.
3.1.3. Adsorption of NO on O2 + SnO2−x (1 1 0) surface As well known, O2 molecules prefer to be adsorbed on the bridging oxygen vacancy site of the SnO2−x (1 1 0) surface, and we marked the two oxygen atoms as Oa and Ob for the convenience (as shown in Fig. 1b). Upon the adsorption of oxygen molecule on the oxygen vacancy of the SnO2−x (1 1 0) surface, marked as “O2 + SnO2−x (1 1 0) surface”, the activity of the support is enhanced. Fig. 2g–i presents three stable adsorption configurations of NO molecule on the “O2 + SnO2−x (1 1 0) surface”. The O3c NO and O3c ONconfigurations are shown in Fig. 2g and (h), respectively. Before the NO adsorption, the Oa Ob bond in the ˚ the lengths of Oa Sn6C and Ob pre-adsorbed O2 molecule is 1.42 A, ˚ respectively. Upon NO -Sn5C bonds are 2.267/2.267 A˚ and 2.221 A, ˚ and Oa Sn6c adsorption, the Oa Ob bond is elongated from 1.44 A, ˚ respectively. and Ob Sn5C bonds are elongated to 2.28 and 2.34 A, The NO molecule is negatively charged by 0.24 |e| (N, 0.18 |e|; O, ˚ The 0.06 |e|), resulting in the shrinkage of the N O bond to 1.14 A. corresponding Eads is 0.87 eV.
Since SnO2 surface have oxidative activity to its adsorbates, such as CO [37], SO2 [19,38], we investigated the oxidation of the NO adsorbed on the various SnO2 surfaces. The most stable oxidized product, i.e., NO2 -like species, on various SnO2 surfaces are summarized in Fig. 3, and the corresponding energy curves of the NO oxidation to NO2 are summarized in Fig. 4. For the perfect SnO2 surface, Fig. 3a presents the most stable adsorption configuration of the formed NO2 -like species, in which the original N O bond and the newly formed N O2c bond ˚ respectively, and the angle of O N O2C is are 1.21 and 1.30 A, 118.6◦ , comparable to that of free NO2 molecules (133.0◦ ). The lengths of these two N O bonds are close to that of free NO2 ˚ indicating the formation of NO2 -like species. molecule (1.20 A), The covalent bond order of the NO2 -like species is confirmed by the charge density (presented in Fig. 3a ). The Mulliken charge analysis indicated that the newly formed NO2 species is negatively charged by 0.22 |e|, resulting in the formation of the NO2 − species.
3.2. NO2 formation on various SnO2 (1 1 0) surfaces
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Fig. 4. The conversion processes of NO on perfect SnO2 (1 1 0), SnO2−x (1 1 0) and O2 + SnO2−x (1 1 0) surfaces.
In the Sn6c N O2c configuration on the SnO2−x (1 1 0) surface (Fig. 3b), the two N O bonds of the newly formed NO2 -like species ˚ respectively, and the angle of O N O2c is are 1.22 A˚ and 1.30 A, 119.4◦ , indicating the formation of NO2 species. The charge density (presented in Fig. 3b ) confirms the covalent bond order of the NO2 -like species. The formed NO2 species is negatively charged by 0.32 |e| as measured by the Mulliken charge analysis, indicating the formation of the NO2 − species. In the Sn5c Ob N configuration as shown in Fig. 3c, upon the formation of NO2 , the bond of the pre-adsorbed O2 on SnO2−x (1 1 0) surface is broken, and Oa heals the oxygen vacancy. Ob binds to the ˚ and the original NO bond N atom with the bond length of 1.21 A, ˚ The of the NO molecule is slightly elongated from 1.15 A˚ to 1.25 A. two NO bond lengths and the bond angle (125.4◦ ) of the formed NO2 -like species are rather close to those of free NO2 molecule (1.24 A˚ and 133.0◦ , respectively). According to Mulliken charge analysis, the newly formed NO2 species is negatively charged by 0.16 |e|, in line with the adsorption of the NO2 species on the perfect SnO2 (1 1 0) surface. The energies’ curves of the NO conversion processes on the perfect SnO2 (1 1 0), SnO2−x (1 1 0) and O2 + SnO2−x (1 1 0) surfaces are presented in Fig. 4. The corresponding reaction energies are 14.1, 22.3 and −42.4 kcal/mol, with corresponding reaction barriers of 21.8, 49.7 and 5.0 kcal/mol, respectively, indicating that
the oxidation of the NO on O2 + SnO2−x (1 1 0) surfaces is exothermic and rather preferable. 4. Conclusions In order to understand the gas-sensing properties of the SnO2 surface with various oxygen content, the NO adsorption and oxidation process on various SnO2 (1 1 0) surfaces were studied using DFT calculations in detail. The current results, shed light on the understanding of the sensing mechanism of the SnO2 based gas sensor, are summarized as follows: a) Only weak adsorption was found for the NO on the perfect SnO2 (1 1 0) surface; b) With the biggest adsorption energy of 1.20 eV, NO molecules preferred to adsorbed on the oxygen vacancy site of the SnO2−x (1 1 0) surface through an N-down adsorption model; The interaction of NO with the SnO2 (1 1 0) surface is significantly increased by the presence of oxygen defects; c) NO molecule prefers to adsorbed on the in-plane O3c site on the O2 + SnO2−x (1 1 0) surface; the activity of the O2 + SnO2−x (1 1 0) substrate was improve by the trapped oxygen molecules; d) Different with that on the SnO2 (1 1 0) surface and SnO2−x (1 1 0) surface, the oxidation of the NO on O2 + SnO2−x (1 1 0)
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surfaces is exothermic and rather preferable; NO molecules could be easily oxidized into NO2 species from the high activity of O2 + SnO2−x (1 1 0) surface. Acknowledgments We are grateful to Computing Center of Jilin Province for essential support. This work was partly supported by the Natural Science Foundation of China, (Grant No. 51401078, and 11147006), the Henan Joint Funds of the National Natural Science Foundation of China (Grant No. U1404216), Science & Technology Innovation Talents in Universities of Henan Province (Grant No. 15HASTIT016). References [1] V. Heinrich, P. Cox, The Surface Science of Metal Oxides, vol. 1004, Cambridge University Press, London, 1994, pp. 266. [2] M. Batzill, U. Diebold, The surface and materials science of tin oxide, Prog. Surf. Sci. 79 (2005) 47–154. [3] A. Heilig, N. Barsan, U. Weimar, W. Göpel, Selectivity enhancement of SnO2 gas sensors: simultaneous monitoring of resistances and temperatures, Sens. Actuators B Chem. 58 (1999) 302–309. [4] A. Cabot, A. Vila, J. Morante, Analysis of the catalytic activity and electrical characteristics of different modified SnO2 layers for gas sensors, Sens. Actuators B Chem. 84 (2002) 12–20. [5] C.T. Bowman, Control of combustion-generated nitrogen oxide emissions: technology driven by regulation, in: Symp. (Int.) Combust. 24, 1992, pp. 859–878. [6] S. Mulla, N. Chen, L. Cumaranatunge, G. Blau, D. Zemlyanov, W. Delgass, W. Epling, F. Ribeiro, Reaction of NO and O2 to NO2 on Pt: kinetics and catalyst deactivation, J. Catal. 241 (2006) 389–399. [7] J. Yang, G. Mestl, D. Herein, R. Schlögl, J. Find, Reaction of NO with carbonaceous materials: 1. Reaction and adsorption of NO on ashless carbon black, Carbon 38 (2000) 715–727. [8] Y.-M. Lin, Y.-H. Tseng, J.-H. Huang, C.C. Chao, C.-C. Chen, I. Wang, Photocatalytic activity for degradation of nitrogen oxides over visible light responsive titania-based photocatalysts, Environ. Sci. Technol. 40 (2006) 1616–1621. [9] H. Ichiura, T. Kitaoka, H. Tanaka, Photocatalytic oxidation of NOx using composite sheets containing TiO2 and a metal compound, Chemosphere 51 (2003) 855–860. [10] L. Zhao, M. Yosef, M. Steinhart, P. Göring, H. Hofmeister, U. Gösele, S. Schlecht, Porous silicon and alumina as chemically reactive templates for the synthesis of tubes and wires of SnSe, Sn, and SnO2 , Angew. Chem. Int. Ed. 45 (2006) 311–315. [11] C. Comninellis, C. Pulgarin, Electrochemical oxidation of phenol for wastewater treatment using SnO2 , anodes, J. Appl. Electrochem. 23 (1993) 108–112. [12] V. Zakharenko, A. Cherkashin, Sensitization of the photoadsorption of O2 and NO on SnO2 , React. Kinet. Catal. Lett. 23 (1983) 131–135. [13] T. Yoshida, N. Ogawa, T. Takahashi, Influence of NO and NO2 composition on resistivity changes of SnO2 , J. Electrochem. Soc. 146 (1999) 1106–1110. [14] A. Chiorino, F. Boccuzzi, G. Ghiotti, Surface chemistry and electronic effects of O2 , NO and NO/O2 on SnO2 , Sens. Actuators B Chem. 5 (1991) 189–192. [15] B. Ruhland, T. Becker, G. Müller, Gas-kinetic interactions of nitrous oxides with SnO2 surfaces, Sens. Actuators B Chem. 50 (1998) 85–94. [16] E. Leblanc, L. Périer-Camby, G. Thomas, R. Gibert, M. Primet, P. Gelin, NOx adsorption onto dehydroxylated or hydroxylated tin dioxide surface. Application to SnO2 -based sensors, Sens. Actuators B Chem. 62 (2000) 67–72. [17] M.A. Mäki-Jaskari, T.T. Rantala, Band structure and optical parameters of the SnO2 (1 1 0) surface, Phys. Rev. B 64 (2001) 075407. [18] M. Batzill, K. Katsiev, J.M. Burst, U. Diebold, A.M. Chaka, B. Delley, Gas-phase-dependent properties of SnO2 (1 1 0),(1 0 0), and (1 0 1) single-crystal surfaces: structure, composition, and electronic properties, Phys. Rev. B 72 (2005) 165414. [19] J.D. Prades, A. Cirera, J.R. Morante, First-principles study of NOx and SO2 adsorption onto SnO2 (1 1 0), J. Electrochem. Soc. 154 (2007) H675–H680. [20] J.D. Prades, A. Cirera, J. Morante, J.M. Pruneda, P. Ordejón, Ab initio study of NOx compounds adsorption on SnO2 surface, Sens. Actuators B Chem. 126 (2007) 62–67.
[21] T. Bredow, G. Pacchioni, NO adsorption on the stoichiometric and reduced SnO2 (1 1 0) surface, Theor. Chem. Acc. 114 (2005) 52–59. [22] O. Safonova, I. Bezverkhy, P. Fabrichnyi, M. Rumyantseva, A. Gaskov, Mechanism of sensing CO in nitrogen by nanocrystalline SnO2 and SnO2 (Pd) studied by Mössbauer spectroscopy and conductance measurements, J. Mater. Chem. 12 (2002) 1174–1178. [23] A. Volodin, V. Zakharenko, A. Cherkashin, ESR studies of spectral dependences and kinetics of O2 photoadsorption on SnO2 , React. Kinet. Catal. Lett. 18 (1981) 321–324. [24] J. Oviedo, M. Gillan, First-principles study of the interaction of oxygen with the SnO2 (1 1 0) surface, Surf. Sci. 490 (2001) 221–236. [25] B. Delley, From molecules to solids with the DMol3 approach, J. Chem. Phys. 113 (2000) 7756–7764. [26] B. Delley, Fast calculation of electrostatics in crystals and large molecules, J. Phys. Chem. 100 (1996) 6107–6110. [27] J.P. Perdew, K. Burke, M. Ernzerhof, Generalized gradient approximation made simple, Phys. Rev. Lett. 77 (1996) 3865. [28] B. Delley, Hardness conserving semilocal pseudopotentials, Phys. Rev. B 66 (2002) 155125. [29] K.G. Godinho, A. Walsh, G.W. Watson, Energetic and electronic structure analysis of intrinsic defects in SnO2 , J. Phys. Chem. C 113 (2009) 439–448. [30] H.J. Monkhorst, J.D. Pack, Special points for Brillouin-zone integrations, Phys. Rev. B 13 (1976) 5188. [31] D.C. Sorescu, J.T. Yates, First principles calculations of the adsorption properties of CO and NO on the defective TiO2 (1 1 0) surface, J. Phys. Chem. B 106 (2002) 6184–6199. [32] H. Duarte, E. Proynov, D. Salahub, Density functional study of the NO dimer using GGA and LAP functionals, J. Chem. Phys. 109 (1998) 26–35. [33] W. Zhao, F.H. Tian, X. Wang, L. Zhao, Y. Wang, A. Fu, S. Yuan, T. Chu, L. Xia, J.C. Yu, Removal of nitric oxide by the highly reactive anatase TiO2 (0 0 1) surface: a density functional theory study, J. Colloid Interface Sci. 430 (2014) 18–23. [34] J. Oviedo, M. Gillan, Reconstructions of strongly reduced SnO2 (1 1 0) studied by first-principles methods, Surf. Sci. 513 (2002) 26–36. [35] S. Munnix, M. Schmeits, Electronic structure of oxygen vacancies on TiO2 (1 1 0) and SnO2 (1 1 0) surfaces, J. Vac. Sci. Technol. A 5 (1987) 910–913. [36] W. Bergermayer, I. Tanaka, Reduced SnO2 surfaces by first-principles calculations, Appl. Phys. Lett. 84 (2004) 909–911. [37] K. Yu, Z. Wu, Q. Zhao, B. Li, Y. Xie, High-temperature-stable Au@SnO2 core/shell supported catalyst for CO oxidation, J. Phys. Chem. C 112 (2008) 2244–2247. [38] B. Gergely, C. Guimon, A. Gervasini, A. Auroux, Multitechnique study of the interaction of SO2 with alumina-supported SnO2 catalysts for lean NOx abatement, Surf. Interface Anal. 30 (2000) 61–64.
Biographies Dr. Guoliang Xu received his PhD from Sichuan University. He is an associate professor in Henan Normal University. His researches include the atomic structure, spectra of molecular clusters and electroluminescent materials’ properties. In recent years, he focuses on the interaction between small molecular and metal oxide support from the first principles study. Lin Zhang received her BS degree in 2012 and now she is a graduate student in Henan Normal University. Her main research is first-principles studies on metal oxide based surface adsorption. Dr. Chaozheng He received his Doctoral degree from Jilin University of China in 2012. He is a Lecturer in Nanyang Normal University. His main research is firstprinciples studies on the reaction of the NO on metal and metal oxide support. Dr. Dongwei Ma received his Doctoral degree from Fudan University of China in 2012. He is a Lecturer in Anyang Normal University. His main research is firstprinciples studies on the reaction of the small molecular on metal and metal oxide support. Dr. Zhansheng Lu was an exchange PhD student in the Ångström Laboratory in Uppsala University of Sweden and received his PhD degree from Henan Normal University in 2011. He is now an associate professor in the College of Physics and Electronic Engineering of Henan Normal University. His research interest is firstprinciples studies on metal oxide based surface adsorption.
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Adsorption and oxidation of NO on various SnO2 (1 1 0) surfaces: A density functional theory study Guoliang Xu a , Lin Zhang a , Chaozheng He b,∗ , Dongwei Ma c , Zhansheng Lu a,∗ a b c
College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, China Physics and Electronic Engineering College, Nanyang Normal University, Nanyang 473061, China School of Physics, Anyang Normal University, Anyang 455000, China
a r t i c l e
i n f o
Article history: Received 18 December 2014 Received in revised form 10 June 2015 Accepted 30 June 2015 Available online 3 July 2015 Keywords: NO adsorption NO oxidation SnO2 (1 1 0) Gas sensor
a b s t r a c t Density functional theory (DFT) calculation was employed to study the adsorption of NO molecules on SnO2 (1 1 0) surface. For comparison, the adsorption of NO on SnO2 , SnO2−x and O2 + SnO2−x surfaces are considered. The most stable configurations were found for NO adsorption on various SnO2 (1 1 0) surfaces, respectively, and NO is preferentially adsorbed on the oxygen vacancy site through an N-down orientation. A further exploration was made about the oxidation of NO molecules. The results show that the highly reactive O2 + SnO2−x (1 1 0) surface can oxidize the NO molecule into a NO2 species easily. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The performance of gas sensor strongly depends on the surface chemical activity of the active materials. The theoretical study of surface–adsorbate interactions, especially by using the density functional theory calculations, provides a valuable tool for understanding the chemistry of gas sensors, which can present accurate energetic and electronic properties of materials. There are many stages involved in the chemical transduction, including the adsorption of the target species and charge transfer from the compound to the sensing material. As a broadband-based metal oxide semiconductor material (E = 3.6 eV) [1,2], SnO2 have been widely exploited as gas sensors [3,4], with its good electrical conductivity, thermal stability, and good surface reactivity for reducing and oxidizing gases. With the development of the industry, the air pollution is getting heavier due to the emission of nitrogen oxide (NOx ) [5,6]. Especially NO, which is mainly produced by automobile exhaust and coal combustion, leads to the formation of acid rain and photochemical smog [7], so it is crucial to remove NO [8,9]. There are several methods for this purpose, such as direct decomposition, catalytic oxidation of NO on molecular sieve and reduction of NO on metal-oxide. The last method recently attracted a great attention and SnO2 has
∗ Corresponding author. E-mail addresses: [email protected] (C. He), [email protected] (Z. Lu). http://dx.doi.org/10.1016/j.snb.2015.06.143 0925-4005/© 2015 Elsevier B.V. All rights reserved.
been often used as a metal oxide catalyst [10–12]. The interaction between nitrous oxides, i.e., NO and NO2 , and SnO2 surfaces has been widely investigated experimentally [13–16]. The experimental studies, which explored the gas-kinetic interaction of nitrous oxides with SnO2 surfaces, presented that NO2 can be converted into different nitrogen-containing species on SnO2 surface, and the properties of interaction depend on the availability of the surface oxygen ions. As the most stable surface with the lowest surface energy, SnO2 (1 1 0) surfaces received a widespread attention [17,18], and several studies on the adsorption of NO on SnO2 (1 1 0) surface have been done [19,20]. It was found that the interaction strength of NO with the SnO2 (1 1 0) surface is significantly increased by the presence of oxygen defects compared with perfect SnO2 (1 1 0) surfaces [21]. Moreover, NO molecules cannot be trapped efficiently on the SnO2 (1 1 0) surface, unless the SnO2 (1 1 0) surface has some modifications, such as deposition, defects and hydrogenation. The oxygen defect could be introduced through CO oxidation on SnO2 (1 1 0) surface, and the trapped O2 on the oxygen defect can promote the activity of the surface [22–24], enhancing the efficiency of the oxidation of NO. Summarily, the SnO2 based catalyst can be recycled: SnO2 + CO → SnO2−x + CO2 ; SnO2−x + O2 + NO → SnO2 + NO2 . Given the importance of oxygen contents to NO adsorption properties on various SnO2 (1 1 0) surfaces, our current study presents the adsorption of NO on various SnO2 (1 1 0) surfaces with different oxygen contents, and the NO conversion mechanism is focused. Here, three SnO2 (1 1 0) surfaces, perfect SnO2 (1 1 0)
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Fig. 1. The structure of SnO2 (1 1 0) surface (a), the substrates selected in this article SnO2 (1 1 0), SnO2−x (1 1 0) and O2 + SnO2−x (1 1 0) (b).
surface, the partially reduced SnO2 (1 1 0) surface, and the partially reduced SnO2 (1 1 0) surface with O2 trapped into the oxygen vacancy are marked as “SnO2 ”, “SnO2−x ”, “O2 + SnO2−x ”, respectively (see Fig. 1). The study of the systems would shed light on the understanding of the sensing mechanism of the SnO2 based gas sensor. 2. Computational details 2.1. Computational method All the spin-polarized density functional theory (DFT) calculations were performed using DMol3 in Material Studio [25,26] with the GGA-PBE exchange-correlation functional [27] and the basic set of double-numeric-quality (DNP). The ion–electron interaction was described using DFT semi core pseudopotentials (DSPPs) [28]. Complete LST/QST calculations were performed to locate transition states (TS). The geometries were considered to be converged until the energy dropped below 1.0 × 10−5 Ha/atom, the force dropped below 0.002 Ha/A˚ and the max displacement dropped ˚ The thickness of the vacuum layer was 15 A˚ and the below 0.005 A. Fermi smearing parameter of 0.005 Ha was used in the calculations. 2.2. Models used As expected for GGA-PBE calculations with the relaxing of the ˚ c = 3.264 A, ˚ which SnO2 unit cell, we obtained values a = 4.838 A, are in good agreement with the previous GGA calculation [29]. The SnO2 (1 1 0) surfaces were simulated by the periodic (2 × 1) slab models with four O Sn O layers, as shown in Fig. 1. During the geometric optimization processes, the Monkhorst-Pack [30] k-point meshes of 2 × 2 × 1 were adopted for the surface. The bottom two trilayers were fixed in the relaxed bulk positions to mimic
the bulk, while the rest atoms were allowed to relax freely. And a 10 × 10 × 10 A˚ 3 unit cell was used for NO molecule. There were four adsorption sites on the (1 1 0) surface (see Fig. 1), including five-fold and six-fold coordinated Sn (denoted as Sn5c and Sn6c ), two-fold and three-fold coordinated O (denoted as O2c and O3c ). Under coordinated atoms were active sites and O2c was more active than O3c which located in the In-plane site. The adsorption energy Eads was calculated as follows: Eads = ENO + Esurface − ENO/surface where ENO is the total energy of an isolated NO molecule, Esurface and ENO/surface are the total energy of the various SnO2 (1 1 0) surfaces without and with NO adsorption, respectively. With this definition, a positive value indicates an exothermic adsorption. 3. Results and discussion This section is organized as follows: firstly, the different adsorption configurations of NO on various SnO2 surfaces (SnO2 , SnO2−x and O2 + SnO2−x ) will be examined in order to find out the most stable adsorption configurations. Secondly, the process of the NO oxidation on these surfaces will be investigated. When N atom of NO molecule interacts with the O2c atom of the surface, it is denoted as ON O2c . Other cases are denoted in the same way hereafter. The calculated parameters of the NO molecule adsorption on SnO2 are listed in Table 1. 3.1. Adsorption of NO on various SnO2 (1 1 0) surfaces 3.1.1. Adsorption of NO on perfect SnO2 (1 1 0) surface Three configurations were found for NO molecules adsorption on the perfect SnO2 (1 1 0) surface, marked as “ON O2c , “ON Sn5c and “NO Sn5c (see Fig. 2a–c, respectively). As the atoms on
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Table 1 Adsorption energy (Eads in kcal/mol) of the various species in Fig.2, and Mulliken charges of NO before and after adsorption (q in |e|). Configuration
Eads (eV)
Before q (|e|)
After q (|e|)
SnO2 (1 1 0)
a b c
ON O2c ON Sn5c NO Sn5c
0.94 0.85 0.64
0 (O: −0.03; N: 0.03) – –
0.221 (O: 0.025; N: 0.196) 0.143 (O: 0.068; N: 0.075) 0.157 (O: 0.027; N: 0.130)
SnO2−x (1 1 0)
d e f
ON O2c NO O2c ON Sn5c
1.20 0.56 0.73
– – –
−0.251 (O: −0.064; N: −0.187) 0.055 (O: −0.033; N: 0.088) 0.015 (O: −0.009; N: 0.026)
O2 + SnO2−x (1 1 0)
g h i
O3c NO O3c ON Ob NO
0.66 0.70 0.87
– – –
0.203 (O: 0.053; N: 0.150) 0.200 (O: 0.068; N: 0.132) 0.236 (O: 0.061; N: 0.175)
Surface
the outer surface are more active than the atoms in-plane, the NO prefers to adsorb on O2c and Sn5c sites of the SnO2 surface, which agrees well with the NO molecules adsorbed on TiO2 surface [31–33], because the similar surface configurations of the SnO2 (1 1 0) surface and TiO2 (1 1 0) surface. The Eads of ON O2c configuration is 0.94 eV, which is close to the previous reports [21]. In the ON O2c configuration, NO adsorbs on the O2c site through an N-down orientation with the O2c N ˚ slight decrease in the length of N O bond bond length of 1.93 A, ˚ and slight elongation of the adjacent Sn6c O2c from 1.16 A˚ to 1.15 A, bond from 2.04 A˚ to 2.11 A˚ (Fig. 2a). The Eads values of the ON Sn5c and NO Sn5c configurations are 0.85 eV and 0.64 eV, respectively. The adsorption of NO induces slight perturbation of the (1 1 0) sur˚ face, and the lengths of N Sn5c and O Sn5c are 2.56 A˚ and 3.05 A, respectively (see Fig. 2b and c). To further understand the electronic properties, the below panel of Fig. 2 presents the Mulliken population analysis of the adsorption configurations. For the ON O2c configuration, comparing to the free NO molecule, the charge of the N atom in the NO molecule changes from 0.03 |e| to 0.20 |e|, losing 0.19 |e|, and the charge of the O atom in the NO molecule changes from −0.03 |e| to 0.025 |e|, losing 0.025 |e|. It indicates that the NO molecule loses 0.22 e due to the
adsorption. The other two configurations (ON Sn5c and NO Sn5c ) show that the NO molecules transfer 0.143 e and 0.157 e to the surfaces, respectively. The smaller charge transfers and adsorption energies and larger heights of the adsorbed NO to the supports indicate that the interaction between the NO molecule and the in-plane Sn5c site is weak. Summarily, ON O2c is most stable for adsorption of NO molecules on the perfect SnO2 (1 1 0) surface. 3.1.2. Adsorption of NO on SnO2−x (1 1 0) surface The defect of bridge oxygen O2c is more stable than the defect of oxygen O3c which located in-plane site [34–36], so only partially reduced SnO2 surface with the defect of bridge oxygen O2c was considered, marked as “SnO2−x (1 1 0) surface”. The calculated three stable configurations of the NO on SnO2−x (1 1 0) surface are presented in Fig. 2d–f. The N atom of the NO molecule interacts with the two Sn6c atoms beside the oxygen vacancy healing the vacancy. The two N Sn6c bond lengths are both ∼2.28 A˚ and the N O bond is slightly ˚ The adsorption energy of this elongated from 1.16 A˚ to 1.20 A. configuration is 1.20 eV (see Table 1). In contrast, the N-up configuration of NO molecule on the oxygen vacancy is weak with the Eads of 0.56 eV, and the O Sn6c distance of 3.262/3.264 A˚ and the
Fig. 2. Three adsorption configurations for NO on perfect SnO2 (1 1 0) surface, (a), (b) and (c), respectively. Three adsorption configurations for NO on SnO2−x (1 1 0) surface, (d), (e) and (f), respectively. Three adsorption configurations for NO on O2 + SnO2−x (1 1 0) surface, (g), (h) and (i), respectively.
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Fig. 3. The catalytic oxidation products for NO on perfect SnO2 (1 1 0), SnO2−x (1 1 0) and O2 + SnO2−x (1 1 0) surfaces.
˚ The ON Sn5c configuralength of N O bond decreased to 1.162 A. tion (see Fig. 2f) shows that NO locates at the top site of the in-plane Sn5c with the N-down adsorption model. The N Sn5c bond length is 2.52 A˚ and the length of N O bond is slightly enlarged from 1.16 A˚ to 1.17 A˚ due to the adsorption. The adsorption energy of this configuration is 0.73 eV which is much lower than that at bridging O2c site on perfect SnO2 (1 1 0) surface. The Mulliken charges analysis showed that NO molecule of the N Sn6c adsorption configuration gains 0.25 |e| from the surface, while the NO molecule in the NO Sn6c and ON Sn5c configurations are negatively charged about 0.06 |e| and 0.02 |e|, respectively. The result of charge analysis matches the change of NO bond length i.e., the bond order weakens when the NO molecule gets electrons, and the bond length will get longer as a result. Summarily, NO molecules prefer to adsorbed on the oxygen vacancy site of the SnO2−x (1 1 0) surface through an N-down adsorption model.
In addition, NO molecule can adsorb on in-plane O2c Sn5C site in both the O-down and N-down adsorption modes. The lengths of Oa Sn6C and Ob Sn5C bonds are almost unchanged upon NO adsorption, however, the Oa Ob bond of the O2 molecule ˚ The NO molecule is negatively charged by is enlarged to 1.44 A. 0.20 |e|, (N, 0.13; O, 0.07) in O-down adsorption model, resulting ˚ and the calculated Eads in a reduced N O bond length (1.14 A), is 0.66 eV. The adsorption properties of the N-down adsorption model are similar to those of the N-up adsorption model. The calculated Eads is 0.701 eV, slightly larger than that of N-up adsorption model (0.66 eV). The adsorbed NO molecule is negatively charged ˚ Sumby 0.20 |e|, and the N O bond length is reduced to 1.14 A. marily, NO molecule prefers to adsorbed on the in-plane O3c site on the O2 + SnO2−x (1 1 0) surface.
3.1.3. Adsorption of NO on O2 + SnO2−x (1 1 0) surface As well known, O2 molecules prefer to be adsorbed on the bridging oxygen vacancy site of the SnO2−x (1 1 0) surface, and we marked the two oxygen atoms as Oa and Ob for the convenience (as shown in Fig. 1b). Upon the adsorption of oxygen molecule on the oxygen vacancy of the SnO2−x (1 1 0) surface, marked as “O2 + SnO2−x (1 1 0) surface”, the activity of the support is enhanced. Fig. 2g–i presents three stable adsorption configurations of NO molecule on the “O2 + SnO2−x (1 1 0) surface”. The O3c NO and O3c ONconfigurations are shown in Fig. 2g and (h), respectively. Before the NO adsorption, the Oa Ob bond in the ˚ the lengths of Oa Sn6C and Ob pre-adsorbed O2 molecule is 1.42 A, ˚ respectively. Upon NO -Sn5C bonds are 2.267/2.267 A˚ and 2.221 A, ˚ and Oa Sn6c adsorption, the Oa Ob bond is elongated from 1.44 A, ˚ respectively. and Ob Sn5C bonds are elongated to 2.28 and 2.34 A, The NO molecule is negatively charged by 0.24 |e| (N, 0.18 |e|; O, ˚ The 0.06 |e|), resulting in the shrinkage of the N O bond to 1.14 A. corresponding Eads is 0.87 eV.
Since SnO2 surface have oxidative activity to its adsorbates, such as CO [37], SO2 [19,38], we investigated the oxidation of the NO adsorbed on the various SnO2 surfaces. The most stable oxidized product, i.e., NO2 -like species, on various SnO2 surfaces are summarized in Fig. 3, and the corresponding energy curves of the NO oxidation to NO2 are summarized in Fig. 4. For the perfect SnO2 surface, Fig. 3a presents the most stable adsorption configuration of the formed NO2 -like species, in which the original N O bond and the newly formed N O2c bond ˚ respectively, and the angle of O N O2C is are 1.21 and 1.30 A, 118.6◦ , comparable to that of free NO2 molecules (133.0◦ ). The lengths of these two N O bonds are close to that of free NO2 ˚ indicating the formation of NO2 -like species. molecule (1.20 A), The covalent bond order of the NO2 -like species is confirmed by the charge density (presented in Fig. 3a ). The Mulliken charge analysis indicated that the newly formed NO2 species is negatively charged by 0.22 |e|, resulting in the formation of the NO2 − species.
3.2. NO2 formation on various SnO2 (1 1 0) surfaces
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Fig. 4. The conversion processes of NO on perfect SnO2 (1 1 0), SnO2−x (1 1 0) and O2 + SnO2−x (1 1 0) surfaces.
In the Sn6c N O2c configuration on the SnO2−x (1 1 0) surface (Fig. 3b), the two N O bonds of the newly formed NO2 -like species ˚ respectively, and the angle of O N O2c is are 1.22 A˚ and 1.30 A, 119.4◦ , indicating the formation of NO2 species. The charge density (presented in Fig. 3b ) confirms the covalent bond order of the NO2 -like species. The formed NO2 species is negatively charged by 0.32 |e| as measured by the Mulliken charge analysis, indicating the formation of the NO2 − species. In the Sn5c Ob N configuration as shown in Fig. 3c, upon the formation of NO2 , the bond of the pre-adsorbed O2 on SnO2−x (1 1 0) surface is broken, and Oa heals the oxygen vacancy. Ob binds to the ˚ and the original NO bond N atom with the bond length of 1.21 A, ˚ The of the NO molecule is slightly elongated from 1.15 A˚ to 1.25 A. two NO bond lengths and the bond angle (125.4◦ ) of the formed NO2 -like species are rather close to those of free NO2 molecule (1.24 A˚ and 133.0◦ , respectively). According to Mulliken charge analysis, the newly formed NO2 species is negatively charged by 0.16 |e|, in line with the adsorption of the NO2 species on the perfect SnO2 (1 1 0) surface. The energies’ curves of the NO conversion processes on the perfect SnO2 (1 1 0), SnO2−x (1 1 0) and O2 + SnO2−x (1 1 0) surfaces are presented in Fig. 4. The corresponding reaction energies are 14.1, 22.3 and −42.4 kcal/mol, with corresponding reaction barriers of 21.8, 49.7 and 5.0 kcal/mol, respectively, indicating that
the oxidation of the NO on O2 + SnO2−x (1 1 0) surfaces is exothermic and rather preferable. 4. Conclusions In order to understand the gas-sensing properties of the SnO2 surface with various oxygen content, the NO adsorption and oxidation process on various SnO2 (1 1 0) surfaces were studied using DFT calculations in detail. The current results, shed light on the understanding of the sensing mechanism of the SnO2 based gas sensor, are summarized as follows: a) Only weak adsorption was found for the NO on the perfect SnO2 (1 1 0) surface; b) With the biggest adsorption energy of 1.20 eV, NO molecules preferred to adsorbed on the oxygen vacancy site of the SnO2−x (1 1 0) surface through an N-down adsorption model; The interaction of NO with the SnO2 (1 1 0) surface is significantly increased by the presence of oxygen defects; c) NO molecule prefers to adsorbed on the in-plane O3c site on the O2 + SnO2−x (1 1 0) surface; the activity of the O2 + SnO2−x (1 1 0) substrate was improve by the trapped oxygen molecules; d) Different with that on the SnO2 (1 1 0) surface and SnO2−x (1 1 0) surface, the oxidation of the NO on O2 + SnO2−x (1 1 0)
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surfaces is exothermic and rather preferable; NO molecules could be easily oxidized into NO2 species from the high activity of O2 + SnO2−x (1 1 0) surface. Acknowledgments We are grateful to Computing Center of Jilin Province for essential support. This work was partly supported by the Natural Science Foundation of China, (Grant No. 51401078, and 11147006), the Henan Joint Funds of the National Natural Science Foundation of China (Grant No. U1404216), Science & Technology Innovation Talents in Universities of Henan Province (Grant No. 15HASTIT016). References [1] V. Heinrich, P. Cox, The Surface Science of Metal Oxides, vol. 1004, Cambridge University Press, London, 1994, pp. 266. [2] M. Batzill, U. Diebold, The surface and materials science of tin oxide, Prog. Surf. Sci. 79 (2005) 47–154. [3] A. Heilig, N. Barsan, U. Weimar, W. Göpel, Selectivity enhancement of SnO2 gas sensors: simultaneous monitoring of resistances and temperatures, Sens. Actuators B Chem. 58 (1999) 302–309. [4] A. Cabot, A. Vila, J. Morante, Analysis of the catalytic activity and electrical characteristics of different modified SnO2 layers for gas sensors, Sens. Actuators B Chem. 84 (2002) 12–20. [5] C.T. Bowman, Control of combustion-generated nitrogen oxide emissions: technology driven by regulation, in: Symp. (Int.) Combust. 24, 1992, pp. 859–878. [6] S. Mulla, N. Chen, L. Cumaranatunge, G. Blau, D. Zemlyanov, W. Delgass, W. Epling, F. Ribeiro, Reaction of NO and O2 to NO2 on Pt: kinetics and catalyst deactivation, J. Catal. 241 (2006) 389–399. [7] J. Yang, G. Mestl, D. Herein, R. Schlögl, J. Find, Reaction of NO with carbonaceous materials: 1. Reaction and adsorption of NO on ashless carbon black, Carbon 38 (2000) 715–727. [8] Y.-M. Lin, Y.-H. Tseng, J.-H. Huang, C.C. Chao, C.-C. Chen, I. Wang, Photocatalytic activity for degradation of nitrogen oxides over visible light responsive titania-based photocatalysts, Environ. Sci. Technol. 40 (2006) 1616–1621. [9] H. Ichiura, T. Kitaoka, H. Tanaka, Photocatalytic oxidation of NOx using composite sheets containing TiO2 and a metal compound, Chemosphere 51 (2003) 855–860. [10] L. Zhao, M. Yosef, M. Steinhart, P. Göring, H. Hofmeister, U. Gösele, S. Schlecht, Porous silicon and alumina as chemically reactive templates for the synthesis of tubes and wires of SnSe, Sn, and SnO2 , Angew. Chem. Int. Ed. 45 (2006) 311–315. [11] C. Comninellis, C. Pulgarin, Electrochemical oxidation of phenol for wastewater treatment using SnO2 , anodes, J. Appl. Electrochem. 23 (1993) 108–112. [12] V. Zakharenko, A. Cherkashin, Sensitization of the photoadsorption of O2 and NO on SnO2 , React. Kinet. Catal. Lett. 23 (1983) 131–135. [13] T. Yoshida, N. Ogawa, T. Takahashi, Influence of NO and NO2 composition on resistivity changes of SnO2 , J. Electrochem. Soc. 146 (1999) 1106–1110. [14] A. Chiorino, F. Boccuzzi, G. Ghiotti, Surface chemistry and electronic effects of O2 , NO and NO/O2 on SnO2 , Sens. Actuators B Chem. 5 (1991) 189–192. [15] B. Ruhland, T. Becker, G. Müller, Gas-kinetic interactions of nitrous oxides with SnO2 surfaces, Sens. Actuators B Chem. 50 (1998) 85–94. [16] E. Leblanc, L. Périer-Camby, G. Thomas, R. Gibert, M. Primet, P. Gelin, NOx adsorption onto dehydroxylated or hydroxylated tin dioxide surface. Application to SnO2 -based sensors, Sens. Actuators B Chem. 62 (2000) 67–72. [17] M.A. Mäki-Jaskari, T.T. Rantala, Band structure and optical parameters of the SnO2 (1 1 0) surface, Phys. Rev. B 64 (2001) 075407. [18] M. Batzill, K. Katsiev, J.M. Burst, U. Diebold, A.M. Chaka, B. Delley, Gas-phase-dependent properties of SnO2 (1 1 0),(1 0 0), and (1 0 1) single-crystal surfaces: structure, composition, and electronic properties, Phys. Rev. B 72 (2005) 165414. [19] J.D. Prades, A. Cirera, J.R. Morante, First-principles study of NOx and SO2 adsorption onto SnO2 (1 1 0), J. Electrochem. Soc. 154 (2007) H675–H680. [20] J.D. Prades, A. Cirera, J. Morante, J.M. Pruneda, P. Ordejón, Ab initio study of NOx compounds adsorption on SnO2 surface, Sens. Actuators B Chem. 126 (2007) 62–67.
[21] T. Bredow, G. Pacchioni, NO adsorption on the stoichiometric and reduced SnO2 (1 1 0) surface, Theor. Chem. Acc. 114 (2005) 52–59. [22] O. Safonova, I. Bezverkhy, P. Fabrichnyi, M. Rumyantseva, A. Gaskov, Mechanism of sensing CO in nitrogen by nanocrystalline SnO2 and SnO2 (Pd) studied by Mössbauer spectroscopy and conductance measurements, J. Mater. Chem. 12 (2002) 1174–1178. [23] A. Volodin, V. Zakharenko, A. Cherkashin, ESR studies of spectral dependences and kinetics of O2 photoadsorption on SnO2 , React. Kinet. Catal. Lett. 18 (1981) 321–324. [24] J. Oviedo, M. Gillan, First-principles study of the interaction of oxygen with the SnO2 (1 1 0) surface, Surf. Sci. 490 (2001) 221–236. [25] B. Delley, From molecules to solids with the DMol3 approach, J. Chem. Phys. 113 (2000) 7756–7764. [26] B. Delley, Fast calculation of electrostatics in crystals and large molecules, J. Phys. Chem. 100 (1996) 6107–6110. [27] J.P. Perdew, K. Burke, M. Ernzerhof, Generalized gradient approximation made simple, Phys. Rev. Lett. 77 (1996) 3865. [28] B. Delley, Hardness conserving semilocal pseudopotentials, Phys. Rev. B 66 (2002) 155125. [29] K.G. Godinho, A. Walsh, G.W. Watson, Energetic and electronic structure analysis of intrinsic defects in SnO2 , J. Phys. Chem. C 113 (2009) 439–448. [30] H.J. Monkhorst, J.D. Pack, Special points for Brillouin-zone integrations, Phys. Rev. B 13 (1976) 5188. [31] D.C. Sorescu, J.T. Yates, First principles calculations of the adsorption properties of CO and NO on the defective TiO2 (1 1 0) surface, J. Phys. Chem. B 106 (2002) 6184–6199. [32] H. Duarte, E. Proynov, D. Salahub, Density functional study of the NO dimer using GGA and LAP functionals, J. Chem. Phys. 109 (1998) 26–35. [33] W. Zhao, F.H. Tian, X. Wang, L. Zhao, Y. Wang, A. Fu, S. Yuan, T. Chu, L. Xia, J.C. Yu, Removal of nitric oxide by the highly reactive anatase TiO2 (0 0 1) surface: a density functional theory study, J. Colloid Interface Sci. 430 (2014) 18–23. [34] J. Oviedo, M. Gillan, Reconstructions of strongly reduced SnO2 (1 1 0) studied by first-principles methods, Surf. Sci. 513 (2002) 26–36. [35] S. Munnix, M. Schmeits, Electronic structure of oxygen vacancies on TiO2 (1 1 0) and SnO2 (1 1 0) surfaces, J. Vac. Sci. Technol. A 5 (1987) 910–913. [36] W. Bergermayer, I. Tanaka, Reduced SnO2 surfaces by first-principles calculations, Appl. Phys. Lett. 84 (2004) 909–911. [37] K. Yu, Z. Wu, Q. Zhao, B. Li, Y. Xie, High-temperature-stable Au@SnO2 core/shell supported catalyst for CO oxidation, J. Phys. Chem. C 112 (2008) 2244–2247. [38] B. Gergely, C. Guimon, A. Gervasini, A. Auroux, Multitechnique study of the interaction of SO2 with alumina-supported SnO2 catalysts for lean NOx abatement, Surf. Interface Anal. 30 (2000) 61–64.
Biographies Dr. Guoliang Xu received his PhD from Sichuan University. He is an associate professor in Henan Normal University. His researches include the atomic structure, spectra of molecular clusters and electroluminescent materials’ properties. In recent years, he focuses on the interaction between small molecular and metal oxide support from the first principles study. Lin Zhang received her BS degree in 2012 and now she is a graduate student in Henan Normal University. Her main research is first-principles studies on metal oxide based surface adsorption. Dr. Chaozheng He received his Doctoral degree from Jilin University of China in 2012. He is a Lecturer in Nanyang Normal University. His main research is firstprinciples studies on the reaction of the NO on metal and metal oxide support. Dr. Dongwei Ma received his Doctoral degree from Fudan University of China in 2012. He is a Lecturer in Anyang Normal University. His main research is firstprinciples studies on the reaction of the small molecular on metal and metal oxide support. Dr. Zhansheng Lu was an exchange PhD student in the Ångström Laboratory in Uppsala University of Sweden and received his PhD degree from Henan Normal University in 2011. He is now an associate professor in the College of Physics and Electronic Engineering of Henan Normal University. His research interest is firstprinciples studies on metal oxide based surface adsorption.