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Methanol Partial Oxidation Over Shaped Silver Nanoparticles Derived from Cubic and Octahedral Ag2O Nanocrystals

  • Min Yang
  • Rui You
  • Dan Li
  • Zhenhua Zhang
  • Weixin HuangEmail author
Article
  • 21 Downloads

Abstract

Ag-catalyzed methanol partial oxidation is an important industrial catalytic reaction. Herein we report the morphology effect of Ag catalysts on the catalytic activity in methanol partial oxidation. Shaped Ag nanoparticles were prepared by reducing the cubic and octahedral Ag2O nanocrystals under methanol vapor atmosphere. Ag nanoparticles were observed to undergo serious restructuring during methanol partial oxidation, but Ag nanoparticles derived from octahedral Ag2O nanocrystals were found to be more intrinsically active than those derived from cubic Ag2O nanocrystals. Ex situ characterizations demonstrated the more facile formation of active oxygen species on Ag nanoparticles derived from octahedral Ag2O nanocrystals than on Ag nanoparticles derived from cubic Ag2O nanocrystals. Therefore, although undergoing serious restructuring under the harsh reaction conditions of methanol partial oxidation, the original morphology of Ag nanoparticles exerts strong influences on the structure and catalytic activity of restructured Ag nanoparticles. These results demonstrate that strong correlations between original surface structure and restructured surface structure of catalyst nanoparticles even under very harsh reaction conditions and add fundamental understandings of methanol partial oxidation over Ag catalysts.

Graphic Abstract

Keywords

Shaped silver nanoparticles Methanol partial oxidation Morphology effect Oxygen species 

1 Introduction

Methanol partial oxidation to formaldehyde is an important industrial process due to an increasing global consumption of formaldehyde which is employed as a vital precursor to produce value-added chemicals such as resins and plastics [1, 2]. Comparing the oxygen-rich process using iron-molybdate catalysts, the methanol-rich process using silver-based catalysts is a preferred industrial route owing to its easier implementation conditions [3]. The methanol-rich process is predominantly operated under an atmospheric pressure at above 900 K [4, 5, 6], in which formaldehyde is produced from methanol via an oxidative pathway (2CH3OH + O2 → 2 CH2O + 2H2O, ∆fH = − 159 kJ mol−1) or a dehydrogenation pathway (CH3OH → CH2O + H2, ∆fH = + 84 kJ mol−1). Owing to the favorable thermodynamics, the oxidative pathway is the superior route for formaldehyde production.

Many studies were carried out on methanol partial oxidation over electrolytic silver and supported-silver catalysts. Results of electrolytic silver obtained from two different commercial suppliers [7] and pre-treated polycrystalline silver [8] demonstrate that the methanol conversion and formaldehyde selectivity are closely related to the surface structure of Ag catalysts. Pumice-supported silver catalyst exhibits a longer life than electrolytic silver catalyst but a lower formaldehyde yield [9]. Silica-alumina-supported silver catalyst was reported to show a much higher formaldehyde yield even at a lower content of silver than the pumice-supported catalyst and even higher than the commercial electrolytic silver [10, 11, 12, 13], which was attributed to the unique surface structure and strong interaction between the support and the Ag active phase.

The Ag–O2 interaction and active oxygen species are the heart of fundamental studies of partial methanol oxidation and ethylene oxidation over Ag-based catalysts, and thus have been extensively studied both experimentally and theoretically employing bulk polycrystalline silver, silver foil, Ag(110) and Ag(111) single crystals [14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59]. Oxygen chemisorption on silver surfaces has been demonstrated extremely versatile and especially complicated as a function of temperature, partial pressure of oxygen, type of silver and its pretreatment history [5]. In addition to molecularly chemisorbed oxygen species with O 1s binding energies at 532.6 and 532.2 eV respectively on Ag(111) [21, 37, 45, 46, 50, 51] and Ag(001) [54] surfaces, nucleophilic, electrophilic and subsurface atomic oxygen species were reported on Ag surfaces under conditions relevant to ethylene epoxidation reaction [14, 15, 16, 55], of which the subsurface and electrophilic oxygen species were proposed beneficial for the ethylene epoxide formation, while three types of atomic oxygen species denoted as Oα, Oβ and Oγ were evidenced on Ag surfaces under conditions relevant to methanol partial oxidation process [5, 19, 20, 21, 22, 23, 24, 25, 26, 30, 31, 32, 33, 34, 35, 36, 37]. Oα is a weakly chemisorbed surface species characterized by an O 1s binding energy between 528.1 and 528.5 eV, a thermal desorption temperature below 600 K [38, 45, 46, 47, 48, 50], and Ag–O stretching vibrational frequencies between 319 and 339 cm−1 on Ag(110) surface [47] and at 485 cm−1 on Ag(111) surface [45, 46, 47, 48]. Due to the strong nucleophile properties, Oα was demonstrated to incline to catalyze CH3OH into total oxidation products CO2 and H2O [23]. Oβ is a subsurface or bulk dissolved species characterized by an O 1s binding energy between 530.0 and 531.0 eV [4, 19, 30, 32, 36] dependent on the O2 partial pressure and temperature, a thermal desorption temperature between 600 and 800 K [5, 20, 24, 25, 37], and Ag–O stretching vibrational frequency at 640 cm−1 [19, 21, 30, 31, 37]. Oβ is located below silver surface and unable to directly participate in the CH3OH oxidation. Oγ is a strongly chemisorbed surface species with a characteristic of terminal Ag=O bonding [21, 32, 37] and characterized by an O 1s binding energy between 529.0 and 529.5 eV [4, 19, 30, 32, 36], a desorption temperature above 873 K [5, 19, 20, 22, 23, 24, 25, 30, 31, 32, 33, 34, 35, 36, 37], and Ag–O stretching vibrational frequency of 800–810 cm−1 [19, 21, 30, 31, 37]. Oγ was reported to selectively catalyze the partial methanol oxidation to formaldehyde by oxi-dehydrogenation [33, 34] or dehydrogenation mechanisms [20, 22, 23, 24, 25, 35]. Meanwhile, the segregation of Oβ species from the subsurface or bulk to the surface could result in the formation of Oγ species [5, 22, 32, 38, 55], and such a transformation process was reported quite crucial for partial methanol oxidation to formaldehyde [4, 19, 24].

Facet effects of silver catalysts on Ag–O2 interactions and methanol partial oxidation were demonstrated previously employing Ag single crystals. Recently uniform nanocrystals preferentially exposing a specific facet have been successfully used to explore facet effects in heterogeneous catalysis under conditions approaching working catalysts as closely as possible [60, 61, 62, 63, 64, 65, 66, 67, 68]. Furthermore, uniform nanocrystals free of capping ligands should be employed for the fundamental studies of facet effects [69]. In this paper, we fabricated shaped Ag nanoparticles by reduction of capping ligands-free cubic and octahedral Ag2O nanocrystals with CH3OH and studied their surface chemistry and catalytic properties in methanol partial oxidation. Although Ag nanoparticles undergo restructuring under the harsh reaction conditions of methanol partial oxidation, the initial shape of Ag nanoparticles strongly affects the Ag–O2 interactions and catalytic properties, in which Ag nanoparticles derived from octahedral Ag2O (denoted as \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)) are more favorable for the formation of Oγ species and methanol partial oxidation than Ag nanoparticles derived from cubic Ag2O (denoted as \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)).

2 Experimental

Silver nitrate (AgNO3, AR), sodium hydroxide (NaOH, AR), ammonium hydroxide (NH3·H2O, AR) and methanol solution (CH3OH, AR), were purchased from Sinopharm Chemical Reagent Co., Ltd. and used as received. Distilled water was made by Water Purifier lab pure water system. All gases were with ultrahigh purity and were obtained from Nanjing Shangyuan Industrial Gas Factory, China.

Cubic and octahedral Ag2O nanocrystals were prepared according to the previous recipes [70]: Typically, for the synthesis of cubic Ag2O nanocrystals, 5 mL 0.01 mol/L NH3·H2O solution was dropwise injected into 2.5 mL 0.01 mol/L AgNO3 solution under magnetic stirring at room temperature. During this procedure, the tawny sediment first appeared in the solution and then gradually dissolved to form a colorless and transparent solution after magnetic stirring for 10 min. Then 0.25 mL of 2 mol/L NaOH was quickly dropwise added into the resulting solution under stirring and mass brownish-black precipitates appeared. The solution was under stirred for another 30 min. Then the precipitates were placed in the solution without disturbance for 12 h at room temperature. The final products were collected by centrifugation and washed several times with distilled water and absolute ethanol. Octahedral Ag2O nanocrystals were prepared in the similar way, except that the concentrations of NH3·H2O and AgNO3 solutions are ten times that of synthesis of cubic Ag2O nanocrystals. All the Ag2O nanocrystals were dried in vacuum drying chamber at room temperature for testing.

The reducibility of Ag2O nanocrystals was investigated by the temperature programmed reduction (TPR) technique employing CH3OH saturated vapor pressure (15 °C) balanced with Ar as the reducing gas with a flow rate of 30 mL/min (CH3OH-TPR). Typically, 50 mg of catalyst in a quartz reactor was heated to 70 °C at a rate of 5 °C/min and kept for 2 h, then was further heated from 70 to 700 °C at a rate of 5 °C/min and the products were analyzed by an online HIDEN QGA gas analysis system.

Ag2O nanocrystals were employed as precursors for the synthesis of corresponding shaped silver nanoparticles. According to the CH3OH-TPR results, the cubic Ag2O nanocrystals in a quartz tube were heated to 120 °C at a rate of 5 °C/min under CH3OH saturated vapor pressure (15 °C) balanced with Ar gas flow (30 mL/min) at the atmospheric pressure and then reduced for 3 h to prepare the corresponding \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanocrystals, while the octahedral Ag2O nanocrystals were similarly reduced at 150 °C for 3 h to prepare the corresponding \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles.

Powder X-ray diffraction (XRD) patterns were recorded on a Philips X’Pert Pro Super diffractometer with Cu Kα radiation (k = 0.15406 nm) operating at 40 kV and 50 mA. Scanning electron microscope (SEM) experiments were performed on a GeminiSEM 500 field emission scanning electron microscope operated at beam energy of 5.0 kV. X-ray photoelectron spectroscopy (XPS) measurements were measured on an ESCALAB 250 high-performance electron spectrometer using monochromatized AlKα (hν = 1486.7 eV) as the excitation source. The likely charging of samples was corrected by setting the binding energy of the adventitious carbon (C 1s) to 284.8 eV. All the XPS spectra were normalized to their baseline intensity. The O 1s XPS spectra were fitted employing a XPSPEAK software (Version 4.1) with fixed full-width at half maximum (FWHM) for the same O 1s component. Raman spectra were recorded at RT with a HORIBA LabRAM HR confocal microscope spectrograph with a spectral resolution of 0.6 cm−1 and an excitation line at 514 nm.

The catalytic performances of the shaped silver nanoparticles for CH3OH oxidation reaction were performed as following: 200 mg cubic/octahedral Ag2O nanocrystals were placed in a quartz reactor and in situ reduced under CH3OH saturated vapor (15 °C) balanced with Ar gas flow (30 mL/min) at 120 or 150 °C for 3 h. The resulting Ag nanoparticles were then cooled to 70 °C and the stream was switched to the reactant of CH3OH and O2 (CH3OH:O2 = 3:1). After the stream became stable, the temperature-programmed reaction was carried out at a heating rate of 5 °C/min to 700 °C, while the steady-state reactions at 150, 520 and 700 °C were carried out at a heating rate of 5 °C/min to corresponding temperatures and kept for 3 h, and the gas-phase compositions were analyzed by an online HIDEN QGA gas analysis system.

O2-TDS (temperature-programmed desorption spectra) experiments were performed on a conventional system equipped with a thermal conductivity detector (TCD). 100 mg silver nanoparticles were firstly pretreated under 10% O2/He at 520 °C for 1 h and then cooled to room temperature under 10% O2/He. The stream was then switched to He with a flow rate of 30 mL/min to sweep the sample, then the sample was heated from room temperature to 800 °C at a heating rate of 10 °C/min and the desorption signal was detected by TCD.

CH3OH-TPRS (temperature-programmed reaction spectra) experiments were carried out as following: 120 mg cubic/octahedral Ag2O nanocrystals were in situ reduced under CH3OH saturated vapor pressure (15 °C) balanced with Ar (30 mL/min), then the obtained silver nanoparticles were pretreated under 10% O2/He at 520 °C for 1 h and cooled down to room temperature. The CH3OH-TPRS experiments were then conducted by heating the 10% O2/He pretreated silver nanocrystals under CH3OH saturated vapor pressure (15 °C) balanced with Ar (30 mL/min) atmosphere, and the products were analyzed by an online HIDEN QGA gas analysis system.

3 Results and Discussion

Figure 1 shows representative SEM images of as-prepared cubic and octahedral Ag2O nanocrystals (denoted as c–Ag2O and o–Ag2O). c–Ag2O and o–Ag2O nanocrystals exhibit size distributions respectively of 335 ± 66 and 824 ± 164 nm and BET specific surface areas respectively of 1.80 and 1.12 m2/g, consistent with our previous report [71]. As shown in Fig. 2, the reduction of c–Ag2O and o–Ag2O nanocrystals by CH3OH initiates at about 110 and 140 °C respectively, giving sharp formation peaks of CO2 and H2O accompanied by temperature fluctuations. This suggests that the reduction of Ag2O nanocrystals by CH3OH proceeds very fast and strongly exothermic. On the basis of CH3OH-TPR results, 120 and 150 °C were chosen respectively to reduce c–Ag2O and o–Ag2O nanocrystals by CH3OH to prepare corresponding Ag2O-derived Ag nanoparticles (denoted as \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)). Representative SEM images of obtained Ag nanoparticles (Fig. 1) show that morphologies of original Ag2O nanocrystals get seriously destroyed during the reduction process.
Fig. 1

Representative SEM images of as-synthesized c–Ag2O, o–Ag2O, Ag nanoparticles derived from c–Ag2O and o–Ag2O by CH3OH vapor reduction, and Ag nanoparticles after methanol oxidation reaction at 150, 520 and 700 °C for 3 h

Fig. 2

CH3OH-TPR profiles of c–Ag2O and o–Ag2O nanocrystals

After the reduction, XRD patterns (Fig. 3a) change from the typical Ag2O pattern (JCPDS No. 12-0793) to the typical Ag pattern (JCPDS No. 040783). Meanwhile, the Ag 3d5/2 binding energy shifts from 368.2 eV (typical Ag2O spectra) to 368.5 eV (typical Ag spectra) (Fig. 3b) [72]; and in the corresponding O 1s XPS spectra (Fig. 3c), the lattice oxygen and hydroxyl O 1s features of Ag2O at 529.5 and 531.3 eV disappear while two new O 1s features of adsorbed oxygen species on Ag surfaces at 531.0 and 532.6 eV [73] emerge. All these results demonstrate complete reduction of Ag2O nanocrystals into Ag nanoparticles.
Fig. 3

a XRD patterns and XPS spectra of Ag 3d (b) and O 1s (c) over c–Ag2O, o–Ag2O, \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) (Ag nanoparticles derived from c–Ag2O and o–Ag2O, respectively)

Figure 4 shows TPRS results of methanol oxidation over \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\). Signals of m/z = 2, 18, 28, 30, 31 and 44 were monitored to represent H2, H2O, CO, HCHO, CH3OH and CO2, respectively. The m/z signal of 31 arises exclusively from CH3OH while the m/z signal of 30 is contributed by both CH3OH and HCHO. However, HCHO is a product of CH3OH oxidation, thus the contributions of HCHO and CH3OH to the m/z signal of 30 can be distinguished by comparing the m/z signal of 31. It can be seen that the CH3OH conversion increases with the reaction temperature while the resulting products vary with the reaction temperature and can be divided into three regions. The CO2 production reaches its maximum at 150 °C, the formaldehyde production reaches its maximum at 520 °C, and the CO production reaches its maximum at 700 °C. These observations are in accordance with methanol partial oxidation behaviors over the electrolytic silver catalysts [20].
Fig. 4

Temperature-programmed CH3OH oxidation reaction over \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) from 70 to 700 °C

Steady-state methanol partial oxidation over \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) at 150, 520 and 700 °C was further examined. At 150 °C, as shown in Fig. 5a, the initial reactivity of \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) are the same, while the reactivity of \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) remains constant and the reactivity of \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) gradually increases as a function of reaction time; as shown in Fig. 5b, only CO2 and H2O were produced upon methanol oxidation, indicating the occurrence of selective methanol combustion. Both the consumption of CH3OH and the formations of CO2 and H2O demonstrate that \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) is slightly more catalytic active than \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\).
Fig. 5

a CH3OH conversion and b product formation over \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) at 150 °C for 3 h reaction

At 520 °C, as shown in Fig. 6a, both the reactivity of \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) gradually increases as a function of reaction time and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) is also more catalytic active than \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\); as shown in Fig. 6b, the dominant products are formaldehyde and water, while only minor CO2, CO and H2 are present. This implies the occurrences of major methanol partial oxidation to formaldehyde and minor methanol combustion to CO2 and methanol decomposition to CO and H2.
Fig. 6

a CH3OH conversion and b product formation over \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) at 520 °C for 3 h reaction

At 700 °C, as shown in Fig. 7a, both the reactivity of \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) remain constant as a function of reaction time and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) is also more catalytic active than \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\); as shown in Fig. 7b, the dominant products are CO, H2 and H2O and the minor product is CO2. This suggests the occurrences of major methanol decomposition to CO and H2 and minor methanol combustion to CO2. Additionally, H2 oxidation also occurs.
Fig. 7

a CH3OH conversion and b product formation over \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) at 700 °C for 3 h reaction

Respective SEM images of various Ag nanoparticles after methanol partial oxidation at 150, 520 and 700 °C, respectively denoted as Ag-150, Ag-520 and Ag-700, are shown in Fig. 1. Both \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles aggregate and restructure during the catalytic reaction. The BET specific surface areas of \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) are respectively of 2.02 and 1.56 m2/g, higher than those of corresponding c–Ag2O and o–Ag2O. \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles with a lower BET specific surface area are always more active in catalyzing methanol oxidation than \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles, thus \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles exhibit surface structures intrinsically much more catalytic active than \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles.

Dynamic restructuring of electrolytic silver catalysts during methanol partial oxidation was previously reported to vary with reaction temperatures and affect oxygen species formed on silver surfaces that are closely relevant to the catalytic activity and selectivity [7, 19, 23]. Various used Ag nanoparticles are characterized by XPS spectra. As shown in Fig. 8, all Ag nanoparticles exhibit two O 1s components at 530.9 and 532.6 eV. The 530.9 eV feature can be assigned to the Oβ species [4, 19, 30, 32, 36] or carbonate species [55] that likely forms during the methanol partial oxidation reactions, and the 532.6 eV feature can arise from molecularly chemisorbed oxygen species [21, 37, 45, 46, 50, 51] or adsorbed H2O molecules [29], both of which likely form after exposures of Ag nanoparticles to air at room temperature. Adsorbed H2O molecule should facilely react with O adatoms on silver surfaces at room temperature to produce surface hydroxyl groups which, however, were not observed, thus we assign the 532.6 eV feature mainly to molecularly chemisorbed oxygen species. As shown in Fig. 9, \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-150 and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-520 exhibit the Ag 3d5/2 binding energies at 368.4 eV while other Ag nanoparticles exhibit the Ag 3d5/2 binding energies at 368.5 eV, suggesting their metallic Ag state. In the C 1s XPS spectra, a major C 1s peak of adventitious carbon at 284.8 eV and another minor C 1s peak of carbonate at 287.8 eV are present for all Ag nanoparticles, and an additional minor C 1s peak of adsorbed CO2 at 292.5 eV [55, 72] appears for \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-150 and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-150 nanoparticles. As the C 1s XPS spectra only give weak carbonate species signals, we consider that the O 1s signal of 530.9 eV is mainly contributed by the Oβ species on Ag surfaces. The Oβ species on polycrystalline silver or Ag(111) single crystal was reported to be capable of transforming into the Oγ species active in catalyzing methanol partial oxidation to formaldehyde at above 700 K [5, 22, 32, 38, 55]. The percentage of Oβ was observed to decrease from 39.3% for \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-150 slightly to 36.2% for \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-520 and 36.4% for \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-700; meanwhile, the surface O/Ag ratio derived from XPS results remained similar for \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-150, \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-520 and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-700, around 1/1.9. The percentage of Oβ was observed to decrease from 55.5% for \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-150 largely to 34.8% for \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-520 and further to 27.1% for \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-700; meanwhile, the surface O/Ag ratio derived from XPS results increased from 1/2.7 for \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-150 to 1/2.1 for \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-520 and further to 1/1.2 for \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-700. These results suggests that the surface structures do not change much among \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-150, \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-520 and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-700 nanoparticles, but vary much among \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-150, \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-520 and \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-700 nanoparticles. This could be related to the exposure of larger fractions of stable Ag{111} facets on original \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles and the exposure of larger fractions of less-stable Ag{100} facets on original \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles. As shown in Fig. 1, the cubic shape of original \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles exposing Ag{100} facets changes into cuboctahedra or irregular shapes with the appearances of {111} facets, accompanied by the formation of additional edge sites consisting of coordination-unsaturated Ag atoms capable of molecularly adsorbing oxygen.
Fig. 8

O 1s XPS spectra of \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) after CH3OH oxidation reaction at 150, 520 and 700 °C for 3 h. The percentage of 530.9 eV was inserted inside

Fig. 9

a Ag 3d and b C 1s XPS spectra of \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) after CH3OH oxidation reaction at 150, 520 and 700 °C for 3 h

Oxygen species on various used Ag nanoparticles were also characterized by Raman spectra (Fig. 10). The Raman shows peaks of molecularly-chemisorbed oxygen species at 225 and 967 cm−1 [21, 37, 45, 46, 50, 51], Oα species at 440 cm−1 [45, 46, 47, 48], Oβ species at 685 and 700 cm−1 [19, 21, 30, 31, 37], Oγ species at 384 and 798 cm−1 [73] and subsurface OH species at 855 cm−1 [31] were observed. Oα and Oβ species are present on all used \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles. However, Oα species does not appear on all used \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles while Oβ and Oγ species are present on \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-150 nanoparticles, and Oβ species dominates on \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-520 nanoparticles, and few oxygen species is present on \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\)-700 nanoparticles. It is noteworthy that both XPS and Raman measurements were ex situ characterizations in the present study, thus the derived information on surface structures and species could deviate those under reaction conditions. However, the observed differences among XPS and Raman results of various Ag nanoparticles suggest that the shapes and surface structures of original Ag nanoparticles strongly affect their restructuring processes in methanol partial oxidation and surface structures of restructured Ag nanoparticles.
Fig. 10

Raman spectra of \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) after CH3OH oxidation reaction at 150, 520 and 700 °C for 3 h

To further explore the different behaviors of \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles in catalyzing methanol partial oxidation to formaldehyde, the shaped silver nanoparticles were pretreated under 10% O2/He atmosphere at 520 °C for 1 h, cooled down to room temperature under 10% O2/He atmosphere and then purged with Ar, and the subsequent O2-TDS and CH3OH-TPRS measurements were carried out. As shown in Fig. 11a, \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles mainly exhibit an O2 desorption peak of Oβ species [5, 20, 24, 25, 37] while \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles exhibit not only a much stronger O2 desorption feature of Oβ species but also another O2 desorption feature of Oα species [38, 45, 46, 47, 48, 50]. In the subsequent CH3OH-TPRS spectra (Fig. 11b), much more formaldehyde is produced from O2-pretreated \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles than that from O2-pretreated \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles. It is noteworthy that the formaldehyde productions from O2-pretreated \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles occur at similar temperatures. Additionally, the formation amounts of CO and H2 over O2-pretreated \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles are also much higher than over O2-pretreated \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles. These observations indicate that the reactivity of active oxygen species on \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles for methanol partial oxidation are similar while the quantity on \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles is much larger than on \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles.
Fig. 11

a O2-TDS and b CH3OH-TPRS over \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) and \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) after pretreatment under 10% O2/He at 520 °C for 1 h

The above results demonstrate that although undergoing serious restructuring under the harsh reaction conditions of methanol partial oxidation, the original morphology of Ag nanoparticles exerts strong influences on the structure and catalytic activity of restructured Ag nanoparticles. Restructured \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles derived from o–Ag2O nanocrystals are more intrinsically catalytic active in catalyzing methanol partial oxidation than restructured \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles derived from c–Ag2O nanocrystals, which can be associated with the more facile formation of active oxygen species on restructured \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles. These results reveal strong correlations between original surface structure and restructured surface structure of catalyst nanoparticles, as reported previously [66, 68, 74]. Since restructured \({\text{Ag}}_{{\left( {{\text{o}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles expose more fractions of {111} facets and less fractions of {100} facets than restructured \({\text{Ag}}_{{\left( {{\text{c}} - {\text{Ag}}_{2} {\text{O}}} \right)}}\) nanoparticles, our results indicate that the Ag(111) surface is more active in forming active oxygen species for methanol partial oxidation than the Ag(100) surface. However, in situ characterizations are needed to further explore the structure–activity relation of shaped Ag nanoparticles in methanol partial oxidation in future.

4 Conclusion

In summary, employing shaped Ag nanoparticles prepared by reduction of cubic and octahedral Ag2O nanocrystals with CH3OH, we have successfully demonstrated the morphology-dependent catalytic performances of Ag catalysts in methanol partial oxidation. Although undergoing serious restructuring, Ag nanoparticles derived from octahedral Ag2O nanocrystals are more intrinsically active in forming active oxygen species and catalyzing methanol partial oxidation than Ag nanoparticles derived from cubic Ag2O nanocrystals. These results demonstrate strong correlations between original surface structure and restructured surface structure of catalyst nanoparticles even under very harsh reaction conditions and add fundamental understandings of methanol partial oxidation over Ag catalysts.

Notes

Acknowledgements

This work was financially supported by the National Key R & D Program of MOST (Grant No. 2017YFB0602205), the National Natural Science Foundation of China (Grant Nos. 21525313, 91745202, 21703227), the Anhui provincial R&D key project, the Chinese Academy of Sciences, and the Changjiang Scholars Program of Ministry of Education of China.

Compliance with Ethical Standards

Conflict of interest

The authors declare that they have no conflict of interest.

References

  1. 1.
    Reuss G, Disteldorf W, Gamer AO, Hilt A (2000) Ullmann’s encyclopedia of industrial chemistry. Wiley, WeinheimGoogle Scholar
  2. 2.
    Reuss G, Disteldorf W, Grundler O, Hilt A, Ullmann IF, Gerhartz W, Yamamoto YS, Campbell FT, Pfefferkorn R, Rounsaville JF (2000) Ullmanns encyclopedia of industrial chemistry, 5th edn. VCH, Deerfield Beach, p 619Google Scholar
  3. 3.
    Bazilio CA, Thomas WJ, Ullah U, Hayes KE (1985) The catalytic oxidation of methanol. Proc R Soc London A 399:181–194CrossRefGoogle Scholar
  4. 4.
    Nagy AJ, Mestl G, Herein D, Weinberg G, Kitzelmann E, Schlögl R (1999) The correlation of subsurface oxygen diffusion with variations of silver morphology in the silver-oxygen system. J Catal 182:417–429CrossRefGoogle Scholar
  5. 5.
    Herein D, Nagy A, Schubert H, Weinberg G, Kitzelmann E, Schlögl R (1996) The reaction of molecular oxygen with silver at technical catalytic conditions: bulk structural consequences of a gas-solid interface reaction. Z Phys Chem 197:67–96CrossRefGoogle Scholar
  6. 6.
    Meyer A, Renken A (1990) Sodium compounds as catalysts for methanol dehydrogenation to water-free formaldehyde. Chem Eng Technol 13:145–149CrossRefGoogle Scholar
  7. 7.
    Waterhouse GIN, Bowmaker GA, Metson JB (2004) Influence of catalyst morphology on the performance of electrolytic silver catalysts for the partial oxidation of methanol to formaldehyde. Appl Catal A 266:257–273CrossRefGoogle Scholar
  8. 8.
    Ren LP, Dai WL, Yang XL, Xu JH, Cao Y, Li H, Fan K (2005) Direct dehydrogenation of methanol to formaldehyde over pre-treated polycrystalline silver catalyst. Catal Lett 99:83–87CrossRefGoogle Scholar
  9. 9.
    Broilovski SM, Ternkin ON, Trofimova IV (1985) Partial oxidation of organic compounds: Oxidation of alcohols on metals of copper subgroup. Khimiya, Moscow, p 147Google Scholar
  10. 10.
    Dai WL, Cao Y, Ren LP, Yang XL, Xu JH, Li HX, He HY, Fan KN (2004) Ag-SiO2-Al2O3 composite as highly active catalyst for the formation of formaldehyde from the partial oxidation of methanol. J Catal 228:80–91CrossRefGoogle Scholar
  11. 11.
    Dai WL, Li JL, Cao Y, Liu Q, Deng JF (2000) Novel sol-gel-derived Ag/SiO2-Al2O3 catalysts for highly selective oxidation of methanol to formaldehyde. Catal Lett 64:37–40CrossRefGoogle Scholar
  12. 12.
    Cao Y, Dai WL, Deng JF (1997) The oxidative dehydrogenation of methanol over a novel Ag/SiO2 catalyst. Appl Catal A 158:27–34CrossRefGoogle Scholar
  13. 13.
    Liu Q, Cao Y, Dai WL, Deng JF (1998) The oxidative dehydrogenation of methanol over a novel low-loading Ag/SiO2–TiO2 catalyst. Catal Lett 55:87–91CrossRefGoogle Scholar
  14. 14.
    Bukhtiyarov VI, Hävecker M, Kaichev VV, Knop-Gericke A, Mayer RW, Schlögl R (2003) Atomic oxygen species on silver: photoelectron spectroscopy and x-ray absorption studies. Phys Rev B 67:235422CrossRefGoogle Scholar
  15. 15.
    Li WX, Stampfl C, Scheffler M (2003) Subsurface oxygen and surface oxide formation at Ag (111): a density-functional theory investigation. Phys Rev B 67:045408CrossRefGoogle Scholar
  16. 16.
    Kaichev VV, Bukhtiyarov VI, Hävecker M, Knop-Gericke A, Mayer RW (2003) The nature of electrophilic and nucleophilic oxygen adsorbed on silver. Kinet Catal 44:432–440CrossRefGoogle Scholar
  17. 17.
    Lefferts L, van Ommen JG, Ross JRH (1986) The oxidative dehydrogenation of methanol to formaldehyde over silver catalysts in relation to the oxygen–silver interaction. Appl Catal 23:385–402CrossRefGoogle Scholar
  18. 18.
    Lefferts L, van Ommen JG, Ross JRH (1988) The interaction between silver and N2O in relation to the oxidative dehydrogenation of methanol. J Catal 114:303–312CrossRefGoogle Scholar
  19. 19.
    Bao X, Muhler M, Pettinger B, Schlögl R, Ertl G (1993) On the nature of the active state of silver during catalytic oxidation of methanol. Catal Lett 22:215–225CrossRefGoogle Scholar
  20. 20.
    Schubert H, Tegtmeyer U, Schlögl R (1994) On the mechanism of the selective oxidation of methanol over elemental silver. Catal Lett 28:383–395CrossRefGoogle Scholar
  21. 21.
    Millar GJ, Metson JB, Bowmaker GA, Cooney RP (1995) In situ Raman studies of the selective oxidation of methanol to formaldehyde and ethene to ethylene oxide on a polycrystalline silver catalyst. J Chem Soc, Faraday Trans 91:4149–4159CrossRefGoogle Scholar
  22. 22.
    Schubert H, Tegtmeyer U, Herein D, Bao X, Muhler M, Schlögl R (1995) On the relation between catalytic performance and microstructure of polycrystalline silver in the partial oxidation of methanol. Catal Lett 33:305–319CrossRefGoogle Scholar
  23. 23.
    Nagy A, Mestl G, Rühle T, Weinberg G, Schlögl R (1998) The dynamic restructuring of electrolytic silver during the formaldehyde synthesis reaction. J Catal 179:548–559CrossRefGoogle Scholar
  24. 24.
    Nagy A, Mestl G (1999) High temperature partial oxidation reactions over silver catalysts. Appl Catal A 188:337–353CrossRefGoogle Scholar
  25. 25.
    Nagy A, Mestl G, Schlögl R (1999) The role of subsurface oxygen in the silver-catalyzed, oxidative coupling of methane. J Catal 188:58–68CrossRefGoogle Scholar
  26. 26.
    Wang CB, Deo G, Wachs IE (1999) Interaction of polycrystalline silver with oxygen, water, carbon dioxide, ethylene, and methanol: in situ Raman and catalytic studies. J Phys Chem B 103:5645–5656CrossRefGoogle Scholar
  27. 27.
    van Santen RA, Kuipers HPCE (1987) The mechanism of ethylene epoxidation. Adv Catal 35:265–321Google Scholar
  28. 28.
    Besenbacher F, Nørskov JK (1993) Oxygen chemisorption on metal surfaces: general trends for Cu, Ni and Ag. Prog Surf Sci 44:5–66CrossRefGoogle Scholar
  29. 29.
    Rehren C, Muhler M, Bao X, Schlögl R, Ertl G (1991) The interaction of silver with oxygen. Z Phys Chem 174:11–52CrossRefGoogle Scholar
  30. 30.
    Pettinger B, Bao X, Wilcock IC, Muhler M, Ertl G (1994) Surface-enhanced Raman scattering from surface and subsurface oxygen species at microscopically well-defined Ag surfaces. Phys Rev Lett 72:1561–1564CrossRefGoogle Scholar
  31. 31.
    Bao X, Muhler M, Pettinger B, Uchida Y, Lehmpful G, Schlögl R, Ertl G (1995) The effect of water on the formation of strongly bound oxygen on silver surfaces. Catal Lett 32:171–183CrossRefGoogle Scholar
  32. 32.
    Bao X, Muhler M, Schedel-Niedrig T, Schlögl R (1996) Interaction of oxygen with silver at high temperature and atmospheric pressure: a spectroscopic and structural analysis of a strongly bound surface species. Phys Rev B 54:2249–2262CrossRefGoogle Scholar
  33. 33.
    Beuhler RJ, Rao RM, Hrbek J, White MG (2001) Study of the partial oxidation of methanol to formaldehyde on a polycrystalline Ag foil. J Phys Chem B 105:5950–5956CrossRefGoogle Scholar
  34. 34.
    van Veen AC, Hinrichsen O, Muhler M (2002) Mechanistic studies on the oxidative dehydrogenation of methanol over polycrystalline silver using the temporal-analysis-of-products approach. J Catal 210:53–66CrossRefGoogle Scholar
  35. 35.
    Qian M, Liauw MA, Emig G (2003) Formaldehyde synthesis from methanol over silver catalysts. Appl Catal A 238:211–222CrossRefGoogle Scholar
  36. 36.
    Schedel-Niedrig T, Bao X, Muhler M, Schlögl R (1997) Surface-embedded oxygen: electronic structure of Ag (111) and Cu (poly) oxidized at atmospheric pressure. Ber Bunsenges Phys Chem 101:994–1006CrossRefGoogle Scholar
  37. 37.
    Waterhouse GIN, Bowmaker GA, Metson JB (2003) Oxygen chemisorption on an electrolytic silver catalyst: a combined TPD and Raman spectroscopic study. Appl Surf Sci 214:36–51CrossRefGoogle Scholar
  38. 38.
    Bao X, Deng JF, Dong SZ (1985) TDS and XPS studies of the adsorption of O2 on electrolytic silver. Surf Sci 163:444–456CrossRefGoogle Scholar
  39. 39.
    Deng JF, Xu X, Wang J, Liao Y, Hong B (1995) In situ surface Raman spectroscopy studies of oxygen adsorbed on electrolytic silver. Catal Lett 32:159–170CrossRefGoogle Scholar
  40. 40.
    Wang JH, Dai WL, Deng JF, Wei XM, Cao YM, Zhai RS (1998) Interaction of oxygen with silver surface at high temperature. Appl Surf Sci 126:148–152CrossRefGoogle Scholar
  41. 41.
    Boronin AI, Koscheev SV, Zhidomirov GM (1998) XPS and UPS study of oxygen states on silver. J Electron Spectrosc Relat Phenom 96:43–51CrossRefGoogle Scholar
  42. 42.
    Boronin AI, Koscheev SV, Malakhov VF, Zhidomirov GM (1997) Study of high-temperature oxygen states on the silver surface by XPS and UPS. Catal Lett 47:111–117CrossRefGoogle Scholar
  43. 43.
    Kondarides DI, Papatheodorou GN, Vayenas CG, Verykois XE (1993) In situ high temperature SERS study of oxygen adsorbed on Ag: support and electrochemical promotion effects. Ber Bunsen-Ges Phys Chem 97:709–719CrossRefGoogle Scholar
  44. 44.
    Kondarides DI, Verykois XE (1993) Oxygen adsorption on supported silver catalysts investigated by microgravimetric and transient techniques. J Catal 143:481–491CrossRefGoogle Scholar
  45. 45.
    Grant RB, Lambert RM (1984) Basic studies of the oxygen surface chemistry of silver: chemisorbed atomic and molecular species on pure Ag (111). Surf Sci 146:256–268CrossRefGoogle Scholar
  46. 46.
    Campbell CT (1985) Atomic and molecular oxygen adsorption on Ag (111). Surf Sci 157:43–60CrossRefGoogle Scholar
  47. 47.
    Bare SR, Griffiths K, Lennard WN, Tang HT (1995) Generation of atomic oxygen on Ag (111) and Ag (110) using NO2: a TPD, LEED, HREELS, XPS and NRA study. Surf Sci 342:185–198CrossRefGoogle Scholar
  48. 48.
    Carlisle CI, Fujimoto T, Sim WS, King DA (2000) Atomic imaging of the transition between oxygen chemisorption and oxide film growth on Ag {111}. Surf Sci 470:15–31CrossRefGoogle Scholar
  49. 49.
    Wang XD, Tysoe WT, Greenler RG, Truszkowska K (1991) A reflection-absorption infrared spectroscopy study of the adsorption of atomic oxygen on silver. Surf Sci 257:335–343CrossRefGoogle Scholar
  50. 50.
    Wang XD, Tysoe WT, Truszkowska K (1991) A reflection-absorption infrared spectroscopy study of the adsorption of dioxygen species on a silver surface. Surf Sci 258:335–345CrossRefGoogle Scholar
  51. 51.
    Wang YP, Yeh CT (1991) Electron paramagnetic resonance study of the interactions of oxygen with silver/titania. J Chem Soc, Faraday Trans 87:345–348CrossRefGoogle Scholar
  52. 52.
    Carter EA, Goddard WA (1989) Chemisorption of oxygen, chlorine, hydrogen, hydroxide, and ethylene on silver clusters: a model for the olefin epoxidation reaction. Surf Sci 209:243–289CrossRefGoogle Scholar
  53. 53.
    Nakatsuji H, Hu ZM, Nakai H, Ikeda K (1997) Activation of O2 on Cu, Ag, and Au surfaces for the epoxidation of ethylene: dipped adcluster model study. Surf Sci 387:328–341CrossRefGoogle Scholar
  54. 54.
    Rocca M, Savio L, Vattuone L, Burghaus U, Palomba V, Novelli N, Buatier de Mongeot F, Valbusa U (2000) Phase transition of dissociatively adsorbed oxygen on Ag (001). Phys Rev B 61:213–227CrossRefGoogle Scholar
  55. 55.
    Rocha TCR, Oestereich A, Demidov DV, Hävecker M, Zafeiratos S, Weinberg G, Bukhtiyarov VI, Knop-Gericke A, Schlögl R (2012) The silver-oxygen system in catalysis: new insights by near ambient pressure X-ray photoelectron spectroscopy. Phys Chem Chem Phys 14:4554–4564CrossRefGoogle Scholar
  56. 56.
    Montoya A, Haynes BS (2009) DFT analysis of the reaction paths of formaldehyde decomposition on silver. J Phys Chem A 113:8125–8131CrossRefGoogle Scholar
  57. 57.
    Montoya A, Haynes BS (2007) Methanol and methoxide decomposition on silver. J Phys Chem C 111:9867–9876CrossRefGoogle Scholar
  58. 58.
    Andreasen A, Lynggaard H, Stegelmann C, Stoltze P (2005) Simplified kinetic models of methanol oxidation on silver. Appl Catal A 289:267–273CrossRefGoogle Scholar
  59. 59.
    Aljama H, Yoo JS, Nørskov JK, Abild-Pedersen F, Studt F (2016) Methanol partial oxidation on Ag (111) from first principles. ChemCatChem 8:3621–3625CrossRefGoogle Scholar
  60. 60.
    Huang W (2013) Crystal plane-dependent surface reactivity and catalytic property of oxide catalysts studied with oxide nanocrystal model catalysts. Top Catal 56:1363–1376CrossRefGoogle Scholar
  61. 61.
    Huang W, Gao Y (2014) Morphology-dependent surface chemistry and catalysis of CeO2 nanocrystals. Catal Sci Technol 4:3772–3784CrossRefGoogle Scholar
  62. 62.
    Huang W (2016) Oxide nanocrystal model catalysts. Acc Chem Res 49:520–527CrossRefGoogle Scholar
  63. 63.
    Huang W, Sun G, Cao T (2017) Surface chemistry of group IB metals and related oxides. Chem Soc Rev 46:1977–2000CrossRefGoogle Scholar
  64. 64.
    Huang W (2018) Surface chemistry of solid catalysts. Sci Sin Chim 48:1076–1093CrossRefGoogle Scholar
  65. 65.
    Huang W, Li W (2019) Surface and interface design for heterogeneous catalysis. Phys Chem Chem Phys 21:523–536CrossRefGoogle Scholar
  66. 66.
    Bao H, Zhang W, Hua Q, Jiang Z, Yang J, Huang W (2011) Crystal-plane-controlled surface restructuring and catalytic performance of oxide nanocrystals. Angew Chem Int Ed 50:12294–12298CrossRefGoogle Scholar
  67. 67.
    Hua Q, Cao T, Gu X, Lu J, Jiang Z, Pan X, Luo L, Li W, Huang W (2014) Crystal-plane-controlled selectivity of Cu2O catalysts in propylene oxidation with molecular oxygen. Angew Chem Int Ed 53:4856–4861CrossRefGoogle Scholar
  68. 68.
    Zhang Z, Wang S, Song R, Cao T, Luo L, Chen X, Gao Y, Lu J, Li W, Huang W (2017) The most active Cu facet for low-temperature water gas shift reaction. Nat Commun 8:488CrossRefGoogle Scholar
  69. 69.
    Huang W, Hua Q, Cao T (2014) Influence and removal of capping ligands on catalytic colloidal nanoparticles. Catal Lett 144:1355–1369CrossRefGoogle Scholar
  70. 70.
    Wang X, Wu HF, Kuang Q, Huang RB, Xie ZX, Zheng LS (2010) Shape-dependent antibacterial activities of Ag2O polyhedral particles. Langmuir 26:2774–2778CrossRefGoogle Scholar
  71. 71.
    Yang M, Zhang J, Cao Y, Wu M, Qian K, Zhang Z, Liu H, Wang J, Chen W, Huang W (2018) Facet sensitivity of capping ligand-free Ag crystals in CO2 electrochemical reduction to CO. ChemCatChem 10:5128–5134CrossRefGoogle Scholar
  72. 72.
    Moulder JF, Stickle WF, Sobol PE, Bomben KD (1992) Handbook of X-ray photoelectron spectroscopy. Perkin-Elmer, MinnesotaGoogle Scholar
  73. 73.
    Waterhouse GIN, Bowmaker GA, Metson JB (2004) Mechanism and active sites for the partial oxidation of methanol to formaldehyde over an electrolytic silver catalyst. Appl Catal A 265:85–101CrossRefGoogle Scholar
  74. 74.
    Zhang Z, Wu H, Yu Z, Song R, Qian K, Chen X, Tian J, Zhang W, Huang W (2019) Site-resolved Cu2O catalysis in CO oxidation. Angew Chem Int Ed 58:4276–4280CrossRefGoogle Scholar

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Authors and Affiliations

  1. 1.Hefei National Laboratory for Physical Sciences at Microscale, Key Laboratory of Surface and Interface Chemistry and Energy Catalysis of Anhui Higher Education Institutes, CAS Key Laboratory of Materials for Energy Conversion and Department of Chemical PhysicsUniversity of Science and Technology of ChinaHefeiChina

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