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Thermal Behavior, Crystal Structure, and Solid-State Transformation of Orthorhombic Mo−V Oxide under Nitrogen Flow or in Air Masahiro Sadakane,*,† Katsunori Kodato,‡ Nobuhiro Yasuda,§ Satoshi Ishikawa,∥ and Wataru Ueda*,∥
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†
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima 739-8527, Japan ‡ Catalysis Research Center, Hokkaido University, N-21, W-10, Sapporo 001-0021, Japan § Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo-gun 679-5198, Japan ∥ Faculty of Engineering, Kanagawa University, Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Kanagawa, Japan S Supporting Information *
ABSTRACT: Orthorhombic Mo−V oxide is one of the most active solid-state catalysts for selective oxidation of alkane, and revealing its detailed structure is important for understanding reaction mechanisms and for the design of better catalysts. We report the single-crystal X-ray structure analysis of orthorhombic Mo−V oxide heated under a N2 flow; V is present in 6-membered rings with partial occupancy, similar to the structure reported by Trunschke’s group for orthorhombic Mo−V oxide heated under an Ar flow (Trunschke, et al. ACS Catal. 2017, 7, 3061). Our previous paper (Ishikawa, et al. J. Phys. Chem. C, 2015, 119, 7195) reported that V is not present in the 6-membered rings when orthorhombic Mo−V oxide is calcined in the presence of oxygen. Furthermore, Trunschke’s paper reported that V in the 6-membered rings moves to the surface of the crystals under oxidation reaction conditions in the presence of H2O. Our present results provide additional evidence for V migration in the 6membered rings during heat treatment. We also report the differences in the thermal behaviors, ultraviolet−visible absorptions, N2 isotherms, and elemental analysis results of Mo−V oxide heated in air and under a N2 flow. Furthermore, we report the solid-state transformation of orthorhombic Mo−V oxide to tetragonal Mo−V oxide by controlled heat treatment.
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the 6- or 7-membered channels.11 Furthermore, we have also reported that Sb is incorporated in both 6- and 7-membered channels in the case of Sb-containing orthorhombic Mo−V− Sb oxide.12 On the other hand, Trunschke’s group has reported that V is partially present in the 6-membered channel when the orthorhombic Mo−V oxide is heated in Ar.13 They also reported that V migrates into the 6-membered channel during heating in Ar and the incorporated V is released from the channel under propane oxidation conditions with H2O. This finding is very important for the design of catalysts because the dynamics of V may affect the catalyst performance. Furthermore, Valent’s group has reported removal of Te from channels of Nb and Te containing orthorhombic Mo− V−Te−Nb oxide at high temperatures that cause destruction of the active orthorhombic structure.14 It is very important to understand the thermal behavior of the orthorhombic Mo−Vbased oxide.
INTRODUCTION Orthorhombic Mo−V oxide is one of the most active solidstate catalysts for selective oxidation of ethane to ethylene,1−3 propane to acrylic acid3,4 or acrylonitrile,5 acrolein to acrylic acid,1 and alcohols to carboxyl compounds.6 Orthorhombic Mo−V oxide features slabs comprising 6- and 7-membered rings of corner-sharing MO6 octahedra (M = Mo or V) and pentagonal Mo6O21 units with a MoO7 pentagonal bipyramidal unit and five edge-sharing MoO6 octahedra (Figure 1a,b).7,8 Stacking of the 6- and 7-membered rings constructs channel structures, and the 7-membered channel is a micropore with a diameter of ca. 0.4 nm that gases smaller than or equal to ethane can enter.9 We have revealed that the pore diameter and volume can be tuned continuously and reversibly through redox treatment such as heating under H2 flow or in air,10 but this cannot be realized in the cases of other microporous materials such as zeolites and metal−organic frameworks. The structure of orthorhombic Mo−V oxide has been examined using single-crystal X-ray structure analysis using synchrotron radiation, atomic-scale transmission electron microscopy techniques, and gas adsorption techniques. We have reported that orthorhombic Mo−V oxide after heating at 673 K in air (AH Mo−V oxide) has no metallic ions in either © XXXX American Chemical Society
Received: April 27, 2019 Accepted: July 23, 2019
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DOI: 10.1021/acsomega.9b01212 ACS Omega XXXX, XXX, XXX−XXX
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Figure 1. Polyhedral representations of (a, b) orthorhombic and (c, d) tetragonal Mo−V oxide: (a, c) a−b plane and (b, d) b−c plane. Dark polyhedra in (a) and (b) represent pentagonal Mo6O21 units. The black circle and dotted circle in (a) indicate 6- and 7-membered rings, respectively.
Table 1. Preparation Conditions of Our Mo−V Oxide and Trunschke’s Mo−V Oxide13 our Mo−V oxide
Trunschke’s Mo−V oxide
Hydrothermal Reaction (NH4)6Mo7O24·H2O VOSO4 H2O temperature and time other obtained solid crude Mo−V oxide oxalic acid solution temperature and time obtained solid atmosphere fresh Mo−V oxide temperature time at 673 K Mo/V atomic ratio
8.82 g (Mo: 50 mmol) 9.18 g (Mo: 52 mmol) 3.28 g (V: 12.5 mmol) 3.30 g (V: 12.9 mmol) 240 g 230 g heated in an oven at 448 K for 48 h heated to 473 K at 1 K/min and kept for 17 h Teflon sheet was inserted into the reactor and mixture was stirred at 100 rpm not stirred 2.3 g 3.4 g Purification Conditions 2.0 g 1.0 g 0.4 M, 50 mL 0.25 M, 25 mL 333 K, 30 min 1.0 g (fresh Mo−V oxide) 0.66 g Heat Treatment in air N2 flow (50 mL/min) Ar flow (100 mL/min) 0.5 g heated to 673 K at 10 K/min 2h AH Mo−V oxide NH Mo−V oxide 71.8:28.2a 71.9:28.1a 70.5:29.5b
a
Elemental analyses were carried out by Mikroanalytisches Labor Pascher. bRatio was estimated using energy-dispersive X-ray spectroscopy.13
V oxide13 (Table 1). It is very interesting to confirm the presence of V in the hexagonal channel when the orthorhombic Mo−V oxide was heated under a nonoxidative atmosphere. In this article, we describe the single-crystal structure analysis of our orthorhombic Mo−V oxide heated under a nitrogen flow (NH Mo−V oxide) and its thermal behavior difference between in air and under a nitrogen atmosphere.
Orthorhombic Mo−V oxide was synthesized from a reaction mixture of ammonium heptamolybdate, (NH4)6Mo7O24· 4H2O, and vanadyl sulfate, VOSO4·nH2O, with a Mo/V ratio of 4 in H2O under hydrothermal conditions. The crude material contained an amorphous species that was removed by washing the products with aqueous oxalic acid to afford pure orthorhombic Mo−V oxide (fresh Mo−V oxide). The preparation conditions and resulting Mo/V ratio of our Mo− V oxide were slightly different from those of Trunschke’s Mo− B
DOI: 10.1021/acsomega.9b01212 ACS Omega XXXX, XXX, XXX−XXX
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fresh Mo−V oxide indicated that both water and NH4+ in the micropores are removed at up to ca. 673 K (Figure S1a). Infrared spectra showed that the absorption at 1410 cm−1 corresponding to NH4+ was absent for both heated samples (Figure S2). On the other hand, elemental analysis indicated the presence of nitrogen in both calcined samples (Table 2). TPD−MS of AH Mo−V oxide and NH Mo−V oxide did not provide signals corresponding to NH3 released from NH4+, but signals corresponding to N2 and O2 for AH Mo−V oxide and N2 for NH Mo−V oxide were detected when water molecules were evaporated from the samples (Figure S1b,c). These results indicate that gases present during heat treatment are trapped in the micropores. The elemental analyses also indicated that the Mo/V ratios did not change as a result of the heating treatments (Table 2). The ultraviolet−visible absorption between 400 and 1000 nm of NH Mo−V oxide was higher than that of AH Mo−V oxide (Figure S3), indicating that Mo and V are more reduced in NH Mo−V oxide. Orthorhombic Mo−V oxide is prepared by mixing Mo6+ and V4+; the valences of Mo are 6+ and 5+ and those of V are 5+ and 4+ in fresh Mo−V oxide.11 We have reported that reduction of orthorhombic Mo−V oxide decreases the micropore volumes in the 7-membered channels, estimated from N2 isotherms, without the collapse of the crystal structure.10 The N2 isotherms indicated that the micropore volume of NH Mo−V oxide is lower than that of AC Mo−V oxide (Figure S4), confirming the presence of more reduced Mo and V in NH Mo−V oxide compared to AH Mo−V oxide. Single-Crystal Structure Analysis of Orthorhombic Mo−V Oxide Heated under a N2 Flow (NH Mo−V Oxide). Single-crystal structure analysis revealed that the metal and oxygen positions of NH Mo−V oxide are similar to those of AH Mo−V oxide and Trunschke’s Mo−V oxide heated
RESULTS AND DISCUSSION Preparation and Characterization of Orthorhombic Mo−V Oxide. Orthorhombic Mo−V oxide was synthesized and purified according to our reported method (fresh Mo−V oxide),11 and fresh Mo−V oxide was heated at 673 K in air or under a N2 flow to produce air-heated or nitrogen-heated Mo− V oxide, AH Mo−V oxide or NH Mo−V oxide, respectively. Powder X-ray diffraction (XRD) of the Mo−V oxides indicated that they are stable after heating at 673 K (Figure 2). No monoxide such as MoO3 and V2O5 is observed.
Figure 2. Powder XRD patterns of (a) fresh Mo−V oxide, (b) AH Mo−V oxide, and (c) NH Mo−V oxide.
Thermal gravimetry (TG) analysis and temperatureprogramed desorption−mass spectroscopy (TPD−MS) of Table 2. Elemental Analysis Data of Mo−V Oxides sample
fresh Mo−V Oxide obtained values for Mo, V, O, N, H (total) (wt %)
51.8, 10.9, 35.8, 1.06, 0.58 (100.14) Mo/V atomic ratio = 2.52 Mo28.8V11.2O112(NH4)4(H2O)8 52.0, 10.7, 35.9, 1.05, 0.34
formulaa calculated values for Mo, V, O, N, H (wt %) AH Mo−V Oxide obtained values for Mo, V, O, N, H (total) (wt %)
52.7, 11.0, 35.8, 1,01, 0.15 (100.66) Mo/V atomic ratio = 2.54 Mo28.8V11.2O112(N2)2(O2)0.5(H2O)4.5 52.3, 10.8, 35.6, 1.6, 0.17
formulaa calculated values for Mo, V, O, N, H (wt %) NH Mo−V Oxide obtained values for Mo, V, O, N, H (total) (wt %)
52.6, 10.9, 35.8, 0.75, 0.36 (100.41) Mo/V atomic ratio = 2.56 Mo28.8V11.2O112(N2)1.4(H2O)5 52.6, 10.9, 35.6, 0.74, 0.19 Mo30.2V11.8O114(N2)1.4(H2O)8 52.6, 10.9, 35.5, 0.71, 0.29
formulaa calculated values for Mo, V, O, N, H (wt %) formulab calculated values for Mo, V, O, N, H (wt %) Tetragonal Mo−V Oxide obtained values for Mo, V, O, N, H (total) (wt %) formulaa calculated values for Mo, V, O, N, H (wt %)
54.2, 11.6, 34.4, 2 s(I))a wR2 (all data)b
Mo30.2V11.8O114(N2)1.4(H2O)8 5489.50 0.05 × 0.001 × 0.001 black, needle 100 orthorhombic Pba2 (32) 21.0912(4) 26.5514(5) 3.97924(7) 2228.38(7) 4 3673/243 0.073 4.091 8.233 0.044 0.137
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. Tel: +81 82 424 4456. Fax: +81 82 424 5494 (M.S.). *E-mail:
[email protected] (W.U.). ORCID
Masahiro Sadakane: 0000-0001-7308-563X Satoshi Ishikawa: 0000-0003-4372-4108 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by JSPS KAKENHI (Grant nos. JP20246116, JP23246135, JP15H02318, and JP19H00843). The synchrotron radiation experiments were performed at the BL40XU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal nos. 2011B1181, 2012A1161, and 2014A1316). This work was also supported by the JSPS Core-to-Core Program and the Center for Functional Nano Oxide at Hiroshima University.
R1 = ∑∥Fo| − |Fc∥/∑|Fo|. bRw = [∑w(Fo2 − Fc2)2]/∑[w(Fo2)2]1/2.
a
(Mo/V = 2.56) estimated through complete elemental analysis was slightly different from that obtained from the single-crystal structure analysis (Mo/V = 2.71), owing to the differences between the crystal and bulk samples. CCDC 1912347 contains the supplementary crystallographic data for this paper. This data can be obtained free of charge from the Cambridge Crystallographic Data Centre. Other Analytical Techniques. Powder X-ray diffraction (XRD) patterns were recorded with a diffractometer (RINT
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REFERENCES
(1) Ishikawa, S.; Ueda, W. Microporous crystalline Mo−V mixed oxides for selective oxidations. Catal. Sci. Technol. 2016, 6, 617−629. (2) Konya, T.; Katou, T.; Murayama, T.; Ishikawa, S.; Sadakane, M.; Buttrey, D.; Ueda, W. An orthorhombic Mo3VOx catalyst most active for oxidative dehydrogenation of ethane among related complex metal oxides. Catal. Sci. Technol. 2013, 3, 380−387. F
DOI: 10.1021/acsomega.9b01212 ACS Omega XXXX, XXX, XXX−XXX
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(19) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (20) Sheldrick, G. M. Crystal structure refinement with SHELXL. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8. (21) Masliuk, L.; Heggen, M.; Noack, J.; Girgsdies, F.; Trunschke, A.; Hermann, K. E.; Willinger, M. G.; Schlögl, R.; Lunkenbein, T. Structural complexity in heterogeneous catalysis: cataloging local nanostructures. J. Phys. Chem. C 2017, 121, 24093−24103.
(3) Wernbacher, A. M.; Kube, P.; Hävecker, M.; Schlögl, R.; Trunschke, A. Electronic and dielectric properties of MoV-oxide (M1 Phase) under alkane oxidation conditions. J. Phys. Chem. C 2019, 123, 13269−13282. (4) Ueda, W.; Vitry, D.; Katou, T. Crystalline MoVO based complex oxides as selective oxidation catalysts of propane. Catal. Today 2005, 99, 43−49. (5) Watanabe, N.; Ueda, W. Comparative study on the catalytic performance of single-phase Mo−V−O-based metal oxide catalysts in propane ammoxidation to acrylonitrile. Ind. Eng. Chem. Res. 2006, 45, 607−614. (6) Wang, F.; Ueda, W. Selective oxidation of alcohols using novel crystalline Mo−V−O oxide as heterogeneous catalyst in liquid phase with molecular oxygen. Catal. Today 2009, 144, 358−361. (7) Ishikawa, S.; Zhang, Z.; Murayama, T.; Hiyoshi, N.; Sadakane, M.; Ueda, W. Multi-dimensional crystal structuring of complex metal oxide catalysts of group V and VI elements by unit-assembling. Top. Catal. 2018, 7, 341. (8) Ishikawa, S.; Zhang, Z.; Ueda, W. Unit synthesis approach for creating high dimensionally structured complex metal oxides as catalysts for selective oxidations. ACS Catal. 2018, 8, 2935−2943. (9) Sadakane, M.; Kodato, K.; Kuranishi, T.; Nodasaka, Y.; Sugawara, K.; Sakaguchi, N.; Nagai, T.; Matsui, Y.; Ueda, W. Molybdenum-vanadium-based molecular sieves with microchannels of seven-membered rings of corner-sharing metal oxide octahedra. Angew. Chem., Int. Ed. 2008, 47, 2493−2496. (10) Sadakane, M.; Ohmura, S.; Kodato, K.; Fujisawa, T.; Kato, K.; Shimidzu, K.; Murayama, T.; Ueda, W. Redox tunable reversible molecular sieves: orthorhombic molybdenum vanadium oxide. Chem. Commun. 2011, 47, 10812−10814. (11) Ishikawa, S.; Kobayashi, D.; Konya, T.; Ohmura, S.; Murayama, T.; Yasuda, N.; Sadakane, M.; Ueda, W. Redox treatment of orthorhombic Mo29V11O112 and relationships between crystal structure, microporosity and catalytic performance for selective oxidation of ethane. J. Phys. Chem. C 2015, 119, 7195−7206. (12) Sadakane, M.; Yamagata, K.; Kodato, K.; Endo, K.; Toriumi, K.; Ozawa, Y.; Ozeki, T.; Nagai, T.; Matsui, Y.; Sakaguchi, N.; Pyrz, W. D.; Buttrey, D. J.; Blom, D. A.; Vogt, T.; Ueda, W. Synthesis of orthorhombic Mo−V−Sb oxide species by assembly of pentagonal Mo6O21 polyoxometalate building blocks. Angew. Chem., Int. Ed. 2009, 48, 3782−3786. (13) Trunschke, A.; Noack, J.; Trojanov, S.; Girgsdies, F.; Lunkenbein, T.; Pfeifer, V.; Hävecker, M.; Kube, P.; Sprung, C.; Rosowski, F.; Schlögl, R. The impact of the bulk structure on surface dynamics of complex Mo−V-based oxide catalysts. ACS Catal. 2017, 7, 3061−3071. (14) Valente, J. S.; Armendáriz-Herrera, H.; Quintana-Solórzano, R.; del Á ngel, P.; Nava, N.; Massó, A.; López Nieto, J. M. Chemical, structural, and morphological changes of a MoVTeNb catalyst during oxidative dehydrogenation of ethane. ACS Catal. 2014, 4, 1292− 1301. (15) Yamazoe, N.; Kihlborg, L. Mo5O14 twinning and threedimensional structure, determined from a partly tantalum-substituted crystal. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1975, 31, 1666−1672. (16) Pyrz, W. D.; Blom, D. A.; Sadakane, M.; Kodato, K.; Ueda, W.; Vogt, T.; Buttrey, D. J. Atomic-scale investigation of two-component MoVO complex oxide catalysts using aberration-corrected high-angle annular dark-field imaging. Chem. Mater. 2010, 22, 2033−2040. (17) Yasuda, N.; Murayama, H.; Fukuyama, Y.; Kim, J.; Kimura, S.; Toriumi, K.; Tanaka, Y.; Moritomo, Y.; Kuroiwa, Y.; Kato, K.; Tanaka, H.; Takata, M. X-ray diffractometry for the structure determination of a submicrometre single powder grain. J. Synchrotron Radiat. 2009, 16, 352−357. (18) Yasuda, N.; Fukuyama, Y.; Toriumi, K.; Kimura, S.; Takata, M.; Garrett, R.; Gentle, I.; Nugent, K.; Wilkins, S. Submicrometer single crystal diffractometry for highly accurate structure determination. AIP Conf. Proc. 2010, 1234, 147−150. G
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