Free-Standing NiO-MgO-Al2O3 Nanosheets Derived from Layered

Free-Standing NiO-MgO-Al2O3 Nanosheets Derived from Layered Double Hydroxides Grown onto FeCrAl-Fiber as ... Publication Date (Web): May 9, 2017...
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Free-Standing NiO-MgO-Al2O3 Nanosheets Derived from Layered Double Hydroxides Grown onto FeCrAl-Fiber as Structured Catalysts for Dry Reforming of Methane Ruijuan Chai, Songyu Fan, Zhiqiang Zhang, Pengjing Chen, Guofeng Zhao,* Ye Liu, and Yong Lu* Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, 3663 North Zhongshan Road, Shanghai 200062, People’s Republic of China S Supporting Information *

ABSTRACT: An FeCrAl-fiber-structured NiO-MgO-Al2O3 nanocomposite catalyst engineered from nano- to macro-scale in one-step is developed via thermally decomposing NiMgAl layered double hydroxides (LDHs) that can be grown onto the FeCrAl-fiber only through a γ-Al2O3/water interface-assisted method. By taking advantages of homogeneous component-distribution in the LDHsderived NiO-MgO-Al2O3 nanocomposites and enhanced heat transfer, this promising catalyst delivers satisfying performance with enhanced coking/sintering resistance in the title reaction. At 800 °C and a gas hourly space velocity of 5000 mL g−1 h−1, CH4/CO2 conversion maintains almost constant at 91%/89% within the initial 90 h and then slides in a smooth downturn (to 80/85%) within another 180 h of reaction. KEYWORDS: Structured catalyst, Nanosheet, Layered double hydroxide, Composite oxide, Dry reforming of methane, Interface-assisted method

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INTRODUCTION Catalytic CO2 conversion to chemicals and fuels is a fast growing research area all over the world, due to the ever increasing concerns regarding the sustainable energy and ecoenvironment future.1 In principle, CO2 can react with CH4 (main component of the natural gas) to form syngas (CO and H2), known as dry reforming of methane (DRM), from which methanol and liquid hydrocarbon fuels can be synthesized using established catalytic method.2,3 Also, the DRM shows great potential for the application in unused renewable storage or mitigating instabilities on the grid, due to its strong endothermicity (ΔH298 = 247 kJ mol−1).4 However, its implementation on an industrial scale is in the infancy because practical catalysts toward this attractive process still remain largely challenging. Enormous endeavors are underway with the aim to develop an efficient and cost-effective catalyst for the DRM process. With consideration of the high cost and limited availability of noble metals, the catalysts based on transition metals are desirable for large-scale applications because of their moderate cost and satisfactory performance.5 Ni-based catalysts are widely explored in academia for the methane reforming, whereas one of the obstacles encountered is the rapid deactivation mainly due to the serious sintering and coke deposition.6 To ameliorate the time-on-stream catalytic performance, several tactics have been already employed. For instance, many research efforts have been devoted to exploit the © 2017 American Chemical Society

catalysts derived from layered double hydroxides (LDHs), which are formed by positively charged layers of edge-sharing partially substituted Mg(OH)6 octahedra and the interlamellar anions together with water molecules.7,8 Satisfactory DRM performance is achievable over these catalysts owing to their specific features, especially the highly uniform distribution of flexible and tunable metal ions in their oxidized and/or reduced products due to topotactic transformation.9 Gonzalez et al. show a Ni-MgO-Al2O3 catalyst derived from NiMgAl-LDHs, showing excellent activity/stability for the DRM reaction originated from not only the highly dispersed nickel species but also catalyst surface basicity that help to suppress carbon deposition by promoting the activation of CO2.10 In spite of the pleasing progress in such development of catalysts for the DRM process, it should be emphasized that most researches up to now are focused on the oxides-supported catalysts including LDHs-derived Ni-MgO-Al2O3.10 However, their poor thermal conductivity will inevitably cause severe intrabed and intraparticle heat transfer limitations and thus cold-spots.11 Recently, development of structured catalyst on the basis of various monolithic metallic substrates (e.g., metalfiber felt, metal foam and metal honeycomb) has been attracting growing interest in heterogeneous catalysis due to Received: March 7, 2017 Revised: April 13, 2017 Published: May 9, 2017 4517

DOI: 10.1021/acssuschemeng.7b00717 ACS Sustainable Chem. Eng. 2017, 5, 4517−4522

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ACS Sustainable Chemistry & Engineering its improved hydrodynamics in combination with enhanced heat/mass transfer, which is of great interest to tailor catalysts for the strongly endo/exothermic and/or high-throughput reaction processes such as autothermal reforming of biofuels, dry reforming of methane and de-NOx.12−21 For example, the monolithic-structured FeCrAl foils are available and practicable supports for the DRM process to maintain a homogeneous temperature gradient within catalyst bed.22 However, such pristine FeCrAl monoliths are not efficient in dispersing the active species due to their ultralow surface area. To increase the surface area, several traditional methods such as wash-coating and dip-coating are usually employed, but result in unexpected traits, e.g., the nonuniform distribution of active component, detachment of coatings, and binder harmful contamination that will always accelerate catalyst deactivation.23 Therefore, seeking a nondip-coating fabrication method for efficiently placing Nicontaining nanocomposites on the metal-foam/-fiber and achieving considerably improved coking and sintering resistance, is highly desirable from academic and industrial standpoints. In this study, we demonstrated a facile and efficient nondipcoating strategy for precisely embedding NiO-MgO-Al2O3 nanocomposites in situ onto a thin-sheet microfibrousstructured felt consisting of 15 vol % of 22 μm FeCrAl-fiber, and checked their catalytic performance for application in the DRM process. Notably, the NiO-MgO-Al2O3 nanocomposites were derived from the NiMgAl-LDHs nanosheets that were grown onto the FeCrAl-fiber in advance with controllable morphology, orientation, and dimensionality. Unfortunately, no NiMgAl-LDHs could be grown onto the pristine FeCrAl-fiber under regular LDHs synthesis conditions. Herein, an effective and efficient interface-assisted method was developed to facilely and firmly grow NiMgAl-LDHs onto the FeCrAl-fiber surface, including three steps: (1) preoxidation of the FeCrAl-fiber felt at 900 °C to create an α-Al2O3 film with certain surface roughness; (2) hydrothermal reaction to embed AlOOH nanosheets on the α-Al2O3 film followed by calcination to form a shell of γ-Al2O3 nanosheets;24 (3) regular LDHs synthesis to anchor uniformly NiMgAl-LDHs on the fiber, with the aid of γ-Al2O3/water interface-assisted effect accordingly.25,26 After a calcination treatment at 550 °C, the NiMgAl-LDHs were transformed into NiO-MgO-Al2O3 nanocomposites, and the monolithic-structured NiO-MgO-Al2O3/ FeCrAl-fiber catalyst was obtained, which demonstrated interesting catalytic performance and high coking/sintering resistance in the DRM process.

Figure 1. Optical photograph and microscope image (a) of the pristine FeCrAl-fiber chips. SEM images (b) of FeCrAl-fiber-900. XRD patterns (c) of the FeCrAl-fiber-900, AlOOH/FeCrAl-fiber-900 and γ-Al2O3/FeCrAl-fiber-900. SEM images of (d) AlOOH/FeCrAl-fiber900 and (e,f) γ-Al2O3/FeCrAl-fiber-900.

LDHs synthesis conditions.28 In light of this information, we conceive a facile synthetic strategy to grow NiMgAl-LDHs on the FeCrAl-fiber via an in situ γ-Al2O3/water interface-assisted growth method. To accomplish this goal, a continuous and uniform shell of AlOOH-nanosheets is first grown onto the FeCrAl-fiber-900 surface via a simple in situ decoration process (Figure 1c,d), which proceeded in a stainless steel autoclave by immersing the FeCrAl-fiber-900 chips in a solution of sodium aluminate and urea at 160 °C for 12 h. The AlOOH-nanosheets coalesce to each other, which is resulted from nucleation and crystal growth during the hydrothermal process (Figure 1d). Moreover, the subsequent calcination treatment at 550 °C turns the AlOOH into γ-Al2O3 accompanied by disappearance of boehmite phase,29 whereas the nanosheet morphology is well preserved (Figure 1c,e). Note no characteristic XRD peaks of γAl2O3 can be detectable because the specific diffraction intensity of γ-Al2O3 is much weaker than that of the boehmite (AlOOH) precursors. Clearly, this in situ decoration method is versatile and simple to embed a uniform γ-Al2O3 shell on the fiber core, with a certain thickness of 1 μm (Figure 1f). In addition, the amount of the deposited γ-Al2O3 layer is 1.2 wt %, determined as a weight difference between γ-Al2O3/FeCrAlfiber-900 and FeCrAl-fiber-900. Surprisingly but interestingly, direct growth of NiMgAlLDHs nanosheets succeeds on the γ-Al2O3/FeCrAl-fiber-900 under regular LDHs synthesis conditions (Figure 2a), showing that our interface-assisted method is indeed working effectively and efficiently. XRD pattern of the as-synthesized NiMgAlLDHs/FeCrAl-fiber-900 precursor displays a series of welldeveloped diffraction peaks (2θ of 11.7, 23.6, 35.1, 39.7 and 47.3°, well-indexed to (003), (006), (012), (015) and (018)

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RESULT AND DISCUSSION Flexibility in geometry of the pristine FeCrAl-fiber felt and its 3D network structure are clearly illustrated by the optical photograph and microscope image (Figure 1a). Initially, we attempted to grow NiMgAl-LDHs nanosheets onto the pristine FeCrAl-fiber surface via the regular LDHs synthesis method, yet we failed. We naturally think roughening the fiber surface should be able to improve the adhesion between the fiber and LDHs layer.27 Therefore, a preliminary calcination of FeCrAlfiber felt at 900 °C for 5 h in air was performed to grow an αAl2O3 film with certain roughness on the fiber (i.e., FeCrAlfiber-900; scanning electronic microscopy (SEM) image and Xray diffraction (XRD) pattern in Figure 1b,c). Unfortunately, LDHs is not feasible to be grown on the fiber if just with a simple calcination treatment yet. Of interest is that the growth of LDHs becomes workable on the γ-Al2O3 under regular 4518

DOI: 10.1021/acssuschemeng.7b00717 ACS Sustainable Chem. Eng. 2017, 5, 4517−4522

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ACS Sustainable Chemistry & Engineering

Figure 2. Fabrication strategy (a) of the NiO-MgO-Al2O3/FeCrAlfiber-900 catalyst derived from the NiMgAl-LDHs/FeCrAl-fiber-900 precursor. XRD pattern (b), SEM images (c,d) and TEM images (e) of the NiMgAl-LDHs/FeCrAl-fiber-900 precursor.

Figure 3. XRD pattern (a), SEM images (b), EDX element mappings (c) and H2-TPR (d) of the NiO-MgO-Al2O3/FeCrAl-fiber-900 catalyst. SEM images (e) and TEM images (f) of the Ni-MgOAl2O3/FeCrAl-fiber-900 catalyst.

planes), representing a hexagonal LDH structure (JCPDS No. 15-0087, Figure 2b). SEM image shows that the flowerlike microspheres are uniform in both size and shape, with LDH nanosheets mutually intercrossed and perpendicularly grafted to FeCrAl-fiber-900 (Figure 2c).30 Moreover, thickness of the LDHs-nanosheets shell is about 0.7 μm (Figure 2d), slightly thinner than that (1 μm; Figure 1e) of the γ-Al2O3 nanosheets shell, likely due to the dissolution of γ-Al2O3 during the growth of NiMgAl-LDHs.25 Furthermore, the high-resolution transmission electron microscopy (HRTEM) image shows the nanosheet morphology and the lattice fringes corresponding to an interplanar distance of ∼0.24 nm corresponding to (009) plane of NiMgAl-LDHs (Figure 2e). All in all, the γ-Al2O3/ water interface-assisted method is indeed paramount for success in a uniform NiMgAl-LDHs shell mounting on the FeCrAl-fiber. A possible explanation is that such γ-Al2O3/water interface-assisted crystallization of LDHs on the fiber is governed by a homogeneous nucleation mechanism accordingly.25 After calcination at 550 °C in air for 2 h, the NiMgAl-LDHs phase in the shell disappears completely (XRD patterns in Figure 3a), indicating the transformation into NiO-MgO-Al2O3 nanocomposites associated with appearance of NiO;10 no any XRD peaks associated with Mg/Al-containing phases such as MgO, Al2O3 and NiAl2O4 can be found because these oxide species are highly dispersed or have low contents. Interestingly, as illustrated in the SEM image (Figure 3b), basic nanosheet morphology of the shell is well conserved without perceptible alternations. The Ni, Mg and Al elements are uniformly distributed in such NiO-MgO-Al2O3 composite shell with a Ni/ Mg atom ratio of around 3.4/5.0 (detected by energy dispersive X-ray (EDX) measurement, Figure 3c and Figure S1), which is

close to that of 4.0/5.0 in the solution for LDHs growth. Notably, the Al content in the NiO-MgO-Al2O3 nanocomposites is unable to be estimated by the EDX element analysis because of the disturbance of the Al presented in the FeCrAl-fiber substrate. Figure 3d shows the H2-temperatureprogrammed reduction (H2-TPR) profile of our microfibrousstructured NiO-MgO-Al2O3/FeCrAl-fiber catalyst, with a clear multipeak feature. The weak low-temperature peak centered at 273 °C is assigned to the reduction of some well-dispersed NiO species. The weak mild-temperature peak at 371 °C indicates the presence of some bulk NiO species, according to the H2TPR peak at 327 °C for the pure NiO powder (Figure S2). The high-temperature peaks above 500 °C are ascribed to the Ni species strongly interacted with the MgO and/or Al2O3; especially, the strong peak at 722 °C is contributed to the Nicontaining spinel-like compounds such as NiAl2O4 that is reported to be reduced at 700−900 °C.31 In addition, on the basis of the H2-comsumption in the H2-TPR experiments (assuming Ni existed in NiO; H2 + NiO = Ni + H2O), the NiO content is estimated to be 1.0 wt %. To determine the composition of LDHs-derived NiO-MgO-Al2O3 composite shell and its content in overall NiO-MgO-Al2O3/FeCrAl-fiber catalyst, some NiO-MgO-Al2O3 composite was quantitatively taken off from the catalyst sample and was measured by means of inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The contents of NiO, MgO and Al2O3 from LDHsderived NiO-MgO-Al2O3 nanocomposite shell are determined to be 0.9, 0.7 and 0.5 wt %, corresponding to a Ni/Mg/Al molar ratio of 3.4/5.0/2.8. Clearly, the Ni/Mg molar ratio by the ICP-AES is identical to that (3.4/5.0) determined by the EDX, whereas the NiO content of 0.9 wt % is consistent with that (1.0 wt %) deduced from the H2-TPR results. After 4519

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ACS Sustainable Chemistry & Engineering reduction in H2 at 700 °C for 2 h, whereas the nanosheet morphology is maintained well (Figure 3e), the Ni nanoparticles appear with clearly observed Ni(111) plane having interplanar distance of about 0.202 nm and are uniformly embedded into nanosheets with the size distribution peaking at 10 nm (Figure 3f).32 Such prereduced microfibrous-structured NiO-MgO-Al2O3/ FeCrAl-fiber catalyst was examined in the DRM reaction. Figure 4a shows the temperature-dependent conversion for a

is a paramount consideration. We therefore check the stability of our microfibrous-structured LDHs-derived NiO-MgO-Al2O3 nanocomposite catalyst in the DRM reaction at 800 °C and a GHSV of 5000 mL g−1 h−1. Figure 4c shows the conversion and syngas H2/CO ratio against time on stream. The CH4/CO2 conversion maintains almost constant at 91%/89% within the initial 90 h and then slides in a smooth downturn (to 80/85%) within another 180 h running, whereas the H2/CO ratio decreases from 0.92 to 0.85. Tracking the source of catalyst deactivation is of great importance for rational catalyst optimization. XRD was first employed to map the variation of Ni particles in the catalyst after 270 h testing, showing a detectable Ni diffraction peak (JCPDS No. 04-0850, Figure 4d). TEM analyses clearly indicate that the average Ni particle size is increased from 10 nm (Figure 3f) for the fresh reduced catalyst to 16 nm (Figure 4e) for the used one after 270 h testing. In addition, a clear graphite peak is also presented in the XRD pattern (Figure 4d), being responsible for an carbon deposit amount of approximate 0.14 g gcat−1 or a coking rate of 0.52 mg gcat−1 h−1 according to the thermogravimetric analysis (TGA, inset of Figure 4d). SEM image shows that the used catalyst is rather robust and the nanosheet morphology is well reserved after 270 h testing (Figure 4f). More interestingly, no carbon filament with a Ni particle head, which is unavoidably formed on normal Ni-based catalyst,33 is observable on this used catalyst (Figure 4f). This observation in turn evidences the firm intercalation of Ni particles in the MgO-Al2O3 composite, which makes the escape of Ni particles from composite structure hard thereby preventing the fast carbon filament formation directly observed using in situ TEM by Nørskov and co-workers. As a result, not surprisingly, our microfibrous-structured LDHs-derived NiOMgO-Al2O3 nanosheet catalyst shows a significantly reduced carbon formation rate by approximate 1 order of magnitude compared to the Ni-MgO/Al2O3 and Ni/Al2O3 catalysts under similar reaction conditions: 0.52 mg gcat−1 h−1 for the NiOMgO-Al2O3/FeCrAl-fiber vs 3.30 mg gcat−1 h−1 (deduced from carbon amount after 30 h reaction) for the Ni-MgO/Al2O3 catalyst34 and 3.68 mg gcat−1 h−1 (deduced from carbon amount after 250 h reaction) for the Ni/Al2O3 catalyst.3 Despite a slow coking rate, gradually blocking of the Ni particle surface is inevitable by the carbon deposit along with prolonged time on stream, which is the main cause for the catalyst deactivation. Indeed, after removing the carbon deposit by calcining the used catalyst in air at 700 °C and subsequently reducing it at 700 °C in H2, the catalyst activity can restore to the fresh level (CH4/ CO2 conversions of 91%/89% and H2/CO ratio of 0.92; at 800 °C). Note that the Ni particle size remains almost unchanged at approximate 16 nm on such regenerated catalyst (Figure S3), suggesting thus the slight sintering of the Ni particle is not the main cause for the catalyst deactivation in this study.

Figure 4. Temperature-dependent (a, at a GHSV = 5000 mL g−1 h−1), GHSV-dependent (b) and longer-term testing (c, at 800 °C and a GHSV = 5000 mL g−1 h−1) results for the DRM reaction using the NiMgO-Al2O3/FeCrAl-fiber-900 catalyst. Note: 0.80 g catalyst, 0.1 MPa, CH4/CO2 = 1.0/1.1. XRD pattern (d), TGA curve (inset of d), TEM images (e) and SEM image (f) of the Ni-MgO-Al2O3/FeCrAl-fiber catalyst after 270 h reaction.

feed of CH4/CO2 = 1.0/1.1 at a gas hourly space velocity (GHSV) of 5000 mL g−1 h−1. Because of the strong endothermicity of the DRM reaction, elevating the reaction temperature favorably drives the equilibrium shift toward syngas production. High CH4/CO2 conversion of 97%/93% can be obtained at 850 °C, whereas the satisfying CH4/CO2 conversion of 36%/42% is achievable even at a low temperature of 600 °C. Although a syngas product with H2/CO ratio close to 1 is obtainable at high temperature of 850 °C, the ratio declines with lowering the reaction temperature. For example, the H2/CO ratio is only 0.77 at 600 °C because the reverse water gas shift reaction is favorable at low temperatures thereby leading to a reduction of the syngas H2/CO ratio. Figure 4b shows the CH4/CO2 conversion against the GHSV in a wide reaction temperature range, showing a decline trend with the increase in the GHSV. At 800 °C, for example, the CH4/CO2 conversion decreases from 92%/90% to 65%/70% when increasing the GHSV from 3000 to 20 000 mL g−1 h−1. In addition, from the industrial point of view, the catalyst stability

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CONCLUSION In summary, we demonstrate an effective and efficient γ-Al2O3/ water interface-assisted method for in situ growth of NiMgAlLDHs along with the fiber of FeCrAl-fiber felt. A promising microfibrous-structured NiO-MgO-Al2O3/FeCrAl-fiber catalyst for the DRM reaction is developed by thermally decomposing as-prepared NiMgAl-LDHs/FeCrAl-fiber, achieving high activity, selectivity and promising stability. Carbon deposition is the main cause for catalyst deactivation whereas the carbon formation rate is reduced significantly by approximate 1 order of magnitude compared to a normal Ni/Al2O3 catalyst. Ni 4520

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(9) Daza, C. E.; Gallego, J.; Mondragon, F.; Moreno, S.; Molina, R. High Stability of Ce-Promoted Ni/Mg-Al Catalysts Derived from Hydrotalcites in Dry Reforming of Methane. Fuel 2010, 89, 592−603. (10) Gonzalez, A. R.; Asencios, Y. J.; Assaf, E. M.; Assaf, J. M. Dry Reforming of Methane on Ni-Mg-Al Nano-Spheroid Oxide Catalysts Prepared by the Sol-Gel Method from Hydrotalcite-Like Precursors. Appl. Surf. Sci. 2013, 280, 876−887. (11) Chen, W.; Sheng, W. Q.; Cao, F. H.; Lu, Y. Microfibrous Entrapment of Ni/Al2O3 for Dry Reforming of Methane: Heat/Mass Transfer Enhancement Towards Carbon Resistance and Conversion Promotion. Int. J. Hydrogen Energy 2012, 37, 18021−18030. (12) Bortolozzi, J. P.; Gutierrez, L. B.; Ulla, M. A. Synthesis of Ni/ Al2O3 and Ni-Co/Al2O3 Coatings onto AISI 314 Foams and Their Catalytic Application for the Oxidative Dehydrogenation of Ethane. Appl. Catal., A 2013, 452, 179−188. (13) Kirillov, V. A.; Fedorova, Z. A.; Danilova, M. M.; Zaikovskii, V. I.; Kuzin, N. A.; Kuzmin, V. A.; Krieger, T. A.; Mescheryakov, V. D. Porous Nickel Based Catalysts for Partial Oxidation of Methane to Synthesis Gas. Appl. Catal., A 2011, 401, 170−175. (14) Cai, S. X.; Zhang, D. S.; Shi, L. Y.; Xu, J.; Zhang, L.; Huang, L.; Li, H. R.; Zhang, J. P. Porous Ni-Mn Oxide Nanosheets in Situ Formed on Nickel Foam as 3D Hierarchical Monolith De-NOx Catalysts. Nanoscale 2014, 6, 7346−7353. (15) Sadykov, V.; Mezentseva, N.; Fedorova, Y.; Lukashevich, A.; Pelipenko, V.; Kuzmin, V.; Simonov, M.; Ishchenko, A.; Vostrikov, Z.; Sadovskaya, E.; Muzykantov, V.; Zadesenets, A.; Smorygo, O.; Roger, A. C.; Parkhomenko, K.; Bobrova, L. Structured Catalysts for Stem/ Autothermal Reforming of Biofuels on Heat-Conducting Substrates: Design and Performance. Catal. Today 2015, 251, 19−27. (16) Meng, G.; Yang, Q.; Wang, Y.; Sun, X.; Liu, J. NiCoFe SpinelType Oxide Nanosheet Arrays Derived from Layered Double Hydroxides as Structured Catalysts. RSC Adv. 2014, 4, 57804−57809. (17) Cai, S. X.; Liu, J.; Li, H.; Shi, L.; Zhang, D. S.; Zha, K. A General Strategy for In-Situ Decorating Porous Mn-Co Bi-Metal Oxides on Metal Mesh/Foam as High Performance De-NOx Monolith Catalysts. Nanoscale 2017, 9, 5648−5657. (18) Liu, Y.; Xu, J.; Li, H.; Cai, S.; Hu, H.; Fang, C.; Shi, L.; Zhang, D. Rational Design and In Situ Fabrication of MnO2@NiCo2O4 Nanowire Arrays on Ni Foam as High-Performance Monolith DeNOx Catalysts. J. Mater. Chem. A 2015, 3, 11543−11553. (19) Huang, L.; Zhao, X.; Zhang, L.; Shi, L.; Zhang, J.; Zhang, D. Large-Scale Growth of Hierarchical Transition-Metal Vanadate Nanosheets on Metal Meshes as Monolith Catalysts for De-NOx reaction. Nanoscale 2015, 7, 2743−2749. (20) Du, X.; Zhang, D.; Shi, L.; Gao, R.; Zhang, J. Coke- and Sintering-Resistant Monolithic Catalysts Derived from In Situ Supported Hydrotalcite-Like Films on Al Wires for Dry Reforming of Methane. Nanoscale 2013, 5, 2659−2663. (21) Li, H.; Zhang, D.; Maitarad, P.; Shi, L.; Gao, R.; Zhang, J.; Cao, W. In Situ Synthesis of 3D Flower-Like NiMnFe Mixed Oxides as Monolith Catalysts for Selective Catalytic Reduction of NO with NH3. Chem. Commun. 2012, 48, 10645−10647. (22) Wang, K.; Li, X. J.; Ji, S. F.; Huang, B. Y.; Li, C. Y. Preparation of Ni-Based Metal Monolithic Catalysts and a Study of Their Performance in Methane Reforming with CO2. ChemSusChem 2008, 1, 527−533. (23) Basile, F.; Benito, P.; Del Gallo, P.; Fornasari, G.; Gary, D.; Rosetti, V.; Scavetta, E.; Tonelli, D.; Vaccari, A. Highly Conductive Ni Steam Reforming Catalysts Prepared by Electrodeposition. Chem. Commun. 2008, 2917−2919. (24) Miao, Y. E.; Wang, R.; Chen, D.; Liu, Z.; Liu, T. Electrospun Self-Standing Membrane of Hierarchical SiO2@γ-AlOOH (Boehmite) Core/Sheath Fibers for Water Remediation. ACS Appl. Mater. Interfaces 2012, 4, 5353−5359. (25) d’Espinose de la Caillerie, J. B.; Kermarec, M.; Clause, O. Impregnation of γ-Alumina with Ni(II) or Co(II) Ions at Neutral pH: Hydrotalcite-Type Coprecipitate Formation and Characterization. J. Am. Chem. Soc. 1995, 117, 11471−11481.

nanoparticles in the reduced catalyst are uniformly nested in MgO-Al2O3 nanosheet composites, which is paramount for inhabitation of fast carbon filament formation.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b00717. Catalyst preparation, characterization and test, SEMEDX analysis results of the NiO-MgO-Al2O3/FeCrAlfiber-900 catalyst, H2-TPR of the pure NiO powder, TEM image of the regenerated Ni-MgO-Al2O3/FeCrAlfiber catalyst after 270 h of reaction (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*G. Zhao. E-mail: [email protected]. *Y. Lu. E-mail: [email protected]. Fax: (+86)2162233424. ORCID

Ye Liu: 0000-0003-3875-2913 Yong Lu: 0000-0002-5126-1476 Author Contributions

R. Chai, S. Fan, Z. Zhang and P. Chen prepared samples, performed the experiments and analyzed the data. G. Zhao and Y. Lu conceived and directed the project. R. Chai, G. Zhao, Y. Liu and Y. Lu composed the manuscript and then critically discussed and revised together. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was funded by the NSF of China (21473057, U1462129, 21273075, 21076083), and the “973 program” (2011CB201403) from the MOST of China.

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REFERENCES

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DOI: 10.1021/acssuschemeng.7b00717 ACS Sustainable Chem. Eng. 2017, 5, 4517−4522

Letter

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DOI: 10.1021/acssuschemeng.7b00717 ACS Sustainable Chem. Eng. 2017, 5, 4517−4522