Host-guest chemistry immobilized nickel nanoparticles on zeolites as efficient catalysts for amination of 1-octanol

Journal of Catalysis 381 (2020) 443–453

Contents lists available at ScienceDirect

Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat

Host-guest chemistry immobilized nickel nanoparticles on zeolites as efficient catalysts for amination of 1-octanol Bo Wang a,b, Yu Ding a, Kun Lu a, Yejun Guan a, Xiaohong Li a, Hao Xu a,⇑, Peng Wu a,⇑ a Shanghai Key Laboratory of Green Chemistry and Chemical Process, School of Chemistry and Molecular Engineering, East China Normal University, North Zhongshan R. 3663, Shanghai 200062, China b Shandong Provincial Key Laboratory of Chemical Energy Storage and Novel Cell Technology, School of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng, Shandong 252059, China

a r t i c l e

i n f o

Article history: Received 18 September 2019 Revised 12 November 2019 Accepted 15 November 2019

Keywords: USY@Ni Ni nanoparticles Reductive amination 1-octanol

a b s t r a c t Nickel silicate and NiAl-LDHs (layered double-hydroxides) have been controllably fabricated on the crystal surface of Si-rich and Al-rich USY zeolites, respectively, through a distinctive in-situ hydrothermal growth approach. This was realized by the host-guest chemistry that induced chemoselective interactions between adscititious Ni source and constituent species of zeolite framework. Upon hydrogen reduction, nickel silicate and NiAl-LDHs were transformed to highly dispersed Ni nanoparticles (NPs) immobilized in the SiO2 and Al2O3 matrix, respectively, which were firmly anchored around the USY crystals. The controllable immobilization of Ni NPs created well preserved hierarchical porosity in USY zeolites. With highly dispersed metallic Ni active sites in Al2O3 matrix supported on USY zeolite, the USY@Ni-3 catalyst exhibited similar conversion but significantly enhanced selectivity in the reductive amination of 1-octanol to corresponding alkylamines in comparison to conventional Raney Ni catalyst. Ó 2019 Elsevier Inc. All rights reserved.

1. Introduction Alkylamines are extensively used as building blocks in a variety of high value-added chemicals including pharmaceuticals, polymers, dyes, pigments, and plasticizing agents, which play essential roles both in bulk and fine chemical industries [1,2]. In the huge alkylamine family, aliphatic primary amines are of particular importance, serving as intermediates for further derivatization reactions, which stimulates researchers to develop eco-efficient synthesis route for the primary amines [3]. Nevertheless, the established traditional strategies for the primary amine synthesis, such as hydroamination of alkene or alkynes, and amination of aryl halides, encounter the disadvantages of poor selectivity, low atom-economy and toxic byproducts [4,5]. As an alternative way, the reductive amination of the corresponding alcohols, producing water as the sole stoichiometric side product, emerges as an atom-economic and environmental-benign method for the production of amines [6]. The reductive amination of aliphatic alcohols proceeds via nucleophilic substitution reaction by means of borrowing hydrogen mechanism [7]. As described in Scheme 1, alcohol is firstly ⇑ Corresponding authors. E-mail addresses: [email protected] (H. Xu), [email protected] (P. Wu). https://doi.org/10.1016/j.jcat.2019.11.021 0021-9517/Ó 2019 Elsevier Inc. All rights reserved.

dehydrogenated to alkanal, which then translates to imine by condensation with ammonia, and finally the hydrogen returns to imine, forming primary amine [8,9]. However, as the primary amine is more nucleophilic than ammonia to react with electrophiles, it is prone to over-alkylate the alcohol producing secondary amines and tertiary amines. Besides, the imine intermediate easily dehydrogenates to the corresponding nitrile or condensates with the primary amine giving rise to N-alkyl-imine and ammonia. Thus, the main challenge is to break thermodynamic equilibrium and minimize the selectivity of the nitrile and undesirable amines, in which case the choice of an effective catalyst is highly desired to achieve high activity and selectivity towards primary amine. The premier catalysts mainly focus on a variety of homogeneous pincer Ru complexes [10–12] and heterogeneous noble metals, such as supported Pd [13], Ru [14], Pt [15] and bimetallic catalysts [16,17]. However, the above catalysts suffer from the problems of the catalyst recovery and the high cost of noble metals in practical industrial applications. Recent years have witnessed the development of a series of heterogeneous supported transition metal catalysts [18–20]. Amongst, Co-based catalysts are always performed in bimetallic format such as Ag-Co [21,22], CoPd [17], Co-Ru [23], and Pt-Co catalysts [24], while the supported Cu catalyst was only reported to produce secondary amines [25]. Raney Ni exhibits excellent catalytic performance in alcohol amination yet the operation security hiders the wide application

444

B. Wang et al. / Journal of Catalysis 381 (2020) 443–453

Scheme 1. The representation of the reaction network for the amination of 1-octanol with ammonia.

[26,27]. Notably, supported-Ni catalysts can be employed as fascinating alternatives for the amination of a series of alcohols owing to the outstanding activity and stability [28–31]. Shimizu and coworkers screened a series of metal-supported catalysts for the amination of 2-octanol and obtained the highest performance over Ni/c-Al2O3 catalyst. They demonstrated the small-sized metallic Ni0 NPs on the alumina surface acting as the active species and acid-base sites of c-Al2O3 support were indispensable for the high activity [32]. Similar conclusions that the reaction rate decreased with the increase of Ni particle size for alcohol amination were reported [33,34]. For supported Ni catalyst, the major disadvantage lies in easy aggregation and poor dispersion in particular under high Ni content conditions. On this basis, Tomer et al. fabricated a series of Ni/Al2O3 catalysts with higher dispersion and narrower size distributions of Ni particles using cyclodextrins as the metal complex, which enhanced the catalytic properties in alcohol amination [35]. Whereas the interaction between Ni NPs and Al2O3 support was weak in above method and the participation of organic additives may result in environmental problems. In order to achieve highly efficient and stable catalyst for alcohol amination, it is highly desirable to develop green synthesis route to prepare the Ni-supported catalysts with high dispersion and strong metal species-support interaction. Crystalline aluminosilicates possessing high surface area, intrinsic acidity and unique microporosity, have been utilized as important supports and catalysts for a variety of industrialized reactions [36,37]. As one of the most used industrial catalysts, Y zeolite with the merits of adjustable acidity and feasible availability has been employed to catalyze the gas-phase 1-octanol amination [38]. Our group previously reported a host-guest chemistry for the insitu formation of metal silicate and layered double-hydroxides (LDHs) precursors on Si-rich and Al-rich zeolite respectively, where the smaller particle size and narrower size distribution of metal particles were obtained arising from the Ni-O-Si and Ni-O-Al hetero-condensation/polymerization on the surface, resulting in the improved catalytic activity and stability in hydrogenation reactions [39–41]. On the basis of aforementioned researches, we here applied USY@Ni catalysts, synthesized by the above mentioned in-situ growth route, in the reductive amination of 1-octanol reaction. A series of USY zeolites with various Si/Al ratios were used as precursors to interact with Ni precursors in different ways, with high Si content ones to form nickel silicate and high Al content ones to NiAl-LDHs, which were then reduced to produce the USY@Ni catalysts. Detailed and thorough characterizations by spectroscopy and microscopy were employed to investigate the distinct USY precursors and the reduced USY@Ni catalysts, and the relationship

between the structure properties and the catalytic performance was established preliminarily in the reductive amination of 1octanol.

2. Experimental 2.1. Synthesis of USY zeolites with different ratios The parent USY zeolites with Si/Al molar ratios of ca. 3 and 6 were purchased from Wenzhou Huahua Group Co., Ltd, China. While USY zeolites with higher Si/Al molar ratios were synthesized by performing the acid treatments over the USY zeolite according to previous literatures [42]. The USY zeolite (Si/Al = 6) was firstly calcined in air at 600 °C for 5 h and then refluxed in 6 M HNO3 solution with a solid-to-liquid ratio of 1 g : 50 mL for 1 h and 18 h, to produce delauminated USY with the Si/Al ratio of 70 and 142, respectively. The USY zeolites including commercial and further acid treated ones were denoted as USY-x, where x represents the Si/Al ratio.

2.2. Synthesis of USY@Ni-P and USY@Ni The precursors of USY@Ni catalysts (denoted as USY@Ni-P) were prepared by in-situ hydrothermal growth method. In a typical procedure, Ni(NO3)2
6H2O (1.454 g) and NH4NO3 (2.4 g) were firstly dissolved in deionized water (100 mL), followed by dropwise addition of the 3 wt% ammonia solution under continuous stirring until the pH value reached 8. Afterwards, the USY zeolite powders were evenly dispersed into the above solution and then ultrasonicated for 0.5 h to obtain a homogenized suspension. Subsequently, the suspension was hydrothermally heated a thermostatic water bath under different conditions. The mixtures containing USY zeolites with low Si/Al ratio (USY-3 and USY-6) were heated at 45 °C for 12 h, while the mixtures containing USY-70 and USY-142 zeolites were heated at 80 °C for 1 h. After cooling down to ambient temperature, the green precipitates were separated by centrifugation, rinsed with ethanol and dried at 60 °C for 10 h. The as-fabricated precursors were denoted as USY@Ni-x-P, where x represents the Si/Al molar ratio of USY. The precursors were then reduced in the presence of H2 atmosphere (40 mL min1) at 500 °C for 5 h with the heating rate of 2 °C min1. After reduction, the reactor slowly cooled down to room temperature under N2 stream to prevent the oxidation of Ni0 species. The resultant black powder was denoted as USY@Ni-x, where x represents the Si/Al molar ratio of USY.

B. Wang et al. / Journal of Catalysis 381 (2020) 443–453

2.3. Synthesis of Ni/USY-3-IM For control experiment, the Ni/USY-3-IM sample was synthesized by a conventional impregnation method. Briefly, Ni (NO3)2
6H2O (0.62 g) and USY-3 powder (0.8 g) were firstly dissolved in deionized water (10 g). The as-formed mixture was stirred at 80 °C for 4 h and then exposed to air allowing for the evaporation of water. After drying overnight at 100 °C, the sample was calcined in air at 500 °C for 5 h, and subsequently reduced under the same reduction conditions as described above for preparing USY@Ni catalysts. 2.4. Characterization methods The X-ray diffraction (XRD) of the USY and USY@Ni samples were collected using Cu Ka radiation (k = 1.5405 Å) at 35 kV and 25 mA on a Rigaku Ultima IV diffractometer. Thermogravimetry (TG) profiles were recorded in the temperature range of 25– 800 °C with a ramping rate of 10 °C min1 under N2 atmosphere using Mettler TGA/SDTA 851e instrument. To determine the specific amount of Si, Al, Ni for the various samples, elemental analysis was performed by inductively coupled plasma emission spectrometry (ICP) on a thermal IRIS Intrepid II XSP atomic emission spectrometer. The specific surface area (SBET) was calculated based on the N2 sorption isotherms measured at 196 °C on BELSORPMAX instrument using Brunauer-Emmett-Teller (BET) method. The adsorbed amount at a relative pressure P/P0 of 0.99 was employed to estimate the total pore volumes. The t-plot method and Barrett-Joyner-Halenda (BJH) method were employed to determine the corresponding micropore volume and mesopore size distribution, respectively. The crystal morphology was revealed by Scanning electron microscopy (SEM) on a Hitachi S-4800 microscopy. Transmission electron microscopy (TEM) images were collected on FEI G2F30 with an accelerating voltage of 200 kV, and the histograms of Ni NPs size distribution were calculated by more than 100 particles. IR spectra were carried out in absorbance mode with a spectra resolution of 2 cm1 using a Nicolet Nexus 670 FT-IR spectrometer. X-ray photoelectron spectra (XPS) were collected on ESCA-LAB 250 (VG) using Al Ka (hv = 1486.6 eV) radiation source. The temperature-programmed reduction of hydrogen (H2-TPR) pulse, CO chemisorption and temperature-programmed desorption of CO2 (CO2-TPD) were executed on Micromeritics Autochem 2920. In H2-TPR experiments, the sample (100 mg) was pretreated at 550 °C in Ar stream of 25 mL min1 for 1 h and then cooled down to the 100 °C. The analysis was carried out in 10 vol% H2/Ar stream with the flow rate of 30 mL min1 and the temperature ramping from 100 °C to 800 °C at a rate of 10 °C min1. In pulse experiment of CO chemisorption, the sample (100 mg) was firstly reduced by 10 vol% H2 stream with the flow rate of 60 mL min1 at 500 °C for 1 h and then flushed in He for 1 h. After cooling down to 50 °C, CO pulse was introduced in the reaction system with the flow rate of 30 mL min1. The dose was repeated for 20 times and the CO gas phase concentration was detected by TCD. During CO2-TPD experiments, the sample (100 mg) was pretreated at 550 °C in Ar stream for 1 h and then cooled down to 50 °C to introduce CO2 gas. The TPD profiles were then recorded from 100 to 600 °C with a heating rate of 5 °C min1.

445

into the reactor, during which the heavier Ar gas deposited in the lower space could protect the catalyst from oxidation by the introduced air. The autoclave was then sealed tightly in the presence of N2 flow and placed in the ice-water bath. Subsequently, the autoclave was thoroughly flushed with H2 atmosphere for several times to minimize oxidation of substrates with residual air. Afterwards, certain amount of gaseous ammonia was introduced into the reactor, and then 5 bar H2 was charged into the system. Due to the low content and light weight of H2, it was not counted in mass. The quantity of ammonia was determined by the mass difference before and after introducing ammonia. Finally, the autoclave was heated to 180 °C for 16 h. After cooling down to ambient temperature, the gaseous ammonia and hydrogen were released from the system, and ethanol was then added into the mixture as a solvent. The used catalysts were removed by centrifugation, and the supernatant was analyzed on a gas chromatograph equipped with HP-5 capillary column and a flame ionization detector.

3. Results and discussion 3.1. Preparation and characterization of USY@Ni-P and USY@Ni materials All the parent USY zeolites exhibited the well-defined reflections attributed to the typical FAU topology (Fig. S1). With the increase of Si/Al ratio, the reflection peak around 6.3° attributed to [1 1 1] plane gradually shifted to higher angle correspondingly (Fig. S1B), due to the lattice shrinkage after removing larger Al ions. Upon hydrothermal treatment in aqueous solution of nickel nitrate and base, Ni-Al layered hydrotalcite (NiAl-LDHs) were formed for USY@Ni-3-P and USY@Ni-6-P samples, while nickel silicate phase were formed for USY@Ni-70-P and USY@Ni-142-P samples (Fig. 1) [39,41]. Simultaneously, the peak intensities of the USY zeolite decreased slightly for USY@Ni-70-P and USY@Ni-142-P samples, possibly because the Si-rich zeolites were fragile in a basic medium [43]. Through the comparison of XRD patterns of the USY@Ni-P materials, it is interesting to find that different Nibased precursors were controllably fabricated on the parent USY zeolites, closely depending on their Si/Al ratios. To further determine the nature and skeletal structure of the precursors, IR spectra in the region of 400 and 1600 cm1 were measured (Fig. 2A). The broad bands around 1090 cm1 and 840 cm1 corresponded to the framework asymmetric and symmetric stretching vibration, respectively, whereas the distinct one at 460 cm1 was assigned to internal TO4 (Si or Al) tetrahedra bending vibration. The above typical vibrations were in good

2.5. Catalytic amination of alcohol The amination of alcohol was conducted in high pressure autoclave equipment with a magnetic stirrer. Prior to catalytic tests, the catalysts were pre-reduced at 500 °C for 1 h under H2 flow (40 mL min1). Typically, 1-octanol (1 mL) was firstly added into the vial, and then Ar was charged into the system to remove the air in autoclave. Afterwards the newly reduced catalyst was placed

Fig. 1. XRD patterns of USY@Ni-3-P (a), USY@Ni-6-P (b), USY@Ni-70-P (c), and USY@Ni-142-P (d).

446

B. Wang et al. / Journal of Catalysis 381 (2020) 443–453

100 B

d

1386

670

Weight loss (%)

Absorsance (a.u.)

A 530

c b a

90

d 80

c b a

70 1600

1200 800 -1 Wavenumbers (cm )

200

400

400 600 o Temperature ( C)

800

Fig. 2. FT-IR spectra (A) and TG curves (B) of USY@Ni-3-P (a), USY@Ni-6-P (b), USY@Ni-70-P (c), and USY@Ni-142-P (d).

agreement with the FAU structure reported in literatures [44]. Apart from the intrinsic bands of USY zeolite, the additional vibration at 1386 cm1 emerged for the USY@Ni-3-P and USY@Ni-6-P precursors (Fig. 2A, a and b), assigned to interlayer NO–3 in LDHs phase. Detailed observation in low-frequency region revealed the band at 530 cm1 of the Al-rich precursors, arising from the Ni-O and Al-O vibration [45]. On the other hand, the broad one at 670 cm1 for the Si-rich precursors corresponded to Ni-O-Si lattice vibration [46,47]. These results were indicative of the intrinsic different interaction between nickel and constituent of zeolites with different Si/Al ratios. In conjunction with IR spectra, the thermal evolution of the various precursors were investigated by TG analysis (Fig. 2B). The weight loss below 200 °C was mainly due to the physisorbed water. As for USY@Ni-3-P and USY@Ni-6-P precursors, the obvious weight loss around 300 °C was attributed to the dehydroxylation of layer and the release of volatile species (NOx) generating from the interlayer NO–3 anions [48]. In contrast, the weight loss above 200 °C for the USY@Ni-70-P and USY@Ni-142-P precursors was assigned to the removal of water molecules between layers in nickel silicate phase [49]. It can be deduced that the intrinsic structural differences between NiAl-LDHs and nickel silicate accounted for the distinct vibration bands in IR spectra and weight loss in TG curves. The morphologies of parent USY zeolites and the various USY@Ni-P precursors were characterized by SEM technique (Fig. 3). The parent USY exhibited typical octahedron-type crystal and the commercial USY-3 particles were agglomerated octahedral crystals (0.5–1 lm) with faint defects on the surface (Fig. 3a), resulting from the steaming-assisted stabilization process. In contrast, USY-6 zeolite, as well as the dealuminated derivatives of USY-70 and USY-142 zeolites, displayed relative smaller crystal size ranging from 200 to 600 nm. After the treatment in the solution containing nickel salt, all the USY@Ni-P materials showed distinguishable morphologies from their parent supports with numerous nanoplates growing on the surface. Despite the distinct crystalline structure of NiAl-LDHs and Ni phyllosilicate revealed by XRD, both of them displayed resemble lamellar structure growing vertically on the surface of parent USY zeolites. Thus, irrespective of the Si/Al ratios in USY, core–shell structured composite materials were achieved in in-situ growth process. As a representative, the micro-structures of USY@Ni-3-P and USY@Ni-70-P were further confirmed by TEM technique. As shown in Fig. 4, the two samples both exhibited core-shell structure with the nanoplates surrounding around the core of USY crystals. From high resolution TEM images, one can found the lattice spacing of 0.26 nm and 0.71 nm for USY@Ni-3-P material corresponded well to the (0 1 2) and (0 0 3) planes of LDHs, in good agreement with

a

e

2 μm

b

2 μm

f

1 μm

c

1 μm

g

1 μm

d

1 μm

h

1 μm

1 μm

Fig. 3. SEM images of USY-3 (a), USY-6 (b), USY-70 (c), USY-142 (d), and the corresponding USY@Ni-3-P (e), USY@Ni-6-P (f), USY@Ni-70-P (g), USY@Ni-142-P (h).

XRD diffraction peaks (Fig. 1). On the other hand, the adjacent lattice fringes of 0.45 nm observed for USY@Ni-70-P was attributed to the (2 0 0) plane of nickel phyllosilicate. The observation gave further proof for the formation of NiSiO2 and NiAl-LDHs phase depending on the Si/Al molar ratio of parent USY zeolite, in good consistent with the XRD results. To investigate the intrinsic mechanism for the formation of different Ni-related phases depended on the Si/Al ratio, the formation process was tracked intentionally. In the solution containing nickel salt, ammonium hydroxide and ammonium nitrate, the reactions probably took place as follows.

B. Wang et al. / Journal of Catalysis 381 (2020) 443–453

b

a

(012) 0.26 nm

0.71 nm (003)

0.5 m

20 nm

c

5 nm

d 0.454 nm (110) 0.452 nm (110)

100 nm 20 nm

5 nm

Fig. 4. TEM images of USY@Ni-3-P (a, b) and USY@Ni-70-P (c, d). The inset images show the enlarged area of LDHs or NiSiO2.

NH3
H2 O NH4  + OH—

a

NH4 NO3 NH4  + NO3 —

b

Ni2þ + OH— Ni(OH)2 #

c

NH3 + Ni2þ [Ni(NH3 )6 ]2þ

d

Notably, the nickel hydroxide precipitate and hexamine Ni(II) complex could be formed in the treatment solution. After adding ammonium nitrate into the nickel salt solution, the color changed from green to light blue subsequently due to the transformation from isolated Ni(II) ions to the [Ni(NH3)6]2+ complex (Fig. S2a and c), which remained unchanged even after the addition of ammonium hydroxide (Fig. S2d). In comparison, the green precipitate of nickel hydroxide was generated speedy by adding the ammonium hydroxide or sodium hydroxide into the nickel salt solution, yet the precipitate was dissolved gradually and changed into the [Ni(NH3)6]2+ phase after the addition of ammonium nitrate (Fig. S2b and d). Considering the coordination constants of nickel hydroxide (2  1015) and hexammine Ni(II) (3.1  108), the asformed [Ni(NH3)6]2+ complex is much stable and therefore was hardly affected by the adding sequence of ammonium hydroxide and ammonium nitrate. Therefore, the nickel species in the ultimate treatment solution for both NiAl-LDHs and nickel silicate existed as [Ni(NH3)6]2+ complex. After immersing USY zeolites into the mixture, the concentration of OH– decreased owing to its reaction with Si or Al species in zeolites. Then the equilibrium reaction (a) shifted to the right hand and more OH– ions were released simultaneously. Owing to the decrease of concentration of soluble NH3, the equilibrium reaction (d) shifted to the left side to release more isolate NH3. In this case, Ni2+ ions were released simultaneously from the complex and reacted with USY support in the solution. As for the USY zeolite with high Si/Al ratio, the desilication phenomenon occurred after the attack of OH–, the dissolved Si species subsequently interacted with the released Ni2+ and formed layered nickel silicate firmly attached on the surface of USY zeolite. As for the USY with low Si/Al ratio, by virtue of the interaction of

447

OH– ions and Al2O3 component in USY, AlOOH phase generated on the surface of USY zeolite, which then reacted with the released Ni2+ species and gave rise to the NiAl-LDHs nanosheets robustly anchored on USY zeolite surface [41]. On basis of the Si/Al ratio of USY zeolite, NiSiO2 and NiAl-LDH phase were selectively grown on the surface of zeolite by virtue of the in-situ growth method, as illustrated in Scheme 2. Upon reduction, the characteristic peaks of NiAl-LDHs and nickel silicate phases both disappeared, and a weak peak around 44.5° appeared simultaneously (Fig. S3), assigned to the (1 1 1) plane of cubic Ni metal (JCPDS No. 04-0850). The NiAl-LDHs and nickel silicate species were readily reduced in H2 atmosphere, forming the metallic Ni particles. These materials possessed comparable bulk Ni loadings of 20.5–20.9 wt% as given by ICP analysis, and then the higher the peak intensity at 44.5° the larger the Ni particle size. In this sense, the supported Ni particle size for the USY@Ni samples gradually increased with the Si/Al ratio. The morphologies of USY@Ni-3 and USY@Ni-70 kept almost unchanged compared to their precursors (Fig. 5a and b), although their XRD patterns altered remarkably upon reduction. Moreover, highly dispersed Ni nanoparticles (NPs) with the average diameter of 4.3 and 5.8 nm were robustly anchored on the Al2O3 and SiO2 matrixes attaching to USY-3 and USY-70 (Fig. 5c and d, and Fig. S4). The Al2O3 and SiO2 matrixes, the hulls of NiAl-LDHs and nickel silicate after Ni reduction, resembled the original morphologies. Supported Ni particles on USY-3 zeolite by conventional impregnation method displayed non-uniform size distribution ranging from 20 to 60 nm (Fig. S5). Therefore, through the unique in-situ growth approach, excellent dispersion with Ni loading as high as 20 wt% on USY zeolites with various Si/Al molar ratios were obtained. The corresponding HRTEM image of USY@Ni-3 and USY@Ni-70 exhibited the distance of adjacent lattice fringes of 0.204 and 0.202 nm, corresponding well to the d111 plane of cubic Ni metal (Fig. 5c and d), which was consistent with XRD patterns. As previously reported [50], during the thermal decomposition of NiAl-LDHs, the LDHs precursors firstly decomposed to generate the Ni(Al)Ox matrix at the temperature below 300 °C, and the NiO phase was in turn stabilized by spinal-type phase at NiOAl2O3 interface. Upon the subsequent hydrogen reduction process, Al3+ ions migrated from central part to the surface of Ni(Al)Ox, and thereby metallic Ni clusters were firmly confined in amorphous AlOx matrix giving rise to highly dispersed Ni nanoparticles in Al2O3 network. Herein, metallic Ni grains were extracted from NiAl-LDHs and nickel silicate precursors during reduction process, meanwhile the remained SiO2 or Al2O3 matrix were left as carpet to disperse numerous Ni NPs. The elemental mapping image taken by energy-dispersive X-ray spectroscopy (EDX) reflected the element distribution on the surface of USY@Ni-3 and USY@Ni-70 material (Fig. 5e and f). Si element concentrated in the internal space of USY@Ni-3 sample, while Ni and Al atoms spread around the crystal due to the formation of NiAl-LDHs phase. As for USY@Ni-70 sample, small amount of Al species located in the core of the crystal, while Si and Ni species spread over the whole crystal, indicating the distinct distribution of elements for the USY@Ni-3 and USY@Ni-70 samples. In addition, the Ni loading for all the samples calculated by XPS spectroscopy were much higher than the bulk Ni loading (Table S2), further confirming the location of Ni nanoparticles was mainly on the surface of the crystals. The porosities of various pristine USY zeolites were firstly determined by N2 adsorption measurement at 77 K (Fig. S6 and Table S1). After suffering dealumination process, USY-70 and USY-142 still possessed comparable surface area as the parent USY-6 zeolite. The total pore volume and mesopore volume both increased with the Si/Al molar ratio owing to the formation of mesopores in the dealumination process. The N2 isotherms as well as BJH distribution of various USY@Ni materials were shown in

448

B. Wang et al. / Journal of Catalysis 381 (2020) 443–453

Scheme 2. Schematic illustration of the different procedures for preparing the USY@Ni catalysts using either Al-rich or Si-rich USY materials.

Fig. 6, and the corresponding textural properties data were summarized in Table 1. Obviously, all the four materials displayed the combination of type-I and IV isotherms, and the hysteresis loops indicated the presence of mesopores. As the Si/Al ratio of the four USY@Ni materials increased from 3 to 142, the specific surface area decreased from 565 to 448 m2 g1 correspondingly. Moreover, the total pore volume and micropore volume exhibited similar descending trend. Compared with pristine USY zeolites, the microporosity decreasing of Ni-containing USY zeolites were more severe for high silica samples and consistent with the reduction of crystallinity revealed in XRD patterns (Fig. S3), due to the partial structural collapse resulting from the desilication of the Si-rich zeolites in the base solution [51]. In contrast, the mesopore volume of the various USY@Ni materials successively increased from 0.18 m2 g1 to 0.22 m2 g1 along with the increase of Si/Al ratio, comparable with the pristine USY samples, indicating the hierarchical porosity were well preserved after supporting Ni NPs. Obviously, the BJH pore size distribution (Fig. 6B) of USY@Ni-3 mainly displayed broad peak near 16 nm, while the mesopore diameter shifted to 30 nm or even 50 nm for USY@Ni-6 sample. The peak around 90 nm for Si-rich materials was presumedly caused by the desilication phenomenon in the base solution. Supporting metal on zeolites is always accompanied with the blockage of micro- and mesopores owing to the poor control of metal location on supports [52]. Whereas the intrinsic hierarchical porosity was well retained for USY@Ni-3 and USY@Ni-6 catalysts derived from LDHs precursor, which mainly resulted from the stability of pristine Al-rich USY zeolites in base solution and the precise confinement of Ni NPs in Al2O3 matrix. In contrast, the micropore volume of Ni-containing Si-rich zeolites decreased due to the partial structural collapse during the treatment in base solution, while the mesopores were well preserved. This in-situ Ni loading method could achieve higher dispersion of metal nanoparticles and avoid the pore blockage. To gain insight to the reducibility and nickel-zeolite interaction, the redox sites of the various USY@Ni-P catalysts were measured by H2-TPR profiles (Fig. 7). With the increase of Si/Al ratio, the peak value gradually shifted to higher temperature. After deconvolution, two reduction peaks centered at around 400 °C and 600 °C respectively were presented for all the samples. The faint peak around 400 °C was ascribed to the reduction of NiO to metallic Nispecie

[53]. In terms of USY@Ni-3-P and USY@Ni-6-P samples, the major peak at 600 °C was attributed to the reduction of Ni2+ ions in NiAl-LDHs precursor. The elevated temperature was raised from the formation of Ni-doped alumina phase during the thermal decomposition of LDHs [54]. In comparison, with respected to USY@Ni-70 and USY@Ni-142 samples, the peak around 630 °C was derived from the reduction of nickel phyllosilicate precursors [55], which was higher than NiAl-LDHs precursor implying stronger interaction between Ni(II) phase and SiO2 interface than Ni (II) phase and AlOx interface. Generally, the interaction between metal and support plays a contradictory role. On one side, the stronger interaction provides higher resistance to sintering and favors higher metallic dispersion. On the other side, too strong interaction prevents the reduction of Ni2+ ions leading to the less reduced metallic Ni0 species [56]. In addition, the corresponding quantitative representations of the different redox sites were listed in Table 2. As the Si/Al of Ni-based materials increased, the redox site assigned to NiO phase decreased correspondingly, whereas the proportion attributed to NiAl-LDHs and nickel phyllosilicate increased gradually. In fact, the Al content was relatively less even for USY zeolites with low Si/Al ratio, and there were more Ni species existing as NiO and less in the form of NiAl-LDHs phase. While it is opposite for USY zeolites with high Si/Al ratio, the large amount of silica made more Ni species react with it. It can be concluded owing to the difference of the interaction between Ni and Al or Si species, the reduction temperature changed with the corresponding Ni-based precursors. In this sense, the metallic Ni0 species for USY@Ni catalysts were further determined by XPS spectroscopy (Fig. S7). With the increase of Si/Al ratio, the percentage of metallic Ni0 species decreased correspondingly, in good accordance with the higher reduction temperature for USY@Ni70-P and USY@Ni-142-P materials. 3.2. The amination of 1-octanol with NH3 The prepared USY@Ni materials were applied as catalysts to the reductive amination reaction of 1-octanol with NH3. According to the acknowledged borrowing hydrogen mechanism, the reaction network for amination of 1-octanol using NH3 including dehydrogenation, C-N coupling, and hydrogenation steps (Scheme 1). The primary amine, secondary imine and nitrile were captured by

449

B. Wang et al. / Journal of Catalysis 381 (2020) 443–453

a

b

500 nm

c

500 nm

d Ni NPs Ni NPs

5 nm

5 nm

e

f

Si

Al

Ni

Si

Al

Ni

Fig. 5. SEM images of USY@Ni-3 (a) and USY@Ni-70 (b); TEM images of USY@Ni-3 (c) and USY@Ni-70 (d); elemental mapping of USY@Ni-3 (e) and USY@Ni-70 (f). The amplified insets show the high resolution images of nanoparticles.

GC-MS technique, while no aldehyde intermediate was captured during the amination reaction. It may be because the initial dehydrogenation step was the rate-determining step, and the as-formed octyl-aldehyde immediately reacted with ammonia forming imine intermediate [16]. The carbon balance data for all the amination reactions were between 89% and 94%, and the partial carbon loss was due to the inevitable carbon deposition on the catalysts. It indicated all the reaction products were collected and the reaction

data were sufficiently reliable. We firstly screened the effect of Ni loading on the catalytic activity for amination of 1-octanol over USY@Ni-3 catalyst. Obviously, the Ni content presented a positive effect on the catalytic properties, and the conversion of 1-octanol was basically linear with the Ni content (Fig. 8). As Ni loading increased from 5.5% to 20%, the conversion of 1-octanol raised from 3% to 76% correspondingly, while the selectivity of primary amine remained close to 90% irrespective of Ni loading. It can be deduced

450

B. Wang et al. / Journal of Catalysis 381 (2020) 443–453

0.6

A

-1

Volume adsorption (cm g )

400

B

3

0.5 d c b a

200

+150

dV/dlog(D)

300

+100 +50

d

+0.3

c

+0.2

b

+0.1

0.4 0.3 0.2

100

a

0.1 0 0.0 0.2 0.4 0.6 0.8 1.0 Relative pressure (P/P0)

0.0 10 100 Pore diameter (nm)

Fig. 6. N2 sorption isotherms (A) and BJH pore size distributions (B) of USY@Ni-3 (a), USY@Ni-6 (b), USY@Ni-70 (c), and USY@Ni-142 (d).

Table 1 Physicochemical properties of various USY@Ni materials with different Si/Al ratios. Catalysts

Si/Al ratioa

SBETb (m2 g1)

Vtotalc (cm3 g1)

Vmicrod (cm3 g1)

Vmesoe (cm3 g1)

USY@Ni-3 USY@Ni-6 USY@Ni-70 USY@Ni-142

2.9 5.7 71 139

565 529 479 448

0.39 0.35 0.33 0.32

0.21 0.14 0.11 0.10

0.18 0.21 0.22 0.22

a

Determined by ICP analysis. Specific surface area obtained from N2 adsorption isotherms at 77 K using BET method. c Given by adsorption capacity at relative pressure of P/P0 = 0.99. d Obtained by t-plot method. e Vmeso = Vtotal - Vmicro. b

Intensity (a.u.)

d c b a 100

200

300

400

500

600

700

800

o

Temperature ( C) Fig. 7. H2-TPR profiles of USY@Ni-3-P (a), USY@Ni-6-P (b), USY@Ni-70-P (c), and USY@Ni-142-P (d).

that the larger Ni loading produced more metallic Ni active sites accessible to reactants during reaction and hence facilitated the conversion of 1-octanol, which was in accordance with the previous report [21]. Fixing the Ni loading at 20 wt%, we then tested the performance of the USY@Ni catalysts with different Si/Al ratio. As shown in Fig. 9, USY@Ni-3 and USY@Ni-6 catalysts exhibited excellent activity with 1-octanol conversion of 76% and 80% respectively, whereas the former one generated much higher selectivity towards primary amine than the latter (92% vs 51%). In contrast, USY@Ni-70 and USY@Ni-142 catalysts only converted 51% and 35% of 1-octanol, accompanied with primary amine selectivity of 79% and 92%. The catalytic performance of supported metal catalysts was highly dependent on the particle size, dispersion, reduction degree and the interaction with support. Generally, small size and high dispersion of metal species favor the exposure of specific faces with high activity [24,57]. The higher reduction degree guarantees the sufficient amount of active metallic species [58]. The strong interaction between metal species with support can prevent the metal leaching during reaction and improve the stability [59]. Considering the aforementioned characteristic data, as for the USY@Ni catalysts with the Si/Al ratio varying from 3 to 142, the calculated Ni dispersion decreased from 6.17 to 3.98 correspondingly (Table 1). Since the distribution of nickel was closely related to the support structure, the decline of Ni dispersion on Si-rich USY zeolites was due to the decrease of surface area and pore volume resulted by the partial collapse during the treatment. Moreover, the metallic Ni0 species decreased with the Si/Al ratio, indicating less amount of Ni NPs reduced at 500 °C for the USY@Ni catalysts with high Si/Al ratios (Fig. S7). Thus, lower dispersion and less amount of reduced metallic Ni NPs mainly led to the disappointed performance for 1octanol amination over Si-rich USY@Ni-70 and USY@Ni-142 catalysts. Generally speaking, it is always difficult to balance the conversion and the selectivity to target product. Taking the amination of 1-octanol for example, high conversion gave rise to faster formation rate of amine, whereas the as-formed primary amine may further react with ketone to generate secondary amine. Therefore, the frustrating activities observed over USY@Ni-142 prevented the consecutive conversion of primary amine and lead to relative high selectivity to primary amine. The main side product over USY@Ni catalysts was primarily secondary amine (Fig. S8), especially for USY@Ni-6 catalyst with a high secondary amine selectivity of 44%. In terms of borrow hydrogen mechanism (Scheme1), the secondary amine was resulted from the further reaction of octylamine with octanal. Due to the introduction of H2 during the reaction, the nitrile was largely suppressed by the introduction of H2 pressure. It was found that small sized Ru nanoparticles can prevent the amine self-coupling and suppress the hydrogenation of secondary imine resulting in higher selectivity towards primary amine [60]. As is revealed by XRD patterns (Fig. S3), the USY@Ni-6 and USY@Ni-70 catalysts possessed the rel-

Table 2 Physicochemical properties and catalytic performances of various USY@Ni catalysts in the amination of 1-octanol.a Catalysts

USY@Ni-3 USY@Ni-6 USY@Ni-70 USY@Ni-142 a b c d e

Ni loadingb (wt%)

20.9 20.5 20.6 20.9

Redox sitesc (mmol g1) Total

Low

High

1.87 1.81 1.79 1.74

0.56 0.20 0.13 0.08

1.31 1.61 1.66 1.66

Dispersiond (%)

Base sitee (mmol g1)

Primary amine yield (%)

6.2 5.9 4.4 4.0

0.142 0.085 0.011 0.008

70 41 38 32

Reaction conditions: cat., 150 mg; 1-octanol, 1 mL; nammonia/noctanol = 13–16; H2 pressure, 5 bar; temp., 180 °C; time, 16 h. Determined by ICP analysis. Determined by H2-TPR profiles. Calculated by CO pulse. Determined by CO2-TPD profiles.

451

Amine sel.

80 60 40

1-Octanol conv.

20 0 5

10 15 Ni loading (wt.%)

20

Fig. 8. Amination of 1-octanol over USY@Ni-3 with different Ni content. Reaction conditions: cat., 150 mg; 1-octanol, 1 mL; nammonia/noctanol = 15; H2 pressure, 5 bar; temp., 180 °C; time, 16 h.

100 80 60 60 40 20 0

40 20

Parimary amine sel. (%)

1-Octanol conv. (%)

80

0

USY U SY U @Ni@Ni- SY@Ni USY@ -6 Ni-70 14 2 3

Fig. 9. Amination of 1-octanol over USY@Ni-3, USY@Ni-6, USY@Ni-70 and USY@Ni142. Reaction conditions: cat., 150 mg; 1-octanol, 1 mL; nammonia/noctanol = 15; H2 pressure, 5 bar; temp., 180 °C; time, 16 h.

atively larger Ni particle size in comparison to USY@Ni-3, which may promote the self-coupling reaction and generate secondary amine as side product. In addition to the effect of metallic Ni active sites, the basic sites of support contributed to stabilize alkoxide intermediates and suppress the side-reaction [23]. In this sense, CO2-TPD profiles were collected to determine the basic sites of USY@Ni catalysts (Fig. S9). With the increase of Si/Al ratio, the total basic quantity decreased from 0.142 mmol g1 to 0.008 mmol g1 (Table 2), indicating largest amount of basic sites for USY@Ni-3 catalyst derived from NiAl-LDHs precursor. Combined with the reaction scheme, the sufficient basic sites of Al2O3 may stabilize the octanol intermediate and prevent the over-alkylation of octanol with primary amine. Notably, the highly dispersed metallic Ni active sites on the surface of USY@Ni-3 catalyst as well as the abundant basic sites contributed to the high conversion of 1octanol, and most importantly prevented consecutive reaction with octanol producing highest octylamine yield of 70% (Table 2). Encouraged by the surprising performance for 1-octanol amination using USY@Ni-3 catalyst, derived from NiAl-LDHs precursor in-situ grown on the surface of USY zeolite, we furtherly applied the in-situ growth method to other Al-rich zeolites with low Si/Al ratio, i.e. Beta, LTL and MAZ zeolites (Si/Al ratio = 4.5, 2.8 and 3.6, respectively). Likewise, the NiAl-LDHs nanosheets were fabricated on Beta, LTL and MAZ zeolites forming core-shell structure, which indicated high universality of this strategy (Figs. S10 and

S11). Upon reduction at 500 °C, the obtained [email protected], [email protected] and [email protected] catalysts with the same Ni loading of 20 wt% were employed to catalyze the reductive amination of 1-octanol under the same reaction conditions. [email protected] and [email protected] catalysts with the lower Si/Al ratio exhibited comparable activity as USY@Ni-3 catalyst with 1-octanol conversion of 72% and 75%, while the corresponding selectivity to primary amine are 76% and 24% (Fig. 10). In contrast, the [email protected] catalyst with higher Si/Al ratio displayed much lower activity of 40% and higher selectivity of 93%, resembling the performance of USY@Ni-142 sample. As aforementioned above, the basic site of support could stabilize alkoxide intermediate and suppress the side reaction significantly contributing to the high selectivity of primary amine [23,61]. The aluminum species were more easy to transfer to NiAl-LDHs phase for USY zeolites with previous hydrothermal treatment, giving rise to basic Al2O3 phase after reduction. While it was difficult to remove the Al species during the formation of NiAl-LDHs for LTL and MAZ zeolite with integrated crystallinity. It has been reported that the dealumination was more difficult for MAZ zeolite compared to Y zeolite under the same conditions [62]. Therefore, it was deduced the small amount of basic Al2O3 phase mainly account for the disappointing primary amine selectivity using LTL and MAZ as the supports. Through screening the Ni-supported zeolite with different Si/Al ratios and topologies prepared by in-situ growth method, USY@Ni-3 catalyst was indispensable for forming high yield of primary amine. To determine the unique superiority of in-situ growth method, we compared the catalytic performance of USY@Ni-3 with Ni/ USY-3-IM prepared by conventional impregnation method and LDH/USY-3-M prepared by physical mixture of LDHs and USY-3 with the same Ni loading. As depicted in Fig. 11, Ni/USY-3-IM catalyst showed much lower 1-octanol conversion of 51%, while LDH/ USY-3-M catalyst displayed the worst conversion below 20%, although the selectivity of primary amine reached close to 90%. H2-TPR experiments of the three Ni-supported materials were further carried out to compare the nature of nickel species (Fig. S12). Ni/USY-3-IM material exhibited a peak at 350 °C attributed to the reduction of NiO species, and the reduction temperature of the physical mixture of LDH and USY-3 shifted high to 700 °C. However, the corresponding reduction temperature of the material after supporting NiAl-LDHs phase on USY zeolite was around 520 °C. Upon reduction at 500 °C, Ni/USY-3-IM catalyst possessed the largest proportion of metallic Ni species, but the agminated Ni particles with the sizes of 20–60 nm limited the exposure of Ni active sites and lowered the catalytic activity for 1-octanol amination (Fig. S5). The results confirmed the significant effect of Ni par-

80 60

100 80 60

40 40 20 0

20

Parimary amine sel. (%)

100

1-Octanol conv. (%)

1-Octanol conv. or primary amine sel. (%)

B. Wang et al. / Journal of Catalysis 381 (2020) 443–453

0

USY B M LTL@ @Ni- [email protected] AZ@Ni-3 4.5 3 .6

Fig. 10. Amination of 1-octanol over USY@Ni-3, [email protected], [email protected] and [email protected]. Reaction conditions: cat., 150 mg; 1-octanol, 1 mL; nammonia/ noctanol = 15; H2 pressure, 5 bar; temp., 180 °C; time, 16 h.

452

B. Wang et al. / Journal of Catalysis 381 (2020) 443–453

100 80 60 60 40

40

20

0

20

USY @

Ni-3

Ni/U LDH Ra N SY-3 /USY i -I M -3-M

Declaration of Competing Interest

Parimary amine sel. (%)

1-Octanol conv. (%)

80

0

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This study is financially supported by China Ministry of Science and Technology under contract of 2016YFA0202804 and the National Natural Science Foundation of China (Grant No. 21872052, 21533002 and 21603075). Appendix A. Supplementary material

Fig. 11. The comparison of 1-octanol conversion over USY@Ni-3, LDH/USY-3-M, Ni/ USY-3-IM and Ra Ni. Reaction conditions: cat., 150 mg; 1-octanol, 1 mL; nammonia)/ noctanol = 15; H2 pressure, 5 bar; temp., 180 °C; time, 16 h.

ticle size and were in good agreement with previous literatures [32,33]. As for LDH/USY-3-M catalyst, only small proportion of Ni (II) were reduced from the physical mixture leading to the poorest conversion of 1-octanol. The USY@Ni-3 catalyst prepared by in-situ growth method not only favored the narrow distribution Ni NPs, but also lowered the reduction temperature of Ni(II) species significantly. Hence the numerous reduced metallic Ni NPs provided the sufficient active sites for amination of 1-octanol. Raney Ni (Ra Ni) is acknowledged as highly active industrial catalyst for hydrogenation and alcohol amination [26,27], we then compared the performance under the identical conditions with the same amount of Ra Ni (150 mg). USY@Ni-3 catalyst not only exhibited 4.73 times higher TON than Raney Ni (10.23 vs 2.16) (Fig. S13), but also yielded higher selectivity to primary amine (92% vs 89%) than Ra Ni (Fig. 11). In addition, the 1-octanol conversion and primary amine selectivity over USY@Ni-3 catalyst was comparable to supported noble metal catalyst and much higher than the supported transition metal ever-reported in previous literatures [63]. Given the simple preparation route for in-situ growth method, the unique property of the as-fabricated Ni-supported catalysts makes it promising candidate for selective preparation of primary amine from aliphatic alcohol and ammonia.

4. Conclusion In summary, we fabricated well-dispersed Ni NPs robustly immobilized on USY zeolites with various Si/Al ratios through a facile in-situ growth method. Specifically, the NiAl-LDHs and nickel silicate precursors could be fabricated respectively on the Al-rich and Si-rich USY zeolites, from which highly dispersed Ni NPs were confined on the Al2O3 and SiO2 matrix upon reduction. Among the comparison of supported Ni zeolites with different Si/Al ratios and topologies in the reductive amination of 1-octanol, USY@Ni-3 catalyst derived from NiAl-LDHs precursors, exhibited the significantly higher amination activity and the selectivity to the high value-added primary amine, which was comparable to the commercial Ra Ni catalyst although with 20 wt% Ni content. The outstanding performance was closely related to the numerous highly dispersed metallic Ni active sites and sufficient basic sites of Al2O3 matrix derived from the unique structure of NiAl-LDHs. The simple in-situ growth strategy by virtue of the interaction of metal and compositions from zeolite could achieve welldispersed metal NPs robustly anchored on zeolites irrespective of the Si/Al ratio and topology, which can be a promising method to obtain the controllably supported transition metal or metal oxides on zeolites for industrial heterogeneous application.

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jcat.2019.11.021. References [1] S.A. Lawrence, Amines: Synthesis, Properties and Applications, Cambridge University Press, 2004. [2] T.E. Müller, K.C. Hultzschm, M. Yus, F. Foubelo, M. Tada, Hydroamination: direct addition of amines to alkenes and alkynes, Chem. Rev. 108 (2008) 3795– 3892. [3] R. Kadyrov, T.H. Riermeier, Highly enantioselective hydrogen-transfer reductive amination: catalytic asymmetric synthesis of primary amines, Angew. Chem. 42 (2003) 5472–5474. [4] J.F. Hartwig, Evolution of a fourth generation catalyst for the amination and thioetherification of aryl halides, Acc. Chem. Res. 41 (2008) 1534–1544. [5] G. Guillena, J.D. Ramón, M. Yus, Hydrogen autotransfer in the N-alkylation of amines and related compounds using alcohols and amines as electrophiles, Chem. Rev. 110 (2010) 1611–1641. [6] M. Pera-Titus, F. Shi, Catalytic amination of biomass-based alcohols, ChemSusChem 7 (2014) 720–722. [7] X. Ye, P.N. Plessow, M.K. Binks, M. Schelwies, T. Schaub, F. Rominger, R. Paciello, M. Limbach, P. Hofmann, Alcohol amination with ammonia catalyzed by an acridine-based ruthenium pincer complex: A mechanistic study, J. Am. Chem. Soc. 136 (2014) 5923–5929. [8] Q. Yang, Q.F. Wang, Z.K. Yu, Substitution of alcohols by N-nucleophiles via transition metal-catalyzed dehydrogenation, Chem. Soc. Rev. 44 (2015) 2305– 2329. [9] H.J. Pan, T.W. Ng, Y. Zhao, Iron-catalyzed amination of alcohols assisted by Lewis acid, Chem. Commun. 51 (2015) 11907–11910. [10] C. Gunanathan, D. Milstein, Selective synthesis of primary amines directly from alcohols and ammonia, Angew. Chem. 47 (2008) 8661–8664. [11] D. Pingen, C. Müller, D. Vogt, Direct amination of secondary alcohols using ammonia, Angew. Chem. 49 (2010) 8130–8133. [12] S. Imm, S. Bhn, L. Neubert, H. Neuman, M. Beller, An efficient and general synthesis of primary amines by ruthenium-catalyzed amination of secondary alcohols with ammonia, Angew. Chem. 49 (2010) 8126–8129. [13] Z. Yan, A. Tomer, G. Perrussel, et al., A Pd/CeO2 ‘‘H2 Pump” for the direct amination of alcohols, ChemCatChem 8 (2016) 3347–3352. [14] D. Ruiz, A. Aho, T. Saloranta, K. Eränen, et al., Direct amination of dodecanol with NH3 over heterogeneous catalysts. Catalyst screening and kinetic modelling, Chem. Eng. J. 307 (2017) 739–749. [15] F. Du, X. Jin, W. Yan, et al., Catalytic H2 auto transfer amination of polyols to alkyl amines in one pot using supported Ru catalysts, Catal. Today 302 (2018) 227–232. [16] M.R. Ball, T.S. Wesley, K.R. Rivera-Dones, et al., Amination of 1-hexanol on bimetallic AuPd/TiO2 catalysts, Green Chem. 20 (2018) 4659–4709. [17] K. Kim, Y. Choi, H. Lee, J.W. Lee, Y2O3-inserted Co-Pd/zeolite catalysts for reductive amination of polypropylene glycol, Appl. Catal. A: Gen. 568 (2018) 114–122. [18] Y. Jeong, Y. Woo, M. Park, Characteristics of Si-Y mixed oxide supported nickel catalysts for the reductive amination of ethanol to ethylamines, Catal. Today (2019), https://doi.org/10.1016/j.cattod.2019.09.025. [19] A.Y.K. Leung, K. Hellgardt, K.K. ‘‘Mimi”Hii, Catalysis in low: Nickel-Catalyzed Synthesis of Primary Amines from Alcohols and NH3, ACS Sustainable Chem. Eng. J. 6 (2018) 5479–5484. [20] X. Cui, X. Dai, Y. Deng, F. Shi, Development of a general non-noble metal catalyst for the benign amination of alcohols with amines and ammonia, Chem. Eur. J. 19 (2013) 3665–3675. [21] J. Ibáñez, M. Araque-Marin, S. Paul, M. Pera-Titus, Direct amination of 1octanol with NH3 over Ag-Co/Al2O3: Promoting effect of the H2 pressure on the reaction rate, Chem. Eng. J. 358 (2019) 1620–1630. [22] J. Ibáñez, B.T. Kusema, S. Paul, Ru and Ag promoted Co/Al2O3 catalysts for the gas-phase amination of aliphatic alcohols with ammonia, Catal. Sci. Technol. 8 (2018) 5858–5874.

B. Wang et al. / Journal of Catalysis 381 (2020) 443–453 [23] T. Wang, J. Ibañez, K. Wang, et al., Rational design of selective metal catalysts for alcohols amination with ammonia, Nat. Catal. 2 (2019) 773–779. [24] T. Tong, W. Guo, X. Liu, Dual functions of CoOx decoration in PtCo/CeO2 catalysts for the hydrogen-borrowing amination of alcohols to primary amines, J. Catal. 378 (2019) 392–401. [25] J. He, K. Yamaguchi, N. Mizuno, Selective synthesis of secondary amines via Nalkylation of primary amines and ammonia with alcohols by supported copper hydroxide catalysts, Chem. Lett. 39 (2010) 1182–1183. [26] A. Mehta, A. Thaker, V. Londhe, S.R. Nandan, Reinvestigating Raney nickel mediated selective alkylation of amines with alcohols via hydrogen autotransfer methodology, Appl. Catal. A: Gen. 478 (2014) 241–251. [27] Y. Liu, K. Zhou, H. Shu, H. Liu, et al., Switchable synthesis of furfurylamine and tetrahydrofurfurylamine from furfuryl alcohol over RANEYÒnickel, Catal. Sci. Technol. 7 (2017) 4129–4135. [28] A. Tomer, B.T. Kusema, J. Paul, C. Przybylski, E. Monflier, M. Pera-Titus, A. Ponchel, Cyclodextrin-assisted low-metal Ni-Pd/Al2O3 bimetallic catalysts for the direct amination of aliphatic alcohols, J. Catal. 368 (2018) 172–189. [29] G. Sewell, C. O’Connor, E. van Steen, Reductive amination of ethanol with silica supported cobalt and nickel catalysts, Appl. Catal. A: Gen. 125 (1995) 99–112. [30] A.S. Dumon, T. Wang, J. Ibañez, A. Tomer, Z. Yan, R. Wischert, P. Sautet, M. PeraTitus, C. Michel, Direct n-octanol amination by ammonia on supported Ni and Pd catalysts: activity is enhanced by ‘‘spectator” ammonia adsorbates, Catal. Sci. Technol. 8 (2018) 611–621. [31] K.-I. Shimizu, S. Kanno, K. Kon, et al., N-alkylation of ammonia and amines with alcohols catalyzed by Ni-loaded CaSiO3, Catal. Today 232 (2014) 134– 138. [32] K.-I. Schimizu, K. Kon, W. Onodera, H. Yamazaki, J.N. Kondo, Heterogeneous Ni catalyst for direct synthesis of primary amines from alcohols and ammonia, ACS Catal. 3 (2013) 112–117. [33] O. Solcová, K. Jirátová, Role of the support of the nickel catalyst in the synthesis of morpholine from diethylene glycol and ammonia, J. Mol. Catal. 88 (1994) 193–203. [34] C.R. Ho, V. Defalque, S. Zheng, A.T. Bell, Propanol amination over supported nickel catalysts: reaction mechanism and role of the support, ACS Catal. 9 (2019) 2931–2939. [35] A. Tomer, F. Wyrwalski, C. Przybylski, J.F. Paul, E. Monflier, M. Pera-Titus, A. Ponchel, Facile preparation of Ni/Al2O3 catalytic formulations with the aid of cyclodextrin complexes: Towards highly active and robust catalysts for the direct amination of alcohols, J. Catal. 356 (2017) 111–124. [36] M. Hartmann, A.G. Machoke, W. Schwieger, Catalytic test reactions for the evaluation of hierarchical zeolites, Chem. Soc. Rev. 45 (2016) 3313– 3330. [37] S. Tao, X. Li, G. Lv, C. Wang, R. Xu, H. Ma, Z. Tian, Highly mesoporous SAPO-11 molecular sieves with tunable acidity: facile synthesis, formation mechanism and catalytic performance in hydroisomerization of n-dodecane, Catal. Sci. Technol. 7 (2017) 5775–5784. [38] A. Azzouz, D. Nibou, B. Abbad, M. Achache, Amination catalytique de l’octanol en phase gazeuse Action de l’ion uranyle sur l’activité catalytique de la faujasite Y, J. Mol. Catal. 68 (1991) 187–197. [39] D. Wang, B. Ma, B. Wang, C. Zhao, P. Wu, One-pot synthesized hierarchical zeolite supported metal nanoparticles for highly efficient biomass conversion, Chem. Commun. 51 (2015) 15102–15105. [40] B. Ma, H. Cui, D. Wang, et al., Controllable hydrothermal synthesis of Ni/H-BEA with a hierarchical core–shell structure and highly enhanced biomass hydrodeoxygenation performance, Nanoscale 9 (2017) 5986–5995. [41] B. Wang, J. Zhang, Y. Ding, H. Peng, H. Xu, Y. Guan, H. Wu, P. Wu, Freestanding cobalt-aluminum oxides on USY zeolite as an efficient catalyst for selective catalytic reduction of NOx, ChemCatChem 10 (2018) 4074–4083. [42] Z.G. Zhu, H. Xu, J.G. Jiang, X. Liu, J.H. Ding, P. Wu, Postsynthesis of FAU-type stannosilicate as efficient heterogeneouscatalyst for Baeyer-Villiger oxidation, Appl. Catal. A: Gen. 519 (2016) 155–164. [43] N. Linares, A.M. Silvestre-Albero, E. Serrano, J. Silvestre-Albero, J. GarciaMartinez, Mesoporous materials for clean energy technologies, Chem. Soc. Rev. 43 (2014) 7681–7717.

453

[44] J. Zhao, Y. Yin, Y. Li, W. Chen, B. Liu, Synthesis and characterization of mesoporous zeolite Y by using block copolymers as templates, Chem. Eng. J. 284 (2016) 405–411. [45] A.A.S. Gonçalves, M.J.G. Costa, L. Zhang, F. Ciesielczk, One-pot synthesis of MeAl2O4 (Me = Ni Co, or Cu) supported on c-Al2O3 with ultralarge mesopores: enhancing interfacial defects in c-Al2O3 to facilitate the formation of spinel structures at lower temperatures, Chem. Mater. 30 (2018) 436–446. [46] X. Wang, S. Zhu, S. Wang, J. Wang, W. Fan, Y. Lv, Ni nanoparticles entrapped in nickel phyllosilicate for selective hydrogenation of guaiacol to 2methoxycyclohexanol, Appl. Catal. A: Gen. 568 (2018) 231–241. [47] X. Kong, Y.F. Zhu, H.Y. Zheng, X.Q. Li, Y.L. Zhu, Y.W. Li, Ni nanoparticles inlaid nickel phyllosilicate as a metalacid bifunctional catalyst for low-temperature hydrogenolysis reactions, ACS Catal. 5 (2015) 5914–5920. [48] M. Li, J.P. Cheng, J.H. Fang, Y. Yang, F. Liu, X.B. Zhang, NiAl-layered double hydroxide/reduced graphene oxide composite: microwave-assisted synthesis and supercapacitive properties, Electrochim. Acta 134 (2014) 309–318. [49] D.R. Wang, B. Wang, Y. Ding, H.H. Wu, P. Wu, A novel acid-base bifunctional catalyst (ZSM-5@Mg3Si4O9(OH)4) with core/shell hierarchical structure and superior activities in tandem reactions, Chem. Comm. 52 (2016) 12817– 12820. [50] Q.N. Fan, X.F. Li, Z.X. Yang, J.J. Han, S.L. Xu, F.Z. Zhang, Double-confined nickel nanocatalyst derived from layered double hydroxide precursor: atomic scale insight into microstructure evolution, Chem. Mater. 28 (2016) 6296–6304. [51] D. Verboekend, N. Nuttens, R. Locus, J. Van Aelst, P. Verolme, J.C. Groen, J. Pérez-Ramírez, B.F. Sels, Synthesis, characterisation, and catalytic evaluation of hierarchical faujasite zeolites: milestones, challenges, and future directions, Chem. Soc. Rev. 45 (2016) 3331–3352. [52] M.W. Schreiber, D. Rodriguez-Niño, O.Y. Gutiérrez, J.A. Lercher, Hydrodeoxygenation of fatty acid esters catalyzed by Ni on nano-sized MFI type zeolites, Catal. Sci. Technol. 6 (2016) 7976–7984. [53] Q. Bi, X. Huang, G. Yin, T. Chen, X. Du, J. Cai, J. Xu, Z. Liu, Y. Han, F. Huang, Cooperative catalysis of nickel and nickel oxide for efficient reduction of CO2 to CH4, ChemCatChem 11 (2019) 1295–1302. [54] F. Trifirò, A. Vaccari, O. Clause, Nature and properties of nickel-containing mixed oxides obtained from hydrotalcite-type anionic clays, Catal. Today 21 (1994) 185–195. [55] J.C. Park, S.W. Kang, J. Kim, J.I. Kwon, S. Jang, G.B. Rhim, M. Kim, D.H. Chun, H. Lee, H. Jung, H. Song, J. Yang, Synthesis of Co/SiO2 hybrid nanocatalyst via twisted Co3Si2O5(OH)4 nanosheets for high-temperature Fischer-Tropsch reaction, Nano Res. 10 (2017) 1044–1055. [56] P. Burattin, M. Che, C. Louis, Ni/SiO2 materials prepared by depositionprecipitation: influence of the reduction conditions and mechanism of formation of metal particles, J. Phys. Chem. B 104 (2000) 10482–10489. [57] X. Kang, H. Liu, M. Hou, X. Sun, H. Han, T. Jiang, Z. Zhang, B. Han, Synthesis of supported ultrafine non-noble subnanometer-scale metal particles derived from metal-organic frameworks as highly efficient heterogeneous catalysts, Angew. Chem. Int. Ed. 55 (2016) 1080–1084. [58] X. Li, D. Li, H. Tian, L. Zeng, Z. Zhao, J. Gong, Dry reforming of methane over Ni/ La2O3 nanorod catalysts with stabilized Ni nanoparticles, Appl. Catal. B: Environ. 202 (2017) 683–694. [59] A. Tomer, Z. Yan, A. Ponchel, M. Pera-Titus, Mixed oxides supported low-nickel formulations for the direct amination of aliphatic alcohols with ammonia, J. Catal. 356 (2017) 133–146. [60] G.G. Liang, Y. Zhou, J. Zhao, A.Y. Khidakov, V.V. Ordomsky, Structure-sensitive and insensitive reactions in alcohol amination over nonsupported Ru nanoparticles, ACS Catal. 8 (2018) 11226–11234. [61] K. Shimizu, N. Imaiida, K. Kon, S.M.A.H. Siddiki, A. Sasuma, Heterogeneous Ni catalysts for N-alkylation of amines with alcohols, ACS Catal. 3 (2013) 998– 1005. [62] B. Chauvin, M. Boulet, P. Massiani, F. Fatula, F. Figueras, T.D. Courieres, Dealumination of faujasite, mazzite, and offretite with ammonium hexafluorosilicate, J. Catal. 126 (1990) 532–545. [63] D. Ruiz, A. Aho, P. Mäki-Arvela, N. Kumar, H. Oliva, D.Y. Murzin, Direct amination of dodecanol over noble and transition metal supported silica catalysts, Ing. Eng. Chem. Res. 56 (2017) 12878–12887.