Structure-Sensitive and Insensitive Reactions in Alcohol Amination

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Research Article Cite This: ACS Catal. 2018, 8, 11226−11234

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Structure-Sensitive and Insensitive Reactions in Alcohol Amination over Nonsupported Ru Nanoparticles Guanfeng Liang,† Yage Zhou,‡,§ Jingpeng Zhao,†,§ Andrei Y. Khodakov,*,† and Vitaly V. Ordomsky*,§

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†

Univ. Lille, CNRS, Centrale Lille, ENSCL, Univ. Artois, UMR 8181-UCCS-Unité de Catalyse et Chimie du Solide, F-59000 Lille, France ‡ State Key Laboratory of Chemical Engineering, School of Chemical Engineering, East China University of Science and Technology, 130 Mei long Road, Shanghai 200237, China § E2P2L, UMI 3464 CNRS-Solvay, 3966 Jin Du Road, 201108 Shanghai, China S Supporting Information *

ABSTRACT: The reaction rates and selectivity of many metal-catalyzed reactions depend on the size of the metal particles in the nanoscale range. Primary amines are important platform molecules in the chemical industry. In this work, the catalytic performance of nonsupported Ru nanoparticles with sizes from 2 to 9 nm was investigated in direct amination of octanol and other alcohols into primary amines in the presence of ammonia. The 90% selectivity to octylamine was obtained over small Ru nanoparticles (d = 2 nm) even at 92% conversion, whereas for larger Ru nonsupported and supported nanoparticles, the octylamine selectivity dropped as the octanol conversion approached 70−80%. The primary reaction of alcohol amination into octylamine was found to be nearly a structure-insensitive reaction. The selectivity to primary amine drops over large Ru particles at higher conversions, because of the secondary highly structure-sensitive reaction of amine self-coupling. Over small metal nanoparticles, amine selfcoupling is hindered, because of suppression of secondary imine hydrogenation. Similar structure sensitivities of the reactions involved in alcohol amination were observed for different substrates. KEYWORDS: ruthenium, size, nanoparticles, amination, alcohols

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INTRODUCTION Primary amines are important intermediates in the production of various valuable N-containing chemicals, such as dyes, plastics, rubber, herbicides, pharmaceuticals, and agrochemicals.1−3 Several technologies have been developed for the synthesis of primary amines, including hydroaminomethylation/hydroamination,4 alcohol amination,5−7 and reductive amination of aldehydes and ketones.8−11 The direct amination of alcohols with ammonia is considered as green and promising procedure because ammonia is cheap and highly accessible and water is the only byproduct generated by this procedure. Homogeneous Ru, Ir, Pd, and Cu complex catalysts were designed for alcohol amination.12−18 Alcohol amination proceeds according to a “hydrogen borrowing” mechanism:19 (i) alcohol is dehydrogenated to the corresponding aldehyde or ketone, and (ii) the imine intermediate is formed by noncatalytic reaction of aldehyde or ketone with ammonia followed by (iii) hydrogenation of imine to alkyl amine. The reaction results in the formation of the primary, secondary, and tertiary amines. The major goal of alcohol amination is the selective synthesis of the primary amine, which is a much more valuable © XXXX American Chemical Society

product in comparison with secondary and tertiary amines. Because of their higher nucleophilicity, primary amines are generally more reactive than ammonia, which results in the sequential formation of secondary and tertiary amines.20 Promising results in selective amination of alcohols have also been recently reported by the groups of Fujita,16 Williams,17 Kempe,21 and Tomishige.22 The best yields have been achieved in the continuous flow reactor.23 Ru-based organometallic catalysts have recently been proven to be highly efficient in alcohol amination.24,25 However, supported heterogeneous Ru catalysts showed lower selectivity in comparison with those of other metal catalysts (Ni and Co)26−29 toward primary amines. For instance, Mizuno et al. reported the direct amination of 1-octanol with aqueous NH3 (28 wt %) on Ru(OH)x/TiO2, obtaining the tertiary amine as the main product with a yield of 88%.30 This is due to the selfcoupling of primary amines, which readily occurs and yields secondary and tertiary amines. The development of efficient Received: July 21, 2018 Revised: October 18, 2018

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ACS Catalysis and selective heterogeneous Ru catalysts for alcohol amination remains a challenging problem. Only a few patents have demonstrated the selective synthesis of cyclohexylamine over Ru/Al2O3.31 Most of the successful syntheses of primary amines have been performed using aldehydes/ketones as reagents,3,7 which are more expensive than alcohols. Selective amination of secondary alcohols also has been successfully performed using ruthenium hydroxyapatite catalysts.32 To overcome these problems for amination of primary alcohols, a fundamental understanding of the reaction mechanism and the effect of nanoparticle (NP) size, support, and promoters on tuning the selectivity and activity of heterogeneous Ru catalysts is highly essential. On the other hand, most of the previous studies have focused on the amination of cyclic, aromatic, and branched alcohols, and the literature about direct amination of aliphatic alcohols is limited. The application of metal NPs in catalysis has received a great deal of attention because of their potential role in bridging the gap between surface chemistry and real industrial catalytic processes.33−37 Metal NPs with a controlled size, shape, morphology, and composition provide highly important information about the structure-performance correlations under “realistic” reaction conditions. In particular, the metallic NPs can offer important insights into the structural sensitivity of many catalytic reactions. Boudart classified heterogeneous catalytic reactions into two groups based on the sensitivity of the catalytic activity to particle size.38 Structure-sensitive reactions are those for which the intrinsic activity of active sites is dependent on the particle size, while in the structureinsensitive reactions, the surface site intrinsic activity is independent of particle size. For structure-sensitive reactions, the turnover frequency (TOF), or reaction rate normalized per surface atom, changes with particle size. For structureinsensitive reactions, the rate remains directly proportional to the number of surface sites in a broad particle size range. Herein, we have synthesized and characterized a series of Ru NPs with a uniform size, shape, and structure and tested them in direct amination of alcohols in the presence of NH3 and H2. The particular goal of this work was to elucidate the influence of ruthenium particle sizes on the selectivity of amination of octanol to octylamine. On the basis of the obtained correlations, a new strategy for selective synthesis of primary amine was proposed. This approach was further extended for the selective synthesis of other valuable amines.

Table 1. Metallic Ru NP Catalysts Prepared Using Microemulsions with Different Compositions catalyst Ru NP-2 nm Ru NP-3 nm Ru NP-5 nm Ru NP-9 nm Ru/Al2O3

CTAB/hexanol/ H2O

water content (%)

particle size from TEM (nm)

5.0/4.5/0.5

5

2.2

4.7/4.3/1

10

3.2

4.2/3.8/2

20

5.2

2.9/2.6/4.5

45

8.8

−

−

5.2

aqueous RuCl3 solution. Another reference catalyst, Ru NP-2 nm/Al2O3 with a 5 wt % metal loading, has been prepared by incipient wetness impregnation with an aqueous solution of Ru NP-2 nm. The resulting solid were dried at 80 °C overnight. Then, the powders were calcined in air at 400 °C for 4 h with a heating rate of 1 °C min−1. The catalysts have been reduced in the reactor prior the test at 200 °C for 1 h. Catalytic Tests. The catalytic tests were conducted in a 50 mL high-pressure autoclave. Ru NPs have been used without any additional pretreatment. For a typical test of 1-octanol amination with ammonia, 10−200 mg of catalyst and 1.0 mL of 1-octanol were added to the autoclave and then gaseous NH3 was charged into the autoclave by cooling the autoclave to 0 °C to provide the necessary NH3/octanol ratio. Afterward, the reactor was pressurized with 2.0 bar of H2. The reaction was conducted at 180 °C for 1−24 h. Other alcohols (benzyl alcohol, furfuryl alcohol, and 2-butanol) were aminated in the same way. To evaluate the rate of secondary conversion of octylamine, the following experimental conditions were used: 16 mg of Ru NPs (80 mg for Ru/Al2O3), 1 mL of octylamine, NH3/ octylamine ratio of 17, and PH2 of 2 bar. The reaction was conducted at 180 °C for 2 h. The liquid products were analyzed after conducting the reaction with a gas chromatography system equipped with a HP-5 column and a FID detector using biphenyl as the external standard. The TOFs were defined as the number of moles of octanol converted to the product per mole of Ru surface atoms per hour. The product selectivity (S) was reported as the percentage of octanol converted into a given product and expressed on a molar basis. Characterization. For TEM analysis, a JEOL 2100 instrument with Filament LaB6 having an acceleration voltage of 200 kV equipped with a Gatan 832 CCD camera was used. Prior to TEM characterization, the samples were dispersed in an ethanol solution with ultrasonic treatment for 5 min and then dropped onto a carbon film on a copper grid. The size distribution was measured by analysis of ∼100 nanoparticles using ImageJ. The X-ray diffraction (XRD) patterns were collected by using a PANalytical X’Pert-Pro diffractometer equipped with Cu Kα radiation (λ = 0.154 nm) and a beam voltage of 40 kV in the 2θ range 10−80°. X-ray photoelectron spectra (XPS) were acquired using a Thermo Scientific ESCALAB 250Xi X-ray photoelectron spectrometer incorporating a 165 mm hemispherical electron energy analyzer. The incident radiation consists of monochromatic Al Kα X-rays (1486.6 eV) at 225 W (15 kV, 15 ma).

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EXPERIMENTAL SECTION Synthesis of Ru NPs with the “Water-in-Oil” Microemulsion Method. Four reverse micellar microemulsions with different CTAB/1-hexanol/water ratios (as shown in Table 1) were prepared. First, 20 g of microemulsion A comprising 0.22 g of RuCl3 and 20 g of microemulsion B comprising 0.13 g of NaBH4 were prepared. The two microemulsions were mixed by adding microemulsion B to microemulsion A drop by drop for 1 h under vigorous stirring. After that, Ru NPs with a uniform particle size distribution were formed inside the micelles. The microemulsion was broken by centrifugation, and the precipitate was washed with hot water three times and dried at 80 °C for 12 h. The synthesized sample was denoted as Ru NP-X nm, where X is the average particle size in nanometers from transmission electron microscopy (TEM). The first reference Ru/γ-Al2O3 with a 5 wt % metal loading was prepared by incipient wetness impregnation with an 11227

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ACS Catalysis The deconvolution was performed on Thermo Scientific Avantage Software. O2 titration was conducted with a Micromeritics AutoChem II 2920 System. A 0.05 g sample was pretreated with a H2 flow in a quartz reactor at 200 °C for 1 h with a ramp of 10 °C/min with subsequent hydrogen desorption at the same temperature and then cooled to 0 °C. The chemisorption of oxygen on the samples was performed by 0.5 mL pulses of 3% O2 in He until full saturation was achieved. The ζ potential of the particles was measured at ambient temperature at neutral pH by the Zetasizer from Malvern Instruments and its software, Dispersion Technology Software (DTS). Water was used as the dispersant with a 1 wt % catalyst concentration at pH 7. The analysis was performed with 12 ζ runs and a 2 mm measurement position at a scattering angle of 90°.

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RESULTS AND DISCUSSION Ru NPs with Different Particle Sizes. A water-in-oil microemulsion with water droplets formed by reverse micelles dispersed in a continuous hexanol phase was used for the synthesis of metal NPs. The size of reverse micelles might be easily controlled by the amount of water with dissolved Ru salt in a certain compositional range of the hexanol/CTAB/water phase diagram (Figure S1). This method has been demonstrated earlier for the synthesis of Pt, Pd, and Rh NPs of different sizes.39 Table 1 demonstrates the compositions of water/oil microemusions, which were used for the synthesis of metal NPs. The TEM images and histograms shown in Figure 1 indicate a uniform size distribution in all the synthesized Ru NPs. A series of Ru NPs with diameters of 2, 3, 5, and 9 nm (Table 1) were synthesized with water contents of 5, 10, 20, and 45%, respectively. The reference catalyst Ru/Al2O3 prepared by conventional impregnation exhibited a broader particle size distribution with an average size of 5 nm. The XRD patterns in Figure 2 show typical diffraction peaks attributed to the hexagonal close-packed (hcp) metallic Ru at 2θ = 38.4°, 42.2°, and 44.0°.37 XRD peak broadening with a decrease in the water content of the microemulsion indicates smaller Ru particle sizes, which is consistent with TEM analysis. XRD profiles of the calcined Ru/Al2O3 catalyst show broad patterns of RuO2. The metal areas of Ru NPs and Ru/Al2O3 were determined by the titration by oxygen and are summarized in Table 2. The oxygen uptake values for Ru NP-2 nm, -3 nm, -5 nm, and -9 nm were 1.10, 0.99, 0.59, and 0.36 mmol (g of Ru)−1, respectively. Assuming that one Ru atom adsorbs one O atom,40 the calculated surface areas for Ru NP-2 nm, -3 nm, -5 nm, and -9 nm were 81, 73, 44, and 26 m2 (g of Ru)−1. This indicates a larger metal surface as the particle size decreases. Oxygen adsorption over reduced reference catalyst Ru/Al2O3 gives results similar to those for the 5 nm metallic particle sample. The oxygen chemisorption data are also consistent with TEM analysis. XPS analysis of Ru 3p was used to identify oxidized species and electronic state of the catalysts (Figure 2b). The peak of metallic Ru (∼461 and ∼483 eV) shifts to a higher binding energy with a decrease in the size of metal NPs. This might be explained by the final state coming from differences in atomic relaxation between large and small metallic NPs. One assumes that the emitted photoelectrons are not quickly replaced with small size metal NPs, which leads to a net positive charge in the final photoemission state. At the same time, the decrease in

Figure 1. TEM images and histograms of the ruthenium particle size in (A) Ru NP-2 nm, (B) Ru NP-3 nm, (C) Ru NP-5 nm, (D) Ru NP9 nm, and (E) Ru/Al2O3.

the size of metal NPs leads to a significantly higher fraction of Ru4+ (binding energies of ∼464 and ∼486 eV). Easier oxidation of smaller NPs has been observed earlier for different metals.41 When the fact that Ru NPs do not demonstrate the presence of oxide phase (Figure 2a) or adsorb oxygen (Table 2) is taken into account, this signal might be assigned to Ru− OH species over defect sites. Figure S2 shows the ζ potential of Ru NPs with different sizes and those supported on alumina. The results show that the ζ potential of small metal NPs (2 and 3 nm) is approximately −35 mV. This is indicative of the strong negative charge of metal NPs. An increase in the size of metal NPs and the use of an alumina support lead to a significant shift of the ζ potential to smaller values. The negative charge of colloidal metal NPs has been explained by partial oxidation of surface metal atoms to M-OH and M-O−.42 Small metal NPs emit protons to an environment at neutral pH, which results in a negative charge. Amination of Octanol. The catalytic performance of Ru NPs was studied in the amination of 1-octanol with ammonia. 11228

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amount of exposed surface sites. This suggests that at moderate conversions in the absence of secondary reactions, octanol amination can be considered as a structure-insensitive reaction with a similar intrinsic Ru site activity for both nonsupported and supported metal NPs. There have been very few studies of structural sensitivity for Ru NPs in the reactions of amination. Alcohol dehydrogenation is usually considered as the rate-limiting step of alcohol amination. Note that oxidative and non-oxidative dehydrogenations of alcohols are usually considered as structure-sensitive reactions. The intrinsic activity in these dehydrogenation reactions either decreases or passes through the maximum as a function of particle size for several metals like Ru, Ag, Pd, etc.43,44 The effect has been ascribed to the enhanced C−H bond activation over weakly coordinated atoms (edges, corners). However, the TOF numbers for the dehydrogenation were in the range of 500−1000 h−145,46 and much higher in comparison with the intrinsic activities of metal surface sites in amination reactions. Indeed, different sites might be present in the same working catalysts during dehydrogenation or amination. The presence of ammonia leads to the deactivation of the most unsaturated metal sites, which might contribute to the reaction rate in the dehydrogenation reactions but are not available during amination.47 Figure 3 shows the conversion−selectivity curves measured for different Ru NPs and Ru/Al2O3. Note that all the tested

Figure 2. (a) XRD patterns and (b) Ru 3p XPS of Ru NPs with different particle sizes and Ru/Al2O3.

The reaction time and the amount of the catalyst were varied to obtain different octanol conversions. The reaction rate for the amination of 1-octanol decreases with an increase in the size of metal NPs (Figure S3). The corresponding TOF values for Ru NPs measured at octanol conversions of 20−40% are listed in Table 2. Interestingly, the TOF values for octanol amination to primary amine at relatively low conversions are comparable for different metal NPs and close to 20 h−1. The similar intrinsic activity is observed over Ru/Al2O3 prepared by impregnation with the RuCl3 salt. Also, comparable activity is observed for amination over Ru NP-2 nm supported over alumina. The high activity observed over smaller Ru NPs was principally due to the larger

Figure 3. Selectivity−conversion curves for Ru NPs and Ru/Al2O3 (40 mg of NPs or 160 mg of Ru/Al2O3, 1.0 mL of 1-octanol, NH3/ octanol ratio of 17, PH2 = 2.0 bar, T = 180 °C, time of 1−24 h).

samples display >90% selectivity to 1-octylamine at 90% conversion (Figure 3). It is interesting to note that although Ru/Al2O3 contains Ru NPs with an average size of 5 nm with a broad particle size distribution, the selectivity to primary amine is significantly lower on the supported catalyst compared to that of Ru NPs at the same conversions and comparable NP sizes. Secondary and tertiary amines can form under the reaction conditions by at least two mechanisms: amination of remaining octanol with primary octylamine49 or amine coupling via intermediate formation of imine.50 Note that at a higher conversion (>90%), the octanol concentration is very low and amine self-coupling seems to be a preferential reaction route. The secondary reactions of 1-octylamine are likely to readily occur at high octanol conversions (>90%), where the concentration of octylamine is the highest. Thus, octylamine self-coupling seems to be the main reason for the selectivity loss at high octanol conversions. We therefore investigated conversion of 1-octylamine on Ru NPs under reaction conditions similar to those for octanol amination. To identify the primary products of 1-octylamine conversion, the experiments were conducted at relatively low 1-octylamine conversions (6−7%). Figure 5 shows the distribution of octylamine conversion products on Ru NPs and Ru/Al2O3 at a similar conversion level. Octylnitrile and secondary imine were obtained as the 11230

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NP-9 nm and the reference Ru/Al2O3 catalyst, octylamine selectivity decreases dramatically to 75% at ∼50% conversion with a decrease in the NH3/octanol ratio from 17 to 7 (Table S2). This suggests that the coupling reaction occurs much easier at low NH3/octanol ratios over large Ru NPs. Importantly, small Ru NPs (Ru NP-2 nm) still provided the same high selectivity (95%) as the ratio of NH3/alcohol decreased to 7, indicating that the coupling reaction was still suppressed over smaller Ru NPs even at a low NH3/octanol ratio. Substrate Scope. To determine the generality of the observed phenomena, we extend the substrate scope to other alcohols. Furfuryl alcohol, benzyl alcohol, and 2-butanol were aminated in the presence of NH3 under solvent free conditions over Ru NP-2 nm and the reference Ru/Al2O3 catalyst. The catalytic tests have been conducted to provide similar conversion levels over both types of catalysts. Table 3 shows that Ru NP-2 nm was able to afford 96% selectivity to benzyl amine in comparison with 71% over Ru/Al2O3 at comparable conversions. Table 3 shows that the amination of furfural alcohol with Ru NP-2 nm gave >90% selectivity to furfurylamine at 42% conversion. Note that the selectivity to furfurylamine was only 67% at 15% conversion over Ru/ Al2O3. Amination of the secondary alcohol (2-butanol) also proceeds much more selectively over Ru NP-2 nm with a 2fold higher yield of the product. The main side products of the reactions were secondary amines; however, other undesirable reactions such as condensation for furfuryl alcohol and imine formation for benzyl alcohols have also been observed (Table S3). It seems important to emphasize that a decrease in the size of Ru NPs suppresses not only amine self-coupling but also other side reactions, which reduce the selectivity to the target products. Recyclability. The stability of the catalyst toward deactivation is an important issue in catalysis. The stability of the Ru NP-2 nm catalyst has been tested in amination of octanol. Figure S5 displays the performance of the Ru NP-2 nm catalyst after three cycles with intermediate separation of the catalyst by high-speed centrifugation. The activity and selectivity of the catalyst do not change significantly. Analysis of the liquid phase obtained after catalyst separation using centrifugation did not show the presence of metal after the

amination of 1-octanol over Ru/Al2O3. The high structural sensitivity of cross-coupling of amines has been observed earlier over a Pd/Al2O3 catalyst.51 According to the authors, amine cross-coupling requires coordinatively unsaturated positively charged Pd NPs. Apparently, the size of Ru NPs and interaction with a support greatly influence the intrinsic activity of the coupling reaction, and small nonsupported Ru NPs had inferior activity compared to that of the large NP. That was the reason why Ru NP-2 nm exhibited higher 1octylamine selectivity at high octanol conversion. Effect of the Ammonia/Alcohol Ratio. A high NH3/ alcohol ratio (20−60) is usually essential in alcohol amination to inhibit the coupling reaction of the formed primary amines.19 Large amounts of secondary and tertiary amines are usually obtained at low NH3/alcohol ratios. A larger amount of NH3 in the reactor significantly increases, however, the cost of the amination process because of the expensive separation and recycling of ammonia and application of special materials for the reaction in a corrosive medium. The results of this work suggest that the monoamine coupling reaction is greatly suppressed on small Ru NPs. We may suggest therefore that the high selectivity to 1-ocylamine can still be obtained over small Ru NPs even with the low NH3/octanol ratio in the reactor. Figure 6 shows that for Ru

Figure 6. Effect of the NH3/alcohol ratio on the selectivity to octylamine at ∼50% conversion. Conditions: 40 mg of NPs or 160 mg of Ru/Al2O3, 1.0 mL of 1-octanol, NH3/octanol ratios of 17 and 7, PH2 = 2.0 bar, T = 180 °C, time of 1−24 h.

Table 3. Comparison of Catalytic Performances of Amination of Different Substrates (40 mg of NPs or 160 mg of Ru/Al2O3, 1.0 mL of alcohol, NH3/alcohol ratio of 17, PH2 = 2.0 bar, T = 180 °C, time of 1−24 h)

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Characterization of Ru NPs by analysis of the ζ potential (Figure S2) has shown the presence of a strong negative charge over small Ru metal nanoparticles. These sites according to XPS analysis are due to oxidation of surface Ru atoms with formation of hydroxyl sites Ru-O−. The negative charge and the presence of surface oxygen species on smaller Ru NPs could make them less favorable for adsorption over isolated metal domains and activation of the electron-rich secondary imine (Figure 7). The negative charge with smaller NPs in the liquid phase could also explain the slower hydrogenation of secondary imines, which makes primary amine self-coupling a structure-sensitive reaction. The catalytic performance of small Ru NP-2 nm is compared with the amination results over other homogeneous and heterogeneous catalysts in Table S4. The yield of primary amines is lower over Ni and Ru catalysts than over Ru NP-2 nm under similar reaction conditions even in the presence of an inert solvent, which is favorable for selective amination. The comparable catalytic performance has been observed only over a Ni catalyst in a continuous flow reactor, where secondary processes of primary amine transformation might be hindered. Homogeneous catalysts like Ru pincer and triphos complexes provide selective amination of alcohols to primary amines with comparable or higher yields (Table S4) under mild reaction conditions. Thus, Ru nonsupported nanoparticles of 2 nm combine the advantages of homogeneous and heterogeneous catalysts in terms of selectivity and recyclability of the catalyst, respectively. It can create new opportunities and lead to new green processes for selective synthesis of primary compounds with different heteroatoms like nitrogen, oxygen, sulfur, and phosphorus.

reaction had been performed. This implies that the catalyst remains stable under the reaction conditions. Effect of the Size and Support. Our results show that the primary reactions of alcohol amination are structureinsensitive. At the same time, the size of NPs affects much more strongly octylamine coupling to dioctylamine and trioctylamine with almost no activity observed for Ru NP-2 nm and a significant increase in activity for larger and in particular supported NPs. Thus, amine self-coupling seems to be a structure-sensitive reaction. Coupling of primary amines with formation of the secondary imine easily happens over all types of metal NPs; however, smaller metal NPs have lower activity in hydrogenation of secondary imines to amines (Figure 7). There are several

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CONCLUSION In conclusion, the octylamine selectivity in octanol amination was found to be a function of the rates of octanol amination and octylamine self-coupling. It is strongly influenced by the size of Ru NPs. The amination of octanol into octylamine on Ru NPs was found to be a structure-insensitive reaction, because all Ru NPs presented comparable TOF values. The self-coupling of octylamine was sensitive to the size of Ru NPs. A lower rate of amine self-coupling was observed over smaller nonsupported Ru NPs. The structural sensitivity of Ru NPs to octylamine self-coupling was attributed to the structural and electronic effects during hydrogenation of the secondary imine, which is an important reaction intermediate. A similar structural sensitivity of the selectivity to the primary amine on the Ru NP size was also observed for a wide range of other alcohols (furfuryl alcohol, benzyl alcohol, and 2-butanol).

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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/acscatal.8b02866. Catalytic results, phase diagram, TOF amination and coupling, stability, and ζ potential (PDF)

Figure 7. Ru NP size and effect of support on self-coupling of primary amines.

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possible reasons that can explain this effect. First, secondary imines are more bulky than primary imines. Adsorption and hydrogenation of secondary imines over small nonsupported metal nanoparticles might be limited in comparison with that over large or supported counterparts. Another effect could be related to the different basicity of primary and secondary imines, which should affect their interaction with metal NPs.

AUTHOR INFORMATION

Corresponding Authors

*Unité de Catalyse et de Chimie du Solide, UMR 8181, CNRS, Ecole Centrale de Lille, Université de Lille Bât. C3, 59655 Villeneuve d’Ascq, France. E-mail:andrei.khodakov@ univ-lille.fr. 11232

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ACS Catalysis *E2P2L, UMI 3464 CNRS-Solvay, 3966 Jin Du Rd., 201108 Shanghai, China. E-mail: [email protected].

with Aqueous Ammonia: Selective Synthesis of Primary Allylamines. Angew. Chem., Int. Ed. 2012, 51, 150−154. (16) Yamaguchi, R.; Kawagoe, S.; Asai, C.; Fujita, K.-I. Selective Synthesis of Secondary and Tertiary Amines by Cp*IridiumCatalyzed Multialkylation of Ammonium Salts with Alcohols. Org. Lett. 2008, 10, 181−184. (17) Hamid, M. H. S. A.; Allen, C. L.; Lamb, G. W.; Maxwell, A. C.; Maytum, H. C.; Watson, A. J. A.; Williams, J. M. J. RutheniumCatalyzed N-Alkylation of Amines and Sulfonamides Using Borrowing Hydrogen Methodology. J. Am. Chem. Soc. 2009, 131, 1766−1774. (18) Fujita, K.-I.; Furukawa, S.; Morishima, N.; Shimizu, M.; Yamaguchi, R. N-Alkylation of Aqueous Ammonia with Alcohols Leading to Primary Amines Catalyzed by Water-Soluble NHeterocyclic Carbene Complexes of Iridium. ChemCatChem 2018, 10, 1993−1997. (19) Bähn, S.; Imm, S.; Neubert, L.; Zhang, M.; Neumann, H.; Beller, M. The Catalytic Amination of Alcohols. ChemCatChem 2011, 3, 1853−1864. (20) Imm, S.; Bähn, S.; Neubert, L.; Neumann, H.; Beller, M. An Efficient and General Synthesis of Primary Amines by RutheniumCatalyzed Amination of Secondary Alcohols with Ammonia. Angew. Chem., Int. Ed. 2010, 49, 8126−8129. (21) Blank, B.; Michlik, S.; Kempe, R. Synthesis of Selectively Mono-N-Arylated Aliphatic Diamines via Iridium-Catalyzed Amine Alkylation. Adv. Synth. Catal. 2009, 351, 2903−2911. (22) Takanashi, T.; Nakagawa, Y.; Tomishige, K. Amination of Alcohols with Ammonia in Water over Rh-In Catalyst. Chem. Lett. 2014, 43, 822−824. (23) Leung, A. Y. K.; Hellgardt, K.; Hii, K. K. Catalysis in flow: Nickel-catalyzed synthesis of primary amines from alcohols and NH3. ACS Sustainable Chem. Eng. 2018, 6 (4), 5479−5484. (24) Gunanathan, C.; Milstein, D. Selective Synthesis of Primary Amines Directly from Alcohols and Ammonia. Angew. Chem., Int. Ed. 2008, 47, 8661−8664. (25) Derrah, E. J.; Hanauer, M.; Plessow, P. N.; Schelwies, M.; da Silva, M. K.; Schaub, T. Organometallics 2015, 34 (10), 1872−1881. (26) Shimizu, K.-I.; Kon, K.; Onodera, W.; Yamazaki, H.; Kondo, J. N. Heterogeneous Ni Catalyst for Direct Synthesis of Primary Amines from Alcohols and Ammonia. ACS Catal. 2013, 3, 112−117. (27) Li, S.; Wen, M.; Chen, H.; Ni, Z.; Xu, J.; Shen, J. Amination of isopropanol to isopropylamine over a highly basic and active Ni/ LaAlSiO catalyst. J. Catal. 2017, 350, 141−148. (28) Dumon, A. S.; Wang, T.; Ibañez, J.; Tomer, A.; Yan, Z.; Wischert, R.; Sautet, P.; Pera-Titus, M.; Michel, C. Direct n-octanol amination by ammonia on supported Ni and Pd catalysts: activity is enhanced by “spectator” ammonia adsorbates. Catal. Sci. Technol. 2018, 8, 611−621. (29) Tomer, A.; Wyrwalski, F.; Przybylski, C.; Paul, J.-F.; Monflier, E.; Pera-Titus, M.; Ponchel, A. 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. 2017, 356, 111−124. (30) He, J.; Kim, J. W.; Yamaguchi, K.; Mizuno, N. Efficient catalytic synthesis of tertiary and secondary amines from alcohols and urea. Angew. Chem. 2009, 121, 10072−10075. (31) Uehara, K. (Idemitsu Petrochemical Co.). JP Patent JP5,148,191, 1993. (32) Peeters, A.; Claes, L.; Geukens, I.; Stassen, I.; De Vos, D. Alcohol amination with heterogeneous ruthenium hydroxyapatite catalysts. Appl. Catal., A 2014, 469, 191−197. (33) Uehara, K. (Idemitsu Petrochemical Co.). JP Patent JP6,001,758, 1994. (34) Ohyama, J.; Sato, T.; Yamamoto, Y.; Arai, S.; Satsuma, A. Size Specifically High Activity of Ru nanoparticles for Hydrogen Oxidation Reaction in Alkaline Electrolyte. J. Am. Chem. Soc. 2013, 135, 8016− 8021. (35) Crooks, R. M.; Zhao, M.; Sun, L.; Chechik, V.; Yeung, L. K. Dendrimer-Encapsulated Metal nanoparticles: Synthesis, Character-

ORCID

Andrei Y. Khodakov: 0000-0003-4599-3969 Vitaly V. Ordomsky: 0000-0002-4814-5052 Author Contributions

G.L. and Y.Z. contributed equally to this work. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Solvay for financial support of this work. G.L. is grateful to the CNRS-K. C. Wong foundation for providing him funding for postdoctoral research in France. J.Z. is grateful for CIFRE scholarship.

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REFERENCES

(1) Lawrence, S. A. Amines: Synthesis, Properties and Applications; Cambridge University Press, 2004. (2) Willcox, D.; Chappell, B.; Hogg, K.; Calleja, J.; Smalley, A.; Gaunt, M. A general catalytic β-C-H carbonylation of aliphatic amines to β-lactams. Science 2016, 354, 851−857. (3) Jagadeesh, R.; Murugesan, K.; Alshammari, A.; Neumann, H.; Pohl, M.-M.; Radnik, J.; Beller, M. MOF-derived cobalt nanoparticles catalyze a general synthesis of amines. Science 2017, 358, 326−332. (4) Huang, L.; Arndt, M.; Gooßen, K.; Heydt, H.; Gooßen, L. J. Late transition metal-catalyzed hydroamination and hydroamidation. Chem. Rev. 2015, 115, 2596−2697. (5) Elangovan, S.; Neumann, J.; Sortais, J.-B.; Junge, K.; Darcel, C.; Beller, M. Efficient and selective N-alkylation of amines with alcohols catalysed by manganese pincer complexes. Nat. Commun. 2016, 7, 12641−12648. (6) Yan, Z.; Tomer, A.; Perrussel, G.; Ousmane, M.; Katryniok, B.; Dumeignil, F.; Ponchel, A.; Liebens, A.; Pera-Titus, M. A Pd/CeO2 “H2 Pump” for the Direct Amination of Alcohols. ChemCatChem 2016, 8, 3347−3352. (7) Liang, G.; Wang, A.; Li, L.; Xu, G.; Yan, N.; Zhang, T. Production of Primary Amines by Reductive Amination of BiomassDerived Aldehydes/Ketones. Angew. Chem., Int. Ed. 2017, 56, 3050− 3054. (8) Nakamura, Y.; Kon, K.; Touchy, A. S.; Shimizu, K.; Ueda, W. Selective Synthesis of Primary Amines by Reductive Amination of Ketones with Ammonia over Supported Pt catalysts. ChemCatChem 2015, 7, 921−924. (9) Gross, T.; Seayad, A. M.; Ahmad, M.; Beller, M. Synthesis of primary amines: First homogeneously catalyzed reductive amination with ammonia. Org. Lett. 2002, 4, 2055−2058. (10) Gallardo-Donaire, J.; Ernst, M.; Trapp, O.; Schaub, T. Direct Synthesis of Primary Amines via Ruthenium-Catalysed Amination of Ketones with Ammonia and Hydrogen. Adv. Synth. Catal. 2016, 358, 358−363. (11) Jagadeesh, R. V.; Stemmler, T.; Surkus, A.-E.; Junge, H.; Junge, K. M.; Beller, M. Hydrogenation using iron oxide-based nanocatalysts for the synthesis of amines. Nat. Protoc. 2015, 10, 548−557. (12) Pingen, D.; Müller, C.; Vogt, D. Direct Amination of Secondary Alcohols Using Ammonia. Angew. Chem., Int. Ed. 2010, 49, 8130− 8133. (13) Enyong, A. B.; Moasser, B. Ruthenium-catalyzed N-alkylation of amines with alcohols under mild conditions using the borrowing hydrogen methodology. J. Org. Chem. 2014, 79, 7553−7563. (14) Ruch, S.; Irrgang, T.; Kempe, R. New iridium catalysts for the selective alkylation of amines by alcohols under mild conditions and for the synthesis of quinolines by acceptor-less dehydrogenative condensation. Chem. - Eur. J. 2014, 20, 13279−13285. (15) Das, K.; Shibuya, R.; Nakahara, Y.; Germain, N.; Ohshima, T.; Mashima, K. Platinum-Catalyzed Direct Amination of Allylic Alcohols 11233

DOI: 10.1021/acscatal.8b02866 ACS Catal. 2018, 8, 11226−11234

Research Article

ACS Catalysis ization, and Applications to Catalysis. Acc. Chem. Res. 2001, 34, 181− 190. (36) Cushing, B. L.; Kolesnichenko, V. L.; O’Connor, C. Recent Advances in the Liquid-Phase Syntheses of Inorganic nanoparticles. Chem. Rev. 2004, 104, 3893−3946. (37) Kelly, K. L.; Coronado, E.; Zhao, L. L.; Schatz, G. C. The optical properties of metal nanoparticles: the influence of size, shape, and dielectric environment. J. Phys. Chem. B 2003, 107, 668−677. (38) Iglesia, E.; Boudart, M. Structure-sensitivity and ensemble effects in reactions of strongly adsorbed intermediates. Catalytic dehydrogenation and dehydration of formic acid on nickel. J. Phys. Chem. 1991, 95, 7011−7016. (39) Boutonnet, M.; Kizling, J.; Stenius, P.; Maire, G. The preparation of monodisperse colloidal metal particles from microemulsions. Colloids Surf. 1982, 5, 209−225. (40) Rossetti, I.; Pernicone, N.; Forni, L. Characterisation of Ru/C Catalysts for Ammonia Synthesis by Oxygen Chemisorption. Appl. Catal., A 2003, 248, 97−103. (41) Karim, W.; Kleibert, A.; Hartfelder, U.; Balan, A.; Gobrecht, J.; van Bokhoven, J. A.; Ekinci, Y. Size-dependent redox behavior of iron observed by in-situ single nanoparticle spectro-microscopy on welldefined model systems. Sci. Rep. 2016, 6, 18818−18826. (42) Pfeiffer, C.; Rehbock, C.; Hühn, D.; Carrillo-Carrion, C.; Jimenez de Aberasturi, D.; Merk, V.; Barcikowski, S.; Parak, W. J. Interaction of colloidal nanoparticles with their local environment: the (ionic) nanoenvironment around nanoparticles is different from bulk and determines the physico-chemical properties of the nanoparticles. J. R. Soc., Interface 2014, 11, 20130931. (43) Shimizu, K.; Sugino, K.; Sawabe, K.; Satsuma, A. Oxidant-free dehydrogenation of alcohols heterogeneously catalyzed by cooperation of silver clusters and acid-base sites on alumina. Chem. - Eur. J. 2009, 15, 2341−2351. (44) Zhang, Q.; Deng, W.; Wang, Y. Effect of size of catalytically active phases in the dehydrogenation of alcohols and the challenging selective oxidation of hydrocarbons. Chem. Commun. 2011, 47, 9275− 9292. (45) Mori, K.; Hara, T.; Mizugaki, T.; Ebitani, K.; Kaneda, K. Hydroxyapatite-Supported Palladium Nanoclusters: A Highly Active Heterogeneous Catalyst for Selective Oxidation of Alcohols by Use of Molecular Oxygen. J. Am. Chem. Soc. 2004, 126, 10657−10666. (46) Mallat, T.; Baiker, A. Oxidation of Alcohols with Molecular Oxygen on Solid Catalysts. Chem. Rev. 2004, 104, 3037−3058. (47) Cho, J. H.; Park, J.-H.; Chang, T.-S.; Kim, J.-E.; Shin, C.-H. Reductive Amination of 2-Propanol to Monoisopropylamine Over Ni/c-Al2O3 Catalysts. Catal. Lett. 2013, 143, 1319−1327. (48) Ruiz, D.; Aho, A.; Mäki-Arvela, P.; Kumar, N.; Oliva, N.; Murzin, D. Y. Direct Amination of Dodecanol over Noble and Transition Metal Supported Silica Catalysts. Ind. Eng. Chem. Res. 2017, 56 (45), 12878−12887. (49) Sprung, M. A. Summary of the Reactions of Aldehydes with Amines. Chem. Rev. 1940, 26 (3), 297−338. (50) Ikawa, T.; Fujita, Y.; Mizusaki, T.; Betsuin, S.; Takamatsu, H.; Maegawa, T.; Monguchi, Y.; Sajiki, H. Selective N-alkylation of amines using nitriles under hydrogenation conditions: facile synthesis of secondary and tertiary amines. Org. Biomol. Chem. 2012, 10, 293− 304. (51) Shimizu, K.-I.; Shimura, K.; Ohshima, K.; Tamura, M.; Satsuma, A. Selective cross-coupling of amines by alumina-supported palladium nanocluster catalysts. Green Chem. 2011, 13, 3096−3100.

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DOI: 10.1021/acscatal.8b02866 ACS Catal. 2018, 8, 11226−11234