Ultrafine Bimetallic PdCo Alloy Nanoparticles on Hollow Carbon

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Ultrafine Bimetallic PdCo Alloy Nanoparticles on Hollow Carbon Capsules: An Efficient Heterogeneous Catalyst for Transfer Hydrogenation of Carbonyl Compounds. Basuvaraj Suresh Kumar, Pillaiyar Puthiaraj, Arlin Jose Amali, and Kasi Pitchumani ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02754 • Publication Date (Web): 14 Nov 2017 Downloaded from http://pubs.acs.org on November 16, 2017

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ACS Sustainable Chemistry & Engineering

Ultrafine Bimetallic PdCo Alloy Nanoparticles on Hollow Carbon Capsules: An Efficient Heterogeneous Catalyst for Transfer Hydrogenation of Carbonyl Compounds Basuvaraj Suresh Kumar,a Pillaiyar Puthiaraj,a Arlin Jose Amali*a,b and Kasi Pitchumani*a,b. a

Department of Natural Products Chemistry, School of Chemistry, Madurai Kamaraj University,

Madurai - 625021, Tamilnadu, India. b

Centre for Green Chemistry Processes, School of Chemistry, Madurai Kamaraj University,

Madurai - 625021, Tamilnadu, India. Email id: [email protected] & [email protected] KEYWORDS. Nanoalloys; Bimetallic PdCo; Hollow carbon capsules; Transfer hydrogenation; Heterogeneous catalyst.

ABSTRACT. Monodispersed ultrafine bimetallic palladium-cobalt alloy nanoparticles (PdxCoy) are prepared and immobilized on hollow carbon capsules (HCCs). Studies on the effect of metal composition on the catalytic activity of the PdxCoy reveal that the nanoparticulate alloy with the atomic composition of Pd36Co64 is more active than the Co and Pd monometallic nanoparticles in the transfer hydrogenation of carbonyl compounds. The composition of the catalyst and its alloy

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formation is extensively characterized and variety of ketones and aldehydes are hydrogenated successfully with excellent yield and high turnover number (TON), displaying the ability of the synthesised ultrafine Pd36Co64 bimetallic nanoalloy to attain and retain both high catalytic activity and stability. This catalytic system is heterogeneous, stable and does not require additives for activation. Other advantages include milder reaction conditions (does not use gaseous hydrogen), low metal content (0.17 mol %) for a catalytic transfer hydrogenation reaction, functional group tolerance, environmentally benign nature and reusability.

INTRODUCTION Transfer hydrogenation is a simple and versatile method for the reduction of polar multiple bonds and number of high-value chemical products, including alcohols and amines, can be efficiently produced using transfer hydrogenation processes.1-4 However, the common hydrogen source for transfer hydrogenation reactions is molecular hydrogen which is difficult and dangerous to handle and store in the laboratory. Consequently, efficient methods for the transition metal catalyzed transfer hydrogenation reactions with environmentally benign hydrogen sources are desired in industrial and academic laboratories.5-7 In this regard, 2-propanol and hydrazine hydrate are considered as good hydrogen donors since they are inexpensive, involve environmentally benign end products, easy to handle and do not require elaborate experimental setups, such as high pressure reactors and are more stable than molecular hydrogen.8-11 Noble metal nanocatalysis has emerged in the past decade as an effective method for generating high-surface-area, efficient, and recyclable heterogeneous catalysts for transfer hydrogenation reactions. There are various noble metals such as Ir, Rh, Ru, Pd, and Pt playing lead roles as catalytically active sites in transfer hydrogenation reactions.12-17 Though these


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catalysts are very active, they are highly expensive. The limited resources of these noble metals, their cost and necessity for sustainable development have prompted chemists to develop newgeneration catalysts in which noble metal contents are effectively reduced while optimum catalytic reactivity being maintained. In this context, alloying with a second metal is considered to be an effective method for obtaining a highly active and selective catalyst compared with their monometallic counterparts, and hence possesses a great potential to be new-generation catalysts by partially or even completely replacing noble metals with non-noble metals.18-22 Thus, consequent dilution of costly noble metals by inexpensive non-noble metals in bimetallic catalysts is of interest because of the potential savings in materials cost, while the catalytic performance is still maintained or even enhanced.23-26 The properties of bimetallic catalysts are significantly different from their monometallic analogues because of the “synergistic effect” between the two metals.27-28 The synergistic effect of such bimetallic catalysts will lead to an increase in the catalytic activity of its monometallic counterparts. Tang et al. have reported uniformly dispersed RuPd alloy nanoparticles on N-doped carbon, as highly active catalysts in the hydrogenation of benzoic acid to cyclohexanecarboxylic acid with turnover frequency upto 2066 h-1.29 The synergistic effect of bimetal catalysts not only increases the activity, but also increases the selectivity in several organic transformations. Goulas et al. have studied the synergistic effect of Pd and Cu (ratio 3:1) dramatically decreases decarbonylation product and increases the oxygenative coupling product due to its synergism.30 Recently, cobalt based heterogeneous catalysts are found to be highly attractive in hydrogenation reactions.31-38 Alloying of non-noble Co NPs with expensive noble metal catalysts is an effective way to improve the catalytic activity of non-noble metal catalysts in transfer hydrogenation reactions. There are only few Co based bimetal catalysts reported for the hydrogenation


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reactions. For example, Lin et al. have reported that a 4:1 ratio of Rh and Co bimetal NPs is more active than the Rh monometallic NPs for selective hydrogenation of C-C unsaturated bonds with hydrazine hydrate and it was reused upto 10 cycles without loss of its activity.39 Udumula et al. have reported40 that Ru-Co NPs supported on polystyrene (Ru:Co-PS) are shown to catalyze nitroarene reductions at room temperature. The immobilization of metal NPs on high-surfacearea materials is a promising route for achieving high-performance heterogeneous catalysts, and significant advances have been made worldwide.41-42 A wide variety of porous materials,43-44 as well as graphene,45 have been used as supports for this purpose. Hollow carbon capsules (HCCs) are presently attracting great attention due to their unique properties such as encapsulation ability, controllable permeability, surface functionality, high surfaces-to-volume ratio and excellent chemical and thermal stabilities. In addition, the presence of confined environment may enhance the catalytic activity due to increase in the local concentration of substrate.46 In consideration of the confined environment of HCCs, synergistic effects in bimetallic catalysts and the advantage of lowering the cost of the catalyst, a bimetallic catalyst by alloying of Pd with Co on HCCs (Pd36Co64@HCCs) is prepared that efficiently promotes the transfer hydrogenation of carbonyl compounds using isopropanol as a hydrogen donor. The Pd36Co64@HCCs nanocatalyst exhibit higher activity than the monometallic Pd and Co nanoparticles as illustrated by the fact that the TOF of the Pd36Co64@HCSs catalyst over a 12 h of period is more than 3.5 times higher than that of the Co monometallic catalyst and can be reused several times without loss of its catalytic activity. RESULTS AND DISCUSSION

PdxCoy (x =100, 75, 50, 25, 0; y = 0, 25, 50, 75, 100) of varying compositions were prepared by the reduction of cobaltous chloride (CoCl2.6H2O) and sodium tetrachloropalladate (Na2PdCl4)


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with sodium borohydride (NaBH4) in an ice-cold aqueous solution of polyvinylpyrrolidone (PVP). NaBH4 reduced the Pd2+ and Co2+ ions to PdxCoy, which were stabilized and prevented from agglomeration by PVP. The synthesized PdxCoy are black in color and have magnetic properties except Pd100Co0 (Figure S1, Supporting Informaion).

Scheme 1: Schematic representation of the synthesis of PdxCoy and PdxCoy@HCCs. A facile and sustainable method was used to fabricate HCCs. Ferrite nanospheres (Fe3O4 NSs) were synthesized using a robust hydrothermal reaction based on high temperature reduction of Fe(III) ions with ethylene glycol, serving both as a solvent and a reducing agent, and urea as the capping agent. The SEM, TEM and PXRD pattern of synthesized Fe3O4 NSs are present in supporting information section (Figure S2, supporting information). A thin layer of carbon shell was coated on the surface of the Fe3O4 NSs through the carbonization of D-glucose under hydrothermal conditions. The hard Fe3O4 template was etched using hydrochloric acid to furnish HCCs. The N2 adsorption/desorption isotherms collected at 77 K for glucose derived HCCs and PdxCoy loaded HCCs, show a surface area of 30.8 m2g-1 and 3 m2g-1 (Figure S3a-b, Supporting Information). The bands at 3600-3250 (broad), 2950, 1699 and 1612 cm-1 in FT-IR spectra correspond to –O-H, -C-H, C=O and C=C stretching frequencies respectively, confirming their presence in HCCs (Figure S3c, Supporting Information). The Raman spectrum of HCCs shows


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the ID/IG value of carbon matrix as 0.70, indicating its amorphous nature (Figure S3d, Supporting Information).47-48 The pre-synthesized PdxCoy were incorporated onto the HCCs by refluxing, to result in a nanocomposite of PdxCoy@HCCs (Scheme 1). The presence of functional groups such as COOH, -OH and -C=O in HCCs can be beneficially used to immobilize and stabilize the catalytically active nanoalloy, PdxCoy on the surface and inner cavity of HCCs.49 This approach is also found to be highly reproducible and scalable. The bimetallic nanoalloy PdxCoy catalyst was prepared at different ratios and the total concentration of the Pdx and Coy and the optimization loading was fixed as 0.2 mmol. The concentration ratios of Pd and Co in the prepared bimetallic NPs are 100:0, 75:25, 50:50, 75:25 and 0:100 respectively (Table S1, Supporting Information).


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(e)

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(d)

(c) (b)

(a)

40

45

50

55

60

65

2 Theta (Θ) Figure 1. PXRD patterns of (a) Pd100@HCCs; (b) Pd75:Co25@HCCs; c) Pd50:Co50@ HCCs; d) Pd25:Co75@HCCs; e) Co100@HCCs. Powder X-ray diffraction (PXRD) was used to determine the crystallinity and phase composition of the PdxCoy@HCCs. The peaks at 2θ values 40.3 and 46.7 correspond to Pd (111) and (200) crystal planes respectively.50-51 The crystal structures of PdxCoy@HCCs are found to be face centered cubic structures (Figure 1). As can be seen from the XRD patterns, the diffraction peaks of the PdxCoy composition at different ratios are shifted slightly to lower 2θ values when compared to those of pure Pd(0), which indicates the formation of an alloy of


7


PdxCoy.52. Due to the relatively strong signal for the Pdx species, no significant diffraction peaks of the Coy species (while zooming at the expected 2θ values for Co) were detected in the XRD pattern for the PdxCoy, which is related to their amorphous structure.53-54 In addition, to confirm the same, we have also analysed the PXRD pattern of a freshly synthesized Co NPs without supported on the HCCs (Figure S4, Supporting information). Here too we observe no significant diffraction in the PXRD pattern. From these results we conclude that the synthesized Co nanoparticles show amorphous behaviour.51 Hence, it does not shows any significant diffraction in the PXRD pattern of PdxCoy. The above synthesized catalysts Pd50Co50@HCCs show higher catalytic activity in the transfer hydrogenation of 4-chloroacetophenone (Figure 4). Hence, we further characterized the active catalyst Pd50Co50@HCCs in ICP-OES, TEM and XPS analyses. Inductively coupled plasma optical emission spectrometric (ICP-OES) analyses show that the Pd50Co50@HCCs contains 1.26 x 10-6 mol for Pd and 2.27 x 10-6 mol of Co (Total metal content 3.53 x 10-6 mol) indicating that the synthesized highly active catalyst is Pd36Co64@HCCs (Figure S5, Supporting information). The size, morphology and composition of the Pd36Co64@HCCs are investigated by TEM analysis (Figure 2). a)

60

b)

e)

50

Number of Particles

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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40 30 20 10 0 2

4

6

8

10

Diameter (nm)


8

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c)

d)

g)

20 nm

f)

h)

i)

Co

Pd

Figure 2. HRTEM images of Pd36Co64@HCCs (a-d); particle size distribution histogram for image b (e); SAED pattern (f) of Pd36Co64@HCCs; TEM‐EDX analysis of Pd and Co elemental distribution in Pd36Co64@HCCs (g-i). 5500

5000

b)

a) 5000

Intensity (a.u.)

4900

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4800

4700

4600

4500 805

4500

4000

3500

800

795

790

785

Binding energy (eV)

780

775

770

3000 344

342

340

338

336

334

332

Binding Energy (eV)

Figure 3: XPS spectrum of Co 2p (a) and Pd 3d (b) of Pd36Co64@HCCs. HRTEM images show that all the impregnated Pd36Co64 are present uniformly on the HCCs (Figures 2a-d) and the particle size is found to be 2-5 nm from the particle size histogram analysis (Figure 2e). It is also noticed that none of the Pd36Co64 are free and all of them were impregnated on HCCs (Figure 2a-d). The morphology of the prepared Pd36Co64 shows a


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spherical shape in the synthesized catalyst. The SAED pattern of the synthesized Pd36Co64@HCCs (Figure 2f) shows slightly crystalline nature and this is in accordance with PXRD data also. TEM−EDX elemental mapping was carried out on the Pd36Co64@HCCs catalyst (containing both Pd and Co) to determine the Pd and Co locations on the catalyst. The results from the images show that the particles are composed of both Pd and Co (Figure 2g-i). XPS measurements are also carried out to obtain a deeper insight into the oxidation state of Co in the Pd36Co64@HCCs catalyst. The peak position of Co 2p3/2 is at ∼778.5 eV corroborates the metallic form of Co (Figure 3a).55 Similarly the oxidation state of Pd was ascertained by XPS which shows the binding energies of 335.5 eV and 342 eV, which are attributed to the Pd 3d5/2 and Pd 3d3/2 levels of Pd(0) (Figure 3b).56 The catalytic activity of PdxCoy@HCCs is checked in transfer hydrogenation of carbonyl compounds. Typically, reaction vessels are sealed after being charged with 2-propanol (which served both as the solvent and hydrogen transfer agent) and 2 mmol of substrate. 4Chloroacetophenone is used as a model substrate for transfer hydrogenation reactions (Table 1). Blank experiments are performed which demonstrate that the metal species are essential (Table 1, Entries 1-2). When compared to other hydrogen sources like isopropanol, hydrazine hydrate, and formic acid, ispropanol with KOH is better (Table 1, entries 3 & 18-19). In addition, the reaction was carried out in 1 atm H2 at room temperature shows no significant activity (Table 1, entry 20). Base is also required for product formation, as yield has dropped in its absence (Table 1, Entry 3). Among the various inorganic and organic bases studied, KOH gives excellent yields (Table 1, Entries 4-7). KOH concentrations are also varied and it is found that 0.5 mmol of KOH and 4 mL of 2-propanol are optimum for this reaction (Table 1, Entries 8-11). An increase in the amount of isopropanol causes a small decrease in yield and this may be attributed to marginal


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decrease in effective concentration of isopropanolate ion (via hydrogen exchange), which prevents its binding to the Pd36Co64@HCCs nanoalloy (Table 1, Entry 11). Among the different catalysts, Pd75Co25 and Pd50Co50 show good conversion (when compared to Pd25Co75, Pd100 and Co100) and this may be due to the synergistic effect (Table 1, Entries 13-17). Based on the observed results, the optimized reaction conditions are 2 mmol of substrate, 4 mL of 2-propanol, 0.5 mmol of base and 40 mg of catalyst in 90 oC for 12 h. Table 1: Optimization of reaction conditions in PdxCoy@HCCs catalyzed transfer hydrogenation of 4-chloroacetophenonea

Entry

Catalyst

Metal Loading (mmol)

Base

i-PrOH (mL)

Time (h)

Conver.h (%)

1

-

-

KOH

6

24

Nil

2

-

-

KOH

6

24

Nilb

3

Pd50Co50@HCCs

0.2

-

6

24

Nil

4

Pd50Co50@HCCs

0.2

KOH

6

16

99

5

Pd50Co50@HCCs

0.2

TEA

6

16

Nil

6

Pd50Co50@HCCs

0.2

K2CO3

6

16

Nil

7

Pd50Co50@HCCs

0.2

Cs2CO3

6

16

29

8

Pd50Co50@HCCs

0.2

KOH

6

16

48c

9

Pd50Co50@HCCs

0.2

KOH

6

16

20d

10

Pd50Co50@HCCs

0.2

KOH

4

16

100

11

Pd50Co50@HCCs

0.2

KOH

8

16

90

12

Pd50Co50@HCCs

0.2

KOH

4

12

99


11


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13

Pd50Co50@HCCs

0.2

KOH

4

10

93

14

Pd75Co25@HCCs

0.2

KOH

4

10

93

15

Pd25Co75@HCCs

0.2

KOH

4

10

80

16

Pd100@HCCs

0.2

KOH

4

10

68

17

Co100@HCCs

0.2

KOH

4

10

60

18

Pd50Co50@HCCs

0.2

-

4

10

25e

19

Pd50Co50@HCCs

0.2

TEA

4

10

Tracef

20

Pd50Co50@HCCs

0.2

-

4

10

Nilg

a

Reaction conditions: Substrate (2 mmol), catalyst (40 mg), solvent (iPrOH),temp (90 oC), base (0.5 mmol); b1 mmol of KOH; c0.25mmol of KOH; d 0.12 mmol of KOH; eN2H4.H2O (6 mmol); fHCOOH (6 mmol); greaction at 1 atm H2 under room temperature; hIsolated yield. A comparative study in which the catalytic performances of synthesized compositions of the bimetallic nanoalloys (Pd50Co50, Pd75Co25, Pd25Co75, Pd100 and Co100) investigated for hydrogenation of 4-chloroacetophenone, establishes clearly the formation of the alloys and the synergistic effect of PdxCoy@HCCs (Figure 4). The experiments reveal that the prepared PdxCoy@HCCs have high efficiency for the catalytic transfer hydrogenation reaction. Figure 4 shows the conversion versus time (h) plot in hydrogenation of 4-chloroacetophenone. Better conversions and similar reactivities are obtained in Pd50Co50 and Pd75Co25 catalysts. Complete conversion is obtained in 12 h when compared to other catalysts, which need 18 h for the same. From the observed results, it is clear that the composition Pd50Co50 ratio is much more active in the catalytic transfer hydrogenation of 4-chloroacetophenone, when compared to other compositions of PdxCoy nanoparticles, due to higher synergistic effect.


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100

Pd50:Co50 Pd100

80

Conversion (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Pd75:Co25 Co100

60

Pd25:Co75

40

20

0 0

2

4

6

8

10

Time (hrs)

Figure 4: Percentage conversion of 4-chloroacetophenone to 1-(4-chlorophenyl)ethanol at different time intervals with different compositions of PdxCoy@HCCs catalysts; Reaction conditions: 4-Chloroacetophenone (2 mmol), catalyst (40 mg), solvent (i-PrOH, 4 mL), base (0.5 mmol), temperature (90 oC). Under the optimized reaction conditions (Table 1, entry 12 and Figure 4), studies are extended further to catalytic hydrogenation of various substituted ketones and aldehydes using Pd36Co64@HCCs as catalyst (Table 2). 2-Acetylnaphthalene, 1-acetylbiphenyl and parasubstituted compounds such as 4-chloro- and 4-bromoacetophenones show good conversion upto 99 % (Table 2, entries 1-4). The yield of the product slightly decreases in the case of 3,4dichloro- and 2-chloroacetophenone and this may due to the electronic effect of the substrate (Table 2, entries 5 and 6). In case of 3,4-dimethoxy- and 3-methoxyacetophenone, slightly lower yields are obtained (Table 2, entries 7 and 8) and this may be due to its – I and +R effect, the effects manifesting themselves unequally in different situations. It is generally accepted that when conjugated to an aryl ring, + R effect has dominance over – I effect, which may have resulted in the slightly lower yield during the reduction. Studies are also extended to aldehydes


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(Table 2, entries 9 and 10) and here also good yields are obtained. We have also compared the catalytic activity of Pd36Co64@HCCs with commercially available Pd/C (5 wt. %). The commercially available Pd/C takes 10 h for completion of the reaction, whereas the Pd36Co64@HCCs (with relatively very low metal content) takes 12 h for completion of the reaction under similar experimental conditions. On the other hand, the Pd36Co64@HCCs catalyst exhibits 47 h-1 of TOF in contrast to 10 h-1 for the Pd/C (Table 2, entry 4). In addition, after completion of the reaction in Pd/C, the filtrate of the reaction becomes brown in colour, indicating significant leaching of Pd after just one run.57 But in the case of Pd36Co64@HCCs, there is no significant colour change and metal leaching was observed after the reaction. Table 2: Substrate scope in Pd36Co64@HCCs catalysed transfer hydrogenation of carbonyl compoundsa Entry

Reactant

Product

Yieldb

TON

TOF (h-1)

99

556

46

99

556

46

99

556

46

99

106

10

99

556

46

1

2

3

c

4

5


14

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6 96

539

45

92

517

43

90

506

42

94

528

44

97

549

45

94

528

44

7

8

9

10

11

a

Reaction conditions: Substrate (2 mmol), Pd36Co64@HCCs (40 mg, 0.17 mol %), solvent (i-PrOH, 4 mL), KOH = 0.5 mmol, time (12 h), temperature (90 oC); b Isolated yield. cReaction conditions: Reactant (2 mmol), Pd/C (40 mg, 0.93 mol %), solvent (i-PrOH, 4 mL), KOH = 0.5 mmol, time (10 h), temperature (90 oC); c Isolated yield.

To account for the observed catalytic activity by Pd36Co64@HCCs, the following tentative mechanism (scheme 2) involving Pd36Co64 nanoalloy hydride intermediate is proposed, by analogy with previously reported system.8 Initial binding of isopropanolate ion (I) to nanoalloy Pd36Co64 and subsequent elimination of ketone yields a nanoalloy Pd36Co64 hydride species (II). 1,2-Insertion of the carbonyl substrate gives intermediate (III) which then undergoes exchange with isopropanol affording the alcohol end product. The base KOH plays a key role in generating isopropanolate ion which enters into the catalytic cycle. Since the combination of Pd and Co nanoparticles results in the formation of Pd36Co64 nanoalloy, evidenced in the present which also


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shows synergism in the catalytic applications, the initial binding of isopropanolate ion as to whether Pd or Co can not be established unequivocally.

Pd36Co64@HCCs OK

OH + KOH

+ H2O

H O

OH R1

O

(I)

R2

Product H

OH

R1

R2

H

Pd36Co64 hydride species on HCCs (II)

O

R2

R1 O

Reactant (III)

Scheme 2: Proposed mechanism for the transfer hydrogenation of ketones by Pd36Co64@HCCs in isopropyl alcohol. To provide additional support for the proposed heterogeneous mechanism, Sheldon's hot filtration test is carried out (Table 3). First, Pd36Co64@HCCs are subjected to the regular catalytic conditions, wherein the reaction of 4-chloroacetophenone is allowed to run for 6 h, then the catalyst is filtered hot to remove Pd36Co64@HCCs catalyst and then the supernatant liquid is allowed for another 6 h of reaction time. The product yield does not increase appreciably from the pre-filtering value of 49 %, indicating absence of leaching. This illustrates


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that the synthesized catalyst is heterogeneous in nature and it can be easily separated from the reaction mixture and reused. Table 3: Sheldon's hot filtration test for the Pd36Co64@HCCs catalyzed transfer hydrogenation reaction.a Catalyst

a

Pd36Co64@HCCs

6h

(6+6) h

Reused catalyst

49

51

99

Yield (%)

a

Reaction Conditions: 4-chloroacetophenone (2 mmol), i-PrOH (4 mL), KOH (0.5 mmol), Pd36Co64@HCCs (40 mg, 0.17 mol %), temperature (90 oC); bIsolated yield.

a)

b)

Figure

5:

Recycling

c)

experiments

for

hydrogenation

of

4-chloroactophenone

using

Pd36Co64@HCCs (a); TEM images of reused Pd36Co64@HCCs catalyst (b & C). The obvious advantage of heterogeneous catalysts compared to their molecularly defined homogeneous counterparts is their easy recycling. In order to demonstrate the stability and


17


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recyclability of the Pd36Co64@HCCs, the catalyst was reused for the transfer hydrogenation of 4chloroacetophenone under optimized conditions upto 5 times (Figure 5a). The catalyst is not only stable under air atmosphere but also showed good conversion upto five cycles without any significant loss of its activity. Even after five reaction cycles, the product yield remains as 94 %. The stability of Pd36Co64@HCCs, after five cycles, was also confirmed by TEM (Figure 5b-c) and XPS analyses (Figure S6, Supporting Information), which confirm the presence of Pd36Co64 NPs in HCCs with unchanged oxidation state. In addition, our catalytic system is also compared with previously reported catalytic systems containing monometallic Co, Pd and alloying of Pd and Co with other metal systems for transfer hydrogenation of carbonyl compounds (Table 4). The reported catalytic systems involve high noble-metal loading, use of gaseous hydrogen, longer reaction time and some of them are homogeneous in nature. On the other hand, our catalytic system is much simpler in terms of both catalyst preparation, catalytic procedure for environmental benign organic synthesis with higher activity, easy separability, reusability, contains low amount of metal loading (0.17 mol %) for catalytic hydrogenation reaction and involve high TONs and TOFs. CONCLUSIONS In summary, a highly active and stable heterogeneous nanoalloy catalyst, supported on HCCs (synthesised via a hydrothermal route using environmentally benign reagents), Pd36Co64@HCCs, is developed to efficiently catalyse the transfer hydrogenation of carbonyl compounds with isopropanol and KOH. A variety of carbonyl compounds are hydrogenated successfully with excellent yields involving high TONs and TOFs. These results not only demonstrate the incorporation of a non-noble metal into the noble metal nanocatalyst (which ensures low cost) but also enables an enhancement in the activity of the precursor metal catalysts, attributed to the


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synergetic effect between the two metal components in the alloy NPs. This optimal catalyst system thus constitutes one of the most general, heterogeneous, highly stable catalysts which does not require additives for activation, need only mild reaction conditions (does not use gaseous hydrogen), low metal content (0.17 mol %) for a catalytic hydrogenation reaction, functional-group tolerance and is environmentally benign. It can also be reused several times without loss in its activity. This approach can thus potentially make it possible to partially or even completely replace noble metals in catalysts with non-noble metals.


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Table 4: Comparison with previously reported monometallic Co, Pd and alloying of Pd, Co with other metal containing transfer hydrogenation of carbonyl compounds. S. No 1

Catalyst Pd0CoIII/Al2O3 II

Metal loading H2 (mol %) Source 7.4 30 bar H2

Solvent

Base

Solvent free

Temp (oC) 80

Yield (%) 65

TON

Ref.

-

Time (h) 24

1133

58

2

Pd (C7H7Cl2N4)2

0.1

-

i-PrOH

t-BuOK

8

80

98

1000

59

3

CoH -Zr-MTBC

0.5

40bar H2

Toluene

-

48-72

80-90

64-90

200

60

4

Pd50 -Pt50/ZrO2

1.0

60bar H2

Solvent-free

-

3

140

96

540

61

5

[Co2+Au25(SR)18/CeO2 ]

2.6

18bar- H2

H2O

Pyridine

10

50

100

708

62

6

Co-Cu/SBA-15

0.32

20bar-H2

i-PrOH

-

4

170

80

313

63

7

Cy

2.0

H2 1atm

THF

-

24-72

25-60

84-97

1100

32

8

[(PNP )Co(CH2SiMe3)] (PNPCy)Co(CH2SiMe3)

2.0

-

i-PrOH

K2CO3

24

25-80

94-99

50

33

9 10

Co-HMA Co3(CO)9CCl-S,S-2

5 1.0

-

i-PrOH i-PrOH

KOH KOH

6-8 93

83 82

67-91 74

330 100

64 65

11

Pd(CF3CO2)2

2.0

68bar H2

TFE

-

12

50

95

50

66

12

Pd0EnCat

10

-

EtOAc

18-68

24

90-99

10

67

13

Pd0EnCat™ 30NP

10

H2 1atm

EtOH

16

RT

>99

100

68

14

Pd36Co64 NPs@HCSs

0.17

i-PrOH

i-PrOH

HCOOH / Et3N HCOOH / Et3N KOH

12

90

99

556

This work MTBC = Methane-tetrakis(p-biphenylcarboxylate); SR = thiolate ligands; HMA = Hexagonal mesoporousaluminophosphate; TFE = 2,2,2-Trifluoroethanol;S,S-2 = Chiral PNNP complex; EnCat = Encapsulated catalyst.


20

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EXPERIMENTAL METHODS Synthesis of PdCo bimetallic nanoparticles (PdxCoy NPs): PdxCoywere synthesized by adding an aqueous solution of NaBH4 into an ice cold aqueous solution of CoCl2.6H2O, Na2PdCl4 and PVP. In a typical procedure, an aqueous ice-cold solution (8 mL) containing PVP (10.5 mg) and CoCl2.6H2O (0.1 mmol, 23.7 mg), Na2PdCl4 (0.1 mmol, 29.4 mg) was stirred (10 min) under nitrogen atmosphere. Subsequently, an aqueous ice-cold solution (3 mL) containing NaBH4 (10 mg) was added drop wise. The reaction was allowed to continue in ice-cold condition for 3 h to afford PdxCoy. Hydrothermal synthesis of Fe3O4 nanospheres69,49 (Fe3O4 NSs): Iron (III) chloride hexahydrate (1 mmol, 0.270 gm) and urea (9 mmol, 0.540 gm) were added into ethylene glycol (10 mL) under magnetic stirring. The resultant solution was transferred into a teflon lined stainless steel autoclave, sealed, and heated to 200 oC for 12 h. The precipitated black products were collected by an external magnet and washed several times with ethanol. Finally, the black colored product was dried in vacuum for 24 h at 60 oC. Synthesis of carbon@Fe3O4 nanospheres69,49 (C@Fe3O4): Carbon@Fe3O4 were synthesized by hydrothermal carbonization of glucose in presence of Fe3O4. The synthesized Fe3O4 solid spheres (100 mg) were dispersed in water (10 mL) containing glucose (1.6 gm) by ultrasonication. The mixture was transferred into a teflon lined stainless steel autoclave, sealed, and heated at 160 oC for 10 h, and then cooled at room temperature. The precipitated black solid was collected from the solution by an external magnet and washed several times with ethanol. Finally, the black coloured product was dried in vacuum for 24 h at 60 oC to afford C@Fe3O4. Synthesis of Hollow Carbon Capsules (HCCs): The as synthesized C@Fe3O4 nanospheres (1 gm) were dispersed in water (10 mL) to which HCl (40 mL, 3 N) solution was added and


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allowed to stir for 5 h. After completion of the reaction, the reaction mixture was centrifuged (3000 rpm, 15 min), the residue was collected, washed and dried (60 oC, 5 h) to obtain hollow carbon capsules (HCCs). Incorporation of PdxCoy on Hollow Carbon Capsules (PdxCoy@HCCs): PdxCoy@HCCs was prepared by deposition method. Typically, HCCs (300 mg) were well dispersed in ethylene glycol (100 mL) under magnetic stirring. To this, a solution containing PdxCoy (0.2 mmol, 11 mL) was added drop wise (30 min) under vigorous stirring. The above prepared reaction mixture was stirred for 2 h at 80 oC. After completion of the reaction, the PdxCoy NPs incorporated HCCs (PdxCoyNPs@HCCs) were separated by centrifugation (3000 rpm, 10 min), washed three times with water and acetone and dried in vacuum to obtain PdxCoyNPs@HCCs. General procedure for transfer hydrogenation of carbonyl compounds using Pd36Co64@HCCs: Pd36Co64@HCCs (40 mg, 0.17 mol % Pd36Co64), carbonyl compounds (2 mmol), isopropanol (4 mL) and KOH (0.5 mmol) were taken in a Schlenk tube with a teflon stopcock, sealed and heated at 90 oC for a given time with constant stirring. After the completion of reaction, the catalyst was separated by centrifugation and reaction mixture was decanted. The reaction mixture was further washed with water and extracted with ethylacetate and the solvent was evaporated by rotary evaporator and the residue was subjected to column chromatography for further purification. The purified compounds were characterized by 1H and

13

C-NMR

spectroscopy using CDCl3 as solvent and TMS as internal standard (Figure S7-S16, Supporting Information)


22

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ASSOCIATED CONTENT Supporting Information. Chemicals and Instrumentation; concentration ratio of Pd/Co for synthesizing nanoalloy PdxCoy; 1H & 13C-NMR spectral data; 1H & 13C-NMR spectral data and references. AUTHOR INFORMATION Corresponding Author Kasi Pitchumani “Email: [email protected]” Arlin Jose Amali “Email: [email protected]” ACKNOWLEDGMENTS BSK gratefully acknowledges financial support from UGC, New Delhi, India for UGC-BSRSRF. AJA thanks to DST, New Delhi, India for DST-INSPIRE Faculty Fellowship. KP acknowledges financial support provided by CSIR, New Delhi, India. REFERENCES (1) Gladiali, S.; Alberico, E. Asymmetric Transfer Hydrogenation: Chiral Ligands and Applications. Chem. Soc. Rev. 2006, 35, 226–236; DOI: 10.1039/B513396C. (2) Robertson, A.; Matsumoto, T.; Ogo, S. The Development of Aqueous Transfer Hydrogenation Catalysts. Dalton Trans. 2011, 40, 10304–10310; DOI: 10.1039/C1DT10544B. (3) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Mechanisms of the H2-Hydrogenation and Transfer Hydrogenation of Polar Bonds Catalyzed by Ruthenium Hydride Complexes. Coord. Chem. Rev. 2004, 248, 2201–2237; DOI: 10.1016/j.ccr.2004.04.007.


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 35

(4) Wu, J.; Wang, F.; Ma, Y.; Cui, X.; Cun, L.; Zhu, J.; Deng, J. Yu, B. Asymmetric Transfer Hydrogenation of Imines and Iminiums Catalyzed by a Water-Soluble Catalyst in Water. Chem. Commun. 2006, 1766 – 1768; DOI: 10.1039/B600496B. (5) Sonnenberg, J. F.; Coombs, N.; Dube, P. A.; Morris, R. H. Iron Nanoparticles Catalyzing the Asymmetric Transfer Hydrogenation of Ketones. J. Am. Chem. Soc. 2012, 134, 5893-5899; DOI: 10.1021/ja211658t. (6) Hydrazine and its Derivatives: Preparation, Properties, and Applications, 2nd edn. (Ed.: E. W. Schmidt), John Wiley & Sons, New York, 1984. (7) Frust, A.; Berlo, R. C.; Hooton, S. Hydrazine as a Reducing Agent for Organic Compounds (Catalytic Hydrazine Reductions). Chem. Rev. 1965, 65, 51–68; DOI: 10.1021/cr60233a002. (8) Hudson, R.; Chazelle, V.; Bateman, M.; Roy, R.; Li, C.-J.; Moores, A. Sustainable Synthesis of Magnetic Ruthenium-Coated Iron Nanoparticles and Application in the Catalytic Transfer Hydrogenation of Ketones. ACS Sustainable Chem. Eng. 2015, 3, 814-820; DOI: 10.1021/acssuschemeng.5b00206. (9) NasirBaig, R. B.; Varma, R. S. Magnetic Silica-Supported Ruthenium Nanoparticles: An Efficient Catalyst for Transfer Hydrogenation of Carbonyl Compounds. ACS Sustainable Chem. Eng. 2013, 1, 805-809; DOI: 10.1021/sc400032k. (10) Smit, C.; Fraaije, M. W.; Minnaard, A. J. Reduction of Carbon−Carbon Double Bonds Using Organocatalytically Generated Diimide. J. Org. Chem. 2008, 73, 9482–9485; DOI: 10.1021/jo801588d.


24

Page 25 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(11) Jang, Y.; Kim, S.; Jun, S. W.; Kim, B. H.; Hwang, S.; Song, I. K.; Kim, B. M.; Hyeon, T. Simple One-pot Synthesis of Rh-Fe3O4 Heterodimer Nanocrystals and their Applications to a Magnetically Recyclable Catalyst for Efficient and Selective Reduction of Nitroarenes and Alkenes. Chem. Commun. 2011, 47, 3601-3603; DOI: 10.1039/C0CC04816J. (12) deVries, J. G.; Elsevier, C. J. The handbook of homogeneous hydrogenation; Eds. Wiley-VCH Verlag GmbH; Weinheim, 2008. (13) Fang, Z.; Wills, M. Asymmetric Reduction of Diynones and the Total Synthesis of (S)Panaxjapyne A. Org. Lett. 2014, 16, 374-377; DOI: 10.1021/ol4032123. (14) Guo, R.; Elpelt, C.; Chen, X.; Song, D.; Morris, R. H. A Modular Design of Ruthenium Catalysts with Diamine and BINOL-derived Phosphinite Ligands that are EnantiomericallyMatched for the Effective Asymmetric Transfer Hydrogenation of Simple Ketones. Chem. Commun. 2005, 3050-3052; DOI: 10.1039/B502123E. (15) Zhang, Y.; Lim, C. S.; Sim, D. S. B.; Pan, H. J.; Zhao, Y. Catalytic Enantioselective Amination of Alcohols by the Use of Borrowing Hydrogen Methodology: Cooperative Catalysis by Iridium and a Chiral Phosphoric Acid. Angew. Chem. Int. Ed. 2014, 53, 1399-1403; DOI: 10.1002/anie.201307789. (16) Dai, X.; Cahard, D. Enantioselective Synthesis of α-Trifluoromethyl Arylmethylamines by Ruthenium-Catalyzed Transfer Hydrogenation Reaction. Adv. Synth. Catal. 2014, 356, 13171328; DOI: 10.1002/adsc.201301115.


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 35

(17) Modugno, G.; Monney, A.; Bonchio, M.; Albrecht, M.; Carraro, M. Transfer Hydrogenation Catalysis by a N-Heterocyclic Carbene Iridium Complex on a Polyoxometalate Platform. Eur. J. Inorg. Chem. 2014, 2356-2360; DOI: 10.1002/ejic.201402020. (18) Yang, X.; Chen, D.; Liao, S.; Song, H.; Li, Y.; Fu, Z.; Su, Y. High-Performance Pd–Au Bimetallic Catalyst with Mesoporous Silica Nanoparticles as Support and its Catalysis of Cinnamaldehyde Hydrogenation. J. Catal. 2012, 291, 36-43; DOI: 10.1016/j.jcat.2012.04.003. (19) Henning, A. M.; Watt, J.; Miedziak, P. J.; Cheong, S.; Santonastaso, M.; Song, M.; Takeda, Y.; Kirkland, A. I.; Taylor, S. H.; Tilley, R. D. Gold-Palladium Core-Shell Nanocrystals with Size and Shape Control Optimized for Catalytic Performance. Angew. Chem. Int. Ed. 2013, 52, 1477−1480; DOI: 10.1002/anie.201207824. (20) Hirasawa, S.; Watanabe, H.; Kizuka, T.; Nakagawa, Y.; Tomishige, K. Performance, Structure and Mechanism of Pd–Ag Alloy Catalyst for Selective Oxidation of Glycerol to Dihydroxyacetone. J. Catal. 2013, 300, 205 – 216; DOI: 10.1016/j.jcat.2013.01.014. (21) Wang, D.; Li, Y. Bimetallic Nanocrystals: Liquid-Phase Synthesis and Catalytic Applications. Adv. Mater. 2011, 23, 1044 – 1060; DOI: 10.1002/adma.201003695. (22) Ferrando, R.; Jellinek, J.; Johnston, R. L. Nanoalloys: From Theory to Applications of Alloy Clusters and Nanoparticles. Chem. Rev. 2008, 108, 845 – 910; DOI: 10.1021/cr040090g. (23) Hermannsdörfer, J.; Friedrich, M.; Miyajima, N.; Albuquerque, R. Q.; Kümmel, S.; Kempe, R. Ni/Pd@MIL-101: Synergistic Catalysis with Cavity-Conform Ni/Pd Nanoparticles. Angew. Chem. Int. Ed. 2012, 51, 11473 – 11477; DOI: 10.1002/anie.201205078.


26

Page 27 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(24) Vicente, A.; Lafaye, G.; Especel, C.; Marecot, P.; Williams, C. T. The Relationship between the Structural Properties of Bimetallic Pd-Sn/SiO2 Catalysts and their Performance for Selective Citral Hydrogenation. J. Catal. 2011, 283, 133 – 142; DOI: 10.1016/j.jcat.2011.07.010. (25) Sun, J.; Karim, A. M.; Zhang, H.; Kovarik, L.; Li, X. S.; Hensley, A. J.; McEwen, J.-S.; Wang, Y. Carbon-Supported Bimetallic Pd-Fe Catalysts for Vapor-Phase Hydrodeoxygenation of Guaiacol. J. Catal. 2013, 306, 47 – 57; DOI: 10.1016/j.jcat.2013.05.020. (26) Lee,

J.;

Kim,

Y. T.;

Huber,

G.

W.

Aqueous-Phase

Hydrogenation

and

Hydrodeoxygenation of Biomass-derived Oxygenates with Bimetallic Catalysts. Green Chem. 2014, 16, 708 – 718; DOI:10.1039/C3GC41071D. (27) Singh, A. K.; Xu, Q. Synergistic Catalysis over Bimetallic Alloy Nanoparticles, ChemCatChem. 2013, 5, 652 – 676; DOI: 10.1002/cctc.201200591. (28) Gilroy, K. D.; Ruditskiy, A.; Peng, H. C.; Qin, D.; Xia, Y. Bimetallic Nanocrystals: Syntheses, Properties, and Applications, Chem. Rev. 2016, 116, 10414 – 10472; DOI: 10.1021/acs.chemrev.6b00211. (29) Tang, M.; Mao, S.; Li, M.; Wei, Z.; Xu, F.; Li, H.; Wang, Y. RuPd Alloy Nanoparticles Supported on N-Doped Carbon as an Efficient and Stable Catalyst for Benzoic Acid Hydrogenation. ACS Catal. 2015, 5, 3100 – 3107; DOI: 10.1021/acscatal.5b00037. (30) Goulas, K. A.; Sreekumar, S.; Song, Y.; Kharidehal, P.; Gunbas, G.; Dietrich, P. J.; Johnson, G. R.; Wang, Y. C.; Grippo, A. M.; Grabow, L. C.; Gokhale, A. A.; Toste, F. D. Synergistic Effects in Bimetallic Palladium–Copper Catalysts Improve Selectivity in Oxygenate Coupling Reactions. J. Am. Chem. Soc. 2016, 138, 6805 – 6812; DOI: 10.1021/jacs.6b02247.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 35

(31) Audemar, M.; Ciotonea, C.; Vigier, K. D. O.; Royer, S.; Ungureanu, A.; Dragoi, B.; Dumitriu, E.; Jerome, F. Selective Hydrogenation of Furfural to Furfuryl Alcohol in the Presence of a Recyclable Cobalt/SBA-15 Catalyst. ChemSusChem. 2015, 8, 1885 – 1891; DOI: 10.1002/cssc.201403398. (32) Zhang, G.; Scott, B. L.; Hanson, S. K. Mild and Homogeneous Cobalt-Catalyzed Hydrogenation of C=C, C=O, and C=N Bonds. Angew. Chem. Int. Ed. 2012, 51, 12102 – 12106; DOI: 10.1002/anie.201206051. (33) Zhang, G.; Hanson, S. K. Cobalt Catalyzed Transfer Hydrogenation of C=O and C=N Bonds. Chem. Commun. 2013, 49, 10151 – 10153; DOI:10.1039/C3CC45900D. (34) Rosler, S.; Obenauf, J.; Kempe, R. A Highly Active and Easily Accessible Cobalt Catalyst for Selective Hydrogenation of C═O Bonds. J. Am. Chem. Soc. 2015, 137, 7998 – 8001; DOI: 10.1021/jacs.5b04349. (35) Long, J.; Zhou, Y.; Li, Y. Transfer Hydrogenation of Unsaturated Bonds in the Absence of base Additives Catalyzed by a Cobalt-based Heterogeneous Catalyst. Chem. Commun. 2015, 51, 2331-2334; DOI: 10.1039/C4CC08946D. (36) Jagadeesh, R. V.; Junge, H.; Pohl, M.-M.; Radnik, J.; Brückner, A.; Beller, M. Selective Oxidation of Alcohols to Esters Using Heterogeneous Co3O4-N@C Catalysts under Mild Conditions. J. Am. Chem. Soc. 2013, 135, 10776 – 10782; DOI: 10.1021/ja403615c. (37) Jagadeesh, R. V.; Stemmler, T.; Surkus, A.-E.; Bauer, M.; Pohl, M.-M.; Radnik, J.; Junge, K.; Junge, H.; Bruckner, A.; Beller, M. Cobalt-based nanocatalysts for green oxidation and hydrogenation processes. Nat. Protoc. 2015, 10, 916 – 926; DOI:10.1038/nprot.2015.049.


28

Page 29 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(38) Chen, F.; Topf, C.; Radnik, J.; Kreyenschulte, C.; Lund, H.; Schneider, M.; Surkus, A.E.; He, L.; Junge, K.; Beller, M. Stable and Inert Cobalt Catalysts for Highly Selective and Practical Hydrogenation of C≡N and C═O Bonds. J. Am. Chem. Soc. 2016, 138, 8781 – 8788; DOI: 10.1021/jacs.6b03439. (39) Lin, J.; Chen, J.; Su, W. Rhodium-Cobalt Bimetallic Nanoparticles: A Catalyst for Selective Hydrogenation of Unsaturated Carbon-Carbon Bonds with Hydrous Hydrazine. Adv. Synth. Catal. 2013, 355, 41-46; DOI: 10.1002/adsc.201200576. (40) Udumula, V.; Tyler, J. H.; Davis, D. A.; Wang, H.; Linford, M. R.; Minson, P. S.; Michaelis, D. J. Dual Optimization Approach to Bimetallic Nanoparticle Catalysis: Impact of M1/M2 Ratio and Supporting Polymer Structure on Reactivity. ACS Catal. 2015, 5, 3457-3462; DOI: 10.1021/acscatal.5b00830. (41) Zhu, Q.-L.; Xu, Q. Immobilization of Ultrafine Metal Nanoparticles to High-SurfaceArea Materials and Their Catalytic Applications, Chem 2016, 1, 220 – 245; DOI: 10.1016/j.chempr.2016.07.005. (42) Zhu, Q.-L.; Li, J.; Xu, Q. Immobilizing Metal Nanoparticles to Metal-Organic Frameworks with size and Location Control for Optimizing Catalytic Performance, J. Am. Chem. Soc. 2013, 135, 10210 – 10213; DOI: 10.1021/ja403330m. (43) Puthiaraj, P.; Pitchumani, K. Palladium Nanoparticles Supported on Triazine Functionalised Mesoporous Covalent Organic Polymers as Efficient Catalysts for Mizoroki– Heck

Cross

Coupling

Reactions.

Green

Chem.

2014,

16,

4223

–

4233;

DOI:

10.1039/C4GC00412D.


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 35

(44) Kumar, B. S.; Amali, A. J.; Pitchumani, K. Mesoporous Microcapsules through D‑ Glucose Promoted Hydrothermal Self-Assembly of Colloidal Silica: Reusable Catalytic Containers for Palladium Catalyzed Hydrogenation Reactions, ACS Sustainable Chem. Eng. 2017, 5, 667 – 674; DOI: 10.1021/acssuschemeng.6b02025. (45) Goswami, A.; Rathi, A. K.; Aparicio, C.; Tomanec, O.; Petr, M.; Pocklanova, R.; Gawande, M. B.; Varma, R. S.; Zboril, R. In Situ Generation of Pd−Pt Core−Shell Nanoparticles on Reduced Graphene Oxide (Pd@Pt/rGO) Using Microwaves: Applications in Dehalogenation Reactions and Reduction of Olefins, ACS Appl. Mater. Interfaces 2017, 9, 2815 – 2824; DOI: 10.1021/acsami.6b13138. (46) Li, S.; Pasc, A.; Fierro, V.; Celzard, A. Hollow Carbon Spheres, Synthesis and Applications - A Review. J. Mater. Chem. A, 2016, 4, 12686 – 12713; DOI: 10.1039/C6TA03802F. (47) Liu, S.; Wang, X.; Zhao, H.; Cai, W. Micro/Nano-Scaled Carbon Spheres based on Hydrothermal Carbonization of Agarose, Colloids Surf. A Physicochem Eng Asp. 2015, 484, 386 – 393; DOI: 10.1016/j.colsurfa.2015.08.019. (48) Haibo, O.; Cuiyan, L.; JianFeng, H.; Jie, F. Synthesis of Carbon/Carbon Composites by Hydrothermal Carbonization Using Starch as Carbon Source, RSC Adv. 2014, 4, 12586–12589; DOI: 10.1039/c3ra47857b. (49) Zhu, M.; Diao, G. Magnetically Recyclable Pd Nanoparticles Immobilized on Magnetic Fe3O4@C Nanocomposites: Preparation, Characterization, and Their Catalytic Activity toward


30

Page 31 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Suzuki and Heck Coupling Reactions. J. Phy. Chem. C 2011, 115, 24743-24749; DOI: 10.1021/jp206116e. (50) Liu, Z.; Feng, Y.; Wu, X.; Huang, K.; Feng, S.; Dong, X.; Yang, Y.; Zhao, B. Preparation and Enhanced Electrocatalytic Activity of Graphene Supported Palladium Nanoparticles with Multi-Edges and Corners, RSC Adv. 2016, 6, 98708 – 98716; DOI: 10.1039/C6RA20827D. (51) Çelik, B.; Yıldız, Y.; Sert, H.; Erken, E.; Koskun, Y.; Sen, F. Monodispersed Palladium–Cobalt Alloy Nanoparticles Assembled on Poly(N-vinylpyrrolidone) (PVP) as a Highly Effective Catalyst for Dimethylamine Borane (DMAB) Dehydrocoupling, RSC Adv. 2016, 6, 24097 – 24102; DOI:10.1039/C6RA00536E. (52) Xue, H.; Tang, J.; Gong, H.; Guo, H.; Fan, X.; Wang, T.; He, J.; Yamauchi, Y. Fabrication of PdCo Bimetallic Nanoparticles Anchored on Three-Dimensional Ordered NDoped Porous Carbon as an Efficient Catalyst for Oxygen Reduction Reaction. ACS Appl. Mater. Interfaces 2016, 8, 20766 – 20771; DOI: 10.1021/acsami.6b05856. (53) Inoue, A.; Zhang, T.; Takeuchi, A. Bulk Amorphous Alloys with High Mechanical Strength and Good Soft Magnetic Properties in Fe–TM–B (TM=IV–VIIITM=IV–VIII group transition metal) System. Appl. Phys. Lett., 1997, 71, 464; DOI: 10.1063/1.119580. (54) Song, Y.; Henry, L. L.; Yang, W. Stable Amorphous Cobalt Nanoparticles Formed by an in Situ Rapidly Cooling Microfluidic Process. Langmuir 2009, 25, 10209 – 10217; DOI: 10.1021/la9009866.


31


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 35

(55) Fei, H.; Yang, Y.; Peng, Z.; Ruan, G.; Zhong, Q.; Li, L.; Samuel, E. L. G.; Tour, J. M. Cobalt Nanoparticles Embedded in Nitrogen-Doped Carbon for the Hydrogen Evolution Reaction. ACS Appl. Mater. Interfaces 2015, 7, 8083 – 8087; DOI: 10.1021/acsami.5b00652. (56) Wagner, C. D.; Riggs, W. M.; Davis, L. E.; Moulder, J. F. Handbook of X Ray Photoelectron Spectroscopy (Ed.: G. E. Muilenberg), Perkin Elmer Corporation, Minnesota, 1978. (57) Erathodiyil, N.; Ooi, S.; Seayad, A. M.; Han, Y.; Lee, S. S.; Ying, J. Y. Palladium Nanoclusters Supported on Propylurea-Modified Siliceous Mesocellular Foam for Coupling and Hydrogenation

Reactions,

Chem.

-Eur.

J.

2008,

14,

3118

–

3125;

DOI:

10.1002/chem.200701361. (58) Erasmus, E. Hydrogenation of Cinnamaldehyde over an Ionic Cobalt Promoted Alumina-Supported Palladium Catalyst. S. Afr. J. Chem. 2013, 66, 216–220. (59) Dehury, N.; Maity, N.; Tripathy, S. K.; Basset, J. M.; Patra, S. Dinuclear Tetrapyrazolyl Palladium Complexes Exhibiting Facile Tandem Transfer Hydrogenation/Suzuki Coupling Reaction of Fluoroarylketone. ACS Catal. 2016, 6, 5535-5540; DOI: 10.1021/acscatal.6b01421. (60) Ji, P.; Manna, K.; Lin, Z.; Urban, A.; Greene, F X.; Lan, G.; Lin, W. Single-Site Cobalt Catalysts at New Zr8(µ2-O)8(µ2-OH)4 Metal-Organic Framework Nodes for Highly Active Hydrogenation of Alkenes, Imines, Carbonyls, and Heterocycles. J. Am. Chem. Soc. 2016, 138, 12234 – 12242; DOI: 10.1021/jacs.6b06759.


32

Page 33 of 35

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(61) Jiang, Y.; Buchel, R.; Huang, J.; Krumeich, F.; Pratsinis, S. E.; Baiker, A. Efficient Solvent-free Hydrogenation of Ketones over Flame-Prepared Bimetallic Pt-Pd/ZrO2 catalysts. ChemSusChem 2012, 5, 1190 – 1194; DOI: 10.1002/cssc.201200126. (62) Li, G.; Abroshan, H.; Chen, Y.; Jin, R.; Kim, H. J. Experimental and Mechanistic Understanding of Aldehyde Hydrogenation Using Au25 Nanoclusters with Lewis Acids: Unique Sites for Catalytic Reactions. J. Am. Chem. Soc. 2015, 137, 14295 – 14304; DOI: 10.1021/jacs.5b07716. (63) Srivastava, S.; Mohanty, P.; Parikh, J. K.; Dalai, A. K.; Amritphale, S. S.; Khare, A. K. Cr-free Co-Cu/SBA-15 Catalysts for Hydrogenation of Biomass Derived α-, β-Unsaturated Aldehyde to Alcohol, Chin. J. Catal. 2015, 36, 933 – 942; DOI:10.1016/S1872-2067(15)60870-1 (64) Mohapatra, S. K.; Sonavane, S. U.; Jayaram, R. V.; Selvam, P. Heterogeneous Catalytic Transfer Hydrogenation of Aromatic Nitro and Carbonyl Compounds Over Cobalt(II) Substituted Hexagonal Mesoporous Aluminophosphate Molecular Sieves. Tetrahedron Lett. 2002, 43, 8527 – 8529; DOI: 10.1016/S0040-4039(02)02080-4. (65) Li, Y.-Y.; Yu, S.-L.; Shen, W.-Y.; Gao, J.-X. Iron-, Cobalt-, and Nickel-Catalyzed Asymmetric Transfer Hydrogenation and Asymmetric Hydrogenation of Ketones. Acc. Chem. Res. 2015, 48, 2587 – 2598; DOI: 10.1021/acs.accounts.5b00043. (66) Wang, Y. Q.; Lu, S. M.; Zhou, Y. G. Palladium-Catalyzed Asymmetric Hydrogenation of Functionalized Ketones. Org. Lett. 2005, 7, 3235 - 3238; DOI: 10.1021/ol051007u.


33


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 35

(67) Yu, J.-Q.; Wu, H.-C.; Ramarao, C.; Spencer, J. B.; Ley, S. V. Transfer Hydrogenation Using Recyclable Polyurea-Encapsulated Palladium: Efficient and Chemoselective Reduction of Aryl Ketones. Chem. Commun. 2003, 1, 678 – 679; DOI: 10.1039/b300074p. (68) Ley, S. V.; Stewart-Liddon, A. J. P.; Pears, D.; Perni, R. H.; Treacher, K. Hydrogenation of Aromatic Ketones, Aldehydes, and Epoxides with Hydrogen and Pd(0)EnCat 30NP. Beilstein J. Org. Chem. 2006, 2, 15; DOI:10.1186/1860-5397-2-15. (69) Kumar, B. S.; Amali, A. J.; Pitchumani, K. Fabrication of Pd Nanoparticles Embedded C@Fe3O4 Core-Shell Hybrid Nanospheres: An Efficient Catalyst for Cyanation in Aryl Halides. ACS Appl. Mater. Interfaces 2015, 7, 22907-22917; DOI: 10.1021/acsami.5b08875.


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For Table of Content Use Only

Bimetallic Pd36Co64@HCCs nanoparticulate alloy serves as more active, stable and reusable catalyst in transfer hydrogenation of carbonyl compounds using isopropanol.


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Ultrafine Bimetallic PdCo Alloy Nanoparticles on Hollow Carbon

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