Reductive Cyclization of Levulinic Acid to Î³-Valerolactone over Non

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Reductive cyclization of levulinic acid to #valerolactone over non-noble bimetallic nanocomposite Brijesh S Kadu, Amol M. Hengne, Narayan S. Biradar, Chandrashekhar V. Rode, and Rajeev C. Chikate Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b03900 • Publication Date (Web): 29 Nov 2016 Downloaded from http://pubs.acs.org on December 4, 2016

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Industrial & Engineering Chemistry Research

Reductive cyclization of levulinic acid to γ-valerolactone over non-noble bimetallic nanocomposite

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Brijesh S. Kadua, Amol M. Hengneb, Narayan S. Biradarb, Chandrashekhar V. Rodeb and Rajeev

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C. Chikatea*

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a

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Abasaheb Garware College, Pune 411004, India

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b

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Nanoscience Group, Department of Chemistry, Post-graduate & Research Centre, MES

Chemical Engineering and Process Development Division, CSIR-National Chemical

Laboratory, Pune 411008, India

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*corresponding author email: [email protected]

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Fax: +91 20 25438165

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Telephone: +91 20 41038263

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1

ACS Paragon Plus Environment


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ABSTRACT

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Bimetallic nanoparticles have diverse applications in catalytic processes owing to the differences

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in individual properties that contribute to their increased catalytic activity. To further improve

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the efficiency, they are dispersed in an inert support that enhances the catalytic activity towards

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organic transformations. In this study, we report simple, facile and cost-effective chemical route

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for the fabrication of nanocomposites with Fe-Ni bimetallic nanoparticles supported on

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montmorillonite (MMT) possessing variation in the Fe and Ni content. These composites are

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characterized with X-ray diffraction, transmission electron microscopy surface area, and NH3-

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TPD. Fe-Ni bimetallic nanoparticles are well dispersed within MMT structure having particle

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size of about 30 – 40 nm. Amongst various compositions of Fe-Ni/MMT catalysts, 25% Fe and

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25% Ni exhibits > 99% LA conversion with 98% selectivity to GVL within 1 h. IPA is found to

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be better solvent for levulinic acid (LA) to γ-valerolactone (GVL) conversion while substantial

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leaching of iron takes place when water is used as a solvent. It is observed that bimetallic sites

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are responsible for reduction of LA while strong acidic sites of MMT are favoring subsequent

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cyclization to GVL. XPS analysis of fresh and reused Fe-Ni/MMT composites suggests that the

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catalyst surface does not undergo any chemical change during successive cycles and the catalytic

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activity is retained up to six cycles. The plausible mechanism for LA to GVL conversion

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involves reductive cyclization process through formation of levulinate ester that undergoes

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lactonisation due to synergism in bimetallic nanoparticles and MMT clay.

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Key Words: Fe-Ni Bimetallic nanocomposites, heterogeneous catalysis, reductive cyclization,

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levulinic acid, GVL

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1. INTRODUCTION

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Bimetallics are of great importance owing to their tunable composition, size, and electronic

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properties that are responsible for various applications including magnetism, electronics,

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photonics, and especially catalysis.1-4 Designing of such a bimetallic catalyst essentially involves

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two metals possessing different characteristics like one of them being an electron donor and

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other metal acts as an electron shuttle. Although they are very well investigated for variety of

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organic transformations5, majority of them are noble metal based catalysts which are expensive,

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undergoes surface passivation and less environmental benign.6 For example; Pd, Pt, Ru, Au, and

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Ag based bimetallic nanoparticles usually involves noble or non-noble metals to achieve

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enhancement in specific physical and chemical properties due to synergistic effects.7 However,

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non-metal based bimetallic systems are less explored as catalyst for organic conversions

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probably due to their high affinity towards aqueous medium, less thermal and chemical stability,

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surface passivation and leaching. Zero valent iron (nZVI) based bimetallics is one of such

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catalyst which is efficiently been used for mitigation of variety of aquatic pollutants including

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organics.8, 9 These catalysts often tend to deactivate after their usage and therefore, dispersing

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them onto porous/chemically inert support seems to be viable approach.10 Such a tailor-made

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heterogeneous bimetallic composite possess wide adaptability in various harsh conditions due to

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chemical inertness and stability. Mesoporous carbon is one such neutral support used for

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dispersion of bimetallic nanoparticles,11-13 uneven distribution of metal sites on the hydrophobic

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carbon leads to particle aggregation and leaching.14 Mesoporous clays are much favored supports

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since they offer great advantages due to their well controlled mesoporous structures that are

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favorable for transportation of the substrate and product, besides being thermally and chemically

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stable.15 It also acts as good dispersing media for nanoparticles due to their layered structure and

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beneficial cation-exchange capacity. Montmorillonite (MMT), a 2:1 type natural mineral is

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composed of silicates and alumina in the form of layered sheets with a strong cation exchange

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capacity (97 mequi./100 g). Based on these properties of both Fe-based bimetallics and MMT,

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we thought of exploring their catalytic efficiency towards reductive cyclization of levulinic acid

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(LA) to γ-valerolactone (GVL) that involves simultaneous reduction followed by ring closure

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phenomenon. GVL is listed as one of the top value added chemicals and a sustainable liquid that

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has potential applications as solvent, food additive and a better substitute for ethanol in ethanol3



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gasoline blend as it does not form azeotropic mixture with water.16 Although supported noble

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metal catalysts exhibit promising catalytic activity for such a conversion, their applications for

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practical purposes are restricted due to cost of precious metals, their sensitive surface, stringent

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reaction conditions involving high pressure, and usage of other ancillary reagents. On the other

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hand, non-noble metal based supported catalysts are explored in recent past for the production of

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GVL because they are cheaper, stable and can be operated under mild conditions.

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conversion is efficiently been carried out with various non-noble metals like Ni and Cu

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supported on different supports17 as well as Cu-Cr18 and Cu-Fe19 bimetallic catalysts.

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This

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Earlier, we reported ~100% conversion of nitro-arenes to corresponding mono-amines with

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99% selectivity via transfer hydrogenation using Fe-Ni catalyst.20 In continuation of these

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findings, we thought of dispersing these nanoparticles on MMT matrix so as to generate

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nanocomposites and explore their catalytic activity towards simultaneous in-situ hydrogenation

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followed by cyclization process. To test this hypothesis, LA to GVL conversion is selected as

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model reaction wherein it is envisaged that transfer hydrogenation of LA to 4-hydroxypentnoic

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would occur at Fe-Ni site while subsequent lactonization is facilitated by MMT surface due to its

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acidic nature. In the present work, we have synthesized series of catalysts with varying amount

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of Fe and Ni and investigated their catalytic efficiency towards LA to GVL conversion.

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2. EXPERIMENTAL

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2.1. Chemicals

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Analytical grade chemicals were purchased from Loba Chemie, UK and used as received: Iron

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(II) Sulphate (FeSO4.7H2O), Nickel (II) chloride (NiCl2.6H2O), Sodium borohydride (NaBH4)

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and MMT {(Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2·nH2O}. LA (99%) and methyl, ethyl, butyl

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levulinates were purchased from Sigma-Aldrich, Bangalore, India while, isopropanol (>99.9%)

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was purchased from Rankem, India.

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2.2.1. Pretreatment of MMT

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Pre-treatment of pristine MMT with 1 M NaCl solution is essential so as to enhance its cation

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exchange capacity (CEC). It is modified as follows: MMT clay was treated with excess 1 M

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NaCl aqueous solution for several times and then dried at 50°C. The powder obtained is

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dispersed in distilled water to prepare the colloidal suspension of clay particles which was

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filtered, dried and used for preparation of nanocomposites. CEC of MMT and pre-treated MMT 4


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clay estimated by nephelometric method21 was found to be 97 and 136 mequi./100 g

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respectively.

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2.2.3. Synthesis of in-situ formed Fe-Ni nanocomposites on MMT.

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A general procedure adopted for the synthesis of in-situ formed monometallic and bimetallic-

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nanocomposites with various compositions of Fe and Ni such 10, 25, and 50% w/w is as follows:

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Synthesis of 25% Fe-Ni/MMT

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To a suspension of 0.75 g of Na-MMT in 50 mL of deionized water, 20 mL aqueous solution

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containing FeSO4.7H2O (0.6222 g) and NiSO4.6H2O (0.5598 g) was added with constant stirring

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under N2 atmosphere. The whole mixture was stirred for 30 min followed by drop wise addition

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of 0.08 M NaBH4 over a period of 1 h under nitrogen atmosphere. It was centrifuged at 3000

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rpm, washed with acetone and dried under vacuum. Similar procedure was followed for the

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synthesis of other compositions like 10 and 50 % by varying appropriate amount of iron

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sulphate, nickel sulphate and Na-MMT.

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2.3 Characterization of nanocomposite.

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X-ray powder diffraction (XRD) patterns were obtained using Phillips X’pert MPD X-ray

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diffractometer using Cu-Kα radiation. Transmission electron microscopic (TEM) images are

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obtained using JEOL electron microscope (model 1200X). Brunnaer-Emmett-Teller (BET)

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surface area analysis is performed using nitrogen adsorption method with surface analyzer

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system CHEMBET 3000, Quantichrome Instruments, U.S. NH3-TPD experiments were carried

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out on a Chemisoft TPx (Micromeritics-2720) instrument. In order to evaluate acidity of the

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catalysts, ammonia TPD measurements were carried out by: (i) pre-treating the samples from

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room temperature to 300oC under helium flow rate of 25 mL/min. (ii) adsorption of ammonia at

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50oC (iii) desorption of ammonia with a heating rate of 10oC min-1 starting from the adsorption

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temperature to 973 K. XPS spectra were recorded using ESCA-3000 (VG Scientific Ltd.,

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England) equipped with CLAM4 analyzer at 1 x 10-8 Torr vacuum using MgKα radiation. The

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metal leaching was estimated by ICP-OES (Perkin Elmer, Optima 8000 ICP-OES Spectrometer)

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analysis of solid isolated from the evaporation of the supernatant. The solid thus obtained was

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treated with aquaregia (HNO3: HCl; 1:3), heated at 60 °C on a sand bath for 2 h and than made

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up to 25 mL by distilled water.

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2.4 Reductive cyclization of LA to GVL: 5



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LA hydrogenation reactions are carried out in a 300 mL capacity autoclave (Parr Instruments

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Co., USA) at a stirring speed of 1000 rpm. The typical hydrogenation conditions are:

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temperature, 473 K; LA concentration, 5-20 wt%; solvent, 95 mL; total volume, 100 mL;

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catalyst loading, 0.5 g; substrate: catalyst mole ratio, (10:1), H2 pressure 500 psi, reaction time 1

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h. Initially the reactor is flushed with N2 and when the desired temperature is achieved, it is H2 is

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introduced with 500 psi pressure. These reactions are carried out in different solvents such as

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water, methanol, ethanol, n-propyl alcohol and isopropyl alcohol. Liquid samples are withdrawn

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periodically and analyzed by GC (Thermo-Trace-700) having an HP-5 column with a FID

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detector.

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3. RESULTS AND DISCUSSION

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3.1 Characterization of nanocomposites:

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To assess the structural features of Fe-Ni/MMT nanocomposites, XRD and TEM analyses are

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performed on 10% Fe–Ni/MMT, 25% Fe–Ni/MMT and 50% Fe–Ni/MMT composites. XRD

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patterns of MMT and its Fe-Ni nanocomposites are depicted in Figure 1. MMT shows peaks at

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20.9° and 26.9° due to (0211) and (005) planes.22 The shifting of these peaks on the lower angle

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suggests the insertion of Fe-Ni NP’s in the MMT matrix and formation of intercalated

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nanocomposite.23 The peaks corresponding to Fe-Ni NP’s in the range of 40 – 65° are assigned

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to (111) and (200) crystal planes of fcc (JCPDS 47-1417) as well as bcc (JCPDS 37-0474)

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structures of Fe-Ni NP’s.24 The gradual increase in the intensity pattern with Fe-Ni content

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augurs well for high degree of crystalinity for nanocomposites. The morphology of Fe-Ni/MMT

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composites (Fig. 2) is found to be of spherical shape (20-40 nm diameters) that are connected in

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chains of beads probably due to the electronic and magnetic interactions between the metals.25

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The interaction of Fe-Ni nanoparticles with MMT promoted due to the presence of hydroxyl

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groups present on the MMT surface. The surface area 10%, 25% and 50% Fe-Ni/MMT is found

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to be 82, 61 and 75 m2 g-1 while the pore volume and average pore diameter are depicted in

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Table 1. It is interesting to note that not much of variation is observed with these parameters

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with increasing the Fe-Ni content in these composites, however, there seems to be combine

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effect of different factors like number of active-sites and acidity of nanocomposites that govern

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the catalytic activity of nanocomposites plausibly through synergistic effect of Fe-Ni and MMT

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support.26 Since cyclization of hydrogenated LA is favored under acidic conditions, the NH36


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TPD measurements are carried out on 10%, 25% and 50% Fe-Ni/MMT (Fig. 3). Amongst these

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compositions, 50% exhibited two peaks in the region of 270 – 370°C as well as small hump

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around 550°C while there is absence of first peak for other two compositions. It implies that

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higher loading of Fe and Ni results in the reduction of strong acidic Bronstead sites with

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concomitant increase in Lewis sites.

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3.2 Catalyst screening:

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In our earlier contribution,20 we have shown that Fe-Ni bimetallic nanoparticles possesses

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excellent reducing ability towards selective reduction of nitroarenes with better recycling

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capability. To further extrapolate this activity, simultaneous reduction followed by cyclization of

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LA is carried out with these nanoparticles as well as their clay composites. Initially, the reaction

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is carried out with 10% Fe-Ni/MMT catalyst in water which showed only 10% conversion with

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100% selectivity to GVL (Table 2). To enhance the conversion, the amount of Fe and Ni is

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increased from 10% to 50% on MMT (Set I). It is observed that maximum conversion (90%)

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takes place with 50% Fe-Ni/MMT with 98% selectivity. Since the reaction is carried out in

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aqueous medium, the color of reaction mixture changed from colorless to dark yellow probably

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due to leaching of iron and nickel from composite which is further confirmed with ICP-OES

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analysis of reaction mixture. It is observed that (Table 2) amount of Fe and Ni leached from

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these catalysts goes on increasing with increase in metal content with maximum leaching of iron

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is observed for 50% Fe-Ni/MMT composition. As Fe is most susceptible for dissolution and

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subsequent leaching under aqueous medium, another set of experiment (Set II) is carried out

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with low Fe content keeping total metal content constant (50%). Although the leaching of Fe is

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found to be considerably reduced, the amount of Ni lixiviation remained almost constant with

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about 55% conversion. It implies that leaching of both Fe and Ni is takes place under aqueous

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conditions due to hydrophilic nature of the catalysts. This observation is further corroborated

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with monometallic composites such as 50% Fe/MMT and 50% Ni/MMT (Set III) where

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maximum Fe leaching takes place for former composite with only 31% conversion. Moreover,

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variation in the amounts of Fe and Ni (Supporting information Fig. S1) suggests that less amount

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of Fe content for composite adversely affect La to GVL conversion implying that this metal is

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responsible for reduction of ketone to alcohol. These findings suggest that bimetallic composite

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with 25% Fe and 25% Ni on MMT is appropriate for higher conversion with excellent selectivity 7



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towards GVL. However, it is observed that water is not a good solvent for reductive cyclization

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of LA to GVL due to leaching of significant amount of metals under these reaction conditions.

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To overcome this lacuna, LA to GVL conversion is carried out with different alcohols (Set IV)

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with 50% Fe-Ni/MMT. It is reported that leaching of iron does not occur in alcohols as solvent

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even when equal amount of Cu and Fe present in the bimetallic Cu-Fe catalyst.19 In our case,

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similar observation is noted where leaching of both Fe and Ni is found to be less than 1 ppb.

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Another facet for the choice of alcohol as solvent stems from the fact that it can also act as H-

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donor as exemplified in transfer hydrogenation of a range of substrates such as carboboranes,

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aldehydes, alkynes, dienes and alkenes,27 although utilization of linear alcohols is restricted due

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to the formation of dehydrogenated products that cause catalyst poisoning.28 However, alcohols

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like IPA containing α-hydrogen is more favored owing to its better efficiency towards H2

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generation as well as restricting the formation of by-products during hydrogenation process.29

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This observation is already been noted for Ni/MMT catalyst used for transfer hydrogenation of

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LA to GVL with ~ 99% selectivity.30 It is also reported that esterification of LA in alcohol

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medium pre-requisite step conversion that subsequently undergoes hydrogenation and

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cyclization during LA to GVL.31 Considering these properties of alcohols, we screened primary

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and secondary alcohols like MeOH, EtOH, nPrOH and IPA to assess their effectiveness towards

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LA to GVL conversion. Although, >98% conversion is observed, selectivity to GVL is found to

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be hampered due to formation of products like alkyl-4-Hy-LA and esters of LA (Fig. 4). It is

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interesting to note that the selectivity increases concomitantly with increase in the number of

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carbon atoms present in alcohol. Moreover, IPA is found to be only candidate amongst them

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possessing highest selectivity towards GVL. The order of selectivity towards formation of GVL

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is found to be IPA> n-propanol > ethanol > methanol which suggests that IPA certainly plays a

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pivotal role in hydride generation that ultimately improves the catalytic efficiency Fe-Ni/MMT

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composite. This feature is significantly noticed in conversion/selectivity vs. time profile (Fig. 5)

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where more than 85% conversion with > 50% selectivity is achieved within 10 min. that can be

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attributed to faster rate of esterification. With increase in reaction time, IPA ester of LA is

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hydrogenated to hydroxyl ester that undergoes ring closure phenomenon due to acidic sites of

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MMT and eventually leads to formation of GVL with > 99% selectivity.

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To highlight the advantage of our work, we compared the catalytic activity of different

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catalysts that are explored for the conversion of LA to GVL (Supporting information Table T1).

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Inspection of this table suggests this conversion is achieved at faster rate with excellent

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selectivity to GVL using Fe-Ni/MMT nanocomposites. This fact may be explained on the basis

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of synergism in Fe-Ni bimetallic system and acidic character of MMT that induces simultaneous

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reduction and cyclization of LA to GVL in a beneficial manner at considerably lower energy.

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3.2.1. Influence of hydrogen pressure

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The influence of hydrogen pressure on the catalytic activity of 50% Fe-Ni/MMT towards

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reductive cyclization of LA is depicted in Figure 6. It is observed that with increase in H2

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pressure, the conversion is almost 100% while there is a gradual increase in selectivity to GVL

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from 100 – 500 psi. For example, only GVL is formed at 100 psi where as formation of IP LA

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and IP-4-Hy-LA is observed at 300 psi H2 pressure. It implies that at lower pressure, the

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solubility of H2 in IPA is low further increase in pressure leads to improved selectivity to GVL

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with concomitant formation of IPA related esters. On the other hand, complete conversion and

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selectivity is achieved at 500 psi due to continuous hydrogenation of IPA esters that

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subsequently undergoes cyclization to GVL. Moreover, highly acidic character of MMT

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possessing both Bronsted and Lewis sites are beneficial for ring closure phenomenon.

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3.2.2. Effect of initial concentration of LA

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Effect of initial concentration of LA (5-30%) on the conversion and selectivity pattern is

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performed so as to evaluate maximum productivity of GVL. It is observed that (Fig. 7) the

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conversion of LA decreased from 99% to 46% with increase in LA concentration from 5 to 30%

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with lowering selectivity to GVL by almost three times. Such a decrease in conversion and

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selectivity may be ascribed to the limited number of available active sites on the catalytic surface

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for effective conversion to GVL at higher LA loading. Moreover, generation of IPA related

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products such as IP-4-hy-LA and IP-LA also compete for the active sites and remain unreacted

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during the course of the reaction. Thus, it can be argued that at higher LA concentrations,

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formation of IPA adducts is predominant that eventually hampers the LA to GVL transformation.

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Therefore, dropdown in conversion and selectivity towards GVL may be attributed to: (i)

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decrease in the ratio of active sites to LA at higher concentration; (ii) generation of IPA related

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products that hamper the catalytic activity and (iii) inhibition of 4-hydroxy valeric acid

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intermediate to undergo cyclization due to occupation of reactive sites by IPA related moieties. 9



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Thus, 5% (w/w) LA concentration is selected as an optimum concentration for reduction

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reactions which could deliver maximum amount of GVL (99%) with optimal selectivity (98%).

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3.2.3. Reusability studies

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The efficiency of 50% Fe-Ni/MMT is further evaluated for repeated use without sacrificing its

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catalytic activity. After first hydrogenation run is completed, the reaction mixture is allowed to

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settle down and the supernatant is removed from the reactor. A fresh charge of reactants is added

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to the catalyst retained in the reactor and the subsequent run is continued under identical

257

experimental conditions. The procedure is followed for five catalytic runs and the results are

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depicted in Figure 8. It can be seen from this figure that the catalyst remains highly active up to

259

six cycles without any change in conversion and selectivity for each cycle. A slight decrease in

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GVL selectivity is plausibly due loss of small amount of catalyst during sampling from time to

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time. We have also carried out the catalyst recycle experiments after 30 min. so as to evaluate the

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efficacy of catalyst at partial LA conversion (Supporting information Fig. S2). It is observed that

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the LA conversion is 87% with 68% selectivity to GVL remains almost constant along with 24%

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IP-4-hy-LA during each recycle within 30 min. It implies that formation of IPA esters of LA is

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predominant step during LA to GVL conversion in IPA; a feature already been reported during

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production of GVL.31 Such behavior can be explained on the basis of several aspects: (i)

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presence of Ni controls the iron corrosion via formation of galvanic cell on the catalyst surface;

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(ii) facile electron transfer from Fe to IPA/H2 generating Ni-H species; (iii) stabilization of Fe-Ni

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NP’s in the layers of MMT that enhances rate of hydrogenation; (iv) Bronsted as well as Lewis

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acid sites on MMT surface are effective towards cyclization; (v) being supercritical, IPA is

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capable of generating its own pressure forming hydride which may be regarded as another asset

272

that enables LA reduction at higher rates; (vi) acetone formed as a by-product of IPA may be

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reduced again to IPA by H2 gas; (vii) H2 gas and hydrides generated from IPA drastically

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improve the catalytic efficiency and (viii) synergistic association of Fe and Ni along with their

275

dispersion in the acidic MMT structure efficiently convert LA to GVL selectively.

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3.2.4 XPS analysis

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In order to establish that the catalyst surface remained active during successive cycles, XPS

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analysis is performed on fresh and reused 50% Fe-Ni/MMT after 6th cycle (Supporting

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information Figure S3). Besides Fe and Ni, the whole spectrum comprises of Si (2p 103 eV and

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2s 154 eV) and O (1s 533 eV) due to MMT for both fresh and reused composite. Iron region of 10


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this spectrum (Fig. 9 a, c) comprises of peaks corresponding to Fe 2p3/2 and Fe 2p1/2 around

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713.0 and 726.6 eV due to Fe (II) and Fe (III) species respectively.32, 33 The deconvoluted Fe

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2p3/2 and Fe 2p1/2 curves results in two four resolved peaks at 712.9, 717.3, 726.6 and 735.3 eV

284

corresponding to oxides and hydroxides of iron in their respective states. Inspection of this

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region for fresh and reused 50% Fe-Ni/MMT catalysts suggests that there is not much of

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difference in the peak positions for both Fe 2p3/2 and Fe 2p1/2. Ni region (Supporting information

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Fig. S4) for fresh catalyst exhibited deconvoluted peaks at 856.8, 862.5, 873.9 and 880.7 eV

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corresponding to Ni 2p3/2 and Ni 2p1/2 respectively34 which remained unaffected even after five

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cycles. Both these observations indicated that the catalyst surface remains active during six

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cycles probably due to presence of reducing atmosphere maintained during the conversion of LA

291

to GVL. The broad O1s peak centered at 533.0 eV for fresh catalyst (Fig. 9 b) splits into three

292

satellite bands due to formation of oxides and hydroxides35,

293

comparatively sharper nature as a consequence of insertion of Fe-Ni NP’s within MMT layers.

294

3.3. Proposed mechanism

36

while used catalyst exhibits

295

It is well established that metal nanoparticles, either monometallic or multi-metallic, being

296

electronically conducting solids, strongly catalyzes redox reactions. The proposed mechanism for

297

chemo-selective reduction of LA by external H2 in the presence of 50% Fe-Ni/MMT is depicted

298

in Scheme 1. It is well understood that LA to GVL conversion in alcohol solvent essentially

299

proceeds through formation of LA-esters31 followed by their hydrogenation with adsorbed H2 on

300

the catalytic surface.37, 38 The adsorbed H2 on Fe-Ni NP’s is further cleaved to generate hydride

301

species (H−) that are utilized for reduction of LA to IPA ester of 4-hydroxy pentanoic acid as an

302

intermediate. Finally, this intermediate undergoes cyclization due to presence of Bronsted and

303

Lewis sites on MMT surface that facilitates ring closure through removal of water and formation

304

of GVL.

305

The important features of the hydrogenation of LA to GVL may be summarized as: (i)

306

esterification of LA is key step for the initiation of the catalytic transformation of LA to GVL (ii)

307

faster rate of hydrogen reaction (iii) the molecular hydrogen assists in maintaining optimal H−

308

concentration by reducing acetone formed as by-product from IPA (iv) the cyclization is

309

accelerated due to presence of acidic sites on MMT surface (v) the intercalation of Fe-Ni NP’s in

310

the MMT clay matrix enhances their catalytic efficiency. 11



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

311

Page 12 of 30

4. CONCLUSIONS

312

Present work clearly demonstrates that nano-engineered functionalized bimetallic Fe-Ni/MMT

313

composite exhibits promising catalytic activity with complete conversion and selectivity (>99%)

314

towards reductive cyclization of LA to GVL. Amongst various catalysts, 25%Fe–25%Ni/MMT

315

composition possesses excellent catalytic activity due where Fe site acts as an e- donor while Ni

316

site is responsible for transfer hydrogenation reaction. However, increase in either Fe or Ni

317

content in the composite affects the GVL selectivity (~50%) implying that synergistic effect

318

exerted by the presence of equal amounts of Fe and Ni significantly contributes towards

319

beneficial catalytic activity. This reaction is found to be dependent on the solvent used for such a

320

conversion. For example, aqueous medium promotes better conversion with good selectivity;

321

however, substantial amounts of both Fe and Ni are leached out from catalyst surface due to

322

corrosion of metal sites in water. On the other hand, use of alcohol as solvent completely

323

prevents this phenomenon. However, primary alcohols significantly decrease the selectivity to

324

GVL due to formation of esters of LA and it’s hydroxylated LA. IPA being a secondary alcohol

325

and good H-donor, it acts as a protecting group for carboxylic acid thereby preventing the

326

leaching of metals. The reversible nature of IPA to acetone conversion through catalytic redox

327

process maintains optimal hydrogen concentration during the entire course of hydrogenation

328

step. This feature could be attributed to well dispersed bimetallic nanoparticles within MMT

329

structure that enhances the rate of hydrogenation. Presence of both Bronsted and Lewis acidic

330

sites on MMT effectively brings about the subsequent step of cyclization. Increasing LA loading

331

leads to decrease in selectivity by about three times because of decrease in the ratio of available

332

active sites to number of LA molecules and accumulation of unconverted IPA related products.

333

The catalytic activity is retained up to six cycles without substantial change activity and

334

selectivity as evident from pre- and post XPS analysis of the catalyst. Moreover, the reusability

335

studies at partial conversion of LA also confirm such a feature with almost 86% conversion and

336

68% selectivity is achieved after 30 min. Thus, it can be argued that designing of non-noble

337

metal based bimetallic nanocomposites may be regarded as viable and sustainable approach

338

towards effective conversion of LA to GVL.

339

ACKNOWLEDGEMENTS

12


Page 13 of 30

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340

BSK and RCC are thankful to Principal, Abasaheb Garware College and DST, New Delhi for

341

Infrastructural Grant. Authors thank Alok Jakhade for deconvolution of XPS spectra.

342 343

SUPPORTING INFORMATION

344

It includes:

345

Effect of metal loading on conversion of LA to GVL

346

Reusability studies of 50%Fe-Ni/MMT at partial LA conversion.

347

XPS spectra of (a) fresh and (b) used 50% Fe-Ni/MMT

348

XPS spectra for Ni region of (a) fresh and (b) used 50% Fe-Ni/MMT

349

Conversion of LA to GVL using non-noble bimetallic nanocomposites

350

13



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 14 of 30

351

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14. Fulvio, P. F.; Liang, C.D.; Dai, S.; Jaroniec, M. Mesoporous Carbon Materials with Ultra-

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Separable Catalysts. Chem. Eur. J. 2012, 18, 7601−7607.

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17. Yan, K.; Yang, Y.; Chai, J.; Lu, Y. Catalytic reactions of gamma-valerolactone: A platform to fuels and value-added chemicals. Appl. Catal. B 2015, 179, 292–304. 18. Yan, K.; Chen, A. Efficient hydrogenation of biomass-derived furfural and levulinic acid on the facilely synthesized noble-metal-free Cu-Cr catalyst. Energy 2013, 58, 357-363. 19. Yan, K.; Chen, A. Selective hydrogenation of furfural and levulinic acid to biofuels on the ecofriendly Cu–Fe catalyst. Fuel 2014, 115, 101–108.

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20. Petkar, D.R.; Kadu, B.S.; Chikate, R.C. Highly efficient and chemoselective transfer

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hydrogenation of nitroarenes at room temperature over magnetically separable Fe–Ni

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21. Adams, J. M.; Evans, S. Determination of the cation exchange capacity of small quantities o

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clay minerals by nephelometry. Clays and Clay Minerals 1979, 27, 137-139.

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22. Strawhecker, K.; Manias, E. Structure and Properties of Poly(vinyl alcohol)/Na+

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Montmorillonite Nanocomposites. Chem. Mater. 2000, 12, 2943-2949. 23. Hur, S.; Kim, T.; Hwang, S.; Hwang, S.; Yang, J.; Choy, J. Heterostructured Nanohybrid of Zinc Oxide-Montmorillonite Clay. J. Phys. Chem. B 2006, 110, 1599-1604.

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24. Xiang, J.; Shen, X.; Song, F.; Liu, M.; Zhou, G.; Chu, Y. Fabrication and characterization of

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25. Bokare, A.; Chikate, R.; Rode, C.; Paknikar, K. Effect of Surface Chemistry of Fe−Ni

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Nanoparticles on Mechanistic Pathways of Azo Dye Degradation. Environ. Sci. Technol.

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2007, 41, 7437-7443.

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26. Kadu, B. S.; Sathe, Y.D.; Ingale, A.B.; Chikate, R.C.; Patil, K.S.; Rode, C.V. Efficiency and

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recycling capability of montmorillonite supported Fe–Ni bimetallic nanocomposites towards

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hexavalent chromium remediation. Appl. Catal. B: Environ. 2011, 104, 407–414.

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27. Cronauer, D.; Jewell, D.; Shah, Y.; Modi, R. Mechanism and kinetics of selected hydrogen

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transfer reactions typical of coal liquefaction. Ind. Eng. Chem. Fundament. 1979, 18, 153-

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162.

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28. Johnstone, R.; Wilby, A.; Entwistle, I. Heterogeneous catalytic transfer hydrogenation and its

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relation to other methods for reduction of organic compounds. Chem. Rev. 1985, 85, 129-

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29. Brieger, G.; Nestrick, T.J. Catalytic transfer hydrogenation. Chem. Rev. 1974, 74, 567–580.

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30. Hengne, A.M.; Kadu, B.S.; Biradar, N.S.; Chikate, R.C.; Rode, C.V. Transfer hydrogenation

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of biomass-derived levulinic acid to γ-valerolactone over supported Ni catalysts. RSC Adv.

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2016, 6, 59753-59761.

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31. Hengne, A. M.; Rode, C. V. Cu–ZrO2 nanocomposite catalyst for selective hydrogenation of levulinic acid and its ester to γ-valerolactone. Green Chem., 2012, 14, 1064-1072.

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32. Grosvenor, A. P.; Kobe, B. A.; Biesinger, M. C.; McIntyre, N. S. Investigation of multiplet

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33. Yamashita, T.; Hayes, P. Analysis of XPS spectra of Fe 2+ and Fe 3+ ions in oxide materials. Appl. Surf. Sci. 2008, 254, 2441–2449. 34. Grosvenor, A. P.; Biesinger, M. C.; Smart, R. S. C.; McIntyre, N. S. New interpretations of XPS spectra of nickel metal and oxides. Surf. Sci. 2006, 600, 1771–1779. 35. Dupin, J. C.; Gonbeau, D.; Vinatier, P.; Levasseur, A. Systematic XPS studies of metal oxides, hydroxides and peroxides. Phys. Chem. Chem. Phys. 2000, 2, 1319-1324

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36. Biesinger, M. C.; Payne, B. P.; Grosvenor, A. P.; Laua, L. W. M.; Gerson, A. R.; Smart, R.

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439 440


37. Fegyverneki, D.; Orha, L.; Láng, G.; Horvath, I. Gamma-valerolactone-based solvents. Tetrahedron 2010, 66, 1078-1091.

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38. Azadi, P.; Flores, R. C.; Torres, Y.P.; Gürbüz, E.; Farnood, R.; Dumesic J. Catalytic

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conversion of biomass using solvents derived from lignin. Green Chem. 2012, 14, 1573-

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1576.

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Page 18 of 30

445

Captions:

446

Figure 1: X-ray diffraction patterns Fe–Ni/MMT nanocomposites

447

Figure 2: TEM images of (a) 10% Fe-Ni/MMT (b) 25% Fe-Ni/MMT (c), (d) 50% Fe-Ni/MMT

448

Figure 3: NH3-TPD studies for acidity measurement of (a) 10%, (b) 25% and 50% Fe-Ni/MMT

449

Figure 4: Effect of solvent on LA to GVL conversion [Reaction conditions: levulinic acid, 5%

450

(w/w); solvent, 95 mL; temperature, 473 K; H2 pressure, 500 psi; catalyst, 0.5 g;

451

reaction time, 1 h]

452

Figure 5: CT profile for reductive cyclization of LA to GVL [Reaction conditions: levulinic

453

acid, 5% (w/w); IPA (95 mL); temperature, 473 K; H2 pressure, 500 psi; catalyst, 0.5

454

g]

455

Figure 6: Effect of H2 pressure on LA to GVL conversion [Reaction conditions: levulinic acid,

456

5 % (w/w); IPA (95 mL); temperature, 473 K; H2 pressure, 100-500 psi; catalyst, 0.5

457

g; reaction time, 1 h]

458

Figure 7: Effect of initial LA concentration on conversion and selectivity towards GVL

459

[Reaction conditions: levulinic acid, 5-30% (w/w); IPA (95 mL); temperature, 473

460

K; H2 pressure, 500 psi; catalyst, 0.5 g; reaction time, 1 h]

461

Figure 8: Reusability of 50%Fe-Ni/MMT for chemo-selective reduction of LA [Reaction

462

conditions: levulinic acid, 5 % (w/w); IPA (95 mL); temperature, 473 K; H2 pressure,

463

500 psi; catalyst, 0.5 g; reaction time, 1 h]

464

Figure 9: XPS spectra of Fe and O region for (a) fresh and (b) used Fe-Ni/MMT

465

Scheme 1: Proposed mechanistic pathway for chemo-reductive cyclization of LA

466

Table 1:

Physicochemical characterization of Fe-Ni/MMT nanocomposites

467

Table 2:

Effect of metal loading on catalytic efficiency of nanocomposites towards LA to

468

GVL conversion

469 470 471 472 473 474 475 18


Page 19 of 30

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476 477

Fig.1:

478 479 480

Fig.2:

19



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Page 20 of 30

481 482 483

Fig.3:

484 485

486 20


Page 21 of 30

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

487 488 489 490


Fig.4:

491 492

21



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

493

Page 22 of 30

Fig. 5:

494 495 496

Fig. 6:

497

498 499

22


Page 23 of 30

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

500


Fig. 7:

501 502 503 504

Fig. 8:

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 30

505 506

24


Page 25 of 30

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

507


Fig. 9:

508

509 510

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

511

Page 26 of 30

Scheme 1:

512 513

26


Page 27 of 30

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

514


Table 1: Sr. No

Catalyst

1 2 3 4 5

10% Fe-Ni/MMT 25% Fe-Ni/MMT 50% Fe-Ni/MMT Fe-Ni Na-MMT

Specific Surface Area (m2/gm) 82 61 75 27 98

Pore volume (CC/g) 0.098 0.091 0.086 0.015 0.104

Average Pore diameter (Å) 48 44 42 13 51

515

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

516

Page 28 of 30

Table 2: Set of Experiments

I

II

III

Solvent

Catalyst composition

Conversion (%)

% Selectivity GVL

Others*

10% Fe-Ni/MMT

10

100

Nil

25% Fe-Ni/MMT

41

100

Nil

50% Fe-Ni/MMT

90

100

Nil

5% Fe-45% Ni/MMT

51

100

Nil

10% Fe-40% Ni/MMT

55

100

Nil

50% Fe/MMT

31

100

Nil

50% Ni/MMT

85

100

Nil

MeOH

50% Fe-Ni/MMT

99

19

81

EtOH

50% Fe-Ni/MMT

98

26

74

nPrOH

50% Fe-Ni/MMT

99

61

39

IPA

50% Fe-Ni/MMT

99

98

2

H2O

H2O

H2O

IV

Meal leaching (ppm) Fe

Ni

2.7

Nil

286.5

12.7

732.1

37.5

2.4

58.2

56.3

49.8

987.9

Nil

Nil

72.5

Nil

Nil

Nil

Nil

Nil

Nil

Nil

Nil

517 518

[Reaction conditions: levulinic acid, 5-30% (w/w); solvent, (95 mL); temperature, 473 K; H2

519

pressure, 500 psi; catalyst, 0.5 g; reaction time, 1 h].

520

28


Page 29 of 30

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521


TOC

522

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

1273x679mm (96 x 96 DPI)


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Reductive Cyclization of Levulinic Acid to Î³-Valerolactone over Non

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