Selective hydrogenation of furfural to tetrahydrofurfuryl alcohol using

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Kinetics, Catalysis, and Reaction Engineering

Selective hydrogenation of furfural to tetrahydrofurfuryl alcohol using supported nickel-cobalt catalysts Jigisha K. Parikh, Sanjay Srivastava, and Giriajsinh C Jadeja Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.9b01443 • Publication Date (Web): 19 Aug 2019 Downloaded from pubs.acs.org on August 23, 2019

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Industrial & Engineering Chemistry Research

Selective hydrogenation of furfural to tetrahydrofurfuryl alcohol using supported nickel-cobalt catalysts Jigisha Parikh*, Sanjay Srivastava, Giriajsinh C Jadeja Department of Chemical Engineering, Sardar Vallabhbhai National Institute of Technology, Surat-395007, Gujarat, India

* Corresponding author, Tele: + 91261-2201689 E-mail: [email protected], Jigisha Parikh

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Industrial & Engineering Chemistry Research 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

Abstract In this study, bimetallic nickel-cobalt catalysts supported on SiC, ɣ-Al2O3 and SBA-15 with different compositions of nickel and cobalt were explored for one step hydrogenation of furfural (FAL) to tetrahydrofurfuryl alcohol (THFOL). Detailed characterization of the synthesized catalysts revealed that smaller size and higher dispersion of Ni-CoOx sites in 10N-10C-MS catalyst are responsible to convert almost 100% FAL and the maximum selectivity towards THFOL. 10N-10C-Al showed almost 99% conversion but had slightly less THFOL selectivity, while 10N-10C-SiC showed poor conversion having maximum selectivity towards furfuryl alcohol (FOL) owing to the large size Ni particles. Bimetallic catalysts exhibited superior activity in contrast to their monometallic counterparts wherein, 10N-10C-MS displayed the best catalytic performance with 90.4% selectivity to THFOL at 210 oC and 7 MPa. Further, the Power law and the proposed LHHW models were found fit for the experimental data for the conversion of both FAL and FOL.

Keywords: Furfural, tetrahydrofurfuryl alcohol, Ni-Co, SBA-15, hydrogenation


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1. Introduction Worldwide increasing demand for fine chemicals and fuels together with depleting petroleum resources emphasises renewable biomass as a possible substitution for the progress of chemical industries in the near future.1 In this regards, researchers focus on the up-gradation of biomass derived platform molecules such as furfural (FAL), 5-hydroxymethylfurfural (HMF) and levullinic acid towards value-added chemicals and fuels.2 Among these, FAL is obtained by acid hydrolysis of C-5 xylose.3 It is also found in pyrolysis oil.4 Recently, an industrial importance of FAL has grown as it can be effectively converted to variety of chemicals and fuels such as furfuryl alcohol (FOL), tetrahydrofurfuryl alcohol (THFOL), furan (FU), tetrahydrofuran (THFU), 2-methylfuran (2-MF), 2-methyltetrahydrofuran (MTHF), cyclopentanone (CPN), cyclopentanol (CPL) and n-pentane etc, which are industrially important.5 Among them, THFOL obtained by C=C hydrogenation of furan ring in FAL (ref. Scheme 1) is one of the typical products from FAL hydrogenation. THFOL is absolutely miscible in water and has very high boiling point with good transparency. It is a versatile chemical having various applications, viz. utilized as a high-boiling solvent in making of printing ink, pharmaceutical industry etc. However, primarily, it is used for the synthesis of 3,4-dihydro-2H-pyran (dihydropyran) and 1,5-pentanediol which are known as speciality chemicals.6-12 In FAL hydrogenation, a lot of literature published on the selective hydrogenation of FAL to FOL.3,

5

However, direct transformation of FAL into THFOL as one pot synthesis via

intermediate FOL is still under progress and limited researches have been reported on the said process.3, 5 Commercial production of THFOL is reported on supported Ni catalyst under moderate temperatures (323–373 K) in vapour or liquid-phase by the hydrogenation of FOL.6-7



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O OH

2H2

H2

furfuryl alcohol

O

O O

Furfural

OH

2H2 H2

O

tetrahydrofurfuryl alcohol

O

tetrahydrofurfural

Scheme.1 Formation of tetrahydrofurfuryl alcohol via furfural Conventionally, THFOL is formed through FAL hydrogenation via intermediate FOL over Cu-Cr and various noble metal catalysts in two steps.8 Tomishige et al. have studied gas phase hydrogenation of FAL and reported 94% yield of THFOL over Ni/SiO2.9 They also reported the aqueous phase reduction of FAL using Ni–Pd/SiO2 or Pd–Ir/SiO2 as catalysts, wherein, the maximum yield (96%) of THFOL was obtained.10 Recently, Rode's group reported excellent yield towards THFOL (95%) through FAL using Pd/MFI catalyst. 11 Chen et al.7 explored the hydrogenation of FAL to THFOL over Ni-Pd/ TiO2-ZrO2 catalyst. Bhogeswararao et al.12 reported that Pd/Al2O3, at 25 oC and 60 bar H2, converted 79.5 wt% FAL to 100 wt% of THFOL. Noble metal catalysts are reported to be reasonably good for one-pot synthesis of THFOL from FAL owing to have excellent C=C reduction capacity. However, the main disadvantage with noble metal catalyst is its cost. In addition, supported or unsupported Ni catalysts are associated with the rapid deactivation and require harsh reaction conditions. Although Ni based catalysts progressively deactivated during the reaction, still the hydrogenation of FAL to THFOL is being frequently studied. 9


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To overcome these challenges, we developed less expensive supported Ni-Co catalysts to attain higher yield of THFOL from FAL under mild conditions. The synergy between nickel and cobalt reduces the Ni particle size to such level that conquer the carbon depostion.13 Moreover, this synergy improves the stability by forming Ni-Co alloy.14 Addition of cobalt to Ni/Yb2O3, Ni/ZrO2 and Ni/ThO2 catalysts was found beneficial in terms of reduction in carbon deposition during oxidative conversion of methane as reported by Choudhary et al.15, 16

. Malobela et al.17 have studied hydrogenation of cinnamaldehyde using Ni-Co/MWCNT

catalyst and reported that the interaction between Ni and Co improves the stability of active Ni species because the presence of Co reduces the carbon deposition onto active sites. In our previous studies, we have successfully cleavage C=O bond of FAL on copper-cobalt and copper-nickel catalysts in liquid phase.

18-19

However, these catalysts were found to be

least selective towards C=C hydrogenation owing to C=O adsorption mode of FAL over active Cu species. The bimetallic Ni−Co catalysts were effectively utilized as a promising C=C reduction catalyst, wherein, Ni acts as a strong C=C reducing agent and Co helps in inhibiting coke formation, thus improving selectivity as well as the stability in various applications such as methane combustion, steam reforming etc.20-24 Nabgan et al. (2016) used CeO2, ZrO2, La2O3 and Al2O3 as support material for 5:5 wt% of Ni and Co for steam reforming.

25

They suggested that strong interaction between metal and support and large

surface area of support facilitated dispersion of metal particles with the lowest coke formation. Lim et al. (2015) used 50:50 and 50:67 as Co:Ni ratio and revealed that at equal loading synergy between both metals was higher which emerges highly dispersed metal particles for methane combustion reaction.26 Furthermore, Ceria-Zirconia supported Ni-Co catalysts were reported for dry reforming of methane.27 This work has been shaped by considering aforementioned back-ground. It has focused on the tuning of the selectivity from C=O to C=C hydrogenation of FAL towards THFOL using synergism of appropriate bi-metallic supported Ni-Co catalysts. Consequently, the foremost 5 ACS Paragon Plus Environment


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purpose of this work was to explore the effect of supports (SiC, ɣ-Al2O3 and SBA-15) and Ni/Co ratio (5:15, 10:10 and 15:5) on the properties of Ni-Co catalysts. Afterwards, the activity of these catalysts was explored towards selective hydrogenation of FAL to THFOL in a single step. Influence of reaction variables for instance temperature, catalyst amount, hydrogen pressure, FAL to 2-propanol ratio and time were also studied for the optimal production of THFOL. Eventually, the kinetic behaviour for the conversion of FAL to THFOL using both POWER law and LHHW mechanism was described. 2. Experimental Work 2.1 Material Tetraethylorthosilicate,

pluronic

(P123),

metal

salts

such

as

Co(NO3)2·6H2O,

Ni(NO3)2·6H2O, HCl (37%), ethanol, furfural, furfuryl alcohol, tetrahydrofurfuryl alcohol, 2methylfuran, furan, tetrahydrofuran, methyltetrahydrofuran, etc., were purchased from Sigma-Aldrich (Mumbai, India). ɣ-Al2O3 and SiC supports were received from Sterling Pvt. Ltd., Surat, India. All the chemicals were 99% pure. 2.2 Catalysts Synthesis In order to remove soluble impurities from ɣ-Al2O3 and SiC, both were placed in a furnace at 550oC in nitrogen atmosphere for 4 h.19 SBA-15 was synthesized by adopting the procedure given by Zhao et al.,

28

the typical procedure is described in detail in our previous work.29

The sizes of SiC, ɣ-Al2O3 and SBA-15 were found to be 30-40 μm, 20-25 μm, and 20–35 μm, respectively. Bimetallic Ni-Co and monometallic (Ni & Co) onto different supports such as amorphous SiC, ɣ-Al2O3 and SBA-15 were prepared by wet-impregnation method using the 100 mL aqueous solutions of nickel nitrate (Ni(NO3)2.6H2O), and cobalt nitrate (Co(NO3)2.6H2O). The total metal loading in all the catalysts was kept constant i.e. Ni (X)+Co(Y)=20%. The doping of metals is carried out in a simple glass beaker, which was placed on magnetic stirrer with constant stirring speed of 300-350 rpm for 4 hr at room temperature. The doped catalysts 6 ACS Paragon Plus Environment

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were kept in oven at 100±2°C for 12 h. After drying, the samples were calcined at 450±5 °C for 4h in programmable muffle furnace to get the desired oxide catalysts. The catalysts are assigned as XN-CY-SiC, XN-CY-Al and XN-CY-MS, respectively, wherein X=% Ni loading and Y=% Co loading, MS= mesoporous silica (SBA-15), Al=ɣ-Al2O3 and SiC=silicon carbide. 2.3 Catalysts Characterization All the prepared catalysts were characterized by X-ray diffraction (XRD), N2-sorption method, Transmission electron microscopy (TEM), H2-Temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and CHNS analysis. 2.4 Catalytic activity An autoclave reactor of 100 mL capacity is used to perform all the designed experiments. Initially, 0.5g catalyst was reduced at 410 oC under hydrogen flow at 0.1 MPa. After cooling at ambient temperature; FAL and isopropyl alcohol (4.32 mL FAL in 20 mL IPA) were kept into an autoclave under inert environment. The catalytic activity was tested in the temperature range of 100-200 oC at 7MPa hydrogenation pressure. Additionally, effect of various operating parameters was studied and optimization studies were carried out using Taguchi method to achieve a higher yield of THFOL. Products were analysed by Sigma GC-FID system using Carbowax capillary column (30 m x 0.25 mm x 0.32μm) and nitrogen as a carrier gas. The GC program which is used to identify and quantify the various compounds can be found in our previous work.30 Carbon was balanced in each run and it was recorded >94% in each run owing to few anonymous products. The detail procedure to calculate carbon balance can be found in our previous work.31 3. Result and discussion 3.1 Physicochemical properties of materials 3.1.1 X-ray diffraction analysis 7 ACS Paragon Plus Environment


The X-ray diffraction patterns of bi-metallic 10N-10C-MS, 10N-10C-Al and 10N-10C-SiC catalysts after reduction in hydrogen are shown in Fig.1. All three catalysts evidenced the presence of Ni phase at 2θ= 43.8, 52 and 75.9o (JCPDS: 00-004-0850). However, the intensity of diffraction patterns pertaining to the Ni is varied in all three catalysts. This may be ascribed to the difference in metal dispersion and its size emerged on different supports. The 10N-10C-SiC catalyst showed sharp diffraction patterns, indicating the bigger size metallic particles. However, both the 10N-10C-MS and 10N-10C-Al catalysts displayed the highly dispersed small nanoparticles. The size of the metallic nano-crystallites were found to be 8-10, 12-15 and 30-35 nm, over SBA-15, ɣ-Al2O3 and SiC supports, respectively as calculated by the Scherrer formula at 2θ= 43.8 degree. The difference in the size of metal particles over various supports can be described by considering the intimate contact between metal and supports as well as morphological structure/nature of supports. In present catalytic system, the metal-support interaction is found to be SBA-1599% conversion and 20Co-MS gave nearly 90% conversions. This may be attributed to poor hydrogenation ability of Co metal as well as partially reduced CoO as compared to Ni.53-54 Further, both 20Ni-MS and 20Co-MS were found to be less selective towards THFOL, wherein, 20Ni-MS gave slightly more THFOL because Co is least active in C=C bond scission than Ni.54 The main product resulting from these catalysts is FOL. The superior activity of Ni relative to Co is further noticeable, as Ni attains relatively more yields towards THFOL. To comprehend this in easier way, it should be believed that Ni is mostly identified for its C=C reduction activity. Consequently, catalyst which includes larger number of Ni sites could perhaps increase the THFOL yield through the C=C reduction of furan ring, which in turn leads to higher THFOL yield than the monometallic Co catalyst. Conversely, C-O is less to be expected to dissociate on the Co catalysts that results higher FOL/2-MF yield than the Ni catalysts. In comparison with mono metallic counterparts, bimetallic Ni-Co catalysts are found to be highly active, as all the three catalysts have shown >99% conversion of FAL. However, the selectivity towards THFOL was found to be highly dependent on the synergy between Ni and Co loading. As observed, a higher yield of THFOL around (82.9 %) was obtained over 10N10C-MS amongst all the samples, whereas 5N-15C-MS exhibited the lowest selectivity towards THFOL (16%) and 15N-5C-MS exhibited the modest yield about (71%). The outstanding catalytic activity (i.e., conversion and selectivity) of 10N-10C-MS may be attributed to distinctive surface properties Ni-CoO sites. The change in electronic structure of Ni caused by alloying effect (due to synergy between Ni and Co metals) improved the 22 ACS Paragon Plus Environment

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catalyst surface which facilitated improved selectivity towards THFOL. These results were in line with the previous reports, wherein, the smaller size of Ni atom was reported the most favourable non-precious metal for C=C/C-C bond scission.20-24,

55

Moreover, it is clearly

observed, based on the effect of Ni and Co loading on physicochemical properties of various catalysts, that at equal loading of Ni and Co; highly dispersed, small size metal particles (Ni/Co) have emerged. These smaller size Ni/Co entities are the active species for total hydrogenation of FAL to THFOL. It is well known that the dispersion of metals and/or their structural properties very much depend on the synergy between two metals which is the key factor for better catalytic activity and selectivity in bimetallic catalysts. The reason for this betterment was reported due to the formation of Ni-Co alloy which enhances the movement as well as concentration of surface hydrogen at high temperature and turn out to be a more approving hydrogenation.52, 54, 56 In our bimetallic catalysts system under mild reaction conditions, two major products were observed via hydrogenation of FAL; FOL via hydrogenation of C=O and further hydrogenation of FOL to THFOL. It is essential to calculate the turn over frequency (TOF, S 1

) for the conversion of both FAL and FOL by considering the reaction rate below 20% X FAL

or XFOL (Table S1). Higher TOF values for the conversion of FAL to FOL relative to FOL to THFOL confirmed that C=C reduction was the rate-determining step. In addition, it was interesting to see that TOF values referred to the bimetallic catalysts are found to be higher than that of monometallic catalysts, revealed the synergistic effect between Ni and Co. As discussed above the various physiochemical properties of catalysts are the important factors determining the catalytic performances and could be used to explain the difference among them. However, reaction conditions to the catalyst behavior cannot be discarded and hence, an optimization study was carried out for the said reaction.54-55



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Table 3 Effect of Ni/Co molar ratio on the total hydrogenation of FAL to THFOL Entry

Catalysts

% XFAL

%SFOL

%STHFOL

%S2-MF

%Soth

1

20Ni-MS

99.1

52.1

11.8

4.6

31.5

2

10N-10C-MS

100

-

82.9

1.8

15.3

3

15N-5C-MS

99.6

1.2

71

1.7

26.1

4

5N-15C-MS

98.5

79.1

15.8

0.2

9.2

5

20Co-MS

90.5

69.5

1.65

16.1

12.75

(Reaction Conditions; T=190 oC, P = 7MPa, 4.32mL FAL in 20mL IPA, Time=6h, Oth=other by products) 3.3 Optimization study 3.3.1 Preliminary study 3.3.1.1 Effect of temperature on the total hydrogenation of FAL to THFOL Role of temperature on FAL conversion towards THFOL was studied using 10N-10C-MS catalyst in the temperatures ranges of 150-230 oC at 7MPa (Fig.8). As observed, at low temperature about 150 oC, the selectivity towards THFOL was almost equal to FOL (>40%). However, when temperature was improved from 150 to 210 oC, the selectivity towards FOL decreased (from >40 to 0) and the selectivity towards THFOL increased leading to a maximal of 90%. In addition, the production of other by products and 2-MF was observed to be nearly constant. Further an increase in temperature was found to be insignificant as the selectivity towards THFOL sharply decreased to 56% owing to the development of other by-products. At low temperature, little amount of THFOL was formed owing to the existence of intermediate FOL. This FOL was converted into THFOL when further temperature was increased that may be ascribed to the improved rate of C=C bond scission at higher temperature (210 oC). Results are in line with the previous reports on hydrogenation of FAL to THFOL.6, 11 24 ACS Paragon Plus Environment

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Figure 8 Effect of temperature on the total hydrogenation of FAL to THFOL over 10N-10CMS catalyst (Reaction Conditions; P = 7MPa, 4.32mL FAL in 20mL IPA, Time=6h, Oth=other by products)

3.3.1.2 Effect of hydrogenation pressure on the total hydrogenation of FAL to THFOL Role of hydrogen pressure on FAL conversion towards THFOL using 10N-10C-MS catalyst in the ranges of 5-8MPa at 210 oC was displayed in Fig.9. As observed, at low pressure about 5MPa, there were two major products 2-MF (55%) and FOL (20%). At this point, selectivity towards THFOL was very low (>10%). However, when pressure was increased from 5 to 7MPa, the selectivity towards 2-MF and FOL decreased and the selectivity towards THFOL increased and attained a maximal of 90%. Further an increase in pressure was found to be insignificant as the selectivity towards THFOL almost remained constant, which might be due to saturation of the active sites. At low pressure, the selectivity towards THFOL was low due to the side reaction of FAL to 2-MF. However, at high pressure the reaction shifted towards FAL to THFOL via C=C bond cleavage rather than C-O hydrogenolysis over Ni sites.6 Furthermore, the improved selectivity towards THFOL with increase in hydrogen



pressure may be caused by a larger attentiveness of hydrogen accessible on the active sites in catalyst, which made possible the FAL hydrogenation to THFOL.11

Figure 9 Effect of hydrogen pressure on the total hydrogenation of FAL to THFOL over 10N10C-MS catalyst (Reaction Conditions; T = 210 oC, 4.32mL FAL in 20mL IPA, Time=6h, Oth=other by products)

3.3.1.3 Effect of time on the total hydrogenation of FAL to THFOL Reactions were also carried out within a range of 2-7 h at 210oC and 7MPa (Fig.10) so as to notice the effect of time for complete conversion of FAL to THFOL. It was observed that hydrogenation of FAL to FOL was completely achieved within 2-3h. However, the complete transformation of FOL to THFOL or other by-products requires a long time. The maximum selectivity towards THFOL (90%) was attained at the said conditions within 6h reaction. Further increase in time leads to the development of other by-products via conversion of THFOL on the active sites. Therefore, it is suggested that 6 h is the maximum time limit for the total hydrogenation of FAL to THFOL over 10N-10C-MS at 210oC and 7MPa. Moreover, successive transformation of FAL to FOL and then FOL to THFOL is observed with respect to time as Temperature >Catalyst (Wt.) > Time >FAL composition. 3.4 Stability and reusability of the catalyst 10N-10C-MS catalyst that demonstrated the greatest catalytic performance was reused upto five cycles to estimate its strength for the said reaction. After 5th cycle, the used catalyst is dried in oven at 100 oC and then analyze by using TEM, X-ray diffraction and CHNS techniques to visualize the difference in its properties before and after (refer Figs. S4, S5 and Table S7). The X-ray diffraction spectra of recycled catalyst fairly look like the freshly reduced 10N-10C-MS catalyst; exhibited alike peaks pertaining to the most desirable Ni (0) in the used catalyst. Any peak pertaining to carbon was not appeared (Fig. S5). The XRD result of spent sample is in agreement with CHNS and TEM results that divulged the nonexistence or diminutive occurrence of carbon (Fig. S4, Table S7). Nevertheless, sintering of metal particles is not denied after 5th cycle as observed in TEM results that might be the cause for a little plunge in the selectivity of catalysts. As far as reusability of 10N-10C-MS is concerned, it was found to be highly recyclable as only 5% reduction in selectivity towards THFOL was observed along with nearly 8% decrease in the conversion of FAL (Fig. 12). It was reported that a small amount of Co prevents the carbon deposition on active Ni sites21 and therefore, the presence of Co was crucial factor which helps in the prompt dispersion of active Ni and carbon inhibition. It can be explained on the basis of synergy between two metals (Ni and Co). As reported in the activity section, the synergy between nickel and cobalt 30 ACS Paragon Plus Environment

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results in the decrease size of Ni particle to a such degree wherein, the least probability of carbon formation and its development.1 In addition, it is suggested that smaller Ni particles might be partially covered by the CoOx and hence inhibiting the formation of coke during reaction.13-14 Consequently, we say that catalyst is reusable and stable during the reaction. Moreover, when compare our results to the most recent literature on one step transformation of FAL to THFOL; it is mostly centred using supported Pt, Ru, and Ni 2 catalysts. As can be seen that other than noble metal catalysts, supported Ni is the most preferred for hydrogenation of FAL to THFOL but required harsh reaction conditions. Recently, almost >90% yield of THFOL was reported on Ni/C, Ni/ Ba-Al2O3 and CuNi/MgAlO.55,

58-59

However, study revealed that Ni species were progressively getting deactivated during the reaction for all three catalysts. Therefore, our catalytic system can be added as a robust catalyst which can be eliminate the drawback of being progressively deactivated and incorporated strongly in the literature for this reaction.

Figure 12 Reusability Study of 10N-10C-MS for total hydrogenation of FAL to THFOL (Reaction Conditions: T= 210 oC, P= 7.0 MPa, FAL composition = 4.32g of FAL in 20 mL of IPA, Time = 6 h) 31 ACS Paragon Plus Environment


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4. Developing Kinetic model for the transformation of FAL to THFOL The hydrogenation of FAL to THFOL can be expressed as: k1

k2

𝐹𝐴𝐿 → FOL → THFOL,

(2)

Where, k1 and k2 are the rate constants. The disappearance of both FAL and FOL with respect to time was studied at hydrogen pressure (6-8 MPa), reaction temperature (180-200 oC), initial composition of both FAL and FOL (1.75-3.25 gmol/L) and catalyst loading (0.051.25g). Initial rates were determined based on concentration by accepting the procedure reported elsewhere.60 The initial rates showed linear patterns with respect to hydrogen pressure and temperature (Fig.S6 a). The initial rate is also varied linearly with catalyst amount (Fig.S6 b) at 200oC and 8MPa. Fig.S6 c depicts how the values of initial rate changes with composition of FAL. The reaction rate increases linearly up to FAL concentration of 2.25 gmol/L suggested that the reaction order be one or slightly less than one. However, beyond FAL concentration of 2.25 gmol/L order of reaction was zero as no significant change in the reaction rate was observed until 3.25gmol/L of FAL concentration. Using linear regression analysis, the orders of reaction for FAL and hydrogen are determined which found in the range of 0.9-1.0 and 1.1-1.5 respectively (Table S8). The activation energy (11.25 kcal/mol) for the transformation of FAL to FOL is determined using Arrhenius plot (Fig. S6d). When compared the transformation of FOL to THFOL with the FAL to FOL, it appears to be slow reaction having similar linear trends for initial rates with respect to temperature and hydrogen pressure (Fig.S7 a & b). In contrast, reaction order was found to be 0.6 for the FOL concentration ( 10N-10C-Al>10N-10C-SiC. Further, the effect of Ni/Co ratio was examined for this reaction over screened SBA-15 supported catalysts by varying Ni:Co = 10:10, 5:15 and 15:5 and the results were matched with their monometallic counter parts. The bimetallic catalysts were of much superior than their monometallic counterparts for total hydrogenation of FAL to THFOL. Furthermore, equal loading was found to be advantageous which was driven by the synergy between both Ni and Co resulting in the highly dispersed smaller particles which was the most responsible for high activity as well as selectivity towards desired THFOL. In addition, reaction parameters for instance temperature, hydrogen pressure, time, catalysts amount and FAL to solvent ratio were optimised and found to be 200 oC, 8 MPA, 8h, 0.75g and 2.25 respectively which provided 93% yield of THFOL. The initial rate of reaction followed the linear path for both furfural to furfuryl alcohol and furfuryl alcohol to tetrahydrofurfuryl alcohol with respect to H2 pressure, temperature and the catalyst amount. On the other hand, this was not the case for reactant concentration. The experimental data was best fitted using a dual-site mechanism having dissociative adsorption of H2, wherein, the surface reaction is found to be 34 ACS Paragon Plus Environment

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the rate controlling step. The existence of cobalt strengthens the recyclability of bimetallic catalysts by minimizing the coke deposition on active sites.

Supporting Information The supporting information is available which contains XRD pattern for fresh and used materials, CHNS & TEM image of used sample, XPS patterns, TOFs values and data regarding Taguchi and kinetics study.

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Selective hydrogenation of furfural to tetrahydrofurfuryl alcohol using supported nickel-cobalt catalysts Jigisha Parikh*, Sanjay Srivastava, Giriajsinh C Jadeja Department of Chemical Engineering, Sardar Vallabhbhai National Institute of Technology, Surat-395007, Gujarat, India

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