1 Characterization and Application of Nanomaterials (2021) Volume 4 Issue 1 doi:10.24294/can.v4i1.523 ARTICLE INFO Received: 13 November 2020 Accepted: 4 January 2021 Available online: 11 January 2021 COPYRIGHT Copyright © 2021 Hari Prasad Reddy Kannapu, et al. EnPress Publisher LLC. This work is licensed under the Creative Commons Attribution- NonCommercial 4.0 International License (CC BY-NC 4.0). https://creativecommons.org/licenses/by- nc/4.0/ Original Research Article Nano CoO-Cu-MgO catalyst for vapor phase simultaneous synthesis of ortho-chloroaniline and γ-butyrolactone from ortho-cholonitrobenzne and 1,4-butanediol Hari Prasad Reddy Kannapu1,2,3*, Young-Woong Suh2,3*, Veeralakshmi Vaddeboina1, Anand Narani1, David Raju Burri1, Seetha Rama Rao Kamaraju1 1 Catalysis, Indian Institute of Chemical Technology, Hyderabad 500007, India. E-mail: kannapuhari@gmail.com/ hari83@hanyang.ac.kr 2 Department of Chemical Engineering, Hanyang University, Seoul 133-791, Republic of Korea. E-mail: ywsuh@ha- nyang.ac.kr 3 Research Institute of Industrial Science, Hanyang University, Seoul 133-791, Republic of Korea ABSTRACT The article aims at developing an efficient and stable catalysts for simultaneous hydrogenation of o-chloronitro- benzene to o-chloroaniline and 1,4-butanediol dehydrogenation to γ-butyrolactone. A series of CoO-Cu-MgO catalysts, composed of 10 wt% of copper, various amount of cobalt loadings (1, 5 and 10 wt%) and remaining of MgO were de- veloped by co-precipitation followed by thermal treatment. o-Chloroaniline and γ-butyrolactone were the main products with high yield of 85% and 90%, respectively. The advantage of the coupling process is that the hydrogenation reaction was conducted without external hydrogen, demonstrating minimize the hydrogen consumption known as hydrogen economy route. From N2O characterization results, the high activity of 5CoO-10Cu-MgO was found that it has high amount of Cu species (Cu0/Cu+1) which govern the stable activity and selectivity on time on stream study in presence of cobalt in Cu-MgO. Keywords: Transfer Hydrogenation; Ortho-chloro Aniline; γ-Butyrolactone; Atomic H2; Basic Sites; Nano CoO-Cu- MgO 1. Introduction Owing to an enormous importance of aromatic halo amines in the chemical industry, specifically for synthesis of herbicides, dyes, drugs, and pesticides, synthesis of aromatic halo amines from halo ni- trobenzene research has been gained a great attention in academia and industry point of view[1–9]. Despite high demanding of this reaction, the hydrogenation of ortho-chloronitrobenzene (o-CNB) to ortho-chlo- roaniline (o-CAN) has been studied extensively over precious metals e.g., platinum, palladium, nickel, rhodium, ruthenium and iridium[1–9]. Moreover, it has been mostly carried out under external hydrogen at an elevated temperatures and pressures which makes this process more complex and cost-ineffective in the industry point of view. Further, dehalogenation and ring hydrogenation are common side reactions that lead to formation of common side reactions that lead to formation of aniline and cyclohexylamine particularly over Pt, Pd and Ni catalysts. In this scenario, developing a highly selective and cost-effective cat- 2 alytic system still remains a challenge. Generally, alcohols are highly active for dehydrogenation over supported copper catalysts[10–18]. 1,4-butanediol (BDO) is one of the alcohols that can make γ-butyrolactone (GBL) and two moles of hydrogen in its cyclodehydro- genation over copper-based catalysts. Another import- ant point is noticed that the GBL has been demonstrated to be involved in the synthesis of N-vinylpyrrolidone, N-methylpyrrolidone, herbicides, and rubber additives and more over it is a green solvent. Commercially, the major production route for GBL is gas-phase dehydro- genation of BDO over supported copper metal cata- lysts, especially copper chromite catalysts, which are environmentally unacceptable. As described above, owing to the high com- mercial value of these products, these two reactions would have great impression. Currently, coupling of hydrogenation and dehydrogenation[10–17] is a prom- ising and an alternative method to the conventional hydrogenation. In this method, the above mentioned two reactions can be carried out simultaneously at a time over a same catalyst bed. Copper-based cata- lysts were found to be outstanding for the coupling of hydrogenation and dehydrogenation reaction[10–16]. However, the activity and stability of catalysts mainly depends on the preparation of the catalysts. A numerous results documented in the literature have found that the addition of second metal oxide to base catalyst will result in the local composition, the size and structure of active species significantly affecting the catalytic activity and selectivity of sup- ported metal catalysts[19]. It is generally agreed that for supported metal catalysts, highly dispersed active species can provide more active sites and thus confer the resulting catalysts with higher catalytic activ- ity[20]. To best of our knowledge, selective o-CNB hydrogenation to o-CAN has not been reported using 1,4-butanediol (BDO) dehydrogenation over nano CoO-Cu-MgO. Herein, we have investigated the vapor phase selective hydrogenation of o-CNB to o-CAN with dehydrogenation of BDO to γ-butyrolactone (GBL) over CoO-Cu-MgO catalysts. All the catalysts were developed by co-precipitation followed by thermal treatment. Catalysts preparation, characterization us- ing different analytical techniques such as BET sur- face area, N2O pulse chemisorption, XRD, TPR-H2, and TEM analysis and activity in hydrogenation and dehydrogenation have been delineated. 2. Experimental 2.1 Preparation of catalysts An aqueous homogeneous mixed metal ni- trate solution containing Cu(NO3)2•3H2O and Mg(NO3)2•6H2O was prepared followed immediate precipitation by drop-wise addition of 10% aqueous K2CO3 solution at a pH of 9.0 under constant stirring at room temperature. The resultant mixed Cu-Mg precipitate (precipitate of 10 wt% Cu-MgO catalyst, ppt1) has been separated under reduced pressure and washed thoroughly with hot distilled H2O until the complete removal of potassium ion. In a separate experiment, requisite amount of Co(NO3)2•6H2O aqueous solution has been precipitated at a pH of 9 with K2CO3 solution under vigorous stirring. The obtained cobalt precipitate (ppt2) was filtered and washed thoroughly with hot distilled water. Cu-Mg precipitate (ppt1) and Co precipitate (ppt2) were mixed in water under neutral condition and the resul- tant slurry was subjected to hydrothermal treatment at 373 K for 12 h followed by filtration with repeated washings. The precipitate was dried in oven at 393 K for 12 h followed by calcination at 723 K for 5 h. Similar procedure has been adopted for the prepara- tion of other CoO promoted Cu-MgO catalysts. The prepared catalysts were labeled as 1CoO-10Cu-MgO, 5CoO-10Cu-MgO, and 10CoO-10Cu-MgO, here the numerical value represents the loadings of Co and Cu by weight percentage. For example, 1CoO-10Cu-MgO represents a catalyst containing 1 wt% Co, 10 wt% Cu and the remaining balance MgO. 2.2 Characterization techniques All the CoO-Cu-MgO catalysts were thorough- ly characterized by using the following analytical techniques. The Brunauer, Emmett and Teller (BET) surface area of all catalysts was measured by N2 physisorption after degasification at 473 K for 4 h, under liquid nitrogen adsorption at 77 K using 3 Quadrasorb-SI surface area analyzer (M/s. Quanta- chrome instruments, USA). The surface properties of all CoO-Cu-MgO catalysts such as Cu metal surface area (MSA), Cu dispersion (DCu), particle size (PCu) and surface coverage of Cu atoms (SCu ) were estimated by N2O pulse chemisorption on pre-reduced (553 K for 3 h) catalyst under dynamic conditions. The detailed procedure was described elsewhere[10–13]. The X-ray diffraction (XRD) patterns of both calcined and reduced catalysts were recorded on a Miniflex diffractometer (M/s. Rigaku Instru- ments, Japan) using Ni filtered Cu Kα radiation in the 2θ range of 10°–80° at a scan rate of 2° min–1. The average crystallite size of copper was calculated us- ing Debye-Scherrer principle. Transmission electron microscopy (TEM) was recorded using a Phillips Tecnai G2 FEI F12 electron microscope. The re- duction behavior of the catalysts was determined by temperature programmed reduction (TPR) studies on a home-made system as per the procedure described elsewhere[10]. The CHNS elemental analysis was carried out on Elementar, Model: VarioMicrocube to estimate the carbon content in the catalyst before and after the reaction. 2.3 Activity studies A down flow fixed-bed reactor was used to in- vestigate the activity of the CoO-Cu-MgO catalysts for the individual hydrogenation of o-CNB (dissolved in ethanol) to o-CAN and dehydrogenation of BDO to GBL as well as coupling of both reactions. For separate experiments, first tests were carried out on o-CNB hydrogenation. Approximately, 500 mg of the catalyst powder (sieved to < 200 µm) diluted with an equal amount of quartz beads was charged to the reactor and supported on a quartz wool bed. The catalyst was reduced at 553 K for 3 h under hydro- gen. Then, the reactor was fed with o-CNB under H2 (18 ml∙min–1), using as a reducing gas. Similarly, the dehydrogenation of BDO was conducted under N2 atmosphere. Finally, the coupling of o-CNB hydro- genation and BDO dehydrogenation was performed at the molar ratio of 2:3 under nitrogen atmosphere. The liquid products, such as o-CAN and GBL were analyzed by using GC-17A (M/s. Shimadzu, Japan) with ZB-wax capillary column equipped FID detec- tor. The products were identified and analyzed by using GCMS–QP5050 (M/s. Shimadzu instruments, Japan) equipped with ZB-5 capillary column (25 m × 0.32 mm) supplied by M/s. J&W Scientific, USA. 3. Results and discussion 3.1 Catalyst characterization 3.1.1 BET Surface area studies Table 1 presents BET surface area, crystalline phases of various cobalt loadings of Cu-MgO cata- lysts both in calcined and reduced form. The surface area of the CoO-Cu-MgO catalysts is higher com- pared to MgO (42 m2∙g–1) alone. This indicates that addition of cobalt to Cu-MgO increases the surface areas of Cu-MgO. The BET surface area of catalysts increases with Table 1. BET surface area and XRD results of CoO-Cu-MgO catalysts Catalyst BET surface area (m2∙g–1) XRD phases Cu0 (nm) reduced Cu0 (nm) spent Calcined Reduced 1CoO-10Cu-MgO 78 CuO, MgO Cu0, Cu2 O,MgO 20 30.48 5Co-10Cu-MgO 88 CuO, MgO Cu0, Cu2 O,MgO 15 20.30 10CoO-10Cu-MgO 50 CuO, MgO Cu0, Cu2 O,MgO 13 26.48 increasing in CoO loading and displayed maximum surface area (88 m2∙g–1) at 5 wt% CoO loading and thereafter decreases with further increasing in the Co content. It was found that hydrothermal treatments of Fe/MgO catalysts transformed into lamella-like Fe/ Mg(OH)2 catalysts, resulted in increasing the specif- ic surface areas[21]. Since, in the present study, due to hydrothermal treatment, CoO-CuO-MgO interacted species in large number is responsible for high sur- face area of 5CoO-10Cu-MgO catalyst. Formation of an interacted phase (CuCo3O4) between Cu and Co was reported to be appeared at a temperature of 573 K which was stable up to 1073 K[22]. Such interacted phase might be accountable for the increasing trend of surface area and pore volume with the increase in Co content up to 5 wt%. Contrarily, beyond 5 wt% 4 Co loading, a reverse trend was observed due to sur- face coverage by cobalt oxide. The crystallite size of copper in reduced and spent catalysts is calculated and depicted in Table 1. It is obvious that the devel- opment of copper size influenced by the cobalt ad- dition is inevitable. In the case of reduced catalysts copper crystallite size linearly minimized whereas in spent catalysts, only 5CoO-10Cu-MgO has stability and maintain lower crystallite size among other two catalysts. 3.1.2 X-Ray diffraction studies (XRD) The XRD patterns of calcined catalysts are shown in Figure 1. A low intense diffractions of CuO phase (d values of 2.52 at 2θ = 35.6°, 2.32 at 2θ = 38.78 and 2.53 at 2θ = 35.45°, ICDD Card No. 5-661) and high intensity of MgO (d values of 2.11 at 2θ = 42.82°, 1.49 at 2θ = 62.25° and 1.22 at 2θ = 78.30°, ASTM Card No. 4-829) are observed in all cobalt loading catalysts. Interestingly, no diffractions were noticed for CoO oxide phase at all loadings which indicates amorphous form of cobalt species. It was reported that in 11% Co-MgO catalyst, MgO is in amorphous form when it is calcined at 673 K and it is in crystalline phase above 973 K[23]. In addition, CoO is formed after calcination at 773 K through the decomposition of Co(NO3)2 and might have diffused into the matrix of MgO or form a solid solution or oxidized to Co2O3, which on reaction either with CoO or with MgO to yield Co3O4 or MgCo2O4 [24]. Figure 1. XRD patterns of calcined CoO-Cu-MgO catalysts. (a) 1CoO-10Cu-MgO; (b) 5CoO-10Cu-MgO; (c) 10CoO-10Cu- MgO. Figure 2. XRD patterns of reduced CoO-Cu-MgO catalysts. (a) 1CoO-10Cu-MgO; (b) 5CoO-10Cu-MgO; (c) 10CoO-10Cu- MgO. XRD patterns of reduced (at 523 K in H2 flow) CoO-Cu-MgO catalysts are shown in Figure 2. The Cu0 phase with corresponding d values of 2.09 at 2θ = 43.25°, 1.81 at 2θ = 50.37° and 1.28 at 2θ= 73.99°, ICDD Card No. 4-836 is observed for all catalysts. But, the d values of Cu0 and MgO are closer; there- fore, the diffraction lines are not separated properly. As evidenced from the XRD results almost all CuO phases are reduced to Cu0 or Cu2O. It can also be seen that MgO phase decreased with addition of co- balt oxide representing the formation of amorphous MgCo2O4 species particularly at 10 wt% CoO. XRD pattern of 10CoO-10Cu-MgO catalyst revealed that Cu0, Cu2O and MgO crystallites were lower than other two catalysts. 3.1.3 N2O pulse chemisorption The estimated surface properties of Cu-MgO with cobalt catalysts such as (i) number of surface copper sites, (ii) dispersion, (iii) metal surface area, and (iv) particle size are shown in Table 2. N2O pulse chemisorption is a facile and proven technique for the estimation of metal area and allied surface properties of supported copper catalysts. Even though Co oxides are hard to get reduced at 523 K (the temperature at which the catalysts of the present investigation are reduced prior to N2O pulse chemisorption), small amount of lower oxi- dation states of Co species might have resulted to participate in the decomposition of N2O thus giving 5 a chance to over estimation of Cu dispersion[12]. As shown in Table 2, the number active surface sites of copper catalysts are higher in 5CoO-10Cu-MgO. Similarly, dispersion of active metal (copper plus co- balt) and active metal surface area (copper plus co- balt) are higher in all the cobalt promoted catalysts. Contrarily, the particle size (copper plus cobalt) of metal is lower in all cobalt promoted catalysts. 5CoO-10Cu-MgO catalyst possesses a little higher surface density (copper plus cobalt) compared to other Co promoted catalysts. The surface density of 5CoO-10Cu-MgO catalyst is nearly double than that of 1CoO-10Cu-MgO catalyst. 3.1.4 TEM analysis Figures 3a, b and c are copper particles with an appearance of dark contrasts as well as cop- per-free MgO particles with an appearance of light contrasts. At lower cobalt loadings the morphology of catalysts seems to be rod type structure, whereas at 10CoO-10Cu-MgO, catalyst regains its particle type structure. Such a gathering of copper species in CoO-Cu-MgO catalysts has also been reported in the literature[21–25]. However, no obvious copper particles can be found in the hydrothermal-treated catalyst (Figure 4). Figure 3. TEM images of CoO-Cu-MgO. (a) 1CoO-10Cu-MgO; (b) 5CoO-10Cu-MgO; (c) 10CoO-10Cu-MgO. Figure 4. Suggested mechanism of hydrothermal treatment and nanoparticle growth. 3.1.5 Temperature programmed reduction (TPR) studies The reducibility of the catalysts can be deter- mined by temperature programmed reduction with H2/Ar mixture and results are depicted in Figure 5. According to the TPR results of 10Cu-MgO catalyst, the catalyst characterized by a single symmetric peak centered at a temperature maximum (Tm) of 710 K[16]. The present results showed that the 1CoO-10Cu- MgO catalyst exhibits a single reduction, indicating the 1 wt% CoO did not affect Cu-MgO interactions. However, presence of a shoulder on an asymmetric peak is the indication of two-stage reduction: (i) CuO to Cu0 and (ii) partial reduction of CuCo2O4/ MgCo2O4. In the case of 5CoO-10Cu-MgO catalyst, the high temperature signal corresponds to the re- duction of interacted species formed between CoO precursor and CuO. It is noteworthy to mention that the amount of cobalt oxide species are less at 5 wt% cobalt oxide compared with that of 10 wt% CoO. The reaction between CuO and CoO can make more CuCO2O4 species in 5CoO-10Cu-MgO. Whereas, the high cobalt oxide content in 10CoO-10Cu-MgO might have resulted to have less CuCO2O4 and more MgCo2O4 which are reduced at 850 K. The three- stage reduction including copper oxide, cobalt ox- ides and spinals (CuCO2O4 and MgCO2O4) providing high acidity for 10CoO-10Cu-MgO. Table 2. N2O pulse chemisorption results for different CoO-10Cu-MgO catalysts Catalyst SCu atoms × 10–19 (atoms g–1) D Cu (%) Metal surface area (m2∙g–1) Particle size (nm) Surface density SCu/BET S.A 1CoO-10Cu-MgO 10 19 07 13 10/78 5CoO-10Cu-MgO 18 21 13 06 18/88 10CoO-10Cu-MgO 12 14 11 10 12/50 Note: Smetal = Number of surface metal sites (Cu); Dmetal = Dispersion of metal (Cu); SAmetal = Surface area of metal (Cu); Pmetal = Parti- cle size of metal (Cu) 6 Figure 5. TPR patterns of CoO-Cu-MgO. (a) 1CoO-10Cu-MgO; (b) 5CoO-10Cu-MgO; (c) 10CoO-10Cu-MgO. Due to high cobalt oxide content in 10CoO- 10Cu-MgO, the reduction behavior is unlike to other two catalysts. It was reported that the peaks at 650 and 730 K were assigned to reduction of large crys- talline Co3O4 to CoO and CoO to Co metal, respec- tively, but a shoulder peak at 850 K was attributed to the reduction of MgCo2O4 [26]. As reported by Wang and Ruckenstein[24], Co3O4 is getting reduced below 773 K while MgCo2O4 below 973 K and the solid solution of Co-MgO at higher than 1273 K temperature. The TPR results of this study are well collaborated with those reported in the literature[12]. The shifting of Tmax to lower temperature in 5 wt% and 10 wt% Co catalysts is an indication of interac- tion between Co and Cu species. It was reported that when a mixture of Cu and Co oxides were supported on Al2O3, cobalt oxide reacts during calcination not only with CuO but also with Al2O3, which leads to formation of the spinel CoAl2O4 [27]. When the same oxides were supported on non-interacted supports like silica, they interact to form the spinel Cu- Co2O4 [28]. Thus, the TPR patterns clearly indicate the presence of Co oxide interacted species with both Cu and Mg-oxides. 3.2 Activity studies 3.2.1 Hydrogenation of ortho-chloronitroben- zene (o-CNB) The catalytic activity of CoO-Cu-MgO catalysts evaluated for the vapor phase selective hydrogena- tion of o-CNB to o-CAN at atmospheric pressure with H2/o-CNB required mole ratio at a reaction temperature in the range of 548 K–723 K and results are shown in Figure 6. The conversion of o-CNB to o-CAN increases significantly with the increasing of temperature from 540 K to 680 K. Thereafter conver- sion is nearly about 95% and 90% for 5CoO-10Cu- MgO and 1CoO-10Cu-MgO, respectively. Precisely, 5CoO-10Cu-MgO has shown highest conversion about 98% at 720 K. But, the conversion of o-CNB to o-CAN is maximum of 63% at 673 K and reached to 50% at final temperatures over 10CoO-10Cu- MgO. These results demonstrated the effect of cobalt loadings on hydrogenation of o-CNB to o-CAN over CoO-Cu-MgO. The high activity of 5CoO-10Cu- MgO is associated to the presence of more number of surface active Cu0 particles as observed from N2O pulse chemisorption. Figure 6. Effect of temperature on hydrogenation of ortho- chloronitrobenzene over CoO-Cu-MgO catalysts. Figure 7. Time on studies over 5CoO-10Cu-MgO at 623 K for 10 h. 7 Figure 7 shows the conversion of o-CNB to o-CAN at 623 K over a period of 10 h reaction. It is found that the activity of the catalyst is stable with 90% conversion up to 6 h and then reached to 85% at final hours. It is concluded that agglomeration of copper might responsible for loss of the activity. These results are good agreement with that the crys- tallite size of copper after reaction is bigger than re- duced copper as shown in Table 1. 3.2.2 Dehydrogenation of 1,4-butanediol (BDO) Figure 8 illustrates BDO conversion as a func- tion of temperature. The dehydrogenation of BDO is an endothermic reaction; hence the conversion of BDO to GBL increases with the rise of temperature over CoO-Cu-MgO catalysts. The result shows that the maximum catalytic activity of CoO-Cu-MgO catalysts is noticed at 523 K, which is best tempera- ture to obtain the GBL with high yields. In contrast, conversion of BDO is falling gradually for all cata- lysts except over 5CoO-Cu-MgO. The highest BDO conversion (> 97%) and GBL selectivity (99%) can be seen at 5 wt% CoO loading Cu-MgO. Important- ly, the selectivity towards GBL is all most same for all the catalysts. Figure 8. Effect of temperature on BDO dehydrogenation over CoO-Cu-MgO catalysts. Figure 9. Time on stream study of BDO dehydrogenation over 5Co-10CM-H catalyst. Based on above results, the stability of 5CoO- 10Cu-MgO for BDO to GBL was evaluated for 10 h at 523 K. The conversion of BDO is above 95% at beginning of the reaction whereas with increasing in the time the conversion declines slowly from 95% to 75%. Interestingly, selectivity to GBL remains constant up to 10 h (Figure 9). The deactivation of the catalyst is mainly due to agglomeration of copper particles during course of the reaction. 3.2.3 Coupling of o-chloronitrobenzene hy- drogenation and 1,4-butanediol dehydrogena- tion Figure 10. Time on stream study coupling of BDO dehydroge- nation and o-CNB hydrogenation over 5Co-10CM-H catalyst. The independent reactions: (i) hydrogenation of o-CNB to o-CAN and (ii) dehydrogenation of BDO to GBL provide the best catalyst and temperature to conduct the titled reactions. The mole ratio of BDO 8 versus o-CNB is 1.5:1, which is an optimum for coupling process and results are shown in Figure 10. The reaction results clearly demonstrate that conversions of BDO and o-CNB are 90% and 85%, respectively, in early hours. When reaction time increases, the conversion of both reactions linearly dropped which could be attributed to the agglomer- ation of copper and finally reached to 54% and 50% with 99% selectivity of their corresponding products. Surprisingly, the individual hydrogenation of o-CNB at 523 K with 1.5 moles of external hydrogen is very low (< 5%). But, in coupling process, hydrogenation of o-CNB with dehydrogenation of BDO was sub- stantially increased from 5% to 90%. This enhance- ment of o-CNB conversion in the coupling reaction is ascribed to the active role of in-situ production of hydrogen atom from BDO to GBL reaction which gets instantaneously utilized[10–18]. The deactivation of catalysts may be due to agglomeration copper. The color of the catalyst physically changed to black, which further indicates the coke deposition on the catalyst during course of the reaction. 4. Conclusions The different amount of CoO incorporated 10Cu-MgO prepared by co-precipitation followed by hydrothermal treatment has shown excellent catalytic activity compared to unpromoted Cu-MgO catalyst. The best catalytic activity of 5Co-10Cu-MgO is due to the addition of cobalt increased number of surface copper atoms and decreased the reduction ability of copper as observed from TPR results. Contrarily, in 10CoO-10Cu-MgO the high amount of cobalt oxide covered active copper sites. Deactivation of catalyst in coupling reaction is mainly due to agglomeration as well the coke formation during the course of re- action. In summary, two industrially important reac- tions can be carried out over CoO-Cu-MgO catalyst simultaneously. Conflict of interest The authors declare that they have no conflict of interest. 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