An Escape from Noble Metals for Generating Urethanes Via Reductive Carbonylation of † Nitroarenes Over Fese2/Γ-Al2o3

catalysts

Article An Escape from Noble Metals for Generating Urethanes via Reductive Carbonylation of † Nitroarenes over FeSe2/γ-Al2O3

Anh Vy Tran 1, Thuy Tram Huynh Nguyen 1, Thanh Tung Nguyen 1, Hye Jin Lee 1, Jayeon Baek 2 and Yong Jin Kim 1,2,* 1 Department of Green Process and System Engineering, Korea University of Science and Technology (UST), 89 Yangdaegiro-gil, Ipjang-myeon, Cheonan 31056, Korea; [email protected] (A.V.T.); [email protected] (T.T.H.N.); [email protected] (T.T.N.); [email protected] (H.J.L.) 2 Green Chemistry & Material Group, Korea Institute of Industrial Technology, 89 Yangdaegiro-gil, Cheonan-si 31056, Korea; [email protected] * Correspondence: [email protected]; Tel.: +82-41-589-8469; Fax: +82-41-589-8580 This article is based on a study ﬁrst reported in Applied Catalysis A, General, 2019, 587, 117245. † Received: 14 September 2020; Accepted: 16 October 2020; Published: 22 October 2020

Abstract: The reaction of FeCl3, SeO2, and Pyridine (Py) in the presence of methanol (MeOH) under CO pressure generates a black precipitate, which has been confirmed as ferric di-selenide, FeSe2 through different structure characterization methods. Furthermore, impregnation of 5 wt% of FeSe2 onto γ-Al2O3 exhibits better catalytic performance than FeSe2 due to the highly dispersed and smaller particle sizes ca. 200–300 nm. The reductive carbonylation of nitrobenzene (NB) was investigated over FeSe2/γ-Al2O3 as a heterogeneous catalyst, delivering an excellent yield and high selectivity of methyl-N-phenyl carbamate (MPC). Moreover, a set of reactions was performed with variation in the reaction time, temperature, and pressure to investigate the effects of these factors. In particular, FeSe2/γ-Al2O3 is highly stable and can be recycled for up to five cycles without significant loss in catalytic performance. A mechanistic study was also conducted on this low-cost catalyst system, especially proposing a crucial role of FeSe2 (µ-CO) active species.

Keywords: ferrous selenide; nitrobenzene; reductive carbonylation; urethane

1. Introduction Urethanes (carbamates) are essential precursors for producing isocyanates, the main material for manufacturing polyurethane, due to their transformation ability into isocyanates via thermal cracking. Conventionally, the production of urethanes involves the employment of phosgene, which is extremely toxic and harmful to the environment and human beings. Therefore, there have been tons of endeavors for producing carbamates via phosgene-free pathways [1–19]. Among them, the catalytic reductive carbonylation of nitroarenes is regarded as one of the promising routes [6–8,20–27]. Noble metal complexes containing Ru, Rh, and Pd have been commonly employed as main catalysts in this process [5,9,10,24,28–37]. Ragaini’s research group showed that [Pd(phen)2][BF4]2 could produce 71.05% yield of methyl-N-phenyl carbamate (MPC). In his work, the use of [Pd(phen)2][BF4]2 resulted in 1 ca. 6000 h− turnover frequency (TOF), which is the highest reported record to date [6,38]. Even though these catalyst systems showed high eﬃciency, there are still some limits in recyclability and leaching problems of noble metals-based catalysts. Meanwhile, selenium metal or selenium compounds have been widely used in catalytic reductive or oxidative carbonylation processes to produce carbamates from the corresponding aliphatic and aromatic amines. In the oxidative carbonylation of aromatic amine compounds, the active species were conﬁrmed as Se(IV) such as SeO2, MSeO3, MSeO2(OR), M2Se2O5,

Catalysts 2020, 10, 1228; doi:10.3390/catal10111228 www.mdpi.com/journal/catalysts Catalysts 2020, 10, 1228 2 of 19

and QSeO2(OR) (with M = alkali metal; Q = imidazolium, phosphonium) [1,2,39]; however, Se(0) is applied in reductive carbonylation [40–44]. Indeed, it has been reported that only Se(0) can convert nitrobenzene (NB) to urethanes and/or disubstituted ureas through reductive carbonylation [41,45]. Throughout our study on the reductive carbonylation of NB over diﬀerent catalyst combinations II consisting of Se-based and other metal halides to prepare MPC, we found that not only Cu Se2, which has been already found by our research group as an active and novel heterogeneous II II catalyst [46], but also Fe Se2 is found to be far more active than Cu Se2 species. Like the case II of Cu Se2, the ferrous diselenide (FeSe2) is also generated during the carbonylation reaction using the catalyst system consisting of FeCl3 and SeO2, but its activity was enhanced with the co-presence of pyridine. Additionally, FeSe2 is a heterogeneous system that gives a simple separation and high selectivity toward urethanes. Furthermore, the catalyst can be prepared from the ﬁrst-row transition metals, providing a promising route for replacing the precious metals in the reductive carbonylation of nitroarenes. In this work, the authors provide the preparation of FeSe2 and FeSe2/γ-Al2O3 and characterization by various spectroscopic methods. Additionally, the catalytic activities of the FeSe2/γ-Al2O3 in the reductive carbonylation will be investigated (Scheme1). A plausible mechanism is also provided based on this active heterogeneous catalyst system, especially emphasizing the critical role of FeSe2(µ-CO) species.

Scheme 1. The reductive carbonylation of nitroarenes over FeSe2/γ-Al2O3.

2. Results and Discussion

2.1. Screening of the Catalyst Systems The reductive carbonylation of NB for producing MPC was conducted over a catalyst system consisting of three compounds, FeCl3, SeO2, and pyridine (Py) in MeOH at 160 ◦C, 8.3 MPa of CO for 4 h. Table1 shows that this catalyst combination generates MPC with a remarkable yield of 93.8% with complete conversion of NB (Entry 1). It is worth mention that the reductive carbonylation of NB is only effective when three components of FeCl3, SeO2, and Py are applied concomitantly. The absence of any components results in a decrease in the activities (Entry 2~4). Moreover, the single system (Entry 5~7) gives even worse outcomes. However, SeO2 itself delivers 25.8% yield of MPC (Entry 6), (SeO2 + Py), affording 37.8% (Entry 3), and (FeCl3 + SeO2) delivers 32.1% (Entry 2), demonstrating the importance of the presence of selenium in the reductive carbonylation. Furthermore, Se(0) itself could deliver 50.3% yield of MPC (Entry 8). Hence, 25.8% yield of MPC obtained from SeO2 could be explained from an incomplete reduction of SeO2 to Se(0) under this reducing conditions [41,42]. On the other hand, an insoluble solid was always formed during the reductive carbonylation of NB using the three-compound catalyst system. Being encouraged by this phenomenon, a reaction of FeCl3 and SeO2 in the methanolic Py solution is conducted without NB under otherwise identical conditions. After the reaction, the insoluble solid was collected by filtration, washed with methanol, and vacuum dried. The FT-IR results of this compound show there are no organic moieties; thus, it is thought to be an inorganic compound, and we tentatively named it as FexSey. Catalysts 2020, 10, 1228 3 of 19

Table 1. Screening of the catalysts system a.

NB Conv. MPC AN Yield. Entry Catalyst Composition TON (%) Yield (%) (%)

1 FeCl3 SeO2 Py >99 93.8 6.2 11.7 2 FeCl3 SeO2 - 50.3 32.1 18.2 4.0 3 SeO2 Py 46.5 37.8 8.7 4.7 4 FeCl3 - Py 0 0 0 0 5 FeCl3 - - 0 0 0 0 6 - SeO2 - 30.5 25.8 4.7 3.2 7 - - Py 0 0 0 0 8 - Se0 - 66.9 50.3 16.6 6.3 a Conditions: NB (2.46 g, 20 mmol), FeCl3 (0.054 g, 0.4 mmol), SeO2 (0.177 g, 1.6 mmol), Py (0.158 g, 2 mmol), molar ratio of NB/[Se] = 12.5, MeOH 30 mL, T = 160 ◦C, pCO = 8.3 MPa, t = 4 h.

2.2. Characterization of Active Species and Its Supported System

Figure1 shows that XRD spectra of Fe xSey contains mainly ferroselite FeSe2 phase [JCPDS 65-1455, Figure S1] [47,48]. To ﬁnd out the stoichiometry of FexSey, EDX/EDS analysis was carried out. The EDX/EDS spectra indicate the appearance of only Fe and Se, and Fe is combined with Se in the ratio of 1:2 (Supplementary Materials, Figure S3); thus, the stoichiometry of FexSey is assumed to be FeSe2.

Figure 1. X-ray diﬀraction spectra (XRD) of (a) FexSey, which is the black solid synthesized from the reaction of FeCl3, SeO2 in the presence of methanolic Py solution under CO pressure, and (b) standard pattern of ferroselite FeSe2.

XPS analysis of FeSe2 was conducted to examine the oxidation state of Fe and Se elements (Supplementary Materials, Figure S5). As shown in Figure S5, the XPS survey of FeSe2 indicates that it comprises only Fe and Se. Furthermore, the Fe2p region depicted in Figure S7a shows that the band 2+ of Fe 2p1/2 and Fe 2p3/2 at 711.5 and 724.8 eV exhibits the presence of Fe [49]. The minor peak at 707.1 eV is attributed to metallic Fe0, which could be resulting from the further reduction of Fe2+ to 0 Fe [49]. Meanwhile, the peak at 55.07 eV and 59.1 eV in Figure S7b belong to Se 3d5/2 and Se 3d3/2 2 of Se2 − species in FeSe2 [49,50]. The C 1s XPS spectra was also investigated to check the formation of carbonaceous species of the sample. As can be seen in Figure S7c, the spectra did not exhibit the Catalysts 2020, 10, 1228 4 of 19 presence of peaks belonging to carbonaceous compounds except the standard carbon peak at 284.8 eV for XPS calibration. These studies clearly demonstrate that the black compound generated during the II reductive carbonylation is deﬁned as ferrous diselenide (Fe Se2). The heterogeneous catalyst FeSe2 was employed as the catalyst in the reductive carbonylation of NB for producing MPC. Table2 reveals that FeSe 2 exhibits the best catalytic performance that shows 96.6% of MPC yield at the complete conversion of NB (Entry 1). After the reaction, aniline (AN, about 3.4%) was found as the only by-product, regarded as an intermediate in the reductive carbonylation of NB. Furthermore, when similar process is performed over FeSe2, which was prepared without Py, the MPC yield is reduced to 85. 3%, suggesting the important role of Py, which is thought to render the particle size of the FeSe2 smaller and uniformed (Entry 2). In comparison with the catalytic performance of 2 II other Se − species, a commercial chemical of Fe Se was tested. However, it shows poorer activity in terms of both conversion and yield (Entry 3). A reported catalyst, CuSe2/CeO2 was also tested at the same conditions; however, it gives lower yield (63.5% yield of MPC at 68% conversion of NB) than that of FeSe2 (Entry 9) [46].

a Table 2. Activities of various MSe2 and their supported systems .

Molar Ratio NB Conv. MPC Yield AN Yield Entry Catalyst TON (NB/Cat) (%) (%) (%) II 1 Fe Se2 4 >99 96.6 3.4 3.9 b II 2 Fe Se2 4 97.4 85.3 12.1 3.4 3 FeIISe 4 79.4 69.1 10.3 2.8 II 4 Fe Se2 85 25.8 21.7 4.1 18.4 c 5 FeSe2/γ-Al2O3 85 >99 98.9 1.1 84.1 FeSe /basic 6 c 2 85 >99 91.6 8.4 77.9 Al2O3 c 7 FeSe2/α-Al2O3 85 98.1 87.8 10.3 74.6 c 8 FeSe2/AlPO4 85 87.0 85.7 1.3 72.8 d 9 CuSe2/CeO2 85 68 63.5 4.5 53.9 a Conditions: NB (2.46 g, 20 mmol), catalyst (5 mmol), molar ratio of NB/catalyst = 4, MeOH (30 mL), T = 160 ◦C, b II P (CO) = 8.3 MPa, t = 4 h. NB (2.46 g, 20 mmol), Fe Se2 synthesized without Py (1.07 g, 5 mmol), MeOH (30 mL), c T = 160 ◦C, P (CO) = 8.3 MPa, t = 4 h. NB (2.46 g, 20 mmol), 4~5 wt% FeSe2/support (1 g, [FeSe2]: 0.2338 mmol), d molar ratio of NB/FeSe2 = 85, MeOH (30 mL), T = 160 ◦C, P (CO) = 8.3 MPa, t = 4 h. NB (2.46 g, 20 mmol), 4~5 wt% CuSe2/CeO2 (1.04 g, [CuSe2]: 0.235 mmol). Molar ratio of NB/CuSe2 = 85, MeOH (30 mL), T = 160 ◦C, P (CO) = 8.3 MPa, t = 4 h.

2 From these observations, it is concluded that Se2 − is the most responsible species for providing high activity toward MPC, and this trend is significantly noticeable when using ferrous diselenide (FeSe2). To enhance the catalytic performance of FeSe2 by an impregnation approach, a wet impregnation technique has been adopted with different types of supports such as γ-Al2O3, basic Al2O3, α-Al2O3, and AlPO4 with 5 wt% of FeSe2 loadings. As shown in entries from 5 to 9 in Table2, γ-Al2O3 supported FeSe2 exhibits the highest catalytic activity toward MPC (98.9% yield, Entry 5). It is noteworthy to mention that the molar ratio of NB/FeSe2 of this reaction over FeSe2/γ-Al2O3 is almost twenty times higher than that of the neat FeSe2 in terms of the molar ratio basis (Entry 1), indicating that the catalytic performance of FeSe2/γ-Al2O3 was enhanced without any loss of selectivity. Indeed, the MPC yield when using neat FeSe2 at the same molar ratio of 85 is found to be very low (21.7%, Entry 4). Basic Al2O3, α-Al2O3, and AlPO4 did not show as good activity as γ-Al2O3 (entries 6~8), and activities of other supporting materials are also provided in the Supplementary Materials (Table S1), and XRD results of FeSe2/γ-Al2O3 and its XPS spectra are presented therein (Figures S2 and S6). To examine the role of Py, the possible correlation between morphologies and activities of the catalysts was studied using SEM image and MPC yields. As shown in Figure2, FeSe 2 synthesized without Py exhibits the irregular rod-typed morphology, whereas the one made with Py exhibits the identical flake typed and well-dispersed morphologies. The observed size of FeSe2 without Py is about Catalysts 2020, 10, 1228 5 of 19

1–1.1 µm (Figure2a), while that of FeSe 2 prepared with Py decreased to ca. 400–450 nm (Figure2c). The catalytic activity is also correlated with the size of catalysts, that is, the smaller the particle size, the better the performance on the formation of MPC (see Table3). When we compare the SEM images of the supported system, FeSe2/γ-Al2O3 prepared without Py shows irregular rod and ﬂake typed structures with a size of 0.75 µm (Figure2b). However, FeSe 2/γ-Al2O3 prepared with the presence of Py exhibits regular and well-dispersed particles of 200–300 nm (Figure2d), almost two times smaller than the prepared with Py without the support. These results indicate that the presence of Py helps to render the size of FeSe2 regular and smaller. Therefore, it is concluded that the improvement of catalytic activity in the FeSe2/γ-Al2O3 system is attributed to the higher dispersion of FeSe2 particles onto γ-Al2O3. High-resolution TEM images of FeSe2 and FeSe2/γ-Al2O3 are also provided in Figure S9.

Figure 2. Scanning Electron Microscopy (SEM) images of (a) FeSe2 prepared without pyridine, (b) FeSe2/γ-Al2O3 prepared without pyridine, (c) FeSe2 prepared with pyridine, and (d) FeSe2/γ-Al2O3 prepared with pyridine.

Table 3. Correlation between morphologies and activities a.

Molar Ratio NB Conversion MPC Yield Entry Catalyst Morphology Size (NB/Cat) (%) (%) Irregular rod-type and 1 FeSe without Py 4 97.4 85.3 1–1.1 µm 2 aggregated flakes 2 FeSe2 with Py 4 >99 96.6 Uniformed flake-type 400–450 nm FeSe /γ-Al O 3 b 2 2 3 85 78.7 73.8 Irregular rod-type 0.7–0.75 µm without Py FeSe /γ-Al O Uniformed flake-type 4 b 2 2 3 85 >99 98.9 200–300 nm with Py dispersed on support a Conditions: NB (2.46 g, 20 mmol), FeSe2 (1.01 g, 5 mmol), molar ratio of NB/FeSe2 = 4, MeOH (30 mL), T = 160 ◦C, b P (CO) = 8.3 MPa, t = 4 h. NB (2.46 g, 20 mmol), 5 wt% FeSe2/γ -Al2O3 (1 g, [FeSe2]: 0.2338 mmol), molar ratio of o NB/FeSe2 = 85, MeOH (30 mL), T = 160 C, P (CO) = 8.3 MPa, t = 4 h. Catalysts 2020, 10, 1228 6 of 19

2.3. Catalytic Activities of FeSe2/γ-Al2O3 To investigate product proﬁle as a span of reaction time in the reductive carbonylation of NB over FeSe2/γ-Al2O3, a set of experiments was conducted with variable reaction time ranging from 0.5 h to 6.0 h. The results illustrated in Figure3 show that the amount of MPC arises upon elevating time from 0.5 to 4 h and then keeps constant. Upon prolonging the time to 4 h, the amount of NB reduced rapidly. Moreover, this time-course study also shows that aniline (AN) is the only by-product during the conversion of NB, and it is suppressed within 0.14 mmol level.

Figure 3. Product compositional changes as a function of time in the reductive carbonylation of NB at

160 ◦C, 8.3 MPa of CO in the presence of 1 g of 5 wt% FeSe2/γ-Al2O3. Conditions: NB (20 mmol), 5 wt% FeSe2/γ-Al2O3 (1 g, [FeSe2]: 0.2338 mmol), molar ratio of NB/FeSe2 = 85, MeOH (30 mL), T = 160 ◦C, p = 8.3 MPa of CO.

The influence of the reaction temperature on the reductive carbonylation of NB over FeSe2/γ-Al2O3 was tested with a variable thermal scale from 120–180 ◦C. As shown in Figure4, the higher MPC yield was obtained when elevating the temperature until 160 ◦C, thereafter both conversion and yield are decreased. The generation of AN could not be neglected at a low temperature of 120 ◦C, which is ascribed to a simple reduction of NB to AN. However, AN reduces with a further increase in the temperature up to 160 ◦C. The lower yield of MPC, together with the increase in the aniline (AN) formation at 180 ◦C might be due to the thermal decomposition of MPC. The influence of CO pressure was also studied by elevating pressure from 6.2 to 10.3 MPa at 160 ◦C for 4 h. As shown in Figure5, the results reveal that the pressure e ffect is not as strong as the reaction temperature; however, at least 6.8 MPa of CO is needed to achieve an acceptable MPC yield. It is worth mentioning that the AN formation is suppressed with the increase in the pressure, suggesting that the high pressure of CO is beneficial for the generation of selenium-carbonyl species which might act as an intermediate. Catalysts 2020, 10, 1228 7 of 19

Figure 4. Eﬀect of temperature on the formation of MPC at 8.3 MPa of CO for 4 h in the presence of 1 g

of 5 wt% FeSe2/γ-Al2O3. Conditions: NB (20 mmol), 5 wt% FeSe2/γ-Al2O3 (1 g, [FeSe2]: 0.2338 mmol), molar ratio of NB/FeSe2 = 85, MeOH (30 mL), p = 8.3 MPa of CO, t = 4 h.

Figure 5. Eﬀect of pressure on the formation of MPC at 160 ◦C for 4 h in the presence of 1 g of 5 wt% FeSe2/γ-Al2O3. Conditions: NB (20 mmol), 5 wt% FeSe2/γ-Al2O3 (1 g, [FeSe2]: 0.2338 mmol), molar ratio of NB/FeSe2 = 85, MeOH (30 mL), T = 160 ◦C, t = 4 h. Catalysts 2020, 10, 1228 8 of 19

To broaden the scope of applicability of the FeSe2/γ-Al2O3-catalyzed reductive carbonylation, different nitroaromatic compounds were applied as substrates under 160 ◦C, 8.3 MPa for 4 h (hereafter these conditions will be regarded as standard conditions). As demonstrated in Table4, 4-nitroanisole having an electron-donating group (EDG) at para position is transformed to methyl-N-4-methoxyphenyl) carbamate with very high yield (98.5%, Entry 1), while 4-nitrotoluene and 4’-nitroacetophenone is converted to the corresponding carbamates only in 50.1% and 48% yields, respectively (Entry 3 and 4). Additionally, 3-nitroanisole, bearing (EWG) at the meta-position, was transformed to the corresponding carbamate in lower yield (80%, Entry 2). When it was carried out with 4-bromonitrobenzene with an electron-withdrawing group (EWG) at the para position, carbamate yield dropped significantly to 19.7%. These results imply that the EDG/EWG capability of the substituents might affect the catalytic performance of the reductive carbonylation of nitroarenes, i.e., the presence of electron-withdrawing group at the para position tended to reduce the catalyst activity of the carbonylation reaction. The 2,4-dinitrotoluene (2,4-DNT), a main precursor for manufacturing toluene diisocyanate (TDI), is also converted to the corresponding dicarbamate, but the yield was 41.5% even at higher temperature (180 ◦C), longer reaction time (6 h), and higher catalyst amount (molar ratio of sub/cat = 42), (Entry 6). Surprisingly, the carbonylation of 1,4-nitroaniline gives 40.5% yield of the corresponding diurethane under the optimized conditions. Being encouraged by this outcome, a set of experiments has been conducted by adding a variety amount of aniline (AN) with varying from 20% to 200% based on NB (mol/mol). Figure6 shows that the MPC yield dramatically increases upon adding AN with 180% (substrate: NB 10 mmol and AN 18 mmol) then reduces. The highest yield of MPC is 204% based on NB, which is almost two times higher than that in the case of without AN. The positive effect of adding AN in the reductive carbonylation has been reported, and it accelerates the reductive carbonylation reaction of NB over a palladium-phenanthroline catalyst system [51]; however, this protocol eventually gave rise to a decrease in the selectivity due to the generation of large amounts of azoxybenzene [6]. Nevertheless, the FeSe2/γ-Al2O3 catalyst did not show any azoxybenzene as a side-product. The additional formation of MPC by adding AN can be rationalized by the following in situ cascade reactions: (i) a reaction between AN and isocyanato species produces diphenyl urea (DPU), then (ii) methanolysis of DPU affords MPC (2.5. Mechanism study). This is fairly acceptable because a quantitative production of MPC was verified from the alcoholysis of DPU by methanol in the absence of a catalyst. It should be clear that the MPC was not obtained when AN was used as a sole substrate (Table4, Entry 11), which indicates that AN itself cannot be carbonylated or work as an intermediate in the reductive carbonylation over FeSe2 for producing MPC. On the other hand, AN works as a reactant for the generation of DPU via in situ reaction with an isocyanato intermediate, which might be a reasonable explanation about the high reactivity of nitroaniline in the FeSe2-catalyzed reductive carbonylation. To confirm this, a reductive carbonylation over 5 wt% FeSe2/γ-Al2O3 (1 g, with a molar ratio of sub/cat = 170) was conducted by employing the dual substrates system consisting –nitro (20 mmol) and –amino (20 mmol) substrate bearing the same functional group at the para-position of the aromatic ring under standard conditions. After the reaction, the corresponding urethanes were generated in 148.4 and 161.1% yields based on nitro substrate, respectively (Entries 8 and 9, Table4), which are 1.5 and 3.2 times higher than in the case of the sole substrate system (Entry 1 and 3, Table4). Moreover, a dual substrates 2,4-dinitrotoluene and 2,4-diaminotoluene were also applied for the reductive carbonylation, catalyzed by only 1 g of FeSe2/γ-Al2O3 (sub/cat molar ratio = 170) under the standard conditions. Interestingly, the di-carbamate yield was found to be 92.5% (Entry 10, Table4). Compared to the yield of the nitro substrate (41.5%) at a longer reaction time (6 h), higher temperature (180 ◦C), and higher catalyst amount, the catalytic performance of this dual substrate system in the standard conditions can be regarded as astonishing. Catalysts 2020, 10, 1228 9 of 19

CatalystsCatalysts 2020, 10 2020, x , 10, x 9 of 19 9 of 19 a CatalystsCatalysts 2020 2020, 10,, 10x , x Table 4. Reductive carbonylation of various nitro compounds . 9 of9 19 of 19 Catalysts 2020, 10, x 9 of 19 CatalystsCatalysts 20202020,, 1010,, xx a. a. 99 ofof 1919 CatalystsCatalysts 20202020,, 1010,, xx Table Table4. Reductive 4. Reductive carbonylation carbonylation of various of various nitro compounds nitro compounds 99 ofof 1919 CatalystsCatalysts 2020 2020, 10, ,10 x , x a. Conv. 9 of9 of19 19Yield EntryCatalysts 2020, 10, x Table SubstratesTable 4. Reductive 4. Reductive carbonylation carbonylation of variousof various Product nitro nitro compounds compounds a. 9 of 19 Catalysts 2020, 10, x a.a. Conv. Conv.(%) Yield9 ofYield 19 (%) CatalystsCatalystsCatalysts 2020 2020 2020, ,10 ,10 10, ,x ,x x TableTable 4. 4. Reductive Reductive carbonylation carbonylation of of various various nitro nitro compounds compounds a . a . 99 9of of of 19 19 19 Entry Entry TableTableSubstrates 4. Substrates4. Reductive Reductive carbonylation carbonylation of of various various Product nitro nitro Product compounds compounds aa . . CatalystsCatalystsCatalysts 2020 2020 2020, 10, ,10x 10 , ,x x TableTable 4.4. ReductiveReductive carbonylationcarbonylation ofof variousvarious nitronitro compoundscompoundsa. (%) Conv.(%) (%)9 of Yield9 199 of(%) of 19 19 Entry NitroTableTable 4.Substrates 4.Reductive Reductive Amino carbonylation carbonylation of ofvarious various nitro Product nitro compounds compounds a. NitroConv. AminoYield CatalystsCatalystsCatalystsEntry 2020 2020 2020, 10, ,10 ,10 x, ,x Nitrox TableSubstrates 4. Reductive Amino carbonylation of various Product nitro compounds Nitro aa.. Conv.Conv.Amino(%) YieldYield 9 of99(%) of 19of 19 19 EntryEntry NitroTableSubstratesSubstrates 4. Reductive carbonylation Amino of various Product Product nitro compounds aa.a. . Conv. NitroConv.(%) AminoYieldYield(%) EntryEntry TableTableTableSubstratesSubstrates 4. 4.4. Reductive ReductiveReductive carbonylation carbonylationcarbonylation of ofof various variousvarious Product Product nitro nitronitro compounds compoundscompounds Conv.Conv.(%)(%) YieldYield(%)(%) EntryEntry NitroTableSubstratesSubstrates 4. Reductive Amino carbonylation of various Product Product nitro compoundsa. a.a Conv. Nitro. Conv.(%) AminoYield Yield(%) EntryEntry NitroTable SubstratesTableSubstrates 4. Reductive 4. Reductive Amino carbonylation carbonylation of various of various Product Product nitro nitro compounds compounds Nitro Conv. (%)(%)Amino Yield(%)(%) NitroNitro Amino Amino Nitro Nitroa. Conv. AminoAmino Yield Entry NitroNitroTable Table TableSubstrates 4. 4. Reductive4. Reductive Reductive Amino Amino carbonylation carbonylation carbonylation of of ofvarious various various Product nitro nitro nitro compounds compounds compounds a Nitro. Nitroa. (%)Conv.Conv. Conv. (%) AminoAmino (%)YieldYieldYield(%) EntryEntry1Entry 1 NitroNitro SubstratesSubstratesSubstrates Amino Amino Product Product Product >99 Nitro Nitro (%)(%)Conv.>99AminoAmino 98.5(%)(%)Yield 98.5 1 Entry NitroNitro Substrates Amino Amino Product Nitro NitroConv. >(%) 99(%)Amino(%)Conv. Amino Yield(%) (%)(%)Yield 98.5 EntryEntry 1 NitroNitro Substrates Substrates Amino Amino Product Product Nitro Nitro>99 (%) AminoAmino (%) 98.5 1 Nitro Amino Nitro>99Conv.(%) Conv. Conv. (%)Amino Yield(%)Yield98.5Yield (%) EntryEntryEntry1 1 NitroNitro SubstratesSubstratesSubstrates Amino Amino Product Product Product Nitro>99 Nitro>99 AminoAmino 98.598.5 1 1 NitroNitroNitro Amino Amino Amino Nitro>99 Nitro>99 Nitro (%) Amino(%) (%) Amino Amino (%)98.5 (%)98.5(%) 11 >99>99 98.598.5 1 1 Catalysts 2020Nitro,Nitro 10Nitro, x Amino Amino Amino Nitro>99 Nitro Nitro>99 AminoAminoAmino 98.5998.5 of 19 1 >99 98.5 1 >99 98.5 2 1 1 2 92.5>99>99 92.5 80.098.598.5 80.0 1 11 Table 4. Reductive carbonylation of various nitro compounds >99 a. >99 >99 98.598.5 98.5 2 92.5 80.0 2 1 21 1 >9992.5>99>99 92.5 98.580.098.598.5 80.0 2 92.5 80.0 22 92.5 92.5Conv. Yield80.080.0 22 Entry Substrates Product 92.592.5 80.080.0 2 92.5 (%) (%)80.0 2 92.5 80.0 2 Nitro Amino Nitro92.5 Amino 80.0 22 2 92.592.592.5 80.080.080.0 3 56.4 50.1 2 22 3 92.592.5 92.5 56.4 80.080.0 80.0 50.1

2 32 2 3 92.556.492.592.5 56.4 80.050.180.080.0 50.1 1 >99 98.5 3 33 3 56.456.456.4 56.4 50.150.150.1 50.1 33 56.456.4 50.150.1 3 56.4 50.1 3 56.4 50.1 3 56.4 50.1 3 56.4 50.1 4 3 3 4 50.556.456.4 50.5 48.050.150.1 48.0 3 33 56.456.4 56.4 50.150.1 50.1 4 50.5 48.0 3 43 3 2 56.492.550.556.456.4 80.050.148.050.1 50.1 44 50.550.5 48.048.0 4 4 50.550.5 48.048.0 4 44 50.550.550.5 48.048.0 48.0 4 50.5 48.0 4 50.5 48.0 4 50.5 48.0 5 44 4 5 35.550.550.550.5 35.5 19.748.048.048.0 19.7 4 50.5 48.0 4 45 3 50.556.4 50.5 35.5 50.148.0 48.019.7 5 35.5 19.7 45 54 4 50.535.535.550.550.5 48.019.719.748.048.0 5 5 35.535.5 19.719.7 5 55 35.535.535.5 19.719.7 19.7 5 5 35.535.5 19.719.7

5 35.5 19.7 55 5 35.535.535.5 19.719.719.7

5b 55 b 35.535.5 35.5 19.719.7 19.7 6 6 4 >50.5 99 > 99 48.0 41.5 41.5 5 55 6b 35.535.535.5 > 99 19.719.719.7 41.5 6b > 99 41.5 b b 6 b > 99 41.5 6b6 >> 9999 41.541.5 66bb >> 9999 41.541.5 6 b 6b 6b > 99> 99> 99 41.541.5 41.5 6bb > 99 41.5 6 b 5 35.5> 99 19.741.5 66b6 b >> >99 99 99 41.541.541.5 b 66b b >> 99 99 41.541.5 67 7 >98.5 99 98.5 41.540.5 40.5 b b b 6 66 7 > 99>> 99 9998.5 41.541.541.5 40.5 7 98.5 40.5 7 98.5 40.5 77 98.598.5 40.540.5 77 98.598.5 40.540.5

7 7 6b 98.5> 98.599 41.540.540.5 c 7 98.5 40.5 7 8 7 8c 87.298.5 98.5 87.290.0 90.0148.4 40.5 148.4 40.5 77 7 98.598.598.5 40.540.540.5 7 8c 98.587.2 90.0 40.5148.4 7 8c 7 98.587.2 98.5 90.0 40.5148.4 40.5 c c 88 c 87.287.2 90.090.0 148.4148.4 7 c78 7 98.598.587.298.5 90.0 40.5148.440.540.5 8cc 87.2 90.0 148.4 c 8 87.2 90.0 148.4 8 8c 87.287.2 90.090.0 148.4148.4 cc c8 c 87.2 90.0 148.4 c 9 cc c 9 7 99.598.5 99.574.2 74.240.5161.1 161.1 8 888 87.287.287.287.2 90.090.090.0 90.0148.4148.4148.4 148.4 c 8c 9c c 87.299.5 90.0 74.2 148.4161.1 8 9c 8 87.299.5 87.2 90.074.290.0 148.4161.1148.4 c c 9c9 cc c 99.599.5 74.274.2 161.1161.1 8 8c98 87.287.299.587.2 90.090.074.290.0 148.4148.4161.1148.4 99cc 99.599.5 74.274.2 161.1161.1 9c c 99.5 74.2 161.1 9c 99.5 74.2 161.1 9c 8c 87.299.5 90.074.2 148.4161.1 9 c 99.5 74.2 161.1 99c9 c 99.599.599.5 74.274.274.2 161.1161.1161.1 c c 9c c 99.5 74.2 161.1 9 9 c 9 99.5 99.599.5 74.2 74.2 161.1 74.2161.1 161.1 10 10c >99 >99>99 >9992.5 92.5 9c 99c c 99.599.599.5 74.274.274.2 161.1161.1161.1 c 10c 10 >99>99 >99>99 92.592.5 c c c 1010 c 9 99.5>99>99 74.2>99>99 161.192.592.5 10c >99 >99 92.5 1010cc >99>99 >99>99 92.592.5 10c10 c >99>99 >99>99 92.592.5 c 10c >99 >99 92.5 101010cc c >99>99>99 >99>99>99 92.592.592.5 c 10c 1010c >99>99 >99 >99>99 >99 92.592.5 92.5 11 11 AnilineAniline NR NR 0 0 10 c1010c10 c c >99>99>99 > 99 >99>99>99 >92.59992.592.5 92.5 11 Aniline NR 0 11 10c Aniline >99NR >99 92.5 0 11 Aniline NR 0 1111 AnilineAniline NRNR 0 0 a 11Conditions: a SubstrateAniline (20 mmol), 5 wt% FeSe2/γ-Al2O3 (1 g, [FeSe2]: 0.2338 mmol),NR molar ratio of 0 11 Conditions:Aniline Substrate (20 mmol), 5 wt% FeSe2/γ-Al2O3 (1 g, [FeSe 2 ]: 0.2338 NR mmol), molar ratio 0 of 11 11 a AnilineAniline NRNR 0 0 a Conditions: Substrate (20 mmol), 5 wt% FeSe2/γ-Al2O3 (1 g, [FeSeb 2]: 0.2338b mmol), molar ratio of sub/FeSe11Conditions: sub/FeSe2 = 85,Aniline 2SubstrateMeOH = 85, MeOH (30 (20 mL), mmol),(30 T mL), = 160 5 Twt% °C,= 160 PFeSe (CO)°C, 2 /Pγ =-Al(CO) 8.32O MPa, 3= (1 8.3 g, tMPa, [FeSe= 4 h. t2 ]:= Substrate0.23384 h. Substrate mmol), (10NR mmol), molar(10 mmol), 5ratio wt% of5 0 wt% a11 a Aniline NR 0 1111Conditions:a Conditions: Aniline Substrate AnilineSubstrate (20 (20 mmol), mmol), 5 5 wt% wt% FeSe FeSe2/2γ/γ-Al-Al2O2O3 3(1 (1 g, g, [FeSe [FeSe2]:2]: 0.2338 0.2338b mmol), mmol),NRNR molar molar ratio ratio of of 0 0 a Conditions:sub/FeSe2 = Substrate 85, MeOH (20 (30 mmol), mL), T 5 = wt% 160 °C,FeSe 2P2 /(CO)γ-Al2 2 O=3 38.3 (1 MPa,g, [FeSe t =2 24]: bh.0.2338 Substrate mmol), (10 molar mmol), ratio 5 wt%of 11FeSe asub/FeSe11 Conditions:11 2 /γFeSe-Al22O /=γAniline3 -Al 85,(1 SubstrateAniline Anilineg, 2OMeOH [FeSe3 (1 g, 2 ]:(30(20[FeSe 0.2338 mL),mmol),2]: 0.2338 mmol),T = 5 160wt% mmol), molar°C, FeSe P molarratio(CO)22/γ-Al of =ratio2 2 O8.3sub/FeSe33 (1 MPa,of g, sub/FeSe [FeSe 2t == 42,4 22]:h. 2MeOH =0.2338 Substrate42, MeOH (30mmol),NR mL), NR(10 (30NR molarTmmol), mL), = 180 T ratio °C,5= 180wt% 0Pof °C, 0 0 P a Conditions:Conditions: SubstrateSubstrate (20(20 mmol),mmol), 55 wt%wt% FeSeFeSe//γγ-Al-AlOO (1(1 g,g, [FeSe[FeSe]:]: b0.23380.2338 b mmol),mmol), molarmolar ratioratio ofof sub/FeSeConditions:sub/FeSea 2 2= = 85, Substrate85, MeOH MeOH (20(30 (30 mmol),mL), mL), T T =5 = 160 wt%160 °C, °C,FeSe P P (CO) 2/(CO)γ2-Al = 2= O8.3 28.33 (1 3MPa, MPa, g, [FeSe t t= = 4 24 ]:h. 2h.0.2338 SubstratebSubstrate mmol), (10 (10 molar mmol), mmol), ratio 5 5 wt% wt%of 11a11 sub/FeSe11Conditions: FeSe2/γ2 -Al=Aniline 85,Aniline 2AnilineSubstrateO 3MeOH (1 g, [FeSec (30(20 2mL),]:mmol),c 0.2338 T = 5 mmol),160 wt% °C, FeSe molarP (CO)/γ -Alratio = 8.3O of (1MPa, sub/FeSe g, [FeSet = 42 =h.]: b42, 0.2338 Substrate MeOH mmol),NR (30NR NR(10 mL), molarmmol), T =ratio 1805 wt% 0°C,of 0 0 P 11(CO)sub/FeSeaFeSe Conditions: =(CO)2 /8.3γ11-Al2 MPa, Aniline==2 O85,8.3 3Substrate (1 tMeOHMPa, g,= 6Aniline[FeSe h. t (30=(20 Nitro2 6]: mL),h.0.2338mmol), compoundNitro T mmol),= 5 160compound wt% °C, molar(20 FeSe P mmol),(CO)22 /(20ratioγ-Al =mmol), 22of8.3anilineO 33sub/FeSe MPa,(1 anilineg, compound [FeSet =2 =4 compound 42,22h.]: b 0.2338bMeOH Substrate (20 mmol), mmol), (30(20NR (10mL),mmol), 5wt%NR mmol),molar T =5wt%FeSe 180 ratio 5 2°C,wt%/ γ 0FeSe -of P 2/γ- 0 sub/FeSesub/FeSeaa Conditions: 2 == 85,85, Substrate MeOHMeOH (30(30(20 mL),mL),mmol), TT == 5 160160 wt% °C,°C, FeSe PP (CO)(CO)/γ-Al == 8.38.3O MPa,(1MPa, g, [FeSett == 44 h.h.]:b 0.2338SubstrateSubstrate mmol), (10(10 mmol),molarmmol), ratio 55 wt%wt% of sub/FeSeFeSea Conditions:2/2γ-Al2 = 285,O2 3 3 (1Substrate MeOH g, [FeSe (30 2(20]:2 mL), 0.2338 cmmol), T =mmol), 160 5 wt% °C, molar PFeSe (CO) 2ratio22/γ =-Al 8.3of222O sub/FeSe3MPa,33 (1 g, t [FeSe=2 42= h.42,22 2]: SubstrateMeOH0.2338b (30mmol), (10 mL), mmol), molar T = 180 5ratio wt%°C, Pof FeSesub/FeSeFeSeConditions:Conditions:2//γγ-Al-Al2 =2O O 85,Substrate 3(1Substrate (1 MeOH g,g, [FeSe[FeSe (20 (30(202]:]: 0.2338mmol),mL), 0.2338mmol), T mmol), mmol),=5 5 160wt% wt% °C, molarmolarFeSe FeSe P (CO) / ratioγratio/γ-Al-Al = ofOof8.3O sub/FeSe sub/FeSe (1 MPa,(1 g, g, [FeSe [FeSet =2 ==4 42, 42,]:h.]: 0.2338 b MeOH 0.2338MeOHSubstrate mmol), mmol), (30(30 mL),(10mL), molar mmol),molar TT == 180 180ratio ratio 5 °C,°C,wt% of of PP2 aAl FeSesub/FeSe2aO a (CO)3 2(1/γ g,-Al2 =2 [FeSe3 =2 8.3O 85,3 (1MPa,2 ]:MeOH g, 0.2338 [FeSe t 2= (306 2mmol), ]:ch. 0.2338mL), Nitro molarT mmol), =compound 160 ratio °C, molar ofP (CO)(20(nitro ratio2 mmol), = + of8.3 aniline)/FeSe2 sub/FeSe 3MPa, aniline t 2= compound =4 242, h.=2 170,MeOHb Substrate2 MeOH (20 (30 mmol), mL), (10(30 mmol),mL), T 5wt%= 180T =5 °C,FeSe160wt%2 P /γ- Conditions:FeSesub/FeSeFeSe(CO)Conditions:Conditions:2Al2/ /γ=γ -Al-Al8.3O2 =2 (12O MPa, OSubstrate85, 3g,3 (1 (1Substrate MeOH[FeSe Substrate g, g,t =[FeSe[FeSe 6 ]:(20h. (300.23382c 2 ]:(20 ]:mmol),(20Nitro 0.2338mL),0.2338 mmol), mmol), mmol), compoundT mmol), 5mmol),= wt% 1605 5 molarwt% wt% °C, FeSemolarmolar (20FeSe PratioFeSe 2(CO)/ γ mmol), ratioratio-Al/ 2ofγ/γ -Al2= O-Al (nitro ofof8.33 anilineO 2sub/FeSe(1sub/FeSeO MPa, 3 g,(1 +(1 aniline)/FeSe[FeSeg, g, compound t [FeSe 2=[FeSe2 ==24 ]: 42, 42,h. 0.2338]: 2 ]:MeOHb MeOH Substrate0.2338 0.2338 (20= mmol),170, mmol), (30(30mmol), mmol), MeOH mL),(10mL), molar mmol),5wt% molar TTmolar (30 == ratio180180 FeSemL), 5ratio ratio°C,°C, wt%of /T γ PP of -= of 160 (CO)sub/FeSe2 = 8.3222 MPa,=3 85, MeOHt = 6 h.2 (30cNitroc mL), compound T = 160 °C, (20 P (CO)mmol), = 8.3aniline MPa, compound 2t = 4 h. b bSubstrate (20 mmol), (10 5wt% mmol), FeSe 5 wt%2/2γ- FeSea sub/FeSe(CO)aFeSesub/FeSe a /γ2 2-Al/=γ a8.3-Al3 2 O= 2= MPa,O85, (185,3 (1 g,MeOH MeOH g,t[FeSe = 2[FeSe 6 h.(30 ]:(30 c 2 0.2338]: NitromL), 0.2338mL), mmol),Tcompound T mmol),= = 160 160 molar°C, °C, molar (20P P (CO) ratio (CO)mmol), ratio =of = 8.3 of sub/FeSe8.3 aniline sub/FeSeMPa, MPa, compoundt t= 2= 42,4= 4 h.42, h.MeOH MeOHSubstrate2 Substrate (20 (30 mmol), (30 mL), (10 mL),(10 mmol),T 5wt%mmol), =T 180= 180 FeSe 5°C, 5 wt%°C, wt% P2/γ P- a (CO)Conditions:(CO)Conditions:Conditions:Al2 = O= 8.3 8.3Conditions:(1 2MPa, g, MPa,Substrate3 [FeSe SubstrateSubstrate t t= =Substrate6]: 6 h.0.2338 (20h. 2 (20c c (20Nitro Nitrommol), mmol),mmol),(20 compound mmol),compound 5 5wt%molar5 wt%wt% 5 wt%FeSe (20ratio FeSe(20FeSe FeSe2mmol),/ γmmol),2of/2-Alγ/γ2 -Al/(nitro-Alγ2-AlO2 O2aniline3 O 2aniline(1O3 3+ 3(1 (1g,aniline)/FeSe(1 g, g, [FeSeg,compound [FeSecompound [FeSe2 2]:22 b]:2]:0.2338 ]: 0.2338b0.2338 b= (20 (20170, mmol), mmol), mmol), mmol),MeOH molar5wt% molar5wt%(30molar mL), ratio ratioFeSe FeSe ratioratio ofT 2of/ γ=/ ofγ - of160- Conditions:sub/FeSe°C,(CO)FeSe(CO)Alsub/FeSe sub/FeSep2 O(CO)2 °C, /3= =γ(1 2-Al8.38.3 p= g,= 2(CO) Substrate85, 2 MPa,28.3O[FeSeMPa,= = 3 85, (1MeOH85,MPa, = g, 2 tMeOH t8.3]: MeOH = =[FeSe0.2338 (20 6t6MPa, =(30 h.h. 4 mmol), 2(30 ]:h.mL), (30Nitro Nitrommol), t 0.2338 =mL), mL),4 T 5h. compound compound wt%= mmol),T molarT160 = = FeSe160 160°C, ratio molar°C, P °C, /(20γ(20 (CO) -Al P of P mmol), mmol),(CO) ratio(nitro(CO)O = 8.3(1 of= = +g, aniline8.3 anilineMPa, sub/FeSe8.3aniline)/FeSe [FeSe MPa, MPa, t compoundcompound=]: t 24 0.2338t = = h.= 42,42,4 4 2h. Substrate h.= MeOHMeOH mmol),170, Substrate (20Substrate(20 MeOH mmol), mmol),(30(30 molar (10 mL),mL), (10 mmol),(10(30 5wt% ratio5wt% mmol), TTmL),mmol), == of180180 FeSe5FeSe subTwt% °C,5°C, =5 2/wt%2160 /FeSe/wt%γ γPP-- = 85, 2 2 3 c 2c 2 2 3 2 2 2 (CO)AlFeSeFeSeAl(CO)FeSe2O2 O=23/ 32 (1/γ8.3 /=γ(1γ-Al -Al8.3g,-Al g,MPa, 2[FeSe O[FeSe2OMPa,O3 (13(1 (1t 2 g,]:2 g,=g,]:t 0.2338 6[FeSe= [FeSe0.2338[FeSe h.6 h.2Nitro ]:2]:mmol), ]: mmol),Nitro 0.2338 0.23380.2338 compound compound molar mmol), mmol),molarmmol), ratio ratio molar molar(20molar (20 of mmol),of (nitrommol), ratio ratio(nitroratio of anilineof+ of+ aniline)/FeSesub/FeSeaniline sub/FeSeaniline)/FeSesub/FeSe compound compound2 2 = == 42, 42,242, 2=b = MeOH MeOHb170, MeOH b170,(20 (20 MeOHmmol), MeOH (30mmol), (30(30 mL), mL), mL), (30 5wt%(30 5wt% mL),T TmL),T = == FeSe 180 180 180TFeSe T = °C,2 °C,= /°C,160γ 1602-/ Pγ PP - sub/FeSeAlsub/FeSe2 °C,2O3 3 p(1sub/FeSe2 (CO) =g,22 85, =[FeSe 85,= MeOH 8.322 =MeOH2]: 85,MPa, 0.2338 MeOH(30 c(30ct mL), =mmol), 4 mL),(30 h. TmL), =T molar 160= T 160 =°C, 160ratio °C, P °C, (CO)P of P(CO) (nitro(CO) =b 8.3= = +8.3 8.3 MPa,aniline)/FeSe MPa,MPa, t = t 4== h.44 2 h.h.2 =Substrateb Substrate170,Substrate MeOH (10(10 (10 mmol),(30 mmol), mL), 55 wt%T wt%5 = wt%160 MeOHFeSeAl(CO)Al°C,sub/FeSeFeSeFeSe22O O/p (30γ3 3 =-Al(CO)(12 (1/ 2γ8.3/ mL), γg,-Alg,2O-Al [FeSe=MPa,=[FeSe32 (1O285,8.3 TO 3g,= 3(1 2MPa,(1MeOH2 ]:t160 [FeSe]: g, == g,0.23380.2338 6[FeSe6 ◦[FeSe th.C,h.2 =]: (30 P4 0.2338 2mmol),Nitro mmol),]:2h.(CO) ]: mL),0.2338 0.2338 compoundmmol),= T molarmolar8.3 mmol),= mmol), 160 MPa, molar ratio ratio°C, molar (20tmolar =P of of ratio4(CO)mmol), (nitro(nitro h. ratio ratio of =Substrate +sub/FeSe 8.3of+ aniline of aniline)/FeSeaniline)/FeSe sub/FeSe MPa,sub/FeSe compound (102 t= = 242,mmol), 24= = 2 h.42,2 MeOH42, == 170,170,MeOH Substrate MeOH 5(20wt% MeOH(30MeOH mmol), (30 mL), FeSe(30 (10 mL), (30mL),(30 25wt%T /mmol), γ mL),=mL), -AlT 180T = 2= FeSe 180O T180T°C, 35 == (1 wt%°C, 21602 P160/°C,γ g, - P [FeSeP 2]: cc c 2 Al°C,(CO)(CO)°C,Al(CO)2O 2p3 Op (1 (CO) =3 (CO)= = (1g, 8.3 FeSe8.38.3 g,[FeSe = MPa, =MPa, [FeSe2MPa,8.3 /8.3γ-Al2 MPa,]: MPa, t 2 2t0.2338 ]:tO = = = 30.2338 6(1 6 6 t h. t h.=g, h.= 4mmol), [FeSe 4 Nitro h.Nitro mmol),Nitroh. 2]: compound0.2338 molarcompoundcompound molar mmol),ratio ratio (20 (20of(20 molar of (nitro mmol), mmol),mmol), (nitro ratio + aniline)/FeSe aniline+ anilineofaniline aniline)/FeSe sub/FeSe compound compoundcompound2 =2 42,=2 170,= MeOH 170, (20 (20(20MeOH MeOH mmol), mmol),(30mmol), mL), (30 (30 5wt% 5wt%mL),T5wt% =mL), 180 T FeSe FeSe FeSe°C,=T 160= 2P /1602/ γ/γ γ--- c 0.2338FeSe°C,FeSe2 mmol), /pγ2 2(CO)-Al/γ-Al2O 2= molar23O (18.33 3 (1g, MPa, g,[FeSe ratio [FeSe t 2 of=]:2 420.2338c]: subch. 0.2338 /FeSe mmol), mmol),2 = 42, molar molar MeOH ratio ratio (30 of mL),ofsub/FeSe sub/FeSe T =2180 =22 42, = ◦42,C, MeOH PMeOH (CO) (30 (30= mL),8.3 mL), MPa,T =T 180 = t180 =°C,6 °C, h.P P Nitro (CO)°C,Al°C,FeSe(CO)(CO)22 O p=p 33 (CO) (CO)8.3/(1 γ= =-Al g, 8.3 MPa,8.3 =[FeSe= O MPa,8.3 8.3MPa, (1 t MPa, MPa,22 =]:g, t 60.2338 t[FeSe = h.= t6 t 6 =c=h. Nitroh. 44 ]:mmol), h.h. Nitro0.2338Nitro compound compound molar compoundmmol), ratio (20molar (20 ofmmol),(20 (nitro mmol), ratiommol), aniline of+ aniline)/FeSeanilinesub/FeSe aniline compound compound compound = 42,22 == MeOH170,170,(20 (20 mmol),(20MeOHMeOH mmol),(30 mmol), mL), (305wt%(30 5wt% mL),mL),5wt%T =FeSe 180 TTFeSe FeSe 2== /°C, γ160160-2/ 2γP/ γ- - 2 3 2 c 2 compound°C,AlAl°C,Al p2O 2O (CO)Op3 3(1(CO)(1 (1 (CO) (20 g, g,=g, [FeSe 8.3 [FeSe= mmol),[FeSe =8.3 MPa,8.3 2MPa,]: 2]:MPa,]: 0.2338aniline 0.2338 0.2338t = t t 4= c= h. 4 mmol),6 cmmol),compound mmol), h.h. Nitro molar molarmolar compound (20 ratio ratio mmol),ratio of of of(20 (nitro (nitro 5(nitro mmol), wt% + + FeSe+ aniline)/FeSe aniline)/FeSe aniline)/FeSeaniline/γ-Al compoundO 2 2(1 = == 170, g,170,170, (20 [FeSe MeOH MeOH MeOHmmol),]: 0.2338 (30 (305wt%(30 mL), mL),mL), mmol), FeSe T TT 2 = /==γ 160 molar160-160 ratio (CO)(CO)(CO) = = 8.3= 8.3 8.3 MPa, MPa, MPa, t =t t = 6= 6 h.6 h. h. Nitroc NitroNitro compound compound compound (20 (20 (20 mmol), mmol), mmol), aniline aniline aniline2 compound compound compound2 3 (20 (20 (20 mmol), mmol), mmol),2 5wt% 5wt% 5wt% FeSe FeSe FeSe2/γ2/2-γ/γ-- Al°C,2AlOAl 3p2 (1O2 (CO)O(CO) 3g, 3(1 (1 [FeSeg, g,== [FeSe8.3 8.3[FeSe2 ]: MPa,MPa, 0.23382]:2]: 0.2338 0.2338t == mmol), 44 h.h. mmol), mmol), molar molar molar ratio ratio ratio of (nitroof of (nitro (nitro + aniline)/FeSe + + aniline)/FeSe aniline)/FeSe2 = 2170, 2= = 170, 170, MeOH MeOH MeOH (30 (30 mL),(30 mL), mL), T = T 160T = = 160 160 of (nitro °C,°C,°C, p pp (CO)+ (CO)(CO)aniline)Al2 O = == 3 8.3 8.3(18.3/ FeSeg, MPa, MPa,MPa, [FeSe2 =t t 2t =]: =170,= 40.2338 44 h. h.h.MeOH mmol), (30 molar mL), ratio T = 160 of (nitro◦C, p +(CO) aniline)/FeSe= 8.3 MPa,2 = 170,t = MeOH4 h. (30 mL), T = 160 AlAl°C,Al2O2O23 O p(13 3(1(CO) (1g, g, g,[FeSe [FeSe =[FeSe 8.32]: 2MPa, ]:20.2338]: 0.2338 0.2338 t =mmol), 4mmol), mmol),h. molar molar molar ratio ratio ratio of of of(nitro (nitro (nitro + + aniline)/FeSe+ aniline)/FeSe aniline)/FeSe2 =2 2 = 170,= 170, 170, MeOH MeOH MeOH (30 (30 (30 mL), mL), mL), T T =T = 160= 160 160 °C, p°C, (CO) p (CO)°C, = 8.3p (CO)= MPa,8.3 = MPa, 8.3 t = MPa, 4 t h.= 4t =h. 4 h. °C,°C,°C, p p(CO) p (CO) (CO) = =8.3 = 8.3 8.3 MPa, MPa, MPa, t =t t=4 = 4h. 4 h. h.

Catalysts 2020, 10, 1228 10 of 19

Figure 6. Eﬀect of the addition of aniline on the activity of the reductive carbonylation of nitrobenzene.

Conditions: NB (10 mmol), 5 wt% FeSe2/γ-Al2O3 (0.5 g, [FeSe2]: 0.1169 mmol), molar ratio of NB/FeSe2 = 85, MeOH (30 mL), T = 160 ◦C, p = 8.3 MPa of CO, t = 4 h. 2.4. Catalyst Recyclability

To investigate the reusability of FeSe2/γ-Al2O3, a set of experiments was conducted under milder conditions, that is, 140 ◦C (original temperature was 160 ◦C), under 6.8 MPa of CO pressure (original 8.3 MPa) for 2 h (original 4 h), and using 1.0 g of FeSe2/γ-Al2O3 (molar ratio of NB/[FeSe2] = 85) to exclude the effects of high temperature and pressure as well as long reaction time that could maintain high yield of MPC in every cycle. After reaction for 2 h, the solid FeSe2/γ-Al2O3 was filtered and washed with methanol, vacuum dried overnight, and recycled for the subsequent reaction with newly charged NB. The results illustrated in Figure7 indicate that FeSe 2/γ-Al2O3 did not show any loss in the catalytic activity until three consecutive recycles; however, there seems to be a small loss in the activity from the 4th recycling, implying that this low-cost heterogeneous FeSe2/γ-Al2O3 is fairly recyclable. Furthermore, the XRD result of the used catalyst depicted in Figure S22 shows that the diffraction patterns maintained their initial 2-theta value and intensity, demonstrating there is no change in the structure of this catalyst. Furthermore, no remarkable differences in the morphology after the reaction (Figure S21). To examine the change in the oxidation state of the used catalyst, XPS analysis was conducted. As shown in Figure S23, the reused catalyst shows a small shift in the Se 3d region from 54.57 eV to 55.3 eV, implying a partial generation of Se (0) species during reductive carbonylation, which is in high agreement with the generation of the Se0-CO as observed using IR analysis (Figure8), while the oxidation state of Fe did not change. These phenomena will be described in more detailed in the Section 2.5. The possible leaching of ferric or selenium elements was investigated by examining the liquid phase after the reaction using the ICP-MS method. The results show that there are no leached selenium species, indicating that FeSe2/γ-Al2O3 is a highly robust heterogeneous catalyst. Catalysts 2020, 10, 1228 11 of 19

Figure 7. Catalyst recyclability in the reductive carbonylation of NB at 140 ◦C, 6.8 MPa of CO for 2 h in the presence of 1 g of 5 wt% FeSe2/γ-Al2O3. 2.5. Mechanism Study

To determine the active species of the reductive carbonylation, FeSe2 was reacted with CO (8.3 MPa) in the presence of methanol at 160 ◦C for 4 h. The resulting solids were collected and dried under vacuum, and then pelletized with KBr. The sample was analyzed by FT-IR spectroscopy, but no carbonyl band of FeSe2 was observed (Scheme2, Figure8a). On the other hand, when the same process was carried out in the presence of O2 with CO, i.e., CO/O2 mixture (v/v = 80:20) (Scheme3), 1 FT-IR spectra of this sample exhibits a carbonyl peak at 1796 cm− (Figure8b).

Scheme 2. The reaction of FeSe2 and CO in the presence of methanol at 160 ◦C for 4 h.

Scheme 3. The reaction of FeSe2 and CO in the presence of oxidant.

As CO does not tend to bind to Fe(II), it might be bound to Se(0) in FeSe2, which demonstrates that the carbonyl species binds through Se, then forms carbonyl FeSe2 is possible only when Se− is oxidized to Se0 in the presence of an oxidant (Se 1 Se0). In this FeSe -catalyzed reductive carbonylation, − → 2 NB contributes as an oxidant. Indeed, the IR experiment conducted on a sample treated in the existence of NB (1 equiv. to FeSe2) under CO pressure in the absence of oxygen also exhibits the CO band at the same wavelength (Figure8c). These spectroscopic observations suggest that some part of the Se − species in FeSe2 seems to be oxidized to pseudo-Se(0), and is then partially converted to Se-CO moiety. Catalysts 2020, 10, 1228 12 of 19

In consideration of the fact that the synthesis of the terminal (Se-CO) proceeds in severe conditions such as metal Se reacting with carbon monoxide at 500–700 ◦C[52] or the reaction between phosgene and Al2Se3 at 210 ◦C[53], the clear observation of Se-CO species using FeSe2 seems to be very encouraging. In fact, Sonoda et al. reported the vapor phase of prepared Se-CO at ambient condition. Furthermore, the Se-CO was prepared by using distillation at 50 C/5 torr, then cooling at 196 C by introducing − ◦ − ◦ ammonium selenocarbamate into the mixture of THF/strong acid at 78 ◦C[54]. Bearing in mind 1 − these facts, it seems that the CO peak obtained at 1796 cm− from the IR result could be ascribed as bridging structure. Based on the well-known fact that the IR stretching vibration of the terminal Se-CO 1 as a vapor phase is around 2009 cm− [55], and the IR spectra of CO stretching vibration as bridging 1 1 form fall to 1720–1850 cm− [56], the CO peak at 1796 cm− can be deﬁned as bridging form.

Figure 8. FT-IR spectra of (a) FeSe2 obtained from the reaction with CO only, (b) FeSe2 obtained from the reaction in CO/O2 gas mixture (v/v = 80:20), (c) FeSe2 obtained from the reaction with CO by adding NB as oxidant, (d) spent FeSe2 after the carbonylation reaction.

Scheme 7 provides a plausible mechanism of the reductive carbonylation of nitroarene catalyzed by FeSe2. The ﬁrst step of the carbonylation would be the reaction of FeSe2 with methanol to form (1a) (Scheme4), then the generation of active catalyst, FeSe 2(µ-CO) (1b) via the reaction between 1a and CO in the presence of NB. Once again, it is worth emphasizing that 1b is not able to generate by the direct reaction between FeSe2 and carbon monoxide (Scheme2) without the presence of an oxidant like oxygen or NB, as studied using FT-IR analysis (Figure8). The combination of Schemes4 and5 generates Scheme6, indicating that the formation of FeSe 2(µ-CO) (1b) can be assisted by the conditions of the reductive carbonylation of NB. Catalysts 2020, 10, 1228 13 of 19

Scheme 4. The reaction of FeSe2 with methanol for producing 1a.

Scheme 5. The generation of 1b via the reaction of 1a with CO in the presence of NB.

Scheme 6. The combination of Schemes4 and5.

Although it was not successful in observing 1a by reacting FeSe2 with MeOH even for a longer time (overnight), the observation of AN and dimethyl carbonate (DMC) was conﬁrmed through GC-MS analysis, as shown in Scheme6 (SI, Figure S11). Meanwhile, Cotton reported the semi-bridging carbonyl with the CO group is an intermediate between terminal and bridging form [57]. The suggested structure of FeSe2(µ-CO) (1b) is proposed as semi-bridging carbonyl as well, where the µ-CO is bound 2 asymmetrically to two Se. The length of Se(δ −)–CO bond might be longer than that of Se(0)–CO, allowing the insertion of NB between Se and carbonyl carbon to be more comfortable through comparatively weaker interaction. Therefore, the reaction of 1b with NB will form 2b via the weaker bond, followed by subsequent decarboxylation (-CO2) to generate 3b. Then, one CO will be inserted between Se and O bond to generate 4b, and the second decarboxylation will produce a ferrous diselenide nitrido moiety, 5b. The formation of 5b is very important, because it is well known as the formation of LnM = NR in the noble metal-catalyzed reductive carbonylation of nitroarenes [7] This is due to the labile property that can be converted to other compounds such as isocyanates, carbamates, amines, and ureas [7,13,23,24]. Next, 5b is carbonylated with another CO to produce an isocyanato species, 6b. In the end, 6b can aggressively react with methanol to generate urethane with simultaneous regeneration of 1b. We should mention, here, the reason for the noticeable enhancement in the carbamates productivity by employing corresponding amino compounds into the nitro substrate. It can be understood as follows: (i) 6b interacts with RNH2 to produce disubstituted urea (DSU, (RNH)2CO, (ii) DSU will be transformed into carbamate and amine via methanolysis, and (iii) the produced amino compound takes part in this small repeated cycle, resulting in an additional generation of carbamates (solid box in Scheme7). Catalysts 2020, 10, 1228 14 of 19

Scheme 7. Plausible mechanism of FeSe2-catalyzed reductive carbonylation of nitroarene to produce urethane. The solid box explains about the enhanced urethane productivity when adding corresponding amino compound to the nitro compound-based main catalytic cycle.

3. Experimental

3.1. Materials

All chemicals, including iron (III) chloride (FeCl3, 97%), selenium dioxide (SeO2, 98.0%), pyridine (Py > 99.0%), and nitrobenzene (NB 99.0%), were purchased from Sigma-Aldrich ≥ (St. Louis, MO, USA). The support γ-Al2O3 (99.97%), α-alumina (α-Al2O3, 99.9%), basic-Al2O3 (99.8%), and neutral-Al2O3 (99.9%) were obtained from Alfa-Aesar (Ward Hill, MA, USA). Nitrobenzene (NB) and MeOH were freshly distilled under atmosphere of nitrogen. CO with 99.95% purity was supplied from Uniongas (Seoul, South Korea) and without further puriﬁcation.

3.2. Catalyst Characterization

The surface structure of FeSe2/γ-Al2O3 was examined by using scanning electron microscopy (SEM, JEOL JSM-6701F) and transmission electron microscopy analysis [TEM, JEM-2100F (UHR)]. The elemental compositions of catalysts were investigated by the associated EDX system (INCA). The oxidation states of each element on the surface of FeSe2 and its supports were examined by X-ray photoelectron spectroscopy (XPS) analysis on the Thermo Scientific K-AlphaTM+ spectrometer (Thermo Fisher Scientific Korea Ltd., Seoul, South Korea). X-ray diffraction (XRD) studies were analyzed on the Bruker D8 Advance (Waltham, MA, USA) to investigate the crystallinity and purity of catalysts. FT-IR analysis was studied by using the Nicolet FT-IR spectrometer (Waltham, MA, USA). Catalysts 2020, 10, 1228 15 of 19

3.3. Catalyst Synthetic Procedure

3.3.1. Preparation of Ferrous Diselenide (FeSe2)

Firstly, FeCl3 (0.98 g, 6.1 mmol) and SeO2 (3.2 g, 24.3 mmol) were dissolved in methanol (30 mL). Subsequently, pyridine (Py) (2.45 g, 31 mmol) was then added to the methanolic solution. The mixture was introduced into the glass-lined high-pressure reactor and filled with 2.5 MPa of CO at room temperature after purging with CO three times to remove air. The system was heated and stirred vigorously at a certain temperature. The reaction system was further charged with 8.3 MPa of CO at 160 ◦C and maintain during the reaction by using a gas reservoir. After the reaction, the solid part was filtered off and washed with MeOH (20 mL) for five times. The obtained catalyst was soxhleted with methanol in the reflux condenser for 8 h and dried under vacuum overnight. The obtained FeSe2 was ground to get fine powder before applying to the reaction.

3.3.2. Preparation of 5 wt% FeSe2 Supported on γ-Al2O3 (FeSe2/γ-Al2O3)

The preparation of FeSe2/γ-Al2O3 was similar for preparing FeSe2 under otherwise identical conditions except for adding 3.1 g of dried γ-Al2O3 (γ-Al2O3 was ﬁrstly dried at 110 ◦C for 5 h) into the methanolic solution FeCl3, SeO2, and pyridine. The slurry was stirred for 30 min before introducing into the glass liner inside the high-pressure reactor.

3.4. Carbonylation Reaction As a typical reaction, a carbonylation reaction was performed in a high-pressure reactor installed with a magnetic stirrer and electrical heater. The system was filled with CO (2.5 MPa) at room temperature after purging with CO three times to remove air and then heated to the required temperature with stirring. The system was further charged with 8.3 MPa CO at 160 ◦C and kept constant during the reaction using a gas reservoir equipped with a pressure regulator and a pressure transducer. After the reaction, the system was cooled to room temperature, followed by depressurization to unseal. The liquid sample obtained from the syringe filter was quantified using a gas chromatography installed with an HP-5 column (30 nm 0.32 mm 0.25 µm) and a flame ionization detector (FID), and a constant × × volume of heptane was added as a standard to calculate the yield of urethane. GC-Mass spectrometer and 1H, 13C NMR spectra (Bruker 300MHz NMR spectrometer) were used for the identities of products.

3.5. FT-IR Analysis of Carbonyl Selenide

3.5.1. Using O2 as an Oxidant

The FT-IR experiment was performed in a high-pressure reactor by reacting 0.1 g of FeSe2 with 8.3 MPa of a mixture gas of CO/O2 (v/v = 80/20) in methanol (30 mL) as solvent at 100 ◦C. After 4 h reaction, the product was obtained by ﬁltration and dried under vacuum for 12 h. The collected sample was pelletized with KBr and analyzed by the FT-IR spectrometer. The same procedure was also performed with FeSe2/γ-Al2O3 and Se (0) metal.

3.5.2. Using Nitrobenzene (NB) as an Oxidant A CO chemisorption study was performed using nitrobenzene (NB) as an oxidant instead of using oxygen. For this, 0.1 g of FeSe2 was reacted with 8.3 MPa of CO in a high-pressure reactor with 1 equivalent NB to FeSe2 in MeOH at 100 ◦C for 4 h. After the reaction, the sample was ﬁltrated and vacuum dried for 12 h. The FT-IR analysis was conducted on the collected sample.

4. Conclusions In this study, a remarkable yield of MPC was obtained via the reductive carbonylation of NB over a catalyst system consisting of FeCl3, SeO2, and Py, which appeared to be converted into a heterogeneous ferrous diselenide, FeSe2. The FeSe2 was impregnated onto γ-Al2O3 as support to synthesize a 5 wt% Catalysts 2020, 10, 1228 16 of 19

FeSe2/γ-Al2O3, which exhibited an impressive enhancement in terms of catalytic performance in the conversion of NB to MPC. The FeSe2/γ-Al2O3-catalyzed carbonylation reaction was strongly affected by temperature and reaction time. The substituent at the para position of the aromatic ring has a significant impact on the yields of the corresponding carbamates, that is, the presence of the electron-withdrawing group at the para position tended to reduce the catalytic activity of the carbonylation reaction. Furthermore, the FeSe2/γ-Al2O3 could be reused five times without a significant decrease in activity. Based on the FT-IR experiments on FeSe2, it was likely to form asymmetric semi-bridging carbonyl diselenide, FeSe2 (µ-CO) (1b) during the carbonylation, thus making it possible for the insertion of NB and complete the catalytic cycle, to regenerate 1b. Moreover, a much higher yield of mono- and di-urethanes could be obtained through the FeSe2/γ-Al2O3–catalyzed reductive carbonylation of a dual substrate system comprising nitro- and its corresponding amino-compound. The superiority of this FeSe2/γ-Al2O3 catalyst is its low cost and simple preparation compared to the previously used noble metals such as Pd, Rh, and Ru for the reductive carbonylation of many different kinds of nitroarenes.

Supplementary Materials: The following are available online at http://www.mdpi.com/2073-4344/10/11/1228/s1, Figure S1: X-ray diffraction spectra (XRD) of standard Ferroselite FeSe2, Figure S2: (a) X-ray diffraction spectra (XRD) of FeSe2/γ Al2O3, (b) XRD standard spectra of Al2.144O3.2 (γ - Aluminium oxide) PDF-number 79-1558-Cubic Fd-3m (227), Figure S3: EDX/EDS spectra of FeSe2 and the atomic ratio calculation of Fe/Se, Figure S4: EDX/EDS spectra of FeSe2/γ-Al2O3 and the atomic ratio calculation, Figure S5: X-ray photoelectron spectroscopy (XPS) survey spectra of FeSe2, Figure S6: X-ray photoelectron spectroscopy (XPS) survey spectra of FeSe2/γ Al2O3, Figure S7: X-ray photoelectron spectroscopy (XPS) spectra of FeSe2 in the region of (a) Fe3p, (b) Se3d, and (c) C1s, Figure S8: X-ray photoelectron spectroscopy (XPS) of FeSe2/ γ-Al2O3 in the region of (a) Fe3p and (b) Se3d, Figure S9: High resolution TEM images of (a) neat FeSe2 prepared with the presence of pyridine, and (b) FeSe2/γ-Al2O3 prepared with the presence of pyridine, Figure S10 Thermogravimetric analysis (TGA) of FeSe2, Figure S11: GC-MS of the filtrate obtained in the reductive carbonylation reaction using FeSe2 as catalyst with molar ratio NB/FeSe2 = 1, Figure S12: GC-MS of the filtrate obtained in the reductive carbonylation reaction using FeSe2 as catalyst with molar ratio NB/FeSe2 = 4, Figure S13: 1H-NMR spectra of Methyl N-phenyl carbamate (MPC) product obtained from the reductive carbonylation rxn. 1H NMR (300 MHz, CDCl3, δ 3.66 (s, 3H, OCH3); 6.59 (s, 1H, NH); 6.95 (t, 1H, ArH); 7.17(m, 2H, ArH); 7.27 (d, 2H, ArH), Figure S14: 13C-NMR of MPC product obtained from the reductive 13 carbonylation reaction of nitrobenzene. C NMR (300 MHz, CDCl3, δ 52.5 (OCH3); 118.85 (C6H5-); 123.6 (C6H5-); 129.1 (C6H5-); 137.9 (C6H5-); 154.19 (C6H5-), Figure S15: GC-MS of Methyl (4-methoxyphenyl) carbamate, Figure S16: GC-MS of Methyl (4-methylphenyl) carbamate, Figure S17: GC-MS of Methyl (4-bromophenyl) carbamate, Figure S18: GC-MS of Methyl (4-acetylphenyl) carbamate, Figure S19: GC-MS of Dimethyl toluene-2,4-dicarbamate, Figure S20: GC-MS of dimethyl 1,4-phenylenebiscarbamate, Figure S21: Scanning electron microscopy (SEM) figures of (a) fresh FeSe2/γ-Al2O3 catalyst, and (b) spent FeSe2/γ-Al2O3, Figure S22: X-ray diffraction spectra of (a) fresh catalyst FeSe2, (b) recovered FeSe2 after 5th recycling in the reductive carbonylation reaction of NB, Figure S23: XPS of the fresh and spent FeSe2/ γ-Al2O3 in the region of (a) Fe 3p; (b) Se 3d, Table S1: Different types of a FeSe2/support for the formation of MPC , Table S2: TON value of the reductive carbonylation reaction using FeSe2/γ-Al2O3 as catalyst. Author Contributions: Conceptualization, A.V.T., T.T.H.N. and Y.J.K.; methodology, A.V.T. and T.T.H.N.; validation, T.T.N., H.J.L. and J.B.; formal analysis, A.V.T. and T.T.H.N.; investigation, A.V.T. and T.T.H.N.; data curation, A.V.T.; writing-original draft preparation, A.V.T. and T.T.H.N.; writing-review and editing, A.V.T. and Y.J.K.; supervision, Y.J.K. All authors have read and agreed to the published version of the manuscript. Funding: This study has been conducted with the support of the Korea Institute of Industrial Technology as “Development of eco-friendly production system technology for total periodic resource cycle (Kitech EO-20-0022)” and was funded by the Ministry of Science and ICT as “C1 Gas Refinery Program” (2015M3D3A1A01064895) through the National Research Foundation (NRF) of Korea Conflicts of Interest: The authors declare no conflict of interest.

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