Efficient dehydrogenation of dodecanol to dodecanal in a continuous fixed bed reactor over supported Cu catalyst

doi:10.21203/rs.3.rs-3697554/v1

Download PDF

Research Article

Efficient dehydrogenation of dodecanol to dodecanal in a continuous fixed bed reactor over supported Cu catalyst

https://doi.org/10.21203/rs.3.rs-3697554/v1

This work is licensed under a CC BY 4.0 License

You are reading this latest preprint version

The anaerobic dehydrogenation of dodecanol to dodecanal has been investigated in a continuous fixed bed reactor over a series of Cu-based catalysts with different supports (SiO₂, Al₂O₃, ZnO and MgO). These catalysts have been systematically characterized by XRD, H₂-TPR, NH₃-TPD, CO₂-TPD, XPS and N₂-adsorption/desorption measurements. And the results indicate that the support has significant effect on the physicochemical properties of the catalysts and their catalytic performances, and Cu/SiO₂ exhibited the highest catalytic activity in the dehydrogenation. Synergistic effect between Cu⁺ and Cu⁰ species has been observed, and proper ratio of Cu⁺/Cu⁰ is believed to be able to improve the catalytic performance of Cu-based catalysts. The surface acidity and basicity demonstrate significant effect on the distribution of the products and the selectivity to aldehyde. Under the optimized conditions, an 82.3% conversion of dodecanol with an excellent 98.9% selectivity toward dodecanal could be obtained. Moreover, the catalytic performance of Cu/SiO₂kept almost steady in 200 hours, indicating its good stability and application potential in the dehydrogenation process.

dodecanol dehydrogenation

dodecanal

copper

support

synergistic effect

Dodecanal is a quite important compound, and has been extensively used in cosmetics, cleaning products, chemical industry, food and beverage, etc (Jang et al. 2021; Tae et al. 2010; Pandey et al. 2018). In terms of spices, it is always used in the synthesis of jasmine, moonshine, lily of the valley and violet. Industrially, dodecanal is mainly obtained through a two-step process from dodecanol as follows: dodecanol is firstly oxidized to dodecaldeic acid, which is then reduced to afford dodecanal. Although the technology has been matured with high conversion of the starting material, the reaction process requires two steps and is not convenient and economical. In addition, the selectivity is low, resulting in complicated separation processes and high production of cost.

Direct oxygenation of primary alcohols to corresponding aldehyde is a particularly important protocol, and various reaction systems have been explored (De Maron et al. 2023; Poreddy et al. 2015; Liao et al. 2015). However, some drawbacks including the utilization of expensive catalysts or hazardous peroxides, harsh reaction conditions, low selectivity, et al., seriously limit the practical application. Alternatively, olefins or ketones as hydrogen acceptors are introduced into the reaction system to realize the hydrogen transfer of alcohols to produce carbonyl compounds in the absence of oxidants (Xia et al. 2021; Shi et al. 2010; Zaccheria et al. 2006). These reaction systems avoid the safety hazards caused by oxidants, but converting hydrogen acceptors (alkenes or ketones) into other organic by-products leads to complicated purification process. Obviously, the more ideal process is the direct dehydrogenation of alcohols to carbonyl compounds in the absence of hydrogen acceptor.

Recently, Cu-based catalysts have been extensively used in the catalytic alcohol dehydrogenation reaction for its lower activation temperature, high activity and selectivity (Cheng et al. 2022; Yu et al. 2019; Quan et al. 2022). For instance, Crivello and coworkers investigated the dehydrogenation of 1-octanol over Cu⁰ obtained from Al-Cu-Mg mixed oxides, and satisfactory results were obtained (Crivello et al. 2008). Dixit et al. developed a Mg-Al mixed oxide supported copper catalyst, which exhibited good performance in the dehydrogenation of aromatic alcohols but was less active for primary aliphatic alcohols. For example, the selectivity to 1-octanal was only 13% in the dehydrogenation of 1-octanol (Dixit et al. 2013). Lu et al. have reported a Cu-Ni/γ‐Al₂O₃ bimetallic catalyst for the anaerobic dehydrogenation of primary aliphatic alcohols, but the catalytic performance was not satisfied. For example, only a 38% conversion could be obtained for C8 aliphatic alcohols (Lu et al. 2014). Hosaka et al. developed a 12-crown-4-ether (12C4) catalyst for the transformation of 1-decanol to decanal, and a high yield of 90.8% could be attained under the optimized conditions (Hosaka et al. 2023). An efficient Cu/SiO₂-HP catalyst has been prepared by Lu et al. via a hydrolysis-precipitation method, which exhibited an 85.4% conversion in the dehydrogenation of ethyl lactate (Lu et al. 2023). Mitsudome and coworkers prepared hydrotalcite-supported Cu nanoparticles (Cu/HT) that could efficiently promote the anaerobic dehydrogenation of various alcohols, but only a 19% conversion and 47% selectivity could be obtained for octanol (Mitsudome et al. 2008).

In conclusion, the oxygen-free dehydrogenation of long primary aliphatic alcohol remains a challenge due to the relative stability (Putro et al. 2018). Furtherly, although much progress has been made in the catalytic dehydrogenation of alcohol to aldehyde, less attention is paid to the dehydrogenation of dodecanol. Wang and coworkers prepared a copper nanoparticles dispersed rod-shaped La₂O₂CO₃ catalyst (Cu/La₂O₂CO₃), but only a 75% yield of dodecanal was observed (Wang et al. 2013). In addition, complicated synthesis process for the catalyst also seriously limits their practical application.

The previous reported results have demonstrated that the surface acidity and basicity have significant influence on the selectivity of the dehydrogenation of primary aliphatic alcohols (Dixit et al. 2013; Wang et al. 2013; Kamiguchi et al. 2015; Marella et al. 2012). Surface acid site would lead to the dehydration of alcohol to olefin, while the basic site would promote the aldol condensation of the product. Therefore, it is particularly important to select an environmentally friendly material with appropriate acid-base strength as the carrier of copper-based catalyst. In the study, a series of copper based catalysts have been prepared on different supports, and the effects of supports on the physic-chemical properties and the product distribution in the dehydrogenation of dodecanol have been studied. The results proved that the support has significant effect on the catalytic behavior of Cu-based catalysts, and Cu/SiO₂ displayed the highest catalytic performance due to the possible synergistic effect between Cu⁺ and Cu⁰ species and proper surface acidity and basicity.

The chemical reagents used in the experiments are all analytically pure and were purchased from Energy-Chemical.

Preparation of Cu-based catalysts

The procedure for the preparation of Cu/SiO₂ by coprecipitation is described as follows: Cu(NO₃)₂·3H₂O (0.13 mol, 31.41 g) and (C₂H₅O)₄Si (0.59 mol, 122.91 g) were dissolved in deionized water (125 mL) and ethanol (122.91 g), respectively, to obtain two solutions. Subsequently, the two solutions were added dropwise to 650 mL of NaHCO₃ solution (1.3 mol/L) under vigorous stirring at 80°C. The solution was then stirred at 80°C for another 4 h, and aged at room temperature for 4 h. The sample collected by filtration was washed with deionized water, dried at 90°C, and calcined at 400°C for 4 h. Finally, Cu/SiO₂ catalyst was obtained via reduction at 240°C for 5 h under a flow of hydrogen and nitrogen mixed gas.

Cu/Al₂O₃, Cu/ZnO and Cu/MgO catalysts were prepared via a coprecipitation method. Taking Cu/ZnO as an example, NaHCO₃ (0.84 mol, 70.57 g) was dissolved in 650 mL of deionized water under stirring. A solution of Cu(NO₃)₂·3H₂O (0.13 mol, 31.41 g) and Zn(NO₃)₂·6H₂O (0.25 mol, 74.37 g) in deionized water (400 mL) were added dropwise to the NaHCO₃ solution in a 2000 mL flask under vigorous stirring at 80°C. The solution was stirred at 80°C for another 4 h, and aged at room temperature for 4 h. The sample collected by filtration was washed with deionized water, dried at 90°C overnight, and calcined at 400°C for 4 h. Cu/ZnO catalyst was obtained after reducing the calcined sample at 240°C for 5 h under a flow of hydrogen and nitrogen mixed gas. Cu/Al₂O₃, Cu/ZnO and Cu/MgO catalysts were prepared through similar procedures.

All the prepared catalysts were formed into a pill shape with a diameter of 3 mm via molding process before being investigated in a fixed bed reactor.

Characterization of catalysts

The crystallographic information of the sample was characterized by collecting X-ray diffraction (XRD) pattern using a Rigaku D/max 2500 X-ray powder diffractometer. The ICP measurements were carried out for quantitative analysis of metal elements using an Thermo Fisher iCAP PRO (OES). X-ray photoelectron spectroscopy (XPS) patterns of these catalysts were recorded using a Thermo Scientific K-Alpha, which was operated at a pressure of 12 kV. The C 1s peak at 284.80 eV was used as calibration. The N₂ adsorption/desorption isotherms were obtained at ‒196°C on a Micromeritics ASAP2460, and the specific surface area was calculated by the BET method, and the aperture distribution of desorption section of isotherm was calculated using Barrett-Joyner-Halenda (BJH) method.

Temperature-programmed reduction of H₂ (H₂-TPR), temperature-programmed desorption of NH₃ (NH₃-TPD) and temperature-programmed desorption of CO₂ (CO₂-TPD) were all performed on a Micromeritics AutoChem II 2920 instrument with a thermal conductivity detector. For the H₂-TPR analysis: a calcined sample (40 mg) was loaded into a fixed-bed quartz tube and outgassed in He flow for 1 h. Next, the sample was exposed to 10% H₂/Ar mixture gas (50 mL/min) at 50°C for 0.5 h and then purged with He for 1 h to remove excess H₂. TPR analysis was carried out to 600°C at a heating rate of 10°C /min. For the NH₃-TPD analysis: The as-synthesized catalyst (100 mg) was purged in He flow (50 mL/min) at 300°C for 1 h. After the sample being saturated with ammonia in 10% NH₃/He flow, the physisorbed ammonia was removed by He at 50°C. The NH₃-TPD profile was recorded from 50 to 600°C with a 10°C /min heating rate in a 50 mL/min He flow. For the CO₂-TPD analysis: the catalyst sample (100 mg) was purged in He gas flow (50 mL/min) at 300°C for 1 h. Thereafter, the sample was saturated by introducing 10% CO₂/He mixture gas (50 mL/min) to pass the sample at 50°C for 1 h and then purged with He for 1 h to remove physisorbed CO₂. TPD analysis was carried out from 50 to 600°C at a heating rate of 10°C/min for CO₂ desorption.

The procedure for the catalytic dehydrogenation of dodecanol

The dehydrogenation of dodecanol was operated in a continuous flow fixed bed reactor (Ø15 mm × 600 mm). 20 mL of catalyst was packed in the isothermal region of the reactor, and the other region was filled with sand. After being preheated at the selected reaction temperature for 1 h under a N₂ flow rate of 5 mL/min, 5 vol% dodecanol solution in cyclohexane was pumped from the top of the reactor using a piston pump. The residence time was adjusted by changing the flow velocity of the dodecanol solution. The reaction mixture was cooled by water and collected in a gas-liquid separator. The reaction solution was analyzed by GC-FID (Shimadzu GC-2010AF) using internal standard method (chlorobenzene as the reference compound). The value for the conversion, yield and selectivity were obtained via the following formulae.

Catalysts characterization

The XRD analysis was firstly conducted for the precursors of catalysts, and the patterns are summarized in Fig. 1. All the calcined samples show two diffraction peaks at 2θ = 35.5° and 38.7 °, which are related to CuO species (JCPDS Card no. 74-1230). A series of diffraction peaks can be observed at 2θ = 31.8°, 34.5°, 36.2°, 47.5°, 56.6° for calcined Cu/ZnO samples, which are assigned to ZnO species. There is no obvious characteristic peak of the carrier Al₂O₃, indicating that Al₂O₃ is amorphous. The results also suggest that Al₂O₃ plays a role in dispersing the active component Cu in the sample, and provides skeleton support for Cu species. A new diffraction peak formed at 67ºcorresponds to the spinel CuAl₂O₄ (JCPDS Card no. 33–0448), which might lead to high reduction temperature, because the structure of spinel is stable and the reduction is difficult. The SiO₂ has an obvious "steamed bun" peak at 2θ = 22.5° in the XRD pattern, in line with the previous reports (Hosaka et al. 2023; Yuan et al. 2020). These observations indicate that the influence of these supports on the Cu-based catalysts is different, which should result in different catalytic behaviors.

The N₂-adsorption/desorption isotherms and physico-chemical properties for the Cu-based catalysts with various supports are shown in Fig. 2 and Table 1. The ICP analysis demonstrated that all the four samples had the similar content of Cu species. The isotherms of these prepared samples are IV type, which is a typical mesoporous material. The specific surface area was determined by the BET method, and the data in Table 1 show that the BET surface area of these Cu-based samples varied with the supports. Cu/SiO₂ demonstrated the highest value of 114.5 m²/g, and the lowest value was observed for Cu/ZnO (34.4 m²/g). The high value of S_BET would increase the dispersity of the active sites and improve the catalytic efficiency. The pore volume and pore size changed irregularly, and Cu/ZnO and Cu/MgO show marked larger value than that of Cu/SiO₂ and Cu/Al₂O₃, which should be benefited to the motion of molecules during the reaction.

Table 1

Physico-chemical properties of the Cu-based catalysts.
Catalyst	Cu loading /%	Surface Area /m²∙g^− 1	Pore Volume /mL∙g^− 1	Pore Size /nm
Cu/SiO₂	32.9	85.2	0.152	7.151
Cu/Al₂O₃	33.6	49.5	0.087	7.001
Cu/ZnO	33.3	33.1	0.268	31.752
Cu/MgO	37.9	48.6	0.368	30.235

The surface chemical state of Cu species should play a crucial role in the catalytic dehydrogenation of alcohol. Therefore, XPS analysis of these Cu-based samples was performed to assign the copper species with different supports (Fig. 3). The XPS spectra of the Cu 2p_3/2 for all the samples can be fitted by two peaks, and B.E. (Binding Energy) of ca. 934 eV and ca. 932 eV are identified to Cu²⁺ and Cu⁺ or Cu⁰, respectively (Yuan et al. 2020; Prabu et al. 2014; Jiang et al. 2015). In order to accurately distinguish between Cu⁰ and Cu⁺, the Cu LMM spectrum was also performed (Fig. 4). Asymmetric peaks for all the four samples can be deconvolved into two peaks centered at ca. 569.9 eV and ca. 573.0 eV, corresponding to Cu⁰ and Cu⁺, respectively (Song et al. 2022; Chen et al. 2020). According to the XPS and LMM analysis, the distribution of the surface copper species has been calculated and summarized in Table 2. The content of Cu²⁺ was found in the order as follows: Cu/MgO > Cu/Al₂O₃ > Cu/ZnO > Cu/SiO₂, which should be related to the varied reduction activities of Cu²⁺ and the stabilization of Cu⁺ and Cu⁰ over different supports. The order of Cu⁰ contents of these catalysts from high to low was Cu/SiO₂, Cu/MgO, Cu/ZnO and Cu/Al₂O₃, which should be mainly responsible for their catalytic performance. Some research has demonstrated that Cu⁺ and Cu⁰ act synergistically to catalyze the dehydrogenation of alcohol (Lu et al. 2023), thus, the molar ratios of Cu⁺/Cu⁰ on the surface of these catalysts have also been calculated. And an order can be found as the follows: Cu/ZnO > Cu/SiO₂ > Cu/Al₂O₃ > Cu/MgO.

Table 2

The distribution of the surface copper species
Samples	Content of Cu²⁺ /mmol∙g^− 1	Content of Cu⁺ /mmol∙g^− 1	Content of Cu⁰ /mmol∙g^− 1	Cu²⁺/ (Cu²⁺+Cu⁺+Cu⁰) /%	Cu⁺/Cu⁰
Cu/SiO₂	0.43	1.02	1.69	13.7	0.6
Cu/Al₂O₃	0.16	0.21	0.43	20.0	0.49
Cu/ZnO	0.29	0.79	0.45	19.0	1.75
Cu/MgO	1.10	0.38	1.02	45.0	0.37

The reducibility and interaction between the copper oxides and supports are studied by H₂-TPR, and there have been some studies on the calcined Cu-based catalysts. Most researchers believe that the reduction peak at low temperature is the reduction of copper oxide species or copper oxide microclusters highly dispersed on the surface of carrier, while the reduction peak at high temperature is the reduction of larger CuO_x grains (Koppadi et al. 2018). The H₂-TPR curves in (Fig. 5) demonstrate that the reduction of CuO_x on ZnO and MgO is easier than that on SiO₂ and Al₂O₃, suggestive of the interactions between CuO_x and support. The lower reduction temperatures of ZnO and MgO are mainly due to the high dispersion of copper oxide species on the surface of the support. Of note is that an even high reduction temperature peak of about 366°C is found for MgO, which should be related to the reduction of larger CuO_x grains. These observations can well explain the high content of Cu²⁺ in Cu/MgO sample. The different reduction behavior found for the precursor of Cu/SiO₂ catalyst with that of Cu/ZnO catalyst may be related to the reduction of highly dispersed CuO_x to Cu⁰ in the later and bulk CuO particles on the calcined Cu/SiO₂ sample (Yuan et al. 2020). The reduction temperature of calcined Cu/Al₂O₃ sample is higher, which should be related to the formation of the stable spinel CuAl₂O₄ species. The reduction performance of catalyst directly affects the activity of catalyst. The lower the reduction temperature, the better the catalytic activity of catalyst.

Due to the different properties of these supports used, it is expected that they should have different surface properties and affect the catalytic performance. The acidic properties of these catalysts were characterized by NH₃-TPD (Fig. 6). The obtained NH₃-TPD spectra were deconvoluted by Gaussian fitting, the number and intensity of acid sites were evaluated by the desorption area and temperature of the fitting peak. Acid sites responsible for NH₃ desorption below 200°C are classified as weak acid sites, between 200°C and 300°C as medium acid sites, and above 300°C as strong acid sites. Coordination-unsaturated MO_6 − x octahedron is used as a site for Lewis acid, thus, the presence of Cu²⁺ and Cu⁺ introduce acid sites into the catalyst.

According to the calculated data in Table 3, the amount of strong acid sites in these Cu-based catalysts can be ordered as follows: Cu/MgO > Cu/Al₂O₃ > Cu/SiO₂ > Cu/ZnO. Combined with XPS analysis, coordination-unsaturated Cu²⁺ species on the surface should be responsible for the results, consistent with the previous reports (Yuan et al. 2020; Nauert et al. 2018). In addition, a large number of weak and medium acid sites in Cu/SiO₂ catalyst are observed, which might be ascribed to the coordination-unsaturated Cu⁺ species. However, Cu/Al₂O₃ was an exception, which had lowest Cu²⁺ and Cu⁺ contents but with high amount of acid sites, suggesting that the acid site should be predominantly ascribed by Al species.

Table 3

The surface acidic properties of the Cu-based catalysts.
Sample	Total acid site /µmol NH₃ ∙ g^− 1	Acid sites distribution/µmol NH₃ ∙ g^− 1
Sample	Total acid site /µmol NH₃ ∙ g^− 1	50‒200 ℃	200‒300 ℃	300‒600 ℃
Cu/SiO₂	509.9	226.5	142.6	140.8
Cu/Al₂O₃	842.8	0	0	842.8
Cu/ZnO	88.5	5.4	0	83.1
Cu/MgO	6242.0	208.4	0	6033.6

CO₂-TPD analysis displays (Fig. 7) that the surface basicity also varied with the supports. The CO₂ adsorption sites on these catalysts can be generally divided into three types. Strong physical CO₂ adsorption sites with desorption temperature between 50–220°C are assigned to the weak basic sites; Weak chemical CO₂ adsorption sites (desorption at around 220–360°C) found on these catalysts can be ascribed to the medium basic sites; strong chemical CO₂ adsorption sites (CO₂ desorption above 360°C) are related to the strong basic sites on the catalyst. According to the calculated data in Table 4, Cu/MgO contained the highest amount of total basic sites, as well as the strong basic sites. By contrast, Cu/ZnO exhibited the lowest surface basicity. Actually, there are a large number of strong physical and chemical CO₂ adsorption sites on Cu/Al₂O₃ and Cu/MgO samples, while moderate amount of physical CO₂ adsorption sites is found for Cu/SiO₂.

Table 4

The surface basic properties of the Cu-based catalysts.
Sample	Total basic sites /µmol CO₂ ∙ g^− 1	Basic sites distribution /µmol CO₂ ∙ g^− 1
Sample	Total basic sites /µmol CO₂ ∙ g^− 1	50–220 ℃	220–360 ℃	360–600 ℃
Cu/SiO₂	80.5	44.4	13.4	22.7
Cu/Al₂O₃	257.9	103.6	29.1	125.2
Cu/ZnO	34.1	4.6	14.4	15.1
Cu/MgO	465.1	102.6	101.3	261.2

Catalytic performance of Cu-based catalysts in the dehydrogenation of dodecanol

The catalytic performace of these prepared Cu-based catalysts were studied in the anaerobic dehydrogenation of dodecanol (Table 3). The conversion varied in the order as follows: Cu/Al₂O₃ < Cu/SiO₂ < Cu/MgO < Cu/ZnO, albeit the difference was not marked. Of note is that ester, olefin and ketone were also detected in the reaction besides the objective product aldehyde. We speculated that the reactivity should be influenced by multiple properties of the catalysts. Concerning on the distribution of products, Cu/SiO₂ gave the highest aldehyde selectivity of 98.9% with a satisfactory 82.3% conversion, significantly superior to the reported catalytic system based on Cu/La₂O₂CO₃ (Wang et al. 2013). Cu⁰ species has been generally believed as the active site for the dehydrogenation, therefore, the excellent selectivity obtained over Cu/SiO₂ should be due to its highest amount of Cu⁰. The high value of S_BET might be also partly responsible for the high catalytic performance, because more active sites can be exposed on Cu/SiO₂ with similar Cu contents (Chen et al. 2020).

In contrast, although the highest conversion was obtained for Cu/ZnO, only a 35.6% selectivity was observed with the formation of ester as the main byproducts. Under the anaerobic conditions, we speculated that the ester was generated from dodecanol and dodecanal via a coupling reaction (Miura et al. 2017; Sato et al. 2012). It can also explain the highest conversion, because a proportion of dodecanol transformed via coupling reaction instead of dehydrogenation. The results also suggest that the surface properties had little effect on the coupling reaction, because highest selectivity of ester was observed for Cu/ZnO but with lowest acidity and basicity. Under the catalysis of Cu/MgO, a 32.9% selectivity to ketone was observed, which might be produced via ketonisation of ester for its high amount of surface acidic sites ( Prabu et al. 2014; Gaertner et al. 2009; Shen et al. 2012). Similar phenomenon can be observed for Cu/Al₂O₃ catalyst but with relatively lower level, probably due to its reduced surface acidity. Of note is that the pore property of these catalysts should also has effect on the product distribution. Cu/SiO₂ and Cu/Al₂O₃ with small pore size (~ 7.0 nm) offered high selectivities toward aldehyde, while Cu/ZnO and Cu/MgO with larger value (~ 31.0 nm) gave more products of ester or ketone. These results suggest that larger pore size is benefitial to the entrance and exit of the large molecules, namely ester and ketone. Consequently, the excellent selectivity with satisfied conversion observed for Cu/SiO₂ catalyst should be related to its proper surface acidity and basicity, and its small pore size.

Concerning on the side-reactions and the paths for the generation of these byproducts mentioned above, the exact dehydrogenation yields over different catalyst have been estimated in term of aldehyde (Table 5). The results demonstrate an order of dehydrogenation activity as follows: Cu/ZnO < Cu/MgO < Cu/Al₂O₃ < Cu/SiO₂, not exactly in line with the amount of Cu⁰. Although Cu/MgO has markedly higher amount of Cu⁰ than Cu/Al₂O₃, but lower yield of dehydrogenation was obtained. These results suggest that the Cu⁺ species might also play a role in the dehydrogenation (Lu et al. 2023), and synergistic effect between Cu⁺ and Cu⁰ species might exist. Concerning on the varied ratios for these catalysts (Table 2), proper ratio of Cu⁺/Cu⁰ is beneficial to the catalytic performance of Cu-based catalysts.

Table 5. The results for the catalytic dehydrogenation of dodecanol over different Cu-based catalysts.

Effect of reaction conditions on the catalytic dehydrogenation of dodecanol

The effects of reaction conditions on the catalytic dehydrogenation of dodecanol were subsequently studied using Cu/SiO₂as the catalyst. The reaction temperature was initially investigated. When the reaction temperature was elevated from 200 ℃ to 260 ℃, the conversion of dodecanol increased gradually from 67% to 82% (Fig. 8). In contrast, the selectivity remained basically constant when the temperature was set above 240 ℃. Further increasing the reaction temperature led to a slight decreasement of the conversion, which might be due to the reversible hydrogenation of aldehyde.

We then focused on the reaction pressure. With a reaction pressure increasing from normal pressure to 0.8 MPa, the conversion of dodecanol decreased from 83.6% to 61.2%, and the selectivity of dodecanal dropped sharply from 98.3% to below 60% (Fig. 9). The anaerobic dehydrogenation of dodecanol to dodecanal is a reversible reaction, associated by the release of H₂. With the increase of pressure, the reaction is promoted in the reverse direction, and the dehydrogenation of alcohol is suppressed, in line with the obtained results. Therefore, normal pressure was determined as the optimal condition.

As can be seen from Fig. 10, when the (gas hourly space velocity) of carrier gas increases from 300 h^-1 to 600 h^-1, the conversion of dodecanol gradually increases. However, when the GHSV continues to increase, the conversion decreases significantly. For the selectivity of dodecanal, it increases slightly as the increase of GHSV. Therefore, the optimal GHSV value was set as 600 h^-1.

The effect of LHSV (liquid hourly space velocity) on the catalytic dehydrogenation of dodecanol was finally studied. With the increasement of LHSV of dodecanol, the conversion of dodecanol decreases gradually, whilst the selectivity of dodecanal increases slightly (Fig. 11). The conversion remains around 85% when the LHSV is lower than 0.3 h^-1, which is mainly due to the fact that excessive raw material shortens the residence time of the raw material.

In summary, Cu/SiO₂ presents excellent catalytic activity for the dehydrogenation of dodecanol to dodecanal in vapor-phase fixed bed reactor. Under the optimized conditions, the conversion and the selectivity reach 82.3% and 98.9%, respectively. And the catalytic dehydrogenation process probably provides a continuous process for the production of dodecanal.

The catalytic stability of Cu/SiO₂in the dehydrogenation of dodecanol

The catalytic stability of the Cu/SiO₂ catalyst was also investigated in a continuous vapor-phase fixed bed reactor. The results in Fig. 12 demonstrate that the conversion of dodecanol decreased slightly in the reaction period of 125 h, and then remained basically unchanged. On the other hand, the selectivity of dodecanal showed an upward trend and tended to remain constant above 97.5% as the reaction proceeding. These results suggest that the prepared Cu/SiO₂ catalyst had good stability in the continuous dehydrogenation of dodecanol.

XRD analysis of the used Cu/SiO₂catalysts was carried out to gain insight into the evolution of the catalytic structure during the dehydrogenation process. The XRD pattern (Fig. 13) show that the main diffraction peaks for Cu⁰species at 2θ = 43.3°, 50.9° and 73.6° (JCPDS Card no. 04-0836) generally remained after continuous reaction for 200 h. An enhanced diffraction peak of 2θ = 36.2°, 42.3° and 61.3° (JCPDS Card no. 47-1230) generally assigned to the Cu₂O phase is observed, (Yuan et al. 2020) indicating the agglomeration of copper ions due to the destruction of the Cu₂O-like phase, which might be responsible for the slight reduction of the catalytic activity. However, it was difficult to absolutely eliminate the presence of the CuO phase (2θ = 35.6°, 38.7°, 41.2° and 61.5°, JCPDS Card no. 72-0629) in the catalysts because both exhibited the close position of the characteristic diffraction peaks.

In the study, four Cu-based catalysts with different supports have been prepared and investigated in the dehydrogenation of dodecanol in a fixed bed reactor. Cu/SiO₂ exhibited the highest catalytic activity in the dehydrogenation, which should be related to its highest content of Cu⁰ proper ratio of Cu⁺/Cu⁰. Excellent selectivity to dodecanal was also observed under the catalysis of Cu/SiO₂, probably ascribed by the proper surface acidity and basicity, avoiding the formation of by-products of olefin, ester or ketone. The effects of reaction conditions on the anaerobic dehydrogenation have been detailedly studied, and an 82.3% conversion of dodecanol with an excellent 98.9% selectivity of dodecanal was obtained under the optimized conditions. The catalytic process for the production of dodecanal also demonstrated good stability and application potential.

Acknowledgements

This work was supported by Advanced Catalysis and Green Manufacturing Collaborative Innovation Center of Changzhou University, A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX22_3093), Natural Science Foundation for Colleges and Universities in Jiangsu Province (20KJA530003), Qinglan Project of Jiangsu Province and CNPC Innovation Found (2021DQ02-0707).

Declarations Conflict of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Jang JH, Choi KY (2021) Whole cell biotransformation of 1-dodecanol by escherichia coli by soluble expression of ADH enzyme from yarrowia lipolytica. Biotechnol Bioproc E 26:247-255. https://doi.org/10.1007/s12257-020-0176-5
Tae J, Park Y (2010) Facile synthesis of (-)-6-acetoxy-5-hexadecanolide by organocatalytic α-oxygenation-allylation-RCM strategy. Synthesis 21:627-3630. https://doi.org/10.1055/s-0030-1258248
Pandey R, Garg Y, Prakash R, Pandey SK (2018) Enantioselective synthesis of (-)-(5R,6S)-6-acetoxyhexadecan-5-olide via tandem α-aminooxylation-henry reaction. Arkivoc 7:20-27. https://doi.org/10.24820/ark.5550190.p010.635
De Maron J, Tabanelli T, Ospitali F, Lopez Cruz C, Righi P, Cavani F (2023) Gas-phase oxidative dehydrogenation of long chain alkenols for the production of key fragrance ingredients: from rosalva isomers to costenal analogues. Catal Sci Technol 13:1059-1073. https://doi.org/10.1039/d2cy01836e
Poreddy R, Engelbrekt C, Riisager A (2015) Copper oxide as efficient catalyst for oxidative dehydrogenation of alcohols with air. Catal Sci Technol. 5:2467-2477. https://doi.org/10.1039/c4cy01622j
Liao SY, Ko AN (2015) Potassium-promoted Mo/MWCNTs catalysts for effective partial oxidation of 1-dodecanol to 1-dodecanal. Appl Catal A-Gen 496:79-85. https://doi.org/10.1016/j.apcata.2015.02.017
Xia YY, Lv QY, Yuan H, Wang JY (2021) Selective oxidation of alcohols to nitriles with high-efficient Co-[Bmim]Br/C catalyst system. Chem Pap 75:3957-3964. https://doi.org/10.1007/s11696-021-01593-z
Shi R, Wang F, Tana, Li Y, Huang X, Shen W (2010) A highly efficient Cu/La₂O₃ catalyst for transfer dehydrogenation of primary aliphatic alcohols. Green Chem 12:108-113. https://doi.org/10.1039/b919807p
ZaccheriaF, Ravasio N, Psaro R, Fusi A (2006) Synthetic scope of alcohol transfer dehydrogenation catalyzed by Cu/Al₂O₃: A new metallic catalyst with unusual selectivity. Chem Eur J 12 (2006) :6426-6431. https://doi.org/10.1002/chem.200501619
Cheng SQ, Weng XF, Wang QN, Zhou BC, Li WC, Li MR, He L, Wang DQ, Lu AH (2022) Defect‐rich BN‐supported Cu with superior dispersion for ethanol conversion to aldehyde and hydrogen. Chinese J Catal 43:1092-1100. https://doi.org/10.1016/s1872-2067(21)63891-3
Yu DN, Dai WL, Wu GJ, Guan NJ, Li LD (2019) Stabilizing copper species using zeolite for ethanol catalytic dehydrogenation to acetaldehyde. Chinese J Catal 40:1375-1384. https://doi.org/ 10.1016/s1872-2067(19)63378-4
Quan Y, Jin Y, Wang N, Zhao J, Ren J (2022) Efficient CuZn/SiO₂ lamellar catalysts for methanol dehydrogenation: New insights into the role of zinc. Appl Catal A-Gen 637:118585. https://doi.org/10.1016/j.apcata.2022.118585
Crivello ME, Pérez CF, Mendieta SN, Casuscelli SG, Eimer GA, Elías VR, Herrero ER (2008) n-Octyl alcohol dehydrogenation over copper catalysts. Catal Today 133:787-792. https://doi.org/10.1016/j.cattod.2007.11.037
Dixit M, Mishra M, Joshi PA, Shah DO (2013) Physico-chemical and catalytic properties of Mg–Al hydrotalcite and Mg–Al mixed oxide supported copper catalysts. J Ind Eng Chem. 19:458-468. https://doi.org/10.1016/j.jiec.2012.08.028
Lu TL, Du ZT, Liu JX, Chen C, Xu J (2014) Dehydrogenation of primary aliphatic alcohols to aldehydes over Cu‐Ni bimetallic catalysts. Chinese J. Catal. 35:1911-1916. https://doi.org/10.1016/s1872-2067(14)60208-4
Hosaka S, Kurniawan E, Yamada Y, Sato S (2023) Vapor-phase dehydrogenation of 1-decanol to decanal over Cu/SiO₂ catalyst prepared by organic additives-assisted impregnation. Appl Catal A-Gen 653:119079. https://doi.org/10.1016/j.apcata.2023.119079
Lu S, Zhang J, Meng H, Qin X, Huang J, Liang Y, Xiao FS (2023) Catalytic direct dehydrogenation of ethyl lactate to produce ethyl pyruvate over a synergetic Cu⁰/Cu⁺ interface. Appl Catal B-Environ 325:122329. https://doi.org/10.1016/j.apcatb.2022.122329
Mitsudome T, Mikami Y, Ebata K, Mizugaki T, Jitsukawa K, Kaneda K (2008) Copper nanoparticles on hydrotalcite as a heterogeneous catalyst for oxidant-free dehydrogenation of alcohols. Chem Commun 39:4804–4806. https://doi.org/10.1039/b809012b
Putro WS, Kojima T, Hara T, Ichikuni N, Shimazu S (2018) Acceptorless dehydrogenation of alcohols using Cu–Fe catalysts prepared from Cu–Fe layered double hydroxides as precursors. Catal Sci Technol 8:3010-3014. https://doi.org/10.1039/c8cy00655e
Wang F, Shi R, Liu ZQ, Shang PJ, Pang X, Shen S, Feng Z, Li C, Shen W (2013) Highly efficient dehydrogenation of primary aliphatic alcohols catalyzed by Cu nanoparticles dispersed on rod-shaped La₂O₂CO₃. ACS Catal 3:890-894. https://doi.org/10.1021/cs400255r
Kamiguchi S, Okumura K, Nagashima S, Chihara T (2015) Catalytic dehydrogenation of alcohol over solid-state molybdenum sulfide clusters with an octahedral metal framework. Mater Res Bull 72:188-190. https://doi.org/10.1016/j.materresbull.2015.07.027
Marella RK, Prasad Neeli CK, Rao Kamaraju SR, Burri DR (2012) Highly active Cu/MgO catalysts for selective dehydrogenation of benzyl alcohol into benzaldehyde using neither O₂ nor H₂ acceptor. Catal Sci Technol 2:1833–1838. https://doi.org/10.1039/c2cy20222k
Yuan E, Ni P, Xie J, Jian P, Hou X (2020) Highly efficient dehydrogenation of 2,3-butanediol induced by metal–support interface over Cu-SiO₂ catalysts. ACS Sustainable Chem Eng 8:15716-15731. https://doi.org/10.1021/acssuschemeng.0c05589
Prabu M, Ketpang K, Shanmugam S (2014) Hierarchical nanostructured NiCo₂O₄ as an efficient bifunctional non-precious metal catalyst for rechargeable zinc-air batteries. Nanoscale 6:3173-3181. https://doi.org/10.1039/c3nr05835b
Jiang J, Zhang A, Li L, Ai L (2015) Nickel–cobalt layered double hydroxide nanosheets as high-performance electrocatalyst for oxygen evolution reaction. J Power Sources 278:445-451. https://doi.org/10.1016/j.jpowsour.2014.12.085
Song T, Qi Y, Zhao C, Wu P, Li X (2022) Sorbitol-derived carbon overlayers encapsulated Cu nanoparticles on SiO₂: Stable and efficient for the continuous hydrogenation of ethylene carbonate. iScience 25:105239. https://doi.org/10.1016/j.isci.2022.105239
Chen H, Lin W, Zhang Z, Yang Z, Jie K, Fu J, Yang SZ, Dai S (2020) Facile benzene reduction promoted by a synergistically coupled Cu–Co–Ce ternary mixed oxide. Chem Sci 11:5766-5771. https://doi.org/10.1039/d0sc02238a
Koppadi KS, Chada RR, Gurram VRB, Kancharakuntla SR, Kamaraju SRR, Burri DR (2018) Synthesis of hydrocinnamaldehyde via vapor phase dehydrogenation of hydrocinnamyl alcohol over rice-derived MgO-supported copper catalysts. ChemistrySelect 3:3079-3086. https://doi.org/10.1002/slct.201702980
Nauert SL, Savereide L, Notestein JM (2018) Role of support lewis acid strength in copper-oxide-catalyzed oxidative dehydrogenation of cyclohexane. ACS Catal 8:7598-7607. https://doi.org/10.1021/acscatal.8b00935
Miura H, Nakahara K, Kitajima T, Shishido T (2017) Concerted functions of surface acid–base pairs and supported copper catalysts for dehydrogenative synthesis of esters from primary alcohols. ACS Omega 2:6167-6173. https://doi.org/10.1021/acsomega.7b01142
Sato AG, Volanti DP, de Freitas IC, Longo E, Bueno JMC (2012) Site-selective ethanol conversion over supported copper catalysts. Catal Commun 26:122-126. https://doi.org/10.1016/j.catcom.2012.05.008
Keller TC, Isabettini S, Verboekend D, Rodrigues EG, Pérez-Ramírez J (2014) Hierarchical high-silica zeolites as superior base catalysts. Chem Sci 5:677-684. https://doi.org/10.1039/c3sc51937f
Gaertner CA, Serrano-Ruiz JC, Braden DJ, Dumesic JA (2009) Catalytic coupling of carboxylic acids by ketonization as a processing step in biomass conversion. J Catal 266:71-78. https://doi.org/10.1016/j.jcat.2009.05.015
Shen W, Tompsett GA, Xing R, Curtis Conner W, Huber GW (2012) Vapor phase butanal self-condensation over unsupported and supported alkaline earth metal oxides. J Catal 286:248-259. https://doi.org/10.1016/j.jcat.2011.11.009

Download PDF

Reviewers agreed at journal
21 Jan, 2024
Reviewers invited by journal
20 Jan, 2024
Editor invited by journal
14 Dec, 2023
Editor assigned by journal
14 Dec, 2023
First submitted to journal
13 Dec, 2023

You are reading this latest preprint version

Efficient dehydrogenation of dodecanol to dodecanal in a continuous fixed bed reactor over supported Cu catalyst

Status:

Version 1

Abstract

Figures

Introduction

Experimental

Preparation of Cu-based catalysts

Characterization of catalysts

The procedure for the catalytic dehydrogenation of dodecanol

Results and discussion

Catalysts characterization

Catalytic performance of Cu-based catalysts in the dehydrogenation of dodecanol

Conclusions

Declarations

References

Status:

Version 1