Application of Mo / SiO2-Cu / ZnO / Al2O3 catalyst in preparation of ethanol by DMO hydrogenation
By using a two-stage packed system of Mo/SiO2-Cu/ZnO/Al2O3 catalyst, the problems of catalyst deactivation and low ethanol yield in the traditional ethylene glycol hydrogenation to ethanol process were solved, achieving efficient conversion of dimethyl oxalate to methyl acetate and ethanol, improving ethanol selectivity and reducing energy consumption.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA UNIV OF MINING & TECH
- Filing Date
- 2025-07-11
- Publication Date
- 2026-06-23
AI Technical Summary
Traditional ethylene glycol hydrogenation to ethanol processes suffer from rapid catalyst deactivation due to carbon deposition and sintering, resulting in high operating costs, low ethanol yield, numerous byproducts, high energy consumption, and difficulty in achieving efficient conversion of dimethyl oxalate to methyl acetate at low temperatures.
A two-stage packed system of Mo/SiO2-Cu/ZnO/Al2O3 catalysts was adopted. The Mo/SiO2 catalyst first converted dimethyl oxalate to methyl acetate, and the Cu/ZnO/Al2O3 catalyst then converted methyl acetate to ethanol. The Mo/SiO2 catalyst was prepared by hydrogen thermal reduction method to enhance its hydrogenation activity, and the hydrogenation reaction was carried out at 220℃.
The high-selectivity conversion of dimethyl oxalate to methyl acetate and ethanol was achieved at low temperatures, with the ethanol selectivity increasing from 21% to 70%. This significantly reduced byproduct formation, lowered energy costs, and improved catalyst stability and ethanol yield.
Smart Images
Figure CN120961144B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalytic hydrogenation of dimethyl oxalate to ethanol, specifically involving the application of Mo / SiO2-Cu / ZnO / Al2O3 catalyst in the catalytic hydrogenation of DMO to ethanol. Background Technology
[0002] The industrial application of coal-to-ethylene glycol technology has promoted the diversification of syngas catalytic conversion routes. Among them, dimethyl oxalate (DMO) hydrogenation to ethanol (EtOH), as an extension of the DMO-EG process, is of great significance for meeting the growing market demand for ethanol. However, the traditional ethylene glycol (EG) hydrogenation to EtOH process has significant technical bottlenecks: the reaction needs to be carried out at high temperatures (>260℃), which leads to rapid deactivation of the catalyst due to carbon deposition and sintering, thereby increasing the operating costs of catalyst regeneration and replacement. Recent studies have shown that there are two competing reaction pathways for DMO hydrogenation to EtOH: (1) an indirect hydrogenation pathway via an ethylene glycol (EG) intermediate; and (2) a direct hydrogenation pathway via a methyl acetate (MA) intermediate. Mechanistic analysis reveals that the second pathway offers significant advantages: the MA hydrogenation reaction can efficiently hydrogenate to ethanol at lower temperatures (<220℃), a characteristic that brings several technological advantages: First, low-temperature operation effectively suppresses carbon deposition and metal sintering on the catalyst surface; second, improved product selectivity significantly reduces the formation of C3-C4 alcohols and ethers as byproducts; and most importantly, the increased ethanol yield significantly reduces the energy consumption cost of product separation. These characteristics make the DMO-MA-EtOH pathway exhibit significant economic viability and feasibility in industrial applications, providing a more optimized technical solution for coal-based ethanol production. The key to this pathway lies in achieving the conversion of DMO to MA at low temperatures, thereby enabling subsequent hydrogenation to EtOH production.
[0003] Recent studies have shown that transition metal carbides (such as Mo₂C and Fe₅C₂) can modulate the conversion pathway of methyl glycolate (MG), promoting the selective conversion of dimethyl oxalate (DMO) to methyl acetate (MA) rather than ethylene glycol (EG). This provides a research direction for achieving the conversion of DMO to MA at low temperatures. Mo-based catalysts have been widely used in reactions such as hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrodeoxygenation (HDO), but their industrial applications are mostly limited to compound forms (such as MoS₂, Mo₂C, and MoO). x Molybdenum (MoP, Mo2N) can be used as an additive to construct synergistic catalytic systems with active metals (Ni, Co, W, etc.). However, elemental molybdenum (Mo) 0 The catalytic performance of highly dispersed Mo in hydrogenation reactions has not been fully studied, mainly due to limitations in its properties. 0The synthesis of catalysts presents a challenge. Therefore, a method for synthesizing elemental molybdenum (Mo) for hydrogenation reactions is sought. 0 The use of catalysts, and their coupling with other catalysts, is of great significance for the hydrogenation of dimethyl oxalate to ethanol. Summary of the Invention
[0004] The purpose of this invention is to provide the application of Mo / SiO2-Cu / ZnO / Al2O3 catalyst in the hydrogenation catalytic preparation of ethanol from DMO. The simultaneous application of Mo / SiO2 catalyst and Cu / ZnO / Al2O3 catalyst in the synergistic catalytic preparation of ethanol from dimethyl oxalate hydrogenation exhibits stronger hydrogenation activity, excellent catalytic activity and higher ethanol selectivity.
[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:
[0006] The application of Mo / SiO2-Cu / ZnO / Al2O3 catalyst in the hydrogenation catalytic production of ethanol from DMO involves the Mo / SiO2 catalyst in the Mo / SiO2-Cu / ZnO / Al2O3 catalyst first catalyzing the hydrogenation of dimethyl oxalate to methyl acetate, and then the Cu / ZnO / Al2O3 catalyst in the Mo / SiO2-Cu / ZnO / Al2O3 catalyst catalyzing the hydrogenation of methyl acetate to ethanol.
[0007] Furthermore, the Mo / SiO2-Cu / ZnO / Al2O3 catalyst is a two-stage packed catalytic system, and the packing method is divided into Mo-CuZnAl two-stage packing, Mo-mix-CuZnAl physical mixing packing, and CuZnAl-Mo two-stage packing. The Mo-CuZnAl two-stage packing involves filling the upper section of the reaction tube with Mo / SiO2 catalyst and the lower section with Cu / ZnO / Al2O3 catalyst. The Mo-mix-CuZnAl physical mixing packing involves physically mixing Mo / SiO2 catalyst and Cu / ZnO / Al2O3 catalyst in equal mass and then packing them into the reaction tube. The CuZnAl-Mo two-stage packing involves filling the upper section of the reaction tube with Cu / ZnO / Al2O3 catalyst and the lower section with Mo / SiO2 catalyst.
[0008] Furthermore, the specific application process is as follows: hydrogen is used as the feed gas, and a methanol solution containing 13% dimethyl oxalate by mass is used as the feed liquid; under the synergistic catalytic action of Mo / SiO2-Cu / ZnO / Al2O3 catalyst, hydrogenation to synthesize ethanol is carried out at 220℃; the molar ratio between hydrogen and dimethyl oxalate is 100:1, the reaction pressure is 2 MPa, and the liquid hourly space velocity is 0.1 h⁻¹. -1 .
[0009] Preferably, the Mo / SiO2 catalyst comprises an active component and a support, wherein the active component is elemental Mo and the support is virus-like SiO2, wherein the content of elemental Mo is 11-34% of the total mass of the catalyst and the content of virus-like SiO2 is 66-89% of the total mass of the catalyst.
[0010] Furthermore, the preparation method of the Mo / SiO2 catalyst includes the following steps:
[0011] S1. Preparation of carrier: Dissolve hexadecyltrimethylammonium bromide in water, add NaOH solution and stir, then add cyclohexane solution containing tetraethyl orthosilicate, stir, centrifuge, collect precipitate, wash precipitate with water and ethanol several times, dry the obtained sample and calcine in muffle furnace to obtain virus-like SiO2.
[0012] S2, Weigh out an appropriate amount of (NH4)6Mo7O 24 Add 4H2O to the reaction vessel, then add water to make (NH4)6Mo7O 24 • Dissolved by ultrasonication with 4H2O, then the virus-like SiO2 prepared in step S1 was added, ultrasonicated again and impregnated at room temperature for a period of time, then rotary evaporated until the water evaporated, then transferred to an oven to dry and pressed into tablets, and then cut and screened to obtain the catalyst precursor of the target mesh size.
[0013] S3. The catalyst precursor obtained in step S2 is reduced with hydrogen in a fixed-bed reactor, and then cooled by purging with inert gas to obtain Mo / SiO2 catalysts with different Mo contents.
[0014] Preferably, in step S1, the mass-to-volume ratio of hexadecyltrimethylammonium bromide to water is 4.2 g: 100 mL; the concentration of NaOH solution is 0.1 M; the concentration of tetraethyl orthosilicate in the cyclohexane solution containing tetraethyl orthosilicate is 20 v / v%; and the volume ratio of the cyclohexane solution containing tetraethyl orthosilicate to water is 0.4:1.
[0015] Preferably, in step S1, the stirring temperature is 60°C; drying is carried out in an oven at 100°C for 12 hours; and calcination is carried out in a muffle furnace at 550°C for 5 hours.
[0016] Preferably, in step S2, (NH4)6Mo7O 24 The mass ratio between 4H2O and the virus-like SiO2 prepared in step S1 is (0.2445~0.9321):1; (NH4)6Mo7O is dissolved by ultrasonication. 24 • 4H2O for 5 min; after adding SiO2, sonicate again for 30 min, then soak at room temperature for 24 h.
[0017] Preferably, in step S2, rotary evaporation is performed at 75°C; drying is carried out in an oven at 100°C for 12 hours; the target mesh size is 40-60 mesh.
[0018] Preferably, in step S3, H2 is introduced at 500°C at a rate of 100 mL / min for 24 h for reduction, followed by purging and cooling with Ar at a rate of 100 mL / min.
[0019] Compared with the prior art, the present invention has the following advantages:
[0020] (1) This invention provides a Mo / SiO2-Cu / ZnO / Al2O3 dual-stage packed catalytic system for the hydrogenation of dimethyl oxalate to ethanol; wherein the Mo / SiO2 catalyst can achieve a high conversion of DMO to MA, and on this basis, the Cu / ZnO / Al2O3 catalyst is added to further hydrogenate MA to ethanol through a series reaction, which greatly improves the selectivity of ethanol.
[0021] (2) The present invention uses hydrogen thermal reduction method to prepare Mo / SiO2 catalyst. Instead of calcining the ammonium molybdate precursor in a muffle furnace, it is directly decomposed at high temperature under 500℃ and H2 conditions to obtain a reduced Mo / SiO2 catalyst with strong hydrogenation activity. The strong interaction between virus-like SiO2 and Mo enhances the oxidation resistance of reduced Mo, so that Mo / SiO2 can be stored in air and is not easily affected by instantaneous oxidation upon contact with air.
[0022] (3) When the Mo / SiO2 catalyst prepared in this invention is applied to the hydrogenation of dimethyl oxalate to methyl acetate, under the reaction conditions of 220°C, dimethyl oxalate (DMO) can be completely converted and highly selectively converted to methyl acetate (MA, ~70%) and ethanol (EtOH, ~21%). This result provides a good reaction basis for the subsequent directional conversion of MA to EtOH. Attached Figure Description
[0023] Figure 1 The images show the X-ray diffraction patterns of the Mo / SiO2 catalyst and the MoO2 / SiO2 catalyst prepared in the specific embodiments.
[0024] Figure 2 These are the H2-TPR spectra of the Mo / SiO2 catalyst and the MoO2 / SiO2 catalyst prepared in the specific embodiments;
[0025] Figure 3 These are the XPS spectra of the Mo / SiO2 catalyst and the MoO2 / SiO2 catalyst prepared in the specific embodiments.
[0026] Figure 4This is a comparison chart of the catalytic performance test results of the Mo / SiO2 catalyst and the MoO2 / SiO2 catalyst prepared in the specific implementation method;
[0027] Figure 5 This is a comparison chart showing the catalytic performance test results of the Mo / SiO2-Cu / ZnO / Al2O3 two-stage catalytic system in Examples 1-3 and the Cu / ZnO / Al2O3 catalyst in Comparative Example 1. Detailed Implementation
[0028] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0029] Unless otherwise specified, all raw materials and reagents used in the following examples are commercially available products with a purity of analytical grade or higher.
[0030] The Cu / ZnO / Al2O3 catalyst used in the following examples was prepared according to the following method:
[0031] A Cu / ZnO / Al₂O₃ catalyst with a Cu / Zn / Al molar ratio of 1:1:0.2 was prepared by urea hydrolysis. 14.4144 g of urea, 5.7984 g of copper nitrate trihydrate, 7.1398 g of zinc nitrate hexahydrate, and 1.8006 g of aluminum nitrate nonahydrate were added to 300 mL of deionized water and heated at 95 °C for 6 h with constant stirring at 500 rpm. The resulting precipitate was then filtered, washed with sufficient deionized water, and dried at 100 °C for 12 h. Finally, the obtained catalyst precursor was calcined in a muffle furnace at a rate of 2 °C / min to 350 °C and held for 2 h.
[0032] The Mo / SiO2 catalyst used in the following examples includes an active component and a support. The active component is elemental Mo, and the support is virus-like SiO2. The content of elemental Mo is 11% to 34% of the total mass of the catalyst, and the content of virus-like SiO2 is 66% to 89% of the total mass of the catalyst.
[0033] The preparation method of the Mo / SiO2 catalyst used in the following examples includes the following steps:
[0034] S1. Preparation of the carrier: 12.6 g of cetyltrimethylammonium bromide (CTAB) was dissolved in 300 mL of H2O, 4.8 mL of 0.1 M NaOH solution was added, and the mixture was stirred at 60 °C for 2 h. Then, 120 mL of cyclohexane solution containing tetraethyl orthosilicate was added. The concentration of tetraethyl orthosilicate in the cyclohexane solution containing tetraethyl orthosilicate was 20 v / v%. The mixture was then stirred at 60 °C for 48 h. The precipitate was centrifuged and collected. The precipitate was washed several times with water and ethanol. The obtained sample was dried in an oven at 100 °C for 12 h and then calcined in a muffle furnace at 550 °C for 5 h to finally obtain virus-like SiO2.
[0035] S2, Weigh out (NH4)6Mo7O 24 · Add 5 mL of H2O to a round-bottom flask, sonicate to dissolve for 5 min, then add 1 g of virus-like SiO2 prepared in step S1, sonicate again for 30 min, and impregnate at room temperature for 24 h. Then, rotary evaporate at 75 °C until the water evaporates, then transfer to an oven at 100 °C to dry for 12 h, then press into tablets and cut and screen catalyst precursors with a mesh size of 40-60.
[0036] S3. The catalyst precursor obtained in step S2 is reduced in a fixed bed reactor at 500°C by passing 100 mL / min H2 for 24 h, and then purged and cooled by 100 mL / min Ar to obtain the Mo / SiO2 catalyst.
[0037] In the above method for preparing Mo / SiO2 catalyst, when 0.2445g of (NH4)6Mo7O is weighed in step S2... 24 When ·4H2O is added, step S3 yields a Mo / SiO2 catalyst supported on 11.7% Mo; when 0.5777g of (NH4)6Mo7O is weighed in step S2... 24 When ·4H2O is added, step S3 yields a Mo / SiO2 catalyst supported on 23.8% Mo; when 0.9321g of (NH4)6Mo7O is weighed in step S2... 24 When 4H2O is applied, step S3 yields a Mo / SiO2 catalyst supported on 33.6% Mo;
[0038] A MoO2 / SiO2 catalyst includes an active component and a support, wherein the active component is MoO2 and the support is virus-like SiO2, wherein the content of MoO2 is 25% of the total mass of the catalyst and the content of virus-like SiO2 is 75% of the total mass of the catalyst.
[0039] The preparation method of the above-mentioned MoO2 / SiO2 catalyst includes the following steps:
[0040] S1. Preparation of the carrier: This step is consistent with Example 1;
[0041] S2, Weigh out 0.5777g of (NH4)6Mo7O 24 · Add 5 mL of H2O to a round-bottom flask, sonicate to dissolve for 5 min, then add 1 g of virus-like SiO2 prepared in step S1, sonicate again for 30 min, impregnate at room temperature for 24 h, then rotary evaporate at 75 °C until the water evaporates, then transfer to an oven at 100 °C to dry for 12 h, then calcine in a muffle furnace by introducing air at 2 °C / min to raise the temperature to 500 °C and hold for 4 h to obtain the catalyst precursor;
[0042] S3. The catalyst precursor obtained in step S2 is reduced in a fixed-bed reactor at 500°C by passing 100 mL / min H2 for 24 h, and then purged and cooled by 100 mL / min Ar to obtain the MoO2 / SiO2 catalyst.
[0043] Two catalysts, Mo / SiO2 and MoO2 / SiO2, with the same amount of ammonium molybdate impregnation, were successfully prepared by differentiating the treatment of ammonium molybdate-impregnated catalysts using hydrogen thermal reduction and muffle furnace calcination. XRD analysis showed that both methods formed characteristic crystalline phases: the catalyst obtained by hydrogen thermal reduction was dominated by elemental Mo, while the catalyst obtained by muffle furnace calcination was dominated by MoO2. Furthermore, the peak intensity of the MoO2 phase was significantly higher than that of the elemental Mo phase. This difference stems from the fundamental difference between the two preparation methods: during muffle furnace calcination, the high-temperature oxidation environment easily induces the sintering effect of MoO2 particles, while strong metal-support interaction (SMSI) promotes particle aggregation; whereas the hydrogen thermal decomposition environment achieves nanoscale dispersion through a dual mechanism—H2 not only reduces the oxide to a metallic state, but its reducing atmosphere also effectively suppresses surface migration energy, hindering the grain oxidation and sintering kinetics. Meanwhile, the strong interaction between the virus-like SiO2 and Mo inhibits the deep oxidation of elemental Mo in air. Therefore, the 25% Mo / SiO2 catalyst obtained by the hydrogen thermal reduction method can exhibit reduced elemental Mo. Furthermore, the strong electronic interactions (such as Mo-O-Si bonding) between the virus-like SiO2 support and Mo species effectively stabilize the elemental state of metallic Mo, significantly suppressing its tendency for deep oxidation in air. Therefore, the Mo / SiO2 catalyst prepared by the hydrogen thermal reduction method can stably maintain the elemental state of metallic Mo, rather than transforming it into a higher-valence oxide.
[0044] like Figure 2 As shown, the Mo / SiO2 catalyst prepared by the hydrogen thermal reduction method exhibits a significantly lower reduction peak temperature than MoO2 / SiO2 because only surface oxidation occurs. Specifically, Mo / SiO2 shows two reduction peaks in the ranges of 300-400℃ and 500-600℃, corresponding to Mo... 6+ →Mo 4+ and Mo4+ →Mo 0 The gradual reduction process. In contrast, MoO2 / SiO2 prepared by muffle furnace calcination exhibits a strong reduction peak in the 500-600℃ range, corresponding to the Mo in MoO2. 4+ →Mo 0 The high H2 consumption during the reduction process confirms the reduction characteristics of the MoO2 crystalline phase. Of particular note is the rising peak trend that appears after 700℃, which confirms the existence of a strong interaction (SMSI) between MoO2 and the SiO2 support. This interaction may significantly increase the reduction barrier of Mo species by forming a stable Mo-O-Si interface structure.
[0045] The Mo / SiO2 and MoO2 / SiO2 catalysts were characterized by XPS, such as... Figure 3 The Mo3d energy spectrum shown was fitted using the following fixed parameters: 3d 5 / 2 and 3D 3 / 2 The spacing between the spin-orbit splitting peaks was fixed at 3.2 eV, the peak area ratio was fixed at 3:2, and the two peaks maintained the same full width at half maximum (FWHM). The characteristic peaks at 228.74 eV, 229.83 eV, and 232.05 eV were assigned to Mo, respectively. 4+ 3D 5 / 2 Mo 5+ 3D 5 / 2 and Mo 6+ 3D 5 / 2 XPS spectra of Mo / SiO2 and MoO2 / SiO2 were compared. No Mo was detected in MoO2 / SiO2. 0 The presence of Mo is evident, with the valence states of Mo primarily being +6 and +4, and the intermediate valence state of +5 being less abundant. Mo can be detected in Mo / SiO2. 0 The peak is visible, but oxidized Mo still exists. 4+ Mo 5+ And Mo 6+ This may be because when Mo is relatively dispersed, as evidenced by the high dispersion and weak diffraction peaks observed in XRD, it easily leads to a high degree of surface oxidation. Simultaneously, the binding energy of Mo3d in Mo / SiO2 shifts to a lower level relative to the overall MoO2 / SiO2 structure. This may be due to molybdenum existing in a metallic state (Mo... 0 ) or low oxidation state (Mo) 4+ / Mo 5+ The presence of Mo in MoO2 / SiO2 results in a high valence electron density, which weakens the nuclear binding of inner-shell electrons and leads to a lower binding energy. 6+ The strong electron-withdrawing effect enhances the attraction of inner-shell electrons to the nucleus, thus increasing the binding energy.
[0046] Example 1
[0047] The specific catalytic performance of a two-stage packed catalytic system consisting of 23.8% Mo / SiO2 catalyst and Cu / ZnO / Al2O3 catalyst was investigated in a fixed-bed reactor for the selective hydrogenation of dimethyl oxalate to ethanol.
[0048] A stainless steel reaction tube was used as the reactor, with an outer diameter of 20 mm, an inner diameter of 8 mm, and a length of 300 mm. The catalyst loading was 0.4 g. After the reaction tail gas was condensed and separated, the product was quantitatively analyzed using a Fuli GC9790PLUS gas chromatograph.
[0049] Conversion rate and selectivity were both calculated using the normalization method:
[0050] Conversion rate (%) = (1-A) DMO f DMO / ∑A i f i )×100%;
[0051] Selectivity (%) = (A) i f i / ∑A i f i )×100%;
[0052] Where A i Indicates the peak area of FID chromatography; f i This represents the relative molar correction factor for FID.
[0053] Reaction conditions: Hydrogen was used as the feed gas, and a methanol solution containing 13% dimethyl oxalate was used as the feed liquid. The molar ratio of hydrogen to dimethyl oxalate was 100:1, the reaction temperature was 220℃, the reaction pressure was 2 MPa, and the liquid hourly space velocity was 0.1 h⁻¹. -1 .
[0054] The 23.8% Mo / SiO2 catalyst and the Cu / ZnO / Al2O3 catalyst were packed in a two-stage manner. First, 0.4g of Cu / ZnO / Al2O3 catalyst was packed in the lower section of the reaction tube, with 0.2g of quartz sand added in the middle as an inert spacer to prevent direct mixing of the two catalyst stages and to adjust the temperature gradient between the two catalyst stages. Then, 0.4g of 23.8% Mo / SiO2 catalyst was added in the upper section. Both the catalyst and the quartz sand were 40-60 mesh.
[0055] Example 2
[0056] The difference between this embodiment and Example 1 lies in the filling method of the 23.8% Mo / SiO2 catalyst and the Cu / ZnO / Al2O3 catalyst. In this embodiment, a physical mixing filling method is used. 0.4g of Cu / ZnO / Al2O3 catalyst, 0.2g of quartz sand, and 0.4g of 23.8% Mo / SiO2 catalyst are physically mixed evenly and then filled into the reaction tube. Both the catalyst and the quartz sand are 40-60 mesh. All other processes are the same as in Example 1.
[0057] Example 3
[0058] The difference between this embodiment and Example 1 lies in the two-stage filling method of the 23.8% Mo / SiO2 catalyst and the Cu / ZnO / Al2O3 catalyst. First, 0.4g of 23.8% Mo / SiO2 catalyst is loaded into the lower section of the reaction tube, with 0.2g of quartz sand added in the middle as an inert spacer to prevent direct mixing of the two catalysts and to adjust the temperature gradient between the two catalysts. Then, 0.4g of Cu / ZnO / Al2O3 catalyst is added to the upper section. Both the catalyst and the quartz sand are 40-60 mesh. All other processes remain the same as in Example 1.
[0059] Example 4
[0060] The difference between this embodiment and Example 1 is that the 11.7% Mo / SiO2 catalyst and the Cu / ZnO / Al2O3 catalyst are packed in a two-stage manner. First, 0.4g of Cu / ZnO / Al2O3 catalyst is packed in the lower section of the reaction tube, with 0.2g of quartz sand added in the middle as an inert spacer to prevent direct mixing of the two catalyst stages and to adjust the temperature gradient between the two catalyst stages. Then, 0.4g of 11.7% Mo / SiO2 catalyst is added in the upper section. Both the catalyst and the quartz sand are 40-60 mesh. All other processes are the same as in Example 1.
[0061] Example 5
[0062] The difference between this embodiment and Example 1 is that the 33.6% Mo / SiO2 catalyst and the Cu / ZnO / Al2O3 catalyst are packed in a two-stage manner. First, 0.4g of Cu / ZnO / Al2O3 catalyst is packed in the lower section of the reaction tube, with 0.2g of quartz sand added in the middle as an inert spacer to prevent direct mixing of the two catalyst stages and to adjust the temperature gradient between the two catalyst stages. Then, 0.4g of 33.6% Mo / SiO2 catalyst is added in the upper section. Both the catalyst and the quartz sand are 40-60 mesh. All other processes are the same as in Example 1.
[0063] Comparative Example 1
[0064] The difference between this comparative example and Example 1 is that the two-stage packed system of Mo / SiO2 catalyst and Cu / ZnO / Al2O3 catalyst is not used. Instead, only 0.4g of Cu / ZnO / Al2O3 catalyst is added to the reaction tube. All other processes are the same as in Example 1.
[0065] Comparative Example 2
[0066] The difference between this comparative example and Example 1 is that the two-stage packed system of Mo / SiO2 catalyst and Cu / ZnO / Al2O3 catalyst is not used. Instead, only 0.4g of 23.8% Mo / SiO2 catalyst is added to the reaction tube; all other processes are the same as in Example 1.
[0067] Comparative Example 3
[0068] The difference between this comparative example and Example 1 is that the two-stage packed system of Mo / SiO2 catalyst and Cu / ZnO / Al2O3 catalyst is not used. Instead, only 0.4g of MoO2 / SiO2 catalyst is added to the reaction tube (the amount of ammonium molybdate impregnation is the same as in Example 1); all other processes are the same as in Example 1.
[0069] Table 1. Catalytic performance test results of Mo / SiO2-Cu / ZnO / Al2O3 two-stage catalytic systems with different Mo loadings.
[0070] Catalyst types Methyl acetate selectivity / % Ethanol selectivity / % Dimethyl oxalate conversion rate / % 11.7% Mo-CuZnAl 10.2％ 68.7％ 100％ 23.8% Mo-CuZnAl 9.1％ 70.1％ 100％ 33.6% Mo-CuZnAl 8.8％ 69.5％ 100％
[0071] The reaction results are as follows Figure 4 (Comparative Examples 2 and 3) and Figure 5 (As shown in Examples 1-3 and Comparative Example 1):
[0072] like Figure 4 As shown, in the Mo / SiO2-catalyzed hydrogenation reaction of dimethyl oxalate, the selectivity of EtOH is approximately 21%, and the selectivity of MA is approximately 70%. At this point, the conversion rate of DMO reaches 99%, demonstrating the best reaction activity. The byproduct methyl formate (MF) shows the opposite trend; the selectivity of MF is lowest when the hydrogenation activity is strongest. This is because MF and MA compete in this hydrogenation reaction. MA is obtained by further hydrogenation of MG, the initial hydrogenation product of DMO, while MF is a byproduct generated by the cleavage of methyl glycolate (MG). Mo / SiO2 and MoO2 / SiO2 catalysts prepared by hydrogen thermal reduction and direct air calcination, respectively, were tested for activity under the same conditions. The Mo / SiO2 catalyst showed a significantly stronger activity advantage compared to Mo / SiO2, while the latter had a DMO conversion rate of less than 38% and, due to its low hydrogenation activity, produced MG (methyl glycolate), the previous hydrogenation product of MA.
[0073] The activity of the two-stage catalytic systems obtained using the three catalyst loading methods shown in Examples 1-3 was compared with that of the Cu / ZnO / Al2O3 catalyst prepared in Comparative Example 1. Figure 5 The activity test results show that loading the upper section with Mo / SiO2 and the lower section with Cu / ZnO / Al2O3 is most favorable for the conversion of DMO to EtOH. At this point, the conversion rate of DMO reaches 100%, the selectivity of EtOH reaches 70%, and the selectivity of MA is less than 10%. Simultaneously, byproducts such as MF (methyl formate) due to acidic sites of the catalyst and C3-C4 alcohols generated from basic sites are produced. Compared to the pure Mo / SiO2 catalyst, this significantly increases the EtOH content from 21% to 70%. As shown in Table 1, the Mo / SiO2 catalysts prepared in Examples 4 and 5 with different loadings (11.7% and 33.6%) can also achieve similar synergistic catalytic effects with Cu / ZnO / Al2O3. This is because the MA generated under the catalysis of Mo / SiO2 enters the Cu / ZnO / Al2O3 section and is then absorbed by the highly dispersed Cu... 0 Selective hydrogenation of ester groups occurs at the active site: Cu 0 Providing an electron-rich environment promotes MA adsorption and the cleavage of the C-OCH3 bond, generating acetyl groups and methanol. ZnO enhances Cu adsorption through electronic effects (Cu-ZnO interface). 0 The polarization of C=O allows for rapid hydrogenation of the acetyl group to ethanol. The basic sites of Al2O3 neutralize potential acidic byproducts (such as acetic acid) generated during the reaction, preventing catalyst poisoning. However, the single-component Cu / ZnO / Al2O3 catalyst exhibits low activity in the DMO hydrogenation reaction, with a DMO conversion of only 73%, and the main product is ethylene glycol (EG) rather than EtOH. This is primarily due to the insufficient selective hydrogenation ability of its active sites on the C=O bond in the DMO molecule, and the low activity of Cu. 0 It tends to hydrogenate both C=O bonds simultaneously, leading to excessive hydrogenation to produce ethylene glycol (EG) or the breaking of C=C bonds to produce byproducts such as CH4 / CO, rather than selectively generating the key intermediate MA for further hydrogenation to EtOH.
[0074] The design of a two-stage catalytic system of Mo / SiO2 and Cu / ZnO / Al2O3, through a tandem pathway of selective activation of C=O bonds → directional hydrogenation of ester bonds, achieves precise control of the reaction intermediate (MA), thereby increasing the ethanol selectivity from ~21% in single-stage Mo-based catalysts to >70%. This mechanism highlights the core advantages of two-stage catalysts in multi-step complex reactions. By synergistically designing spatially partitioned catalyst configurations and reaction conditions, the key challenges of active site compatibility and intermediate regulation in the multi-step tandem reaction of DMO hydrogenation are solved. Simultaneously, an inert silica sand transition layer is introduced between the two catalyst stages to regulate the concentration gradient and temperature transfer of the intermediate (MA), avoiding Cu sintering caused by thermal shock.
[0075] In summary, this invention provides a Mo / SiO2-Cu / ZnO / Al2O3 dual-stage packed catalytic system for the hydrogenation of dimethyl oxalate to ethanol. The Mo / SiO2 catalyst enables a high conversion of DMO to MA, and the addition of the Cu / ZnO / Al2O3 catalyst, through a tandem reaction, synergistically catalyzes the further hydrogenation of MA to ethanol, significantly improving the selectivity of ethanol production. This provides inspiration for the rational design of industrial technologies for the hydrogenation of DMO to ethanol.
[0076] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. Application of Mo / SiO2-Cu / ZnO / Al2O3 catalyst in the hydrogenation of DMO to ethanol: The Mo / SiO2 catalyst in the Mo / SiO2-Cu / ZnO / Al2O3 catalyst first catalyzes the hydrogenation of dimethyl oxalate to methyl acetate, and the Cu / ZnO / Al2O3 catalyst in the Mo / SiO2-Cu / ZnO / Al2O3 catalyst then catalyzes the hydrogenation of methyl acetate to ethanol. The Mo / SiO2-Cu / ZnO / Al2O3 catalyst is a two-stage packed catalytic system, with three packing methods: Mo-CuZnAl two-stage packing, Mo-mix-CuZnAl physical mixing packing, and CuZnAl-Mo two-stage packing. The Mo-CuZnAl two-stage packing involves filling the upper section of the reaction tube with Mo / SiO2 catalyst and the lower section with Cu / ZnO / Al2O3 catalyst. The Mo-mix-CuZnAl physical mixing packing involves physically mixing Mo / SiO2 catalyst and Cu / ZnO / Al2O3 catalyst in equal mass before packing them into the reaction tube. The CuZnAl-Mo two-stage packing involves filling the upper section of the reaction tube with Cu / ZnO / Al2O3 catalyst and the lower section with Mo / SiO2 catalyst. The specific application process is as follows: hydrogen is used as the feed gas, and a methanol solution containing 13% dimethyl oxalate (MCO) is used as the feed liquid; under the synergistic catalytic action of Mo / SiO2-Cu / ZnO / Al2O3 catalyst, hydrogenation to synthesize ethanol is carried out at 220 °C; the molar ratio of hydrogen to dimethyl oxalate is 100:1, the reaction pressure is 2 MPa, and the liquid hourly space velocity (LISH) is 0.1 h⁻¹. -1 ; The Mo / SiO2 catalyst comprises an active component and a support, wherein the active component is elemental Mo and the support is virus-like SiO2, wherein the content of elemental Mo is 11-34% of the total mass of the catalyst and the content of virus-like SiO2 is 66-89% of the total mass of the catalyst; The preparation method of the Mo / SiO2 catalyst includes the following steps: S1. Preparation of carrier: Dissolve hexadecyltrimethylammonium bromide in water, add NaOH solution and stir, then add cyclohexane solution containing tetraethyl orthosilicate, stir, centrifuge, collect precipitate, wash precipitate with water and ethanol several times, dry the obtained sample and calcine in muffle furnace to obtain virus-like SiO2. S2, Weigh out an appropriate amount of (NH4)6Mo7O 24 Add 4H2O to the reaction vessel, then add water to make (NH4)6Mo7O 24 • Dissolve the catalyst by ultrasonication with 4H2O, then add the virus-like SiO2 prepared in step S1, ultrasonicate again, impregnate at room temperature for a period of time, then rotary evaporate until the water evaporates, continue to transfer to an oven for drying, then press into tablets, and cut and screen to obtain the catalyst precursor with the target mesh size; S3, reduce the catalyst precursor obtained in step S2 in a fixed bed reactor at 500 °C by passing 100 mL / min H2 for 24 h, and then purge and cool it with 100 mL / min Ar to obtain Mo / SiO2 catalysts with different Mo contents.
2. The application according to claim 1, characterized in that, In step S1, the mass-to-volume ratio of hexadecyltrimethylammonium bromide to water is 4.2 g: 100 mL; the concentration of NaOH solution is 0.1 M; the concentration of tetraethyl orthosilicate in the cyclohexane solution containing tetraethyl orthosilicate is 20 v / v%; and the volume ratio of the cyclohexane solution containing tetraethyl orthosilicate to water is 0.4:
1.
3. The application according to claim 1, characterized in that, In step S1, the stirring temperature is 60℃; drying is carried out in an oven at 100℃ for 12 h; and calcination is carried out in a muffle furnace at 550℃ for 5 h.
4. The application according to claim 1, characterized in that, In step S2, (NH4)6Mo7O 24 The mass ratio of 4H2O to the virus-like SiO2 prepared in step S1 is (0.2445~0.9321):1; (NH4)6Mo7O is dissolved by ultrasonication. 24 • 4H2O for 5 min; after adding SiO2, sonicate again for 30 min, then soak at room temperature for 24 h.
5. The application according to claim 1, characterized in that, In step S2, rotary evaporation is performed at 75 °C; drying is carried out in an oven at 100 °C for 12 h; the target mesh size is 40-60 mesh.