A Mo / SiO2 catalyst, its preparation method, and its application in the hydrogenation catalytic preparation of methyl acetate from dimethyl oxalate.

Abstract

A Mo / SiO2 catalyst and its preparation method are disclosed, along with its application in the hydrogenation catalytic synthesis of methyl acetate (MA) from dimethyl oxalate (DMO). The method employs a hydrogen thermal reduction process to prepare the Mo / SiO2 catalyst. Instead of calcining the ammonium molybdate precursor in a muffle furnace, it is directly decomposed at 500°C under H2 conditions to obtain a reduced Mo / SiO2 catalyst with strong hydrogenation activity. The strong interaction between the virus-like SiO2 and Mo enhances the antioxidant properties of the reduced Mo, allowing the Mo / SiO2 to be stored in air without being easily affected by instantaneous oxidation upon contact with air, thus maintaining its hydrogenation activity. When the Mo / SiO2 catalyst is applied to the hydrogenation synthesis of MA from DMO, under reaction conditions of 220°C, DMO can be completely converted and highly selectively converted to MA, providing a good reaction basis for the subsequent directional conversion of MA to EtOH.

Description

Technical Field

[0001] This invention belongs to the field of dimethyl oxalate hydrogenation catalyst preparation technology, specifically relating to a Mo / SiO2 catalyst, its preparation method, and its application in the catalytic hydrogenation of dimethyl oxalate to prepare methyl acetate. 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 catalyst is of great significance for the hydrogenation catalysis of dimethyl oxalate to methyl acetate. Summary of the Invention

[0004] The purpose of this invention is to provide a Mo / SiO2 catalyst, its preparation method, and its application in the hydrogenation catalytic preparation of methyl acetate from dimethyl oxalate. Applying the Mo / SiO2 catalyst to the hydrogenation catalytic preparation of methyl acetate from dimethyl oxalate can exhibit stronger hydrogenation activity, excellent catalytic activity, and higher selectivity for methyl acetate.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0006] A Mo / SiO2 catalyst includes 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% 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.

[0007] To achieve the objective of the invention, the present invention also provides a method for preparing the above-mentioned Mo / SiO2 catalyst, comprising the following steps:

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] To achieve the purpose of the invention, the present invention also provides the application of the above-mentioned Mo / SiO2 catalyst in the hydrogenation catalytic preparation of methyl acetate from dimethyl oxalate.

[0017] 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 action of the above-mentioned Mo / SiO2 catalyst, hydrogenation is carried out at 220°C to synthesize methyl acetate; 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 .

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) 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 the reduced Mo, so that Mo / SiO2 can be stored in the air and is not easily affected by instantaneous oxidation upon contact with air.

[0020] (2) 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

[0021] Figure 1 These are X-ray diffraction patterns of the supported molybdenum-based catalysts prepared in Examples 1-5 and the comparative examples, respectively.

[0022] Figure 2 These are the infrared spectra of the supported molybdenum-based catalysts prepared in Examples 1-5 and the comparative examples, respectively;

[0023] Figure 3 These are the H2-TPR spectra of the supported molybdenum-based catalysts prepared in Examples 1-5 and the comparative examples, respectively;

[0024] Figure 4 Comparison of catalytic performance test results of the supported molybdenum-based catalysts prepared in Examples 1-5 and the comparative example: (a) Examples 1-5; (b) Example 3 and the comparative example. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] 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.

[0027] Example 1

[0028] A Mo / SiO2 catalyst includes 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 11.7% of the total mass of the catalyst and the content of virus-like SiO2 is 88.3% of the total mass of the catalyst.

[0029] The preparation method of the above-mentioned Mo / SiO2 catalyst includes the following steps:

[0030] 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.

[0031] S2, Weigh 0.2445g 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, 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.

[0032] 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 a Mo / SiO2 catalyst loaded with 11.7 wt% Mo.

[0033] Example 2

[0034] A Mo / SiO2 catalyst includes 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 15.8% of the total mass of the catalyst and the content of virus-like SiO2 is 84.2% of the total mass of the catalyst.

[0035] The above-mentioned method for preparing Mo / SiO2 catalyst involves only step S2, in which 0.3462 g of (NH4)6Mo7O is weighed. 24 ·4H2O, and other steps are kept consistent with Example 1 to obtain a Mo / SiO2 catalyst loaded with 15.8 wt% Mo.

[0036] Example 3

[0037] A Mo / SiO2 catalyst includes 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 23.8% of the total mass of the catalyst and the content of virus-like SiO2 is 76.2% of the total mass of the catalyst.

[0038] The above-mentioned method for preparing Mo / SiO2 catalyst involves only step S2, in which 0.5777g of (NH4)6Mo7O is weighed. 24 ·4H2O, and other steps are kept consistent with Example 1 to obtain a Mo / SiO2 catalyst loaded with 23.8 wt% Mo.

[0039] Example 4

[0040] A Mo / SiO2 catalyst includes 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 28.5% of the total mass of the catalyst and the content of virus-like SiO2 is 71.5% of the total mass of the catalyst.

[0041] The above-mentioned method for preparing Mo / SiO2 catalyst involves only step S2, in which 0.7341 g of (NH4)6Mo7O is weighed. 24 ·4H2O, and other steps are kept consistent with Example 1 to obtain a Mo / SiO2 catalyst loaded with 28.5 wt% Mo.

[0042] Example 5

[0043] A Mo / SiO2 catalyst includes 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 33.6% of the total mass of the catalyst and the content of virus-like SiO2 is 66.4% of the total mass of the catalyst.

[0044] The above-mentioned method for preparing Mo / SiO2 catalyst involves only step S2, in which 0.9321 g of (NH4)6Mo7O is weighed. 24 ·4H2O, and other steps are kept consistent with Example 1 to obtain a Mo / SiO2 catalyst loaded with 33.6 wt% Mo.

[0045] Comparative Example

[0046] 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 impregnation amount of ammonium molybdate is the same as in Example 3, 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.

[0047] The preparation method of the above-mentioned MoO2 / SiO2 catalyst includes the following steps:

[0048] S1. Preparation of the carrier: This step is consistent with Example 1;

[0049] S2, Weigh out 0.5777g of (NH4)6Mo7O24 · 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;

[0050] 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.

[0051] The catalyst impregnated with ammonium molybdate precursor was differentiated by hydrogen thermal reduction and muffle furnace calcination to successfully prepare xMo / SiO2 ( Figure 1 (a)-(e)) and MoO2 / SiO2 (ammonium molybdate addition amount is the same as in Example 3) Figure 1 (f) Two catalysts. XRD analysis showed that both methods formed characteristic crystalline phases: the catalyst obtained by the hydrogen thermal reduction method was dominated by elemental Mo, while that obtained by muffle furnace calcination was dominated by MoO2. Notably, as the Mo loading increased from 11.7% to 33.6%, the diffraction peak intensity of metallic Mo significantly increased. Figure 1 (a)-(e)), this phenomenon can be attributed to the following mechanism: when the loading is below 15.8%, the Mo species are highly dispersed on the SiO2 surface, resulting in weak diffraction signals; however, when the loading reaches the 23.8% threshold, the size effect of Mo grains and crystallinity increase simultaneously, and characteristic peaks begin to appear; when the Mo loading further increases to 28.5% and 33.6%, the metal grain size and crystallinity further increase, and the intensity of Mo characteristic peaks increases significantly. Diffraction characteristics of the 23.8% loading sample ( Figure 1(c) and (f) show that the peak intensity of the MoO2 phase is 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 the metallic state, but its reducing atmosphere also effectively suppresses surface migration energy, hindering the grain oxidation and sintering kinetics. Simultaneously, the strong interaction between the virus-like SiO2 and Mo inhibits the deep oxidation of elemental Mo in air. Therefore, the xMo / SiO2 series catalysts obtained by the hydrogen thermal reduction method can all exhibit reduced elemental Mo. Furthermore, the strong electronic interactions (such as Mo-O-Si bonding) formed 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 xMo / SiO2 series catalysts prepared by the hydrogen thermal reduction method can stably maintain the elemental state of metallic Mo, rather than transforming it into a high-valence oxide.

[0052] Figure 2 The FTIR spectroscopic analysis results of xMo / SiO2 and MoO2 / SiO2 catalysts are presented. Among them, the values ​​located in the 1000-1100 cm⁻¹ region are shown. -1 The most significant absorption peak within the specified range is a broad and intense peak, which is attributed to the asymmetric stretching vibration mode of the Si-O-Si bond and is a typical characteristic peak of the SiO2 support. Notably, the position and shape of this main peak remain stable in samples with different Mo loadings, indicating that the basic framework structure of the SiO2 support remains intact during catalyst preparation. Mo loading on SiO2 may have led to the formation of Mo-O-Si bonds. However, since the Mo-O-Si vibration peak and the SiO2 main peak (Si-O-Si asymmetric stretching vibration) are located in the 1000-1100 cm⁻¹ range... -1 The overlapping within the range causes the composite peak to shift towards lower wavenumbers overall. This redshift becomes increasingly significant with increasing Mo loading, confirming the enhanced interaction between Mo species and the SiO2 support. Furthermore, at 440 cm⁻¹... -1 and 800cm -1 The characteristic peaks observed correspond to the bending vibrations of the Si-O bond and the symmetric stretching vibrations of the Si-O-Si bond, respectively. The stability of these peak positions further verifies the integrity of the SiO2 framework structure during the Mo loading process. Metallic Mo in the Mo / SiO2 catalyst did not exhibit obvious characteristic absorption peaks, mainly due to the unique electronic structure characteristics of metallic Mo: its highly delocalized d electrons and metallic bonding result in vibrational energy levels far below the conventional detection range of infrared spectroscopy (4000-400 cm⁻¹). -1Meanwhile, significant support-metal interactions exist in the MoO2 / SiO2 system, forming Mo-O-Si interfacial bonds. However, the Mo-O-Si vibrational modes differ from the Si-O-Si stretching vibration peaks (1000-1100 cm⁻¹) dominated by the SiO2 support. -1 The severe spectral overlap, coupled with the weak characteristic vibrational signals of the Mo-O-Mo bond itself, makes it difficult to clearly identify these characteristic peaks associated with Mo species in the infrared spectrum.

[0053] like Figure 3 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 Mo 4+ →Mo 0 The reduction process is gradual. Notably, as the Mo loading increases to 33.6%, the reduction temperature shifts to higher temperatures and H2 consumption increases. This reflects that the formation of larger Mo grains increases the difficulty of complete reduction, indicating that the metal-support interaction strengthens with increasing grain size. In contrast, the 23.8% MoO2 / SiO2 prepared by muffle furnace calcination exhibits a strong reduction peak in the 500-600℃ range, corresponding to the Mo content 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.

[0054] The catalysts prepared in Examples 1-5 and the comparative examples were all investigated using a fixed-bed reactor to examine their specific catalytic performance in the selective hydrogenation of dimethyl oxalate to methyl acetate.

[0055] 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.

[0056] Conversion rate and selectivity were both calculated using the normalization method:

[0057] Conversion rate (%) = (1-A) DMO f DMO / ∑A i fi )×100%;

[0058] Selectivity (%) = (A) i f i / ∑A i f i )×100%;

[0059] Where A i Indicates the peak area of ​​FID chromatography; f i This represents the relative molar correction factor for FID.

[0060] 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 .

[0061] Mo / SiO2 catalysts with different Mo contents were prepared by hydrogen thermal reduction and tested on the hydrogenation reaction of dimethyl oxalate. The results are as follows: Figure 4 As shown, the conversion rate of DMO first increases and then decreases with increasing Mo loading. The catalyst exhibits the strongest hydrogenation activity for DMO when the Mo loading is 23.8%. However, the overall trend is relatively gradual. This is because when the Mo loading reaches a certain limit, the limited defect sites on the support surface are occupied by Mo species, making it difficult for additional Mo to be effectively anchored, leading to a saturation of active sites. The conversion rate increases rapidly at low metal loadings and plateaus after high loadings. Therefore, the change in Mo loading after reaching 33.6% has a less significant impact on DMO conversion than on its product selectivity.

[0062] The hydrogenation product of this reaction is mainly methyl formate (MA). The selectivity of EtOH initially increases and then decreases with the loading of Mo. When the Mo loading reaches 23.8%, 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 optimal reactivity. 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 with each other 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 the C14 junctions of MG. When the catalyst exhibits strong hydrogenation activity, MG preferentially hydrogenates to form MA, accompanied by the formation of the byproduct MF due to the cleavage of the C14 junctions of MG under the influence of the acidic sites of Mo. Conversely, as the hydrogenation activity decreases, the selectivity of MF increases. Throughout the process, the selectivity of other byproducts (including C3-C4 alcohols, ethers, etc.) remains below 5%. Based on a Mo loading of 23.8%, 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 significant activity advantage over MoO2 / SiO2, while the latter achieved a DMO conversion rate of less than 38%, and due to its low hydrogenation activity, it produced MG, the previous hydrogenation product of MA.

[0063] In summary, this invention successfully synthesized a SiO2-supported Mo / SiO2 catalyst using a simple hydrogen thermal reduction method. Compared with MoO2, it exhibits stronger hydrogenation activity in the DMO hydrogenation reaction and achieves highly selective conversion of DMO to MA, providing a new research approach for the application of Mo-based catalysts in hydrogenation reactions.

[0064] 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. An application of a Mo / SiO2 catalyst in the hydrogenation catalytic preparation of methyl acetate from dimethyl oxalate, the specific application process being 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 action of the Mo / SiO2 catalyst, hydrogenation to synthesize methyl acetate is carried out at 220 °C; 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 ; 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 • 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. 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.

2. The application of the Mo / SiO2 catalyst according to claim 1 in the catalytic hydrogenation of dimethyl oxalate to methyl acetate, 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 of the Mo / SiO2 catalyst according to claim 1 or 2 in the catalytic hydrogenation of dimethyl oxalate to methyl acetate, 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 of the Mo / SiO2 catalyst according to claim 1 or 2 in the catalytic hydrogenation of dimethyl oxalate to methyl acetate, 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 of the Mo / SiO2 catalyst according to claim 1 or 2 in the catalytic hydrogenation of dimethyl oxalate to methyl acetate, 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 hours; the target mesh size is 40-60 mesh.

6. The application of the Mo / SiO2 catalyst according to claim 1 or 2 in the catalytic hydrogenation of dimethyl oxalate to methyl acetate, characterized in that, In step S3, at 500 o At temperature C, H2 was introduced at a flow rate of 100 mL / min for 24 h for reduction, followed by purging and cooling with Ar at a flow rate of 100 mL / min.

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