A supported pre-transition metal-based catalyst, its preparation method and use

Abstract

This invention relates to a supported pre-transition metal-based catalyst, its preparation method, and its application. The catalyst comprises an active component and a support, wherein the active component is at least one selected from MoO3, WO3, V2O3, and Cr2O3, and the metal oxide support is one selected from MgO, γ-Al2O3, SiO2, TiO2, ZrO2, and CeO2; the mass of the elemental metal in the active component is 4.2–29.4 wt% of the total mass of the support; the preparation method utilizes CO products in the reaction atmosphere to perform in-situ carbonization of the dispersed oxide species, avoiding the complex steps of high-temperature carburizing, passivation, and re-reduction in traditional carbide preparation, making the operation simple and easy to scale up. The pre-transition metal-based catalyst prepared by this invention exhibits excellent activity and stability in the reverse water-gas shift reaction and has good application prospects.

Description

Technical Field

[0001] This invention belongs to the fields of catalytic chemistry and carbon dioxide resource utilization technology, specifically relating to a supported pre-transition metal-based catalyst for reverse water-gas shift (RWGS) reaction and its preparation method. Background Technology

[0002] Global greenhouse gas emissions, particularly carbon dioxide (CO2), are increasing at an alarming rate, leading to numerous serious environmental problems. In response, researchers have primarily proposed carbon dioxide capture, utilization, and storage (CCUS) technology. CCUS technology emphasizes green chemistry, converting captured CO2 into high-value-added chemicals, offering significant advantages. Among these, the reverse water-gas shift (RWGS) reaction (CO2 + H2 → CO + H2O, ΔH = +41.2 kJ / mol) is a key pathway for converting CO2 into CO. The resulting CO can be directly used in mature industrial processes such as Fischer-Tropsch synthesis and methanol synthesis, playing a crucial role in realizing the resource utilization of CO2 and a carbon circular economy.

[0003] The RWGS reaction is endothermic, and high temperatures are beneficial for improving CO2 conversion, but they also pose challenges to catalyst stability. An ideal RWGS catalyst must possess high CO selectivity, high activity, and good thermal stability. While noble metal catalysts (such as Pt, Pd, and Rh) exhibit excellent catalytic performance, their high cost limits their large-scale industrial application. Non-noble metal catalysts (such as Ni, Co, and Cu) are less expensive, but Ni and Co tend to cause excessive hydrogenation of CO to form CH4, while Cu has poor thermal stability. Pre-transition metal oxides (such as V, Cr, Mo, and W) have attracted attention due to their lower cost, excellent activity, and high CO selectivity; in recent years, carbides have been considered one of the most promising non-noble metal RWGS catalysts.

[0004] Currently, the preparation of carbide catalysts requires complex high-temperature carburizing, passivation, and re-reduction steps, resulting in high energy consumption and complex operations, which are not conducive to large-scale applications. Chinese invention patent document CN202410082704.1 discloses a method for preparing high specific surface area pure-phase α-type molybdenum carbide by hydrogen intercalation modification of MoO3. However, this method involves complex carburizing and passivation processes. Similarly, Chinese invention patent CN201911040302.0 proposes a method for preparing Mo2C catalysts; however, this method requires hydrothermal reaction, carburizing under a reducing atmosphere, surface passivation, and acid treatment, which are also cumbersome and cannot simply and quickly prepare molybdenum carbide catalysts. The complex preparation process and technology restrict the application of highly efficient transition metal-based catalysts.

[0005] Therefore, developing a transition metal-based RWGS catalyst that is easy to prepare, requires no complex pre-carbonization, and has high activity and selectivity is of great scientific significance and application value in realizing the resource utilization of CO2 and the carbon circular economy. Summary of the Invention

[0006] The purpose of this invention is to address the limitations of current technologies by providing a supported pre-transition metal-based catalyst, its preparation method, and its applications. This catalyst utilizes an impregnation method to support a pre-transition metal salt on an oxide support, followed by air calcination to obtain a supported oxide precursor. This precursor eliminates the need for separate ex-situ carbonization treatment, allowing for direct in-situ generation of a catalyst containing a highly active carbide phase in an RWGS reaction atmosphere. The key to the preparation method lies in utilizing CO products in the reaction atmosphere to perform in-situ carbonization of dispersed oxide species, avoiding the complex steps of high-temperature carburizing, passivation, and re-reduction in traditional carbide preparation. This method is simple to operate and easily scaled up. The pre-transition metal-based catalyst prepared by this method exhibits excellent activity and stability in the reverse water-gas shift reaction, demonstrating promising application prospects.

[0007] The technical solution of this invention is as follows: A supported pre-transition metal carbon oxide catalyst, the catalyst comprising an active component and a support, wherein the active component is at least one of Group VB and VIB transition metal oxides MoO3, WO3, V2O3, and Cr2O3, and the metal oxide support is one or more of MgO, γ-Al2O3, SiO2, TiO2, ZrO2, and CeO2; the mass of the elemental metal in the active component is 4.2-29.4 wt% of the total mass of the support.

[0008] Preferably, the active component is one or both of transition metal oxides MoO3 and WO3; the metal oxide support is one or more of SiO2, TiO2 and ZrO2.

[0009] The preparation method of the supported pre-transition metal carbon oxide catalyst includes the following steps: 1) Impregnation: Dissolve the precursor salt in deionized water to prepare the corresponding salt solution, then add the carrier oxide to the solution and stir at room temperature for 10-24 h to obtain a viscous mixture; The precursor salt is one or more of Mo salt, W salt, V salt and Cr salt; the salt is one or more of ammonium salt, oxyacid acid salt, halide and nitrate. The oxide is one or more of MgO, γ-Al2O3, SiO2, TiO2, ZrO2, and CeO2; The total concentration of the salt solution is 0.05~0.50 mol / L; The mass ratio of precursor salt to support oxide is 0.1~1.2:1; 2) Drying: The viscous mixture obtained in step 1) is dried at 60-100 °C for 12-18 h to obtain a solid mixture; 3) Calcination: The solid mixture obtained in step 2) is ground to obtain powder particles, and then heated to 300-600 ℃ and calcined for 4-6 h to obtain a supported pre-transition metal carbon oxide catalyst.

[0010] In step 1), mechanical stirring is used at a speed of 500-1000 rpm.

[0011] In step 3), the heating rate is 2-10 ℃ / min.

[0012] The aforementioned supported pre-transition metal carbon oxide catalyst is applied to the reverse water-gas shift reaction.

[0013] Specifically, the steps include the following: A supported pre-transition metal oxide catalyst was packed into a fixed-bed reactor, activated and reduced under a reducing atmosphere, and then a mixture of CO2 and H2 was introduced to obtain a product gas containing CO and H2O. The reaction pressure was 0.1-1 MPa, the reaction temperature was 400-600 ℃, and the gas hourly space velocity was 100,000-300,000 mL / (g) cat The flow rate ratio of H2 to CO2 is (1-3):1.

[0014] The catalyst needs to be activated and reduced before application. The reducing atmosphere is hydrogen, the flow rate of the reducing gas is 20-60 mL / min, the reduction temperature is 300-500 ℃, the pressure is 0.1-1 MPa, and the reduction time is 1-4 h.

[0015] The essential features of this invention are: The key feature of this invention lies in the in-situ formation mechanism of the highly active carbide phase in the catalyst. Traditional carbide catalysts require carburizing treatment at high temperatures using a CH4 / H2 or CO / H2 mixture for several hours or even tens of hours, followed by passivation to prevent spontaneous combustion in air, and then reduction activation before use. This process is complex and energy-intensive. This invention discovers that when a pre-transition metal (such as Mo, W) is loaded in a highly dispersed state onto an oxide support (such as SiO2, ZrO2, TiO2), in an RWGS reaction atmosphere (CO2+H2), the resulting CO product can react in-situ with highly dispersed metal oxide species (e.g., 2MoO3+8CO→Mo2C+7CO2), generating surface carbides (such as Mo2C, WC) within minutes. The high efficiency of this in-situ carburization process is attributed to the synergistic effect of the following three key factors: (1) High dispersibility: In the supported oxide precursor prepared by impregnation-calcination method, the active components exist on the surface of the support in the form of nanoclusters or even monolayer dispersion, with abundant edge sites and defect sites, which significantly enhances the adsorption and activation ability of CO. (2) In-situ reaction environment: The RWGS reaction itself produces CO, which acts as a carburizing agent and comes into direct contact with the metal oxide at the reaction temperature, without the need for an external carbon source or additional carburizing steps; (3) Synergistic effect of the support: The hydroxyl groups and weak Lewis acid sites on the surface of supports such as SiO2 and ZrO2 help stabilize small-sized metal oxide species. At the same time, the support itself does not participate in excessive carbonization, so that once the surface carbide phase is formed, it can remain stable and will not be further carbonized into an inactive phase with higher carbon content.

[0016] Therefore, the catalyst described in this invention spontaneously forms a highly active metal carbide surface layer under reaction conditions. This surface layer provides abundant CO2 activation sites and suitable CO desorption characteristics, thereby achieving excellent RWGS performance (high activity, high selectivity, and high stability). This method breaks through the conventional thinking that carbide catalysts must be prepared in advance, providing a completely new and simplified path for the design of highly efficient RWGS catalysts.

[0017] The present invention has the following beneficial effects: 1. The preparation process is significantly simplified: the catalyst does not require the independent high-temperature carburizing, passivation and re-reduction steps in the traditional carbide route. The highly active carbide phase is directly generated in situ from the supported oxide in the RWGS reaction atmosphere, which greatly reduces the energy consumption and operation complexity of the preparation and makes it easy to scale up production.

[0018] 2. Significantly enhanced catalytic activity: The active components are highly dispersed on the support surface, and the in-situ generated carbide phase provides abundant active sites. In Example 2, the CO generation rate on the 8.4 wt% Mo / SiO2 catalyst reached 388.8 mol / L. CO / mol Mo / h, is pure MoO3 (90.4 mol) CO / mol Mo The CO generation rate was 4.3 times that of the 8.4 wt% W / SiO2 catalyst in Example 6, which had a CO generation rate of 273.8 mol / h. CO / mol W / h, is pure WO3 (94.9 mol) CO / mol W 2.9 times that of / h).

[0019] 3. Excellent CO selectivity: Under all test conditions in Examples 1-6 and the comparative examples, the catalyst exhibited nearly 100% CO selectivity in the range of 400-600 °C, effectively suppressing the methanation side reaction.

[0020] 4. Good stability: In Example 5, the CO2 conversion rate of the Mo / SiO2 catalyst remained basically stable during a continuous 50-hour RWGS reaction, and the CO selectivity remained at 100% throughout (see Example 5). Figure 10 ).

[0021] 5. Low cost: The precursor metals used (Mo, W, etc.) are abundant and their prices are much lower than those of precious metals such as Pt and Ru (based on 2025 market prices, the prices of Mo and W are only about 1 / 500 and 1 / 300 of Pt, respectively), which helps to reduce catalyst costs and promote industrial applications. Attached Figure Description

[0022] Figure 1 The XRD patterns of different metal oxides after reduction obtained in Example 1 are shown below; Figure 1 a) in the text is WO3. Figure 1 b) in the text is MoO3. Figure 1 c) in the equation is V2O5. Figure 1 In this context, d) represents Cr2O3. Figure 1 e) in the text represents ZrO2. Figure 1 f) is TiO2, g) is Nb2O5; Figure 2 The XRD patterns of different metal oxides obtained after the reaction in Example 1 are shown below. Figure 2 a) in the text is WO3. Figure 2 b) in the text is MoO3. Figure 2c) in the equation is V2O5. Figure 2 In this context, d) represents Cr2O3. Figure 2 e) in the text represents ZrO2. Figure 2 f) in the text represents TiO2. Figure 2 g) is Nb2O5; Figure 3 The images show the XRD patterns of calcined and reduced molybdenum metal loaded on different supports, obtained in Example 4. Figure 3 a) in the figure represents Mo / SiO2. Figure 3 b) in the equation represents Mo / ZrO2. Figure 3 c) in the equation represents Mo / TiO2. Figure 3 In the figure, d) represents Mo / γ-Al2O3. Figure 3 e) in the equation represents Mo / CeO2. Figure 3 f) in the figure represents Mo / MgO; Figure 4 The XRD patterns of post-reaction molybdenum loaded on different supports obtained in Example 4 are shown below: a) Mo / SiO2, b) Mo / ZrO2, c) Mo / TiO2, d) Mo / γ-Al2O3, e) Mo / CeO2, f) Mo / MgO. Figure 5 The images shown are transmission electron microscopy (TEM) images and corresponding energy dispersive spectroscopy (EDX) elemental mapping images of calcined molybdenum loaded on different supports, obtained in Example 4. Figure 5 a) in the figure represents Mo / SiO2. Figure 5 b) in the equation is Mo / ZrO2. Figure 5 c) in the equation represents Mo / TiO2. Figure 5 In the figure, d) represents Mo / γ-Al2O3. Figure 5 e) in the equation represents Mo / CeO2. Figure 5 f) in the figure represents Mo / MgO; Figure 6 The images shown are transmission electron microscopy (TEM) images and corresponding energy-dispersive X-ray spectroscopy (EDX) elemental mapping images of molybdenum loaded on different supports after the reaction, obtained in Example 4. Figure 6 a) in the figure represents Mo / SiO2. Figure 6 b) in the equation is Mo / ZrO2. Figure 6 c) in the equation represents Mo / TiO2. Figure 6 In the figure, d) represents Mo / γ-Al2O3. Figure 6 e) in the equation represents Mo / CeO2. Figure 6 f) in the figure represents Mo / MgO; Figure 7The graph shows a comparison of the catalytic activities of Mo / SiO2 and W / SiO2 obtained in Examples 2 and 6, where... Figure 7 In the figure, a) represents the CO2 conversion rate of the Mo / SiO2 and W / SiO2 catalysts. Figure 7 b) represents the reaction rate between Mo / SiO2 and the W / SiO2 catalyst; Figure 8 The activities of different supported Mo-based catalysts obtained in Example 4; Figure 9 The different loadings of Mo / SiO2 obtained in Example 3, wherein, Figure 9 a) in the figure represents the activity test result. Figure 9 b) in the figure is the XRD pattern; Figure 10 The results are the stability test results of Mo / SiO2 obtained in Example 5. Detailed Implementation

[0023] The present invention will be described below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions and conditions described in the manual, or according to the manufacturer's recommendations. The general equipment, materials, reagents, etc. used are commercially available unless otherwise specified. The raw materials required in the following embodiments and comparative examples are all commercially available.

[0024] Example 1: Comparison of RWGS performance of different pre-transition metal oxides Weigh 60 mg each (40-60 mesh) of commercial WO3, MoO3, V2O5, Cr2O3, ZrO2, TiO2, and Nb2O5, compress them into tablets (15 MPa, 60 s), crush them, and screen the 40-60 mesh catalysts. These catalysts are then loaded into fixed-bed quartz reactors for catalytic performance evaluation. The catalysts are reduced in 500 °C at 0.1 MPa with 50 mL / min H2 for 2 h (the structure of the reduced catalyst samples was confirmed by XRD, see Appendix). Figure 1 The reaction mixture was then purged with N2 for 0.5 h and heated to 550 °C. The reaction gas was then switched to a flow rate of 100 mL / min and a space velocity of 100,000 mL·g⁻¹. -1 ·h -1 The reaction pressure was 0.1 MPa. The reduction and bulk structure of all catalyst samples were determined by XRD, see Appendix. Figure 1 and 2 The products were analyzed online by gas chromatography. The CO2 conversion rate and CO selectivity results are shown in Table 1.

[0025] Table 1. Summary of catalytic activity and structural changes of different pre-transition metal oxides

[0026] a The surface metal carbide content was determined by XPS. Table 1 shows that among the pure oxides, MoO3 and WO3 exhibited the highest CO2 conversion and CO generation rates, and XPS detected the formation of surface carbides, while no carbides were detected in other oxides (V2O5, TiO2, ZrO2, Nb2O5, Cr2O3). This indicates that Mo and W-based oxides can generate carbide active phases in situ under RWGS conditions, thus achieving excellent catalytic performance.

[0027] Example 2: Preparation and RWGS Performance of Mo / SiO2 Catalyst The impregnation method was used: 0.464 g (0.375 mmol) of ammonium heptamolybdate tetrahydrate was dissolved in 10 mL of deionized water, and 3 g of SiO2 support (target Mo loading was 8.4 wt%) was added. The mixture was stirred at 500 rpm for 15 h at room temperature to obtain a viscous mixture. The mixture was dried in a forced-air oven at 100 °C for 10 h. The dried solid was then ground and calcined in a muffle furnace at 500 °C for 4 h at a rate of 2 °C / min to obtain an 8.4 wt% Mo / SiO2 catalyst (Note: the "Mo" in "Mo / SiO2" is only to indicate that Mo is not in its elemental state). After calcination, molybdenum was highly dispersed on the SiO2 surface in the form of MoO3. Figure 3 As shown in the XRD pattern, no obvious MoO3 diffraction peaks were observed (the reason for the lack of obviousness at this time is due to the low loading; as the content increases, the MoO3 diffraction peaks of subsequent related catalysts will be enhanced with the increase of Mo content).

[0028] The catalyst evaluation conditions are the same as in Example 1.

[0029] Results: CO2 conversion rate 31.3%, CO selectivity 100%, CO generation rate 388.8 mol CO / mol Mo / h, is pure MoO3 (90.4 mol) CO / mol Mo The concentration of Mo on the surface was 4.3 times that of the previous reaction ( / h). XPS analysis after the reaction showed that the surface Mo... 2+ The content was 24.2%, indicating that some MoO3 was converted to Mo2C in situ under the reaction conditions.

[0030] Example 3: Performance of Mo / SiO2 catalysts with different molybdenum loadings Following the method of Example 2, six other Mo / SiO2 catalysts with Mo loadings of 4.2 wt%, 12.6 wt%, 16.8 wt%, 21 wt%, 25.2 wt%, and 29.4 wt% were prepared by varying only the amount of ammonium heptamolybdate tetrahydrate added. The evaluation conditions were the same as in Example 1. The results are shown in Table 2.

[0031] Table 2 Performance of Mo / SiO2 catalysts with different molybdenum loadings

[0032] Example 4: Effect of different supports on the performance of Mo-based catalysts Following the method of Example 2, catalysts with a Mo loading of 8.4 wt% were prepared using ZrO2, TiO2, γ-Al2O3, CeO2, and MgO as supports, respectively. The evaluation conditions were the same as in Example 1. The results are shown in Table 3.

[0033] Table 3 Summary of the activities of different supported Mo-based catalysts

[0034] a The surface metal carbide content was determined by XPS.

[0035] Example 5: Long-term activity evaluation of Mo / SiO2 An 8.4 wt% Mo / SiO2 catalyst was prepared according to the method in Example 2. The evaluation conditions were the same as in Example 1.

[0036] Results: During the 50-hour activity evaluation, the CO2 conversion rate remained essentially stable, and the CO selectivity remained at 100% throughout (see [link to relevant documentation]). Figure 10 ).

[0037] Example 6: Preparation of WO3 catalyst and performance of W / SiO2 catalyst Pure WO3 was evaluated according to the method of Example 1. An 8.4 wt% W / SiO2 catalyst (using ammonium metatungstate as a precursor) was prepared according to the method of Example 2. The evaluation conditions were the same as in Example 1.

[0038] Results: The CO2 conversion rate of pure WO3 was 33.9%, and the CO selectivity was 100%; the CO2 conversion rate of 8.4 W / SiO2 was 28.5%, the CO selectivity was 100%, and the CO formation rate was 273.8 mol. CO / mol W / h, is pure WO3 (94.9 mol) CO / mol W 2.9 times that of / h).

[0039] Comparative Example 1: Catalyst-free blank experiment Under the same reaction conditions, no catalyst was loaded, only SiC diluent was loaded.

[0040] Results: CO2 conversion rate <0.5%, indicating that the contribution of non-catalytic thermal reaction is negligible.

[0041] Comparative Example 2: Carrier Blank Experiment Under the same reaction conditions, pure carriers of SiO2, ZrO2, TiO2, γ-Al2O3, CeO2, and MgO (60 mg) were loaded respectively.

[0042] Results: The CO2 conversion rate of each support was less than 3.5%, and the CO selectivity was 100%. This indicates that the catalytic activity of the support itself is very low. Unless otherwise specified, the raw materials and equipment used in this invention are commonly used in the art; unless otherwise specified, the methods used in this invention are conventional methods in the art.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

[0044] Matters not covered in this invention are common knowledge.

Claims

1. A supported pre-transition metal carbon oxide catalyst, characterized in that, The catalyst comprises an active component and a support, wherein the active component is at least one of MoO3, WO3, V2O3, and Cr2O3, and the metal oxide support is MgO, γ-Al2O3, SiO2, TiO2, ZrO2, and CeO2; the mass of the elemental metal in the active component is 4.2-29.4 wt% of the total mass of the support.

2. The supported pre-transition metal carbon oxide catalyst as described in claim 1, characterized in that, The active component is one or both of transition metal oxides MoO3 and WO3; the metal oxide support is one or more of SiO2, TiO2 and ZrO2.

3. The method for preparing the supported pre-transition metal carbon oxide catalyst as described in claim 1, characterized in that, Includes the following steps: 1) Impregnation: Dissolve the precursor salt in deionized water to prepare the corresponding salt solution, then add the carrier oxide to the solution and stir at room temperature to obtain a viscous mixture; The precursor salt is one or more of Mo salt, W salt, V salt and Cr salt; the salt is one or more of ammonium salt, oxyacid acid salt, halide and nitrate. The oxide is one or more of MgO, γ-Al2O3, SiO2, TiO2, ZrO2, and CeO2; The total concentration of the salt solution is 0.05~0.50 mol / L; The mass ratio of precursor salt to support oxide is 0.1~1.2:1; 2) Drying: The viscous mixture obtained in step 1) is dried at 60-100 °C for 12-18 h to obtain a solid mixture; 3) Calcination: The solid mixture obtained in step 2) is ground to obtain powder particles, and then heated to 300-600℃ and calcined for 4-6 h to obtain a supported pre-transition metal carbon oxide catalyst.

4. The method for preparing the supported pre-transition metal carbon oxide catalyst as described in claim 3, characterized in that, In step 1), mechanical stirring is used at a speed of 500-1000 rpm; In step 1), the stirring time is 10-24 hours.

5. The method for preparing the supported pre-transition metal carbon oxide catalyst as described in claim 3, characterized in that, In step 3), the heating rate is 2-10 ℃ / min.

6. The application of the supported pre-transition metal carbon oxide catalyst as described in claim 1, characterized in that, It is applied to the reverse water-gas shift reaction.

7. The application of the supported pre-transition metal carbon oxide catalyst as described in claim 6, characterized in that, Includes the following steps: A supported pre-transition metal oxide catalyst was packed into a fixed-bed reactor, activated and reduced under a reducing atmosphere, and then a mixture of CO2 and H2 was introduced to obtain a product gas containing CO and H2O. The reaction pressure was 0.1-1 MPa, the reaction temperature was 400-600 ℃, and the gas hourly space velocity was 100,000-300,000 mL / (g) cat The flow rate ratio of H2 to CO2 is (1-3):

1.

8. The application of the supported pre-transition metal carbon oxide catalyst as described in claim 7, characterized in that, The catalyst needs to be activated and reduced before application. The reducing atmosphere is hydrogen, the flow rate of the reducing gas is 20-60 mL / min, the reduction temperature is 300-500 ℃, the pressure is 0.1-1 MPa, and the reduction time is 1-4 h.

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