A molybdenum disulfide / zirconia composite catalyst and its preparation and application

Abstract

This invention discloses a MoS2 / a-ZrO2 composite catalyst, its preparation method, and its application, belonging to the field of catalyst preparation technology. The composite catalyst is prepared by first synthesizing amorphous zirconium dioxide with abundant oxygen vacancies using a combination of solvothermal and thermal treatment, and then using it as a support through impregnation and in-situ sulfidation. The resulting amorphous zirconium dioxide possesses a high specific surface area, abundant oxygen vacancies, and a stable structure, which not only enhances the catalyst's adsorption and dissociation capabilities for CO2 and H2S but also facilitates the dispersion of the active component MoS2, promoting the synergistic effect between the support and the active component. When applied to the reaction of H2S and CO2 to co-produce methanethiol, the obtained composite catalyst exhibits excellent catalytic activity.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a method for preparing a MoS2 / a-ZrO2 composite catalyst and its application in the synergistic reaction of H2S and CO2 to prepare methanethiol. Background Technology

[0002] Methanethiol is an important chemical intermediate used in the production of pesticides, the synthesis of vitamins, methionine, and other pharmaceuticals, and as a food and feed additive. However, there are few domestic producers of methanethiol, and annual production falls far short of market demand, necessitating heavy reliance on imports. A one-step synthesis of methanethiol from H2S and CO2 (CO2 + H2S + 3H2 → CH3SH + 2H2O) not only simultaneously converts H2S and CO2 but also yields the high-value-added product methanethiol, maximizing resource utilization. This reaction is a volume-reducing exothermic reaction, potentially involving the hydrogenation of CO2 to CH3OH, which further reacts with H2S to form methanethiol. These reactions typically occur under pressure and are suitable for temperatures between 300 and 400 °C. Therefore, developing this reaction requires constructing catalysts capable of adsorbing and activating CO2, H2S, and H2, achieving directional catalysis, and maintaining stability at specific temperatures.

[0003] MoS2 has a typical two-dimensional layered structure and belongs to the hexagonal crystal system. As a layered transition metal binary compound, MoS2 mainly exists in nature as molybdenite, with a black appearance and consisting of monolayers. Strong Mo-S covalent bonds exist between monolayers, while weak van der Waals forces exist between adjacent monolayers. Due to the presence of unsaturated Mo coordination sites at its edges, its excellent performance as an active component in hydrodesulfurization has attracted widespread attention in the field of catalysis. ZrO2 is a p-type semiconductor. Its oxygen vacancies can not only anchor active components and regulate the electronic structure of the catalyst, but also promote the adsorption and activation of reactants (such as H2S, CO2, and H2), thereby improving reaction efficiency. Furthermore, ZrO2 also possesses abundant acid-base sites and excellent sulfur resistance.

[0004] Based on this, Mo-based materials supported on ZrO2 show promise as catalysts for the hydrogenation of H2S and CO2 to methanethiol. Controlling the crystal form is an effective means of regulating the oxygen vacancy concentration in ZrO2. Depending on the preparation process parameters, ZrO2 may exist in amorphous (non-crystalline) or crystalline (monoclinic, tetragonal, cubic) forms. Among different structures, amorphous non-crystalline structures with short-range order and long-range disorder have higher oxygen vacancy concentrations. Therefore, preparing ZrO2 with a specific crystal form and uniformly dispersing the active component MoS2 on the ZrO2 surface, through the synergistic effect of MoS2 and ZrO2 oxygen vacancies, is expected to effectively improve the reactivity of the hydrogenation of H2S and CO2 to methanethiol. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a MoS2 / a-ZrO2 composite catalyst and its preparation method, aiming to improve the conversion rate and selectivity of existing catalysts for the hydrogenation of CO2 and H2S to methanethiol.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A MoS2 / a-ZrO2 composite catalyst is prepared by first synthesizing amorphous zirconium dioxide with abundant oxygen vacancies using solvothermal combined with heat treatment, and then using it as a support by impregnation and in-situ sulfidation, wherein the Mo loading is 10 wt%.

[0007] The preparation method of the MoS2 / a-ZrO2 composite catalyst includes the following steps: a. Dissolve zirconium oxynitrate in water and add triethylamine, stirring until well mixed; b. The mixed solution obtained in step a is transferred to a reaction vessel, subjected to a solvothermal reaction, and then naturally cooled at room temperature. The resulting solid is filtered, washed, and dried, and then placed in a muffle furnace for heat treatment to obtain zirconium dioxide with an amorphous structure. c. The amorphous zirconium dioxide obtained in step b is impregnated in ammonium heptamolybdate tetrahydrate solution, dried, and then calcined and sulfided in situ to obtain the MoS2 / a-ZrO2 composite catalyst.

[0008] Furthermore, the molar ratio of zirconium oxynitrate, water, and triethylamine used in step a is 1:555:10.

[0009] Furthermore, the solvothermal reaction in step b is carried out at a temperature of 90 °C for a time of 40 h.

[0010] Furthermore, the heat treatment in step b is performed at a temperature of 400 °C for a duration of 4 h.

[0011] Furthermore, the soaking time in step c is 12 hours.

[0012] Furthermore, the calcination in step c is carried out in air at 400 °C for 3 hours.

[0013] Further, the in-situ sulfidation in step c involves treating the gas in a 10% H2S / H2 mixture at 250 °C for 4 h, then raising the temperature to 350 °C and treating for another 4 h.

[0014] The obtained MoS2 / a-ZrO2 composite catalyst can be used for the synergistic reaction of H2S and CO2 to prepare methanethiol, and exhibits good catalytic activity.

[0015] The reaction conditions were as follows: catalyst dosage was 1 g; the components and contents of the feed gas were 4% H2S, 4% H2 and 1% CO2, with N2 as the equilibrium gas; and the reaction space velocity was 300 h⁻¹. -1 The feed gas flow rate is 5 mL / min. -1 The reaction temperature is 200 ℃~400 ℃, and the reaction pressure is 1.5 MPa.

[0016] This invention involves the reaction of zirconium oxynitrate with hydroxyl groups provided by triethylamine at the water-triethylamine two-phase interface to form a hydroxide. This hydroxide, under hydrothermal self-pressurization, becomes supersaturated and further condenses to form ZrO2. Subsequent calcination yields amorphous zirconium dioxide (a-ZrO2) with a high specific surface area, abundant oxygen vacancies, and a stable structure. This amorphous zirconium dioxide enhances the catalyst's adsorption and dissociation capabilities for CO2 and H2S, promotes the dispersion of the active component MoS2, and improves the synergistic effect between the support and the active component. The synthesis method of MoS2 / a-ZrO2 in this invention is simple, highly reproducible, and applicable in the synergistic preparation of methanethiol from H2S and CO2.

[0017] The present invention has the following advantages and beneficial effects: 1. The amorphous zirconium dioxide prepared by the present invention has more oxygen vacancies, which can promote the adsorption and dissociation of CO2 and H2S by the catalyst. Then, by in-situ sulfidation, the active component MoS2 is uniformly loaded onto its surface, which can promote the full contact between H2S and CO2 and the active sites of the catalyst, thereby improving the catalytic activity.

[0018] 2. The amorphous zirconium dioxide prepared by this invention has a large number of medium-to-strong alkaline sites and a high specific surface area, which can enhance the adsorption capacity for acidic gases such as H2S and CO2. Moreover, the raw materials are inexpensive, the preparation process is simple, and it is easy to achieve industrial production, thus having broad application prospects. Attached Figure Description

[0019] Figure 1 The X-ray powder diffraction patterns of ZrO2 prepared in Examples 1 and 2 are shown.

[0020] Figure 2 Raman spectra of ZrO2 (a) and MoS2 / ZrO2 (b) prepared for Examples and Comparative Examples 1 and 2.

[0021] Figure 3 The N2 adsorption isotherms and pore size distribution diagrams of ZrO2 prepared in Examples and Comparative Examples 1 and 2 are shown.

[0022] Figure 4 SEM images of ZrO2 prepared in Examples 1 and 2 and Comparative Examples 2 are shown.

[0023] Figure 5 TEM images of MoS2 / ZrO2 prepared in Examples 1 and 2.

[0024] Figure 6 XPS plots of O 1s for MoS2 / ZrO2 prepared in Examples 1 and 2 and Comparative Examples 2.

[0025] Figure 7 EPR diagrams of MoS2 / ZrO2 prepared in Examples 1 and 2 and Comparative Examples 2 are shown.

[0026] Figure 8 The CO2-TPD diagrams of MoS2 / ZrO2 prepared in Examples 1 and 2 are shown.

[0027] Figure 9 The activity diagrams of MoS2 / ZrO2 prepared in Examples and Comparative Examples 1 and 2 are shown. Detailed Implementation

[0028] The preparation of a MoS2 / a-ZrO2 composite catalyst includes the following steps: a. Dissolve zirconium oxynitrate in water and add triethylamine, stirring for 0.5 h; the molar ratio of zirconium oxynitrate, water and triethylamine used is 1:555:10; b. The mixed solution obtained in step a was transferred to a hydrothermal reactor and reacted at 90 °C for 40 h. After natural cooling at room temperature, the resulting solid was filtered, washed alternately with distilled water and anhydrous ethanol, dried at 110 °C for 12 h, and then placed in a muffle furnace. The temperature was increased to 400 °C at a rate of 2-5 °C / min and calcined at a constant temperature for 4 h to obtain zirconium dioxide with an amorphous structure. c. The amorphous zirconium dioxide obtained in step b is impregnated in ammonium heptamolybdate tetrahydrate solution for 12 h and then dried. It is then calcined in air at 400 ℃ for 3 h, and then in 10% H2S / H2 mixed gas at 250 ℃ for 4 h. After that, the temperature is increased to 350 ℃ and in situ is sulfided for another 4 h to obtain the MoS2 / a-ZrO2 composite catalyst, in which the Mo loading is 10 wt%.

[0029] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto. Example

[0030] 6.92 g of zirconium oxynitrate was dissolved in 300 mL of distilled water, and 30 mL of triethylamine was added. The mixture was magnetically stirred for half an hour. The solution was then transferred to a high-pressure reactor and reacted at 90 °C for 48 h. After natural cooling at room temperature, the resulting solid was filtered and washed three times each with anhydrous ethanol and distilled water. The powder was then dried at 110 °C for 12 h and then heated to 400 °C at a rate of 2 °C / min in a muffle furnace and held for 4 h to obtain amorphous α-ZrO2.

[0031] The equal-volume impregnation method was used. 1 g of the above-prepared α-ZrO2 was added to an aqueous solution containing 0.1225 g of ammonium heptamolybdate tetrahydrate. After impregnation for 12 h, the product was dried at 80 ℃ for 12 h. Then, it was placed in a muffle furnace and calcined at 400 ℃ for 3 h. After cooling to room temperature, it was in-situ sulfided at 250 ℃ for 4 h in a 10% H2S / H2 mixed gas. The temperature was then increased to 350 ℃ and in-situ sulfided for another 4 h. The final product was named MoS2 / α-ZrO2, with a Mo loading of 10 wt%.

[0032] Comparative Example 1 5.6 g of zirconium oxychloride octahydrate and 0.65 g of hexadecyltrimethylammonium bromide were added to 80 mL of distilled water and dissolved. After dissolving, 2 g of urea was added and the mixture was magnetically stirred for half an hour. The mixture was then transferred to a high-pressure reactor and hydrothermally treated at 150 °C for 24 h. After cooling naturally at room temperature, the resulting solid was filtered and washed three times each with anhydrous ethanol and distilled water. The resulting powder was dried at 80 °C for 12 h and then heated to 500 °C at a rate of 2 °C / min in a muffle furnace and held for 4 h to obtain monoclinic m-ZrO2.

[0033] The equal-volume impregnation method was used. 1 g of the above-prepared m-ZrO2 was added to an aqueous solution containing 0.1225 g of ammonium heptamolybdate tetrahydrate. After impregnation for 12 h, the solution was dried at 80 ℃ for 12 h. Then, it was placed in a muffle furnace and calcined at 400 ℃ for 3 h. After cooling to room temperature, it was in-situ sulfided at 250 ℃ for 4 h in a 10% H2S / H2 mixed gas. The temperature was then increased to 350 ℃ and in-situ sulfided for another 4 h. The final product was named MoS2 / m-ZrO2, with a Mo loading of 10 wt%.

[0034] Comparative Example 2 1.26 g of zirconium nitrate pentahydrate was added to 100 mL of methanol and dissolved. After dissolving, 9 g of urea was added and the mixture was magnetically stirred for half an hour. The mixture was then transferred to a high-pressure reactor and hydrothermally treated at 160 °C for 20 h. After cooling naturally at room temperature, the resulting solid was filtered and washed three times each with anhydrous ethanol and distilled water. The resulting powder was dried at 110 °C for 12 h and then heated to 400 °C at a rate of 2 °C / min in a muffle furnace and held for 4 h to obtain tetragonal t-ZrO2.

[0035] The t-ZrO2 prepared above was added to an aqueous solution containing 0.1225 g of ammonium heptamolybdate tetrahydrate using an equal-volume impregnation method. After impregnation for 12 h, the product was dried at 80 ℃ for 12 h and then placed in a muffle furnace. After calcination at 400 ℃ for 3 h, the product was cooled to room temperature and then in 10% H2S / H2 mixed gas was in situ sulfided at 250 ℃ for 4 h. The temperature was then increased to 350 ℃ and in situ sulfided for another 4 h to obtain the final product, named MoS2 / t-ZrO2, in which the Mo loading was 10 wt%.

[0036] X-ray powder diffraction (XRD): The phase characterization of the samples was performed using an X'pert3 powder diffractometer with an X'celerator as the detector, a copper target (Cu Kα, λ = 0.154 nm) as the excitation source, and an operating voltage of 45 kV and an operating current of 40 mA.

[0037] Raman spectroscopy: Structural information of the samples was analyzed using an in-Via Reflex Raman spectrometer (RENIS-HAW, UK). The scanning range was 300–2500 cm⁻¹. –1 The excitation source was λ=325 nm, the exposure time was 2~10 s, the laser intensity was 1%, and the number of scans was 6.

[0038] N2 physical adsorption-desorption: This method determines the specific surface area and pore size distribution of a sample through N2 physical adsorption. The instrument used is a Micrometric 3Flex fully automated analyzer. The test conditions are as follows: 0.1 g of sample is weighed, pretreated and degassed at 250 °C for 4 h, cooled to room temperature, and then the sample's texture information is obtained by static adsorption in a cold trap cooled to -196 °C with liquid nitrogen. The specific surface area and pore size distribution of the sample are calculated using the BET equation and the BJH model, respectively.

[0039] Scanning electron microscopy (SEM): The morphology of the catalyst was observed using an S-4800 field emission scanning electron microscope. The vacuum level in the analysis chamber was less than 2.7 × 10⁻⁶. -6Pa, scanning voltage and current were 5 kV and 7 μA, respectively. The sample powder was adhered to conductive adhesive and sputtered with gold before observation.

[0040] Field emission transmission electron microscopy (TEM): TEM images of the samples were observed on a JEM-F200 transmission electron microscope (TEM) with an accelerating voltage of 200 kV.

[0041] X-ray photoelectron spectroscopy (XPS): The elemental composition and chemical state of the catalyst surface were analyzed using an EscaLab 250Xi spectrometer. The excitation source was an Al target Kα beam, and the vacuum level in the analysis chamber was <10. -8 The excitation power was 22.5 W, and the binding energy of C 1s at 284.8 eV was used for calibration.

[0042] Electron paramagnetic resonance (EPR) spectroscopy: Information on defects or oxygen vacancies in a sample can be obtained using an E-500 electron paramagnetic resonance spectrometer (Bruker). Testing is performed at room temperature and a frequency of 100 kHz. After placing the sample in a quartz tube, ensure the tube is upright and that the instrument's operating environment is stable and well-ventilated.

[0043] CO2 temperature-programmed desorption-mass spectrometry (CO2-TPD): The basic sites of the catalyst were analyzed using an AutoChem 2920II chemisorption analyzer. The test conditions were: 100 mg catalyst and U-shaped quartz tubes. First, the catalyst was pretreated with helium at 300 °C for one hour to remove adsorbed water and impurities. After cooling to room temperature, the catalyst was purged with pure CO2 for 1 hour (30 mL / min), followed by purging with He for 30 minutes to remove physically adsorbed CO2. Then, the temperature was increased from room temperature to 900 °C (10 °C / min), and the amount of CO2 desorbed was detected using a TCD detector and a Hiden HPR-20 mass spectrometer.

[0044] Figure 1 X-ray powder diffraction patterns of ZrO2 with different crystal forms prepared in Examples 1 and 2. Figure 1 As shown, based on the diffraction peaks, the three samples can be identified as m-ZrO2, t-ZrO2, and a-ZrO2, respectively, and no impurity peaks are observed.

[0045] Figure 2 Raman spectra of different crystal forms of ZrO2 (a) and corresponding MoS2 / ZrO2 (b) prepared for Examples and Comparative Examples 1 and 2. Figure 2 As shown, the peaks further confirm that the three samples are classified as m-ZrO2, t-ZrO2, and a-ZrO2, respectively, with no impurity peaks appearing (a). Meanwhile, the MoS2 in the catalyst reaches a peak at 381 cm⁻¹. −1 and 405cm−1 There are two obvious peaks corresponding to the in-plane Mo-S phonon mode (E 1 2g ) and out-of-plane Mo-S mode (A 1g ) of the typical layered structure of MoS2, indicating that MoS2 has been successfully loaded on the surface of the catalyst (b).

[0046] Figure 3 shows the N2 adsorption isotherms and pore size distribution diagrams of ZrO2 with different crystal forms prepared in the example and comparative examples 1 and 2. As Figure 3 shown, the adsorption isotherms of all samples are of type IV, and all samples have a mesoporous structure.

[0047] Table 1 shows the pore structure parameters of ZrO2 with different crystal forms prepared in the example and comparative examples 1 and 2.

[0048] Table 1

[0049] It can be seen from Table 1 that the order of specific surface area of each sample is a-ZrO2>t-ZrO2>m-ZrO2, and the increase of specific surface area is conducive to exposing more surface reactive sites.

[0050] Figure 4 are SEM images of ZrO2 with different crystal forms prepared in the example and comparative examples 1 and 2. It can be seen from the images that m-ZrO2 (a) prepared in comparative example 1 has a spherical morphology with a size of about 50 nm, while t-ZrO2 (b) prepared in comparative example 2 and a-ZrO2 (c) prepared in the example have a stacked morphology of small particles.

[0051] Figure 5 are TEM images of MoS2 / ZrO2 prepared in the example and comparative examples 1 and 2. The lattice fringes of MoS2 can be observed in the images, with a crystal plane spacing of 0.62 nm. The lattice fringes of m-ZrO2 (a) and t-ZrO2 (b) can also be observed, with crystal plane spacings of 0.37 nm and 0.295 nm respectively, but no lattice fringes of a-ZrO2 (c) are observed. This indicates that MoS2 supported on zirconia with different crystal forms has been successfully prepared in the present invention.

[0052] Figure 6 are O 1s XPS spectra of MoS2 / ZrO2 prepared in the example and comparative examples 1 and 2. It can be seen from the spectra that the adsorbed oxygen content of the three catalysts is in the order of MoS2 / m-ZrO2 < MoS2 / t-ZrO2 < MoS2 / a-ZrO2. This indicates that MoS2 / a-ZrO2 has the highest oxygen vacancy concentration, and oxygen vacancies can improve the adsorption and dissociation capacity of the catalyst for CO2 and H2S, thereby improving the catalytic activity.

[0053] Figure 7 is EPR spectra of MoS2 / ZrO2 prepared in the example and comparative examples 1 and 2. It can be observed from the figure that there is a spectral peak corresponding to oxygen vacancies at the position of g=2.003, and the order of oxygen vacancy concentration of the three catalysts is MoS2 / m-ZrO2 < MoS2 / t-ZrO2 < MoS2 / a-ZrO2. This is consistent with the O 1s XPS result.

[0054] Figure 8 is CO2-TPD spectra of MoS2 / ZrO2 prepared in example 1 and comparative examples 1 and 2. It can be seen from the figure that there is a CO2 desorption peak at about 450 ℃, which can be assigned to the medium-strength basic sites of the catalyst, and the content order is MoS2 / m-ZrO2 < MoS2 / t-ZrO2 < MoS2 / a-ZrO2. Medium-strength basic sites are conducive to the adsorption and dissociation of acidic gases CO2 and H2S, and improve the reaction activity.

[0055] Figure 9 is a catalytic activity curve diagram for hydrogenation of CO2 / H2S to methyl mercaptan at 300 ℃ over MoS2 / ZrO2 prepared in example 1 and comparative examples 1 and 2. It can be seen from the figure that MoS2 / a-ZrO2 has the best selectivity and yield for preparing methyl mercaptan, indicating that the crystal form difference of zirconium dioxide will affect the selectivity of the catalyst for methyl mercaptan.

[0056] The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the coverage scope of the present invention.

Claims

1. The application of a MoS2 / a-ZrO2 composite catalyst in the synergistic reaction of H2S and CO2 to prepare methanethiol, characterized in that, Amorphous zirconium dioxide with abundant oxygen vacancies was first synthesized by solvothermal combined with heat treatment. Then, using it as a support, the MoS2 / a-ZrO2 composite catalyst was obtained by impregnation and in-situ sulfidation. The Mo loading in the composite catalyst was 10 wt%. The preparation of the MoS2 / a-ZrO2 composite catalyst specifically includes the following steps: a. Dissolve zirconium oxynitrate in water and add triethylamine, stirring until well mixed; b. The mixed solution obtained in step a is transferred to a reaction vessel, subjected to a solvothermal reaction, and then naturally cooled at room temperature. The resulting solid is filtered, washed, and dried, and then placed in a muffle furnace for heat treatment to obtain zirconium dioxide with an amorphous structure. c. The amorphous zirconium dioxide obtained in step b is impregnated in ammonium heptamolybdate tetrahydrate solution, dried, and then calcined and sulfided in situ to obtain the MoS2 / a-ZrO2 composite catalyst.

2. The application according to claim 1, characterized in that, The molar ratio of zirconium oxynitrate, water, and triethylamine used in step a is 1:555:

10.

3. The application according to claim 1, characterized in that, The solvothermal reaction in step b is carried out at a temperature of 90 °C for 40 h.

4. The application according to claim 1, characterized in that, The heat treatment in step b is performed at a temperature of 400 °C for 4 hours.

5. The application according to claim 1, characterized in that, The soaking time in step c is 12 hours.

6. The application according to claim 1, characterized in that, The calcination described in step c is performed in air at 400 °C for 3 hours.

7. The application according to claim 1, characterized in that, The in-situ sulfidation described in step c involves treating the gas in a 10% H2S / H2 mixture at 250 °C for 4 h, then raising the temperature to 350 °C and treating for another 4 h.

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