CN118022779A - Molybdenum disulfide/zirconia composite catalyst and preparation and application thereof - Google Patents

Abstract

The invention discloses a MoS ₂/a-ZrO₂ composite catalyst and a preparation method and application thereof, and belongs to the technical field of catalyst preparation. The composite catalyst is prepared by synthesizing amorphous zirconium dioxide with rich oxygen vacancies by solvothermal combination heat treatment, and then taking the amorphous zirconium dioxide as a carrier in a dipping and in-situ vulcanization mode. The formed amorphous zirconium dioxide has higher specific surface area, abundant oxygen vacancies and stable structure, which is not only beneficial to enhancing the adsorption and dissociation capability of the obtained catalyst to CO ₂ and H ₂ S, but also beneficial to the dispersion of the active component MoS ₂ and promotes the synergistic effect of the carrier and the active component. The obtained composite catalyst can show good catalytic activity when applied to the reaction of preparing methyl mercaptan by the cooperation of H ₂ S and CO ₂.

Description

A molybdenum disulfide/zirconium oxide composite catalyst and its preparation and application

Technical Field

The invention belongs to the technical field of catalyst preparation, and particularly relates to a preparation method of a _MoS2 /a- _ZrO2 composite catalyst and application thereof in preparing methyl mercaptan through the coordinated reaction of _H2S and _CO2 .

Background technique

Methyl mercaptan is an important chemical intermediate that can be used to produce pesticides, synthesize vitamins, methionine and other drugs, and can also be used as a food and feed additive. However, there are few domestic companies producing methyl mercaptan, and the annual output is far from meeting market demand, and a large amount of imports are required. The one-step synthesis of methyl mercaptan using H ₂ S and CO ₂ as raw materials (CO ₂ +H ₂ S+3H ₂ →CH ₃ SH+2H ₂ O) can not only convert H ₂ S and CO ₂ at the same time, but also obtain high value-added product methyl mercaptan, so as to maximize the utilization of resources. This reaction is an exothermic reaction with reduced volume, and may undergo processes such as CO ₂ hydrogenation to generate CH ₃ OH and further react with H ₂ S to generate methyl mercaptan. The related reactions are usually carried out under pressure and the suitable temperature range is between 300 and 400 ℃. Therefore, the development of this reaction must construct a catalyst that has the ability to adsorb and activate CO ₂ , H ₂ S and H ₂ and can achieve directional catalysis, while remaining stable at a certain temperature.

MoS ₂ has a typical two-dimensional layered structure and belongs to the hexagonal system. As a layered transition metal binary compound, MoS ₂ mainly exists in the form of molybdenite in nature. It is black in appearance and consists of monolayers. There are strong Mo-S covalent bonds between monolayers, and there are weak van der Waals forces between adjacent monolayers. Because its edges have active sites such as unsaturated Mo coordination, its excellent performance as an active component in hydrodesulfurization has attracted widespread attention in the field of catalysis. ZrO ₂ is a p-type semiconductor, and 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 H ₂ S, CO ₂ and H ₂ ), thereby improving the reaction efficiency. In addition, ZrO ₂ also has abundant acid and base sites and excellent sulfur resistance.

Based on this, Mo-based materials with ZrO ₂ as a carrier are expected to be used as catalysts for the hydrogenation of H ₂ S and CO ₂ to produce methyl mercaptan. Regulating the crystal form is an effective means to regulate the oxygen vacancy concentration of ZrO _2. Depending on the preparation process parameters, ZrO ₂ may exist in an amorphous (non-crystalline) form or a crystalline (monoclinic, tetragonal, cubic) form. Among the different structures, the amorphous non-crystalline structure with short-range order and long-range disorder has a higher oxygen vacancy concentration. Therefore, by preparing ZrO ₂ with a specific crystal form and uniformly dispersing the active component MoS ₂ on the surface of ZrO ₂ , the reaction activity of hydrogenation of H ₂ S and CO ₂ to produce methyl mercaptan is expected to be effectively improved through the synergistic effect of MoS ₂ and ZrO ₂ oxygen vacancies.

Summary of the invention

In view of the deficiencies of the prior art, the present invention provides a MoS ₂ /a-ZrO ₂ composite catalyst and a preparation method thereof, aiming to improve the conversion rate and selectivity of the catalyst for preparing methyl mercaptan by hydrogenation of CO ₂ and H ₂ S in the prior art.

To achieve the above object, the present invention adopts the following technical solution:

A _MoS2 /a- _ZrO2 composite catalyst is prepared by firstly synthesizing amorphous zirconium dioxide with abundant oxygen vacancies by solvent thermal combined with heat treatment, and then using the amorphous zirconium dioxide as a carrier through impregnation and in-situ sulfidation, wherein the loading amount of Mo is 10wt%.

The preparation method of the MoS ₂ /a-ZrO ₂ composite catalyst comprises the following steps:

a. Dissolve zirconium nitrate in water and add triethylamine and stir to mix;

b. The mixed solution obtained in step a was transferred to a reactor, and after the solvothermal reaction, it was naturally cooled at room temperature. The resulting solid was filtered, washed, dried, and placed in a muffle furnace for heat treatment to obtain zirconium dioxide having an amorphous structure;

c. The amorphous zirconium dioxide obtained in step b is added to an ammonium heptamolybdate tetrahydrate solution, impregnated and dried, and then calcined and in-situ sulfided to obtain the MoS ₂ /a-ZrO ₂ composite catalyst.

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

Furthermore, the temperature of the solvent thermal reaction in step b is 90° C. and the time is 40 h.

Furthermore, the heat treatment in step b is performed at a temperature of 400°C and for a time of 4 hours.

Furthermore, the immersion time in step c is 12 hours.

Furthermore, the calcination in step c is carried out in air at 400° C. for 3 h.

Furthermore, the in-situ sulfidation in step c is carried out in a 10% H ₂ S/H ₂ mixed gas at 250° C. for 4 h, then raised to 350° C. and further treated for 4 h.

The obtained MoS ₂ /a-ZrO ₂ composite catalyst can be used for the synergistic reaction of H ₂ S and CO ₂ to prepare methyl mercaptan and exhibits good catalytic activity.

The reaction conditions are as follows: the catalyst dosage is 1 g; the raw gas components and contents are: 4% H ₂ S, 4% H ₂ and 1% CO ₂ , with N ₂ as the balance gas; the reaction space velocity is 300 h ^-1 ; the raw gas flow rate is 5 mL·min ^-1 ; the reaction temperature is 200 ℃~400 ℃, and the reaction pressure is 1.5 MPa.

The invention allows zirconium oxynitrate to react with hydroxyl provided by triethylamine at the water-triethylamine two-phase interface to form hydroxide, which is in a supersaturated state in a hydrothermal self-pressurized environment and further polycondenses to form ZrO ₂ , and then calcined to obtain amorphous zirconium dioxide (a-ZrO ₂ ) with a high specific surface area, abundant oxygen vacancies and a stable structure, which can enhance the catalyst's adsorption and dissociation ability for CO ₂ and H ₂ S, promote the dispersion of the active component MoS ₂ , and enhance the synergistic effect of the carrier and the active component. The synthesis method of MoS ₂ /a-ZrO ₂ of the invention has simple process and strong repeatability, and is used in the synergistic preparation of methyl mercaptan by H ₂ S and CO ₂ .

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. The active component _MoS2 is evenly loaded on its surface by in-situ sulfidation, which can promote the full contact between _H2S and _CO2 and the active sites of the catalyst, thereby improving the catalytic activity.

2. The amorphous zirconium dioxide prepared by the present invention has a large number of medium-strong alkaline sites and a high specific surface area, which can improve the adsorption capacity of acidic gases such as _H2S and _CO2 . In addition, the raw materials are inexpensive, the preparation process is simple, and industrial production is easy to achieve, so it has broad application prospects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is an X-ray powder diffraction spectrum of ZrO ₂ prepared in Example and Comparative Examples 1 and 2.

FIG2 is a Raman spectrum of ZrO ₂ (a) and MoS ₂ /ZrO ₂ (b) prepared in Example and Comparative Examples 1 and 2. ...

FIG3 is a diagram showing the N ₂ adsorption isotherms and pore size distribution of ZrO ₂ prepared in Example and Comparative Examples 1 and 2.

FIG. 4 is a SEM image of ZrO ₂ prepared in Example and Comparative Examples 1 and 2.

FIG5 is a TEM image of MoS ₂ /ZrO ₂ prepared in Example and Comparative Examples 1 and 2.

FIG6 is an XPS graph of O 1s of MoS ₂ /ZrO ₂ prepared in Example and Comparative Examples 1 and 2.

FIG. 7 is an EPR graph of MoS ₂ /ZrO ₂ prepared in Example and Comparative Examples 1 and 2.

FIG8 is a CO ₂ -TPD graph of MoS ₂ /ZrO ₂ prepared in Example and Comparative Examples 1 and 2.

FIG. 9 is an activity diagram of MoS ₂ /ZrO ₂ prepared in Example and Comparative Examples 1 and 2.

Detailed ways

The preparation of a MoS ₂ /a-ZrO ₂ composite catalyst comprises the following steps:

a. Dissolve zirconium oxynitrate in water and add triethylamine and stir 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, reacted at 90 ° C for 40 h, and then naturally cooled at room temperature. The obtained solid was filtered, washed alternately with distilled water and anhydrous ethanol, dried at 110 ° C for 12 h, placed in a muffle furnace, heated 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 added to an ammonium heptamolybdate tetrahydrate solution and immersed for 12 hours, then dried, and then calcined at 400°C in an air environment for 3 hours, and then in-situ sulfurized at 250°C for 4 hours in a 10% _H2S / _H2 mixed gas, and then raised to 350°C and continued in-situ sulfurization for 4 hours to obtain the _MoS2 /a- _ZrO2 composite catalyst, wherein the Mo loading in the catalyst is 10wt%.

In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

Example

6.92 g of zirconium oxynitrate was dissolved in 300 mL of distilled water, and 30 mL of triethylamine was added. The mixture was stirred magnetically for half an hour, and then the mixed solution was transferred to a high-pressure reactor. After reacting at 90 °C for 48 hours, it was naturally cooled at room temperature. The obtained solid was filtered, cross-washed with anhydrous ethanol and distilled water three times each, and the obtained powder was dried at 110 °C for 12 hours, and then heated to 400 °C at a rate of 2 °C/min in a muffle furnace and kept warm for 4 hours to obtain amorphous a-ZrO ₂ .

By adopting the equal volume impregnation method, 1 g of the a-ZrO ₂ prepared above was added to an aqueous solution containing 0.1225 g of ammonium heptamolybdate tetrahydrate. After impregnation for 12 hours, the mixture was dried at 80 ℃ for 12 hours and then placed in a muffle furnace. It was calcined at 400 ℃ for 3 hours. After cooling to room temperature, it was in-situ sulfurized at 250 ℃ for 4 hours in a 10% H ₂ S/H ₂ mixed gas and then increased to 350 ℃. The in-situ sulfurization was continued for 4 hours to obtain the final product named MoS ₂ /a-ZrO ₂ , in which the Mo loading was 10wt%.

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 2 g of urea was added after dissolution. After magnetic stirring for half an hour, the mixed solution was transferred to a high-pressure reactor, hydrothermally treated at 150 °C for 24 h, and naturally cooled at room temperature. The obtained solid was filtered, cross-washed with anhydrous ethanol and distilled water three times each, and the obtained 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 kept warm for 4 h to obtain monoclinic m-ZrO ₂ .

By adopting the equal volume impregnation method, 1 g of the m-ZrO ₂ prepared above was added to an aqueous solution containing 0.1225 g of ammonium heptamolybdate tetrahydrate. After impregnation for 12 hours, the mixture was dried at 80 ℃ for 12 hours and then placed in a muffle furnace. It was calcined at 400 ℃ for 3 hours. After cooling to room temperature, it was in-situ sulfurized at 250 ℃ for 4 hours in a 10% H ₂ S/H ₂ mixed gas and then increased to 350 ℃. The in-situ sulfurization was continued for 4 hours to obtain the final product named MoS ₂ /m-ZrO ₂ , in which the Mo loading was 10wt%.

Comparative Example 2

1.26 g of zirconium nitrate pentahydrate was added to 100 mL of methanol, and 9 g of urea was added after dissolution. After magnetic stirring for half an hour, the mixed solution was transferred to a high-pressure reactor and hydrothermally treated at 160 °C for 20 h. The mixture was naturally cooled at room temperature. The obtained solid was filtered, cross-washed with anhydrous ethanol and distilled water three times each, and the obtained powder was dried at 110 °C for 12 h. Then, the temperature was raised to 400 °C at a rate of 2 °C/min in a muffle furnace and kept at this temperature for 4 h to obtain tetragonal t-ZrO ₂ .

By adopting the equal volume impregnation method, 1 g of the t-ZrO ₂ prepared above was added to an aqueous solution containing 0.1225 g of ammonium heptamolybdate tetrahydrate. After impregnation for 12 hours, the mixture was dried at 80 ℃ for 12 hours and then placed in a muffle furnace. It was calcined at 400 ℃ for 3 hours. After cooling to room temperature, it was in-situ sulfurized at 250 ℃ for 4 hours in a 10% H ₂ S/H ₂ mixed gas and then increased to 350 ℃. The in-situ sulfurization was continued for 4 hours to obtain the final product named MoS ₂ /t-ZrO ₂ , in which the Mo loading was 10wt%.

X-ray powder diffraction (XRD): The phase characterization of the samples was measured using an X’pert3 powder diffractometer. The detector was an X’celerator, the copper target (Cu Kα, λ = 0.154 nm) was the excitation radiation source, the operating voltage was 45 kV, and the operating current was 40 mA.

Raman: The structural information of the samples was analyzed by in Via Reflex Raman spectrometer (RENIS-HAW, UK). The scanning range was 300~2500 cm ^–1 , the excitation light source was λ=325 nm, the exposure time was 2~10 s, the laser intensity was 1%, and the number of scans was 6 times.

N ₂ physical adsorption and desorption (N ₂ Physisorption): The specific surface area, pore size distribution, etc. of the sample were determined by N ₂ physical adsorption. The instrument was a 3Flex fully automatic analyzer produced by Micrometric, USA. The test conditions were as follows: 0.1 g of sample was weighed, pre-treated and degassed at 250 °C for 4 h, cooled to room temperature, and the texture information of the sample was obtained by static adsorption method in a cold trap cooled to -196 °C by liquid nitrogen. The specific surface area and pore size distribution of the sample were calculated according to the BET equation and the BJH model, respectively.

Scanning electron microscopy (SEM): The morphology of the catalyst was observed by S-4800 field emission scanning electron microscope. The vacuum degree of the analysis chamber was less than 2.7×10 ^-6 Pa, and the scanning voltage and current were 5 kV and 7 μA, respectively. The sample powder was adhered to the conductive glue and sprayed with gold before observation.

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.

X-ray photoelectron spectroscopy (XPS): EscaLab 250Xi spectrometer was used to analyze the elemental composition and chemical state of the catalyst surface. The excitation light source was Al target Kα ray, the vacuum degree of the analysis chamber was <10 ^-8 bar, the excitation power was 22.5 W, and the binding energy of C 1s at 284.8 eV was used for calibration.

Electron paramagnetic resonance spectroscopy (EPR): The defect or oxygen vacancy information of the sample can be obtained by using an E-500 electron paramagnetic resonance spectrometer (Bruker). The test is carried out at room temperature with a test frequency of 100 kHz. After the sample is placed in a quartz tube, the tube should be kept vertical and the working environment of the instrument should be stable and air circulated.

CO ₂ programmed temperature desorption-mass spectrometry (CO ₂ -TPD): The basic position of the catalyst was analyzed using an AutoChem 2920II chemical adsorption instrument. The test conditions were: 100 mg of catalyst was used and the sample tube was a U-shaped quartz tube. First, the sample was pretreated with helium at 300 °C for one hour to remove the adsorbed water and impurities; after the temperature dropped to room temperature, pure CO ₂ was purged for 1 hour (30 mL/min), and then He gas was purged for 30 minutes to remove the physically adsorbed CO ₂ ; then the temperature was raised from room temperature to 900 °C (10 °C/min), and the CO ₂ desorption amount was detected by TCD detector and Hiden HPR-20 mass spectrometer.

Figure 1 is an X-ray powder diffraction spectrum of different crystalline ZrO ₂ prepared in Example and Comparative Examples 1 and 2. As shown in Figure 1 , the three samples can be identified as m-ZrO ₂ , t-ZrO ₂ and a-ZrO ₂ , respectively, based on the diffraction peaks that appear, and no impurity peaks appear.

Figure 2 shows the Raman spectra of different crystalline ZrO ₂ (a) and corresponding MoS ₂ /ZrO ₂ (b) prepared in Example and Comparative Examples 1 and 2. As shown in Figure 2, it can be further confirmed based on the peaks that the three samples are respectively classified as m-ZrO ₂ , t-ZrO ₂ and a-ZrO ₂ , and no impurity peaks appear (a). The MoS ₂ in the catalyst has two obvious peaks at 381 cm ⁻¹ and 405 cm ⁻¹ , which correspond to the in-plane Mo-S phonon mode (E ¹ _2g ) and out-of-plane Mo-S mode (A _1g ) of the typical MoS ₂ layered structure, respectively, indicating that MoS ₂ has been successfully loaded on the surface of the catalyst (b).

Figure 3 shows the N ₂ adsorption isotherms and pore size distribution diagrams of different crystalline ZrO ₂ prepared in Example and Comparative Examples 1 and 2. As shown in Figure 3, the adsorption isotherms of all samples are type IV, and the samples are all mesoporous structures.

Table 1 shows the pore structure parameters of different crystalline ZrO ₂ prepared in Example and Comparative Examples 1 and 2.

Table 1

As can be seen from Table 1, the order of the specific surface areas of the samples is a-ZrO ₂ >t-ZrO ₂ >m-ZrO ₂ , and the increase in specific surface area is beneficial to exposing more surface reactive sites.

Figure 4 is a SEM image of different crystalline ZrO2 prepared in Example and Comparative Examples 1 and _2. It can be seen from the figure that m- _ZrO2 (a) prepared in Comparative Example 1 is spherical in shape with a size of about 50 nm, while t- _ZrO2 (b) prepared in Comparative Example 2 and a- _ZrO2 (c) prepared in Example are small particle accumulation morphologies.

FIG5 is a TEM image of MoS ₂ /ZrO ₂ prepared in Example and Comparative Examples 1 and 2. From the figure, lattice fringes of MoS ₂ can be observed, and the interplanar spacing is 0.62 nm. It can also be observed that the interplanar spacing of the lattice fringes of m-ZrO ₂ (a) and t-ZrO ₂ (b) are 0.37 nm and 0.295 nm, respectively, but the lattice fringes of a-ZrO ₂ (c) are not observed. It shows that the present invention successfully prepares MoS ₂ loaded with zirconium dioxide of different crystal forms.

Figure 6 is the O 1s XPS spectra of MoS ₂ /ZrO ₂ prepared in Example and Comparative Examples 1 and 2. It can be seen from the figure that the adsorbed oxygen content of the three catalysts is MoS ₂ /m-ZrO ₂ <MoS ₂ /t-ZrO ₂ <MoS ₂ /a-ZrO _2. This shows that MoS ₂ /a-ZrO ₂ has the highest oxygen vacancy concentration, and oxygen vacancies can improve the catalyst's adsorption and dissociation ability for CO ₂ and H ₂ S, thereby improving the catalytic activity.

Figure 7 is the EPR spectra of MoS ₂ /ZrO ₂ prepared in Example and Comparative Examples 1 and 2. It can be observed from the figure that there is a peak corresponding to oxygen vacancies at the position of g=2.003 and the order of oxygen vacancy concentrations of the three catalysts is MoS ₂ /m-ZrO ₂ <MoS ₂ /t-ZrO ₂ <MoS ₂ /a-ZrO _2. This is consistent with the O 1s XPS results.

FIG8 is a CO ₂ -TPD spectrum of MoS ₂ /ZrO ₂ prepared in Example 1 and Comparative Examples 1 and 2. As can be seen from the figure, there is a CO ₂ desorption peak at about 450 °C, which can be attributed to the medium-strong alkaline site of the catalyst, and its content is MoS ₂ /m-ZrO ₂ <MoS ₂ /t-ZrO ₂ <MoS ₂ /a-ZrO _2. The medium-strong alkaline site is conducive to the adsorption and dissociation of acidic gases CO ₂ and H ₂ S, and improves the reaction activity.

Figure 9 is a catalytic activity curve of _MoS2 /ZrO2 prepared in Example 1 and Comparative Examples 1 and ₂ for hydrogenation of _CO2 / _H2S to methyl mercaptan at 300°C. It can be seen from the figure that _MoS2 /a- _ZrO2 has the best selectivity and yield for preparing methyl mercaptan, indicating that the difference in the crystal form of zirconium dioxide will affect the selectivity of the catalyst for methyl mercaptan.

The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims (10)

1. A method for preparing a _MoS2 /a- _ZrO2 composite catalyst, characterized in that amorphous zirconium dioxide with abundant oxygen vacancies is first synthesized by solvent thermal combined with heat treatment, and then the _MoS2 /a- _ZrO2 composite catalyst is obtained by impregnation and in-situ sulfidation using the amorphous zirconium dioxide as a carrier. 2. The method for preparing the _MoS2 /a- _ZrO2 composite catalyst according to claim 1, characterized in that it specifically comprises the following steps: a. Dissolve zirconium nitrate in water and add triethylamine and stir to mix; b. The mixed solution obtained in step a was transferred to a reactor, and after the solvothermal reaction, it was naturally cooled at room temperature. The resulting solid was filtered, washed, dried, and placed in a muffle furnace for heat treatment to obtain zirconium dioxide having an amorphous structure; c. The amorphous zirconium dioxide obtained in step b is added to an ammonium heptamolybdate tetrahydrate solution, impregnated and dried, and then calcined and in-situ sulfided to obtain the MoS ₂ /a-ZrO ₂ composite catalyst. 3 . The method for preparing the MoS ₂ /a-ZrO ₂ composite catalyst according to claim 2 , characterized in that the molar ratio of zirconium oxynitrate, water and triethylamine used in step a is 1:55:10. 4 . The method for preparing the MoS ₂ /a-ZrO ₂ composite catalyst according to claim 2 , characterized in that the temperature of the solvothermal reaction in step b is 90° C. and the time is 40 h. 5 . The method for preparing the MoS ₂ /a-ZrO ₂ composite catalyst according to claim 2 , characterized in that the heat treatment in step b is performed at a temperature of 400° C. for 4 h. 6 . The method for preparing the MoS ₂ /a-ZrO ₂ composite catalyst according to claim 2 , characterized in that the impregnation time in step c is 12 hours. 7. The method for preparing the _MoS2 /a- _ZrO2 composite catalyst according to claim 2, characterized in that the calcination in step c is carried out in air at 400°C for 3h. 8. The method for preparing the _MoS2 /a- _ZrO2 composite catalyst according to claim 2, characterized in that the in-situ sulfidation in step c is carried out in a 10% _H2S / _H2 mixed gas at 250°C for 4 hours, then raised to 350°C for another 4 hours. 9. A _MoS2 /a- _ZrO2 composite catalyst prepared by the method of claim 1, characterized in that the loading amount of Mo in the composite catalyst is 10wt%. 10. Use of the _MoS2 /a- _ZrO2 composite catalyst as claimed in claim 9 in the preparation of methyl mercaptan by the synergistic reaction of _H2S and _CO2 .