Carbon layer coated modified catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and particularly relates to a carbon layer coated modified catalyst as well as a preparation method and application thereof. The carbon layer coated modified catalyst comprises a carrier and an active component, the active component is carbon layer coated nickel nanoparticles, and the loading capacity of the active component in the catalyst is 10-45wt%. According to the carbon layer coated modified catalyst provided by the invention, the active components are coated inside the carbon material, so that the loss and inactivation of the active components in the catalyst can be greatly reduced in the reaction process, and the stability of the catalyst is improved, thereby prolonging the service life of the catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a carbon layer coated modified catalyst and a preparation method and application thereof. Background Art

[0002] Methyl chloride is an important raw material for organic synthesis, widely used as a solvent, extractant, propellant, refrigerant, local anesthetic, and methylating agent in the production of pesticides, fragrances, and pharmaceuticals. It is also used as a pharmaceutical anesthetic and as an intermediate in methane chloride, serving as a solvent in the production of isobutyl rubber. 90% of methyl chloride is used to produce methylchlorosilane, a key raw material for synthesizing organosilicon, which is widely used in construction, textiles, electronics, machinery, transportation, chemicals, pharmaceuticals, food, aerospace, and other fields. Furthermore, methyl chloride is more reactive than methane and can be used as an intermediate in the synthesis of downstream products, similar to methanol in the coal chemical industry.

[0003] Currently, gas-solid phase catalysis is the primary method for synthesizing methyl chloride both domestically and internationally. Methanol and hydrogen chloride are the raw materials for this process. This process uses γ-Al₂O₃ as a catalyst. Gaseous methanol reacts with a slight excess of dry hydrogen chloride in a fixed bed at a temperature of 250–350°C and a pressure of 0.1–0.2 MPa. The methanol conversion rate exceeds 98%, and the methyl chloride selectivity exceeds 99%. The product exiting the reactor is quenched, resulting in a liquid mixture consisting of hydrochloric acid (22% by mass) containing a small amount of methanol and dimethyl ether (DME). This mixture enters a recovery system. The gaseous mixture undergoes water and alkali washing, then drying with concentrated sulfuric acid, compression, and cooling to yield the finished product.

[0004] Catalyst deactivation is currently a major challenge facing existing vapor-phase catalytic synthesis processes for methanol and hydrogen chloride. Traditional catalysts, such as alumina and molecular sieves, are susceptible to deactivation during the reaction due to carbon deposition, water vapor poisoning, and hydrogen chloride corrosion, resulting in shortened catalyst life and reduced production efficiency. Carbon deposition is one of the main causes of catalyst deactivation. The carbonaceous deposits formed during the reaction can cover the catalyst's active sites, hindering contact between the reactants and the catalyst, thereby reducing catalytic activity or even completely deactivating it.

[0005] In order to solve the problem of catalyst deactivation due to carbon deposition, researchers have proposed a variety of methods, including developing new anti-carbon deposition catalysts, optimizing reaction conditions, and improving catalyst preparation processes. Among them, carbon layer coating modification is an effective strategy. Carbon layer coating can form a protective layer on the surface of the catalyst to prevent reactants or intermediates from directly contacting the active sites of the catalyst, thereby reducing the formation of carbon deposition and the loss of active components. However, the existing carbon layer coated modified catalysts still have some shortcomings, such as the difficulty in controlling the thickness of the carbon layer, the weak bonding between the carbon layer and the catalyst, and the easy oxidation of the carbon layer at high temperatures. These problems limit the application of carbon layer coated modified catalysts in the synthesis of monochloromethane. Therefore, developing a new carbon layer coated modified catalyst to solve the problems existing in the prior art is of great significance for improving the efficiency and economy of the monochloromethane synthesis process. The present invention aims to provide a preparation method of a carbon layer coated modified catalyst, and apply it to the synthesis of monochloromethane to improve the anti-carbon deposition performance of the catalyst, extend the catalyst life, and improve product selectivity. Summary of the Invention

[0006] To address the deactivation problem of existing catalysts for synthesizing methyl chloride due to carbon deposition, the present invention provides a carbon-coated catalyst, its preparation method, and its application. The catalyst exhibits advantages such as resistance to carbon deposition, high activity, low cost, long life, and resistance to hydrogen chloride corrosion. The preparation method is simple and, when applied to the reaction of synthesizing methyl chloride from methanol and hydrogen chloride, exhibits high conversion rates and high product selectivity, thus possessing great application prospects.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A carbon layer coated modified catalyst comprises a carrier and an active component, wherein the active component is carbon layer coated nickel nanoparticles, the loading amount of the active component in the catalyst is 10-45wt%, and the carbon layer coated nickel nanoparticles are composed of layered carbon material coated nickel nanoparticles. Preferably, the loading amount of the active component in the catalyst is 15-40 wt%; Preferably, the carrier is Raschig ring-type activated alumina, and the average radial length of the carrier is 6.5-7.5 mm, and the average axial length is 6.2-7.1 mm.

[0008] The present invention also provides a method for preparing the above-mentioned carbon layer coated modified catalyst, comprising the following steps: The carbon layer coated nickel nanoparticles prepared above were dispersed in water, impregnated on Raschig ring type activated alumina in equal volume, dried at 100-120°C and calcined at 400-700°C to obtain a carbon layer coated modified catalyst.

[0009] The carbon layer coated nickel nanoparticles are prepared by any one of one-step pyrolysis, vapor deposition, solvent thermal, hydrothermal, electrochemical and redox methods. Preferably, the carbon layer coated nickel nanoparticles are prepared by one-step pyrolysis.

[0010] Further preferably, the preparation method of the carbon layer-coated nickel nanoparticles is specifically as follows: Nickel acetylacetonate and potassium chloride are dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture is dried at 90-110°C to obtain a mixed powder. The mixed powder is heated to 350-800°C in a nitrogen atmosphere for annealing treatment, kept warm for 2-4 hours, and then washed and dried to obtain carbon layer-coated nickel nanoparticles.

[0011] During the pyrolysis process, the metal precursor nickel acetylacetonate is melted into a liquid and decomposed on the surface of potassium chloride. Potassium chloride acts as a hard template, suppressing the aggregation phenomenon by changing the diffusion rate of metal atoms during the nucleation process, thereby forming a carbon layer-coated metal structure.

[0012] Preferably, the annealing temperature is 550°C.

[0013] Preferably, the mass ratio of the nickel acetylacetonate to potassium chloride is 1:1.5-4, and further preferably, the mass ratio of the nickel acetylacetonate to potassium chloride is 1:1.5-2.5. Preferably, the temperature is raised by programmed heating at a rate of 2 to 10° C. / min, more preferably at a rate of 5° C. / min.

[0014] The present invention also discloses the application of the carbon layer coated modified catalyst in the reaction of synthesizing monochloromethane using methanol and hydrogen chloride as raw materials. Specifically, the carbon layer coated modified catalyst is applied to the reaction of synthesizing monochloromethane using methanol and hydrogen chloride in the gas phase.

[0015] Preferably, the reaction for synthesizing methyl chloride using methanol and hydrogen chloride as raw materials is specifically as follows: Hydrogen chloride gas and methanol gas are introduced into a fixed bed reactor loaded with the above catalyst. The reaction temperature is 200-280°C and the methanol mass space velocity is 0.5-1.8h -1 The mass ratio of hydrogen chloride gas to methanol is 1.1-1.4:1, and the pressure of the synthesis monochloromethane reaction is 1-4 atm.

[0016] Preferably, the pressure of the methyl chloride synthesis reaction is 1-2 atm. Preferably, the temperature of the reaction for synthesizing monochloromethane is 200-250°C. Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects: (1) The carbon-coated catalyst provided by the present invention, because the active components are encapsulated within the carbon material, can significantly reduce the loss and deactivation of active components in the catalyst during the reaction, improve the stability of the catalyst, and thus increase the service life of the catalyst. After 300 hours of reaction, the methanol conversion rate remained high and the catalytic activity was almost unchanged, indicating that the nickel loss rate was extremely low.

[0017] (2) The present invention adopts a one-step pyrolysis method to prepare a carbon layer-coated modified catalyst, so that the metal precursor is melted into a liquid during the pyrolysis process and decomposed on the surface of potassium chloride. At the same time, potassium chloride acts as a hard template to change the diffusion rate of nickel atoms in the nucleation process to inhibit aggregation, thereby forming carbon layer-coated nickel nanoparticles. The preparation method is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 TEM image of carbon layer-coated nickel nanoparticles prepared in Example 1; Figure 2 TEM image of the carbon layer-coated nickel nanoparticles prepared in Example 1 at another magnification; Figure 3 This is the XPS spectrum of the carbon layer-coated nickel nanoparticles prepared in Example 1; Figure 4 This is the XRD pattern of the carbon layer-coated nickel nanoparticles prepared in Example 1. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention are described clearly and completely below. Unless otherwise specified, the reagents, equipment and materials described in the following examples and experimental examples are all prior art and can be obtained from commercial channels.

[0020] 1. The X-ray diffractometer used for XRD measurement is the Rigaku Dmax-Ultima model.

[0021] 2. XPS verification was performed using a Thermo Fisher 250Xi photoelectron spectrometer.

[0022] Example 1 The preparation of a carbon layer coated modified catalyst comprises the following steps: (1) Preparation of carbon-coated nickel nanoparticles: 5 g of nickel acetylacetonate (Ni(acac)2) and 10 g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100 °C for 24 h to obtain a mixed powder. The mixed powder was annealed at 550 °C in a nitrogen atmosphere for 2 h at a heating rate of 5 °C min -1 The product was washed and dried several times to obtain carbon-coated nickel nanoparticles.

[0023] Figure 1 、 Figure 2 TEM images of the prepared carbon-coated nickel nanoparticles at different magnifications show that the nickel nanoparticles are successfully encapsulated in a carbon matrix derived from the thermal decomposition of metal acetylacetonate. The black portion represents the nickel nanoparticles, surrounded by a carbonaceous layer.

[0024] Figure 3 This is the XPS energy spectrum of carbon layer coated nickel nanoparticles, from which we can see the presence of C, O and Ni elements.

[0025] Figure 4 The XRD pattern of the prepared carbon layer coated nickel nanoparticles can be seen from the figure. The XRD spectrum shows that the nickel element has corresponding diffraction peaks at 2θ of 44.507, 51.846, and 76.370°, which correspond to the (111), (200), and (220) crystal planes of metal Ni with a face-centered cubic (fcc) structure, respectively.

[0026] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type activated alumina in equal volume. After drying and calcination, a carbon-coated modified catalyst was obtained. The loading amount of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0027] The prepared carbon layer coated modified catalyst was loaded into a fixed bed reactor, and the mass space velocity of methanol was 0.8h -1 The feed mass ratio of hydrogen chloride gas to methanol was 1.2:1, the reaction temperature was 250°C, and the reaction pressure was 2.0 atm. The initial methanol conversion was 99.88%, and the initial methyl chloride selectivity was 99.90%. After 300 hours of reaction, the methanol conversion was 99.78%, and the methyl chloride selectivity was 99.87%. The catalytic activity did not decrease, indicating extremely low nickel loss.

[0028] Example 2 The preparation of a carbon layer coated modified catalyst comprises the following steps: (1) Preparation of carbon-coated nickel nanoparticles: 5 g of nickel acetylacetonate (Ni(acac)2) and 10 g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100 °C for 24 h to obtain a mixed powder. The mixed powder was annealed at 350 °C in a nitrogen atmosphere for 2 h at a heating rate of 5 °C min -1 The product was washed and dried several times to obtain carbon-coated nickel nanoparticles.

[0029] (2) Carbon-coated nickel nanoparticles were loaded onto Raschig ring-type activated alumina with a loading amount of 20 wt%.

[0030] Under the catalytic conditions of Example 1, the initial conversion of methanol was 99.42%, and the initial selectivity of chloroform was 99.58%. After 300 hours of reaction, the conversion of methanol was 99.34%, and the selectivity of chloroform was 99.44%.

[0031] Example 3 The preparation of a carbon layer coated modified catalyst comprises the following steps: (1) Preparation of carbon-coated nickel nanoparticles: 5 g of nickel acetylacetonate (Ni(acac)2) and 10 g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100 °C for 24 h to obtain a mixed powder. The mixed powder was annealed at 750 °C in a nitrogen atmosphere for 2 h at a heating rate of 5 °C min -1 The product was washed and dried several times to obtain carbon-coated nickel nanoparticles.

[0032] (2) Carbon-coated nickel nanoparticles were loaded onto Raschig ring-type activated alumina with a loading amount of 20 wt%.

[0033] Under the catalytic conditions of Example 1, the initial conversion rate of methanol was 99.38%, and the initial selectivity of chloroform was 99.52%. After 300 hours of reaction, the conversion rate of methanol was 99.31%, and the initial selectivity of chloroform was 99.41%.

[0034] Example 4 The preparation of a carbon layer coated modified catalyst comprises the following steps: (1) Preparation of carbon-coated nickel nanoparticles: 5 g of nickel acetylacetonate (Ni(acac)2) and 10 g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100 °C for 24 h to obtain a mixed powder. The mixed powder was annealed at 550 °C in a nitrogen atmosphere for 4 h at a heating rate of 10 °C min -1 The product was washed and dried several times to obtain carbon-coated nickel nanoparticles.

[0035] (2) Carbon-coated nickel nanoparticles were loaded onto Raschig ring-type activated alumina with a loading amount of 20 wt%.

[0036] Under the catalytic conditions of Example 1, the initial conversion rate of methanol was 99.52%, and the initial selectivity of chloroform was 99.68%. After 300 hours of reaction, the conversion rate of methanol was 99.43%, and the initial selectivity of chloroform was 99.55%.

[0037] Example 5 (1) Preparation of carbon-coated nickel nanoparticles: 5 g of nickel acetylacetonate (Ni(acac)2) and 10 g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100 °C for 24 h to obtain a mixed powder. The mixed powder was annealed at 650 °C in a nitrogen atmosphere for 4 h at a heating rate of 10 °C min -1 The product was washed and dried several times to obtain carbon-coated nickel nanoparticles.

[0038] (2) Carbon-coated nickel nanoparticles were loaded onto Raschig ring-type activated alumina with a loading amount of 20 wt%.

[0039] Under the catalytic conditions of Example 1, the initial conversion rate of methanol was 99.47%, and the initial selectivity of chloroform was 99.61%. After 300 hours of reaction, the conversion rate of methanol was 99.33%, and the initial selectivity of chloroform was 99.56%.

[0040] Example 6 The carbon layer-coated nickel nanoparticles obtained in Example 1 were loaded onto Raschig ring-type activated alumina, with a loading amount of 30 wt %.

[0041] Under the catalytic conditions of Example 1, the initial conversion rate of methanol was 99.79%, and the initial selectivity of chloroform was 99.83%. After 300 hours of reaction, the conversion rate of methanol was 99.68%, and the initial selectivity of chloroform was 99.79%.

[0042] Example 7 The carbon layer-coated nickel nanoparticles obtained in Example 1 were loaded onto Raschig ring-type activated alumina, with a loading amount of 40 wt %.

[0043] Under the catalytic conditions of Example 1, the initial conversion rate of methanol was 99.12%, and the initial selectivity of chloroform was 99.21%. After 300 hours of reaction, the conversion rate of methanol was 99.04%, and the initial selectivity of chloroform was 99.02%.

[0044] Example 8 The preparation of a carbon layer coated modified catalyst comprises the following steps: (1) Preparation of carbon-coated nickel nanoparticles: 5 g of nickel acetylacetonate (Ni(acac)2) and 15 g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100 °C for 24 h to obtain a mixed powder. The mixed powder was annealed at 550 °C in a nitrogen atmosphere for 2 h at a heating rate of 5 °C min -1 The product was washed and dried several times to obtain carbon-coated nickel nanoparticles.

[0045] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type activated alumina in equal volume. After drying and calcination, a carbon-coated modified catalyst was obtained. The loading amount of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0046] Under the catalytic conditions of Example 1, the initial conversion of methanol was 98.61%, and the initial selectivity of chloroform was 99.04%. After 300 hours of reaction, the conversion of methanol was 98.14%, and the initial selectivity of chloroform was 98.97%.

[0047] Example 9 (1) Preparation of carbon-coated nickel nanoparticles: 3 g of nickel acetylacetonate (Ni(acac)2) and 10 g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100 °C for 24 h to obtain a mixed powder. The mixed powder was annealed at 550 °C in a nitrogen atmosphere for 2 h at a heating rate of 5 °C min -1 The product was washed and dried several times to obtain carbon-coated nickel nanoparticles.

[0048] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type activated alumina in equal volume. After drying and calcination, a carbon-coated modified catalyst was obtained. The loading amount of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0049] Under the catalytic conditions of Example 1, the initial conversion rate of methanol was 98.28%, and the initial selectivity of chloroform was 99.12%. After 300 hours of reaction, the conversion rate of methanol was 98.12%, and the initial selectivity of chloroform was 98.99%.

[0050] Comparative Example 1 (1) Preparation of carbon-coated nickel nanoparticles: 5 g of nickel acetylacetonate (Ni(acac)2) and 5 g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100 °C for 24 h to obtain a mixed powder. The mixed powder was annealed at 550 °C in a nitrogen atmosphere for 2 h at a heating rate of 5 °C min -1 The product was washed and dried several times to obtain carbon-coated nickel nanoparticles.

[0051] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type activated alumina in equal volume. After drying and calcination, a carbon-coated modified catalyst was obtained. The loading amount of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0052] Under the catalytic conditions of Example 1, the initial conversion rate of methanol was 95.32%, and the initial selectivity of chloroform was 96.47%. After 300 hours of reaction, the conversion rate of methanol was 94.08%, and the initial selectivity of chloroform was 95.87%.

[0053] Comparative Example 2 (1) Preparation of carbon-coated nickel nanoparticles: 3 g of nickel acetylacetonate (Ni(acac)2) and 15 g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100 °C for 24 h to obtain a mixed powder. The mixed powder was annealed at 550 °C in a nitrogen atmosphere for 2 h at a heating rate of 10 °C min -1 The product was washed and dried several times to obtain carbon-coated nickel nanoparticles.

[0054] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type activated alumina in equal volume. After drying and calcination, a carbon-coated modified catalyst was obtained. The loading amount of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0055] Under the catalytic conditions of Example 1, the initial conversion of methanol was 96.74%, and the initial selectivity of chloroform was 97.92%. After 300 hours of reaction, the conversion of methanol was 96.25%, and the initial selectivity of chloroform was 96.99%.

[0056] Comparative Example 3 (1) Preparation of carbon-coated nickel nanoparticles: 5 g of nickel acetylacetonate (Ni(acac)2) and 10 g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100 °C for 24 h to obtain a mixed powder. The mixed powder was annealed at 900 °C in a nitrogen atmosphere for 2 h at a heating rate of 5 °C min -1 The product was washed and dried several times to obtain carbon-coated nickel nanoparticles.

[0057] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type activated alumina in equal volume. After drying and calcination, a carbon-coated modified catalyst was obtained. The loading amount of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0058] Under the catalytic conditions of Example 1, the initial conversion rate of methanol was 96.77%, and the initial selectivity of chloroform was 97.55%. After 300 hours of reaction, the conversion rate of methanol was 96.35%, and the initial selectivity of chloroform was 96.99%.

[0059] Comparative Example 4 (1) Preparation of carbon-coated nickel nanoparticles: 5 g of nickel acetylacetonate (Ni(acac)2) and 10 g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100 °C for 24 h to obtain a mixed powder. The mixed powder was annealed at 300 °C in a nitrogen atmosphere for 2 h at a heating rate of 5 °C min -1 The product was washed and dried several times to obtain carbon-coated nickel nanoparticles.

[0060] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type activated alumina in equal volume. After drying and calcination, a carbon-coated modified catalyst was obtained. The loading amount of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0061] Under the catalytic conditions of Example 1, the initial conversion of methanol was 95.34%, and the initial selectivity of chloroform was 96.66%. After 300 hours of reaction, the conversion of methanol was 94.78%, and the initial selectivity of chloroform was 96.12%.

[0062] Comparative Example 5 (1) Preparation of carbon-coated nickel nanoparticles: 5 g of nickel acetylacetonate (Ni(acac)2) and 10 g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100 °C for 24 h to obtain a mixed powder. The mixed powder was annealed at 550 °C in a nitrogen atmosphere for 2 h at a heating rate of 15 °C min -1 The product was washed and dried several times to obtain carbon-coated nickel nanoparticles.

[0063] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type activated alumina in equal volume. After drying and calcination, a carbon-coated modified catalyst was obtained. The loading amount of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0064] Under the catalytic conditions of Example 1, the initial conversion of methanol was 97.78%, and the initial selectivity of chloroform was 98.86%. After 300 hours of reaction, the conversion of methanol was 96.88%, and the initial selectivity of chloroform was 98.12%.

[0065] Comparative Example 6 (1) Preparation of carbon-coated nickel nanoparticles: 5 g of nickel acetylacetonate (Ni(acac)2) and 10 g of potassium bromide were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100 °C for 24 h to obtain a mixed powder. The mixed powder was annealed at 550 °C in a nitrogen atmosphere for 2 h at a heating rate of 5 °C min-1 The product was washed and dried several times to obtain carbon-coated nickel nanoparticles.

[0066] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type activated alumina in equal volume. After drying and calcination, a carbon-coated modified catalyst was obtained. The loading amount of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0067] Under the catalytic conditions of Example 1, the initial conversion of methanol was 96.98%, and the initial selectivity of chloroform was 97.72%. After 300 hours of reaction, the conversion of methanol was 96.35%, and the initial selectivity of chloroform was 96.66%.

[0068] Comparative Example 7 Preparation of carbon layer coated modified catalyst: NiCl2·6H2O and deionized water were added dropwise to the activated carbon (AC) support, ultrasonicated for 20 minutes, and the obtained sample was placed in a 100°C oven to dry for 24 hours. After that, the obtained sample was ground, and the mixed powder was annealed at 550°C in a nitrogen atmosphere for 2 hours, with a heating rate of 5°C·min. -1 , and naturally cooled to room temperature in a tube furnace to prepare a Ni / AC catalyst, in which the loading amount of the active component carbon layer-coated nickel nanoparticles in the catalyst was 20 wt%.

[0069] Under the catalytic conditions of Example 1, the initial conversion rate of methanol was 93.25%, and the initial selectivity of chloroform was 93.86%. After 300 hours of reaction, the conversion rate of methanol was 91.86%, and the initial selectivity of chloroform was 93.25%.

[0070] Comparative Example 8 Preparation of carbon-coated modified catalyst: An impregnation solution of NiCl2·6H2O and deionized water was added dropwise to an acetylene black (AB) support, ultrasonicated for 20 minutes, and the resulting sample was placed in a 100°C oven to dry for 24 hours. Afterwards, the resulting sample was ground, and the mixed powder was annealed at 550°C in a nitrogen atmosphere for 2 hours at a heating rate of 5°C·min. -1 , and naturally cooled to room temperature in a tube furnace to prepare a Ni / AB catalyst, in which the loading amount of the active component carbon layer-coated nickel nanoparticles in the catalyst was 20 wt%.

[0071] Under the catalytic conditions of Example 1, the initial conversion of methanol was 94.15%, and the initial selectivity of chloroform was 93.99%. After 300 hours of reaction, the conversion of methanol was 92.76%, and the initial selectivity of chloroform was 94.23%.

[0072] In summary, it can be seen from Examples 1 to 9 that in the gas-phase catalytic synthesis of chloromethane, when the carbon layer-coated modified catalyst prepared by the present invention is used, the initial conversion rate of methanol and the initial selectivity of chloromethane are both high. After 300 hours of reaction, the catalytic activity does not decrease significantly, and the nickel loss rate is extremely low.

[0073] From the comparison between Example 1 and Comparative Examples 1 to 5, it can be seen that when preparing carbon-coated nickel nanoparticles, too high or too low an amount of potassium chloride added, too high or too low an annealing temperature, or too fast a heating rate will affect the activity of the final prepared catalyst.

[0074] From the comparison between Example 1 and Comparative Example 6, it can be seen that when other hard templates are used, or other methods are used to prepare catalysts whose active components are carbon layer-coated nickel nanoparticles, the catalytic activity of the prepared catalysts is not ideal.

Claims

1. A carbon layer coated modified catalyst, characterized in that, The catalyst comprises a carrier and an active component, wherein the carrier is Raschig ring-type activated alumina, the active component is a carbon layer-coated nickel nanoparticle, and the loading amount of the active component in the carbon layer-coated modified catalyst is 10-45wt%.

2. The carbon layer coated modified catalyst according to claim 1, characterized in that The loading amount of the active component in the carbon layer coated modified catalyst is 15-40 wt%.

3. The carbon layer coated modified catalyst according to claim 1, characterized in that The average radial length of the Raschig ring type activated alumina is 6.5-7.5 mm, and the average axial length is 6.2-7.1 mm.

4. A method for preparing a carbon layer coated modified catalyst according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: dispersing carbon-coated nickel nanoparticles in water, impregnating an equal volume of the nanoparticles on Raschig ring-type activated alumina, and drying and calcining the nanoparticles to obtain a carbon-coated modified catalyst. The carbon layer-coated nickel nanoparticles are prepared by any one of a one-step pyrolysis method, a vapor deposition method, a solvent thermal method, a hydrothermal method, an electrochemical method and an oxidation-reduction method.

5. The method for preparing a carbon layer coated modified catalyst according to claim 4, characterized in that: The preparation method of the carbon layer-coated nickel nanoparticles is specifically as follows: Nickel acetylacetonate and potassium chloride are dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture is dried to obtain a mixed powder. The mixed powder is heated to 350-800°C in a nitrogen atmosphere for annealing treatment, kept warm for 2-4 hours, and then washed and dried to obtain carbon layer-coated nickel nanoparticles.

6. The method for preparing a carbon layer coated modified catalyst according to claim 5, characterized in that: The mass ratio of the nickel acetylacetonate to potassium chloride is 1:1.5-4.

7. The method for preparing a carbon layer coated modified catalyst according to claim 5, characterized in that: The mass ratio of the nickel acetylacetonate to potassium chloride is 1:1.5-2.

5.

8. The method for preparing a carbon layer coated modified catalyst according to claim 5, characterized in that: The heating rate is 2-10°C / min.

9. Use of the carbon layer coated modified catalyst according to any one of claims 1 to 3, characterized in that: Used in the reaction of synthesizing monochloromethane using methanol and hydrogen chloride as raw materials.

10. The use of the carbon layer coated modified catalyst according to claim 9, characterized in that: The reaction for synthesizing methyl chloride using methanol and hydrogen chloride as raw materials is specifically as follows: Hydrogen chloride gas and methanol gas are introduced into a fixed bed reactor loaded with the carbon layer coated modified catalyst, the reaction temperature is 200-280°C, and the methanol mass space velocity is 0.5-1.8h -1 , the mass ratio of hydrogen chloride gas to methanol is 1.1~1.4:1, and the reaction pressure is 1~4atm.

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