A carbon-coated modified catalyst, its preparation method and application

Abstract

This invention belongs to the field of catalyst technology, specifically relating to a carbon-coated modified catalyst, its preparation method, and its application. The carbon-coated modified catalyst includes a support and an active component, wherein the active component is nickel nanoparticles coated with a carbon layer, and the loading of the active component in the catalyst is 10-45 wt%. Because the active component is encapsulated within the carbon material, the carbon-coated modified catalyst provided by this invention significantly reduces the loss and deactivation of the active component during the reaction process, improves the catalyst's stability, and thus extends its service life.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a carbon-coated modified catalyst, its preparation method, and its application. Background Technology

[0002] Chloromethane 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 raw material for methane chloride production, serving as a solvent in isobutylene rubber production. 90% of chloromethane is used to produce methylchlorosilanes, which are crucial raw materials for synthesizing organosilicones. Organosilicones are widely used in construction, textiles, electronics, machinery, transportation, chemicals, pharmaceuticals, food, and aerospace. Furthermore, chloromethane is more reactive than methane and can be used as an intermediate in the synthesis of downstream products, similar to its role in the coal chemical industry with methanol.

[0003] Currently, the main method for synthesizing chloromethane both domestically and internationally is gas-solid phase catalysis, with methanol and hydrogen chloride as raw materials. This process uses γ-Al₂O₃ as a catalyst, where gaseous methanol and a slightly excess of dry hydrogen chloride undergo a gas-solid phase catalytic reaction in a fixed bed at a temperature of 250–350 °C and a pressure of 0.1–0.2 MPa. The methanol conversion rate is greater than 98%, and the chloromethane selectivity is greater than 99%. The product exiting the reactor is quenched, and the liquid phase mixture, consisting of hydrochloric acid (22% by mass) containing a small amount of methanol and dimethyl ether (DME), enters the recovery system. The gas phase mixture is washed with water and alkali, then dried with concentrated sulfuric acid, compressed, and cooled to obtain the final product.

[0004] Catalyst deactivation is currently one of the major challenges facing existing gas-phase catalytic synthesis processes for methanol and hydrogen chloride. Traditional catalysts, such as alumina and molecular sieves, are prone to deactivation during the reaction due to carbon deposition, water vapor poisoning, and hydrogen chloride corrosion, leading to shortened catalyst life and reduced production efficiency. Carbon deposition is one of the main causes of catalyst deactivation. Carbon deposits generated during the reaction cover the active sites of the catalyst, hindering the contact between reactants and the catalyst, thereby reducing catalytic activity or even causing complete deactivation.

[0005] To address the problem of catalyst deactivation due to carbon deposition, researchers have proposed various methods, including developing novel anti-carbon deposition catalysts, optimizing reaction conditions, and improving catalyst preparation processes. Among these, carbon layer coating modification is an effective strategy. Carbon layer coating can form a protective layer on the catalyst surface, preventing reactants or intermediates from directly contacting the catalyst's active sites, thereby reducing carbon deposition and the loss of active components. However, existing carbon layer-coated catalysts still have some shortcomings, such as difficulty in controlling carbon layer thickness, weak bonding between the carbon layer and the catalyst, and easy oxidation of the carbon layer at high temperatures. These problems limit the application of carbon layer-coated catalysts in the synthesis of chloromethane. Therefore, developing a novel carbon layer-coated catalyst to solve the problems existing in the current technology is of great significance for improving the efficiency and economy of the chloromethane synthesis process. This invention aims to provide a method for preparing a carbon layer-coated catalyst and apply it to the synthesis of chloromethane to improve the catalyst's anti-carbon deposition performance, extend catalyst lifetime, and improve product selectivity. Summary of the Invention

[0006] This invention addresses the problem of deactivation due to carbon buildup in existing catalysts used for the synthesis of chloromethane by providing a carbon-coated catalyst, its preparation method, and its application. This catalyst exhibits advantages such as resistance to carbon buildup, high activity, low cost, long lifespan, and resistance to hydrogen chloride corrosion. The preparation method is simple, and when applied to the synthesis of chloromethane from methanol and hydrogen chloride, it demonstrates high conversion rates and high product selectivity, showing great promise for future applications.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A carbon-coated modified catalyst, the catalyst comprising a support and an active component, wherein the active component is carbon-coated nickel nanoparticles, the loading of the active component in the catalyst is 10~45wt%, and the carbon-coated nickel nanoparticles are composed of layered carbon materials coating nickel nanoparticles.

[0009] Preferably, the loading of the active component in the catalyst is 15-40 wt%;

[0010] Preferably, the carrier is Raschig ring-type activated alumina, with an average radial length of 6.5~7.5 mm and an average axial length of 6.2~7.1 mm.

[0011] The present invention also provides a method for preparing the above-mentioned carbon-coated modified catalyst, comprising the following steps:

[0012] The carbon-coated nickel nanoparticles prepared above were dispersed in water and impregnated in an equal volume onto Raschig ring-type activated alumina. After drying at 100~120℃ and calcining at 400~700℃, a carbon-coated modified catalyst was obtained.

[0013] The carbon-coated nickel nanoparticles are prepared by any one of the following methods: one-step pyrolysis, vapor deposition, solvothermal, hydrothermal, electrochemical, and redox methods. Preferably, the carbon-coated nickel nanoparticles are prepared by one-step pyrolysis.

[0014] More preferably, the method for preparing the carbon-coated nickel nanoparticles is as follows:

[0015] Nickel acetylacetone and potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 90-110℃ to obtain a mixed powder. The mixed powder was annealed at 350-800℃ under a nitrogen atmosphere for 2-4 hours. After washing and drying, carbon-coated nickel nanoparticles were obtained.

[0016] During pyrolysis, the metal precursor nickel acetylacetone is melted into a liquid and decomposed on the surface of potassium chloride. Potassium chloride acts as a hard template, which inhibits aggregation by changing the diffusion rate of metal atoms during nucleation, thereby forming a carbon-coated metal structure.

[0017] Preferably, the annealing temperature is 550°C.

[0018] Preferably, the mass ratio of nickel acetylacetonate to potassium chloride is 1:1.5 to 4; more preferably, the mass ratio of nickel acetylacetonate to potassium chloride is 1:1.5 to 2.5.

[0019] Preferably, the temperature is raised using a programmed temperature rise method with a heating rate of 2~10℃ / min, and more preferably, the heating rate is 5℃ / min.

[0020] The present invention also discloses the application of the above-mentioned carbon-coated modified catalyst in the reaction of synthesizing chloromethane from methanol and hydrogen chloride. Specifically, the above-mentioned carbon-coated modified catalyst is applied to the gas-phase catalytic synthesis of chloromethane from methanol and hydrogen chloride.

[0021] Preferably, the reaction for synthesizing chloromethane from methanol and hydrogen chloride specifically comprises:

[0022] Hydrogen chloride gas and methanol gas are introduced into a fixed-bed reactor loaded with the above-mentioned catalyst. The reaction temperature is 200~280℃, and the methanol mass hourly 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 reaction of chloromethane is 1~4 atm.

[0023] Preferably, the pressure for the synthesis of chloromethane is 1~2 atm.

[0024] Preferably, the temperature for the synthesis of chloromethane is 200~250℃.

[0025] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0026] (1) The carbon-coated catalyst provided by this invention, because the active components are encapsulated inside the carbon material, can greatly reduce the loss and deactivation of the active components in the catalyst during the reaction process, improve the stability of the catalyst, and thus improve the service life of the catalyst. After 300 hours of reaction, the methanol conversion rate is still high and the catalytic activity hardly decreases, indicating that the nickel loss rate is extremely low.

[0027] (2) The present invention uses a one-step pyrolysis method to prepare carbon-coated modified catalysts, so that the metal precursor is melted into liquid and decomposed on the surface of potassium chloride during the pyrolysis process. At the same time, potassium chloride acts as a hard template to change the diffusion rate of nickel atoms during the nucleation process to suppress the aggregation phenomenon, thereby forming carbon-coated nickel nanoparticles. The preparation method is simple. Attached Figure Description

[0028] Figure 1 This is a TEM image of the carbon-coated nickel nanoparticles prepared in Example 1;

[0029] Figure 2 This is a TEM image of the carbon-coated nickel nanoparticles prepared in Example 1, magnified at another level.

[0030] Figure 3 XPS spectra of the carbon-coated nickel nanoparticles prepared in Example 1;

[0031] Figure 4 The image shows the XRD pattern of the carbon-coated nickel nanoparticles prepared in Example 1. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0033] Unless otherwise specified, the reagents, equipment and materials described in the following examples and experimental cases are all prior art and can be obtained commercially.

[0034] Among them, 1. The X-ray diffractometer used for XRD measurement was the Rigaku Dmax-Ultima from Japan.

[0035] 2. XPS verification was performed using a Thermo Fisher Scientific 250Xi photoelectron spectrometer.

[0036] Example 1

[0037] The preparation of a carbon-coated modified catalyst includes the following steps:

[0038] (1) Preparation of carbon-coated nickel nanoparticles: 5g of nickel acetylacetonate (Ni(acac)2) and 10g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100℃ for 24h to obtain a mixed powder. The mixed powder was annealed at 550℃ under a nitrogen atmosphere for 2h at a heating rate of 5℃·min. -1 The mixture was naturally cooled to room temperature in a tube furnace. The resulting product was washed and dried multiple times to obtain carbon-coated nickel nanoparticles.

[0039] Figure 1 , Figure 2 These are TEM images of the prepared carbon-coated nickel nanoparticles at different magnifications. The images show that the nickel nanoparticles were successfully encapsulated within a carbon substrate derived from the thermal decomposition of metal acetylacetonate. The black areas represent the nickel nanoparticles, surrounded by a carbonaceous layer.

[0040] Figure 3 The image shows the XPS energy spectrum of carbon-coated nickel nanoparticles, revealing the presence of C, O, and Ni elements.

[0041] Figure 4 The XRD pattern of the prepared carbon-coated nickel nanoparticles shows that the nickel element has diffraction peaks at 2θ of 44.507, 51.846, and 76.370°, which correspond to the (111), (200), and (220) crystal planes of the face-centered cubic (fcc) structure of metallic Ni, respectively.

[0042] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type active alumina in equal volume. After drying and calcination, the carbon-coated modified catalyst was obtained. The loading of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0043] The prepared carbon-coated modified catalyst was loaded into a fixed-bed reactor, with a methanol mass hourly space velocity (WHSV) of 0.8 h⁻¹. -1 The feed ratio of hydrogen chloride gas to methanol was 1.2:1, the reaction temperature was 250℃, and the reaction pressure was 2.0 atm. The initial methanol conversion rate was 99.88%, and the initial selectivity for chloromethane was 99.90%. After 300 hours of reaction, the methanol conversion rate was 99.78%, and the chloromethane selectivity was 99.87%. The catalytic activity did not decrease, indicating extremely low nickel loss.

[0044] Example 2

[0045] The preparation of a carbon-coated modified catalyst includes the following steps:

[0046] (1) Preparation of carbon-coated nickel nanoparticles: 5g of nickel acetylacetone (Ni(acac)2) and 10g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100℃ for 24h to obtain a mixed powder. The mixed powder was annealed at 350℃ under a nitrogen atmosphere for 2h at a heating rate of 5℃·min. -1 The mixture was naturally cooled to room temperature in a tube furnace. The resulting product was washed and dried multiple times to obtain carbon-coated nickel nanoparticles.

[0047] (2) Carbon-coated nickel nanoparticles were loaded onto Raschig ring-type active alumina with a loading amount of 20 wt%.

[0048] Under the catalytic conditions of Example 1, the initial methanol conversion was 99.42% and the initial selectivity for chloromethane was 99.58%; after 300 hours of reaction, the methanol conversion was 99.34% and the selectivity for chloromethane was 99.44%.

[0049] Example 3

[0050] The preparation of a carbon-coated modified catalyst includes the following steps:

[0051] (1) Preparation of carbon-coated nickel nanoparticles: 5g of nickel acetylacetonate (Ni(acac)2) and 10g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100℃ for 24h to obtain a mixed powder. The mixed powder was annealed at 750℃ under a nitrogen atmosphere for 2h at a heating rate of 5℃·min. -1 The mixture was naturally cooled to room temperature in a tube furnace. The resulting product was washed and dried multiple times to obtain carbon-coated nickel nanoparticles.

[0052] (2) Carbon-coated nickel nanoparticles were loaded onto Raschig ring-type active alumina with a loading amount of 20 wt%.

[0053] Under the catalytic conditions of Example 1, the initial methanol conversion was 99.38% and the initial selectivity for chloromethane was 99.52%; after 300 hours of reaction, the methanol conversion was 99.31% and the initial selectivity for chloromethane was 99.41%.

[0054] Example 4

[0055] The preparation of a carbon-coated modified catalyst includes the following steps:

[0056] (1) Preparation of carbon-coated nickel nanoparticles: 5g of nickel acetylacetonate (Ni(acac)2) and 10g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100℃ for 24 h to obtain a mixed powder. The mixed powder was annealed at 550℃ under a nitrogen atmosphere for 4 h at a heating rate of 10℃·min. -1 The mixture was naturally cooled to room temperature in a tube furnace. The resulting product was washed and dried multiple times to obtain carbon-coated nickel nanoparticles.

[0057] (2) Carbon-coated nickel nanoparticles were loaded onto Raschig ring-type active alumina with a loading amount of 20 wt%.

[0058] Under the catalytic conditions of Example 1, the initial methanol conversion was 99.52% and the initial selectivity for chloromethane was 99.68%; after 300 hours of reaction, the methanol conversion was 99.43% and the initial selectivity for chloromethane was 99.55%.

[0059] Example 5

[0060] (1) Preparation of carbon-coated nickel nanoparticles: 5g of nickel acetylacetonate (Ni(acac)2) and 10g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100℃ for 24h to obtain a mixed powder. The mixed powder was annealed at 650℃ under a nitrogen atmosphere for 4h at a heating rate of 10℃·min. -1 The mixture was naturally cooled to room temperature in a tube furnace. The resulting product was washed and dried multiple times to obtain carbon-coated nickel nanoparticles.

[0061] (2) Carbon-coated nickel nanoparticles were loaded onto Raschig ring-type active alumina with a loading amount of 20 wt%.

[0062] Under the catalytic conditions of Example 1, the initial methanol conversion was 99.47% and the initial selectivity for chloromethane was 99.61%; after 300 hours of reaction, the methanol conversion was 99.33% and the initial selectivity for chloromethane was 99.56%.

[0063] Example 6

[0064] The carbon-coated nickel nanoparticles obtained in Example 1 were loaded onto Raschig ring-type activated alumina with a loading amount of 30 wt%.

[0065] Under the catalytic conditions of Example 1, the initial methanol conversion rate was 99.79% and the initial selectivity for chloromethane was 99.83%; after 300 hours of reaction, the methanol conversion rate was 99.68% and the initial selectivity for chloromethane was 99.79%.

[0066] Example 7

[0067] The carbon-coated nickel nanoparticles obtained in Example 1 were loaded onto Raschig ring-type activated alumina with a loading amount of 40 wt%.

[0068] Under the catalytic conditions of Example 1, the initial methanol conversion was 99.12% and the initial selectivity for chloromethane was 99.21%; after 300 hours of reaction, the methanol conversion was 99.04% and the initial selectivity for chloromethane was 99.02%.

[0069] Example 8

[0070] The preparation of a carbon-coated modified catalyst includes the following steps:

[0071] (1) Preparation of carbon-coated nickel nanoparticles: 5g of nickel acetylacetonate (Ni(acac)2) and 15g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100℃ for 24h to obtain a mixed powder. The mixed powder was annealed at 550℃ under a nitrogen atmosphere for 2h at a heating rate of 5℃·min. -1 The mixture was naturally cooled to room temperature in a tube furnace. The resulting product was washed and dried multiple times to obtain carbon-coated nickel nanoparticles.

[0072] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type active alumina in equal volume. After drying and calcination, the carbon-coated modified catalyst was obtained. The loading of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0073] Under the catalytic conditions of Example 1, the initial methanol conversion was 98.61% and the initial selectivity for chloromethane was 99.04%; after 300 hours of reaction, the methanol conversion was 98.14% and the initial selectivity for chloromethane was 98.97%.

[0074] Example 9

[0075] (1) Preparation of carbon-coated nickel nanoparticles: 3g of nickel acetylacetonate (Ni(acac)2) and 10g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100℃ for 24h to obtain a mixed powder. The mixed powder was annealed at 550℃ under a nitrogen atmosphere for 2h at a heating rate of 5℃·min. -1 The mixture was naturally cooled to room temperature in a tube furnace. The resulting product was washed and dried multiple times to obtain carbon-coated nickel nanoparticles.

[0076] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type active alumina in equal volume. After drying and calcination, the carbon-coated modified catalyst was obtained. The loading of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0077] Under the catalytic conditions of Example 1, the initial methanol conversion was 98.28% and the initial selectivity for chloromethane was 99.12%; after 300 hours of reaction, the methanol conversion was 98.12% and the initial selectivity for chloromethane was 98.99%.

[0078] Comparative Example 1

[0079] (1) Preparation of carbon-coated nickel nanoparticles: 5g of nickel acetylacetonate (Ni(acac)2) and 5g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100℃ for 24h to obtain a mixed powder. The mixed powder was annealed at 550℃ under a nitrogen atmosphere for 2h at a heating rate of 5℃·min. -1 The mixture was naturally cooled to room temperature in a tube furnace. The resulting product was washed and dried multiple times to obtain carbon-coated nickel nanoparticles.

[0080] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type active alumina in equal volume. After drying and calcination, the carbon-coated modified catalyst was obtained. The loading of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0081] Under the catalytic conditions of Example 1, the initial methanol conversion was 95.32% and the initial selectivity for chloromethane was 96.47%; after 300 hours of reaction, the methanol conversion was 94.08% and the initial selectivity for chloromethane was 95.87%.

[0082] Comparative Example 2

[0083] (1) Preparation of carbon-coated nickel nanoparticles: 3g of nickel acetylacetonate (Ni(acac)2) and 15g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100℃ for 24 h to obtain a mixed powder. The mixed powder was annealed at 550℃ under a nitrogen atmosphere for 2 h at a heating rate of 10℃·min. -1 The mixture was naturally cooled to room temperature in a tube furnace. The resulting product was washed and dried multiple times to obtain carbon-coated nickel nanoparticles.

[0084] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type active alumina in equal volume. After drying and calcination, the carbon-coated modified catalyst was obtained. The loading of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0085] Under the catalytic conditions of Example 1, the initial methanol conversion was 96.74% and the initial selectivity for chloromethane was 97.92%; after 300 hours of reaction, the methanol conversion was 96.25% and the initial selectivity for chloromethane was 96.99%.

[0086] Comparative Example 3

[0087] (1) Preparation of carbon-coated nickel nanoparticles: 5g of nickel acetylacetonate (Ni(acac)2) and 10g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100℃ for 24 h to obtain a mixed powder. The mixed powder was annealed at 900℃ under a nitrogen atmosphere for 2 h at a heating rate of 5℃·min. -1 The mixture was naturally cooled to room temperature in a tube furnace. The resulting product was washed and dried multiple times to obtain carbon-coated nickel nanoparticles.

[0088] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type active alumina in equal volume. After drying and calcination, the carbon-coated modified catalyst was obtained. The loading of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0089] Under the catalytic conditions of Example 1, the initial methanol conversion was 96.77% and the initial selectivity for chloromethane was 97.55%; after 300 hours of reaction, the methanol conversion was 96.35% and the initial selectivity for chloromethane was 96.99%.

[0090] Comparative Example 4

[0091] (1) Preparation of carbon-coated nickel nanoparticles: 5g of nickel acetylacetonate (Ni(acac)2) and 10g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100℃ for 24h to obtain a mixed powder. The mixed powder was annealed at 300℃ under a nitrogen atmosphere for 2h at a heating rate of 5℃·min. -1 The mixture was naturally cooled to room temperature in a tube furnace. The resulting product was washed and dried multiple times to obtain carbon-coated nickel nanoparticles.

[0092] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type active alumina in equal volume. After drying and calcination, the carbon-coated modified catalyst was obtained. The loading of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0093] Under the catalytic conditions of Example 1, the initial methanol conversion was 95.34% and the initial selectivity for chloromethane was 96.66%; after 300 hours of reaction, the methanol conversion was 94.78% and the initial selectivity for chloromethane was 96.12%.

[0094] Comparative Example 5

[0095] (1) Preparation of carbon-coated nickel nanoparticles: 5g of nickel acetylacetonate (Ni(acac)2) and 10g of potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100℃ for 24h to obtain a mixed powder. The mixed powder was annealed at 550℃ under a nitrogen atmosphere for 2h at a heating rate of 15℃·min. -1 The mixture was naturally cooled to room temperature in a tube furnace. The resulting product was washed and dried multiple times to obtain carbon-coated nickel nanoparticles.

[0096] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type active alumina in equal volume. After drying and calcination, the carbon-coated modified catalyst was obtained. The loading of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0097] Under the catalytic conditions of Example 1, the initial methanol conversion was 97.78% and the initial selectivity for chloromethane was 98.86%; after 300 hours of reaction, the methanol conversion was 96.88% and the initial selectivity for chloromethane was 98.12%.

[0098] Comparative Example 6

[0099] (1) Preparation of carbon-coated nickel nanoparticles: 5g of nickel acetylacetonate (Ni(acac)2) and 10g of potassium bromide were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried at 100℃ for 24h to obtain a mixed powder. The mixed powder was annealed at 550℃ under a nitrogen atmosphere for 2h at a heating rate of 5℃·min. -1 The mixture was naturally cooled to room temperature in a tube furnace. The resulting product was washed and dried multiple times to obtain carbon-coated nickel nanoparticles.

[0100] (2) The prepared carbon-coated nickel nanoparticles were dispersed in water and impregnated on Raschig ring-type active alumina in equal volume. After drying and calcination, the carbon-coated modified catalyst was obtained. The loading of the active component carbon-coated nickel nanoparticles in the catalyst was 20 wt%.

[0101] Under the catalytic conditions of Example 1, the initial methanol conversion was 96.98% and the initial selectivity for chloromethane was 97.72%; after 300 hours of reaction, the methanol conversion was 96.35% and the initial selectivity for chloromethane was 96.66%.

[0102] Comparative Example 7

[0103] Preparation of carbon-coated modified catalyst: An impregnation solution prepared from NiCl2·6H2O and deionized water was added dropwise to an activated carbon (AC) support, and the sample was ultrasonically treated for 20 min. The resulting sample was then dried in an oven at 100 °C for 24 h. Afterward, the sample was ground, and the mixed powder was annealed at 550 °C under a nitrogen atmosphere for 2 h at a heating rate of 5 °C·min. -1 The Ni / AC catalyst was prepared by naturally cooling to room temperature in a tube furnace. The loading of the active component, carbon-coated nickel nanoparticles, in the catalyst was 20 wt%.

[0104] Under the catalytic conditions of Example 1, the initial methanol conversion was 93.25% and the initial selectivity for chloromethane was 93.86%; after 300 hours of reaction, the methanol conversion was 91.86% and the initial selectivity for chloromethane was 93.25%.

[0105] Comparative Example 8

[0106] Preparation of carbon-coated modified catalyst: An impregnation solution prepared from NiCl2·6H2O and deionized water was added dropwise to an acetylene black (AB) support, and the sample was ultrasonically treated for 20 min. The resulting sample was then dried in an oven at 100 °C for 24 h. Afterward, the sample was ground, and the mixed powder was annealed at 550 °C under a nitrogen atmosphere for 2 h at a heating rate of 5 °C·min. -1 The Ni / AB catalyst was prepared by naturally cooling to room temperature in a tube furnace. The loading of the active component, carbon-coated nickel nanoparticles, in the catalyst was 20 wt%.

[0107] Under the catalytic conditions of Example 1, the initial methanol conversion was 94.15% and the initial selectivity for chloromethane was 93.99%; after 300 hours of reaction, the methanol conversion was 92.76% and the initial selectivity for chloromethane was 94.23%.

[0108] In summary, as can be seen from Examples 1-9, in the gas-phase catalytic synthesis of chloromethane, the carbon-coated modified catalyst prepared in this invention exhibits high initial conversion rates of methanol and high initial selectivity for chloromethane. After 300 hours of reaction, the catalytic activity does not decrease significantly, and the nickel loss rate is extremely low.

[0109] As can be seen from the comparison between Example 1 and Comparative Examples 1-5, when preparing carbon-coated nickel nanoparticles, excessive or insufficient addition of potassium chloride, excessive or insufficient annealing temperature, and excessively rapid heating rate will all affect the activity of the final catalyst.

[0110] As can be seen from the comparison between Example 1 and Comparative Example 6, when other hard templates are used or other methods are used to prepare catalysts with carbon-coated nickel nanoparticles as active components, the catalytic activity of the prepared catalysts is not ideal.

Claims

1. A carbon-coated modified catalyst, characterized in that, The catalyst comprises a support and an active component, wherein the support is Raschig ring-type activated alumina, and the active component is carbon-coated nickel nanoparticles, wherein the loading of the active component in the carbon-coated modified catalyst is 10~45 wt%. The preparation method of the carbon-coated modified catalyst includes the following steps: dispersing carbon-coated nickel nanoparticles in water, impregnating them in equal volume on Raschig ring-type active alumina, and then drying and calcining to obtain the carbon-coated modified catalyst. The specific method for preparing the carbon-coated nickel nanoparticles is as follows: Nickel acetylacetone and potassium chloride were dissolved in a mixed solution of ethanol and water under magnetic stirring. The solution mixture was dried to obtain a mixed powder. The mixed powder was annealed at 350~800℃ under a nitrogen atmosphere for 2~4 hours. After washing and drying, carbon-coated nickel nanoparticles were obtained.

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

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

4. The carbon-coated modified catalyst according to claim 1, characterized in that, The mass ratio of nickel acetylacetonate to potassium chloride is 1:1.5~4.

5. The carbon-coated modified catalyst according to claim 1, characterized in that, The mass ratio of nickel acetylacetone to potassium chloride is 1:1.5~2.

5.

6. The carbon-coated modified catalyst according to claim 1, characterized in that, The heating rate is 2~10℃ / min.

7. The application of a carbon-coated modified catalyst according to any one of claims 1 to 6, characterized in that, It is used in the reaction of synthesizing chloromethane from methanol and hydrogen chloride.

8. The application of the carbon-coated modified catalyst according to claim 7, characterized in that, The specific reaction for synthesizing chloromethane from methanol and hydrogen chloride is as follows: Hydrogen chloride gas and methanol gas are introduced into a fixed-bed reactor loaded with the carbon-coated modified catalyst. The reaction temperature is 200-280°C, and the methanol mass hourly space velocity is 0.5-1.8 h⁻¹. -1 The mass ratio of hydrogen chloride gas to methanol is 1.1~1.4:1, and the reaction pressure is 1~4 atm.

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