Preparation method of surface-modified carbon carrier loaded iron-based catalyst and application thereof

Abstract

The application provides a preparation method of a surface modified carbon carrier loaded iron-based catalyst, comprising the following steps: S1, preparing a carbon carrier: uniformly mixing phenolic resin and urea according to a certain proportion, grinding sufficiently, and then performing calcination carbonization to obtain a nitrogen-doped carbon carrier; S2, surface modification of the carbon carrier: placing the nitrogen-doped carbon carrier in a hydrogen peroxide solution and stirring sufficiently, and then performing washing and drying to obtain a surface oxidized carbon carrier CMS-N-H2O2; S3, preparing an iron-based catalyst by an impregnation method: uniformly mixing the CMS-N-H2O2 with Fe(NO3)3.9H2O at a fixed ratio, stirring uniformly, ultrasonic mixing, drying, and then performing calcination to obtain a Fe / CMS-N-H2O2 catalyst. The catalyst prepared by the application has more hydroxyl groups on the surface, provides a larger specific surface area, N doping is beneficial to increasing carrier defects, reducing the particle size of an active phase metal, improving mass transfer efficiency, promoting the reduction of an active phase to generate Fe5C2, in a CO hydrogenation reaction process, can improve the olefin selectivity and CO conversion rate, reduces the CH4 selectivity, and can effectively improve the product distribution of the catalyst.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of synthesis gas Fischer-Tropsch synthesis catalyst, in particular to a preparation method of surface modified carbon carrier loaded iron-based catalyst and application thereof. BACKGROUND

[0002] Energy is the foundation of modern society to survive and develop, the supply capacity of clean liquid fuel is related to the sustainable development of national economy, and is one of the foundations of national strategic security. Due to the pollution and non-renewable of traditional fossil fuels, the development and utilization of renewable energy is paid more and more attention. In typical countries such as Germany and the United States, the development and utilization of renewable energy is relatively early. These countries have more research and application on energy development methods. In a certain period of time, the development mode of renewable energy is closely related to its development and utilization. Catalytic CO hydrogenation is one of the most common large-scale chemical synthesis of variable chemical raw materials. At present, the most widely studied CO is the preparation of light olefins. With the increasingly serious world environmental problems and the current situation of "rich coal, poor oil and little gas" in China, it is of great strategic importance to develop a non-petroleum route for preparing high value-added products from synthesis gas.

[0003] Under the severe environment, in order to meet the huge demand of ethylene, propylene, butene and other chemical raw materials, direct synthesis of light olefins from CO hydrogenation is a possible solution and practical significance, which can provide a more economical method than traditional catalytic cracking of naphtha and dehydrogenation of alkanes. Because synthesis gas is considered to be a short process for preparing low carbon olefins by Fischer-Tropsch synthesis (FTS), which has less equipment investment and high resource utilization rate, and has been widely used in research and industry. In recent years, the preparation of a series of hydrocarbons, especially C2-C4 light olefins, from one-step conversion of synthesis gas (a mixture of H2 and CO) has attracted widespread attention.

[0004] Carbon materials have high specific surface area and pore volume, electronic conductivity and chemical stability, and are promising candidate materials in the fields of gas adsorption, catalysis, energy storage, and electrochemical double-layer capacitors and fuel cells. Carbon materials have many advantages for preparing supported iron-based catalysts. Compared with metal oxide carriers, the interaction between the carrier and the active component is reduced, the high specific surface area and pore structure are helpful to the dispersion of active metal, and the mechanical strength is improved. Schulte et al. prepared Fe-based catalysts using CNT as carrier and studied the influence of CNT surface modification on reaction performance. The results showed that the Fe / O-CNT catalyst prepared on the CNT carrier treated by oxygen had the highest selectivity of low carbon olefins and lower CH4 selectivity, and the CO conversion rate could reach 45%. Therefore, carbon material is a good Fischer-Tropsch synthesis catalyst carrier, but the carbon carrier loaded iron-based catalyst usually has the problem of low single product selectivity. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing iron-based catalysts supported on surface-modified carbon supports and their application, addressing the problem of low selectivity of single products in existing Fischer-Tropsch reactions. This method solves the problem of wide product distribution and low selectivity of single products in traditional iron-based catalysts.

[0006] This invention provides the following technical solution:

[0007] This invention provides a method for preparing a surface-modified carbon-supported iron-based catalyst, comprising the following steps:

[0008] S1. Preparation of carbon support: Phenolic resin and urea are mixed evenly in a certain proportion, ground thoroughly, and then calcined and carbonized to obtain nitrogen-doped carbon support CMS-N.

[0009] S2. Modification of the carbon support surface: Nitrogen-doped carbon support CMS-N is placed in hydrogen peroxide solution and stirred thoroughly. After washing and drying, surface-oxidized carbon support CMS-N-H2O2 is obtained.

[0010] S3. Preparation of iron-based catalyst by impregnation method: CMS-N-H2O2 and Fe(NO3)3·9H2O are mixed in a fixed ratio, stirred evenly, ultrasonically mixed, dried and calcined to obtain black Fe / CMS-N-H2O2 powder catalyst.

[0011] Carbon supports possess high specific surface area and pore volume, as well as good electronic conductivity and chemical stability. The raw materials for carbon support preparation are abundant, inexpensive, and readily available, making them promising candidate materials in the field of catalysis. Carbon supports themselves have abundant surface groups, and their high surface modifiability provides conditions for surface oxidation treatment. The precursor phenolic resin has more surface hydroxyl groups, and after carbonization, the carbon support has more hydroxyl groups. The increase in surface hydroxyl groups is conducive to olefin formation. Nitrogen doping helps to increase the defects of the support, reduce the particle size of the active phase metal Fe, and promote dispersion. As the active phase in the Fischer-Tropsch synthesis process, Fe has a wider operating temperature range and higher olefin selectivity, which is beneficial to olefin formation.

[0012] The nitrogen-doped carbon support of the present invention provides a larger specific surface area, improves mass transfer efficiency, promotes the reduction of the active phase to Fe5C2, and improves olefin selectivity; the surface treatment of the carbon support with hydrogen peroxide reduces iron agglomeration, promotes dispersion, and effectively improves the product distribution of the catalyst.

[0013] Further, the preparation of the carbon carrier further comprises etching the sample after calcination and carbonization, specifically: mixing the sample after calcination and carbonization with KOH solution to obtain a suspension, magnetically stirring the suspension in a water bath, washing with ethanol and deionized water after drying, and drying to obtain a nitrogen-doped carbon carrier CMS-N.

[0014] Further, the phenolic resin is a thermoplastic powder phenolic resin, preferably a commercial phenolic resin (2123).

[0015] Further, the mass ratio of the phenolic resin and urea is (1-3): 1.

[0016] Further, the mass ratio of the phenolic resin and urea is 1:1.

[0017] Further, KOH solid is used to prepare a KOH solution with a concentration of (0.2-0.6) g / ml, and then mixed with the sample after calcination and carbonization, and the concentration of the KOH solution is preferably 0.4 g / ml.

[0018] Further, the suspension is magnetically stirred in a water bath at 80°C for 6h.

[0019] Further, the sample after magnetic stirring treatment is placed in a vacuum drying oven and dried at 160°C for 10h.

[0020] Further, the sample after drying is washed with ethanol 3 times to remove residual organic matter in the sample, and then washed with deionized water until the solution PH=7.

[0021] Further, the sample after washing is dried in a vacuum drying oven at 80°C for 10h.

[0022] Further, the concentration of the hydrogen peroxide solution is (2-30)%, preferably 5%.

[0023] Further, the sample after hydrogen peroxide treatment is washed with deionized water 3 times until the sample solution is neutral, and vacuum dried at 80°C for 10h.

[0024] Further, the mass ratio of CMS-N-H2O2 and Fe(NO3)3·9H2O is 0.9:(0.1-0.5).

[0025] Further, the mass ratio of CMS-N-H2O2 and Fe(NO3)3·9H2O is 0.9:0.25.

[0026] Further, in step S1, the calcination and carbonization is carried out in a tube furnace at 300-800°C for 2h in a stable N2 atmosphere, and the heating rate is 2°C / min.

[0027] Further, in step S3, the calcination is performed in a tube furnace at 500 DEG C for 3h under a stable N2 atmosphere, wherein the temperature increasing rate is 2 DEG C / min.

[0028] Another object of the present application is to provide the application of the surface-modified carbon support loaded iron-based catalyst prepared by the above method in catalyzing CO hydrogenation, and the reaction conditions are as follows: raw gas H2 / CO=2, temperature is 300 DEG C, pressure is 1.5 MPa, space velocity (GHSV) is 1000h-1. -1 .

[0029] The present application has the following beneficial effects:

[0030] 1. The modified carbon support loaded iron-based catalyst prepared by the present application has more surface hydroxyl groups of the precursor phenolic resin of the carbon support, and the carbon support itself has more hydroxyl groups after carbonization, and N doping is conducive to increasing the carrier defects and reducing the particle size of the active phase metal and promoting dispersion.

[0031] 2. The raw material for preparing the carbon support is abundant in reserves, cheap and easy to obtain, and can be used for industrial production, and the carbon support provides a larger specific surface area, improves the mass transfer efficiency, promotes the reduction of the active phase to generate Fe5C2, and improves the selectivity of low-carbon olefins.

[0032] 3. In the modified carbon support, different concentrations of hydrogen peroxide solution are used for surface oxidation treatment of the support, and the treatment effect is best when the concentration of the hydrogen peroxide solution is 5% and the stirring time is 4h, which can reduce the agglomeration of iron and promote dispersion.

[0033] 4. In the CO hydrogenation reaction process, the carbon support promotes the reduction of iron, increases the hydroxyl groups on the surface of the catalyst, improves the selectivity of olefins, improves the CO conversion rate, reduces the CH4 selectivity, improves the C5 + selectivity, thereby effectively improving the product distribution of the catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0035] Fig. 1 The SEM test result graph of the catalyst prepared in Example 3 of the present application;

[0036] Fig. 2 The SEM test result graph of the catalyst prepared in Comparative Example 1 of the present application;

[0037] Fig. 3 SEM test results of the catalyst prepared for Invention Comparative Example 2. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0039] Example 1

[0040] The preparation method of the modified carbon carrier loaded iron-based catalyst in this embodiment comprises the following steps:

[0041] (1) Preparation of modified carbon carrier

[0042] (a) Preparation of N-doped carbon carrier: 4 g of phenolic resin powder and 4 g of urea were uniformly mixed, and after being thoroughly ground in a mortar, they were placed in a horizontal tube furnace, with a N2 flow rate of 40 mL / min, and the temperature was increased to 500℃ at a rate of 2℃ / min and maintained for 2 h.

[0043] (b) Etching of carbon carrier: the carbon carrier obtained in the above process was mixed with 20 mL of KOH solution with a concentration of 0.2 g / mL, and was magnetically stirred in a water bath at 80℃ for 6 h, and was vacuum dried at 160℃ for 10 h. The dried sample was washed with ethanol and deionized water for 3 times respectively until the pH was neutral, and was dried at 80℃ for 10 h. The obtained carbon carrier was marked as CMS-N.

[0044] (c) Treatment of carbon carrier with hydrogen peroxide solution: the CMS obtained in the above process was stirred in 50 mL of hydrogen peroxide solution with a concentration of 5% for 4 h, and was washed and vacuum dried at 80℃ to obtain the modified carrier, which was marked as CMS-N-H2O2.

[0045] (2) Preparation of carbon carrier loaded iron-based catalyst by impregnation method

[0046] (a) 0.25 g of Fe(NO3)3·9H2O was dissolved in 10 mL of deionized water, and after being thoroughly dissolved, 0.9 g of the carrier CMS-N-H2O2 was poured into the iron nitrate nonahydrate solution and was ultrasonically mixed for 0.5 h until it was uniformly mixed, and was dried at 80℃, and was calcined in a horizontal tube furnace at 500℃ in N2 atmosphere for 3 h. A black 1-Fe / CMS-N-H2O2 powder catalyst was obtained.

[0047] Example 2

[0048] The preparation method of the modified carbon carrier loaded iron-based catalyst of the embodiment is basically the same as that of embodiment 1, except that the mass ratio of phenolic resin to urea in step (1a) is different, and the others are similar to those of embodiment 1. The specific operation steps are as follows:

[0049] (1) Preparation of modified carbon carrier

[0050] (a) Preparation of N-doped carbon carrier: 12 g of phenolic resin powder and 4 g of urea were uniformly mixed, and after being fully ground in a mortar, they were placed in a horizontal tube furnace, with a N2 flow rate of 40 mL / min, and increased to 500°C at a rate of 2°C / min and maintained for 2 h.

[0051] (b) Etching of carbon carrier: The carbon carrier obtained in the above process was mixed with 20 mL of KOH solution with a concentration of 0.2 g / mL, and was magnetically stirred in a water bath at 80°C for 6 h, and was vacuum dried at 160°C for 10 h. The dried sample was washed with ethanol and deionized water for 3 times until the pH was neutral, and was dried at 80°C for 10 h. The obtained carbon carrier was marked as CMS-N.

[0052] (c) Treatment of carbon carrier with hydrogen peroxide solution: The CMS obtained in the above process was stirred in 50 mL of hydrogen peroxide solution with a concentration of 5% for 4 h, and was washed and vacuum dried at 80°C to obtain the modified carrier, marked as CMS-N-H2O2.

[0053] (2) Preparation of carbon carrier loaded iron-based catalyst by impregnation method

[0054] (a) 0.25 g of Fe(NO3)3·9H2O was dissolved in 10 mL of deionized water, and after being fully dissolved, 0.9 g of the carrier CMS-N-H2O2 was poured into the iron nitrate nonahydrate solution and was ultrasonically mixed for 0.5 h until it was uniformly mixed, and was dried at 80°C, and was calcined in a horizontal tube furnace at 500°C in a N2 atmosphere for 3 h. A black 2-Fe / CMS-N-H2O2 powder catalyst was obtained.

[0055] Example 3

[0056] The preparation method of the modified carbon carrier loaded iron-based catalyst of the embodiment is basically the same as that of embodiment 1, except that the concentration of KOH solution in step (1b) is different, and the others are similar to those of embodiment 1. The specific operation steps are as follows:

[0057] (1) Preparation of modified carbon carrier

[0058] (a) Preparation of N-doped carbon carrier: 12 g of phenolic resin powder and 4 g of urea were uniformly mixed, and after being fully ground in a mortar, they were placed in a horizontal tube furnace, with a N2 flow rate of 40 mL / min, and increased to 500°C at a rate of 2°C / min and maintained for 2 h.

[0059] (b) Etching of carbon support: The carbon support obtained in the above process was mixed with 20 mL of KOH solution with a concentration of 0.4 g / mL, and magnetically stirred in a water bath at 80 °C for 6 h. The sample was then vacuum dried at 160 °C for 10 h. The dried sample was washed three times with ethanol and deionized water until the pH was neutral. The sample was then dried at 80 °C for 10 h. The resulting carbon support was denoted as CMS-N.

[0060] (c) Treatment of carbon support with hydrogen peroxide solution: The CMS obtained in the above process was stirred in 50 mL of 5% peroxide solution for 4 h, washed, and dried under vacuum at 80 °C to obtain the modified support, denoted as CMS-N-H2O2.

[0061] (2) Preparation of carbon-supported iron-based catalysts by impregnation method

[0062] (a) 0.25 g of Fe(NO3)3·9H2O was dissolved in 10 ml of deionized water. After complete dissolution, 0.9 g of the resulting support CMS-N-H2O2 was poured into a ferric nitrate nonahydrate solution and sonicated for 0.5 h until homogeneous. After drying at 80 °C, it was calcined at 500 °C for 3 h in a horizontal tube furnace under N2 atmosphere. A black 3-Fe / CMS-N-H2O2 powder catalyst was obtained.

[0063] Example 4

[0064] This embodiment describes a method for preparing a modified carbon-supported iron-based catalyst, which is basically the same as that in Example 1, except that the concentration of hydrogen peroxide solution in step (1c) is different; otherwise, it is similar to Example 1. The specific operating steps are as follows:

[0065] (1) Preparation of modified carbon support

[0066] (a) Preparation of N-doped carbon support: Weigh 4g of phenolic resin powder and mix it evenly with 4g of urea. After grinding it thoroughly in a mortar, place it in a horizontal tube furnace. The N2 flow rate is 40mL / min, and the temperature is increased to 500℃ at 2℃ / min and maintained for 2h.

[0067] (b) Etching of carbon support: The carbon support obtained in the above process was mixed with 20 mL of KOH solution with a concentration of 0.2 g / mL, and magnetically stirred in a water bath at 80 °C for 6 h. The sample was then vacuum dried at 160 °C for 10 h. The dried sample was washed three times with ethanol and deionized water until the pH was neutral. The sample was then dried at 80 °C for 10 h. The resulting carbon support was denoted as CMS-N.

[0068] (c) Treatment of carbon support with hydrogen peroxide solution: The CMS obtained in the above process was stirred in 50 mL of 10% peroxide solution for 4 h, washed, and dried under vacuum at 80 °C to obtain the modified support, denoted as CMS-N-H2O2.

[0069] (2) Preparation of carbon support loaded iron-based catalyst by impregnation method

[0070] (a) 0.25 g of Fe(N03)3-9H20 was dissolved in 10 mL of deionized water, and after complete dissolution, 0.9 g of the obtained carrier CMS-N-H202 was poured into the iron nitrate nine hydrate solution and ultrasonically mixed for 0.5 h to be uniformly mixed. After drying at 80 °C, calcination was carried out in a horizontal tube furnace under N2atmosphere at 500 °C for 3 h. A black 4-Fe / CMS-N-H202 powder catalyst was obtained.

[0071] Example 5

[0072] The preparation method of a modified carbon support loaded iron-based catalyst of this embodiment is basically the same as that of Example 1, except that the mass ratio of CMS-N-H202 to Fe(N03)3-9H20 in step (2a) is different, and the others are similar to those of Example 1. The specific operation steps are as follows:

[0073] (1) Preparation of modified carbon support

[0074] (a) Preparation of N-doped carbon support: 4 g of phenolic resin powder was uniformly mixed with 4 g of urea, and after being thoroughly ground in a mortar, it was placed in a horizontal tube furnace, and the N2flow rate was 40 mL / min, and the temperature was increased to 500 °C at a rate of 2 °C / min and maintained for 2 h.

[0075] (b) Etching of carbon support: The carbon support obtained in the above process was mixed with 20 mL of KOH solution with a concentration of 0.2 g / mL, and was magnetically stirred in a water bath at 80 °C for 6 h. After vacuum drying at 160 °C for 10 h, the dried sample was washed with ethanol and deionized water for 3 times respectively until the pH was neutral. After drying at 80 °C for 10 h, the obtained carbon support was recorded as CMS-N.

[0076] (c) Treatment of carbon support with hydrogen peroxide solution: The CMS obtained in the above process was stirred in 50 mL of hydrogen peroxide solution with a concentration of 5% for 4 h, and then washed and vacuum dried at 80 °C to obtain the modified carrier, which was recorded as CMS-N-H202.

[0077] (2) Preparation of carbon support loaded iron-based catalyst by impregnation method

[0078] (a) 0.25 g of Fe(N03)3-9H20 was dissolved in 10 mL of deionized water, and after complete dissolution, 0.9 g of the obtained carrier CMS-N-H202 was poured into the iron nitrate nine hydrate solution and ultrasonically mixed for 0.5 h to be uniformly mixed. After drying at 80 °C, calcination was carried out in a horizontal tube furnace under N2atmosphere at 500 °C for 3 h. A black 4-Fe / CMS-N-H202 powder catalyst was obtained.

[0079] Comparative Example 1

[0080] (1) Preparation of modified carbon support

[0081] (a) Preparation of undoped carbon support: 4 g of phenolic resin powder was weighed and ground thoroughly in a mortar, and then placed in a horizontal tube furnace, with a N2flow rate of 40 mL / min, and increased to 500°C at a rate of 2°C / min, and maintained for 2 h.

[0082] (b) Etching of carbon support: The carbon support obtained in the above process was mixed with 20 ml of KOH solution with a concentration of 0.2 g / mL, and magnetically stirred in a water bath at 80°C for 6 h, and vacuum dried at 160°C for 10 h. The dried sample was washed with ethanol and deionized water three times, respectively, until the pH was neutral, and dried at 80°C for 10 h. The obtained carbon support was denoted as CMS.

[0083] (2) Preparation of carbon support loaded iron-based catalyst by impregnation method

[0084] (a) 0.25 g of Fe(N03)3-9H20 was dissolved in 10 mL of deionized water, and after complete dissolution, 0.9 g of the carrier CMS was poured into the iron nitrate nonahydrate solution and ultrasonically mixed for 0.5 h until uniform mixing. After drying at 80°C, calcination was performed in a horizontal tube furnace under N2atmosphere at 500°C for 3 h. A black Fe / CMS powder catalyst was obtained.

[0085] Comparative Example 2

[0086] (1) Preparation of modified carbon support

[0087] (a) Preparation of N-doped carbon support: 4 g of phenolic resin powder was uniformly mixed with 4 g of urea, and then ground thoroughly in a mortar, and then placed in a horizontal tube furnace, with a N2flow rate of 40 mL / min, and increased to 500°C at a rate of 2°C / min, and maintained for 2 h.

[0088] (b) Etching of carbon support: The carbon support obtained in the above process was mixed with 20 ml of KOH solution with a concentration of 0.2 g / mL, and magnetically stirred in a water bath at 80°C for 6 h, and vacuum dried at 160°C for 10 h. The dried sample was washed with ethanol and deionized water three times, respectively, until the pH was neutral, and dried at 80°C for 10 h. The obtained carbon support was denoted as CMS-N.

[0089] (2) Preparation of carbon support loaded iron-based catalyst by impregnation method

[0090] (a) 0.25 g of Fe(N03)3-9H20 was dissolved in 10 mL of deionized water, and after complete dissolution, 0.9 g of the carrier CMS was poured into the iron nitrate nonahydrate solution and ultrasonically mixed for 0.5 h until uniform mixing. After drying at 80°C, calcination was performed in a horizontal tube furnace under N2atmosphere at 500°C for 3 h. A black Fe / CMS-N powder catalyst was obtained.

[0091] Catalyst performance test and characterization:

[0092] The catalyst is evaluated by using a micro fixed bed reactor, the catalyst is 0.5-1 mL, the reaction temperature is 300-500℃, the reaction pressure is 0.5-3 MPa, the raw gas is H2 / CO=1 or 2, and the space velocity is 500-5000·h -1 .

[0093] For example, the catalyst prepared in Example 1 is subjected to performance evaluation in a fixed bed reactor, and the specific operation steps are as follows: 1 mL of the catalyst prepared in Example 1 is weighed and loaded into the middle constant temperature zone of the reaction tube, the raw gas is H2 / CO=2, the temperature is 300℃, the pressure is 1.5 MPa, and the space velocity (GHSV) is 1000h -1 , after reaching a stable state, sampling and analysis are performed every 2 hours. The raw gas and the product are subjected to quantitative and qualitative analysis by using gas chromatography. The CO conversion rate and the selectivity of each component are calculated by using the methane correlation method in the determination of H2, N2, CO, CO2 and C1-C8 hydrocarbons in the tail gas of coal-based Fischer-Tropsch synthesis by gas chromatography.

[0094] The performance evaluation of the catalysts prepared in Examples 2-5 and Comparative Examples 1-2 is performed in the same manner, and Table 1 is a comparison table of the hydrogenation catalysis process parameters and performance test results of the catalysts prepared in Examples 1-5 and Comparative Examples 1-2. As can be seen from Table 1, the CO conversion rate is significantly improved in the hydrogenation product distribution of the Fe / CMS-N-H2O2 catalyst modified by hydrogen peroxide solution, and the selectivity of low-carbon olefins and long-chain hydrocarbons changes significantly. Among the modified carbon carrier supported iron-based catalysts prepared in the examples of the present application, the Fe / CMS-N-H2O2 catalyst prepared in Example 3 has the best CO hydrogenation performance, the selectivity of low-carbon olefins is as high as 37.6%, the selectivity of methane is less than 17%, and the olefin / alkane ratio (O / P) of low-carbon hydrocarbons is 2.4.

[0095] Table 1 Comparison table of hydrogenation catalysis process parameters and performance test results of each catalyst

[0096]

[0097] The specific surface area and pore size of the catalyst are characterized by using a Micromeritics ASAP 2460 instrument. The samples are pretreated at 300℃ for 1h before testing, and the adsorption and desorption experiments are carried out at liquid nitrogen temperature (77K) and a gas pressure of 1.33×10-4Pa.

[0098] Table 2 is a comparison table of the BET test results of the catalysts prepared in the above-mentioned Comparative Examples 1-2 and Example 3 of the present application. As can be seen from Table 2, the specific surface area of the catalysts treated with urea and hydrogen peroxide solution gradually increases. The average pore diameter of the catalyst modified by hydrogen peroxide is converted from mesopore to micropore, which can increase the selectivity of low-carbon hydrocarbons, C5 + selectivity is increased.

[0099] Table 2 is a comparison table of the BET test results of the catalysts prepared in the above-mentioned Comparative Examples 1-2 and Example 3 of the present application. As can be seen from Table 2, the specific surface area of the catalysts treated with urea and hydrogen peroxide solution gradually increases. The average pore diameter of the catalyst modified by hydrogen peroxide is converted from mesopore to micropore, which can increase the selectivity of low-carbon hydrocarbons, C5

[0100]

[0101] The morphology and structure of the catalysts were observed by field emission scanning electron microscopy (SEM), instrument model: Hitachi Regulus 8100. The sample was directly adhered to the conductive glue for testing, and the sample was treated with gold spraying before testing, the working voltage was 15kV, and the magnification was 500-10w times.

[0102] Figs. 1-3 Figures 1-3 are comparison charts of the SEM test results of the catalysts prepared in Example 3, Comparative Example 1 and Comparative Example 2 of the present application, respectively. As can be seen from Figures 1-3, Fig. 2 、 3 It can be seen that the iron is easy to agglomerate on the carrier, and the dispersion is low, which can cause poor catalytic activity, and Fig. 1 It can be seen that the agglomeration of iron particles on the catalyst treated with urea and hydrogen peroxide solution is reduced, and the dispersion is increased, which is beneficial to promote the reduction of the catalyst, improve the activity and product selectivity of the catalyst.

[0103] In summary, the carbon carrier prepared by phenolic resin in the present application makes the catalyst surface have more hydroxyl groups, the specific surface area of the catalyst gradually increases by N-doping and surface modification treatment of the carbon carrier, the average pore diameter is converted from mesopore to micropore, the mass transfer efficiency is improved, the active phase reduction to Fe5C2 is promoted, the agglomeration of iron is reduced, the dispersion is promoted, the CO conversion rate is improved, the CH4 selectivity is reduced, and the selectivity of low-carbon hydrocarbons is increased, thereby the product distribution of the catalyst can be effectively improved.

[0104] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for the preparation of a surface-modified carbon support- loaded iron-based catalyst, characterized in that, The method comprises the following steps: S1, preparing a carbon carrier: phenolic resin and urea are mixed uniformly at a certain ratio, and then are ground and calcined to carbonize. The sample obtained after calcination and carbonization is mixed with a KOH solution to obtain a suspension. The suspension is magnetically stirred in a water bath, and then is washed with ethanol and deionized water until the solution is neutral. After drying overnight, a nitrogen-doped carbon carrier CMS-N is obtained, and the mass ratio of the phenolic resin to the urea is (1-3):1; S2, modifying the surface of the carbon carrier: the nitrogen-doped carbon carrier CMS-N is placed in a hydrogen peroxide solution and is stirred thoroughly. After washing and drying, a surface-oxidized carbon carrier CMS-N-H2O2 is obtained; S3, preparing an iron-based catalyst by an impregnation method: the CMS-N-H2O2 and Fe(NO3)3·9H2O are mixed at a fixed ratio, and the mass ratio of the CMS-N-H2O2 to the Fe(NO3)3·9H2O is 0.9:(0.1-0.5). After being stirred and ultrasonically mixed, the mixture is dried and calcined to obtain a black Fe / CMS-N-H2O2 powder catalyst.

2. The method of making a surface-modified carbon support-supported iron-based catalyst of claim 1, wherein: The mass ratio of the phenolic resin to the urea is 1:

1.

3. The method of making a surface-modified carbon support-supported iron-based catalyst of claim 1, wherein: The mass ratio of the CMS-N-H2O2 to the Fe(NO3)3·9H2O is 0.9:0.

25.

4. The method of making a surface-modified carbon support-supported iron-based catalyst of claim 1, wherein: In step S1, the calcination and carbonization is performed at 300-800℃ in a tube furnace in a stable N2 atmosphere for 2h, and the temperature rising rate is 2℃ / min.

5. The method of making a surface-modified carbon support-supported iron-based catalyst of claim 1, wherein: In step S3, the calcination is performed at 500℃ in a tube furnace in a stable N2 atmosphere for 3h, and the temperature rising rate is 2℃ / min.

6. Use of the surface-modified carbon support loaded iron-based catalyst prepared by the preparation method of any one of claims 1-5 in catalyzing CO hydrogenation, characterized in that, The reaction conditions were: raw gas H2 / CO = 2, temperature 300°C, pressure 1.5 MPa, space velocity GHSV 1000 h -1 .

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