Modified indium oxide catalyst, method for preparing the same, and method for preparing methanol by hydrogenation of carbon dioxide

Abstract

The application relates to the technical field of carbon dioxide hydrogenation catalysts, and discloses a modified indium oxide catalyst, a preparation method thereof and a method for preparing methanol through carbon dioxide hydrogenation, the catalyst comprising indium oxide and a modified element, wherein the modified element is zirconium; the indium oxide comprises cubic phase indium oxide and hexagonal phase indium oxide, and the mass ratio of the cubic phase indium oxide to the hexagonal phase indium oxide is 1:0.1-50; the modified element at least partially exists in the form of zirconium oxide, and the zirconium oxide has a monoclinic crystal type. The catalyst provided by the application has high reaction activity, can consider high carbon dioxide conversion rate and methanol selectivity in the reaction for preparing methanol through carbon dioxide hydrogenation, has good reaction stability, and has a low catalyst deactivation rate.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide hydrogenation catalyst technology, specifically to a modified indium oxide catalyst, its preparation method, and a method for producing methanol by carbon dioxide hydrogenation. Background Technology

[0002] Rapid global economic development has led to a continuous increase in CO2 emissions, and the increase in atmospheric carbon dioxide levels is a significant factor contributing to environmental problems such as the greenhouse effect and global warming. Therefore, researching technologies for carbon dioxide emission reduction and conversion has become an urgent issue. Methanol, as an important raw material for chemicals and a substitute for fossil fuels, can be produced by reacting CO2 with H2 from renewable energy sources. This process not only addresses greenhouse gas control but also serves as an effective alternative to fossil fuels. Consequently, the catalytic conversion of carbon dioxide into methanol has attracted increasing attention.

[0003] Because CO2 is chemically stable and difficult to activate, the conversion rate of this reaction is generally low. Methanol production is an exothermic reaction, and thermodynamically, low temperatures are favorable for methanol production but unfavorable for carbon dioxide activation. Therefore, it is necessary to select a suitable reaction temperature and design an efficient catalyst.

[0004] Currently, modified copper-based catalysts, noble metal catalysts, and zinc oxide catalysts are widely studied for methanol synthesis. However, in modified statistical catalysis systems, the high activity of the reverse water-gas shift (RWGS) side reaction, H2O-induced sintering of the active phase, and poor stability limit their further application. In noble metal and zinc oxide catalyst systems, the high cost of noble metals and the low activity and easy migration of zinc oxide also limit their further application in the catalytic hydrogenation of carbon dioxide. In2O3 has moderate CO2 and CO adsorption capacity, exhibits significantly better methanol selectivity than Cu, Co, and noble metal catalysts, and higher catalytic activity than ZnO catalysts, thus attracting widespread attention from researchers. However, the catalytic effect of In2O3 catalysts in existing technologies still needs further improvement. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of insufficient catalytic activity and stability of indium oxide catalysts in the prior art, and to provide a modified indium oxide catalyst, its preparation method and a method for producing methanol by carbon dioxide hydrogenation. The modified indium oxide catalyst has better catalytic effect and can effectively improve methanol selectivity.

[0006] To achieve the above objectives, a first aspect of the present invention provides a modified indium oxide catalyst, the catalyst comprising indium oxide and a modifying element, wherein the modifying element is zirconium;

[0007] The indium oxide comprises cubic indium oxide and hexagonal indium oxide, and the mass ratio of cubic indium oxide to hexagonal indium oxide is 1:0.1-50; the modifying element exists at least partially in the form of zirconium oxide, which has a monoclinic crystal form.

[0008] Preferably, the mass ratio of indium to zirconium, calculated as oxides, is 1-6:1, more preferably 1.5-3:1.

[0009] A second aspect of the present invention provides a method for preparing a modified indium oxide catalyst, the method comprising:

[0010] (1) Mix indium salt, first precipitant and modifier to obtain precipitate mother liquor;

[0011] The modifier is zirconium oxide with a monoclinic crystal structure;

[0012] (2) The precipitated mother liquor is aged;

[0013] The aging conditions include: a temperature of 120-200℃ and a time of 8-48 hours.

[0014] (3) The product obtained in step (2) is subjected to solid-liquid separation, and then dried and calcined.

[0015] A third aspect of the present invention provides a modified indium oxide catalyst prepared by the above-described preparation method.

[0016] A fourth aspect of the present invention provides a method for preparing methanol by hydrogenation of carbon dioxide, the method comprising: contacting carbon dioxide and hydrogen under carbon dioxide hydrogenation conditions in the presence of a catalyst; wherein the catalyst is the modified indium oxide catalyst described in the first or third aspect.

[0017] In the prior art, the indium oxide in indium oxide catalysts is generally cubic crystal structure, such as the supported indium oxide catalysts disclosed in US20200061582A1 and US20210322957A1; in addition, CN110479235A discloses a hexagonal indium oxide with a nano-level structure, but the CO2 conversion rate is low.

[0018] The inventors of this invention discovered in their research that by controlling the content of cubic and hexagonal indium oxide in the indium oxide catalyst, the catalyst's reactivity can be improved, resulting in good reaction stability and a low catalyst deactivation rate, under the synergistic effect of monoclinic zirconium oxide.

[0019] The method for preparing the modified indium oxide catalyst provided by this invention can effectively control the crystal orientation of indium oxide by controlling the reaction conditions and introducing monoclinic zirconium oxide. It can also easily control the content of cubic and hexagonal indium oxide in the catalyst. The process steps are simple, which can effectively reduce its production cost and enable mass production. Attached Figure Description

[0020] Figure 1 This is the XRD pattern of the catalyst prepared in Example 1 of this invention. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] The first aspect of the present invention provides a modified indium oxide catalyst, the catalyst comprising indium oxide and a modifying element, wherein the modifying element is zirconium;

[0023] The indium oxide comprises cubic indium oxide and hexagonal indium oxide, and the mass ratio of cubic indium oxide to hexagonal indium oxide is 1:0.1-50; the modifying element exists at least partially in the form of zirconium oxide, which has a monoclinic crystal form.

[0024] The inventors of this invention discovered in their research that cubic indium oxide has excellent CO2 activation ability and strong anti-water gas reaction, resulting in low CH3OH selectivity, while hexagonal indium oxide has high methanol selectivity and low CO2 conversion rate. In order to make the catalyst have both high methanol selectivity and high CO2 conversion rate, the crystal composition of indium oxide was further studied in depth.

[0025] In the catalyst described in this invention, indium oxide is a mixed-crystal material, meaning that indium oxide simultaneously possesses both cubic and hexagonal crystal structures. These two crystal structures are a mixed phase formed through oriented crystallization in the presence of modifying elements, rather than a purely physical mixture. The inventors discovered that during the synthesis of hexagonal indium oxide, the synergistic effect of monoclinic zirconium oxide can lead to the formation of a cubic / hexagonal indium oxide mixed crystal. This allows the catalyst to maintain high methanol selectivity while improving CO2 conversion, thereby enhancing its reactivity, reaction stability, and deactivation rate.

[0026] In this invention, the crystal morphology of each component in the catalyst is characterized by X-ray diffraction. In the X-ray diffraction pattern of standard cubic indium oxide, characteristic diffraction peaks are observed at 2θ of 21.5°, 30.6°, 35.5°, 51.0°, and 60.7°, which correspond to the (211), (222), (400), (440), and (622) crystal planes of cubic indium oxide, respectively (JCPDS 06-0416). In the X-ray diffraction pattern of standard hexagonal indium oxide, characteristic diffraction peaks are observed at 2θ of 22.4°, 31.0°, 32.6°, and 45.7°, which are attributed to the (012), (104), (110), and (024) crystal planes of hexagonal indium oxide, respectively (JCPDS 22-0336). The content of each crystal form of indium oxide was further calculated using the formula Wc(%) = [Ac / (Ac+3.4Ah)]×100%. Here, Ac and Ah represent the fitting intensity (fitting peak area) of the c-In2O3(222) and h-In2O3(104) crystal planes, respectively, and the constant coefficient 3.4 is the ratio of the fitting intensity of the two peaks, which can be obtained through preliminary XRD experiments.

[0027] In this invention, preferably, the mass ratio of cubic indium oxide to hexagonal indium oxide is 1:0.5-20. For example, it can be a limited but not limited ratio such as 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, etc. Controlling the ratio of cubic indium oxide to hexagonal indium oxide in the catalyst within the above-mentioned preferred range can achieve both high methanol selectivity and high CO2 conversion rate.

[0028] According to the present invention, the modifying element is determined from the X-ray diffraction pattern of the catalyst to exist at least partially in the form of zirconium oxide, and the zirconium oxide has a monoclinic crystal form. The inventors of the present invention have discovered that the monoclinic zirconium oxide in the catalyst helps to stabilize the indium oxide crystal form. Furthermore, through the synergistic effect of monoclinic zirconium oxide, cubic indium oxide, and hexagonal indium oxide, the catalytic activity and stability of the catalyst can be further improved.

[0029] The present invention allows for a wide range of selection for the content of indium and zirconium in the catalyst. Preferably, based on the total weight of the catalyst and calculated as oxides, the content of indium is 40-90 wt%, preferably 60-80 wt%; and the content of zirconium is 10-60 wt%, preferably 20-40 wt%. For example, the indium content, calculated as oxide, can be typical but not limiting, such as 60wt%, 61wt%, 62wt%, 63wt%, 64wt%, 65wt%, 66wt%, 67wt%, 68wt%, 69wt%, 70wt%, 71wt%, 72wt%, 73wt%, 74wt%, 75wt%, 76wt%, 77wt%, 78wt%, 79wt%, 80wt%, etc.; the zirconium content, calculated as oxide, can be typical but not limiting, such as 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt%, 33wt%, 34wt%, 35wt%, 36wt%, 37wt%, 38wt%, 39wt%, 40wt%, etc.

[0030] In this invention, the contents of indium oxide and zirconium oxide are determined by XRF method.

[0031] In this invention, it is not excluded that some of the modifying elements exist in the form of indium / zirconium oxide.

[0032] In existing technologies, zirconium oxide is more often used as a catalyst support, such as the supported indium oxide catalysts disclosed in US20200061582A1 and US20210322957A1. In these catalysts, zirconium oxide has high crystallinity and its content is much higher than that of indium oxide because the zirconium oxide support disperses the indium oxide. However, in this invention, zirconium is used as a modifying element, and the zirconium oxide content in the catalyst is preferably not higher than the indium oxide content.

[0033] In a further preferred embodiment, the modified indium oxide catalyst has an indium to zirconium mass ratio of 1-6:1, based on oxides. For example, typical but not limiting ratios include 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, and 6:1. Preferably, the indium to zirconium mass ratio is 1.5-3:1, based on oxides. In the above preferred embodiments, the formation of cubic indium oxide is facilitated in the preparation of hexagonal indium oxide.

[0034] A second aspect of the present invention provides a method for preparing a modified indium oxide catalyst, the method comprising:

[0035] (1) Mix indium salt, first precipitant and modifier to obtain precipitate mother liquor;

[0036] The modifier is zirconium oxide with a monoclinic crystal structure;

[0037] (2) The precipitated mother liquor is aged;

[0038] The aging conditions include: a temperature of 120-200℃ and a time of 8-48 hours.

[0039] (3) The product obtained in step (2) is subjected to solid-liquid separation, and then dried and calcined.

[0040] The inventors of this invention discovered in their research that during the aging process of the precipitate mother liquor, monoclinic zirconium oxide can induce the crystal orientation of indium oxide, so that the catalyst simultaneously contains cubic and hexagonal indium oxide, forming a cubic / hexagonal indium oxide mixed crystal; and the monoclinic zirconium oxide helps to regulate the oxygen hole concentration in the catalyst, further improving the catalyst activity and stability.

[0041] This invention offers a wide range of options for the amounts of indium salt and modifier. Preferably, the amounts of indium salt and modifier are such that, based on the total weight of the prepared catalyst, the indium content, calculated as oxide, is 40-90 wt%, preferably 60-80 wt%; and the zirconium content is 10-60 wt%, preferably 20-40 wt%. For example, the indium content, calculated as oxide, can be 60 wt%, 61 wt%, 62 wt%, 63 wt%, 64 wt%, 65 wt%, 66 wt%, 67 wt%, 68 wt%, 69 wt%, 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%. Typical, but not limiting, contents such as t%, 75wt%, 76wt%, 77wt%, 78wt%, 79wt%, 80wt%, or a range between the two; the zirconium content, calculated as oxide, can be typical, but not limiting, contents such as 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt%, 33wt%, 34wt%, 35wt%, 36wt%, 37wt%, 38wt%, 39wt%, 40wt%, or a range between the two.

[0042] In a further preferred embodiment, the mass ratio of the indium salt to the modifier, calculated as oxide, is 1-6:1, for example, typical but not limiting ratios or ranges between 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, etc. Preferably, the mass ratio of the indium salt to the modifier, calculated as oxide, is 1.5-3:1.

[0043] According to a preferred embodiment of the present invention, the mixing in step (1) is carried out under stirring conditions. The present invention does not impose any particular limitation on the stirring conditions, as long as sufficient dispersion of the components is ensured. Preferably, the mixing temperature is 20-50°C, and the mixing time is 1-10 hours.

[0044] The present invention does not have a particular limitation on the mixing order. The indium salt, the first precipitant, and the modifier can be added to the reactor together for mixing, or the indium salt and the first precipitant can be mixed first, and then the modifier can be added. In a further preferred embodiment, the mixing in step (1) includes: a first mixing of the indium salt and the precipitant, followed by a second mixing with the modifier. Using the above preferred embodiments facilitates the formation of appropriate amounts of cubic and hexagonal indium oxide, improving the methanol selectivity and CO2 conversion rate of the catalyst.

[0045] According to the present invention, preferably, the precipitate mother liquor further contains a solvent, wherein the solvent is an organic solvent and / or water. More preferably, the solvent is a mixture of an organic solvent and water, wherein the volume ratio of the organic solvent to water is preferably 1-5:1.

[0046] In this invention, the organic solvent may be an alcohol and / or an amide solvent. Preferably, the organic solvent is selected from at least one of ethanol, methanol, isopropanol, ethylene glycol, triethylene glycol, and N,N-dimethylacetamide.

[0047] According to a particularly preferred embodiment of the present invention, the solvent is a mixture of ethanol and water, wherein the volume ratio of ethanol to water is 1-3:1.

[0048] The present invention does not have a particular limitation on the timing of the introduction of the solvent. The indium salt and the first precipitant can be added to the solvent to obtain the indium salt solution and the first precipitant solution, and then the mixing described in step (1) can be carried out. Alternatively, the indium salt, the first precipitant and the modifier can be mixed and then the solvent can be added for dispersion.

[0049] In a further preferred embodiment, the indium salt is provided in the form of an indium salt solution with a concentration of 0.1-0.8 mol / L.

[0050] The present invention allows for a wide range of choices regarding the specific type of indium salt, as long as indium is available. Conventional soluble indium salts in the art can be used in this invention. For example, the indium salt can be selected from at least one of indium nitrate, indium chloride, and indium sulfate. The indium salt may also contain water of crystallization, as is well known to those skilled in the art and will not be elaborated upon here.

[0051] Preferably, the first precipitant is provided in the form of a first precipitant solution, the concentration of which is 1-2 mol / L.

[0052] In this invention, the compositions of the solvents in the indium salt solution and the first precipitant solution may be the same or different, both of which satisfy the definition range of the solvent composition described above.

[0053] Preferably, the first precipitant is selected from at least one of urea, ammonia, (NH4)2CO3, Na2CO3 and NaOH.

[0054] According to the present invention, preferably, the molar ratio of the first precipitant to the indium salt (based on indium element) is 5-8:1, for example, typical but not limiting ratios such as 5:1, 5.2:1, 5.4:1, 5.6:1, 5.8:1, 6:1, 6.2:1, 6.4:1, 6.6:1, 6.8:1, 7:1, 7.2:1, 7.4:1, 7.6:1, 7.8:1, and 8:1. Preferably, the molar ratio of the first precipitant to the indium salt (based on indium element) is 6-7:1.

[0055] In this invention, the modifier is zirconium oxide with a monoclinic crystal form. This invention does not particularly limit the source of the modifier; it can be commercially available or prepared using any method known in the art.

[0056] In one specific embodiment of the present invention, the preparation method of the modifier includes: mixing a zirconium source and a second precipitant, carrying out a hydrothermal reaction at 120-200°C for 15-25 hours, and then drying and calcining the product obtained from the hydrothermal reaction.

[0057] According to a preferred embodiment of the present invention, the drying temperature is 80-150°C and the time is 15-25 hours.

[0058] According to a preferred embodiment of the present invention, the calcination temperature is 400-600℃ and the time is 3-6h.

[0059] The present invention allows for a wide range of choices regarding the specific type of zirconium source, as long as zirconium element can be provided, such as zirconium nitrate and / or zirconium oxynitrate. The zirconium source may also contain water of crystallization, as is well known to those skilled in the art and will not be elaborated upon here.

[0060] In this invention, the second precipitant and the first precipitant are selected from the same range, and their specific selections may be the same or different. This invention does not have any particular limitation on this.

[0061] Preferably, the molar ratio of the second precipitant to the zirconium source (calculated as zirconium element) is 4-11:1, more preferably 4.5-10:1.

[0062] According to the present invention, preferably, in step (2), the aging conditions include: a temperature of 120-150°C, such as typical but not limiting aging temperatures like 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, and 150°C. The aging time is preferably 16-20 hours, such as typical but not limiting times like 16 hours, 17 hours, 18 hours, 19 hours, and 20 hours. Controlling the aging temperature and time is beneficial for the formation of cubic indium oxide in hexagonal indium oxide; however, excessively long aging times may lead to an excessive content of cubic indium oxide.

[0063] In one specific embodiment of the present invention, step (2) further includes: washing and solid-liquid separation of the product obtained from aging. The washing and solid-liquid separation can be performed using conventional operations and conditions in the art; for example, deionized water can be used for washing. The solid-liquid separation can be performed by centrifugation.

[0064] According to the present invention, preferably, in step (3), the drying conditions include: a temperature of 50-100°C, preferably 60-80°C; and a time of 12-25h, preferably 14-22h.

[0065] Preferably, in step (3), the calcination conditions include: a temperature of 350-600℃, for example, 350℃, 360℃, 370℃, 380℃, 390℃, preferably 400-500℃; and a time of 1-8h, preferably 3-6h.

[0066] In one specific embodiment of the present invention, step (3) further includes: shaping and sieving the product obtained from the roasting. The present invention does not particularly limit the shaping method; those skilled in the art can choose according to actual needs, for example, tableting can be used.

[0067] A third aspect of the present invention provides a modified indium oxide catalyst prepared by the above-described preparation method.

[0068] A fourth aspect of the present invention provides a method for preparing methanol by hydrogenation of carbon dioxide, the method comprising: contacting carbon dioxide and hydrogen under carbon dioxide hydrogenation conditions in the presence of a catalyst; wherein the catalyst is the modified indium oxide catalyst described in the first or third aspect.

[0069] According to the present invention, preferably, the carbon dioxide hydrogenation conditions include: a reaction temperature of 200-400°C, a reaction pressure of 1-6 MPa, and a volume hourly space velocity of 4500-18000 h⁻¹. -1 The H2 / CO2 molar ratio is 1-6; more preferably, the carbon dioxide hydrogenation conditions include: a reaction temperature of 240-280℃, a reaction pressure of 3-5 MPa, and a volume hourly space velocity of 8000-12000 h⁻¹. -1 The H2 / CO2 molar ratio is 3-6.

[0070] Preferably, prior to the contact, the method further includes: reducing and activating the catalyst under atmospheric pressure and in a hydrogen atmosphere. The conditions for the reduction and activation include: a reduction temperature of 150-250°C, preferably 180-220°C, and a time of 1-4 hours, preferably 1.5-3 hours.

[0071] The hydrogen atmosphere can be provided by hydrogen or a mixture of hydrogen and an inert gas. Preferably, the hydrogen atmosphere is provided by a mixture of hydrogen and an inert gas, wherein the volume fraction of hydrogen in the mixture is 10%-50%.

[0072] The present invention will be described in detail below through embodiments.

[0073] In the following examples, all raw materials were purchased from Sinopharm Group.

[0074] The phase structure, cubic indium oxide, and hexagonal indium oxide content in the catalyst were determined by X-ray diffraction. The X-ray diffraction pattern of standard cubic indium oxide showed characteristic diffraction peaks at 2θ values ​​of 21.5°, 30.6°, 35.5°, 51.0°, and 60.7°, corresponding to the (211), (222), (400), (440), and (622) crystal planes of cubic indium oxide (JCPDS06-0416), respectively. The X-ray diffraction pattern of standard hexagonal indium oxide showed characteristic diffraction peaks at 2θ values ​​of 22.4°, 31.0°, 32.6°, and 45.7°, belonging to the (012), (104), (110), and (024) crystal planes of hexagonal indium oxide (JCPDS 22-0336), respectively. The content of each crystal form of indium oxide was further calculated using the formula Wc(%) = [Ac / (Ac+3.4Ah)]×100%. Here, Ac and Ah represent the fitting intensity (fitting peak area) of the c-In2O3(222) and h-In2O3(104) crystal planes, respectively, and the constant coefficient 3.4 is the ratio of the fitting intensity of the two peaks, which can be obtained through preliminary XRD experiments.

[0075] The contents of indium oxide and zirconium oxide in the catalyst were determined by XRF method.

[0076] The composition of the products from the reaction of carbon dioxide hydrogenation to methanol was analyzed using a gas chromatograph purchased from Agilent Technologies (China) Co., Ltd.

[0077] Example 1

[0078] (1) Dissolve 9.53 g of ZrO(NO3)2·2H2O in deionized water to a final volume of 100 mL and stir until dissolved. Then weigh 20.67 g of urea and add it to the above solution, stirring until dissolved. After dissolution, pour the solution into a hydrothermal reactor, seal it, and place it in an oven at 180°C for hydrothermal reaction for 20 h. After the hydrothermal reaction is complete, allow it to cool naturally to room temperature. Open the hydrothermal reactor, filter and wash the hydrothermal product. Then dry it in an oven at 120°C for 15 h. Finally, calcine it in a muffle furnace at 400°C for 3 h to obtain monoclinic ZrO2;

[0079] (2) Add 7.6g of In(NO3)3·4H2O to a mixture of 50mL of anhydrous ethanol and 25mL of deionized water to obtain a solution containing indium salt. Add 8g of urea to a mixture of 60mL of anhydrous ethanol and 20mL of deionized water to obtain a precipitant solution. Add the precipitant solution dropwise to the solution containing indium salt at 30℃. Then add 1.2g of monoclinic ZrO2 prepared in step (1) and stir thoroughly at 200rpm for 4h to obtain the precipitate mother liquor.

[0080] (3) Add the precipitate mother liquor obtained in step (2) into a 100mL hydrothermal synthesis reactor lined with polytetrafluoroethylene, place it in a forced-air drying oven and let it stand for aging. The aging temperature is 120℃ and the aging time is 18h to form a precipitate.

[0081] (4) After the product obtained in step (3) is naturally cooled to room temperature, it is centrifuged, washed with deionized water until the centrifuged precipitate reaches pH 8, dried at 60°C for 15 hours, and then calcined at 380°C for 3 hours to obtain catalyst S1, which is then pressed into tablets and sieved to 40-60 mesh.

[0082] The X-ray diffraction pattern of catalyst S1 is as follows: Figure 1 As shown, characteristic diffraction peaks of cubic indium oxide are observed at 2θ values ​​of 21.5°, 30.6°, 35.5°, 51.0°, and 60.7°, while characteristic diffraction peaks of hexagonal indium oxide are observed at 2θ values ​​of 22.4°, 31.0°, 32.6°, and 45.7°, confirming the presence of both cubic and hexagonal indium oxide in the catalyst. Simultaneously, a characteristic peak of monoclinic zirconium oxide is observed at 2θ value of 30.3°, indicating that zirconium in the catalyst exists at least partially in the form of monoclinic zirconium oxide. The component contents of the catalyst are shown in Table 1.

[0083] Example 2

[0084] (1) Weigh 6.23 g of ZrO(NO3)2·2H2O, dilute to 60 mL with deionized water, and stir to dissolve. Then weigh 10.03 g of urea and add it to the above solution, stirring to dissolve. After dissolution, pour into a 100 mL hydrothermal reactor, seal, and place in an oven at 160 °C for hydrothermal reaction for 18 h. After the hydrothermal reaction is complete, allow to cool naturally to room temperature. Open the hydrothermal reactor, filter and wash the hydrothermal product. Then place it in an oven at 110 °C for 12 h to dry. Finally, calcine in a muffle furnace at 450 °C for 3 h to obtain monoclinic ZrO2;

[0085] (2) Add 7.3g of In(NO3)3·4H2O to a mixture of 80mL of anhydrous ethanol and 40mL of deionized water to obtain a solution containing indium salt. Add 9.2g of urea to a mixture of 80mL of anhydrous ethanol and 30mL of deionized water to obtain a precipitant solution. Add the precipitant solution dropwise to the solution containing indium salt at 30℃. Then add 1.0g of monoclinic ZrO2 prepared in step (1) and stir thoroughly at 150rpm for 7h to obtain the precipitate mother liquor.

[0086] (3) Add the precipitate mother liquor obtained in step (2) into a 100mL hydrothermal synthesis reactor lined with polytetrafluoroethylene, place it in a forced-air drying oven and let it stand for aging at 130℃ for 48h to form a precipitate.

[0087] (4) After the product obtained in step (3) is naturally cooled to room temperature, it is centrifuged, washed with deionized water until the centrifuged precipitate reaches pH 7, dried at 80°C for 12 hours, calcined at 450°C for 3 hours, pressed into tablets and sieved to 40-60 mesh to obtain catalyst S2 (the content of each component is shown in Table 1).

[0088] Example 3

[0089] (1) Weigh 6.68 g of ZrO(NO3)2·2H2O, dilute to 50 mL with deionized water, and stir to dissolve. Then weigh 8.67 g of urea and add it to the above solution, stirring to dissolve. After dissolution, pour into a 100 mL hydrothermal reactor, seal, and place in an oven at 190 °C for hydrothermal reaction for 15 h. After the hydrothermal reaction is complete, allow to cool naturally to room temperature. Open the hydrothermal reactor, filter and wash the hydrothermal product. Then place it in an oven at 100 °C for 15 h to dry. Finally, calcine in a muffle furnace at 500 °C for 4 h to obtain monoclinic ZrO2;

[0090] (2) Add 8.5g of In(NO3)3·4H2O to a mixture of 40mL of anhydrous ethanol and 24mL of deionized water to obtain a solution containing indium salt. Add 8g of urea to a mixture of 40mL of anhydrous ethanol and 10mL of deionized water to obtain a precipitant solution. Add the precipitant solution dropwise to the solution containing indium salt at 30℃. Then add 2g of monoclinic ZrO2 prepared in step (1) and stir thoroughly at 150rpm for 6h to obtain the precipitate mother liquor.

[0091] (3) Add the precipitate mother liquor obtained in step (2) into a 100mL hydrothermal synthesis reactor lined with polytetrafluoroethylene, place it in a forced-air drying oven and let it stand for aging. The aging temperature is 120℃ and the aging time is 16h to form a precipitate.

[0092] (4) After the product obtained in step (2) is naturally cooled to room temperature, it is centrifuged, washed with deionized water until the centrifuged precipitate reaches pH 7, dried at 60°C for 20 h, calcined at 350°C for 3 h, and pressed into tablets and sieved to 40-60 mesh to obtain catalyst S3 (the content of each component is shown in Table 1).

[0093] Example 4

[0094] (1) Weigh 4.89 g of ZrO(NO3)2·2H2O, dilute to 70 mL with deionized water, and stir to dissolve. Then weigh 6.63 g of urea and add it to the above solution, stirring to dissolve. After dissolution, pour into a 100 mL hydrothermal reactor, seal, and place in an oven at 180 °C for hydrothermal reaction for 18 h. After the hydrothermal reaction is complete, allow to cool naturally to room temperature. Open the hydrothermal reactor, filter and wash the hydrothermal product. Then place it in an oven at 110 °C for drying for 16 h. Finally, calcine in a muffle furnace at 550 °C for 3 h to obtain monoclinic ZrO2;

[0095] (2) Add 9.3g of In(NO3)3·4H2O to a mixed solution of 80mL anhydrous ethanol and 40mL deionized water to obtain a solution containing indium salt. Add 8g of urea to a mixed solution of 60mL anhydrous ethanol and 25mL deionized water to dissolve and obtain a precipitant solution. Add the precipitant solution dropwise to the solution containing indium salt at 30℃. Then add 1g of monoclinic ZrO2 prepared in step (1) and stir thoroughly at 200rpm for 6h to obtain the precipitate mother liquor.

[0096] (3) Add the precipitate mother liquor obtained in step (2) into a 100mL hydrothermal synthesis reactor lined with polytetrafluoroethylene, place it in a forced-air drying oven and let it stand for aging at 170℃ for 24h to form a precipitate.

[0097] (4) After the product obtained in step (3) is naturally cooled to room temperature, it is centrifuged, washed with deionized water until the pH reaches 8, dried at 60°C for 22 hours, calcined at 500°C for 3 hours, pressed into tablets and sieved to 40-60 mesh to obtain catalyst S4 (the content of each component is shown in Table 1).

[0098] Example 5

[0099] (1) Weigh 5.06 g of ZrO(NO3)2·2H2O, dilute to 80 mL with deionized water, and stir to dissolve. Then weigh 7.23 g of urea and add it to the above solution, stirring to dissolve. After dissolution, pour into a 100 mL hydrothermal reactor, seal, and place in an oven at 160 °C for hydrothermal reaction for 18 h. After the hydrothermal reaction is complete, allow to cool naturally to room temperature. Open the hydrothermal reactor, filter and wash the hydrothermal product. Then place it in an oven at 110 °C for drying for 16 h. Finally, calcine in a muffle furnace at 500 °C for 3 h to obtain monoclinic ZrO2;

[0100] (2) Add 5.4g of In(NO3)3·4H2O to a mixed solution of 40mL anhydrous ethanol and 20mL deionized water to obtain a solution containing metal indium salt. Add 6g of urea to a mixed solution of 50mL anhydrous ethanol and 20mL deionized water. Add the precipitant solution dropwise to the solution containing metal indium salt at 30℃. Then add 0.8g of monoclinic ZrO2 prepared in step (1). Stir thoroughly at 100rpm for 6h to obtain the precipitate mother liquor.

[0101] (3) Add the precipitate mother liquor obtained in step (2) into a 100 mL polytetrafluoroethylene-lined hydrothermal synthesis reactor, place it in a forced-air drying oven and let it stand for aging at 150°C for 28 hours to form a precipitate.

[0102] (4) After the product obtained in step (3) is naturally cooled to room temperature, it is centrifuged, washed with deionized water until the centrifuged precipitate reaches pH 8, dried at 80°C for 14 hours, calcined at 460°C for 3 hours, pressed into tablets and sieved to 40-60 mesh to obtain catalyst S5 (the content of each component is shown in Table 1).

[0103] Example 6

[0104] The method in Example 1 was followed, except that the amount of monoclinic ZrO2 added was 3.6g, and the resulting catalyst was designated as S6. The contents of each component are shown in Table 1.

[0105] Example 7

[0106] The method in Example 1 was followed, except that the amount of monoclinic ZrO2 added was 0.3g, and the resulting catalyst was designated as S7. The contents of each component are shown in Table 1.

[0107] Comparative Example 1

[0108] (1) Add 7.6g of In(NO3)3·4H2O to a mixture of 50mL of anhydrous ethanol and 25mL of deionized water to obtain a solution containing indium salt. Add 8g of urea to a mixture of 60mL of anhydrous ethanol and 20mL of deionized water to obtain a precipitant solution. Add the precipitant solution dropwise to the solution containing indium salt at 30℃ to obtain the precipitant mother liquor.

[0109] (2) Add the precipitate mother liquor obtained in step (1) into a 100mL hydrothermal synthesis reactor lined with polytetrafluoroethylene, place it in a forced-air drying oven and let it stand for aging at 120℃ for 18h to form a precipitate.

[0110] (3) After the product obtained in step (2) is naturally cooled to room temperature, it is centrifuged, washed with deionized water and centrifuged until the pH is 8, then dried at 60°C for 15 hours, then calcined at 380°C for 3 hours, pressed into tablets and sieved to 40-60 mesh to obtain catalyst DS1.

[0111] XRD analysis showed that catalyst DS1 contained only hexagonal indium oxide.

[0112] Comparative Example 2

[0113] (1) 7.6 g of In(NO3)3·4H2O was added to a mixture of 50 mL of anhydrous ethanol and 25 mL of deionized water to obtain a solution containing indium salt. 8 g of urea was added to a mixture of 60 mL of anhydrous ethanol and 20 mL of deionized water to obtain a precipitant solution. The precipitant solution was added dropwise to the solution containing indium salt at 30 °C. Then 1.2 g of cubic ZrO2 (commercially available) was added and stirred thoroughly at 200 rpm for 4 h to obtain the precipitate mother liquor.

[0114] (2) Add the precipitate mother liquor obtained in step (1) into a 100mL hydrothermal synthesis reactor lined with polytetrafluoroethylene, place it in a forced-air drying oven and let it stand for aging at 120℃ for 18h to form a precipitate.

[0115] (3) After the product obtained in step (2) is naturally cooled to room temperature, it is centrifuged, washed with deionized water until the centrifuged precipitate reaches pH 8, dried at 60°C for 15 hours, calcined at 380°C for 3 hours, pressed into tablets and sieved to 40-60 mesh to obtain catalyst DS2 (the content of each component is shown in Table 1).

[0116] Comparative Example 3

[0117] The method was followed as in Example 1, except that the aging temperature in step (3) was 100°C and the aging time was 16 hours. The resulting catalyst was designated as DS3.

[0118] Comparative Example 4

[0119] Commercially available cubic indium oxide was mixed and ground with hexagonal indium oxide prepared in Comparative Example 1 at a mass ratio of 1:19. The resulting product was denoted as DS4.

[0120] Table 1

[0121]

[0122]

[0123] Evaluation of the reaction for producing methanol by hydrogenation of carbon dioxide

[0124] The catalysts prepared in the above examples and comparative examples were used as reaction catalysts and packed in a stainless steel reactor with an inner diameter of 8 mm. First, reduction was carried out at 200°C for 2 hours using 10% H₂ / 90% N₂ under atmospheric pressure and an atmosphere flow rate of 7 L / h. Then, a reaction to produce methanol by carbon dioxide hydrogenation was carried out under the following conditions: reaction pressure of 5 MPa, reaction temperature of 280°C, and feedstock (carbon dioxide and hydrogen) volume hourly space velocity of 15000 h⁻¹. -1 The H2 / CO2 molar ratio was 5. After reacting for 500 h, the liquid product was collected in an ice-water bath. The composition of the product was analyzed by gas chromatography, and the evaluation results are shown in Table 2.

[0125] Table 2

[0126]

[0127]

[0128] As can be seen from the results in Table 2, the catalyst prepared in the embodiments of the present invention can effectively improve the conversion rate of carbon dioxide and improve the selectivity of methanol, indicating that the catalyst within the scope of protection of the present invention has good catalytic effect and good methanol selectivity.

[0129] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A modified indium oxide catalyst, characterized in that, The catalyst comprises indium oxide and a modifying element, wherein the modifying element is zirconium; The indium oxide comprises cubic indium oxide and hexagonal indium oxide, and the mass ratio of cubic indium oxide to hexagonal indium oxide is 1:0.1-50; the modifying element exists at least partially in the form of zirconium oxide, which has a monoclinic crystal form.

2. The catalyst according to claim 1, wherein, The mass ratio of cubic indium oxide to hexagonal indium oxide is 1:0.5-20.

3. The catalyst according to claim 1 or 2, wherein, Based on the total weight of the catalyst, the content of indium is 40-90 wt% and the content of zirconium is 10-60 wt% in terms of oxides.

4. The catalyst according to claim 3, wherein, Based on the total weight of the catalyst, the content of indium is 60-80 wt% and the content of zirconium is 20-40 wt% in terms of oxides.

5. The catalyst according to claim 1, wherein, The mass ratio of indium to zirconium, calculated as oxides, is 1-6:

1.

6. The catalyst according to claim 5, wherein, The mass ratio of indium to zirconium, calculated as oxides, is 1.5-3:

1.

7. A method for preparing a modified indium oxide catalyst, the method comprising: (1) Mix indium salt, first precipitant and modifier to obtain precipitate mother liquor; The modifier is zirconium oxide with a monoclinic crystal structure; (2) The precipitated mother liquor is aged; The aging conditions include: a temperature of 120-200℃ and a time of 8-48 hours. (3) The product obtained in step (2) is subjected to solid-liquid separation, and then dried and calcined.

8. The preparation method according to claim 7, wherein, The amounts of the indium salt and modifier are such that, based on the total weight of the catalyst obtained, the indium content is 40-90 wt% and the zirconium content is 10-60 wt% in terms of oxides.

9. The preparation method according to claim 8, wherein, The amounts of the indium salt and modifier are such that, based on the total weight of the catalyst obtained, the indium content is 60-80 wt% and the zirconium content is 20-40 wt% in terms of oxides.

10. The preparation method according to claim 7, wherein, The mass ratio of the indium salt to the modifier, calculated as oxide, is 1-6:

1.

11. The preparation method according to claim 10, wherein, The mass ratio of the indium salt to the modifier, calculated as oxide, is 1-3:

1.

12. The preparation method according to claim 7, wherein, The mixing described in step (1) is carried out under stirring conditions.

13. The preparation method according to claim 7, wherein, The mixing in step (1) includes: first mixing the indium salt and the first precipitant, and then second mixing with the modifier.

14. The preparation method according to claim 7, wherein, The precipitate mother liquor also contains a solvent, which is an organic solvent and / or water.

15. The preparation method according to claim 14, wherein, The solvent is a mixture of an organic solvent and water.

16. The preparation method according to claim 15, wherein, The organic solvent is selected from at least one of ethanol, methanol, isopropanol, ethylene glycol, triethylene glycol, and N,N-dimethylacetamide.

17. The preparation method according to claim 7, wherein, The molar ratio of the first precipitant to the indium salt (calculated as indium) is 5-8:

1.

18. The preparation method according to claim 17, wherein, The molar ratio of the first precipitant to the indium salt (calculated as indium) is 6-7:

1.

19. The preparation method according to claim 7, wherein, The indium salt is selected from at least one of indium nitrate, indium chloride, and indium sulfate.

20. The preparation method according to claim 7, wherein, The indium salt is provided in the form of an indium salt solution with a concentration of 0.1-0.8 mol / L.

21. The preparation method according to claim 7, wherein, The first precipitant is selected from at least one of urea, (NH4)2CO3, Na2CO3 and NaOH.

22. The preparation method according to claim 7, wherein, The first precipitant is provided in the form of a first precipitant solution, the concentration of which is 1-2 mol / L.

23. The preparation method according to claim 7, wherein, The preparation method of the modifier includes: mixing a zirconium source and a second precipitant, carrying out a hydrothermal reaction at 120-200℃ for 15-25 hours, and then drying and calcining the product obtained from the hydrothermal reaction.

24. The preparation method according to claim 7, wherein, In step (2), the aging conditions include: a temperature of 120-150℃ and a time of 16-28h.

25. The preparation method according to claim 7, wherein, In step (3), the drying conditions include a temperature of 50-100℃ and a time of 12-25h.

26. The preparation method according to claim 7, wherein, In step (3), the calcination conditions include: a temperature of 350-600℃ and a time of 1-8h.

27. The preparation method according to claim 26, wherein, In step (3), the roasting conditions include: a temperature of 400-500℃ and a time of 3-6h.

28. The modified indium oxide catalyst prepared by the preparation method according to any one of claims 7-27.

29. A method for preparing methanol by hydrogenation of carbon dioxide, the method comprising: In the presence of a catalyst, carbon dioxide and hydrogen are brought into contact under carbon dioxide hydrogenation conditions; The catalyst is the modified indium oxide catalyst according to any one of claims 1-6.

30. The method according to claim 29, wherein, The carbon dioxide hydrogenation conditions include: a reaction temperature of 200-400℃, a reaction pressure of 1-6 MPa, and a volume hourly space velocity of 4500-18000 h⁻¹. -1 The H2 / CO2 molar ratio is 1-6.

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