Cerium-based composite oxide, preparation method thereof and application of cerium-based composite oxide in catalyzing methane to continuously and efficiently prepare methanol

Abstract

The invention provides a cerium-based composite oxide, a preparation method thereof and application of the cerium-based composite oxide in continuous and efficient methanol preparation through catalysis of methane, and particularly relates to the technical field of methanol preparation through methane. The chemical formula of the cerium-based composite oxide is CeyMzOx, y is greater than or equal to 1 and less than or equal to 9, and z is greater than or equal to 1 and less than or equal to 9; y and z respectively correspond to the molar ratio of cerium to M; m comprises Zr or La. According to the method, zirconium (Zr) and lanthanum (La) are selected as doping elements, the prepared cerium-based composite oxide shows high stability of activity and selectivity in a test of continuously oxidizing methane into methanol, and the yield and selectivity of methanol are improved by regulating the molar ratio of the doping element M to cerium in the range.

Description

Technical Field

[0001] The invention belongs to the technical field of preparing alcohol from methane, and specifically relates to a cerium-based composite oxide, a preparation method thereof, and application thereof in catalyzing continuous and efficient preparation of methanol from methane. Background Art

[0002] With the depletion of oil resources, the abundant methane reserves have attracted widespread attention. However, as a greenhouse gas, methane has a greenhouse effect more than 80 times that of CO2. Large-scale methane emissions will not only cause waste of resources, but also damage the environment. Therefore, it is very important to use methane effectively and reasonably. Compared with methane, methanol is a potential energy carrier with advantages such as convenient storage and high energy density. Therefore, the ability to directly oxidize methane to methanol has important economic value and environmental significance.

[0003] At present, the indirect conversion method and direct conversion method are mainly used in the industry to produce methanol from methane. The indirect conversion method is to first convert methane into synthesis gas (CO and H2), and then generate methanol from the synthesis gas; this process consumes a lot of energy and has high costs. The catalysts used for direct conversion of methane are concentrated on different types of copper-modified zeolite molecular sieve catalysts, which usually require intermittent operation or complex multi-step operation processes. Therefore, it is particularly important to develop highly active catalysts that can achieve continuous direct conversion of methane to methanol. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a cerium-based composite oxide and its preparation method and application. The cerium-based composite oxide provided by the present invention has high catalytic activity and good stability, and can realize the one-step continuous oxidation of methane to methanol under catalytic gas phase conditions.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] The present invention provides a cerium-based composite oxide, wherein the chemical formula of the cerium-based composite oxide is Ce y M z O x , wherein 1≤y≤9, 1≤z≤9; y and z correspond to the molar ratio of Ce and M respectively; and the M includes Zr or La.

[0007] Preferably, when the M is Zr, the molar ratio of Ce to M is 2 to 9:1;

[0008] When the M is La, the molar ratio of Ce to M is 1:2-9.

[0009] The present invention also provides a method for preparing the cerium-based composite oxide described in the above technical solution, comprising the following steps:

[0010] The aqueous solution containing the cerium source and the M source is mixed with the alkaline solution to generate a hydroxide precipitate to obtain a suspension;

[0011] subjecting the suspension to a hydrothermal reaction to obtain a cerium-based composite oxide precursor;

[0012] The cerium-based composite oxide precursor is calcined to obtain the cerium-based composite oxide.

[0013] Preferably, the alkali in the alkali solution comprises sodium hydroxide and / or potassium hydroxide.

[0014] Preferably, the concentration of the alkali in the suspension is 6-20M.

[0015] Preferably, the temperature of the hydrothermal reaction is 100-180° C., and the time is 20-30 hours.

[0016] Preferably, the calcination temperature is 350-500° C. and the calcination time is 3-6 hours.

[0017] The present invention also provides the use of the cerium-based composite oxide prepared by the preparation method described in the above technical solution as a catalyst in catalyzing the continuous conversion of methane gas phase into methanol;

[0018] The reaction temperature for the continuous conversion of methane gas into methanol is 300-500°C.

[0019] Preferably, when M in the cerium-based composite oxide is Zr, the reaction temperature for the continuous gas phase conversion of methane into methanol is 300-450°C;

[0020] When M in the cerium-based composite oxide is La, the reaction temperature for the gas-phase continuous conversion of methane into methanol is 450-500°C.

[0021] Preferably, the reaction gas used in the continuous gas phase conversion of methane into methanol comprises 20-30 Vol% CH4, 5-15 Vol% O2 and 50-60 Vol% H2O and the balance nitrogen.

[0022] The present invention provides a cerium-based composite oxide, wherein the chemical formula of the cerium-based composite oxide is Ce y M z O x, wherein 1≤y≤9, 1≤z≤9; y and z correspond to the molar ratio of cerium to M, respectively; and M includes Zr or La. The present invention selects zirconium (Zr) or lanthanum (La) as a doping element, which can be used to adjust the ratio and activity of active oxygen, oxygen vacancies and OH groups on the oxide surface, wherein oxygen vacancies mainly serve as active sites for dissociating oxygen and water during the reaction process, and an appropriate amount of active oxygen vacancies can promote the dissociation of oxygen and water, respectively generating active O and OH, which can prevent the oxide surface from being excessively reduced and activate CH, thereby changing the activity of the catalyst; Zr and La can both form solid solutions with Ce, and the main valence states of their oxides are +4 and +3, respectively. The two cerium-based composite oxides obtained have a significant effect on the improvement of catalytic activity in the low temperature and high temperature sections, respectively. The cerium-based composite oxide provided by the present invention shows high activity and stability in the test of continuous oxidation of methane to methanol, and the yield of methanol is improved by regulating the molar ratio of the doping element M to cerium within the above range.

[0023] The present invention also provides a method for preparing the cerium-based composite oxide. The composite oxide catalyst prepared by the hydrothermal method not only simplifies the preparation process and reduces costs, but also improves the methanol yield and reduces energy consumption. The preparation method is simple and is conducive to industrial production.

[0024] The present invention also provides the application of the cerium-based composite oxide, which starts to produce methanol at 300°C in the catalytic methane-to-methanol reaction, with a yield of 2.4 μmol / h / g, and the methanol yield is as high as 48 μmol / g / h at 500°C, achieving gas-phase continuous reaction within 300-500°C and improving the catalytic efficiency. When the molar ratio of Ce to Zr is 4:1, the methanol yield reaches 26 μmol / g / h at 450°C and 0.1MPa; when the molar ratio of Ce to La is 1:4, the methanol yield can reach 48 μmol / g / h at 500°C and 0.1MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0026] Figure 1 TEM images and Raman spectra of the catalysts prepared in Examples 5 to 6 and Comparative Examples 1 and 3;

[0027] Figure 2 The XPS graphs of the catalysts prepared in Examples 5 to 6 and Comparative Examples 1 and 3;

[0028] Figure 3 The curves are as follows: the yield of product methanol in the catalytic methane oxidation reaction in the range of 300-500° C. for the catalysts prepared in a) Comparative Example 1 and b) Example 2 varies with time. DETAILED DESCRIPTION

[0029] The present invention provides a cerium-based composite oxide, wherein the chemical formula of the cerium-based composite oxide is Ce y M z O x , wherein 1≤y≤9, 1≤z≤9; y and z correspond to the molar ratio of cerium to M respectively; and the M includes Zr or La.

[0030] In the present invention, y and z correspond to the molar ratio of cerium to M, 1≤y≤9, 1≤z≤9. In a specific embodiment, y can be 1, 2, 3, 4, 5, 6, 7, 8 or 9; z can be 1, 2, 3, 4, 5, 6, 7, 8 or 9.

[0031] In the present invention, when the M is Zr, the molar ratio of Ce to Zr is preferably 2 to 9: 1, more preferably 2 to 4: 1. In a specific embodiment, the molar ratio of Ce to Zr may be 4: 1, 3: 1 or 2: 1. When the molar ratio of Ce to Zr is 4: 1, the obtained cerium-based composite oxide exhibits higher catalytic activity under low temperature (300 to 450° C.) conditions.

[0032] In the present invention, when M is La, the molar ratio of Ce to La is preferably 1:2 to 9, more preferably 1:2 to 4. In a specific embodiment, the molar ratio of Ce to La may be 1:4, 1:3 or 1:2. When the molar ratio of Ce to La is 1:4, the obtained cerium-based composite oxide exhibits higher catalytic activity under high temperature (450 to 500°C) conditions.

[0033] In the present invention, the specific surface area of ​​the cerium-based composite oxide is preferably 20 to 100 m 2 / g, more preferably 65 to 95 m 2 In the present invention, the cerium-based composite oxide is preferably in the shape of a rod, with a diameter of 8 to 15 nm and a length of 50 to 100 nm.

[0034] In the present invention, the valence state of cerium in the cerium-based composite oxide is preferably +4 and +3, with +4 being the main valence and a small amount of +3. In the present invention, when the M is La, the valence state of La is preferably +3; when the M is Zr, the valence state of Zr is preferably +4.

[0035] The present invention selects zirconium (Zr) and lanthanum (La) as doping elements, and the prepared cerium-based composite oxide shows high activity and stability in the test of continuous oxidation of methane to methanol. By adjusting the molar ratio of the doping element M to cerium within the above range, the methanol yield is improved.

[0036] The present invention also provides a method for preparing the cerium-based composite oxide described in the above technical solution, comprising the following steps:

[0037] The aqueous solution containing the cerium source and the M source is mixed with the alkaline solution to generate a hydroxide precipitate to obtain a suspension;

[0038] subjecting the suspension to a hydrothermal reaction to obtain a cerium-based composite oxide precursor;

[0039] The cerium-based composite oxide precursor is calcined to obtain the cerium-based composite oxide.

[0040] In the present invention, unless otherwise specified, the raw materials and equipment used are commercially available products well known in the art.

[0041] The present invention mixes an aqueous solution containing a cerium source and an M source with an alkaline solution to generate a hydroxide precipitate to obtain a suspension;

[0042] In the present invention, the aqueous solution containing the cerium source and the M source is preferably obtained by mixing an aqueous cerium source solution and an aqueous M source solution.

[0043] In the present invention, the cerium source in the cerium source aqueous solution is preferably cerium nitrate, cerium acetate or cerium trichloride. The concentration of the cerium source aqueous solution is preferably 0.15 to 0.75 mol / L. In a specific embodiment, the concentration of the cerium source aqueous solution can be 0.15 mol / L, 0.18 mol / L, 0.2 mol / L, 0.25 mol / L, 0.25 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.72 mol / L or 0.75 mol / L.

[0044] In the present invention, when the M source in the M source aqueous solution is a Zr source, the Zr source is preferably zirconium nitrate or zirconium oxychloride; when the M source in the M source aqueous solution is a La source, the Zr source is preferably lanthanum nitrate or lanthanum chloride.

[0045] In the present invention, the concentration of the M source aqueous solution is preferably 0.15-0.75 mol / L. In a specific embodiment, the concentration of the M source aqueous solution can be 0.15 mol / L, 0.18 mol / L, 0.2 mol / L, 0.25 mol / L, 0.25 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.72 mol / L or 0.75 mol / L.

[0046] In the present invention, the mixing of the aqueous solution containing the cerium source and the M source with the alkaline solution preferably comprises: dropping the aqueous solution containing the cerium source and the M source into the alkaline solution, the dropping rate is preferably 1 to 3 drops / s, in a specific embodiment, the dropping rate may be 1 drop / s, 2 drops / s or 3 drops / s. In the present invention, the dropping is preferably carried out under stirring conditions, the stirring speed is preferably 500 to 800 rpm, in a specific embodiment, the stirring speed may be 500 rpm, 600 rpm, 700 rpm or 800 rpm; the stirring time is preferably 1 to 3 hours, in a specific embodiment, the stirring time may be 1 hour, 2 hours or 3 hours. During the stirring process, a large amount of hydroxide precipitates are generated.

[0047] In the present invention, the alkali in the alkali solution preferably includes sodium hydroxide and / or potassium hydroxide.

[0048] In the present invention, the concentration of the alkali in the suspension is preferably 6-20M. In a specific embodiment, the concentration of the alkali in the suspension may be 6M, 8M, 10M, 12M, 14M, 16M, 18M or 20M.

[0049] After obtaining the suspension, the present invention performs a hydrothermal reaction on the suspension to obtain a cerium-based composite oxide precursor.

[0050] In the present invention, the temperature of the hydrothermal reaction is preferably 100-180°C. In a specific embodiment, the temperature of the hydrothermal reaction can be 100°C, 150°C or 180°C. The time is preferably 20-30h. In a specific embodiment, the time of the hydrothermal reaction can be 20h, 22h, 25h, 27h or 30h. In the hydrothermal reaction process of the present invention, the hydroxide nuclei of the metal ions grow and arrange to form rod-shaped hydroxides, i.e., cerium-based composite oxide precursors. Due to the different OH groups in the alkali solution, the hydroxide nuclei of the metal ions grow and arrange to form rod-shaped hydroxides, i.e., cerium-based composite oxide precursors. - The concentration and temperature will affect the growth rate of the crystal nucleus and the hydroxide morphology formed after the arrangement and combination. The higher the concentration of the alkali solution and the higher the temperature of the hydrothermal reaction, the easier it is to form larger nano-hydroxide crystals. The present invention controls the size and morphology of the nano-hydroxide crystal growth by controlling the temperature of the hydrothermal reaction and the pH of the solution.

[0051] In the present invention, after the hydrothermal reaction, the process preferably further includes solid-liquid separation of the obtained product liquid, and washing and drying the obtained solid.

[0052] The present invention has no special requirements on the method of solid-liquid separation, and the commonly used technical means of the present invention can be adopted, such as filtration and centrifugation.

[0053] In the present invention, the water washing is preferably to neutrality.

[0054] In the present invention, the drying temperature is preferably 60-100°C. In a specific embodiment, the drying temperature may be 60°C, 80°C or 100°C. The drying time is preferably 6-12h. In a specific embodiment, the drying time may be 6h, 8h, 10h or 12h.

[0055] The cerium-based composite oxide precursor is obtained. In the present invention, the cerium-based composite oxide precursor is calcined to obtain the cerium-based composite oxide.

[0056] In the present invention, the calcination temperature is preferably 350-500°C. In a specific embodiment, the calcination temperature may be 350°C, 400°C, 450°C or 500°C. The calcination time is preferably 3-6h. In a specific embodiment, the calcination time may be 3h, 4h, 5h or 6h.

[0057] In the present invention, the calcination is preferably carried out in an air atmosphere. In the present invention, the cerium-based composite oxide is obtained by calcination, and during the calcination process, the rod-shaped hydroxide generated by hydrothermal reaction is converted into oxide.

[0058] Due to the difference in valence and ionic radius between the added doping element and Ce, the generated cerium-based composite oxide has abundant oxygen vacancies, which can improve the catalytic performance. For example, in the process of replacing +4-valent Ce in the cerium oxide lattice with +3-valent La, different cation numbers need to be coordinated due to different valence states, so oxygen vacancies will be generated. In the process of replacing +4-valent Ce in the cerium oxide lattice with +4-valent Zr, although the valence states are the same, there are differences in ionic radius. In the process of doping into the oxide lattice, the mismatch of ion size causes lattice distortion, thereby generating oxygen vacancies.

[0059] The present invention adopts a hydrothermal method to prepare a cerium-based composite oxide catalyst. In an alkaline environment, a coordination reaction occurs to obtain hydroxide crystals. Under hydrothermal conditions, the crystals grow into rod-shaped hydroxides, which are then calcined to obtain oxides. By controlling the proportion of precursors, the alkaline environment, the hydrothermal conditions and the calcination conditions, a catalyst with uniform structure and excellent performance is obtained, which is used for the direct oxidation of methane to produce methanol.

[0060] The present invention also provides the use of the cerium-based composite oxide prepared by the preparation method described in the above technical solution as a catalyst in catalyzing the continuous conversion of methane gas phase into methanol;

[0061] The reaction temperature for the continuous conversion of methane gas into methanol is 300-500°C.

[0062] In the present invention, when M in the cerium-based composite oxide is Zr, the reaction temperature for the continuous gas-phase conversion of methane into methanol is preferably 300-450°C; in specific embodiments, it may be 300°C, 350°C, 400°C or 450°C.

[0063] When M in the cerium-based composite oxide is La, the reaction temperature for the gas-phase continuous conversion of methane into methanol is preferably 450-500°C.

[0064] In the present invention, the reaction of continuous conversion of methane gas phase into methanol is preferably carried out in a fixed bed flow reactor. In a specific embodiment, the cerium-based composite oxide is placed in a constant temperature section of a quartz tube with an inner diameter of 10 mm, and the cerium-based composite oxide is fixed with quartz wool above and below. The present invention adopts a fixed bed continuous flow reactor, which has the advantages of good gas-solid contact and high mass transfer efficiency.

[0065] In the present invention, the reaction space velocity of the continuous conversion of alkane gas phase into methanol is preferably 96000 mL h -1 g cat -1 , the flow rate of the reaction gas is preferably 160mL / min. The present invention increases the methanol yield by controlling the reaction space velocity (contact time of the reaction gas with the catalyst) within the above range. In the present invention, the pressure of the reaction of continuous conversion of methane gas phase into methanol is preferably atmospheric pressure conditions, and in a specific embodiment, the pressure of the reaction is 0.1MPa.

[0066] In the present invention, the reaction gas used in the continuous gas phase conversion of methane into methanol preferably comprises 20-30 Vol% CH4, 5-15 Vol% O2 and 50-60 Vol% H2O and the balance nitrogen.

[0067] In the present invention, the reaction gas preferably includes 20-30 Vol% CH4. In a specific embodiment, the volume percentage of CH4 in the reaction gas may be 20 Vol%, 22 Vol%, 25 Vol%, 28 Vol% or 30 Vol%.

[0068] In the present invention, the reaction gas preferably includes 5-15 Vol% O2. In a specific embodiment, the volume percentage of O2 in the reaction gas may be 5 Vol%, 7 Vol%, 10 Vol%, 12 Vol% or 15 Vol%.

[0069] In the present invention, the reaction gas preferably includes 50-60 Vol% H2O. In a specific embodiment, the volume percentage of H2O in the reaction gas may be 50 Vol%, 52 Vol%, 55 Vol%, 57 Vol% or 60 Vol%.

[0070] In the present invention, the reaction gas also includes a balance of nitrogen, which is used as a carrier gas to balance the reaction gas.

[0071] The present invention has no special requirements on the reaction time of the continuous conversion of methane gas phase into methanol. In the embodiment of the present invention, the continuous reaction can last for 900 minutes without a significant decrease in conversion rate.

[0072] In the present invention, after the reaction is completed, the liquid phase product is preferably collected by condensation, and the liquid phase and gas phase product analysis is performed by chromatography.

[0073] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described in conjunction with specific embodiments below. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Any modification, equivalent replacement, improvement, etc. made to the implementation methods of the present invention based on the technical essence and general principles of the present invention without creative work should be within the scope of protection of the present invention.

[0074] Example 1

[0075] 3.126 g (7.2 mmol) of Ce(NO3)3·6H2O was weighed and dissolved in 10 mL of deionized water to obtain a cerium nitrate solution. 0.772 g (1.8 mmol) of Zr(NO3)4·5H2O was weighed and dissolved in 10 mL of deionized water to obtain a zirconium nitrate solution. The cerium nitrate solution and the zirconium nitrate solution were mixed to obtain a mixed solution. The mixed solution was added dropwise to a NaOH aqueous solution until the concentration of NaOH was 6 mol / L. The mixture was stirred at room temperature for 1 h to obtain a suspension. The suspension was transferred to an autoclave and subjected to a hydrothermal reaction at 100°C for 24 h. The suspension was cooled naturally and the precipitate was collected. The precipitate was washed with deionized water until neutral, dried at 80°C for 12 h, and calcined at 400°C in air for 4 h to obtain Ce4Zr1O x catalyst.

[0076] Catalytic performance test:

[0077] At normal pressure, 100 mg Ce4Zr1O xThe catalyst powder was placed in a constant temperature section of a quartz tube with an inner diameter of 10 mm in a fixed bed flow reactor. The catalyst powder was fixed with quartz wool on the top and bottom. The CH4 flow rate was 45 mL / min, the O2 flow rate was 15 mL / min, the N2 flow rate was 15 mL / min, and the H2O (l) The flow rate was 0.05 mL / min, the reaction was carried out at 300-500 °C for 900 min, and each temperature within the reaction temperature range was measured for 120 min. At the reaction temperature, liquid water was converted into gaseous water. The total flow rate of the gas during the reaction was 160 mL / min. Liquid and gas products were analyzed on a gas chromatograph, and the methanol yield was measured and obtained in Table 1.

[0078] The methanol yield was calculated according to formula 1:

[0079] Y i =C i ×V / (M i ×m cat ×t) Formula 1;

[0080] In formula 1, Y i is the methanol yield, C i is the methanol concentration (g / mL) measured by gas chromatography, V is the volume of the liquid product, M i is the relative molecular mass of methanol, m cat is the amount of catalyst used, and t is the reaction time.

[0081] Table 1 Ce4Zr1O prepared in Example 1 x The methanol yield of the catalyst in the range of 300-500℃

[0082] Reaction temperature (℃) Methanol yield (μmol / g / h) 300 2.7 350 7.2 400 18 450 26 500 27

[0083] From Table 1, we can see that Ce4Zr1O x The methanol productivity of the catalyst was 2.7 μmol / g / h at 300°C and 27 μmol / g / h at 500°C.

[0084] Example 2

[0085] 8.1 mmol Ce(NO3)3·6H2O was weighed and dissolved in 10 mL of deionized water to obtain a cerium nitrate solution, and 0.9 mmol Zr(NO3)4·5H2O was weighed and dissolved in 5 mL of deionized water to obtain a zirconium nitrate solution. Other conditions were the same as those in Example 1 to obtain Ce9Zr1O x Catalyst was used to continuously convert methane into methanol in the gas phase. Liquid and gas phase product analysis was performed on a gas chromatograph, and the methanol yield was measured and obtained in Table 2.

[0086] Table 2 Ce9Zr1O prepared in Example 2 xThe methanol yield of the catalyst in the range of 300-500℃

[0087] Reaction temperature (℃) Methanol yield (μmol / g / h) 300 2 350 6.9 400 13.8 450 19.5 500 25.6

[0088] From Table 2, we can see that Ce9Zr1O x The methanol productivity of the catalyst was 2 μmol / g / h at 300°C and 25.6 μmol / g / h at 500°C.

[0089] Example 3

[0090] Weigh 1.8mmol Ce(NO3)3·6H2O and dissolve it in 10mL deionized water to obtain cerium nitrate solution, and weigh 7.2mmol Zr(NO3)4·5H2O and dissolve it in 10mL deionized water to obtain zirconium nitrate solution. Other conditions are the same as those in Example 1 to obtain Ce1Zr4O x Catalyst was used to continuously convert methane into methanol in the gas phase. Liquid and gas phase product analysis was performed on a gas chromatograph, and the methanol yield was measured and obtained in Table 3.

[0091] Table 3 Ce1Zr4O prepared in Example 3 x The methanol yield of the catalyst in the range of 300-500℃

[0092]

[0093]

[0094] From Table 3, we can see that Ce1Zr4O x The methanol productivity of the catalyst was 2.5 μmol / g / h at 300°C and 21 μmol / g / h at 500°C.

[0095] Example 4

[0096] 0.782g (1.8mmol) of Ce(NO3)3·6H2O was weighed and dissolved in 10mL of deionized water to obtain a cerium nitrate solution. 2.339g (7.2mmol) of La(NO3)3·xH2O was weighed and dissolved in 10mL of deionized water to obtain a lanthanum nitrate solution. The cerium nitrate solution and the zirconium nitrate solution were mixed to obtain a mixed solution. The mixed solution was added dropwise to a NaOH aqueous solution until the concentration of NaOH was 20mol / L. The mixture was stirred at room temperature for 1h to obtain a suspension. The suspension was transferred to an autoclave and subjected to a hydrothermal reaction at 155°C for 24h. The suspension was cooled naturally, and the precipitate was collected and washed with deionized water until neutral. The mixture was dried at 80°C for 12h and calcined in air at 400°C for 4h to obtain Ce1La4O x -1 catalyst.

[0097] Other conditions were the same as those in Example 1. Liquid and gas phase product analysis was performed on a gas chromatograph, and the methanol yield was measured to obtain Table 4.

[0098] Table 4 Ce1La4O prepared in Example 4 x -1 The methanol yield of the catalyst in the range of 300-500℃

[0099] Reaction temperature (℃) Methanol yield (μmol / g / h) 300 0.3 350 3.7 400 11 450 27 500 45

[0100] From Table 4, we can see that Ce1La4O x -1 catalyst at 300 ° C, the methanol yield is 0.3 μmol / g / h, at 500 ° C, the methanol yield is 45 μmol / g / h.

[0101] Example 5

[0102] The hydrothermal reaction was carried out at 100 °C for 24 h, and the other conditions were the same as those in Example 1 to obtain Ce1La4O x -2 catalyst was used to continuously convert methane into methanol in the gas phase. The liquid and gas phase products were analyzed on a gas chromatograph, and the methanol yield was measured and obtained as shown in Table 5.

[0103] Table 5 Ce1La4O prepared in Example 5 x -2 The methanol yield of the catalyst in the range of 300-500℃

[0104] Reaction temperature (℃) Methanol yield (μmol / g / h) 300 0.5 350 3 400 12 450 31 500 48

[0105] From Table 5, we can see that Ce1La4O x -2 catalyst has a methanol yield of 0.5 μmol / g / h at 300°C and a methanol yield of 48 μmol / g / h at 500°C.

[0106] Example 6

[0107] Weigh 7.2mmol Ce(NO3)3·6H2O and dissolve it in 10mL deionized water to obtain cerium nitrate solution, weigh 1.8mmol La(NO3)3·xH2O and dissolve it in 10mL deionized water to obtain lanthanum nitrate solution. Other conditions are the same as those in Example 1 to obtain Ce4La1O x Catalyst was used to carry out continuous gas phase conversion of methane into methanol. Liquid and gas phase product analysis was performed on a gas chromatograph, and the methanol yield was measured and obtained in Table 6.

[0108] Table 6 Ce4La1O prepared in Example 6 x The methanol yield of the catalyst in the range of 300-500℃

[0109] Reaction temperature (℃) Methanol yield (μmol / g / h) 300 0.9 350 0.9 400 2.0 450 7.6 500 21

[0110] From Table 6, we can see that Ce4La1O x The methanol productivity of the catalyst is 0.9 μmol / g / h at 300°C and 21 μmol / g / h at 500°C.

[0111] Example 7

[0112] Weigh 8.1mmol Ce(NO3)3·6H2O and dissolve it in 15mL deionized water to obtain a cerium nitrate solution. Weigh 0.9mmol La(NO3)3·xH2O and dissolve it in 5mL deionized water to obtain a lanthanum nitrate solution. The other conditions are the same as those in Example 4 to obtain Ce1La9O x Catalyst was used to continuously convert methane into methanol in the gas phase. Liquid and gas phase product analysis was performed on a gas chromatograph, and the methanol yield was measured and obtained in Table 7.

[0113] Table 7 Ce1La9O prepared in Example 7 x The methanol yield of the catalyst in the range of 300-500℃

[0114] Reaction temperature (℃) Methanol yield (μmol / g / h) 300 0.3 350 2.2 400 6.7 450 12 500 18

[0115] From Table 7, we can see that Ce1La9O x The methanol productivity of the catalyst was 0.9 μmol / g / h at 300°C and 18 μmol / g / h at 500°C.

[0116] Comparative Example 1

[0117] Weigh 9mmol 3.907g Ce(NO3)3·6H2O and dissolve it in 15mL deionized water to obtain a cerium nitrate solution. The other conditions are the same as in Example 1 to obtain a CeO2 catalyst. The methane gas phase is continuously converted into methanol. The liquid and gas phase products are analyzed on a gas chromatograph, and the methanol yield is measured and obtained as shown in Table 8.

[0118] Table 8 Methanol yield of CeO2 catalyst prepared in comparative example 1 at 300-500°C

[0119]

[0120]

[0121] It can be seen from Table 8 that the methanol productivity of CeO2 catalyst is 0.9 μmol / g / h at 300°C and 19 μmol / g / h at 500°C.

[0122] Comparative Example 2

[0123] Weigh 9mmol 3.863g Zr(NO3)4·5H2O and dissolve it in 15mL deionized water to obtain zirconium nitrate solution. The other conditions are the same as in Example 1 to obtain ZrO2 catalyst. Carry out gas-phase continuous conversion of methane into methanol. Perform liquid and gas-phase product analysis on gas chromatography, and measure the methanol yield to obtain Table 9.

[0124] Table 9 Methanol yield of ZrO2 catalyst prepared in comparative example 2 at 400-500°C

[0125] Reaction temperature (℃) Methanol yield (μmol / g / h) 400 0.6 450 1.7 500 6.4

[0126] It can be seen from Table 9 that the ZrO2 catalyst cannot catalyze the direct conversion of methane into methanol below 400°C, and the yield of methanol is zero.

[0127] Comparative Example 3

[0128] Weigh 9mmol 2.924g La(NO3)3·xH2O and dissolve it in 15mL deionized water to obtain lanthanum nitrate solution. The other conditions are the same as those in Example 4 to obtain La2O3 catalyst. The methane gas phase is continuously converted into methanol. The liquid and gas phase products are analyzed on a gas chromatograph, and the methanol yield is measured to obtain Table 10.

[0129] Table 10 Methanol yield of La2O3 catalyst prepared in comparative example 3 at 300-500℃

[0130] Reaction temperature (℃) Methanol yield (μmol / g / h) 350 0.5 400 2.2 450 9.4 500 29

[0131] From Tables 1-2 and 8-9 above, it can be seen that the Ce-Zr composite oxide system exhibits higher catalytic activity at low temperature (300-450°C), which is manifested as a higher methanol yield. When the molar ratio of Ce to Zr is 4:1, the methanol yield at 300°C is 2.7 μmol / g / h, which is 3 times that of CeO2 catalyst (0.9 μmol / g / h), and the methanol yield at 350°C is 7 μmol / g / h, which is 2 times that of CeO2 catalyst (3.4 μmol / g / h).

[0132] It can be seen from Tables 4 to 8 and 10 that the Ce-La composite oxide system exhibits better catalytic performance at high temperature (450-500°C). When the molar ratio of Ce to La is 1:4, the methanol yield at 500°C is 48.6 μmol / g / h, which is 1.7 times and 2.5 times that of La2O3 (29 μmol / g / h) and CeO2 (19 μmol / g / h), respectively.

[0133] It can be seen from Tables 1 to 10 above that the cerium-based composite oxide prepared in the present invention exhibits good catalytic activity in a continuous 900 min stability test.

[0134] The specific surface area, pore volume and pore diameter of the composite oxides obtained in Examples 5 to 6 and Comparative Examples 1 and 3 were tested, and Table 11 was obtained.

[0135] Table 11 Physical properties of oxides obtained in Examples 5 to 6 and Comparative Examples 1 and 3

[0136] <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Pore ​​size (nm) Comparative Example 1 91.3 0.42 19.0 Example 5 93.5 0.45 19.1 Example 6 65.1 0.5 25.6 Comparative Example 3 70.1 0.53 24.4

[0137] As can be seen from Table 11, Example 5 has a larger specific surface area, which enables it to have high catalytic performance in the high temperature (450-500°C) catalytic methane reaction. The specific surface area of ​​the oxide prepared in Example 5 is 93.5 m 2 / g, pore size is 19.1nm.

[0138] The catalysts prepared in Examples 5 to 6 and Comparative Examples 1 and 3 were subjected to electron microscope scanning and Raman spectroscopy analysis to obtain Figure 1 XPS analysis was performed on the catalysts prepared in Examples 5 to 6 and Comparative Examples 1 and 3, and the results were Figure 2 .from Figure 1 It can be seen that the morphology of the prepared Ce-La composite oxide catalyst is rod-shaped. XPS and Raman analysis characterization show that oxygen vacancies were successfully obtained, which improved the catalytic performance of the catalyst.

[0139] The yield of methanol product in the catalytic methane oxidation reaction of the catalysts prepared in Comparative Example 1 and Example 2 was analyzed over time, and the results were as follows: Figure 3 By comparison, it can be seen that after a small amount of Zr is doped into cerium oxide, the methanol yield shows a significant improvement in the entire temperature range, and the yield has almost no significant change over time, showing a high degree of stability.

[0140] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A cerium-based composite oxide, characterized in that: The chemical formula of the cerium-based composite oxide is Ce y M z O x , wherein 1≤y≤9, 1≤z≤9; y and z correspond to the molar ratio of Ce and M respectively; and the M includes Zr or La.

2. The cerium-based composite oxide according to claim 1, characterized in that When the M is Zr, the molar ratio of Ce to M is 2 to 9:1; When the M is La, the molar ratio of Ce to M is 1:2-9.

3. The method for preparing the cerium-based composite oxide according to any one of claims 1 to 2, characterized in that: The following steps are involved: The aqueous solution containing the cerium source and the M source is mixed with the alkaline solution to generate a hydroxide precipitate to obtain a suspension; subjecting the suspension to a hydrothermal reaction to obtain a cerium-based composite oxide precursor; The cerium-based composite oxide precursor is calcined to obtain the cerium-based composite oxide.

4. The preparation method according to claim 3, characterized in that: The alkali in the alkali solution includes sodium hydroxide and / or potassium hydroxide.

5. The preparation method according to claim 3 or 4, characterized in that: The concentration of the alkali in the suspension is 6-20M.

6. The preparation method according to claim 3, characterized in that: The temperature of the hydrothermal reaction is 100-180° C. and the time is 20-30 hours.

7. The preparation method according to claim 3, characterized in that: The calcination temperature is 350-500° C. and the calcination time is 3-6 hours.

8. Use of the cerium-based composite oxide according to any one of claims 1 to 2 or the cerium-based composite oxide prepared by the preparation method according to any one of claims 3 to 7 as a catalyst in catalyzing the continuous gas-phase conversion of methane into methanol; The reaction temperature for the continuous conversion of methane gas into methanol is 300-500°C.

9. The use according to claim 8, characterized in that: When M in the cerium-based composite oxide is Zr, the reaction temperature for the continuous conversion of methane gas phase into methanol is 300-450°C; When M in the cerium-based composite oxide is La, the reaction temperature for the gas-phase continuous conversion of methane into methanol is 450-500°C.

10. The use according to claim 8, characterized in that: The reaction gas used in the continuous gas phase conversion of methane into methanol includes 20-30 Vol% CH4, 5-15 Vol% O2, 50-60 Vol% H2O and the balance nitrogen.

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