A doped copper-iron-molybdenum catalyst, its preparation method and application

Abstract

The present invention belongs to the technical field of catalysts, and more specifically, relates to a doped copper-iron-molybdenum catalyst, a preparation method thereof, and an application. The doped copper-iron-molybdenum catalyst of the present invention has a chemical formula of FexCuy(MoO4)3, where 0 < y ≤ 0.2 and x + y = 2; the doped copper-iron-molybdenum catalyst provided by the present invention has a low copper doping amount, high catalyst activity and good stability, and can obtain a single-pass acetaldehyde yield of > 80% and > 3.0 g g at 200 °C

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and more specifically, relates to a doped copper-iron-molybdenum catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Acetaldehyde is an important organic chemical intermediate and can be used to produce common chemical raw materials such as acetic acid, ethyl acetate, vinyl acetate, crotonaldehyde, and pyridine compounds. The traditional industrial production of acetaldehyde uses the Wacker oxidation technology of ethylene, which has the disadvantages of high cost, serious corrosion and pollution, and unsustainability. The gas-phase catalytic oxidation of ethanol to acetaldehyde can be carried out through two routes: anaerobic dehydrogenation and oxidative dehydrogenation. The anaerobic dehydrogenation of ethanol to acetaldehyde is an endothermic reaction, and a relatively high reaction temperature often leads to catalyst sintering and carbon deposition deactivation. The oxidative dehydrogenation of ethanol to acetaldehyde is an exothermic reaction, and the catalyst is not easily carbon-deposited, but it is difficult to obtain a high acetaldehyde yield, and the contradiction between catalyst activity and selectivity still exists. At present, the industrial process of catalytic oxidation of ethanol to acetaldehyde using silver foam exists the disadvantages of high energy consumption, low single-pass yield of acetaldehyde, and short catalyst life. There is an urgent need to develop a more efficient and stable catalyst for the gas-phase oxidative dehydrogenation of ethanol to acetaldehyde.

[0003] Supported nano-gold catalysts show high catalytic activity and selectivity in the gas-phase oxidative dehydrogenation of ethanol. Chinese invention patent CN109569647A reports a gold catalyst supported on a copper-containing composite oxide (spinel type or perovskite type) without Cr, and a >90% acetaldehyde yield can be obtained at 200 °C and the catalyst does not deactivate after continuous reaction for 200 hours. However, due to the low specific surface area (<10 m 2 / g) and high Au loading (>1 wt%) of these powder catalysts, the cost is relatively high and it is difficult to form. For metal oxide catalysts with lower costs, vanadium-containing composite oxides show relatively high low-temperature (200 - 250 °C) catalytic activity for the selective oxidation of ethanol, but V is toxic and environmentally harmful. Iron-molybdenum catalysts are environmentally friendly industrial catalysts that have been widely used in the selective oxidation of methanol to formaldehyde, but this catalyst only shows moderate catalytic activity and selectivity in the reaction of ethanol oxidation to acetaldehyde and has not been taken seriously for a long time. Recently, it has been reported that an iron-molybdenum catalyst prepared by the co-precipitation method obtained a >90% acetaldehyde yield at 280 °C at a relatively low space velocity (ChemCatChem, 2021, 9, 1363), but the space-time yield of acetaldehyde is less than 1.0 g g cat -1 h -1 , and the activity of the catalyst decreased significantly within 50 h. Therefore, it is necessary to develop a more efficient and stable non-noble metal oxide catalyst to promote the industrial application of the gas-phase oxidative dehydrogenation of ethanol to acetaldehyde. Summary of the Invention

[0004] Aiming at the defects of the prior art, the purpose of the present invention is to provide a doped copper-iron-molybdenum catalyst, its preparation method and application, so as to solve the technical problems of low space-time yield of the prior art iron-molybdenum catalyst and easy deactivation of the catalyst.

[0005] To achieve the above object, the present invention provides a doped copper-iron-molybdenum catalyst, the chemical formula of which is Fe x Cu y (MoO4)3, where 0 < y ≤ 0.2 and x + y = 2; in the catalyst, the metal cation Fe contains both +3 and +2 valences, and the metal cation Cu contains both +2 and +1 valences.

[0006] According to another aspect of the present invention, a preparation method of the above-mentioned doped copper-iron-molybdenum catalyst is provided, including the following steps:

[0007] (1) Mix and dissolve iron salt, copper salt, gelling agent and ammonium molybdate in water, and stir to obtain catalyst precursor I;

[0008] (2) Heat and stir the catalyst precursor I to form a colloid to obtain catalyst precursor II;

[0009] (3) Dry and grind the catalyst precursor II to obtain catalyst precursor III;

[0010] (4) Calcinate the catalyst precursor III in an oxygen-containing atmosphere to obtain the doped copper-iron-molybdenum catalyst.

[0011] Preferably, the iron salt is nitrate, acetate or acetylacetonate of iron, the copper salt is nitrate, acetate or acetylacetonate of copper, the total concentration of the iron salt and the copper salt in the catalyst precursor I is 0.2 - 1.0 mol / L, the molar amount ratio of the gelling agent to the total molar amount of the iron salt and the copper salt is 1 - 3:1, and the molar amount ratio of the ammonium molybdate to the total molar amount of the iron salt and the copper salt is 3:2.

[0012] Preferably, the gelling agent in step (1) is citric acid and / or ethylene glycol.

[0013] Preferably, in step (2), the catalyst precursor I is heated and stirred at 90 - 100 °C for 3 - 6 h to form a colloid to obtain catalyst precursor II.

[0014] Preferably, in step (3), the catalyst precursor II is dried at 100 - 140 °C, and ground or ball-milled evenly to obtain the catalyst precursor III.

[0015] Preferably, in step (4), the calcination temperature is 200 - 400 °C and the calcination time is 10 - 30 h.

[0016] According to another aspect of the present invention, there is provided an application of the doped copper-iron-molybdenum catalyst in the preparation of acetaldehyde by gas-phase oxidative dehydrogenation of ethanol.

[0017] Generally speaking, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

[0018] (1) A doped copper-iron-molybdenum catalyst provided by the present invention is obtained by doping Cu into iron molybdate to obtain an Fe x Cu y (MoO4)3 doped catalyst, where 0 < y ≤ 0.2 and x + y = 2. Experiments have found that when used for the oxidative dehydrogenation of ethanol to acetaldehyde, compared with the undoped iron molybdate catalyst, the space-time yield of acetaldehyde at 200 °C increases from 1.42 g g cat -1 h -1 to a maximum of 3.44 g g cat -1 h -1 .

[0019] (2) A doped copper-iron-molybdenum catalyst provided by the present invention is a non-precious metal oxide catalyst. Compared with the supported nano-gold catalyst and precious metal catalysts such as foam silver used for the oxidative dehydrogenation of ethanol to acetaldehyde in the past, the catalyst cost is greatly reduced.

[0020] (3) The doped copper-iron-molybdenum catalyst provided by the present invention is prepared by a sol-gel method combined with high-temperature calcination. The preparation method is simple, has strong controllability and good reproducibility, and effectively reduces the production cost.

[0021] (4) The doped copper-iron-molybdenum catalyst provided by the present invention has a low copper doping amount, high catalyst activity and good stability. At 200 °C, a single-pass yield of acetaldehyde > 80% and a space-time yield of > 3.0 g g cat -1 h -1 can be obtained, and the catalyst does not deactivate after continuous reaction for 60 h. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the XRD pattern of the catalysts of Example 1, Example 4, Comparative Example 9, Comparative Example 13 and Comparative Example 14.

[0023] Figure 2 is the H2-TPR result of the catalysts of Example 1, Example 4, Comparative Example 9, Comparative Example 13 and Comparative Example 14.

[0024] Figure 3 is the SEM image of Example 2(a), Comparative Example 13(b) and Comparative Example 4(c).

[0025] Figure 4 It is the XPS diagram of Example 4, Comparative Example 13 and Comparative Example 14.

[0026] Figure 5 It is the stability test result diagram of Example 2. Detailed implementation manners

[0027] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] A doped copper-iron-molybdenum catalyst provided by the present invention has a chemical formula of Fe x Cu y (MoO4)3 doped catalyst, where 0 < y ≤ 0.2 and x + y = 2; in the catalyst, the metal cation Fe contains both +3 valence and +2 valence, and the metal cation Cu contains both +2 valence and +1 valence.

[0029] The present invention also provides a preparation method of the doped copper-iron-molybdenum catalyst, including the following steps:

[0030] (1) Mix and dissolve an iron salt, a copper salt, a gelling agent and ammonium molybdate in water, and stir to obtain a catalyst precursor I;

[0031] (2) Heat and stir the catalyst precursor I to form a colloid to obtain a catalyst precursor II;

[0032] (3) Dry and grind the catalyst precursor II to obtain a catalyst precursor III;

[0033] (4) Calcinate the catalyst precursor III in an oxygen-containing atmosphere to obtain the doped copper-iron-molybdenum catalyst.

[0034] In some embodiments, the iron salt is a nitrate, acetate or acetylacetonate of iron, the copper salt is a nitrate, acetate or acetylacetonate of copper, the total concentration of the iron salt and the copper salt in the catalyst precursor I is 0.2 - 1.0 mol / L, the molar ratio of the gelling agent to the total molar amount of the iron salt and the copper salt is 1 - 3:1, and the molar ratio of ammonium molybdate to the total molar amount of the iron salt and the copper salt is 3:2. The gelling agent in step (1) is citric acid and / or ethylene glycol. The gelling agent in the present invention plays a role in making the reactant solution form a colloid so as to disperse it evenly, and also plays a certain reduction role during the calcination process.

[0035] In some embodiments, in step (2), the catalyst precursor I is heated and stirred at 90-100 °C for 3-6 h to form a colloid, obtaining the catalyst precursor II. In step (3), the catalyst precursor II is dried at 100-140 °C, ground or ball-milled uniformly to obtain the catalyst precursor III. In step (4), the calcination temperature is 200-400 °C, preferably 250-350 °C, and the calcination time is 10-30 h.

[0036] The doped copper-iron-molybdenum catalyst provided by the present invention can be used for the gas-phase oxidative dehydrogenation of ethanol to prepare acetaldehyde. In some embodiments of the present invention, the synthesized catalyst is evaluated for activity using a fixed-bed reactor. The evaluation method is to load a mixture of 150 mg of the catalyst and 510 mg of α-Al2O3 into the reaction tube, leak-test with nitrogen, and after ensuring good airtightness of the system, start the pre-reduction treatment of the catalyst. First, 10 mL / min of H2 (10% H2, 90% N2) is introduced, and then the fixed-bed temperature is raised to 200 °C at a heating rate of 10 °C / min and kept warm for 2 hours. Then, the activity evaluation is carried out. The feed ethanol enters the fixed bed through an injection pump, is mixed with the feed air after passing through the vaporization chamber, enters the catalyst bed layer to react with the catalyst, and the reaction products enter an on-line gas chromatograph for substance determination. When the gas hourly space velocity of the fixed bed is 30000 mL / g / h, the volume concentration of ethanol is 7%, the volume ratio of oxygen to ethanol is 3:1, and the reaction temperature is 175-225 °C, the catalyst can obtain an ethanol conversion rate of 80-100% and an acetaldehyde selectivity of 80-100%.

[0037] The following are the examples:

[0038] Example 1

[0039] Preparation of Fe 1.98 Cu 0.02 (MoO4)3

[0040] Weigh 4.00 g of ferric nitrate, 0.024 g of copper nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, and then place the flask in a 90 °C oil bath and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it uniformly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0041] A mixture of 150 mg of catalyst and 510 mg of α-Al2O3 was loaded into the reaction tube. After leak testing with nitrogen to ensure good airtightness of the system, pre-reduction treatment of the catalyst was started. First, 20 mL / min of H2 (10% H2, 90% N2) was introduced, and then the fixed bed temperature was raised to 200 °C at a heating rate of 10 °C / min and held for 2 hours. Then, activity evaluation was carried out. The feed ethanol entered the fixed bed through an injection pump, was mixed with the feed air after passing through the vaporization chamber, entered the catalyst bed layer to react with the catalyst, and the reaction products entered an on-line gas chromatograph for substance determination. The reaction conditions were as follows: the liquid hourly space velocity of ethanol was 4 mL / g cat / h, the molar ratio of oxygen to ethanol was 3:1, the gas hourly space velocity was 30000 mL / g cat / h, and the reaction temperature was 150 - 250 °C. The test results of ethanol conversion rate, acetaldehyde selectivity, acetaldehyde yield, and acetaldehyde space-time yield of the catalysts prepared in Examples 1 to 7 and Comparative Examples 1 to 14 are shown in Table 1. The results recorded in Table 1 are the activity results at 200 °C. All the following examples and comparative examples are under this test condition.

[0042] Example 2

[0043] Preparation of Fe 1.95 Cu 0.05 (MoO4)3

[0044] 3.94 g of iron nitrate, 0.06 g of copper nitrate, 2.94 g of ammonium molybdate, and 6.31 g of citric acid were weighed and dissolved in 25 mL of deionized water and placed in a 50 mL round-bottom flask. Then, it was placed in a 90 °C oil bath and magnetically stirred for 5 h. When it still had a certain temperature, it was poured into a 250 mL beaker, placed in an oven at 120 °C and dried for 12 h. Then, it was ground evenly and loaded into a crucible, and calcined in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0045] Using the catalyst Fe 1.95 Cu 0.05 (MoO4)3 of Example 2 for stability test. The test conditions were as follows: the liquid hourly space velocity of ethanol was 4 mL / g cat / h, the molar ratio of oxygen to ethanol was 3:1, the gas hourly space velocity was 30000 mL / g cat / h, the reaction temperature was 200 °C. The final result was that the catalyst could maintain its activity without deactivation for 60 h, Figure 5 which was the graph of the final stability test result.

[0046] Example 3

[0047] Preparation of Fe 1.9 Cu 0.1 (MoO4)3

[0048] Weigh 3.84 g of iron nitrate, 0.12 g of copper nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place it in a 90 °C oil bath and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0049] Example 4

[0050] Preparation of Fe 1.8 Cu 0.2 (MoO4)3 for the gas-phase oxidation of ethanol to acetaldehyde

[0051] Weigh 3.64 g of iron nitrate, 0.24 g of copper nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place it in a 90 °C oil bath and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0052] Example 5

[0053] Preparation of Fe 1.9 Cu 0.1 (MoO4)3 for the gas-phase oxidation of ethanol to acetaldehyde (the gelling agent is ethylene glycol)

[0054] Weigh 3.84 g of iron nitrate, 0.12 g of copper nitrate, 2.94 g of ammonium molybdate, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, add 1.86 g of ethylene glycol and mix well. Then place it in a 90 °C oil bath and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0055] Example 6

[0056] Preparation of Fe 1.9 Cu 0.1 (MoO4)3 for the gas-phase oxidation of ethanol to acetaldehyde (gelling agent: total molar amount of metal salts = 1:1)

[0057] Weigh 3.84 g of iron nitrate, 0.12 g of copper nitrate, 2.94 g of ammonium molybdate and 2.10 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place the flask in an oil bath at 90 °C and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0058] Example 7

[0059] Preparation of Fe 1.9 Cu 0.1 (MoO4)3 (gel agent: total molar amount of metal salts = 2:1)

[0060] Weigh 3.84 g of iron nitrate, 0.12 g of copper nitrate, 2.94 g of ammonium molybdate and 4.20 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place the flask in an oil bath at 90 °C and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0061] Comparative Example 1

[0062] Preparation of Fe 1.98 Mn 0.02 Preparation of (MoO4)3

[0063] Weigh 4.00 g of iron nitrate, 0.025 g of manganese nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place the flask in an oil bath at 90 °C and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0064] Comparative Example 2

[0065] Preparation of Fe 1.98 Co 0.02 Preparation of (MoO4)3

[0066] Weigh 4.00 g of iron nitrate, 0.029 g of cobalt nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place the flask in an oil bath at 90 °C and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0067] Comparative Example 3

[0068] Preparation of Fe 1.98 Ni 0.02 (MoO4)3

[0069] Weigh 4.00 g of iron nitrate, 0.029 g of nickel nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place the flask in an oil bath at 90 °C and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0070] Comparative Example 4

[0071] Preparation of Fe 1.6 Cu 0.4 (MoO4)3

[0072] Weigh 3.23 g of iron nitrate, 0.48 g of copper nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place the flask in an oil bath at 90 °C and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0073] Comparative Example 5

[0074] Preparation of Fe 1.6 Mn 0.4 (MoO4)3

[0075] Weigh 3.23 g of iron nitrate, 0.51 g of manganese nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place the flask in an oil bath at 90 °C and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0076] Comparative Example 6

[0077] Preparation of Fe 1.6 Co 0.4 (MoO4)3

[0078] Weigh 3.23 g of iron nitrate, 0.58 g of cobalt nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place the flask in an oil bath at 90 °C and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0079] Comparative Example 7

[0080] Preparation of Fe 1.6 Ni 0.4 (MoO4)3

[0081] Weigh 3.23 g of iron nitrate, 0.58 g of nickel nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place the flask in an oil bath at 90 °C and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0082] Comparative Example 8

[0083] Preparation of Fe 1.6 Ce 0.4 (MoO4)3

[0084] Weigh 3.23 g of iron nitrate, 0.87 g of cerium nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place it in a 90 °C oil bath and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0085] Comparative Example 9

[0086] Preparation of Fe 1.6 Mn 0.2 Cu 0.2 (MoO4)3 Preparation

[0087] Weigh 3.23 g of iron nitrate, 0.24 g of copper nitrate, 0.25 g of manganese nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place it in a 90 °C oil bath and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0088] Comparative Example 10

[0089] Preparation of Fe 1.6 Co 0.2 Cu 0.2 (MoO4)3 Preparation

[0090] Weigh 3.23 g of iron nitrate, 0.24 g of copper nitrate, 0.29 g of cobalt nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place it in a 90 °C oil bath and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0091] Comparative Example 11

[0092] Preparation of Fe 1.6 Ni 0.2 Cu 0.2 (MoO4)3 Preparation

[0093] Weigh 3.23 g of iron nitrate, 0.24 g of copper nitrate, 0.29 g of nickel nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place it in a 90 °C oil bath and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0094] Comparative Example 12

[0095] Preparation of Fe 1.6 Ce 0.2 Cu 0.2 (Preparation of (MoO4)3

[0096] Weigh 3.64 g of iron nitrate, 0.24 g of copper nitrate, 0.43 g of cerium nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place it in a 90 °C oil bath and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0097] Comparative Example 13

[0098] Preparation of Fe2(MoO4)3 for gas-phase oxidation of ethanol to acetaldehyde

[0099] Weigh 4.04 g of iron nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place it in a 90 °C oil bath and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0100] Comparative Example 14

[0101] Preparation of CuMoO4 for gas-phase oxidation of ethanol to acetaldehyde

[0102] Weigh 2.42 g of copper nitrate, 2.94 g of ammonium molybdate and 6.31 g of citric acid, dissolve them in 25 mL of deionized water, place them in a 50 mL round-bottom flask, then place it in a 90 °C oil bath and stir magnetically for 5 h. When it still has a certain temperature, pour it into a 250 mL beaker, place it in an oven and dry it at 120 °C for 12 h. Then grind it evenly, put it into a crucible, and calcine it in a muffle furnace at 300 °C for 20 h to obtain the final catalyst.

[0103] Figure 1XRD patterns of the catalysts of Example 1, Example 4, Comparative Example 9, Comparative Example 13 and Comparative Example 14. It can be seen that due to the small amount of metal incorporated, the main structure of the catalyst remains the structure of iron molybdate. However, with the increase of the copper doping amount, the structure of copper molybdate gradually becomes obvious.

[0104] Figure 2 H2-TPR results of the catalysts of Example 1, Example 4, Comparative Example 9, Comparative Example 13 and Comparative Example 14. It can be seen that with the increase of the copper doping amount, the position of the reduction peak shifts to lower temperature, indicating that the reducibility of the catalyst is enhanced. Therefore, its catalytic performance for selective oxidation is better.

[0105] Figure 3 SEM images of Example 2 (content (a)), Comparative Example 13 (content (b)) and Comparative Example 4 (content (c)). It can be seen that compared with the catalyst without copper doping (Comparative Example 13), after doping with a small amount of copper, the surface structure of the catalyst becomes regular, and its surface pore structure becomes more ordered (Example 4), which is more conducive to the activation of the catalytic reaction substrate and molecular oxygen, thus improving the catalytic performance. However, when the copper doping amount further increases, the regular surface structure of the catalyst will be destroyed (Comparative Example 4), which may also be the reason for the decline of its catalytic performance.

[0106] Figure 4 XPS spectra of Example 4, Comparative Example 13 and Comparative Example 14. It can be seen that for the Fe 1.8 Cu 0.2 (MoO4)3 catalyst prepared in Example 4, the ratio of Fe 2+ / Fe 3+ is higher than that of Comparative Example 13 and Comparative Example 14, and the ratio of Cu + / Cu 2+ is also higher than that of Comparative Example 13 and Comparative Example 14.

[0107] Table 1 Catalytic activity test results of the catalysts prepared in each example and comparative example

[0108]

[0109]

[0110] As can be seen from Table 1, for the doped copper-iron-molybdenum catalyst Fe x Cu y (MoO4)3 of the present invention, when a small amount of copper is doped into iron molybdate (when y is less than or equal to 0.2), relatively high catalyst activity can be obtained, and the space-time yield of acetaldehyde can reach 3 g g cat -1 h -1 or more, and the highest can reach 3.44 g g cat -1 h-1 When the copper doping amount is excessive, for example, when y is greater than 0.2, the space-time yield of acetaldehyde decreases to a large extent, indicating that the copper doping amount should not be too high. In addition, when the copper salt is replaced with other metal salts in the experiment, significantly lower space-time yields are shown at the same doping amount, indicating that there are significant differences in the catalytic activities of the catalysts obtained by different metal dopings.

[0111] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Application of a doped copper-iron-molybdenum catalyst in the preparation of acetaldehyde by gas-phase oxidative dehydrogenation of ethanol, characterized in that, The chemical formula of the doped copper-iron-molybdenum catalyst is Fe x Cu y (MoO4)3, where 0 < y ≤ 0.2 and x + y = 2; in the catalyst, the metal cation Fe contains both +3 and +2 valence states, and the metal cation Cu contains both +2 and +1 valence states; The preparation method of the doped copper-iron-molybdenum catalyst comprises the following steps: (1) Mix and dissolve an iron salt, a copper salt, a gelling agent and ammonium molybdate in water, and stir to obtain catalyst precursor I; the gelling agent is citric acid and / or ethylene glycol; (2) Heat and stir catalyst precursor I to form a colloid to obtain catalyst precursor II; (3) Dry and grind catalyst precursor II to obtain catalyst precursor III; (4) Calcinate catalyst precursor III in an oxygen-containing atmosphere to obtain the doped copper-iron-molybdenum catalyst.

2. The application according to claim 1, characterized in that, The iron salt is a nitrate, acetate or acetylacetonate of iron, the copper salt is a nitrate, acetate or acetylacetonate of copper, the total concentration of the iron salt and the copper salt in catalyst precursor I is 0.2-1.0 mol / L, the molar amount of the gelling agent to the total molar amount of the iron salt and the copper salt is 1-3:1, and the molar amount of ammonium molybdate to the total molar amount of the iron salt and the copper salt is 3:

2.

3. The application according to claim 1, characterized in that, In step (2), catalyst precursor I is heated and stirred at 90-100 °C for 3-6 h to form a colloid to obtain catalyst precursor II.

4. The application according to claim 1, wherein In step (3), catalyst precursor II is dried at 100-140 °C and ground or ball-milled evenly to obtain catalyst precursor III.

5. The application according to claim 1, characterized in that, In step (4), the calcination temperature is 200-400 °C and the calcination time is 10-30 h.

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