Rare earth metal modified catalyst for preparing methanol through carbon dioxide hydrogenation and preparation method thereof

Abstract

The invention provides a rare earth metal modified carbon dioxide hydrogenation methanol catalyst and a preparation method thereof. The catalytic activity and stability of the catalyst can be greatly improved. The catalyst is xCu / yZnO / zAAlO3; wherein A is rare earth metal Ce or Y; the molar ratio x: y of Cu to ZnO is (0.5-2): 1, and the molar ratio (x + y): z of (Cu + ZnO) to AAlO3 is 7: 3; the preparation method comprises the steps of preparing a precursor solution, preparing a gelatinous precursor, preparing precursor powder and preparing the composite oxide. The catalyst is simple in preparation method and high in selectivity and stability, CO2 can be efficiently converted into CH3OH, the CH3OH selectivity is 70-95%, stable conversion can be conducted for 60 h, and the CH3OH selectivity is obviously improved compared with an existing catalyst.

Description

Technical Field

[0001] The present invention belongs to CO 2 The technical field of catalytic conversion particularly relates to a rare earth metal modified carbon dioxide hydrogenation to methanol catalyst and a preparation method thereof. Background Art

[0002] In the context of global carbon neutrality, CO 2 Hydrogenation to methanol technology in CO 2 It has broad application prospects in resource utilization, and its product methanol, as an important clean renewable resource, plays a vital role in the low-carbon energy path. In recent years, many researchers have been committed to the research and development of 2 Highly active catalyst for hydrogenation to methanol. Currently, due to the relatively high activity and low cost of Cu-based catalysts, they are widely used in many CO 2 Among the hydrogenation catalysts for methanol, Cu-ZnO catalyst stands out. In this catalyst, the coexistence of Cu and ZnO plays a decisive role in the catalytic activity of the catalyst. First, the addition of ZnO is conducive to the dispersion of reduced Cu and increases the number of active sites; second, ZnO is conducive to the 2+ The reduction of active Cu + The sites can be stabilized on the surface of ZnO; the most important thing is that the basic sites of ZnO are in close contact with the metal sites of Cu. 2 However, due to the reverse water gas shift reaction and water-induced deactivation, the catalytic activity and stability of traditional Cu-ZnO catalysts need to be further improved.

[0003] To this end, the present invention provides a new catalyst for preparing methanol by hydrogenating carbon dioxide. Summary of the invention

[0004] In view of the defects and shortcomings of the prior art, the present invention proposes a rare earth metal-modified carbon dioxide hydrogenation to methanol catalyst and a preparation method thereof, the purpose of which is to improve the dispersibility of the active component and its adsorption capacity for CO2 by modification of the rare earth metal, thereby developing an efficient and stable carbon dioxide hydrogenation to methanol catalyst.

[0005] To achieve the above purpose, the technical solution provided by the present invention is:

[0006] A composite oxide, which is special in that it is xCu / yZnO / zAAlO 3 ; Wherein, A is a rare earth metal Ce or Y; the molar ratio of Cu to ZnO is x:y=0.5-2:1, (Cu+ZnO) and AAlO 3 The molar ratio of (x+y):z=7:3.

[0007] The preparation method of the composite oxide is special in that it specifically comprises the following steps:

[0008] Step 1: Prepare the precursor solution

[0009] Copper nitrate, zinc nitrate, aluminum nitrate and cerium nitrate / yttrium nitrate are respectively dissolved in deionized water in proportion, and mixed to obtain a precursor solution; the raw material used in the preparation method is preferably nitrate, which is easily soluble, so the prepared precursor solution is more uniform, which is conducive to precipitation and phase formation, and even if there is excess nitrate residue, it can be removed in the subsequent roasting process without affecting the quality of the final product;

[0010] Step 2: Preparation of gel precursor

[0011] Add ethylene glycol and citric acid to the precursor solution obtained in step 1, mix well, heat and stir until the water evaporates and turns into a gel, so as to obtain a gel precursor; wherein, citric acid is used as a complexing agent, and the lone pair of electrons on the oxygen atom in the citrate ion can form a coordination bond with the metal ion, and this coordination effect enables the citrate ion and the metal ion to form a stable complex; and ethylene glycol can improve the dispersion of metal ions in the precursor solution and improve the stability of the gel, playing the role of a template and a stabilizer in the gel formation process;

[0012] Step 3: Preparation of precursor powder

[0013] Dry the gel precursor obtained in step 2, and grind it after drying (grind until no particles are visible to the naked eye) to obtain a precursor powder;

[0014] Step 4: Preparation of composite oxides

[0015] In an inert atmosphere (e.g. N 2 The precursor powder obtained in step 3 is calcined under Ar, He to obtain the composite oxide xCu / yZnO / zAAlO 3 ;

[0016] Further, in step 1, the molar concentration of copper nitrate, zinc nitrate, aluminum nitrate and cerium nitrate / yttrium nitrate in the precursor solution is 0.1-0.5M, because the size of the particles will first increase and then decrease with the increase of the concentration of the precursor solution, so in order to obtain particles of a suitable size, the precursor concentration needs to be controlled within this range;

[0017] Furthermore, in step 2, ethylene glycol is first added to the precursor solution obtained in step 1, stirred evenly, and then citric acid is added and mixed evenly.

[0018] Furthermore, in step 2, the amount of citric acid added is 1 to 3 times the total amount of all metal (Cu, Zn, Ce / Y and Al) cations; since too little citric acid will lead to colloid instability, and too much citric acid will lead to incomplete combustion of citric acid and decreased product crystallization, the amount of citric acid is controlled within this range;

[0019] The amount of ethylene glycol added is 1 to 3 times the amount of citric acid. Since ethylene glycol has low volatility, too little citric acid cannot fully polymerize and it is difficult to form a stable sol, while too much citric acid cannot dry easily. Therefore, the amount of ethylene glycol is controlled within this range.

[0020] Place in a water bath at 70-90°C and heat with stirring until a gel is formed, usually within 3-4 hours.

[0021] Furthermore, in step 3, the mixture is placed in a drying oven at 100 to 120° C. and dried for 12 to 18 hours.

[0022] Furthermore, in step 4, the mixture is placed in a tubular furnace for calcination at a temperature of 300 to 400° C. and a calcination time of 4 to 6 hours.

[0023] In addition, the present invention also provides the use of the above composite oxide as a catalyst in the hydrogenation of carbon dioxide to methanol, and the composite oxide (i.e., the rare earth metal-modified carbon dioxide hydrogenation to methanol catalyst) catalyzes CO 2 Convert to CH 3 The selectivity of OH is 70-95%.

[0024] A method for preparing methanol by hydrogenating carbon dioxide, which is special in that: the composite oxide is used as a catalyst to catalyze CO 2 The reaction equation for hydrogenation to methanol is:

[0025] CO 2 +3H 2 =====CH 3 OH+H 2 O

[0026] Principle of the present invention:

[0027] Different from the co-precipitation method in which a precipitant is added to a mixed metal salt solution, resulting in excessive local concentration, agglomeration of certain components, and uneven composition, the present invention adopts a sol-gel method to prepare a new type of composite oxide, dispersing the raw metal nitrate into a solvent to form a low-viscosity solution (the molar concentration of copper nitrate, zinc nitrate, aluminum nitrate and cerium nitrate / yttrium nitrate in the precursor solution is 0.1-0.5M). In this way, molecular-level uniformity can be obtained in a very short time. When forming a gel, the reactants are uniformly mixed at the molecular level, and the obtained material composition is uniform, which is not only conducive to precipitation and phase formation, but also can make the active sites of Cu and ZnO in close contact highly dispersed, ensuring that multiple catalytic sites of the catalyst are exposed, thereby improving the catalytic activity of the catalyst.

[0028] In addition, from the perspective of application, the present invention considers the reverse water gas shift reaction as a CO 2 An intermediate step in the hydrogenation process to produce methanol (CO 2 +H 2 =CO+H 2 O, first generate CO, then hydrogenate to synthesize methanol), where CO and CO 2 Competitive adsorption on the active sites of the catalyst will lead to mutual inhibition of the hydrogenation reactions of the two molecules. At the same time, the water produced by the reverse water-gas shift reaction will cause the CO hydrogenation metal active particles to sinter and be partially oxidized, resulting in a reduction in active sites. In addition, the restriction of CH 3 An important factor in OH selectivity is H 2 Therefore, when designing the composite oxide as a catalyst, the present invention introduces alkali metals and rare earth metals to improve the catalyst's adsorption of hydrogen, which is not only beneficial to improve CH 3 OH selectivity and helps disperse Cu particles; in addition, alkali metals can also change the reaction path and utilize the H generated by reverse water gas. 2 O and H 3 CO-synthesizes methanol and weakens the adverse effects of water on catalyst activity.

[0029] Advantages of the present invention:

[0030] 1. The composite oxide designed by the present invention is used as a catalyst, wherein Cu and ZnO are the main active components of the catalyst, Cu can promote the adsorption and dissociation of hydrogen, ZnO can adsorb CO2 to form bicarbonate, and AAlO3 (where A is one of the rare earth metals Ce and Y metals) is used as an active carrier, which can not only adsorb CO2, but also promote the dispersion of the main active components Cu and ZnO, and improve the thermal stability of the catalyst. In this way, the catalytic activity and stability of the catalyst can be greatly improved.

[0031] 2. The preparation method of the rare earth metal modified catalyst of the present invention is simple, and compared with the existing catalyst, the selectivity and stability are significantly improved, and CO 2 Efficient conversion to CH 3 OH, CH 3 The selectivity of OH is 70-95%, and the conversion can be stable for 60 hours. 3 The OH selectivity is around 60%. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 CO of the catalysts of Examples 1-3 and Comparative Examples 1 to 3 of the present invention 2 Reaction activity diagram of hydrogenation to methanol;

[0033] Figure 2 CO of the catalysts of Example 2 and Comparative Example 2 of the present invention 2 Stability diagram of the hydrogenation to methanol reaction. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0035] The present invention provides a method for preparing a rare earth metal-modified carbon dioxide hydrogenation to methanol catalyst, which specifically comprises the following steps:

[0036] Step 1: Dissolve copper nitrate, zinc nitrate, aluminum nitrate and cerium nitrate / yttrium nitrate in deionized water respectively, and mix them to prepare a precursor solution;

[0037] The molar ratio of copper nitrate to zinc nitrate is 0.5-2, the molar ratio of cerium nitrate or yttrium nitrate to (copper nitrate+zinc nitrate) is 3:7, and the molar ratio of cerium nitrate or yttrium nitrate to aluminum nitrate is 1:1; the molar concentrations of copper nitrate, zinc nitrate, aluminum nitrate and cerium nitrate / yttrium nitrate in the precursor solution are 0.1-0.5M; the amount of citric acid added is 1-3 times the total amount of all metal (Cu, Zn, Ce / Y and Al) cations; and the amount of ethylene glycol added is 1-3 times the amount of citric acid;

[0038] Step 2: Ethylene glycol and citric acid are added to the precursor solution obtained in step 1 in sequence, and after being mixed evenly, the mixture is placed in a water bath at 70 to 90° C. and heated and stirred until the water evaporates and turns into a gel state, thereby obtaining a gel precursor;

[0039] Step 3: drying the gel precursor obtained in step 2 in a drying oven at 100 to 120° C. for 12 to 18 hours, and grinding the precursor powder after drying;

[0040] Step 4: Place the precursor powder obtained in step 3 into a tube furnace and calcine at 300-400°C under an inert atmosphere to obtain a composite oxide xCu / yZnO / zAAlO 3 ; Among them, x∶y=0.5~2∶1, (x+y)∶z=7∶3.

[0041] The present invention is described in detail below with specific embodiments:

[0042] Embodiment 1:

[0043] The prepared carbon dioxide hydrogenation to methanol catalyst is Cu / 2ZnO / 1.285CeAlO 3 Catalyst, the specific steps are as follows:

[0044] 2.4160 g of copper nitrate, 5.9498 g of zinc nitrate, 5.5828 g of cerium nitrate and 4.8231 g of aluminum nitrate were dissolved in 100 mL, 200 mL, 130 mL and 130 mL of deionized water respectively, and then the above nitrate solutions were mixed and stirred to obtain a precursor solution; 4.6697 mL of ethylene glycol and 35.1142 g of citric acid were added to the precursor solution in sequence, and after mixing evenly, the mixture was placed in a water bath at 80° C. and stirred until the water evaporated to form a gel precursor; the gel precursor was then placed in a drying oven at 110° C. and dried. After drying, the mixture was ground and placed in N 2 The mixture was calcined in a filled 400°C tube furnace for 4 h to obtain Cu / 2ZnO / 1.285CeAlO with a molar ratio of 1:2:1.285. 3 catalyst.

[0045] Embodiment 2:

[0046] The prepared carbon dioxide hydrogenation to methanol catalyst is Cu / ZnO / 0.857YAlO 3 Catalyst, the specific steps are as follows:

[0047] 2.4160 g of copper nitrate, 2.9749 g of zinc nitrate, 3.2829 g of yttrium nitrate and 3.2154 g of aluminum nitrate were dissolved in 50 mL, 50 mL, 43 mL and 43 mL of deionized water respectively, and then the above nitrate solutions were mixed and stirred to obtain a precursor solution; 0.3533 mL of ethylene glycol and 5.2395 g of citric acid were added to the precursor solution, and the mixture was evenly mixed and then placed in a 90°C water bath and stirred until the water evaporated to form a gel precursor, and then the gel precursor was placed in a drying oven at 100°C for drying, and after drying, it was ground and placed in N 2 The molar ratio of Cu / ZnO / 0.857YAlO was 1:1:0.857 and calcined in a filled 300℃ tube furnace for 6h. 3 catalyst.

[0048] Embodiment 3:

[0049] The prepared carbon dioxide hydrogenation to methanol catalyst is 2Cu / ZnO / 1.285CeAlO 3 Catalyst, the specific steps are as follows:

[0050] 4.9320 g of copper nitrate, 2.9749 g of zinc nitrate, 5.5828 g of cerium nitrate and 4.8231 g of aluminum nitrate were dissolved in 40 mL, 20 mL, 26 mL and 26 mL of deionized water, respectively. The above nitrate solutions were mixed and stirred to obtain a precursor solution. 1.5565 mL of ethylene glycol and 11.7047 g of citric acid were added to the precursor solution. After mixing evenly, the mixture was placed in a 70°C water bath and stirred until the water evaporated to form a gel precursor. The gel precursor was then placed in a drying oven at 120°C for drying. After drying, it was ground and placed in N 2 The mixture was calcined in a filled 350°C tube furnace for 5 h to obtain 2Cu / ZnO / 1.285CeAlO with a molar ratio of 2:1:1.285. 3 catalyst.

[0051] Comparative Example 1:

[0052] The Cu / 2ZnO catalyst was prepared by the following specific steps:

[0053] 2.4660 g of copper nitrate and 5.9498 g of zinc nitrate were dissolved in 100 mL and 200 mL of deionized water, respectively. The above nitrate solutions were mixed and stirred to obtain a precursor solution. 18.9125 g of citric acid and 2.5151 mL of ethylene glycol were added to the precursor solution. After mixing evenly, the mixture was placed in a water bath at 80 °C and stirred until the water evaporated and turned into a gel. The gel was then placed in a drying oven at 110 °C and dried. After drying, it was ground and placed in N 2 The catalyst was calcined in a filled 400°C tubular furnace for 4 h to obtain a Cu / 2ZnO catalyst with a molar ratio of 1:2.

[0054] Comparative Example 2:

[0055] The Cu / ZnO catalyst is prepared in the following steps:

[0056] 2.4660 g of copper nitrate and 2.9749 g of zinc nitrate were dissolved in 50 mL and 50 mL of deionized water, respectively. The above nitrate solutions were mixed and stirred to obtain a precursor solution. 3.493 g of citric acid and 0.2355 mL of ethylene glycol were added to the precursor solution. After mixing evenly, the mixture was placed in a 90°C water bath and stirred until the water evaporated and turned into a gel. The gel was then placed in a drying oven at 100°C for drying. After drying, it was ground and placed in N 2The catalyst was calcined in a filled 300°C tubular furnace for 6 h to obtain a Cu / ZnO catalyst with a molar ratio of 1:1.

[0057] Comparative Example 3:

[0058] The 2Cu / ZnO catalyst was prepared by the following specific steps:

[0059] 4.9320 g of copper nitrate and 2.9749 g of zinc nitrate were dissolved in 40 mL and 20 mL of deionized water, respectively. The above nitrate solutions were mixed and stirred to obtain a precursor solution. 6.30417 g of citric acid and 0.8383 mL of ethylene glycol were added to the precursor solution. After mixing evenly, the mixture was placed in a 70°C water bath and stirred until the water evaporated and turned into a gel. The gel was then placed in a drying oven at 120°C for drying. After drying, it was ground and placed in N 2 The catalyst was calcined in a filled 350°C tubular furnace for 5 h to obtain a 2Cu / ZnO catalyst with a molar ratio of 2:1.

[0060] In order to verify the catalytic activity and stability of the catalyst of the present invention, the present invention used the above catalyst to carry out CO in a fixed bed reactor at 260°C and 3Mpa. 2 Hydrogenation to methanol reaction, the catalyst loading is 500mg, the results are as follows:

[0061] Figure 1 CO is the rare earth modified Cu-based catalyst of Examples 1-3 of the present invention and the Cu-based catalyst of Comparative Examples 1-3 2 Hydrogenation to methanol reaction activity diagram, Figure 2 CO is the rare earth modified Cu-based catalyst of Example 2 of the present invention and the Cu-based catalyst of Comparative Example 2. 2 Stability diagram of the hydrogenation to methanol reaction.

[0062] Depend on Figure 1 It can be seen that the rare earth metal modified carbon dioxide hydrogenation to methanol catalyst CO prepared in the present invention 2 The conversion rate of CH 3 The selectivity of OH is 70-95%; CO on the Cu-based catalyst prepared in Comparative Examples 1-3 2 The conversion rate of CH 3 The OH selectivity is 50-65%.

[0063] Depend on Figure 2 It can be seen that after a 60-hour stability test, the stability of the rare earth metal-modified carbon dioxide hydrogenation to methanol catalyst prepared in the present invention is significantly better than that of the traditional Cu-based catalyst. The performance of the rare earth metal-modified carbon dioxide hydrogenation to methanol catalyst decreases by about 1%, while the performance of the traditional Cu-based catalyst decreases by about 15%.

[0064] In summary, the catalytic activity and stability of the rare earth metal-modified carbon dioxide hydrogenation to methanol catalyst designed and prepared in the present invention are improved.

[0065] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should be included in the protection scope of the present invention.

Claims

1. A composite oxide, characterized in that: It is xCu / yZnO / zAAlO3; wherein A is rare earth metal Ce or Y; the molar ratio of Cu and ZnO is x:y=0.5~2:1, and the molar ratio of (Cu+ZnO) and AAlO3 is (x+y):z=7:

3.

2. The method for preparing the composite oxide according to claim 1, characterized in that: The specific steps include: Step 1: Prepare the precursor solution Dissolve copper nitrate, zinc nitrate, aluminum nitrate and cerium nitrate / yttrium nitrate in deionized water according to proportions, mix and prepare a precursor solution; Step 2: Preparation of gel precursor Add ethylene glycol and citric acid to the precursor solution obtained in step 1, mix well, and heat and stir until the water evaporates and turns into a gel, thereby obtaining a gel precursor; Step 3: Preparation of precursor powder Drying the gel precursor obtained in step 2, and grinding it to obtain precursor powder; Step 4: Preparation of composite oxides The precursor powder obtained in step 3 is calcined under an inert atmosphere to obtain the composite oxide xCu / yZnO / zAAlO3.

3. The method for preparing the composite oxide according to claim 2, characterized in that: In step 1, the molar concentration of copper nitrate, zinc nitrate, aluminum nitrate and cerium nitrate / yttrium nitrate in the precursor solution is 0.1-0.5M.

4. The method for preparing the composite oxide according to claim 3, characterized in that: In step 2, ethylene glycol is first added to the precursor solution obtained in step 1, and then citric acid is added and mixed evenly.

5. The method for preparing the composite oxide according to claim 4, characterized in that: In step 2, the amount of citric acid added in the step is 1 to 3 times the total amount of all metal cation substances; The amount of ethylene glycol added is 1 to 3 times the amount of citric acid; Place in a water bath at 70-90℃ and heat with stirring.

6. The method for preparing the composite oxide according to claim 5, characterized in that: In step 3, place in a drying oven at 100-120° C. and dry for 12-18 hours.

7. The method for preparing the composite oxide according to claim 6, characterized in that: In step 4, the product is placed in a tubular furnace for calcination at a temperature of 300 to 400° C. for a time of 4 to 6 hours.

8. Use of the composite oxide according to claim 1 as a catalyst in the hydrogenation of carbon dioxide to methanol.

9. The use according to claim 8, characterized in that: The selectivity of the composite oxide in catalyzing the conversion of CO2 into CH3OH is 70-95%.

10. A method for preparing methanol by hydrogenating carbon dioxide, characterized in that: The composite oxide according to claim 1 is used as a catalyst.

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