Preparation method and application of rare earth element Er modified transition metal oxide catalyst

Abstract

The invention belongs to the technical field of environmental protection for catalytic decomposition of N2O pollution, and particularly relates to a preparation method and application of a rare earth element Er modified transition metal oxide catalyst. According to the catalyst, the transition metal oxide serves as a catalytic main body, a coprecipitation method serves as a preparation means, and the rare earth element Er is added to assist preparation of the high-activity transition metal oxide catalyst, so that the performance of catalytic decomposition of industrial waste gas N2O pollution is improved. The prepared ErxCo catalyst has excellent low-temperature activity and good impurity gas resistance, all catalysts show the activity superior to that of original Co3O4, Er0. 03Co shows the optimal activity at the reaction temperature of 420 DEG C, and the N2O conversion rate is 100% and is about 80 DEG C lower than that of Co3O4. When 100 ppmv NO, 5 vol.% O2 and 2 vol.% H2O are all introduced at 400 DEG C, the N2O conversion rate (2000 ppmv N2O / Ar) can be stabilized at about 27% for a long time. The preparation method is simple in preparation process, high in repeatability, short in synthesis period, mild in catalytic reaction condition, short in reaction time and good in catalytic effect.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental protection for catalytically decomposing N2O pollution, and particularly relates to a preparation method and application of a rare earth element Er-modified transition metal oxide catalyst. Background Art

[0002] Nitrous oxide (N2O) is the third most powerful greenhouse gas after CO2 and CH4. Its strong atmospheric stability and infrared radiation absorption capacity can persistently damage ozone in the atmosphere, exacerbating the ozone hole and placing significant pressure on the environment. Industrial N2O emissions primarily come from the production of chemical products such as nitric acid and oxalic acid plants, as well as from vehicle exhaust. Because N2O can remain in the atmosphere for up to 150 years, reducing its emissions does not immediately alleviate environmental pressures. Therefore, its elimination has become a major focus of researchers.

[0003] For decades, the direct catalytic decomposition of N2O into N2 and O2 has been recognized as the most promising solution for N2O removal. To date, researchers have developed a variety of catalysts for direct N2O decomposition, including supported precious metal catalysts, molecular sieve-based catalysts, and metal oxide catalysts. Metal oxide catalysts have attracted considerable attention due to their simple preparation methods, environmental friendliness, low raw material costs, easily adjustable composition, and generally excellent catalytic activity at medium and low temperatures.

[0004] The main factors affecting the performance of metal oxide catalysts include preparation method, calcination temperature, doping of additives, specific surface area, grain size and the presence of impurity gases. Researchers have found that introducing another metal or metals as additives into transition metal oxides can help improve their catalytic activity. Catalysis Letters (Catalysis Letters, 118 (2007): 64-68) reported the effect of adding alkali metal Cs on the performance of NiO catalytic N2O decomposition. The experimental results showed that the catalytic decomposition temperature of N2O was reduced from 350°C to 250°C, and T 50 About 200 ° C. Although the addition of alkali metal additives has a significant effect on improving the catalytic performance of transition metal oxides, it is not very effective for NO in the actual tail gas of nitric acid plants, adipic acid plants, etc. x ,H2O, O2, CO2 and other gases have poor resistance, which limits its application in actual N2O treatment.

[0005] Afterwards, scientific researchers have begun to explore many different types of additives, mainly including: alkaline earth metals (Ca, Sr, Ba), transition metals (Cu, Zn, Ni, Fe, Mn), rare earth metals (La, Ce, Y, Pr, Sm, Tb) or other large radius metals (Pb, Ag, Bi). These metals as additives not only increase the number of active sites of transition metal oxides, but also weaken the MO (M = Co, Ni, Cu) bonds to a certain extent. Although the weakening effect of the corresponding additives on the MO bond in the catalyst is far less than that of alkali metals, the introduction of these additives greatly increases the number of active sites of the metal oxide and the tolerance of the catalyst to impurity gases, solving the problem of poor resistance to impurity gases of composite oxide catalysts doped with alkali metals. Patent CN102513117A discloses a composite oxide composed of copper oxide and cerium oxide, which utilizes the synergistic effect formed by cerium atoms entering the copper oxide lattice to greatly improve the activity and stability of the catalyst in catalytic decomposition of N2O, and achieves complete decomposition of N2O at 400°C. Patent CN104624203A uses a simple co-precipitation method to disclose a composite catalyst based on PbO and Co oxide. This type of catalyst maintains high catalytic activity at low temperatures (300°C) and has excellent resistance to impurity gases such as CO2 and SO2.

[0006] It is reported that so far, there has been no report on the use of rare earth metal Er as an auxiliary agent to modify transition metal oxides to directly catalyze the decomposition of N2O, and there has been no report on the use of such catalysts for O2, NO x , research on resistance to impurity gases such as H2O. Summary of the Invention

[0007] In order to solve the problems that existing catalysts for catalytic decomposition of N2O have poor activity in impurity gas atmospheres and the cost of improving performance is high, the present invention provides a preparation method and application of a transition metal oxide catalyst with low cost, simple preparation, good low-temperature activity and good stability.

[0008] The technical solution adopted in the present invention is:

[0009] A method for preparing a rare earth element Er-modified transition metal oxide catalyst comprises the following steps: mixing and dissolving a transition metal soluble salt and an Er-based soluble salt in deionized water to obtain a precursor solution; adding a precipitant solution dropwise to the precursor solution under continuous stirring until the solution pH reaches 9-10; continuously stirring and aging the solution for 2 hours; and filtering the obtained precipitate, washing, drying, and then calcining to obtain a target product.

[0010] Furthermore, in the above preparation method, the soluble transition metal salt is one or more of cobalt nitrate, cobalt acetate, cobalt oxalate, copper nitrate and nickel nitrate.

[0011] Furthermore, in the above preparation method, the Er-based soluble salt is one or more of Er nitrate, chloride, sulfate and oxalate.

[0012] Furthermore, in the above preparation method, the addition amount of transition metal soluble salt and Er-based soluble salt is, according to the atomic ratio, Er / M=0.01-0.05; the total ion concentration of Er and M in the precursor solution is 0.01-1 mol / L, where M refers to the transition metal in the transition metal soluble salt.

[0013] Furthermore, in the above preparation method, during the continuous stirring process, the temperature is maintained at 15° C. to 65° C. for 1 hour to 10 hours.

[0014] Furthermore, in the above preparation method, the precipitant is one or more of sodium carbonate, sodium hydroxide, potassium carbonate, ammonia water and urea.

[0015] Furthermore, in the above preparation method, the concentration of the precipitant solution is 0.01-1 mol / L.

[0016] Furthermore, in the above preparation method, the drying temperature is 90° C. to 150° C., and the drying time is 1 hour to 24 hours.

[0017] Furthermore, in the above preparation method, the calcination temperature is 450° C. to 550° C., and the calcination time is 1 hour to 4 hours.

[0018] Application of the rare earth element Er modified transition metal oxide catalyst prepared by any of the preparation methods described above in the direct catalytic decomposition of N2O.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention utilizes a coprecipitation method. The addition of the additive Er effectively reduces the catalyst's grain size, increases its specific surface area, and correspondingly increases the number of active sites, providing a large number of active sites for the catalytic decomposition of NO. Furthermore, the addition of the additive modifies the catalyst's surface properties, weakening the Co-O bond and reducing the activation energy of the reaction.

[0021] 2. The active components of the catalyst prepared in the present invention are transition metal oxides. The added additive Er not only enhances the activity of the Co3O4 catalyst in catalytic decomposition of N2O, but also demonstrates excellent tolerance to all tested impurity gases. Even in an atmosphere containing 5 vol.% O2, 100 ppmv NO, and 2 vol.% H2O, the catalyst can achieve a conversion rate of nearly 27% for N2O (2000 ppmv) in the reaction gas at 400°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 1 is an activity diagram of catalytic decomposition of N2O by the catalysts prepared in Examples 1-5 and Comparative Example 1.

[0023] Figure 2 This is a test chart of the impurity gas resistance of the catalyst prepared in Example 1.

[0024] Figure 3 This is a catalytic stability test chart of the catalyst prepared in Example 1.

[0025] Figure 4 This is the TEM image of the catalyst sample prepared in Example 1. A and B are B(1)Co3O4 and S(1)Er 0.03 Electron microscope image of catalyst sample C at 100,000 times magnification, with its particle size distribution embedded; C and D are B(1)Co3O4 and S(1)Er, respectively. 0.03 Partially enlarged view of C.

[0026] Figure 5 It is the O2-TPD analysis chart of the catalyst prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to more fully understand the present invention, the present invention is described in more detail through the following non-limiting examples or comparative examples, but the examples or comparative examples do not limit the present invention in any way.

[0028] Example 1 Preparation of S(1)Er by coprecipitation 0.03 Co catalyst

[0029] Weigh 3.52 g of Co(NO3)2·6H2O and 0.17 g of Er(NO3)3·6H2O and dissolve them in deionized water to obtain a concentration of 0.2 mol·L -1 The precursor solution was stirred continuously at 40℃ for 2h, and 0.5mol·L -1 The Na2CO3 solution was added dropwise to the precursor solution until the pH of the mixed solution was 9-10. Subsequently, the mixture was aged for 2 h under the same temperature conditions, the resulting precipitate was filtered, and washed with deionized water until the pH of the filtrate was neutral. The collected filter cake was then transferred to an oven and dried at 110 ° C for 3 h. Finally, the resulting product was calcined at 500 ° C for 3 h at a heating rate of 5 ° C / min to obtain the final catalyst S (1) Er 0.03 Co.

[0030] Example 2 Preparation of S(2)Er by coprecipitation 0.01 Co catalyst

[0031] The catalyst S(2)Er was prepared according to the method described in Example 1, except that 0.06 g of Er(NO3)3·6H2O was used instead of 0.17 g of Er(NO3)3·6H2O in Example 1. 0.01 Co.

[0032] Example 3 Preparation of S(3)Er by coprecipitation 0.02 Co catalyst

[0033] The catalyst S(3)Er was prepared according to the method described in Example 1, except that 0.11 g of Er(NO3)3·6H2O was used instead of 0.17 g of Er(NO3)3·6H2O in Example 1. 0.02 Co.

[0034] Example 4 Preparation of S(4)Er by coprecipitation 0.04 Co catalyst

[0035] The catalyst S(4)Er was prepared according to the method described in Example 1, except that 0.22 g of Er(NO3)3·6H2O was used instead of 0.17 g of Er(NO3)3·6H2O in Example 1. 0.04 Co.

[0036] Example 5 Preparation of S(5)Er by coprecipitation 0.05 Co catalyst

[0037] The catalyst S(5)Er was prepared according to the method described in Example 1, except that 0.28 g of Er(NO3)3·6H2O was used instead of 0.17 g of Er(NO3)3·6H2O in Example 1. 0.05 Co.

[0038] Comparative Example 1 Preparation of Catalyst B (1) Co3O4 (P)

[0039] First, take an appropriate amount of Co(NO3)2·6H2O and dissolve it in a certain amount of deionized water to prepare a 0.2M precursor solution for use. Subsequently, under the condition of continuous stirring at 40°C, add 0.5M Na2CO3 solution dropwise to the above mixed precursor solution to make the pH of the solution = 9-10. After continuous aging for 2 hours, the resulting precipitate is filtered and washed with a large amount of deionized water to clean the residual sodium ions therein, and the pH value of the filtrate reaches neutral (pH = 7) as the standard for cleaning the residual sodium ions. Finally, the resultant is placed in an oven at 110°C for drying, and after drying, it is calcined at 500°C in an air atmosphere for 3 hours to obtain B(1)Co3O4(P) catalyst.

[0040] Example 6 Performance Test of Catalyst

[0041] The general activity determination of the catalyst is carried out on an integral fixed bed at normal pressure. The catalyst samples of Examples 1-5 and Comparative Example 1 are pressed into tablets using a mold, sieved, and 200 mg of a 40-60 mesh catalyst is added to a quartz tube reactor (inner diameter 4 mm). The mixed reaction gas contains 2000 ppmv of N2O, and Ar is a carrier gas. When impurity gases are introduced therein, the types of impurity gases and the corresponding contents are 5 vol.% O2, 2 vol.% H2O or 100 ppmv NO, respectively. In order to examine the effects of impurity gases on the activity of the catalyst, one or more of these impurity gases are introduced according to the circumstances, and the specific circumstances will be directly given in the corresponding charts. The total flow rate of the mixed gas is 50 mL min -1 , and a Varian CP-3800 gas chromatograph (with a phase-stabilized Porapak Q and a thermal conductivity detector, and high-purity Ar as the carrier gas) was used to detect the residual concentration of N2O online.

[0042] like Figure 1 As shown in the figure, the effect of the amount of Er on the catalytic N2O decomposition performance of transition metal oxides (2000ppmvN2O / Ar, 50mL min -1 ) and the influence of Co3O4(P) prepared by precipitation method. The results show that the addition of rare earth element Er during the preparation process greatly improves the catalytic activity of the catalyst. For example, at 350℃, the N2O conversion rate of B(1)Co3O4(P) catalyst is only 24.3%, which is lower than that of Er. x N2O conversion rate of Co catalyst (x = 0.01 ~ 0.05). S(1)Er 0.03 Co exhibits the best activity at a reaction temperature of 420°C, with a N2O conversion rate of 100%, which is about 80°C lower than that of Co3O4. As the proportion of rare earth element Er increases from 0.01 to 0.05, the N2O conversion rate increases first and then decreases slightly, where S(1)Er 0.03 The catalytic activity of Co catalyst is the best. At 400℃, Er 0.03 The N2O conversion rate on the Co catalyst was 93%, while the conversion rate on the Co3O4(P) catalyst at the same temperature was only 60%.

[0043] The impurity gas tolerance of the catalyst with the best activity (the catalyst obtained in Example 1) was tested

[0044] Whether the catalyst has good resistance to impurity gases plays a decisive role in whether it can be used in actual industrial production. 0.03 The resistance of Co catalyst to impurity gases (NO, O2 and H2O) discharged from nitric acid plant, such as Figure 2When no impurity gas is introduced into the system, the T 50 (the temperature at which the N2O conversion rate reaches 50%) is only 350°C; when 100 ppmv NO, 5 vol.% O2 and 2 vol.% H2O enter the reaction system, the corresponding T 50 The temperature increases at 375℃, 370℃ and 400℃ respectively, which means that NO, O2 and H2O all inhibit the activity of the catalyst, but the inhibitory effect is relatively limited. In addition, when all impurity gases (100ppmv NO, 5vol.% O2 and 2vol.% H2O) are introduced into the reaction system, the catalyst S(1)Er 0.03 The N2O conversion rate of Co can still reach more than 60% at 450℃.

[0045] The stability test of the catalyst with the best activity (catalyst obtained in Example 1) was carried out

[0046] Under the specified reaction conditions, the S(1)Er 0.03 The N2O conversion rate of Co catalyst changes with time to determine the stability of the catalyst. The results are as follows Figure 3 First, without any impurity gases introduced, the catalyst conversion rate at 400°C remained constant at 85%. Subsequently, 5 vol.% O2 and 100 ppmv NO were introduced sequentially, and after 5 hours, the catalyst conversion rate remained at 54%. After the introduction of 2 vol.% H2O, the catalyst activity continued to decline, ultimately maintaining at around 27%. Subsequently, by maintaining the temperature constant and cutting off all impurity gases, the catalyst conversion rate gradually rebounded to 85% and remained stable.

[0047] TEM analysis of the catalyst with the best activity (catalyst obtained in Example 1)

[0048] Transmission electron microscopy was used to investigate the S(1)Er 0.03 The morphology of the Co catalyst was studied, and the Er additive and Co3O4 nanoparticles were identified by the lattice fringes taken by high-resolution transmission electron microscopy. Figure 4 ) It can be seen that B(1)Co3O4 and S(1)Er 0.03 Co both showed a spherical shape with smooth edges. By selecting nanoparticles from the TEM image with a scale of 100 nm and performing a statistical analysis of the particle size, the results showed that the particle sizes of both were uniformly normally distributed and widely distributed, and S(1)Er 0.03The average particle size of Co (7.33nm) is much smaller than that of B(1)Co3O4. In the high-resolution transmission electron microscopy images, the lattice spacing of B(1)Co3O4 is 0.246nm and 0.180nm, respectively, which is completely consistent with the (311) and (422) crystal planes of Co3O4 nanocrystals with spinel structure. 0.03 The Co catalyst was found to have exposed other crystal faces of Co3O4 nanocrystals, such as the (511) crystal face, which means that Er did not change the crystal phase of Co3O4, and the exposure of these special crystal faces is likely to be the reason for the improved catalytic performance. 0.03 The (006) crystal plane of Er2O3 was also observed in the transmission electron microscope image of the Co catalyst. Due to the large radius of Er2O3, it is only dispersed on the catalyst surface. Combined with the above characterization, it further indicates that the Er additive exists in the form of oxide (Er2O3) and is highly dispersed on the catalyst surface.

[0049] The catalyst with the best activity (catalyst obtained in Example 1) was subjected to O2-TPD analysis.

[0050] In order to further determine the change in the number of surface oxygen vacancies (acting as active sites) of the catalyst, the B(1)Co3O4(P) of Comparative Example 1 and the S(1)Er 0.03 The Co catalyst was characterized by O2-TPD, such as Figure 5 As shown in the figure, S(1)Er 0.03 The deoxidation capacity of Co catalyst between 100℃ and 300℃ is 23.15μmol g -1 , while the deoxidation capacity of B(1)Co3O4(P) catalyst was only 13.83 μmol g -1 These data indicate that the addition of surfactants increases the number of surface active sites of the catalyst, which may be an important reason for the excellent catalytic performance of the catalyst.

Claims

1. A method for preparing a rare earth element Er modified transition metal oxide catalyst, characterized in that: The method comprises the following steps: mixing and dissolving a transition metal soluble salt and an Er-based soluble salt in deionized water to obtain a precursor solution; adding a precipitant solution dropwise to the precursor solution under continuous stirring until the pH value of the solution reaches 9-10; continuously stirring and aging the solution for 2 hours; and filtering the obtained precipitate, washing, drying and calcining the precipitate to obtain the target product.

2. The preparation method according to claim 1, characterized in that The soluble transition metal salt is one or more of cobalt nitrate, cobalt acetate, cobalt oxalate, copper nitrate and nickel nitrate.

3. The preparation method according to claim 1, characterized in that The Er-based soluble salt is one or more of Er nitrate, chloride, sulfate and oxalate.

4. The preparation method according to claim 1, characterized in that The amount of transition metal soluble salt and Er-based soluble salt added is, according to the atomic ratio, Er / M=0.01-0.05; the total ion concentration of Er and M in the precursor solution is 0.01-1 mol / L, where M refers to the transition metal in the transition metal soluble salt.

5. The preparation method according to claim 1, characterized in that During the continuous stirring process, the temperature is maintained at 15°C to 65°C for 1 hour to 10 hours.

6. The preparation method according to claim 1, characterized in that The precipitant is one or more of sodium carbonate, sodium hydroxide, potassium carbonate, ammonia water and urea.

7. The preparation method according to claim 1, characterized in that The concentration of the precipitant solution is 0.01-1 mol / L.

8. The preparation method according to claim 1, characterized in that The drying temperature is 90° C. to 150° C., and the drying time is 1 hour to 24 hours.

9. The preparation method according to claim 1, characterized in that The calcination temperature is 450° C. to 550° C., and the calcination time is 1 hour to 4 hours.

10. Use of a rare earth element Er-modified transition metal oxide catalyst prepared by the preparation method according to any one of claims 1 to 9 in direct catalytic decomposition of N2O.

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