CN111450894B - A Ce-based organometallic complex catalytic material and its preparation and application - Google Patents

Abstract

The invention discloses a Ce-based organometallic complex catalytic material, a preparation method and an application thereof, which are characterized in that a novel Ce (III) -BDC organometallic complex is synthesized by a solvothermal method through terephthalic acid organic ligands and trivalent cerium ions, and has a hexagonal prism crystal structure, high thermal stability and excellent NO _x The catalytic conversion performance is a novel metal organic complex catalytic material with excellent performance.

Description

A Ce-based organometallic complex catalytic material and its preparation and application

Technical field

The invention relates to a metal organic complex generated by the combination of Ce metal and terephthalic acid and its preparation, and can be used as a catalytic material. It involves the synthesis of a metal-organic complex and has good catalytic reaction performance as a catalytic material.

Background technique

Inorganic metals and organic ligands cooperate to form stable metal-organic complexes. The solidity and stability of the metal are combined with the easy modification of the organic ligands to realize the hybridization of organic and inorganic, making their properties complementary. They are used in gas adsorption and separation, The fields of optics, electricity, magnetism, chemical sensing and heterogeneous catalysis show great application potential. For example, metal organic ligands and bases protonate hydrogen in the gas, and then H reacts with CO ₂ to achieve the hydrogenation effect; metal organic frameworks (MOFs) materials can be used directly as catalysts or as catalyst carriers and are widely used in chemistry, Materials science and some engineering applications. In recent years, metal-organic complexes have attracted widespread attention due to their high activity and selectivity in heterogeneous catalytic reactions. They also have the advantages of easy separation of products, easy recovery and reuse of catalysts, and low metal loss.

The oxide of Ce has good oxygen storage capacity and excellent redox properties. In particular, the reduced Ce ³⁺ ions can increase the number of holes on the catalyst surface and the amount of chemically adsorbed oxygen, such as in the NH ₃ -SCR (denitrification) reaction. , the rare earth metal Ce component as an active component or additive often shows excellent catalytic properties such as activity and selectivity in converting NO _x to N ₂ (DOI:10.1016/j.apcatb.2017.02.060, DOI:10.1016/S1002 -0721(16)60024-8), including the doping of Ce components to modulate the acidity and redox properties of the catalyst, enhance the adsorption of NO _x molecules by the catalyst, and accelerate the interaction of the adsorbed -NH ₄ ⁺ species with NO and O ₂ reaction, improve the performance of the catalyst (http://dx.doi.org/10.1016/j.jre.2017.06.004) and so on. Therefore, in recent years, rare earth cerium-based metal organic complexes have also been researched and developed as a new type of catalytic materials. For example, ceric ammonium nitrate is generated from Ce source and terephthalic acid (H ₂ BDC) (or 2,6-naphthalenedicarboxylic acid (H ₂ NDC) and 4,4′-biphenyldicarboxylic acid (H ₂ BPDC)). Six-core [Ce ₆ O ₄ (OH) ₄ ] ¹²⁺ cluster eight-coordinated metal-organic framework Ce(IV)-MOFs, with UiO-66 topology, the PXRD pattern is also consistent with UiO-66(Zr) (hexa-core zirconium cluster MOFs), this type of cerium-based metal organic complex Ce(IV)-UiO-66 shows redox activity and is used in the aerobic oxidation of benzyl alcohol to show catalytic activity. The metal node Ce(IV) participates in the catalytic cycle ( DOI:10.1039/c5cc02606g). Others, such as the metal-organic complex (Ce ₆ O ₄ (OH) ₄ (DMTDC) ₆ ) with UiO-66 topology generated by Ce metal and 3,4-dimethylthiophene-2,5dicarboxylic acid, have a strong response to thiols. The oxidation of has a catalytic effect (DOI: 10.1039/c7ce01053b). The UiO-66 topological metal-organic complex generated by Ce metal and ligand H ₂ BDC-(CH ₃ ) ₂ has catalytic performance for the oxidation of styrene and cyclohexene ( DOI:10.1039/c6ce01704e) and so on. The Ce@UiO-67 catalyst prepared by loading the Ce component on the metal organic complex UiO-67 (Zr) has good low-temperature SCR performance and good water and sulfur resistance. The proportion of trivalent Ce ions in the catalyst (Ce ³⁺ /Ce ⁴⁺ ) is related to catalytic performance (http://dx.doi.org/10.1016/j.cej.2017.05.128). The synthesis and application of metal-organic complex heterogeneous catalytic materials are currently areas that require further extensive research and development. However, rare earth cerium-based metal-organic complexes synthesized from trivalent Ce ions and used in catalysis for the purification of atmospheric pollutants NO _x have not yet been used. See report. In view of this, the present invention uses trivalent Ce ions as the source of metal nodes and connects them with terephthalic acid organic ligands to form a Ce(III)-BDC metal-organic complex with high thermal stability, and uses it as a NO with excellent SCR activity. _x conversion catalytic materials.

Contents of the invention

The purpose of the present invention is to synthesize a Ce(III)-BDC metal-organic complex with high thermal stability using trivalent Ce ions as a metal node source and connected with terephthalic acid organic ligands, and use it as a NO _x conversion catalytic material with excellent SCR activity. The present invention synthesizes Ce(III)-BDC metal organic complex by solvothermal method through terephthalic acid organic ligand and trivalent cerium ions. The reduced Ce ³⁺ ions can be used to increase the number of hole sites on the catalyst surface and chemically adsorbed oxygen. The amount, as well as the adsorption effect of metal nodes on NO _x molecules, can be used as a NO _x conversion catalytic material with excellent SCR activity.

A Ce-based organometallic complex catalytic material provided by the invention and its preparation and application are carried out according to the following steps:

(1) Dissolve terephthalic acid (H ₂ BDC) in N,N′-dimethylformamide (DMF), stir at room temperature until all terephthalic acid is dissolved, and then add Ce salt (CeCl ₃ ·7H ₂ O ) Add the above mixture and stir at room temperature until all cerium trichloride is dissolved. Finally, add acetic acid regulator and stir evenly. Among them, the molar ratio of H ₂ BDC to CeCl ₃ ·7H ₂ O is 1:2, the volume ratio of DMF to H ₂ BDC is about 60-90mL:1g, and the volume ratio of acetic acid to H ₂ BDC is about 1.5 ~2.0mL:1g.

(2) Transfer the mixed solution obtained in step (1) to a polytetrafluoroethylene-backed reaction kettle, move the reaction kettle to an oven, program the temperature to 100-120°C, and let it stand for crystallization for 12-24 hours. Program to cool down to room temperature and take out the reaction kettle. Among them, the programmed heating and cooling rates are 0.2 to 1°C/min.

(3) Centrifuge the white precipitate obtained in step (2), wash the precipitate three times with DMF to remove unreacted raw materials, then exchange it with anhydrous methanol three times, and then centrifuge and filter. Among them, the volume of DMF used for each washing and the volume of anhydrous methanol used are about one-third of the amount of DMF used in the synthesis reaction.

(4) Dry the solid product obtained in step (3) in an oven at 100-120°C for 6-12 hours, and then dry it in a vacuum drying oven at 180-220°C for 10-14 hours to obtain Ce(III)- from which the solvent is removed BDC metal-organic complexes.

(5) The Ce(III)-BDC metal-organic complex obtained in step (4) is subjected to a catalytic performance test of NH ₃ reduction and elimination of NO _x to N ₂ under certain reaction conditions. The reaction conditions are: fixed bed reactor, operating pressure 0.1MPa, raw gas composition 0.05~0.1vol.% _NOx , _NH3 /NO molar ratio 1.0~1.1, 3~6vol.% _O2 , balance gas is _N2 , The _NOx concentration before and after the reaction was detected to calculate the conversion rate.

Description of the drawings

Figure 1 shows the catalytic performance of NO _x reduction by NH ₃ of the Ce(III)-BDC metal organic complex obtained in the Example.

Figure 2 is the PXRD crystal phase structure of the Ce(III)-BDC metal organic complex obtained in the example.

Figure 3 is an SEM morphology image of the Ce(III)-BDC metal organic complex obtained in the example.

Figure 4 shows the SEM morphology of the Ce(IV)-UiO-66 metal-organic framework reported in the literature.

Figure 5 shows the TG thermal stability performance of the Ce(III)-BDC metal organic complex obtained in Examples.

Figure 6 is a preparation flow chart of the embodiment.

Detailed ways

The present invention will be described in detail through specific examples below, but it should be understood that the present invention is not limited only to the examples.

Example 1

(1) Raw materials

Terephthalic acid (H ₂ BDC) was produced by Shanghai McLean Biochemical Technology Co., Ltd. and was of analytical purity (99%); N,N'-dimethylformamide (DMF) was produced by Xilong Science Co., Ltd. and was of analytical purity. (99.8%); CeCl ₃ ·7H ₂ O was produced by Shanghai McLean Biochemical Technology Co., Ltd., with analytical purity (99.9%); acetic acid (CH ₃ COOH) was produced by Xilong Science Co., Ltd., with analytical purity (99.8%).

(2) Preparation of synthetic liquid

Terephthalic acid (4mmol, 0.6644g) was dissolved in 50mL N,N′-dimethylformamide, stirred magnetically at room temperature until all terephthalic acid was dissolved, and then CeCl ₃ ·7H ₂ O (8mmol, 2.9808g) Add the above mixture and stir at room temperature until all cerium chloride is dissolved. Finally, add 1.2 mL acetic acid and stir evenly.

(3) Synthesis of metal-organic complexes

Transfer the mixture obtained in step (2) to a 100mL polytetrafluoroethylene-backed reaction kettle, move the reaction kettle to an oven, program the temperature to 120°C at a heating rate of 0.75°C/min, and let it stand for crystallization for 24 hours. Then the temperature was lowered to room temperature using a cooling rate program of 0.38°C/min and the reaction kettle was taken out.

(4) Washing and filtration of product

Centrifuge the white precipitate obtained in step (3), wash the precipitate three times with DMF (20 mL/time) to remove unreacted raw materials, and then exchange it with anhydrous methanol three times (20 mL/time), and then centrifuge and filter.

(5) Evaluation of catalytic performance of the product

The solid product obtained in step (4) was dried in an oven at 110°C for 12 hours, and then dried in a vacuum drying oven at 200°C for 12 hours to obtain the Ce(III)-BDC metal organic complex from which the solvent was removed.

(6) The Ce(III)-BDC metal-organic complex obtained in step (5) is subjected to a catalytic performance test of NH ₃ reduction and elimination of NO _x to N ₂ under reaction conditions. The reaction conditions are: fixed bed microreactor, operating pressure 0.1MPa, raw gas composition 0.075vol.% _NOx , _NH3 /NO molar ratio 1.05, 3.0vol.% _O2 , balance gas _N2 , space velocity 5× 10 ⁴ mL/(g·h), and the conversion rate was calculated by detecting the NO _x concentration before and after the reaction with an FGA10 online flue gas analyzer (Shenzhen Better Analytical Instrument Co., Ltd.). The catalytic performance evaluation results are shown in Figure 1 of the description.

(7) Characterization of product metal organic complexes

The Ce(III)-BDC metal organic complex obtained in step (5) was analyzed using the following instruments and methods to analyze the crystal phase structure (PXRD), surface morphology (SEM) and thermal stability (TG) of the product. The results are shown in Figure 2, Figure 3 and Figure 5 of the description.

Powder X-ray diffraction analysis (PXRD): The instrument used is Philips The high-tech field emission scanning electron microscope SU5000 (SEM) was used to characterize the appearance and shape of the product; thermogravimetric analysis (TG): using the American SDT-Q600 synchronous TGA/DSC analyzer, in a nitrogen atmosphere, the temperature range was room temperature to 700°C, and the heating rate 10℃/min.

(8) Analysis of Example Results

From the crystal phase structure (PXRD) of the product synthesized in the Example, the crystal phase structure of the Ce(III)-BDC metal organic complex obtained in the present invention is consistent with the reported and disclosed hexanuclear [Ce ₆ O ₄ (OH) ₄ ] The ¹²⁺ cluster eight-coordinated Ce(IV)-MOFs metal-organic complex is different, and it is also different from the Ce oxide crystal phase structure. The surface morphology (SEM) also shows that the Ce(III)-BDC product obtained in the present invention is a metal-organic complex formed by the coordination of dinuclear [Ce ₂ O] ⁴⁺ clusters and terephthalic acid, and its chemical formula is Ce ₂ O (CO ₂ ) ₄ , the crystal morphology is a hexagonal prism, which is different from the regular octahedral morphology of Ce(IV)-MOFs (see Figure 4 of the specification). It shows that the Ce(III)-BDC metal organic complex obtained in the present invention is a metal organic complex. It can be seen from the TG results of the product that the weight loss before 200°C should be due to the removal of solvent and organic ligands that have not been eluted cleanly, and the weight loss above 500°C should be due to the decomposition of organic ligands, indicating that Ce(III) of the present invention -BDC metal-organic complexes have high thermal stability. When the Ce(III)-BDC metal organic complex obtained by the present invention is used in the catalytic reaction of NH ₃ selective catalytic reduction of NO, T ₅₀ and T ₉₀ are 135°C and 175°C respectively, and the stable conversion rate (98.7-100% ) window reaches 300°C. Compared with the reference sample with T ₅₀ of 205°C and the highest conversion rate of 86.6%, it shows excellent low-temperature denitration performance and stable conversion performance. It is a metal-organic complex with excellent catalytic performance.

Claims (1)

1. A process for preparing the catalyst material of Ce-base organic metal complex includes such steps as solvothermal synthesis of Ce (III) -BDC metal organic complex with high thermal stability, which is dinuclear [ Ce ] ₂ O] ⁴⁺ Metal organic complex formed by coordination of cluster and terephthalic acid and having chemical formula of Ce ₂ O(CO ₂ ) ₄ The crystal morphology is hexagonal prism and is used as NH ₃ Selective catalytic reduction of NO _x NO with excellent activity _x A conversion catalytic material; the method specifically comprises the following steps:

(1) Terephthalic acid (H) ₂ BDC) is dissolved in N, N' -Dimethylformamide (DMF), stirred at normal temperature until terephthalic acid is completely dissolved, and CeCl is added ₃ ·7H ₂ Adding O into the mixed solution, stirring at normal temperature until cerium trichloride is completely dissolved, and finallyAdding an acetic acid regulator, and uniformly stirring; wherein H is ₂ BDC and CeCl ₃ The feeding molar ratio of (2) is 1:2, and the volume of DMF and H are as follows ₂ The mass ratio of BDC is 60-90 mL:1g, acetic acid volume and H ₂ BDC mass ratio is 1.5-2.0 mL:1g;

(2) Transferring the mixed solution obtained in the step (1) into a reaction kettle of a polytetrafluoroethylene substrate, transferring the reaction kettle into an oven, heating to 100-120 ℃ by a program, standing for crystallization for 12-24 hours, then cooling to room temperature by a program, and taking out the reaction kettle; wherein the program temperature rise and temperature fall rate is 0.2-1 ℃/min;

(3) Centrifuging the white precipitate obtained in the step (2), washing the precipitate with DMF for three times, removing unreacted raw materials, exchanging with anhydrous methanol for three times, and centrifuging and filtering; wherein, the volume consumption of DMF and the volume consumption of absolute methanol for each washing are one third of the DMF consumption in the synthesis reaction;

(4) Drying the solid product obtained in the step (3) in a drying oven at 100-120 ℃ for 6-12 hours, and then drying in a vacuum drying oven at 180-220 ℃ for 10-14 hours to obtain Ce (III) -BDC metal organic complex without solvent;

(5) Performing NH on the Ce (III) -BDC metal organic complex obtained in the step (4) under certain reaction conditions ₃ Reduction of NO _x Cancellation to N ₂ Is used for the catalytic performance of the catalyst.