SELECTIVE HYDROGENATION COPPER-BASED CATALYST WITH EXCELLENT THERMAL STABILITY AND ITS PREPARATION METHOD

Abstract

Cu-based catalysts with excellent thermal stability for selective hydrogenation and a preparation method thereof are provided. The method includes: first, six mixed metal salts are instantaneously nucleated in an alkaline solution by the nucleation/crystallization isolation method, to prepare high-entropy composite metal hydroxides (H-LDHs) with uniform element distribution and similar metal proportions. Furthermore, well-crystallized high-entropy oxides (HEOs) are obtained based on the structural topology characteristics of H-LDHs, and a series of Cu-Mx/HEOs catalysts with flexible adjustable catalytic microzone geometries and electronic structures are obtained using the HEOs as precursors.

Claims

1. A method for preparing Cu-based selective hydrogenation catalysts, comprising steps as follows: (1) Dissolving M.sup.2+ and M.sup.3+ metal salts with an M.sup.2+/M.sup.3+ ion molar ratio of 2-3:1 in deionized water to prepare a mixed salt solution, wherein the M.sup.2+ salts is a mixture of three types of salts, in which Cu salts is indispensable, further the M.sup.2+ salts is a mixture of Cu(NO.sub.3).sub.2.Math.3H.sub.2O and any two of Zn(NO.sub.3).sub.2.Math.6H.sub.2O, Mg(NO.sub.3).sub.2.Math.6H.sub.2O, Co(NO.sub.3).sub.2.Math.6H.sub.2O, Ni(NO.sub.3).sub.2.Math.6H.sub.2O; the M.sup.3+ salts is a mixture of any three types of salts seleced from Ga(NO.sub.3).sub.3.Math.3H.sub.2O, Al(NO.sub.3).sub.3.Math.9H.sub.2O, Fe(NO.sub.3).sub.3.Math.9H.sub.2O, Mn(NO.sub.3).sub.4.Math.4H.sub.2O, and Cr(NO.sub.3).sub.3.Math.9H.sub.2O; the total concentration of metal ions in the mixed salt solution is 0.12-0.36 mol.Math.1.sup.1, wherein Cu ions account for 15-20% of the total molar amount of metal ions, the other two types of M.sup.2+ metal ions have similar concentrations, and together account for 35-40% of the total molar amount of metal ions, and the remaining three types of M.sup.3+ metal ions have similar concentrations, and together account for 40-50% of the total molar amount of metal ions; furthermore dissolving a mix of any two of NaOH, KOH, Na.sub.2CO.sub.3, or NaHCO.sub.3 in deionized water to prepare an alkaline solution with a concentration of 0.12-0.36 mol.Math.1.sup.1; (2) starting nucleation reactor, setting the stator-rotor gap of the nucleation reactor to 0.1-1 mm and the speed to 1000-3000 rpm, feeding the mixed salt solution and the alkaline solution in step (1) into the reactor at the same rate of 10-30 ml.Math.min.sup.1 with a peristaltic pump to nucleate rapidly and controling the total number of metal cations in the salt solution to be equal to the number of anions in the alkaline solution, and collecting the nucleation slurry at the outlet; (3) transfering the nucleation slurry to a crystallization vessel, and crystallizing and growing at 60-120 C. for 6-18 hours, cooling naturally to room temperature, centrifuging and washing the crystallization product with deionized water to neutrality, drying in a freeze dryer for 12-24 hours to obtain hexa-element layered composite metal hydroxide high-entropy hydrotalcite denoted as HEHs, with a configurational entropy value Sconfig>1.5 R; (4) heating the HEHs obtained in step (3) with a heating rate of 5-10 C..Math.min.sup.1 to 400-800 C. in air atmosphere and calcining for 3-6 hours to obtain hexa-element high-entropy oxides denoted as HEOs; (5) heating with a rate of 2-10 C./min to 400-800 C. and reducing the HEHs obtained in step (4) in a 10-20 vol. H.sub.2/N.sub.2 atmosphere for 3-6 hours to obtain Cu-Mx/HEOs catalysts.

2. The preparation method according to claim 1, wherein in step (1), the molar ratio of M.sup.2+/M.sup.3+ metal ions in the mixed salt solution is 2-2.2:1.

3. Selective hydrogenation Cu-based catalysts prepared by the preparation method according to claim 1, wherein the catalysts are represented as Cu-Mx/HEOs, where Cu is the active component, M is a reducible auxiliary metal selected from Zn, Fe, Co, Cr, Ni, Ga, Ti, and Mn, x represents the ratio of M to active metal Cu, x is 1 to 5, and HEOs represents the Cu-based high-entropy oxide carrier, wherein the elemental composition in the carrier is Cu and M.sub.1-5 which denotes a mixture of any five of Zn, Mg, Co, Ga, Al, Fe, Mn, Ni, and Cr.

4. Selective hydrogenation Cu-based catalysts according to claim 3, wherein in Cu-Mx/HEOs, M is Co or Fe; M.sub.1-5 is a mixture of Zn, Co, Fe, Ga, and Al.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is the X-ray diffraction (XRD) spectrum of the catalyst precursor HEOs prepared in embodiment 1, indicating a well-defined spinel crystal structure.

[0019] FIG. 2 is the HR-TEM image of the catalyst prepared in embodiment 1, indicating a well-defined carrier crystal structure with some metals reduced to particles.

[0020] FIG. 3 is the Cu 2p XPS spectrum of the catalyst prepared in embodiment 1, indicating that most of the Cu in the carrier is reduced to Cu0/Cu+.

[0021] FIG. 4 is the experimental results of the acetylene selective hydrogenation reaction using the catalyst prepared in embodiment 1, wherein A is the curve of acetylene conversion rate versus temperature, and B is the curve of acetylene selectivity versus acetylene conversion rate.

[0022] FIG. 5 is the stability results of the acetylene selective hydrogenation reaction using the catalyst prepared in embodiment 1, wherein A is the curve of acetylene conversion rate versus time, and B is the curve of acetylene selectivity versus time.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] In order to better illustrate the technological process and technical advantages of the present application, the following embodiments are used to illustrate the effect of the application. But the present application is not limited to the content of the embodiment.

[0024] Unless otherwise specified, percentages in embodiments of the present application are percentages by mass; The raw materials used are all conventional types of raw materials in the field that can be purchased in the market; The methods used are all conventional methods in the art (including detection methods); The equipment used is all conventional equipment in the field.

Embodiment 1

[0025] (1) Dissolve 1.64 g Cu(NO.sub.3).sub.2.Math.3H.sub.2O, 2.36 g Zn(NO.sub.3).sub.2.Math.6H.sub.2O, 2.05 g Mg(NO.sub.3).sub.2.Math.6H.sub.2O, 1.62 g Fe(NO.sub.3).sub.3.Math.9H.sub.2O, 1.02 g Ga(NO.sub.3).sub.3.Math.3H.sub.2O, and 1.5 g Al(NO.sub.3).sub.3.Math.9H.sub.2O in 100 ml deionized water to prepare a mixed salt solution; dissolve 2.03 g Na.sub.2CO.sub.3 and 1.84 g NaOH in 100 ml deionized water to prepare an alkali solution. [0026] (2) Start the nucleation reactor, set the stator-rotor gap to 0.2 mm, and the speed to 3000 rpm. Use a peristaltic pump to deliver the mixed salt solution and alkali solution prepared in step (2) to the reactor at a rate of 20 ml/min for rapid nucleation, and collect the nucleation slurry at the slurry outlet. [0027] (3) Add the nucleation slurry to a three-neck flask, crystallize and grow at 60 C. in water bath for 12 hours, naturally cool to room temperature, centrifuge to separate the crystallization product, and wash with deionized water to neutrality. Freeze-dry the product for 12 hours to obtain the layered composite metal high-entropy hydroxide precursor CuZnMgFeGaAl-LDHs, with an entropy value of 1.65 R. [0028] (4) The CuZnMgFeGaAl-LDHs precursor obtained in step (3) is heated to 600 C. at a rate of 5 C./min in air atmosphere and calcined for 4 hours to obtain the corresponding composite metal high-entropy oxide CuZnMgFeGaAl-HEOs. [0029] (5) Reduce the CuZnMgFeGaAl-HEOs obtained in step (4) to 600 C. at a rate of 10 C./min in a 10 vol. % H.sub.2/N.sub.2 atmosphere for 4 hours. Some Cu and Fe in the precursor are partially reduced, and the catalyst Cu-Fe/HEOs with a Cu/Fe ratio of 1:1 is obtained.

[0030] Apply the prepared catalyst to acetylene selective hydrogenation reaction experiments as the following steps:

[0031] Mix 200 mg catalyst with 1.8 g quartz sand with a particle size of 40-70 mesh and load it into a quartz reaction tube with a diameter of 10 mm. Before the reaction, activate the sample at 150 C. in a 10 vol. % H.sub.2/N.sub.2 mixed gas for 2 hours and naturally cool to room temperature. The testing temperature ranges from 100 to 220 C., with the gas composition of 0.71% acetylene and 2.86% hydrogen and 70.72% ethylene and balanced nitrogen. The test pressure is 1 bar, and the space velocity is 3800 h1. The composition and content of reactants and products are analyzed by gas chromatography, and data processing is performed by normalization. To ensure test accuracy, results are recorded after maintaining the specified temperature for 30 minutes. Three sets of tests are conducted, and the average value represents the catalytic performance data at that temperature, as shown in FIG. 4. When the catalyst performance is stable during the tests, a long-term stability evaluation is performed. Tests are conducted every 100 hours when the acetylene conversion rate is 100% and the ethylene selectivity is >95%, for a total of 500 hours, as shown in FIG. 5.

Embodiment 2

[0032] (1) Dissolve 1.64 g Cu(NO.sub.3).sub.2.Math.3H.sub.2O, 2.36 g Zn(NO.sub.3).sub.2.Math.6H.sub.2O, 2.05 g Mg(NO.sub.3).sub.2.Math.6H.sub.2O, 1.62 g Fe(NO.sub.3).sub.3.Math.9H.sub.2O, 1.02 g Ga(NO.sub.3).sub.3.Math.3H.sub.2O, and 1.5 g Al(NO.sub.3).sub.3.Math.9H.sub.2O in 100 ml deionized water to prepare a mixed salt solution; dissolve 2.03 g Na.sub.2CO.sub.3 and 2.36 g KOH in 100 ml deionized water to prepare an alkali solution. [0033] (2) Start the nucleation reactor, set the stator-rotor gap to 0.1 mm, and the speed to 1500 rpm. Use a peristaltic pump to respectively deliver the mixed salt solution and alkali solution from step (1) into the reactor at a rate of 30 ml/min for rapid nucleation, and collect the nucleation slurry at the slurry outlet. [0034] (3) Add the nucleation slurry to a three-neck flask, crystallize and grow at 80 C. in water bath for 18 hours, naturally cool to room temperature, centrifuge to separate the crystallization product, and wash with deionized water to neutrality. Freeze-dry the product for 24 hours to obtain the layered composite metal high-entropy hydroxide precursor CuZnMgFeGaAl-LDHs, with an entropy value of 1.55 R. [0035] (4) The CuZnMgFeGaAl-LDHs precursor obtained in step (3) is heated to 600 C. at a rate of 5 C./min in air atmosphere and calcined for 3 hours to obtain the corresponding composite metal high-entropy oxide CuZnMgFeGaAl-HEOs. [0036] (5) Reduce the CuZnMgFeGaAl-HEOs obtained in step (4) to 800 C. at a rate of 10 C./min in a 10 vol. % H.sub.2/N.sub.2 atmosphere for 5 hours. Cu and Fe in the precursor are partially reduced, and the catalyst Cu-Fe/HEOs with a Cu/Fe ratio of 1:2 is obtained.

Embodiment 3

[0037] (1) Dissolve 1.64 g Cu(NO.sub.3).sub.2.Math.3H.sub.2O, 2.38 g Co(NO.sub.3).sub.2.Math.6H.sub.2O, 2.05 g Mg(NO.sub.3).sub.2.Math.6H.sub.2O, 1.62 g Fe(NO.sub.3).sub.3.Math.9H.sub.2O, 1.02 g Ga(NO.sub.3).sub.3.Math.3H.sub.2O, and 1.5 g Al(NO.sub.3).sub.3.Math.9H.sub.2O in 100 ml deionized water to prepare a mixed salt solution; dissolve 2.03 g Na.sub.2CO.sub.3 and 1.84 g NaOH in 100 ml deionized water to prepare an alkali solution. [0038] (2) Start the nucleation reactor, set the stator-rotor gap to 0.2 mm, and the speed to 3000 rpm. Use a peristaltic pump to respectively deliver the mixed salt solution and alkali solution from step (1) into the reactor at a rate of 20 ml/min for rapid nucleation, and collect the nucleation slurry at the slurry outlet. [0039] (3) Add the nucleation slurry to a three-neck flask, crystallize and grow at 70 C. in water bath for 6 hours, naturally cool to room temperature, centrifuge to separate the crystallization product, and wash with deionized water to neutrality. Freeze-dry the product for 12 hours to obtain the layered composite metal high-entropy hydroxide precursor CuCoMgFeGaAl-LDHs, with an entropy value of 1.70 R. [0040] (4) The CuCoMgFeGaAl-LDHs precursor obtained in step (3) is heated to 600 C. at a rate of 5 C./min in air atmosphere and calcined for 3 hours to obtain the corresponding composite metal high-entropy oxide CuCoMgFeGaAl-HEOs. [0041] (5) Reduce the CuCoMgFeGaAl-HEOs obtained in step (4) to 600 C. at a rate of 10 C./min in a 10 vol. % H.sub.2/N.sub.2 atmosphere for 6 hours. Cu and Co in the precursor are partially reduced, and the catalyst Cu-Co/HEOs with a Cu/Co ratio of 1:1 is obtained.

Embodiment 4

[0042] (1) Dissolve 1.64 g Cu(NO.sub.3).sub.2.Math.3H.sub.2O, 2.35 g/Ni(NO.sub.3).sub.2.Math.6H.sub.2O, 2.05 g Mg(NO.sub.3).sub.2.Math.6H.sub.2O, 1.62 g Fe(NO.sub.3).sub.3.Math.9H.sub.2O, 1.02 g Ga(NO.sub.3).sub.3.Math.3H.sub.2O, and 1.5 g Al(NO.sub.3).sub.3.Math.9H.sub.2O in 100 ml deionized water to prepare a mixed salt solution; dissolve 2.03 g Na.sub.2CO.sub.3 and 1.84 g NaOH in 100 ml deionized water to prepare an alkali solution. [0043] (2) Start the nucleation reactor, set the stator-rotor gap to 0.2 mm, and the speed to 3000 rpm. Use a peristaltic pump to respectively deliver the mixed salt solution and alkali solution from step (1) into the reactor at a rate of 20 ml/min for rapid nucleation, and collect the nucleation slurry at the slurry outlet. [0044] (3) Add the nucleation slurry to a three-neck flask, crystallize and grow at 70 C. for 6 hours, naturally cool to room temperature, centrifuge to separate the crystallization product, and wash with deionized water to neutrality. Freeze-dry the product for 12 hours to obtain the layered composite metal high-entropy hydroxide precursor CuMgNiFeGaAl-LDHs, with an entropy value of 1.65 R. [0045] (4) The CuMgNiFeGaAl-LDHs precursor obtained in step (3) is heated to 600 C. at a rate of 5 C./min in air atmosphere and calcined for 4 hours to obtain the corresponding composite metal high-entropy oxide CuMgNiFeGaAl-HEOs. [0046] (5) Reduce the CuMgNiFeGaAl-HEOs obtained in step (4) to 600 C. at a rate of 10 C./min in a 10 vol. % H.sub.2/N.sub.2 atmosphere for 5 hours. Cu and Ni in the precursor are partially reduced, and the catalyst Cu-Ni/HEOs with a Cu/Fe ratio of 1:1 is obtained.

Embodiment 5

[0047] (1) Dissolve 1.64 g Cu(NO.sub.3).sub.2.Math.3H.sub.2O, 2.35 g Ni(NO.sub.3).sub.2.Math.6H.sub.2O, 2.05 g Mg(NO.sub.3).sub.2.Math.6H.sub.2O, 1.62 g Fe(NO.sub.3).sub.3.Math.9H.sub.2O, 1.62 g Cr(NO.sub.3).sub.3.Math.3H.sub.2O, and 1.5 g Al(NO.sub.3).sub.3.Math.9H.sub.2O in 100 ml deionized water to prepare a mixed salt solution; dissolve 2.03 g Na.sub.2CO.sub.3 and 1.84 g NaOH in 100 ml deionized water to prepare an alkali solution. [0048] (2) Start the nucleation reactor, set the stator-rotor gap to 0.2 mm, and the speed to 3000 rpm. Use a peristaltic pump to respectively deliver the mixed salt solution and alkali solution from step (1) into the reactor at a rate of 20 ml/min for rapid nucleation, and collect the nucleation slurry at the slurry outlet. [0049] (3) Add the nucleation slurry to a three-neck flask, crystallize and grow at 70 C. for 6 hours, naturally cool to room temperature, centrifuge to separate the crystallization product, and wash with deionized water to neutrality. Freeze-dry the product for 12 hours to obtain the layered composite metal high-entropy hydroxide precursor CuMgNiFeCrAl-LDHs, with an entropy value of 1.75 R. [0050] (4) The CuMgNiFeCrAl-LDHs precursor obtained in step (3) is heated to 600 C. at a rate of 5 C./min in air atmosphere and calcined for 5 hours to obtain the corresponding composite metal high-entropy oxide CuMgNiFeCrAl-HEOs. [0051] (5) Reduce the CuMgNiFeCrAl-HEOs obtained in step (4) to 800 C. at a rate of 10 C./min in a 10 vol. % H.sub.2/N.sub.2 atmosphere for 5 hours. Cu and Ni in the precursor are partially reduced, and the catalyst Cu-Ni/HEOs with a Cu/Fe ratio of 1:2 is obtained.