A low-temperature catalytic methanol oxidation spheroidal catalyst and a preparation method thereof

Abstract

This invention relates to a spherical catalyst for low-temperature catalytic methanol oxidation and its preparation method, belonging to the field of catalyst technology. The steps are as follows: Spherical alumina with a diameter of [diameter missing] is mixed with an appropriate amount of chloroplatinic acid solution, and then dried in an oven to obtain chloroplatinic acid / spherical alumina. Then, the chloroplatinic acid / spherical alumina is placed in a self-made reactor, and methanol gas is introduced to reduce it to obtain platinum / spherical alumina, which is then sealed and stored for later use. This method can produce platinum / spherical alumina with different degrees of reduction.

Description

Technical Field

[0001] This invention relates to a spherical catalyst for low-temperature catalytic methanol oxidation and its preparation method, belonging to the field of catalyst technology. Background Technology

[0002] Methanol is an important organic raw material widely used in formaldehyde production, pesticides, fungicides, pharmaceuticals, agriculture, specialty industries, analytical reagents, antifreeze, cleaning and degreasing agents, and many other fields. Its pollution is widespread in many of these industrial processes. Methanol is not only an important chemical raw material but also a high-performance energy source. The toxicity of methanol has the greatest impact on the human nervous and circulatory systems. It can produce toxic reactions through ingestion via the digestive tract, respiratory tract, or skin. Methanol vapor can damage the respiratory mucosa and vision. In methanol production plants, relevant Chinese authorities stipulate that the concentration of methanol in the air is limited to PC-stel = 50 mg / m³. 3 PC-TWA = 25 mg / m² 3 Workers in areas where methanol fumes are present must wear respirators, and factory wastewater must be treated before discharge, with a permitted methanol concentration of less than 200 mg / L. Furthermore, methanol's metabolic byproducts in the human body, formaldehyde and formic acid, are highly toxic. Therefore, developing efficient technologies for eliminating methanol fumes is of great significance.

[0003] Currently, commonly used technologies for methanol removal include adsorption, photocatalytic degradation, catalytic combustion, plasma degradation, and phytoremediation. Adsorption (physical adsorption) cannot fundamentally eliminate formaldehyde, and the efficiency of the adsorbent gradually decreases or even completely fails over time, greatly limiting its applicability. Photodegradation suffers from slow reaction rates and the easy deactivation of photocatalysts, and requires an external light source, further limiting its applicability. Catalytic combustion is a highly efficient method for removing methanol, but it typically requires external heating facilities and increases energy consumption, also limiting its applicability. Plasma degradation and phytoremediation technologies also cannot be widely used due to their respective drawbacks. Low-temperature catalytic oxidation is an effective method for removing methanol waste gas, offering advantages such as simple process, economic efficiency, and the direct conversion of methanol into less harmful products like carbon dioxide and water. Currently, two types of catalysts are commonly used in the low-temperature catalytic oxidation of methanol: precious metals (platinum, gold, palladium, etc.) and precious metal oxides (such as copper oxide and manganese oxide). Catalysts supported on the precious metal platinum have exhibited very high catalytic activity. However, precious metals are expensive, and in practical applications, it is necessary to ensure efficient room-temperature catalytic oxidation performance while minimizing the amount of precious metal used. Furthermore, catalysts are often prepared in powder form, which creates significant air resistance during use, thus affecting the catalytic effect. Therefore, it is imperative to develop a catalyst that is simple to prepare, has low preparation cost, and can efficiently catalyze the oxidation of methanol at high space velocities. Summary of the Invention

[0004] The purpose of this invention is to provide a simple and low-cost method for preparing a highly efficient catalyst for the room-temperature catalytic oxidation of methanol. Spherical alumina is selected as the support, and a noble metal catalyst is prepared using an equal-volume impregnation-gas-phase reduction method. The equal-volume impregnation method reduces water absorption, significantly shortening the subsequent drying time and saving time and economic costs. High-speed rotary mixing ensures uniform dispersion of the precursor on the support surface, preventing excessive agglomeration of the subsequently reduced elemental platinum, thus improving platinum dispersibility and utilization. Using spherical alumina as the support avoids the high steric hindrance problem under high space velocity conditions, reducing the interference of air resistance on the catalyst's practicality and thus extending its lifespan. Furthermore, using methanol instead of hydrogen as the reducing agent improves the safety and economy of the production process, achieving high catalytic activity while minimizing manufacturing costs.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned objective is as follows: a method for preparing a spherical catalyst for low-temperature catalytic methanol oxidation, characterized by the following steps: using an aqueous solution of chloroplatinic acid and alumina spheres, the chloroplatinic acid solution is rapidly added dropwise to the alumina spheres on a high-speed vortex mixer, wherein the concentration of the chloroplatinic acid aqueous solution is 4.8 mg / ml, and the volume ratio of the chloroplatinic acid aqueous solution to the mass of the alumina spheres is 2.5 ml / 2 g, and then dried at 102 °C; then, five platinum / alumina initiators and chloroplatinic acid / alumina spheres are placed in a self-made gas-phase reduction device to reduce the catalyst, wherein 20 ml of methanol is added to the reduction device, and air is blown into the two-necked flask at a flow rate of 50 ml / min. By means of this method, catalyst products at different positions in the gas-phase reduction device can be taken, and platinum / spherical alumina with different degrees of reduction can be obtained according to their distance from the initiator.

[0006] Preferably, 2g of alumina pellets are placed in a centrifuge tube and rotated at high speed on a vortex for 20s to ensure that the alumina pellets completely and uniformly absorb the aqueous solution, and then dried at 102℃ for 4h.

[0007] Preferably, a layer of chloroplatinic acid / alumina microspheres and five platinum / alumina initiators are placed in a sand core funnel, 20 ml of methanol is added to a flask, and air is blown into the two-necked flask at a flow rate of 50 ml / min. After reacting for a period of time, catalysts with different reduction amounts at different distances from the initiator are obtained.

[0008] Preferably, 2g of alumina microspheres are placed in a centrifuge tube, 2.5mL of chloroplatinic acid aqueous solution with a concentration of 4.8mg / mL is quickly added, and the tube is placed on a vortex and rotated at high speed for 20s to ensure that the alumina microspheres completely and uniformly absorb the aqueous solution. The tube is then dried at 102℃ for 4h.

[0009] A layer of chloroplatinic acid / alumina microspheres and five platinum / alumina initiators were placed in a sintered core funnel. 20 ml of methanol was added to a flask, and air was blown into the two-necked flask at a flow rate of 50 ml / min. After reacting for a period of time, catalysts with different reduction amounts at different distances from the initiators were obtained.

[0010] The first step is to prepare an aqueous solution of chloroplatinic acid. The second step is to place spherical alumina with a diameter of 2.5 mm into a centrifuge tube, quickly add a small amount of chloroplatinic acid solution slightly more than the saturated water absorption volume onto the spheres, and place them on a vortex and rotate them at high speed to mix. The third step is to dry the spheres to obtain white spheres. The fourth step is to place the white spheres in the homemade device shown in the attached figure and reduce them to a low-load noble metal catalyst.

[0011] Compared with existing technologies, the advantages of this invention are as follows: Spherical alumina is used as the support, and the noble metal catalyst is prepared using an equal-volume impregnation-gas-phase reduction method. The equal-volume impregnation method reduces water absorption, significantly lowering subsequent drying time and saving time and economic costs. High-speed rotary mixing ensures uniform dispersion of the precursor on the support surface, preventing excessive agglomeration of the subsequently reduced elemental platinum, thus improving platinum dispersibility and utilization. Using spherical alumina as the support avoids the high steric hindrance problem under high space velocity conditions, reducing the interference of air resistance on catalyst usability and thus improving catalyst lifespan. Furthermore, using methanol instead of hydrogen as the reducing agent improves the safety and economy of the production process, minimizing manufacturing costs while maintaining high catalytic activity. Attached Figure Description

[0012] The present invention will be further described below with reference to the accompanying drawings.

[0013] Figure 1 XPS images of Sample 1 and Sample 2

[0014] Figure 2 For a self-made methanol gas thermal reduction oxidation device

[0015] Figure 3 Scanning electron microscope image of platinum / alumina Detailed Implementation

[0016] Example 1

[0017] The present invention will be further described in detail below with reference to the embodiments.

[0018] Example 1: In this example, spherical alumina was used as the carrier, chloroplatinic acid as the precursor, and the platinum loading was 0.226%. The specific preparation steps are as follows:

[0019] Take 2g of alumina microspheres into a centrifuge tube, quickly add 2.5mL of chloroplatinic acid aqueous solution with a concentration of 4.8mg / mL, and place it on a vortex and rotate at high speed for 20s to ensure that the alumina microspheres completely and uniformly absorb the aqueous solution. Dry at 102℃ for 4h.

[0020] A layer of chloroplatinic acid / alumina microspheres and five platinum / alumina initiators were placed in a sintered core funnel. 20 ml of methanol was added to a flask, and air was blown into the two-necked flask at a flow rate of 50 ml / min. After reacting for a period of time, catalysts with different reduction amounts at different distances from the initiators were obtained. Figure 2 For the self-made methanol gas thermal reduction device, two layers of small balls are placed in a self-made sand core funnel. The upper layer is the initiator and the lower layer is chloroplatinic acid / alumina.

[0021] In the experiment, we found that the original platinum / alumina mixture exhibited varying colors, with the spheres closer to the platinum / alumina catalyst initiator showing a darker color, indicating more complete reduction of chloroplatinic acid. The XPS of the prepared Pt / Al₂O₃ was then analyzed. Figure 3-2 This also confirms that the darker the sample, the less residual chloroplatinic acid it contains. In the figure, Sample 1 and Sample 2 are catalyst products taken from different locations in the reaction apparatus. Sample 1 is closer to the catalytic initiator, so it receives more heat. Under the experimental conditions, the in-situ reduction ratio of chloroplatinic acid in the final obtained Pt / Al2O3 microsphere catalyst ranged from 71.37% to 88.9%, corresponding to the two extreme values ​​of being furthest and closest to the catalytic initiator, respectively.

[0022] The present invention is not limited to the specific technical solutions described in the above embodiments. All technical solutions formed by equivalent substitutions are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a spherical catalyst for low-temperature catalytic methanol oxidation, characterized in that: Includes the following steps: Take 2g of alumina microspheres into a centrifuge tube, quickly add 2.5 mL of chloroplatinic acid aqueous solution with a concentration of 4.8 mg / mL, and place it on a vortex and rotate at high speed for 20 s to ensure that the alumina microspheres completely and uniformly absorb the aqueous solution. Dry at 102℃ for 4 h. Place a layer of chloroplatinic acid / alumina microspheres and five platinum / alumina initiators in a sintered sand funnel. Add 20 mL of methanol to a flask and blow air into the two-necked flask at a flow rate of 50 mL / min. After reacting for a period of time, catalysts with different reduction amounts at different distances from the initiator are obtained. The reduction is carried out using a self-made methanol gas thermal reduction apparatus. Place two layers of microspheres in a self-made sintered sand funnel, with the upper layer being the initiator and the lower layer being chloroplatinic acid / alumina. The platinum / alumina obtained from the reduction has different shades of color. The closer the microspheres are to the platinum / alumina catalyst initiator, the darker the color, indicating that the chloroplatinic acid is reduced more completely.

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