Platinum-supported high-performance VOCs catalysts, their preparation methods and applications

Abstract

This invention discloses a platinum-supported high-performance VOCs catalyst, its preparation method, and its applications. The preparation method of the platinum-supported high-performance VOCs catalyst includes: adding an aqueous solution of platinum salt dropwise onto the surface of a metal support to obtain a catalyst precursor; aging, purifying, drying, and calcining the catalyst precursor sequentially to obtain the platinum-supported high-performance VOCs catalyst. The platinum-supported high-performance VOCs catalyst of this invention uses perovskite-type LaAlO3 as the metal support, which reduces the preparation cost of the catalyst. Compared with traditional commercial noble metal catalysts, the high-performance VOCs catalyst of this invention has an extremely low noble metal loading, further reducing costs. The platinum-supported high-performance VOCs catalyst prepared by this invention exhibits excellent low-temperature catalytic oxidation performance of toluene, as well as excellent water resistance and stability.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a platinum-supported high-performance VOCs catalyst, its preparation method, and its applications. Background Technology

[0002] Volatile organic compounds (VOCs) are a class of complex organic pollutants that are widely present in indoor and outdoor air. Benzene series compounds, as typical aromatic VOCs, usually have an irritating odor and are toxic. They are identified as carcinogens by the World Health Organization. Their sources mainly include the combustion of fossil fuels and emissions from various industrial production processes (Ziemann PJ, Atkinson R. Kinetics, products, and mechanisms of secondary organic aerosol formation [J]. Chemical Society Reviews, 2012, 41(19): 6582-605.).

[0003] Current VOCs control technologies can be mainly divided into two categories: source control and end-of-pipe control. Source control aims to address the issue at the generation stage of pollutants by reducing the use of VOCs-containing raw materials, improving production processes and equipment, and promoting cleaner production methods to reduce VOCs generation and emissions. Although source control of VOCs is the most direct and effective approach, saving raw materials and improving product quality, in actual production, due to technological limitations, it is still difficult to completely avoid emissions of VOCs at different concentrations. Therefore, source control is quite challenging to implement.

[0004] Currently, more reliance is placed on end-of-pipe treatment technologies. Catalytic oxidation, as a common end-of-pipe control method, is based on the complete oxidation of VOCs into carbon dioxide and water at relatively low temperatures in the presence of a catalyst, without producing secondary pollution. It is considered a VOCs control technology with broad application prospects.

[0005] Catalysts are crucial for catalytic oxidation technology. Currently, supported catalysts are the most widely used. These catalysts use noble metals (such as Pt, Pd, Au, Rh, and Ru) as active components, and commonly employ materials such as molecular sieves, activated carbon, silicon carbide, Al₂O₃, SiO₂, and MgO as supports. Cordierite honeycomb is frequently used in commercial monolithic catalysts. However, supported catalysts generally suffer from high costs, and the noble metal active components are prone to aggregation or detachment during the reaction, leading to catalyst deactivation. Therefore, current research focuses on minimizing catalyst costs while maintaining good activity and stability. Simultaneously, it is necessary to actively explore novel support materials to enhance the interaction between the active component and the support, further improving catalytic activity and stability. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing a platinum-supported high-performance VOCs catalyst.

[0007] Another object of the present invention is to provide a high-performance VOCs catalyst supported on platinum obtained by the above preparation method.

[0008] Another object of the present invention is to provide the use of the above-mentioned high-performance VOCs catalyst in the catalytic oxidation of benzene compounds.

[0009] The objective of this invention is achieved through the following technical solutions.

[0010] A method for preparing a platinum-supported high-performance VOCs catalyst includes: adding an aqueous solution of platinum salt to the surface of a metal support to obtain a catalyst precursor; aging, purifying, drying, and calcining the catalyst precursor sequentially to obtain the platinum-supported high-performance VOCs catalyst; wherein, by mass fraction, the ratio of platinum to metal support in the aqueous solution of platinum salt is (0.005~0.01):(99.99~99.995); the metal support is perovskite-type LaAlO3; and the calcination includes constant temperature calcination at 450~500℃ for 3~5 hours.

[0011] In the above technical solution, the method for obtaining a platinum salt aqueous solution includes: mixing platinum salt and water, stirring until uniform, to obtain the platinum salt aqueous solution.

[0012] In the above technical solution, the concentration of platinum in the platinum salt aqueous solution is 3~12 mg / mL.

[0013] In the above technical solution, the stirring speed is 200~400 rpm and the stirring time is 30~60 min.

[0014] In the above technical solution, the platinum salt includes: Pt(NO3)2.

[0015] In the above technical solution, the aging process includes: standing in air at 25~30℃ and 60~80% relative humidity for 1~3 hours.

[0016] In the above technical solution, the purification includes washing the aged catalyst precursor with water and anhydrous ethanol in sequence.

[0017] In the above technical solution, the drying adopts supercritical CO2 drying technology, the drying temperature is 40~50℃, the drying pressure is 10~15MPa, and the drying time is 4~6h.

[0018] In the above technical solution, the heating rate to 450~500℃ is 2~5℃ / min.

[0019] In the above technical solution, the method for preparing the metal support includes: mixing a lanthanum metal source, an aluminum metal source, and water uniformly to obtain a first solution; adding citric acid and ethylene glycol to the first solution and mixing uniformly to obtain a homogeneous solution; wherein, by molar fraction, the ratio of lanthanum in the lanthanum metal source, aluminum in the aluminum metal source, citric acid, and ethylene glycol is 1:1:(1~1.5):(1~2.5); drying the homogeneous solution; and calcining it at 800~900℃ for 4~6 hours to obtain the metal support.

[0020] In the above technical solution, the lanthanum metal source includes lanthanum nitrate hexahydrate, and the aluminum metal source includes aluminum nitrate nonahydrate.

[0021] In the above technical solution, the ratio of the molar amount of lanthanum metal source to the volume fraction of water in the first solution is 1:(6000~7000), with the molar amount in mol and the volume fraction in mL.

[0022] In the above technical solution, the uniform mixing includes stirring at a speed of 500~700 rpm for 30~60 minutes.

[0023] In the above technical solution, the drying temperature of the homogeneous solution is 100~120℃, and the drying time of the homogeneous solution is 24~36h.

[0024] The platinum-supported high-performance VOCs catalyst obtained by the above preparation method.

[0025] The application of the above-mentioned high-performance VOCs catalysts in the catalytic oxidation of benzene compounds.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. The platinum-supported high-performance VOCs catalyst prepared in this invention uses perovskite-type LaAlO3 as a metal support, which reduces the preparation cost of the catalyst. Compared with traditional commercial noble metal catalysts, the high-performance VOCs catalyst of this invention has an extremely low noble metal (Pt) loading, which further reduces the cost and provides a new technical route for the industrial production of noble metal catalysts.

[0028] 2. The preparation method of the present invention uses an impregnation method to prepare a high-performance VOCs catalyst with perovskite-type LaAlO3 as the metal support and extremely low content of Pt as the active component. Compared with the traditional wet chemical method, which is prone to causing the formation of clusters of active noble metals on the catalyst surface and reducing catalytic activity, the Pt element in the VOCs catalyst of the present invention does not undergo clustering, and the active sites exist in a single-atom dispersed form, which makes the active sites in the catalyst have ultra-high utilization efficiency. This is beneficial to improving catalytic activity and saving catalyst usage costs.

[0029] 3. The platinum-supported high-performance VOCs catalyst prepared by this invention has excellent low-temperature catalytic oxidation performance of toluene, and also has excellent water resistance and stability. Attached Figure Description

[0030] Figure 1 XRD patterns of the perovskite-type LaAlO3 catalyst of Example 1 and the platinum-supported high-performance VOCs catalyst of Example 2;

[0031] Figure 2 (a) Nitrogen physical adsorption-desorption curves and (b) pore size distribution diagrams of the perovskite-type LaAlO3 catalyst of Example 1 and the platinum-supported high-performance VOCs catalyst of Example 2.

[0032] Figure 3 The figures are TEM and EDXS-Mapping images, where a and b are TEM images of perovskite-type LaAlO3 of Example 1 at different magnifications, c is the EDXS-Mapping image of perovskite-type LaAlO3 of Example 1, d and e are TEM images of platinum-supported high-performance VOCs catalyst of Example 2 at different magnifications, and f is the EDXS-Mapping image of platinum-supported high-performance VOCs catalyst of Example 2.

[0033] Figure 4 XPS diagrams of the perovskite-type LaAlO3 catalyst of Example 1 and the platinum-supported high-performance VOCs catalyst of Example 2 are shown, where a is the La 3d XPS pattern, b is the Al 2p and Pt 4f XPS pattern, c is the Al 2s XPS pattern, and d is the O 1s XPS pattern.

[0034] Figure 5Toluene conversion of the platinum-supported high-performance VOCs catalyst in Example 2 and the VOCs catalysts in Examples 3-7;

[0035] Figure 6 The figure shows the water resistance and stability test results of the platinum-supported high-performance VOCs catalyst in Example 2. Detailed Implementation

[0036] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0037] In the following examples, the water used is ultrapure water.

[0038] The sources and purities of the reagents used in the following examples and tests are as follows:

[0039]

[0040] The instrument information used in the following embodiments and tests is as follows:

[0041]

[0042] Example 1

[0043] A method for preparing perovskite-type LaAlO3 (LAO) includes: mixing a lanthanum metal source (lanthanum nitrate hexahydrate), an aluminum metal source (aluminum nitrate nonahydrate), and water, stirring for 60 min to obtain a first solution, wherein the molar ratio of the lanthanum metal source to the volume fraction of water in the first solution is 1:6416, with the molar ratio in mol and the volume fraction in mL; adding citric acid and ethylene glycol to the first solution, stirring for 60 min to obtain a homogeneous solution, wherein the molar ratio of lanthanum in the lanthanum metal source, aluminum in the aluminum metal source, citric acid, and ethylene glycol is 1:1:1:1; drying the homogeneous solution at 100℃ for 24 h, grinding until homogeneous, and then calcining at 850℃ for 4 h to obtain perovskite-type LaAlO3 (LAO), wherein the stirring speed is 500 rpm.

[0044] Example 2

[0045] A method for preparing a platinum-supported high-performance VOCs catalyst includes: mixing platinum salt (Pt(NO3)2) and water, stirring at 200 rpm for 30 min until homogeneous, to obtain a platinum salt aqueous solution, wherein the platinum concentration in the platinum salt aqueous solution is 6 mg / mL; applying ultrasound at a frequency of 40 kHz to a metal support, while simultaneously using a precision titration pump to uniformly drop the platinum salt aqueous solution onto the surface of the metal support, to obtain a catalyst precursor. The cavitation effect of the ultrasonic field can significantly improve the mass transfer efficiency of the platinum salt aqueous solution within the narrow pores of the metal support; and sequentially aging, purifying, drying, and calcining the catalyst precursor. Calcination was performed to obtain a platinum-supported high-performance VOCs catalyst (0.005% Pt / LAO), wherein, by mass fraction, the ratio of platinum to metal support in the platinum salt aqueous solution was 0.005:99.995, and the metal support was the perovskite-type LaAlO3 of Example 1. The calcination included: heating to 450°C at a rate of 2°C / min under a dry air flow of 50 mL / min, and calcining at a constant temperature for 4 hours to completely decompose the Pt salt, form Pt species with high catalytic activity, and strengthen the interfacial bonding between Pt species and metal support through solid-phase reaction to form a stable and highly active catalytic center.

[0046] The aging process includes standing in air at 25°C and 80% relative humidity for 2 hours. The purpose of aging is to allow Pt ions to fully chemically bond and rearrange with the activation sites (such as hydroxyl groups and oxygen vacancies) on the surface of the metal carrier, thereby achieving the transformation from physical adsorption to chemical anchoring.

[0047] Purification includes washing the aged catalyst precursor twice with water, centrifuging, washing once with anhydrous ethanol, and centrifuging again. The centrifugation speed is 5000 rpm and the centrifugation time is 10 minutes each time. This process can effectively remove residual nitrate ions.

[0048] Supercritical CO2 drying technology was used: the purified catalyst precursor was mixed with anhydrous ethanol and placed in a high-pressure reactor. CO2 was introduced at a flow rate of 1 L / h, the temperature was raised to 40℃, the pressure was raised to 10 MPa and maintained for 4 h. After cooling to room temperature, the pressure was slowly released to complete the drying.

[0049] Examples 3-7 (for comparison)

[0050] A method for preparing a VOCs catalyst is basically the same as in Example 2, except that the "platinum salt" in Example 2 is replaced with a "noble metal salt", the noble metal salt is X, the concentration of the noble metal element in the noble metal salt aqueous solution is Y, the metal support is Z, and the ratio of the noble metal element to the metal support in the noble metal salt solution by mass fraction is 0.005:99.995. X, Y and Z are shown in Table 1.

[0051] Table 1

[0052]

[0053] The perovskite-type LaAlO3 (LAO) catalyst of Example 1 and the platinum-supported high-performance VOCs catalyst (0.005% Pt / LAO) of Example 2 were used as catalysts, respectively. The XRD diffraction patterns of the catalysts of Example 1 and Example 2 were detected using an X-ray diffractometer. Figure 1 As shown. By Figure 1 It can be seen that both LAO and 0.005% Pt / LAO exhibit good crystallization characteristics, and their characteristic diffraction peaks correspond to the (012), (110), (202), (024), (122), (214), (220), (312), and (128) crystal planes of the hexagonal crystal system (R-3m space group) LaAlO3 (PDF#31-0022). In addition, no obvious lattice distortion phenomenon was observed in the spectrum, and the positions and intensities of each characteristic peak were basically consistent, indicating that the introduction of trace Pt element (0.005wt%) did not cause any change in the crystal structure of perovskite-type LaAlO3.

[0054] The nitrogen physical adsorption-desorption curves of the perovskite-type LaAlO3 (LAO) catalyst of Example 1 and the platinum-supported high-performance VOCs catalyst (0.005% Pt / LAO) of Example 2 were tested using a specific surface area and pore size analyzer, and their pore size distribution was calculated. The results are as follows: Figure 2 As shown. By Figure 2 It can be seen that both LAO and 0.005%Pt / LAO exhibit type IV adsorption isotherms and type H3 hysteresis loops, and the corresponding pore size distribution is mainly concentrated below 20 nm, indicating that the pores in the catalyst are mainly mesoporous. The mesoporous structure can effectively disperse the active components to avoid agglomeration, thereby enhancing the catalytic performance of the catalyst.

[0055] TEM and EDXS-Mapping images of the catalysts in Examples 1 and 2 were determined using transmission electron microscopy, as shown below. Figure 3 As shown. Figure 3 Images a and b are TEM images of perovskite-type LaAlO3 from Example 1 at different magnifications. Figure 3 c is the EDXS-Mapping diagram of perovskite-type LaAlO3 in Example 1. Figure 3 d and e are TEM images of the platinum-supported high-performance VOCs catalyst of Example 2 at different magnifications. Figure 3 It can be seen that the catalysts all exhibit irregular particulate morphology, and the addition of Pt did not change their basic structure. No Pt clusters were observed in the TEM image. Figure 3The uniform distribution of Pt, O, Al and La elements in the EDXS-Mapping of the platinum-supported high-performance VOCs catalyst in Example 2 indicates that Pt is highly dispersed in the 0.005% Pt / LAO catalyst. The high dispersion of the active component (platinum element) is beneficial to improving the catalyst's catalytic oxidation performance for pollutants.

[0056] The XPS spectra of the catalysts in Examples 1 and 2 were determined using X-ray photoelectron spectroscopy, as shown below. Figure 4 As shown. By Figure 4 It can be seen that after loading a trace amount of Pt (0.005 wt%) onto perovskite-type LaAlO3, the oxidation states of La and Al elements in the catalyst remained essentially unchanged, but the surface adsorbed oxygen (O2) in the O element... α ) decreases, lattice oxygen (O) β With increased lattice oxygen, the catalytic activity of the catalyst increases, as lattice oxygen is more catalytic than surface-adsorbed oxygen.

[0057] The platinum-supported high-performance VOCs catalyst of Example 2 and the VOCs catalysts of Examples 3-7 were used as catalysts, and the catalytic oxidation performance of each catalyst was determined according to the method described in "Catalytic Reaction Processes and Control Technologies of Volatile Organic Pollutants" edited by Hao Zhengping et al. (Science Press, 2024: 471-475). The specific operation method included: 0.1 g of catalyst was loaded into a quartz tube, and the quartz tube was placed inside a heatable fixed-bed reactor. Reaction gas was introduced into the fixed-bed reactor through the inlet, and the heating program was started to heat the fixed-bed reactor to temperature T℃. The reaction gas passed through the catalyst and reacted. The reaction tail gas discharged from the fixed-bed reactor was connected to the gas chromatograph inlet. After 30 min of reaction, the concentration of toluene in the reaction tail gas was collected and detected. The toluene conversion rate of the catalyst was calculated. The formula for calculating the toluene conversion rate is as follows:

[0058]

[0059] in, The concentration of toluene (ppm) at the inlet of the fixed-bed reactor. The concentration of toluene (ppm) at the outlet of the fixed-bed reactor.

[0060] The reactant gas consisted of 1000 ppm toluene, 21 vol.% O2, and a balance gas N2. The total flow rate of the reactant gas was 100 mL / min, and the weight hourly space velocity (WHSV) was 30000 mL·g. -1 ·h -1The toluene conversion rates of each catalyst at different temperatures (T℃) are as follows: (T℃ is given as T ... Figure 5 As shown. By Figure 5 It can be seen that 0.005% Pt / LAO has a T 90 The reaction temperature required for a 90% toluene conversion rate is 261℃, and its catalytic oxidation performance for toluene is significantly better than that of other catalysts.

[0061] The Pt content in the platinum-supported high-performance VOCs catalyst of Example 2 was determined using an Agilent-730 inductively coupled plasma atomic emission spectrometer. The result was 0.0065 wt% (which is different from the 0.005 wt% Pt addition, due to experimental error).

[0062] Turnover frequency (TOF) represents the number of substrate molecules converted per unit active site per unit time. It is commonly used to characterize the utilization efficiency of active sites in a catalyst; a higher TOF value indicates higher utilization efficiency of the active site. The TOF of the active site Pt to toluene in the platinum-supported high-performance VOCs catalyst of Example 2 of this invention was calculated using the following formula:

[0063]

[0064] Where TOF is the conversion frequency (×10). -2 s -1 F is the toluene flow rate in the reaction gas (mol / s), X is the toluene conversion rate (%) of 0.005%Pt / LAO at 261℃, m is the mass (g) of the catalyst used in the catalytic oxidation performance test of toluene, M is the molar mass of Pt (195.08g / mol), w is the content of Pt in the catalyst (w is 0.0065%), and D is the dispersion of Pt in the catalyst (in the 0.005%Pt / LAO of this invention, Pt exists in the form of single atoms, so the dispersion is assumed to be 1).

[0065] The conversion frequency of Pt to toluene in the platinum-supported high-performance VOCs catalyst of Example 2 of this invention is shown in Table 2. Compared with other catalysts in the prior art, the 0.005%Pt / LAO catalyst prepared in this invention has a significantly lower Pt loading than other supported Pt catalysts, while its Pt utilization efficiency is significantly better.

[0066] Table 2

[0067]

[0068] The water resistance and stability of the platinum-supported high-performance VOCs catalyst (0.005% Pt / LAO) in Example 2 were tested, which was basically the same as the "Catalytic Oxidation of Toluene Performance Test", with the following differences: The heating program was initiated, heating the fixed-bed reactor to 240°C and holding for 4 hours, then raising the temperature to 250°C and holding for 4 hours, raising it to 260°C and holding for 4 hours, and continuing to raise the temperature to 270°C and holding for 32 hours. Specifically, at the 16th hour after reaching 270°C, 5 vol% water vapor was introduced into the reaction gas using a bubbling method and held for 4 hours. At the 20th hour after reaching 270°C, the concentration of the introduced water vapor was increased to 10 vol% and held for 4 hours. At the 24th hour after reaching 270°C, the concentration of the introduced water vapor was increased to 20 vol% and held for 4 hours. After that, the introduction of water vapor was stopped, and the reaction continued for 4 hours. Then, the temperature was lowered to 260°C and held for another 269 hours. During the reaction, the concentration of toluene in the reaction tail gas was measured every 15 minutes to calculate the toluene conversion rate. The results are as follows: Figure 6 As shown. By Figure 6 It can be seen that after continuous reaction at 240℃, 250℃, and 260℃ for 4 hours, the toluene conversion rate of the catalyst in Example 2 remained at approximately 70%, 80%, and 90%, respectively, confirming that the catalyst's catalytic oxidation performance of toluene did not change during long-term reactions. Furthermore, after maintaining the reaction at 270℃ for 16 hours, its catalytic oxidation performance of toluene remained stable. Moreover, the experimental results of introducing 5 vol%, 10 vol%, and 20 vol% water vapor into the reaction system and continuing the reaction for 4 hours each showed that the introduction of water vapor had no significant effect on the catalyst's catalytic oxidation performance of toluene. Even in the presence of 20 vol% water vapor, the decrease in toluene conversion rate was only about 2%, and after the introduction of water vapor was stopped, its catalytic oxidation performance of toluene rapidly recovered to its original level. After continuing the reaction for a long time after the introduction of water vapor was stopped, with a total reaction time of 313 hours, the toluene conversion rate of the catalyst remained stable. These results indicate that the platinum-supported high-performance VOCs catalyst of Example 2 possesses excellent water resistance and stability.

[0069] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. The application of a high-performance VOCs catalyst in the catalytic oxidation of benzene compounds, characterized in that, The preparation method of platinum-supported high-performance VOCs catalyst includes: adding an aqueous solution of platinum salt to the surface of a metal support to obtain a catalyst precursor; aging, purifying, drying, and calcining the catalyst precursor sequentially to obtain the platinum-supported high-performance VOCs catalyst; wherein, by mass fraction, the ratio of platinum to metal support in the aqueous solution of platinum salt is (0.005~0.01):(99.99~99.995); the metal support is perovskite-type LaAlO3; the calcination includes: constant temperature calcination at 450~500℃ for 3~5 hours; the purification includes: washing the aged catalyst precursor sequentially with water and anhydrous ethanol; the aging includes: standing in air at 25~30℃ and 60~80% relative humidity for 1~3 hours; the drying temperature is 40~50℃; the drying pressure is 10~15MPa; and the concentration of platinum in the aqueous solution of platinum salt is 3~12mg / mL. The conversion frequency of toluene to the active site Pt in the platinum-supported high-performance VOCs catalyst is 117.9 × 10⁻⁶. -2 s -1 .

2. The application according to claim 1, characterized in that, A method for obtaining an aqueous solution of platinum salts includes: mixing platinum salts and water, stirring until homogeneous, to obtain the aqueous solution of platinum salts.

3. The application according to claim 2, characterized in that, The drying process employs supercritical CO2 drying technology, with a drying time of 4-6 hours.

4. The application according to claim 1, characterized in that, The method for preparing the metal support includes: mixing a lanthanum metal source, an aluminum metal source, and water uniformly to obtain a first solution; adding citric acid and ethylene glycol to the first solution and mixing uniformly to obtain a homogeneous solution; drying the homogeneous solution and calcining it at 800~900℃ for 4~6h to obtain the metal support, wherein, by molar fraction, the ratio of lanthanum in the lanthanum metal source, aluminum in the aluminum metal source, citric acid, and ethylene glycol is 1∶1∶(1~1.5)∶(1~2.5).

5. The application according to claim 4, characterized in that, The ratio of the molar fraction of the lanthanum metal source to the volume fraction of water in the first solution is 1:(6000~7000), with the molar fraction in mol and the volume fraction in mL.

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