A bimetallic photocatalyst with cerium dioxide as a carrier, doped with Cu and loaded with Pd, a preparation method and application thereof

Abstract

The application discloses a kind of bimetallic photocatalyst (Pd / Cu-CeO2 catalyst) with cerium dioxide as carrier doped Cu loaded Pd and its preparation method and application.Pd / Cu-CeO2 catalyst is prepared by depositing precipitation method after preparing Cu-CeO2 modified carrier by hydrothermal method.Pd / Cu-CeO2 catalyst has high NO / CO conversion rate and NH3 selectivity in the process of light-assisted NO synthesis ammonia, compared with the high temperature and high pressure conditions required by traditional ammonia synthesis reaction, the energy consumption and economic cost required by reaction are greatly reduced, and the preparation method is simple and easy to operate, and has good application prospect when water vapor exists in the removal of tail gas under the action of light and heat coupling.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of environmental protection and air purification, and particularly relates to a bimetallic photocatalyst with cerium dioxide as a carrier doped with Cu loaded Pd as well as a preparation method and application thereof. The bimetallic modified catalyst can exhibit excellent catalytic performance on the NO+CO+H2O reaction through light-heat coupling. BACKGROUND

[0002] With the development of today's economy and the rapid rise of the automobile industry, vehicle exhaust is not easy to dilute and diffuse, which seriously affects the sustainable development of human health and the environment. With the increasing emission of automobile exhaust, nitrogen monoxide (NO), which accounts for 95% of nitrogen oxides, has caused very serious environmental problems, such as acid rain, photochemical smog, increased PM2.5, and ozone depletion. Most of the atmospheric pollution comes from the emission of exhaust gas during the use of vehicles, accounting for 65-80%, and the current self-purification ability of the atmosphere cannot completely degrade automobile exhaust pollution, so it is imperative to solve the atmospheric pollution of nitrogen oxides. In recent years, the increase in automobile exhaust emissions mainly includes CO, CO2, NO, NO2, hydrocarbons, and lead and sulfur-containing compounds, among which hydrocarbons can catalyze with oxygen in the air to generate CO2 and H2O. In the presence of NO, CO, and H2O, automobile exhaust treatment will inevitably produce NH3, which is not only a key chemical raw material for industry, but also a carbon-free fuel and transportable carrier for future renewable energy. Currently, the synthesis of NH3 in industry still mainly relies on the traditional Haber-Bosch reaction, which requires high temperature of 300-500℃ and pressure of 20-30 MPa. At the same time, it is also a very challenging process to artificially fix N2 in the atmosphere into NH3. In order to overcome the above shortcomings, it has become inevitable to develop a process for converting NO into NH3, and the reaction process is as follows:

[0003] NO + 2.5CO + 1.5H2O → NH3 + 2.5CO2 ΔH (298.15K) = -414.86 KJ / mol

[0004] This reaction process uses NO as raw material to generate high-value NH3 and non-toxic CO2 through the reaction of toxic gas CO and H2O, and the reaction is carried out at medium and low temperatures. However, the reaction temperature is still relatively high, and future industrial application requires high requirements for reaction equipment. Therefore, by introducing light into the pure thermal catalysis process, a light-heat coupling process has emerged.

[0005] Currently, three-way catalysts are generally used to remove automobile exhaust, mainly including a carrier, a coating and an active component. Generally, the active component is a noble metal such as Pd, Pt and Rh, etc. However, the three-way catalysts are prone to poisoning and deactivation at high temperatures. Therefore, in order to improve the thermal stability of the catalyst, the carrier oxide needs to be modified to improve the heat resistance and oxygen storage / release capacity of the carrier during the design of the catalyst. In the past few decades, due to its unique redox performance and high oxygen storage capacity (OCS), Ce 3+ and Ce 4+ are easily oxidized and reduced, and ceria has been used as a high-efficiency three-way catalyst (TWC) for eliminating toxic automobile exhaust, and also shows good development prospects in the field of photocatalysis. Currently, there is no related report on the modification of ceria materials with double metals in the system of photocatalytic and thermal coupling catalytic conversion of NO to NH3. From the perspective of adsorption and activation of H2O, doping metal ions in CeO2 can change the surface element composition, thereby increasing the oxygen vacancy content on the surface of CeO2 to improve the adsorption and activation ability of H2O. From the perspective of adsorption and activation of NO / CO, NO / CO can be adsorbed on the surface of the noble metal Pd, changing the electronic structure of the catalyst, which is beneficial to the adsorption and activation of NO / CO. From the perspective of photocatalysis, light can increase the oxygen vacancy content on the surface of the catalyst and the electronic density on the surface of the noble metal Pd, which is beneficial to the activation of NO / CO reaction molecules, and the increased oxygen vacancies are beneficial to the dissociation of H2O. Therefore, the present application uses a catalyst modification method to realize the above-mentioned synergistic effect mode through the interaction of different metals in the double metal catalyst. SUMMARY

[0006] In view of the shortcomings of the existing simple photocatalytic removal of NO / CO in the presence of water vapor in the exhaust gas, the present application provides a double metal photocatalyst with ceria as a carrier, doped with Cu and loaded with Pd, as well as a preparation method and application thereof, to improve the catalytic performance of the Pd / Cu-CeO2 catalyst for removing NO / CO in the presence of water vapor in the exhaust gas by utilizing the effect of light-thermal coupling. The problems of low catalytic activity and low NH3 selectivity of conventional Pd-supported catalysts and simple carriers for catalyzing NO / CO / H2O reaction at high temperatures are solved, which provides a new idea for the design of subsequent catalysts and has good application prospects.

[0007] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0008] A bimetallic photocatalyst doped with Cu supported by Pd with CeO2 as carrier, the photocatalyst is modified by Cu and Pd bimetallic, two active components of high dispersion supported catalyst synergistic; the content of active component Pd in the photocatalyst is 0.5wt%-2.0wt%, the content of Cu is 2.5at%-7.5at%, and the rest is CeO2 carrier.

[0009] The above-mentioned bimetallic photocatalyst uses a 300w xenon lamp to control the wavelength (lambda) range of lambda<780nm, and the removal of NO / CO in water vapor is realized at medium-low temperature of 90-270℃, and at 270℃, the conversion rate of NO is 100%, the conversion rate of CO is 99.7%, and the selectivity of NH3 is 88.7%.

[0010] The preparation method of the above-mentioned bimetallic photocatalyst is to use cerium nitrate hexahydrate as a precursor, add copper nitrate trihydrate, synthesize Cu-CeO2 carrier modified by copper, and then load active component Pd on the Cu-CeO2 carrier by using deposition precipitation method through PdCl2 solution.

[0011] The preparation method of the above-mentioned bimetallic photocatalyst comprises the following steps:

[0012] S1: dissolve Ce(NO3)3·6H2O in deionized water, add Cu(NO3)2·3H2O to obtain solution A; dissolve NaOH in deionized water to obtain solution B; quickly mix the obtained solution A and solution B, stir at room temperature for 1h to obtain a milky suspension; transfer the obtained milky suspension to a hydrothermal reaction kettle, hydrothermal reaction at 180℃ for 24h, centrifuge after cooling to room temperature, collect the precipitate, wash with deionized water, dry at 80℃ for 12h, then calcine in a muffle furnace at a heating rate of 5℃ / min to 550℃ for 4h to obtain a copper-doped CeO2 carrier;

[0013] S2: add PdCl2 solution and deionized water to the copper-doped CeO2 carrier obtained in step S1, stir at room temperature for 2h, adjust the pH to 11, then add NaBH4 solution, continue to stir for 2h, centrifuge, collect the precipitate, wash with deionized water, vacuum dry at 60℃ for 12h to obtain a bimetallic photocatalyst doped with Cu supported by Pd with CeO2 as carrier.

[0014] The step S1 is specifically: 4.12 g of Ce(NO3)3·6H2O is dissolved in 5 ml of deionized water, 0.12 g of Cu(NO3)2·3H2O is added, and solution A is obtained; 24.0 g of NaOH is dissolved in 35 ml of deionized water to obtain solution B; the obtained solution A and solution B are quickly mixed, and stirred at room temperature for 1 h to obtain a milky suspension; the obtained milky suspension is transferred into a 100 ml hydrothermal reactor, and hydrothermal reaction is carried out at 180 DEG C for 24 h; after cooling to room temperature, centrifugation is carried out, the precipitate is washed with deionized water for 6 times, dried at 80 DEG C for 12 h, and then calcined in a muffle furnace at a temperature increasing rate of 5 DEG C / min to 550 DEG C for 4 h to obtain a copper-doped CeO2 carrier;

[0015] The step S2 is specifically: the copper-doped CeO2 carrier obtained in the step S1 is added with a PdCl2 solution with a concentration of 6 mg / ml and 50 ml of deionized water, wherein the ratio of the copper-doped CeO2 carrier to the PdCl2 solution is 1 g / 0.85-3.35 ml, stirring is carried out at room temperature for 2 h, a sodium hydroxide solution with a concentration of 1.25 M is used to adjust the pH to 11, 20 ml of a NaBH4 solution with a concentration of 0.15 M is further added, stirring is continued for 2 h, centrifugation is carried out, the precipitate is washed with deionized water for 3 times, vacuum drying is carried out at 60 DEG C for 12 h, and a bimetallic photocatalyst with a ceria carrier doped with Cu and loaded with Pd is obtained.

[0016] The application of the bimetallic photocatalyst in the NO-CO-H2O reaction.

[0017] The application of the bimetallic photocatalyst in tail gas purification.

[0018] The significant advantages of the application are:

[0019] (1) The bimetallic photocatalyst with a ceria carrier doped with Cu and loaded with Pd obtained by the application has good NO+CO+H2O photocatalytic and thermal coupling catalytic performance under medium-low temperature and ultraviolet visible light catalysis, the preparation method is simple, convenient and feasible, and the bimetallic photocatalyst has good application prospect in the removal of water vapor in tail gas under the action of photocatalysis and thermal coupling.

[0020] (2) The application modifies CeO2 by introducing two metals of Cu and Pd in a proper proportion, and the modified catalyst has good electron transfer efficiency. After cerium dioxide is used as a carrier to load metal Pd, photo-generated electrons are transferred from a semiconductor with a high Fermi level to Pd metal with a low Fermi level, thereby increasing the electron density on the surface of the active component Pd. After cerium dioxide is used as a carrier to dope Cu, the Fermi level of the semiconductor is lifted, and after loading metal Pd, the electron transfer to metal Pd is further promoted, thereby increasing the electron density on the surface of the active component Pd. The increase of the electron density on the surface of Pd promotes the adsorption and activation of CO and NO, and the increased oxygen vacancies of CeO2 as a carrier doped with Cu are beneficial to the dissociation of H2O. The modification of CeO2 by two metals of Cu and Pd promotes the catalytic reaction of NO+CO+H2O, thereby improving the conversion rate of NO / CO and the selectivity of NH3.

[0021] (3) The application prepares a Pd-loaded bimetallic photocatalyst by selecting a Cu-CeO2 semiconductor with a photoexcitation property as a carrier, and the modified catalyst has good photo-generated carrier transfer efficiency. Compared with a simple thermal catalytic reaction, the catalytic performance of NO / CO in the presence of water is improved by light-heat coupling, effectively reducing the required reaction temperature, thereby greatly reducing the reaction energy consumption and economic cost.

[0022] (4) The Pd / Cu-CeO2 catalyst synthesizes high-value-added NH3 from NO / CO in the presence of water, opens up a new application direction of CeO2 material, the catalyst preparation method is simple and fast, and is conducive to providing a new idea for the reaction mechanism of NO / CO conversion. This also opens up a new way for the conversion and utilization of solar energy. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The XRD spectrum of 1wt% Pd / CeO2 and 1wt% Pd / 5at% Cu-CeO2.

[0024] Figure 2 The DRS spectrum of 1wt% Pd / CeO2 and 1wt% Pd / 5at% Cu-CeO2.

[0025] Figure 3 The TEM graph of 1wt% Pd / CeO2 and 1wt% Pd / 5at% Cu-CeO2.

[0026] Figure 4 The impedance graph of 1wt% Pd / CeO2 and 1wt% Pd / 5at% Cu-CeO2.

[0027] Figure 5Figure for photocatalytic and thermocatalytic evaluation of 1wt%Pd / CeO2, 1wt%Pd / 5at% Cu-CeO2. DETAILED DESCRIPTION

[0028] In order to make the content of the present application more convenient to understand, the technical solutions of the present application will be further described below in combination with specific embodiments, but the present application is not limited to this.

[0029] Example 1: Preparation of 1wt%Pd / CeO2catalyst

[0030] S1: 4.34g Ce(NO3)3·6H2O was dissolved in 5ml deionized water to obtain solution A; 24.0g NaOH was dissolved in 35ml deionized water to obtain solution B; the obtained solution A and solution B were quickly mixed, stirred at room temperature for 1h to obtain a milky suspension; the obtained milky suspension was transferred into a 100ml hydrothermal reactor, hydrothermally reacted at 180℃ for 24h, centrifuged after cooling to room temperature, the precipitate was washed with deionized water for 6 times, dried at 80℃ for 12h, then calcined in a muffle furnace at a temperature increasing rate of 5℃ / min to 550℃ for 4h to obtain a Cu-CeO2support (denoted as 0at%Cu-CeO2).

[0031] S2: To the Cu-CeO2support obtained in S1, a PdCl2solution with a concentration of 6mg / ml and 50ml deionized water were added, wherein the addition amount of PdCl2solution was 1.67ml per 1.0g of Cu-CeO2support, stirred at room temperature for 2h, then the pH was adjusted to 11 with a sodium hydroxide solution with a concentration of 1.25M, then 20ml of a NaBH4solution with a concentration of 0.15M was added, continued to stir for 2h, then centrifuged, the precipitate was washed with deionized water for 3 times, vacuum dried at 60℃ for 12h to obtain a 1wt%Pd / CeO2catalyst.

[0032] Example 2: Preparation of 1wt%Pd / 5at% Cu-CeO2catalyst

[0033] S1: 4.12g Ce(NO3)3·6H2O was dissolved in 5ml deionized water, 0.12g Cu(NO3)2·3H2O was added to obtain solution A; 24.0g NaOH was dissolved in 35ml deionized water to obtain solution B; the obtained solution A and solution B were quickly mixed, stirred at room temperature for 1h to obtain a milky suspension; the obtained milky suspension was transferred into a 100ml hydrothermal reactor, hydrothermally reacted at 180℃ for 24h, centrifuged after cooling to room temperature, the precipitate was washed with deionized water for 6 times, dried at 80℃ for 12h, then calcined in a muffle furnace at a temperature increasing rate of 5℃ / min to 550℃ for 4h to obtain a Cu-CeO2support (denoted as 5at%Cu-CeO2).

[0034] S2: To the Cu-CeO2 support obtained in S1, 6 mg / ml PdCl2 solution and 50 ml deionized water were added, wherein the amount of PdCl2 solution added was 1.67 ml per 1.0 g of Cu-CeO2 support, stirring at room temperature for 2 h, then adjusting the pH to 11 with a 1.25 M NaOH solution, then adding 20 ml of a 0.15 M NaBH4 solution, continuing to stir for 2 h, then centrifuging, collecting the precipitate, washing with deionized water 3 times, and drying at 60°C under vacuum for 12 h to obtain a 1 wt% Pd / 5 at% Cu-CeO2 catalyst.

[0035] Example 3: Performance evaluation of the catalyst

[0036] For the reaction of catalytic removal of NO / CO / H2O by the catalyst, the performance test of the catalyst was carried out in a self-designed fixed bed flow reaction device. The prepared sample was filled in a double-channel micro quartz reactor (length 10 mm x width 10 mm x height 1 mm), and the reactor was provided with the required temperature by a heating device controlled by a temperature programmer, and the internal temperature of the catalyst was detected by a K-type thermocouple inserted into the catalyst reaction bed. The wavelength range of the light emitted by the 300w xenon lamp was controlled to be (λ<760nm), and the light emitted by the xenon lamp was irradiated from the top of the sample to the surface of the catalyst through the quartz reactor. For pure thermal catalysis, the quartz reactor was covered with aluminum foil to exclude the influence of light.

[0037] Specific reaction conditions: 0.2 g of catalyst was loaded in the quartz reactor, and the particle size of the catalyst was about 0.2-0.3 mm (60-80 mesh). The reaction feed gas included 3000 ppm of CO, 1000 ppm of NO, H2O was excessive (1.5 Vol%-2.5 Vol%), N2 was used as the balance gas, the total flow rate of the reaction gas was about 100 mL / min, and the gas hourly space velocity (GHSV) was 60000 h -1 . The experiment was alternately carried out in light and dark for 1 h each time, and the experimental temperature was 90-270°C. The outlet gas was analyzed online by a GASERA One type photoacoustic spectrometer (PAS, Beijing DuKe) to analyze the concentrations of CO, N2O, CO2, H2O, and NH3 in the gas atmosphere, and a nitrogen oxide analyzer (Testo 340) was used to monitor the concentration change of NO online, and the calculation formulas of CO conversion rate, NO conversion rate, and NH3 selectivity were as follows:

[0038] CO conversion rate: COc= {[CO] in -[CO] out} / [CO] in x 100%;

[0039] NO conversion is: NOc= {[NO]} in -[NO] out} / [NO] in x 100 %.

[0040] NH3 selectivity is: NH 3S = [NH3] out / {[NO]} in -[NO] out} x 100 %.

[0041] In the formula, COc is the conversion rate of CO, NOc is the conversion rate of NO, NH 3S is the selectivity of NH3; [CO] in and [CO] out are the CO content (ppm) in the inlet gas and outlet gas, respectively, [NO] in and [NO] out are the NO content (ppm) in the inlet gas and outlet gas, respectively, [NH3] out is the NH3 content (ppm) in the outlet gas.

[0042] Figure 1 XRD patterns of 1wt%Pd / CeO2, 1wt%Pd / 5at% Cu-CeO2 catalysts. From Figure 1 which can be seen, no X-ray diffraction peaks of Pd and Cu metal or metal oxide are detected, indicating that the amount of the two metals introduced is small, and is uniformly distributed in the CeO2 cubic fluorite structure without destroying its inherent crystal structure.

[0043] Figure 2 DRS spectra of 1wt%Pd / CeO2, 1wt%Pd / 5at% Cu-CeO2 catalysts. From Figure 2 which can be seen, the synergistic effect of Cu and Pd shows a significant red shift of the absorption edge and a significant enhancement of visible light absorption ability, reduces the band gap, and significantly improves the transport efficiency of photo-generated carriers.

[0044] Figure 3 TEM images of 1wt%Pd / 5at% Cu-CeO2 catalyst. From Figure 3 which can be seen, 1wt%Pd / 5at% Cu-CeO2 catalyst is made of irregular nano-polyhedral particles, and Pd nanoparticles are closely combined with the catalyst carrier.

[0045] Figure 4 Impedance diagrams of 1wt%Pd / CeO2, 1wt%Pd / 5at% Cu-CeO2 catalysts. From Figure 4As can be seen from the figure, the smaller impedance radius indicates better electron transfer ability, thereby accelerating electron transfer and inhibiting the recombination of photo-generated electron-hole pairs.

[0046] Figure 5 The figure is a photocatalytic evaluation diagram of 1wt%Pd / CeO2, 1wt%Pd / 5at% Cu-CeO2 catalysts. Figure 5 As can be seen from the figure, the 1wt%Pd / 5at% Cu-CeO2 catalyst achieved 100% conversion of NO, 99.7% conversion of CO, and 88.9% selectivity of NH3 at 270℃. Compared with the pure thermal reaction condition, the conversion of CO and NO and the selectivity of NH3 were greatly improved after introducing light under the same condition, which proved that the catalyst had a significant light-promoted effect. However, the 1wt%Pd / CeO2 catalyst achieved 100% conversion of NO, 91.1% conversion of CO, and 70.6% selectivity of NH3 at 270℃. Compared with the 1wt%Pd / 5at% Cu-CeO2 catalyst, the catalytic activity of the 1wt%Pd / CeO2 catalyst was significantly reduced, mainly due to the fact that the doping of Cu improved the electron density on the surface of the active component Pd. Compared with the pure thermal reaction condition, the conversion of CO and NO and the selectivity of NH3 did not appear to be significantly improved after introducing ultraviolet light under the same condition, which indicated that the modified bimetallic catalyst had good photo-generated carrier transfer efficiency and good photo-activated activity in the photocatalytic reaction. This photocatalytic method has been significantly improved compared with the traditional high-temperature, high-pressure, and high-energy consumption ammonia synthesis process, and it is an almost ideal way to generate ammonia.

[0047] The above description is only the preferred embodiment of the present application, and any equivalent changes and modifications made within the scope of the present application should be included in the scope of the present application.

Claims

1. A bimetallic photocatalyst doped with Cu supported on Pd with ceria as a support, characterized in that: The photocatalyst is a high dispersion supported catalyst with CeO2 as a carrier and Cu and Pd bimetallic modification, and the two active components are mutually synergistic; the content of the active component Pd in the bimetallic photocatalyst is 0.5wt%-2.0wt%, the content of Cu is 2.5at%-7.5at%, and the rest is the CeO2 carrier; The preparation method of the bimetallic photocatalyst is as follows: taking cerium nitrate hexahydrate as a precursor, adding copper nitrate trihydrate, synthesizing a Cu-CeO2 carrier modified by copper, and then loading the active component Pd on the Cu-CeO2 carrier by using a deposition precipitation method and a PdCl2 solution; the preparation method comprises the following steps: S1: dissolving Ce(NO3)3·6H2O in deionized water, adding Cu(NO3)2·3H2O to obtain solution A; dissolving NaOH in deionized water to obtain solution B; quickly mixing the obtained solution A and solution B, stirring at room temperature for 1h to obtain a milky suspension; transferring the obtained milky suspension into a hydrothermal reaction kettle, hydrothermal reaction at 180℃ for 24h, centrifuging after cooling to room temperature, collecting the precipitate, washing with deionized water, drying at 80℃ for 12h, and then calcining in a muffle furnace at a temperature increasing rate of 5℃ / min to 550℃ for 4h to obtain a copper-doped CeO2 carrier; S2: adding a PdCl2 solution and deionized water to the copper-doped CeO2 carrier obtained in step S1, stirring at room temperature for 2h, adjusting the pH to 11, then adding a NaBH4 solution, continuing to stir for 2h, centrifuging, collecting the precipitate, washing with deionized water, vacuum drying at 60℃ for 12h to obtain a bimetallic photocatalyst with cerium dioxide as a carrier, doped with Cu and loaded with Pd.

2. The bimetallic photocatalyst of claim 1, wherein: Step S1 is specifically as follows: dissolving 4.12g of Ce(NO3)3·6H2O in 5ml of deionized water, adding 0.12g of Cu(NO3)2·3H2O to obtain solution A; dissolving 24.0g of NaOH in 35ml of deionized water to obtain solution B; quickly mixing the obtained solution A and solution B, stirring at room temperature for 1h to obtain a milky suspension; transferring the obtained milky suspension into a 100ml hydrothermal reaction kettle, hydrothermal reaction at 180℃ for 24h, centrifuging after cooling to room temperature, collecting the precipitate, washing with deionized water for 6 times, drying at 80℃ for 12h, and then calcining in a muffle furnace at a temperature increasing rate of 5℃ / min to 550℃ for 4h to obtain a copper-doped CeO2 carrier.

3. The bimetallic photocatalyst of claim 1, wherein: Step S2 is specifically as follows: adding a PdCl2 solution with a concentration of 6mg / ml and 50ml of deionized water to the copper-doped CeO2 carrier obtained in step S1, wherein the ratio of the copper-doped CeO2 carrier to the PdCl2 solution is 1g / 0.85-3.35ml, stirring at room temperature for 2h, adjusting the pH to 11 with a sodium hydroxide solution, then adding 20ml of a NaBH4 solution with a concentration of 0.15M, continuing to stir for 2h, centrifuging, collecting the precipitate, washing with deionized water for 3 times, vacuum drying at 60℃ for 12h to obtain a bimetallic photocatalyst with cerium dioxide as a carrier, doped with Cu and loaded with Pd.

4. Use of the bimetallic photocatalyst according to any one of claims 1 to 3, characterized in that: Application in NO-CO-H2O reaction.

5. Use of the bimetallic photocatalyst according to any one of claims 1 to 3, characterized in that: Application in tail gas purification.

6. Use according to claim 5, characterized in that: Under the condition of introducing light, the bimetallic photocatalyst is used for removing CO and NO in tail gas under the condition of medium-low temperature and water vapor.

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