Monatomic copper-doped titania nanoplatelet catalyst, method of preparation and use thereof

Abstract

The application discloses a single-atom copper-doped titanium dioxide nanosheet catalyst, a preparation method and application thereof. The method comprises the following steps: grinding and mixing copper oxide, titanium dioxide, potassium carbonate and lithium carbonate in a certain proportion, high-temperature calcination, protonation treatment and wet chemical stripping, and then Cu1-TiO2 nanosheet catalyst is obtained. Compared with pure TiO2 nanosheet without doping single-atom Cu, the Cu1-TiO2 nanosheet catalyst exhibits excellent catalytic performance in the controllable oxidation of benzyl alcohol under mild reaction conditions, and has catalytic universality, and has wide application prospects in the controllable preparation of aromatic aldehyde compounds.

Description

Technical Field

[0001] This invention belongs to the field of alcohol oxidation catalyst technology, and relates to a single-atom copper-doped titanium dioxide nanosheet catalyst, its preparation method and its application. Background Technology

[0002] Benzaldehyde is an important aromatic aldehyde chemical raw material and a crucial intermediate in pharmaceutical synthesis, plastic additives, food processing, and perfume and fragrance synthesis. Therefore, efficient synthesis methods for benzaldehyde and its derivative aromatic aldehydes have long been a research hotspot in organic chemistry and catalysis. Industrial benzaldehyde synthesis methods mainly include the following pathways: toluene chlorination and hydrolysis or gas-phase oxidation, aromatic ester hydrogenation, and benzyl alcohol oxidation. Among these, the toluene-based synthesis route suffers from low benzaldehyde yield, high energy consumption, and significant environmental problems, which does not align with the advocacy of "green chemistry." Aromatic ester hydrogenation is limited to large-scale industrial application due to the high cost of the raw materials. Benzyl alcohol oxidation stands out due to its simple process. However, traditional benzyl alcohol oxidation processes also have certain limitations. First, traditional benzyl alcohol oxidation catalysis often uses homogeneous or heterogeneous catalysts based on precious metals (such as Au, Pd, Ru, and Pt), resulting in high application costs. Second, traditional benzyl alcohol oxidation often uses strongly oxidizing Cr... 4+ Excessive acidity will inevitably produce toxic Cr. 3+ This also causes a certain degree of environmental pollution. Therefore, developing a highly efficient, green, and low-cost benzyl alcohol oxidation catalyst has extremely important economic value and broad application prospects for the entire aromatic aldehyde synthesis industry.

[0003] In recent years, the traditional benzyl alcohol oxidation process has been optimized through catalyst design and the introduction of new catalytic reaction induction mechanisms. Studies have found that adding light radiation to the original reaction conditions can further improve the efficiency of the benzyl alcohol oxidation catalytic reaction. For example, Professor H. Tüysüz of the Max Planck Institute in Germany designed a CsPbBr3 / TiO2(P25) heterojunction catalyst [ChemSusChem, 2018, 11, 2057]. Leveraging the inherent light absorption characteristics of the catalyst, controllable oxidation of benzyl alcohol was achieved under the combined driving force of a reaction temperature of 80℃ and visible light. However, due to the limitations of the heterojunction bulk structure, the number of catalytically active sites directly contacting the reaction substrate is limited, thus restricting the catalytic efficiency of the CsPbBr3 / TiO2(P25) heterojunction catalyst (the conversion rate of benzyl alcohol after 10 hours of reaction is ~35%). Professor Gaik-Khuan Chuah's research group at the National University of Singapore designed a TiO2-coated gold nanosphere (AuNS@TiO2) catalyst for photo-assisted benzyl alcohol oxidation [Catalysis Today, 2021, 375, 558]. The results showed that under 24W visible light irradiation, AuNS@TiO2 can drive efficient benzyl alcohol oxidation at a reaction temperature of 30℃, achieving a conversion rate of 85% after 3 hours, with a benzaldehyde selectivity greater than 99%. The high efficiency of benzyl alcohol oxidation is mainly attributed to the surface plasmon resonance effect of Au under visible light irradiation. However, the introduction of the precious metal gold significantly increases the catalyst's cost and further industrial application. Therefore, designing a photo-assisted benzyl alcohol oxidation catalyst with high active site atom utilization and cost-effectiveness is a key research focus and challenge in this field. Summary of the Invention

[0004] The present invention aims to provide a single-atom copper-doped titanium dioxide (Cu1-TiO2) nanosheet catalyst, its preparation method, and its application. This invention utilizes a "doping-exfoliation" method to control the atomic-level doping of copper atoms on titanium dioxide nanosheets, maximizing the utilization rate of copper atoms. The resulting single-atom copper-doped titanium dioxide nanosheet catalyst can drive the efficient and controlled oxidation of benzaldehyde and its derivatives to prepare aromatic aldehydes under mild conditions.

[0005] The technical solution for achieving the objective of this invention is as follows:

[0006] The catalyst is a single-atom copper-doped titanium dioxide nanosheet catalyst, in which copper is doped into the titanium dioxide nanosheet layer in the form of single atoms, with a doping ratio of 0.5 to 5 wt%, and the thickness of a single layer of titanium dioxide nanosheet is 0.8 to 1.2 nm.

[0007] A method for preparing single-atom copper-doped titanium dioxide nanosheet catalysts involves grinding and mixing copper oxide, titanium dioxide, lithium carbonate, and potassium carbonate in a specific ratio, followed by high-temperature calcination, protonation treatment, and wet chemical exfoliation to obtain Cu1-TiO2 nanosheet catalysts. The method includes the following steps:

[0008] (1) Copper oxide, rutile titanium dioxide, potassium carbonate and lithium carbonate powders are physically mixed uniformly by grinding, wherein the molar ratio of copper oxide, rutile titanium dioxide, potassium carbonate and lithium carbonate is x:(5.2-x) / 3:0.4:(0.8-2x) / 3, x=0.05~0.2;

[0009] (2) Calcine the mixture obtained in step (1) in air at 900-1000°C for 20-40 hours;

[0010] (3) Mix the calcined sample from step (2) evenly by grinding.

[0011] (4) Place the sample obtained in step (3) in hydrochloric acid solution for protonation treatment;

[0012] (5) Wash the sample obtained in step (4) with water until it is neutral and then vacuum dry for more than 24 hours;

[0013] (6) The sample obtained in step (5) is uniformly dispersed in a tetrabutylammonium hydroxide solution and placed in a shaker for wet chemical stripping;

[0014] (7) Centrifuge and freeze dry the suspension obtained in step (6) to obtain Cu1-TiO2 nanosheets.

[0015] In step (1), the molar ratio of copper oxide, rutile titanium dioxide, potassium carbonate, and lithium carbonate is set based on the premise that the structure of titanium dioxide remains unchanged, while also satisfying charge conservation and atom conservation.

[0016] Preferably, in step (4), the concentration of the hydrochloric acid solution is 2-4 wt%.

[0017] Preferably, in step (4), the solid-liquid ratio of the sample to the hydrochloric acid solution is 1g:50-200mL.

[0018] Preferably, in step (4), the protonation treatment time is 24 to 72 hours.

[0019] Preferably, in step (6), the concentration of the tetrabutylammonium hydroxide solution is 0.6–0.8 wt%.

[0020] Preferably, in step (6), the solid-liquid ratio of the sample to the tetrabutylammonium hydroxide solution is 1g:250-500mL.

[0021] Preferably, in step (6), the wet chemical stripping treatment time is 5 to 20 days.

[0022] Preferably, in step (6), the temperature of the shaker is controlled at 25°C and the speed of the shaker is 150-300 rpm.

[0023] The present invention also provides the application of the above-mentioned single-atom copper-doped titanium dioxide nanosheet catalyst in the photo-assisted catalytic oxidation of benzyl alcohol or its derivatives.

[0024] Furthermore, the specific application method is as follows: using benzyl alcohol or its derivatives as reactants, potassium tert-butoxide as a base, toluene as a solvent, and adding a single-atom copper-doped titanium dioxide nanosheet catalyst, a catalytic oxidation reaction is carried out at 60±10℃ in an air atmosphere and under external 365nm light radiation to obtain benzaldehyde or its corresponding derivatives.

[0025] The benzyl alcohol derivatives described in this invention include p-methylbenzyl alcohol, p-chlorobenzyl alcohol, p-bromobenzyl alcohol, p-nitrobenzyl alcohol, etc.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] Compared with undoped Cu-based titanium dioxide nanosheet catalysts, Cu1-TiO2 nanosheet catalysts exhibit significantly superior catalytic conversion and selectivity for the controlled oxidation of benzyl alcohol to benzaldehyde under the same catalytic conditions. Compared with previously reported catalysts of the same type, under the same catalytic conditions (reaction temperature ≤60℃, light irradiation), Cu1-TiO2 achieves a benzyl alcohol conversion >99% and a benzaldehyde selectivity >99%. Cu1-TiO2 demonstrates superior substrate conversion and target product selectivity. Furthermore, Cu1-TiO2 exhibits broad applicability to the oxidation of benzyl alcohol derivatives (e.g., p-methylbenzyl alcohol, p-chlorobenzyl alcohol, p-bromobenzyl alcohol, p-nitrobenzyl alcohol, etc.). Therefore, Cu1-TiO2 nanosheet catalysts show great promise for controlled alcohol oxidation reactions. Attached Figure Description

[0028] Figure 1 This is an atomic force microscopy (AFM) image of the Cu1-TiO2 nanosheet catalyst.

[0029] Figure 2 Transmission electron microscopy (TEM) image of Cu1-TiO2 nanosheet catalyst.

[0030] Figure 3 This is a scanning transmission microscope (STEM) image of the Cu1-TiO2 nanosheet catalyst.

[0031] Figure 4The image shows the K-edge X-ray absorption near-edge structure (K-edge XANES) spectrum of Cu1-TiO2 nanosheet catalyst.

[0032] Figure 5 The image shown is a scanning transmission electron microscope (STEM) image of Cu1-TiO2 synthesized using anatase TiO2 as a precursor, as shown in Comparative Example 1.

[0033] Figure 6 Scanning transmission electron microscope (STEM) image of Cu1-TiO2 prepared by changing the precursor ratio for Comparative Example 2. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0035] In the following examples, benzyl alcohol was selected as the reaction substrate in the catalytic performance evaluation experiment to evaluate the conversion rate and selectivity of the reaction. Potassium tert-butoxide was used as the base, toluene as the solvent, and the reaction conditions were 365 nm light irradiation (25 W), atmospheric pressure, and 60 °C. The specific benzyl alcohol oxidation reaction operation is as follows:

[0036] 0.1 mmol of benzyl alcohol and 0.2 mmol of potassium tert-butoxide were placed in a quartz reaction tube, followed by 2 mL of toluene solution, and then 5 mg of Cu1-TiO2 nanosheet catalyst. The mixture was stirred for 5 minutes to ensure uniform dispersion. A 365 nm UV lamp (25 W) was placed 2 cm away from the reaction solvent system, and the benzyl alcohol oxidation reaction was carried out at 60 °C for 8 hours. As a control group, the catalyst was simply replaced with undoped copper-doped titanium dioxide nanosheet catalyst.

[0037] Finally, the conversion rate of benzyl alcohol and the selectivity of benzaldehyde were determined by gas chromatography.

[0038] Example 1

[0039] At room temperature, 0.79 g (10 mmol) of copper oxide, 6.66 g (83.4 mmol) of titanium dioxide, 0.25 g (3.4 mmol) of lithium carbonate, and 2.76 g (20.0 mmol) of potassium carbonate were physically mixed by grinding. The molar ratio of copper oxide, rutile titanium dioxide, potassium carbonate, and lithium carbonate was 0.20:1.67:0.40:0.13 (i.e., x:(5.2-x) / 3:0.4:(0.8-2x) / 3, x=0.2). The mixture was calcined at 1000 °C for 40 hours. Subsequently, the calcined product was protonated in 4% hydrochloric acid for 72 hours. Subsequently, the above product was washed with deionized water and dried. Then, it was added to a 0.69wt% tetrabutylammonium hydroxide solution at a solid-liquid ratio of 1g:250mL for wet chemical exfoliation for 20 days to obtain Cu1-TiO2 nanosheet catalyst.

[0040] Example 2

[0041] At room temperature, 0.39 g of copper oxide (5 mmol), 6.79 g (85.0 mmol) of titanium dioxide, 0.37 g (5.0 mmol) of lithium carbonate, and 2.76 g (20.0 mmol) of potassium carbonate were physically mixed by grinding. The molar ratio of copper oxide, rutile titanium dioxide, potassium carbonate, and lithium carbonate was 0.10:1.70:0.40:0.20 (i.e., x:(5.2-x) / 3:0.4:(0.8-2x) / 3, x = 0.1). The mixture was calcined at 1000 °C for 30 hours. Subsequently, the calcined product was protonated in 4% hydrochloric acid for 48 hours. Subsequently, the above product was washed with deionized water and dried. Then, it was added to a 0.74wt% tetrabutylammonium hydroxide solution at a solid-liquid ratio of 1g:250mL for wet chemical exfoliation for 10 days to obtain Cu1-TiO2 nanosheet catalyst.

[0042] Example 3

[0043] At room temperature, 0.20 g (2.5 mmol) of copper oxide, 6.87 g (85.8 mmol) of titanium dioxide, 0.42 g (5.7 mmol) of lithium carbonate, and 2.76 g (20.0 mmol) of potassium carbonate were physically mixed by grinding. The molar ratio of copper oxide, rutile titanium dioxide, potassium carbonate, and lithium carbonate was 0.05:1.72:0.40:0.23 (i.e., x:(5.2-x) / 3:0.4:(0.8-2x) / 3, x=0.05). The mixture was calcined at 1000 °C for 20 hours. Subsequently, the calcined product was protonated in 4% hydrochloric acid for 24 hours. Subsequently, the above product was washed with deionized water and dried. Then, it was added to a 0.77wt% tetrabutylammonium hydroxide solution at a solid-liquid ratio of 1g:250mL for wet chemical exfoliation for 7 days to obtain Cu1-TiO2 nanosheet catalyst.

[0044] Table 1 Catalytic performance of Cu1-TiO2 nanosheet catalyst for controlled oxidation of benzyl alcohol

[0045]

[0046] In the above reaction system, the benzyl alcohol conversion rate of the TiO2 nanosheet catalyst without single-atom Cu doping was only 10.5%, indicating the weak benzyl alcohol oxidation catalytic activity of the pure TiO2 nanosheet catalyst. Conversely, Cu1-TiO2 nanosheet catalysts with different doping ratios all exhibited high benzyl alcohol conversion rates. As shown in Table 1, the benzyl alcohol conversion rate of the Cu1-TiO2 nanosheet catalyst in Example 1 reached as high as 95.3%, and the selectivity for benzaldehyde exceeded 99.9%, with a benzaldehyde yield far exceeding that of the undoped TiO2 nanosheet catalyst.

[0047] Example 4

[0048] Using the Cu1-TiO2 nanosheets obtained in Example 1 as a catalyst, the reaction substrates for alcohol oxidation were expanded, as shown in Table 2. Experiments show that, under the catalysis of Cu1-TiO2 nanosheets, benzyl alcohol derivatives can be controllably oxidized to their corresponding aromatic aldehydes, exhibiting considerable catalytic conversion and selectivity. The substrate expansion experiments confirm the universality of the Cu1-TiO2 nanosheet catalyst for the controllable oxidation of benzaldehyde and its derivatives.

[0049] Table 2. Substrate Expansion Table for Alcohol Oxidation Reactions Catalyd by Cu1-TiO2 Nanosheets

[0050]

[0051] The above product conversion rates and selectivity are catalytic performance corresponding to 8 hours of reaction.

[0052] Example 5

[0053] To investigate the morphology of the Cu1-TiO2 nanosheet catalyst and the chemical state of single-atom Cu, the Cu1-TiO2 nanosheet catalyst obtained in Example 1 was subjected to AFM, TEM, STEM, and Cu K-edge XANES tests. Figure 1 As shown in the AFM image, the Cu1-TiO2 nanosheets have a diameter of about 1 μm and a thickness of about 1 nm, confirming that they are monolayer TiO2 nanosheets. Figure 2 TEM images also confirmed the morphology and structure of the Cu1-TiO2 ultrathin nanosheets. Figure 3 The STEM image shows that Cu is embedded in TiO2 nanosheets in the form of single atoms, with circles representing atomically dispersed single-atom Cu. Furthermore, Figure 4 The Cu K-edge XANES spectrum also confirmed that Cu exhibits a state intermediate between Cu and Cu 1+ and Cu 2+ Cu δ+ The chemical state of Cu is mainly due to the fact that the single-atom Cu confinement in the TiO2 lattice modulates a special electronic state of Cu, and this special Cu valence state is the key to improving the alcohol oxidation performance.

[0054] Comparative Example 1

[0055] To investigate the influence of TiO2 crystal structure on the synthesis of Cu1-TiO2 nanosheet catalyst, the rutile phase titanium dioxide used in Example 1 was replaced with anatase phase titanium dioxide.

[0056] according to Figure 5 As shown in the STEM image, the obtained TiO2 is not a completely monolayer, but exhibits multilayer stacking characteristics. Furthermore, uniformly dispersed bright spots appear on the surface of the multilayer TiO2; these bright spots are CuO nanocrystals that failed to be successfully doped into the TiO2 lattice. Since Cu has a higher atomic number than Ti, it exhibits higher density. Therefore, the choice of the crystal structure (rutile phase) of titanium dioxide during the synthesis process is crucial for the successful synthesis of Cu1-TiO2.

[0057] Comparative Example 2

[0058] For the synthesis of Cu1-TiO2 catalyst, in the precursor mixing stage before calcination, the ratio of each precursor needs to satisfy the principles of atomic and charge conservation, i.e., x:(5.2-x) / 3:0.4:(0.8-2x) / 3, where x = 0.05~0.2. To investigate the effect of the precursor mixing ratio on the final product, the above parameters were adjusted. The molar ratio of copper oxide, rutile titanium dioxide, potassium carbonate, and lithium carbonate used in Example 1 (0.20:1.67:0.40:0.13) was changed to 0.30:1.67:0.40:0.13, i.e., the amount of CuO added was increased. After the same subsequent synthesis steps as in Example 1, the final sample structure is as follows. Figure 6 As shown, in addition to uniformly distributed Cu single atoms, Cu nanocrystals also appear on the monolayer of titanium dioxide. This is mainly because excess Cu failed to be doped into the TiO2 lattice, but instead formed Cu nanocrystals on the outer surface.

[0059] Comparative Example 3

[0060] Following the synthesis method of Example 1, Cu was replaced with Ni or Co to synthesize Ni1-TiO2 and Co1-TiO2 nanosheet catalysts, respectively. The catalytic performance of these two catalysts in the oxidation of benzyl alcohol is shown in Table 3.

[0061] Table 3 Catalytic performance of Cu1-TiO2, Ni1-TiO2 and Co1-TiO2 nanosheet catalysts for controlled oxidation of benzyl alcohol

[0062]

[0063]

[0064] As can be seen from Table 3, the catalytic performance of TiO2 nanosheet catalysts with different single-atom doping exhibits significant differences. The Cu1-TiO2 nanosheet catalyst in Example 1 has a benzyl alcohol conversion rate as high as 95.3% and a benzaldehyde selectivity of over 99.9%, while the Ni1-TiO2 nanosheet catalyst in Comparative Example 3 has a benzyl alcohol conversion rate of only 10.4% and a benzaldehyde selectivity of only 60.5%, and the Co1-TiO2 nanosheet catalyst has a benzyl alcohol conversion rate of only 22.3% and a benzaldehyde selectivity of only 44.6%.

[0065] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exemplify all embodiments here. However, obvious variations or modifications derived from this solution are still within the scope of protection of the present invention.

Claims

1. The application of single-atom copper-doped titanium dioxide nanosheet catalyst in the photo-assisted catalytic oxidation of benzyl alcohol or its derivatives, characterized in that, In the single-atom copper-doped titanium dioxide nanosheet catalyst, copper is doped into the titanium dioxide nanosheet layer in the form of single atoms, with a doping ratio of 0.5~5 wt%, and the thickness of the single-layer titanium dioxide nanosheet is 0.8~1.2 nm. It is prepared through the following steps: (1) Copper oxide, rutile titanium dioxide, potassium carbonate, and lithium carbonate powders are physically mixed uniformly by grinding, wherein the molar ratio of copper oxide, rutile titanium dioxide, potassium carbonate, and lithium carbonate is: x :(5.2- x ) / 3: 0.4:(0.8-2 x ) / 3, x =0.05~0.2; (2) Calcine the mixture obtained in step (1) in air at 900~1000 °C for 20~40 hours; (3) Mix the calcined sample from step (2) evenly by grinding; (4) Place the sample obtained in step (3) in hydrochloric acid solution for protonation treatment; (5) Wash the sample obtained in step (4) with water until neutral and vacuum dry for more than 24 hours; (6) The sample obtained in step (5) is uniformly dispersed in a tetrabutylammonium hydroxide solution and placed in a shaker for wet chemical stripping; (7) Centrifuge and freeze dry the suspension obtained in step (6) to obtain Cu1-TiO2 nanosheets.

2. The application according to claim 1, characterized in that, In step (4), the concentration of the hydrochloric acid solution is 2~4 wt%.

3. The application according to claim 1, characterized in that, In step (4), the solid-liquid ratio of the sample to the hydrochloric acid solution is 1g : 50~200 mL.

4. The application according to claim 1, characterized in that, In step (4), the protonation treatment time is 24 to 72 hours.

5. The application according to claim 1, characterized in that, In step (6), the concentration of the tetrabutylammonium hydroxide solution is 0.6~0.8 wt%, and the solid-liquid ratio of the sample to the tetrabutylammonium hydroxide solution is 1 g : 250~500 mL.

6. The application according to claim 1, characterized in that, In step (6), the wet chemical stripping treatment time is 5 to 20 days, the shaking temperature is controlled at 25 ℃, and the shaking speed is 150 to 300 rpm.

7. The application according to claim 1, characterized in that, The specific application method is as follows: using benzyl alcohol or its derivatives as reactants, potassium tert-butoxide as a base, toluene as a solvent, and adding single-atom copper-doped titanium dioxide nanosheet catalyst, the catalytic oxidation reaction is carried out at 60±10℃ in an air atmosphere and under external 365 nm light radiation to obtain benzaldehyde or its corresponding derivatives.

8. The application according to claim 1, characterized in that, The benzyl alcohol derivatives are p-methylbenzyl alcohol, p-chlorobenzyl alcohol, p-bromobenzyl alcohol, or p-nitrobenzyl alcohol.

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