Process for the preparation of a heterogeneous rhodium-based catalyst and use thereof

Abstract

This invention belongs to the field of heterogeneous Rh-based catalyst technology, and discloses a method for preparing a heterogeneous rh-based catalyst and its application. This invention prepares a heterogeneous rh-based catalyst using a one-pot method. By employing a reduction-reoxidation process, the content of different valence states of rhino in the rhino species on the surface of the heterogeneous rh-based catalyst is simply and precisely controlled, increasing the content of the most favorable δ+ valence state from 7.31% to 44.78%, thereby giving the catalyst higher hydroformylation activity. Under reaction conditions of 120℃ and a mixed gas pressure of 2 MPa, the styrene conversion rate reaches 73.9% and the aldehyde selectivity reaches 95.9% within 4 hours, which is superior to most heterogeneous rhino-based catalysts and close to that of homogeneous rhino catalysts. The heterogeneous rhino-based catalyst is prepared by the sol-gel method, which is simple in preparation and control. The prepared catalyst has a uniform rhino distribution, stable performance, and is beneficial for industrial applications.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous Rh-based catalyst technology, and relates to a method for preparing a heterogeneous rhodium-based catalyst and its application. Background Technology

[0002] Olefin hydroformylation is a core chemical process that uses olefins and syngas (CO / H2) as raw materials to produce high-value-added aldehydes with high atom economy. It has wide applications in plasticizers, surfactants, and pharmaceutical intermediates, and is one of the largest homogeneous catalytic industrial reactions currently in operation. Rhodium-based catalytic systems have become the mainstream catalytic system in the field of hydroformylation due to their high activity and mild reaction conditions.

[0003] Traditional homogeneous rhodium catalysts, while possessing excellent catalytic activity and regioselectivity, suffer from challenges such as difficulty in separating the catalyst from the product, complex rhodium recovery processes, and significant loss of rhodium and organic ligands. Given the scarcity and high price of rhodium resources, even minute losses can significantly increase production costs. Furthermore, the difficulty in achieving continuous production in homogeneous systems limits their large-scale application in high-end fine chemicals. To overcome these bottlenecks, developing easily separable, recyclable, and low-metal-loss heterogeneous rhodium-based catalysts has become an important research direction in the field of hydroformylation.

[0004] While existing heterogeneous rhodium-based catalysts offer advantages in separation and recovery, they still face numerous technical challenges. Firstly, the interaction between most supports and rhodium active sites is weak, and rhodium species are prone to leaching and loss under reaction atmospheres, forming volatile carbonyl complexes, leading to poor catalyst cycle stability. Furthermore, the method of controlling catalyst activity and stability by adjusting Rh particle size remains controversial. Some literature suggests that constructing rhodium single atoms supported by strong metal-support interactions in an oxidized form can achieve efficient and stable heterogeneous hydroformylation, while other literature suggests that adjusting the rhodium cluster size to its optimal range can result in the best olefin hydroformylation activity and stability. Secondly, the valence state distribution of rhodium active centers is difficult to precisely control, and Rh... 0 ,Rh δ+ ,Rh +1 ,Rh +3 Different valence states of species have a decisive influence on CO adsorption activation, olefin insertion, and product selectivity. Uncontrollable valence states often lead to a difficulty in achieving both catalytic activity and regioselectivity. In addition, traditional preparation processes struggle to achieve high dispersion of rhodium species and directional adjustment of valence states to highly active valence states. In phosphine-free ligand systems, the activity is often low and aldehyde selectivity is insufficient, failing to meet the dual requirements of catalytic performance and economy in industrial production.

[0005] Patent CN116474768A discloses a heterogeneous rhodium-based catalyst for the hydroformylation of olefins and its preparation method, which modulates the valence state of rhodium on the catalyst surface from 0 to a high valence state. However, there are few technical solutions that can precisely adjust the valence state of rhodium on the surface of heterogeneous rhodium-based catalysts, making it difficult to meet the differentiated requirements of the electronic structure of the active center for the hydroformylation of different olefin substrates. Therefore, developing a simple preparation method for a heterogeneous rhodium-based catalyst with high activity, high content of δ+ valence rhodium species, and both high catalytic activity and selectivity, and realizing its efficient application in the hydroformylation reaction of olefins, has important theoretical value and practical significance for promoting the industrialization of heterogeneous hydroformylation technology. Summary of the Invention

[0006] The purpose of this invention is to address the existing technical challenges by providing a method for preparing a heterogeneous rhodium hydroformylation catalyst. This method overcomes the shortcomings of existing catalytic technologies and, through a simple adjustment method, can significantly enhance the hydroformylation activity of Rh among the rhodium species on the catalyst surface. δ+ The high content of valence states (0 < δ < 1) gives it high hydroformylation catalytic performance. Furthermore, the raw materials are readily available and the preparation method is simple, thus facilitating industrial applications. This invention uses TiO2 as a support to load Rh, and through a reduction-reoxidation strategy, precisely controls the valence state of Rh on the catalyst surface, thereby improving the catalytic performance of olefin hydroformylation to a limited extent. Under certain reaction conditions, the conversion rate and aldehyde selectivity in the olefin hydroformylation reaction are both increased by more than 30%.

[0007] The technical solution of the present invention: A method for preparing a heterogeneous rhodium-based catalyst, comprising the following steps: (1) Mix alcohol, deionized water and glacial acetic acid and stir to obtain a mixed solution; then disperse the rhodium source in the above mixed solution and continue stirring to obtain a rhodium-containing mixed solution; (2) Add titanium source slowly to rhodium-containing mixed solution, stir for 3 h, and age at room temperature for 1-2 days to obtain colloid; dry the obtained colloid overnight, grind the dried colloid thoroughly to obtain heterogeneous catalyst precursor; calcine the catalyst precursor to obtain heterogeneous rhodium-based catalyst, wherein the rhodium loading is 0.01wt%~10wt%; (3) After reduction in a reducing atmosphere, the heterogeneous rhodium-based catalyst is re-oxidized under different temperature oxidation atmospheres to achieve precise control of the rhodium valence state on the surface of the heterogeneous rhodium-based catalyst and improve the Rh content in the catalyst. δ+ The valence state enables highly efficient catalysis of olefin hydroformylation.

[0008] In step (1), the alcohol is selected from one or more of methanol, ethanol, n-butanol, and isopropanol; the volume ratio of alcohol, deionized water and glacial acetic acid in the mixed solution is 63:6:7; the rhodium source is selected from one or more of rhodium trichloride, rhodium dicarbonylacetylacetone, and rhodium tri(triphenylphosphine)chloride; the molar concentration of rhodium in the mixed solution is 0.0005~5 mol / L.

[0009] In step (2), the titanium source is selected from one or more of tetrabutyl titanate, isopropyl titanate, titanium tetrachloride, titanium sulfate, and titanium oxysulfate; the concentration of the titanium source in the mixed solution is 0.5~2 mol / L.

[0010] In step (2), the oven drying temperature is 80~120℃, the calcination temperature is 300~800℃, and the calcination time is 0.5~3h.

[0011] In step (3), the reducing atmosphere is hydrogen or a mixture of H2 and Ar, with the hydrogen component in the mixture being 5% to 100%; the gas flow rate is 10 to 100 mL / min; the reduction temperature is 300 to 800℃; and the heating rate is 1 to 20℃ / min.

[0012] In step (3), the oxidation atmosphere is air or a mixture of O2 and N2, and the volume fraction of oxygen in the mixture is 0.2% to 100%; the oxidation treatment temperature is 100 to 500°C, the treatment time is 0.5 to 4 h, and the heating rate is 1 to 10°C / min.

[0013] Application of the heterogeneous rhodium-based catalyst obtained by the above preparation method in the hydroformylation reaction of olefins.

[0014] The beneficial effects of this invention are: (1) This invention prepares a heterogeneous rhodium-based catalyst using a one-pot method. By reducing and then re-oxidizing, the content of different valence states of rhodium in the rhodium species on the surface of the heterogeneous rhodium-based catalyst is simply and precisely controlled, increasing the content of the δ+ valence state, which is most favorable for the reaction, from 7.31% to 44.78%, thereby giving the catalyst higher hydroformylation activity. Under reaction conditions of 120℃ and a mixed gas pressure of 2 MPa, the styrene conversion rate reaches 73.9% and the aldehyde selectivity reaches 95.9% within 4 hours, which is better than most heterogeneous rhodium-based catalysts and close to that of homogeneous rhodium catalysts.

[0015] (2) The catalyst is prepared by the sol-gel method. The preparation method and control method are simple. The prepared catalyst has uniform rhodium distribution, stable performance, and is conducive to industrial application. Attached Figure Description

[0016] Figure 1 XPS spectra of Rh3d for different catalysts; Figure 2 The images are transmission electron microscopy (TEM) images of the catalyst; where (a) is a TEM image at the 20 nm scale, (b) is a TEM image at the 10 nm scale, and (c) is a TEM image at the 5 nm scale. Detailed Implementation

[0017] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0018] Example 1 The specific preparation method of the multiphase rhodium-based catalyst Rh-TiO2-700-500-200 includes the following steps: Step 1: Add 1.2 mL of deionized water and 1.4 mL of glacial acetic acid to 12.6 mL of n-butanol and stir for 0.5 h.

[0019] Step 2: Weigh 8 mg of rhodium chloride trihydrate and add it to the above mixed solution. Stir for 1 hour to ensure that it is evenly dispersed in the solution.

[0020] Step 3: Slowly add 9.6 mL of tetrabutyl titanate to the mixed solution, stir for 3 hours, and then age at room temperature for 1 day after gelation.

[0021] Step 4: Dry the colloid in an oven at 110°C overnight, grind it thoroughly, and then calcine it in a muffle furnace at 700°C for 3 hours. Set the heating rate to 5°C / min.

[0022] Step 5: Place the calcined powder into a tube furnace and reduce it at 500℃ for 2 hours in a 10% H2 / Ar atmosphere with a gas flow rate of 30 mL / min and a heating rate of 5℃ / min.

[0023] Step 6: The reduced powder is calcined in a muffle furnace at 200℃ for 2 hours in air atmosphere, with a heating rate of 5℃ / min. The catalyst Rh-TiO2-700-500-200 is obtained.

[0024] Example 2 The specific preparation method of the multiphase rhodium-based catalyst Rh-TiO2-700-500-300 includes the following steps: This implementation is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the calcination temperature of the catalyst in the muffle furnace under air atmosphere in step 6 is 300°C.

[0025] Example 3 The specific preparation method of the multiphase rhodium-based catalyst Rh-TiO2-700-500-400 includes the following steps: This implementation is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the calcination temperature of the catalyst in the muffle furnace under air atmosphere in step 6 is 400°C.

[0026] Example 4 The specific preparation method of the heterogeneous rhodium-based catalyst Rh-TiO2-700-500-300-1 includes the following steps: This implementation is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that step 6 is changed to calcining the reduced powder in a tube furnace at 300°C under a 2% O2 / N2 atmosphere, with a heating rate of 5°C / min.

[0027] Example 5 The specific preparation method of the multiphase rhodium-based catalyst Rh-TiO2-700-500-300-2 includes the following steps: This implementation is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the reducing atmosphere in step 5 is changed to pure H2.

[0028] Example 6 The specific preparation method of the multiphase rhodium-based catalyst Rh-TiO2-700-400-300 includes the following steps: This implementation is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the reduction temperature in step 5 is changed to 400°C and the calcination temperature in step 6 is changed to 300°C.

[0029] Example 7 The specific preparation method of the multiphase rhodium-based catalyst Rh-TiO2-700-400-200 includes the following steps: This implementation is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the reduction temperature in step 5 is changed to 400°C.

[0030] Example 8 The specific preparation method of the multiphase rhodium-based catalyst Rh-TiO2-600-500-300 includes the following steps: This implementation is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the roasting temperature in step 4 is changed to 600°C and the roasting temperature in step 6 is changed to 300°C.

[0031] Comparative Example 1 The specific preparation method of the heterogeneous rhodium-based catalyst Rh-TiO2-700 includes the following steps: This implementation is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that steps 5 and 6 are not performed.

[0032] Comparative Example 2 The specific preparation method of the multiphase rhodium-based catalyst Rh-TiO2-700-500 includes the following steps: This implementation is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that step 6 is not performed.

[0033] Comparative Example 3 The specific preparation method of the multiphase rhodium-based catalyst Rh-TiO2-700-400 includes the following steps: This implementation is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the reduction temperature in step 5 is changed to 400°C, and step 6 is not performed.

[0034] The XRS spectra of Rh 3d in Examples 1-3 and Comparative Examples 1-2 are as follows: Figure 1 As shown in Table 2, the content of Rh in different valence states is as follows. The Rh content on the Rh-TiO2-700 surface is mainly in the +3 valence state (66.03%), while the Rh content on the Rh-TiO2-700-500 surface is mainly in the 0 valence state (57.78%). When the catalyst is re-oxidized in air, the valence state of Rh on the catalyst surface gradually shifts towards higher valence states. When the oxidation temperature is 200℃, some of the Rh... 0 Oxidized to Rh δ+ Rh δ+ The content of Rh increases, and when the re-oxidation temperature is 300℃, most of the Rh... 0 It was oxidized to Rh δ+ Rh δ+ The content of Rh reaches its highest value, accounting for 44.78% of all rhino species, but when the oxidation temperature is above 300℃, Rh... δ+ It will be further oxidized to Rh +1 and Rh +3 Rh δ+ The content of Rh decreased. δ+ The content decreased from 44.78% to 23.25%. XPS characterization and the content of rhodium in different valence states demonstrate that the content of rhodium species in different valence states on the surface of this heterogeneous rhodium-based catalyst can be precisely adjusted through re-oxidation.

[0035] The transmission electron microscope of Example 1 is as follows: Figure 2 As shown, Rh is loaded onto the support in the form of nanoparticles with a particle size of approximately 1.7 nm. The particles are uniformly distributed, and reduction and re-oxidation did not alter the morphology of the support or the particle size of Rh. Furthermore, in... Figure 2 Rh can be measured in δ+ The lattice spacing of the nanoparticles is consistent with the XPS results.

[0036] The hydroformylation performance of the experimental examples and comparative examples was investigated, including the following steps: The reaction was carried out in a 25 mL high-pressure batch reactor. A certain amount of catalyst was weighed using an electronic balance and added to the reactor liner, followed by 5 mL of toluene, 2.5 mmol of styrene, and 2.0 mmol of n-hexanol (using n-hexanol as an internal standard). The reactor was purged five times with syngas (CO:H2 = 1:1), and then the syngas pressure was increased to 2 MPa. After heating to 120℃ for 20 minutes, the timer was started and the reaction was carried out for 4 hours. After the reaction was completed and cooled to room temperature, the reaction liquid and catalyst were separated by centrifugation. The products in the reaction liquid were analyzed by chromatography, and the results are shown in Table 1.

[0037] The analytical results show that, compared with Comparative Examples 1–3, the catalysts in Examples 1–8 exhibited relatively higher styrene conversion and aldehyde selectivity in the styrene hydroformylation reaction, indicating that the catalysts prepared by this method possess excellent catalytic performance. The catalyst activity reached its optimal level at an oxidation temperature of 300℃. Compared with Comparative Example 2, Example 2 showed an increase in styrene conversion from 41.6% to 73.9%, and an increase in total aldehyde selectivity from 53.2% to 95.9%. Combined with XPS characterization results, it can be seen that the excellent catalytic performance of Rh-TiO2-700-500-300 is related to its highest Rh content. + Species are closely related. Rh is partially positively charged. + When in the valence state, it possesses a suitable electronic structure and coordination environment. Compared to the metallic Rh... 0 Rh + With a lower electron cloud density, it exhibits a more moderate adsorption strength for reaction intermediates such as CO, effectively avoiding active site poisoning caused by strong adsorption; simultaneously, it interacts with high-valence Rh... 3+ and Rh + In comparison, Rh + It still retains some feedback π electron capability, which can efficiently activate the reaction substrate, thereby leading to Rh + It exhibits better catalytic performance in the hydroformylation reaction. In summary, this catalyst can effectively modulate Rh through a re-oxidation strategy. + The valence distribution significantly enhances the catalytic activity and selectivity of this catalyst in the hydroformylation of styrene.

[0038] Table 1 shows the olefin hydroformylation performance of different heterogeneous rhodium-based catalysts.

[0039] Table 2 shows the content of Rh in different valence states in different catalysts.

[0040] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a heterogeneous rhodium-based catalyst, characterized in that, The steps are as follows: (1) Mix alcohol, deionized water and glacial acetic acid and stir to obtain a mixed solution; then disperse the rhodium source in the above mixed solution and continue stirring to obtain a rhodium-containing mixed solution; (2) Add titanium source slowly to rhodium-containing mixed solution, stir for 3 h, and age at room temperature for 1-2 days to obtain colloid; dry the obtained colloid overnight, grind the dried colloid thoroughly to obtain heterogeneous catalyst precursor; calcine the catalyst precursor to obtain heterogeneous rhodium-based catalyst, wherein the rhodium loading is 0.01wt%~10wt%; (3) After reduction in a reducing atmosphere, the heterogeneous rhodium-based catalyst is re-oxidized under different temperature oxidation atmospheres to achieve precise control of the rhodium valence state on the surface of the heterogeneous rhodium-based catalyst and improve the Rh content in the catalyst. δ+ Price state.

2. The preparation method according to claim 1, characterized in that, In step (1), the alcohol is selected from one or more of methanol, ethanol, n-butanol, and isopropanol; the volume ratio of alcohol, deionized water and glacial acetic acid in the mixed solution is 63:6:7; the rhodium source is one or more of rhodium trichloride, rhodium dicarbonylacetylacetone, and rhodium tri(triphenylphosphine)chloride; the molar concentration of the rhodium source in the mixed solution is 0.0005~5 mol / L.

3. The preparation method according to claim 1, characterized in that, In step (2), the titanium source is one or more of tetrabutyl titanate, isopropyl titanate, titanium tetrachloride, titanium sulfate, and titanium oxysulfate; the concentration of the titanium source in the mixed solution is 0.5~2 mol / L.

4. The preparation method according to claim 1, characterized in that, In step (2), the drying temperature is 80~120℃, the calcination temperature is 300~800℃, and the calcination time is 0.5~3 h.

5. The preparation method according to claim 1, characterized in that, In step (3), the reducing atmosphere is hydrogen or a mixture of H2 and Ar, with the hydrogen component in the mixture being 5% to 100%; the gas flow rate is 10 to 100 mL / min; the reduction temperature is 300 to 800℃, and the heating rate is 1 to 20℃ / min.

6. The preparation method according to claim 1, characterized in that, In step (3), the oxidation atmosphere is air or a mixture of O2 and N2, and the volume fraction of oxygen in the mixture is 0.2% to 100%; the temperature of the re-oxidation treatment is 100 to 500°C, the time of the re-oxidation treatment is 0.5 to 4 h, and the heating rate is 1 to 10°C / min.

7. Application of the heterogeneous rhodium-based catalyst obtained by the above preparation method in the hydroformylation reaction of olefins.

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