Application of Pd / TiO2 photocatalyst in preparation of glycolaldehyde through selective oxidation of glycerol

Abstract

The invention discloses an application of a Pd / TiO2 photocatalyst in preparation of glycolaldehyde by selective oxidation of glycerol, and in the Pd / TiO2 photocatalyst, the particle size range of Pd is 0.5-25 nm. The Pd / TiO2 photocatalyst is used for preparing glycolaldehyde through selective oxidation of glycerol, the particle size of Pd is regulated and controlled, then the adsorption configuration of glycerol molecules is regulated and controlled, selective fracture of C-C bonds is promoted, along with increase of the particle size of Pd, the glycerol conversion rate, the glycolaldehyde selectivity and the formation rate are in a remarkable rising trend, and the stability is good and is far superior to that of an existing reported catalytic system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalysis and high-value utilization of biomass, and particularly relates to application of a Pd / TiO2 photocatalyst in selective oxidation of glycerol to glycolaldehyde. BACKGROUND

[0002] Glycerol is a byproduct in the production process of biodiesel and bioethanol, and is widely available and low in price. By selectively breaking the C-C bond to convert glycerol into glycolaldehyde and other high-value chemicals, the utilization rate of biomass resources can be improved, and environmental pollution can be alleviated. However, due to the similar chemical properties of the terminal hydroxyl group and the intermediate hydroxyl group in the glycerol molecule, and the close bond energy of the C-C bond and the C-H bond, traditional catalytic methods generally have the problems of poor selectivity and insufficient activity.

[0003] At present, the synthesis of glycolaldehyde mainly includes carbonylation method, ethylene glycol oxidation method and biomass pyrolysis method. The carbonylation method generally uses formaldehyde as a raw material, and reacts in the presence of a Co or Rh catalyst under high temperature and high pressure (such as 120℃, 200atm). The selectivity of glycolaldehyde in the Co catalytic system is about 50%, and the selectivity of glycolaldehyde in the Rh catalytic system can reach 90-100%, but there are problems such as high cost, strong toxicity of formaldehyde, and complex separation. The ethylene glycol oxidation method is carried out under mild conditions, and the process is simple, but the selectivity of glycolaldehyde is generally less than 50%, and there are many by-products. The biomass pyrolysis method has complex products, and the yield of glycolaldehyde is generally less than 10wt%, which is difficult to achieve high-purity preparation. SUMMARY

[0004] In view of the technical problems of low catalyst activity and low selectivity of glycolaldehyde in the existing selective oxidation of glycerol to glycolaldehyde, the purpose of the present application is to provide application of a Pd / TiO2 photocatalyst in selective oxidation of glycerol to glycolaldehyde, so as to significantly improve the generation rate and selectivity of glycolaldehyde by using Pd / TiO2 as a photocatalyst and controlling the particle size of Pd.

[0005] In order to achieve the above technical purpose, the technical scheme adopted by the present application is as follows:

[0006] The application of the Pd / TiO2 photocatalyst in selective oxidation of glycerol to glycolaldehyde, wherein the particle size of Pd in the Pd / TiO2 photocatalyst ranges from 0.5nm to 25nm.

[0007] Further, the particle size of Pd ranges from 10nm to 25nm.

[0008] Further, the particle size of Pd ranges from 20nm to 25nm.

[0009] Further, the loading amount of Pd in the Pd / TiO2 photocatalyst is 0.5wt% to 2wt%.

[0010] Furthermore, the preparation process of the Pd / TiO2 photocatalyst is as follows: palladium nitrate or palladium nitrate and citric acid are dispersed in deionized water to obtain a palladium precursor solution; then anatase phase TiO2 is added, mixed thoroughly and dried to obtain a solid precursor I; then the solid precursor I is calcined at 300-600°C to obtain a solid precursor II; finally, the solid precursor II is reduced at 200-300°C in a H2 / Ar atmosphere to obtain a Pd / TiO2 photocatalyst.

[0011] The present invention uses Pd / TiO2 photocatalyst for the selective oxidation of glycerol to ethanolaldehyde. It was unexpectedly discovered that the particle size of Pd in ​​the Pd / TiO2 photocatalyst has a significant impact on the catalytic performance of the catalyst. Based on this, the present invention prepared a series of Pd / TiO2 photocatalysts with different Pd particle sizes (single atom, 0.95nm sub-nano clusters, 11.0nm metal particles, 22.5nm metal particles). The study found that by regulating the Pd particle size, the adsorption configuration of glycerol molecules can be adjusted to promote the selective breakage of C-C bonds. With the increase of Pd particle size, the glycerol conversion rate, ethanolaldehyde selectivity and formation rate showed a significant upward trend. For example, when Pd was 22.5nm metal nanoparticles, the reaction was 2h, the glycerol conversion rate was 36.52%, the ethanolaldehyde selectivity was 87.54%, and the formation rate was 12.05mmol·g -1 h-1, with a carbon balance of 95%, and no significant performance degradation after 8 cycles, which is far superior to the existing reported catalytic systems.

[0012] Beneficial effects of the present invention:

[0013] The present invention uses Pd / TiO2 photocatalyst for the selective oxidation of glycerol to ethanolaldehyde. By regulating the particle size of Pd, the adsorption configuration of glycerol molecules is adjusted, promoting the selective breaking of C-C bonds. As the Pd particle size increases, the glycerol conversion rate, ethanolaldehyde selectivity and formation rate show a significant upward trend. The stability is good and is far superior to existing reported catalytic systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 High-resolution transmission electron microscopy images and particle size distribution diagrams of Pd / TiO2 catalysts with different particle sizes.

[0015] like Figure 1 As shown, the Pd atoms in the Pd single atom samples (a and e) are uniformly dispersed on the TiO2 surface, and no agglomeration is observed; the samples with a Pd particle size of 0.95nm (b and f) present a sub-nanometer cluster structure; the samples with Pd particle sizes of 11.0nm (c and g) and 22.5nm (d and h) are both regular metal nanoparticles with a concentrated particle size distribution.

[0016] Figure 2XPS Pd 3d spectra of Pd / TiO2 catalysts with different Pd particle sizes.

[0017] As shown in Figure 2 , with the increase of Pd particle size, the binding energy of Pd 3d 5 / 2 and Pd 3d 3 / 2 peaks gradually moves to the low energy direction, indicating that Pd changes from high valence state to metal state, which is consistent with the rule that the increase of particle size leads to the enhancement of Pd metallicity, and also mutually confirms the CO-DRIFTS results.

[0018] Figure 3 CO-DRIFTS spectra of Pd / TiO2 catalysts with different Pd particle sizes.

[0019] As shown in Figure 3 , Pd monatomic sample (Pd1 / TiO2) appears two types of CO adsorption peaks at 2120 cm -1 and 2080 cm -1 , corresponding to linearly adsorbed CO on isolated Pd atoms; Pd 0.95 nm (Pd n1 / TiO2) sample, in addition to monatomic peaks, also appears cluster state characteristic peaks in the range of 1968-1860 cm -1 ; Pd 11.0 nm (Pd p1 / TiO2) and 22.5 nm (Pd p2 / TiO2) samples only appear nanoparticle characteristic peaks at 1905 cm -1 , indicating that Pd exists in the form of metal particles after the increase of Pd particle size.

[0020] Figure 4 Performance comparison chart of Pd / TiO2 catalysts with different Pd particle sizes in the photocatalytic glycerol oxidation reaction.

[0021] As shown in Figure 4 a, with the increase of Pd particle size from monatomic, 0.95 nm, 11.0 nm to 22.5 nm, the glycerol conversion rate and the formation rate of glycerol aldehyde of Pd / TiO2 catalysts with different Pd particle sizes show a significant upward trend, indicating that Pd particle size has a significant impact on photocatalytic activity, and reaches the highest performance when the particle size is 22.5 nm, showing the optimal catalytic activity.

[0022] As shown in Figure 4b, the unit activity (i.e. TOF, turnover frequency) was used as the performance evaluation index to eliminate the apparent activity difference caused by different Pd loadings. After normalizing the actual effective site number of Pd, TOF can more fairly reflect the intrinsic catalytic efficiency of a single active site under different particle sizes. The results show that as the Pd particle size increases, the TOF also shows an upward trend, and the selectivity of glycolaldehyde is also synchronously improved, indicating that the particle size not only improves the total activity, but also optimizes the selectivity by changing the adsorption configuration of glycerol on the surface and the C-C bond cleavage path, ruling out the possibility that the effect is only caused by the difference in metal amount.

[0023] As Figure 4 c shows, the glycolaldehyde formation rate and selectivity of the Pd / TiO2 catalyst with a particle size of 22.5 nm in the present application are compared with those of multiple representative glycerol oxidation photocatalytic systems in existing literature (including Au3Pt1 / TiO2-001 [1] , Bi2WO6 [2] , Bi / Bi 3.6 Mo 0.36 O 6.55 [3] , Cu / WO3 [4] , ZnO / InCuS2 [5] , Ni / TiO2 [6] , Cu / TiO2 [7] , etc.). The present catalyst simultaneously achieves high conversion (36.52%) and high selectivity (87.54%) under mild light and oxygen conditions, with a formation rate of 12.05 mmol·g -1 ·h-1, far superior to the performance of existing reported systems in terms of coupling of activity and selectivity.

[0024] As Figure 4 d shows, the Pd / TiO2 catalyst with a particle size of 22.5 nm was subjected to a cycle stability test, and the results show that after 8 continuous cycles, the formation rate and selectivity of glycolaldehyde do not decrease significantly, indicating that the catalyst not only has high catalytic activity, but also has excellent stability.

[0025] Figure 5 Performance curve of the Pd / TiO2 catalyst with a Pd particle size of 22.5 nm in the glycerol oxidation reaction for preparing glycolaldehyde under photocatalysis, as a function of reaction time.

[0026] As Figure 5As shown, with the reaction time prolonged from 1 h to 8 h, the glycerol conversion rate showed a steady upward trend, and the conversion rate was about 78.56% at 8 h, and the ethanol aldehyde selectivity had no obvious change, about 87%, which indicated that the catalyst could effectively inhibit the occurrence of side reactions while prolonging the reaction time and improving the conversion rate, thereby ensuring the high selectivity of the target product.

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[0039] Photocatalytic water reduction with concurrent glycerol oxidation in sunlight. Journal of Catalysis. 2024, 437, 115644. DETAILED DESCRIPTION

[0040] The following examples further illustrate the content of the present application, but the scope of protection of the claims of the present application is not limited by the examples.

[0041] The present application evaluates the performance of Pd / TiO2 catalysts with different particle sizes by photocatalytic glycerol selective oxidation reaction. The reaction system is 25 mM glycerol aqueous solution (volume 10 mL), and the catalyst is added in an amount of 5 mg. The reaction is carried out in a sealed quartz reactor, which is equipped with a constant temperature water jacket to maintain 25±1℃; the light source is a 300W xenon lamp equipped with AM 1.5G filter and homogenizer, the light intensity is 100 mW / cm 2 , the distance between the lamp and the surface of the reaction solution is 10 cm; the reaction atmosphere is 1 atm of high-purity oxygen, and the solution is continuously stirred by magnetic stirring to ensure uniformity during the reaction. The products are filtered through a 0.22 μm filter membrane, and then quantitatively analyzed by HPLC (Agilent 1260, Hi-Plex H column, ultraviolet and differential double detection), to calculate the glycerol conversion rate, glycolaldehyde selectivity and carbon balance.

[0042] Example 1

[0043] (1) 0.05 g of Pd(NO3)2·2H2O (analytical pure) and 0.11 g of citric acid (analytical pure) were weighed and dissolved in 2.6 mL of deionized water, and stirred by magnetic stirring at room temperature for 10 min to obtain a precursor solution;

[0044] (2) 1.73 g of anatase TiO2 powder was slowly added, and stirring was continued for 30 min until a uniform slurry was formed;

[0045] (3) The slurry was placed in a 80℃ water bath and evaporated to dryness, then transferred to a blast drying oven at 125℃ and dried overnight;

[0046] (4) The dried product was placed in a muffle furnace and heated to 300°C at a rate of 5°C / min, and then kept for 5 h before naturally cooling to room temperature;

[0047] (5) The calcined product was placed in a tube furnace and heated to 250°C at a rate of 1°C / min, and then reduced for 1 h under 10% H2 / Ar mixed gas (total flow rate 50 mL / min). After cooling, it was stored in argon and marked as Pd / TiO2. n1 / TiO2;

[0048] (6) The average Pd particle size was 0.95±0.1 nm, and the Pd particles showed a sub-nanometer cluster structure, as measured by HAADF-STEM.

[0049] After 2 h of reaction, the glycerol conversion rate was 21.73%, the glycolaldehyde selectivity was 68.50%, and the carbon balance was 96%.

[0050] Example 2

[0051] (1) 0.10 g of Pd(NO3)2·2H2O (analytical pure) and 0.11 g of citric acid (analytical pure) were weighed and dissolved in 2.6 mL of deionized water, and then magnetically stirred at room temperature for 10 min to obtain a precursor solution;

[0052] (2) 1.73 g of anatase TiO2 powder was slowly added, and stirring was continued for 30 min until a uniform slurry was formed;

[0053] (3) The slurry was placed in a 80°C water bath and evaporated to dryness, and then transferred to a forced air drying oven at 125°C and dried overnight;

[0054] (4) The dried product was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min, and then kept for 5 h before naturally cooling to room temperature;

[0055] (5) The calcined product was placed in a tube furnace and heated to 250°C at a rate of 1°C / min, and then reduced for 1 h under 10% H2 / Ar mixed gas (total flow rate 50 mL / min). After cooling, it was stored in argon and marked as Pd / TiO2. p1 / TiO2;

[0056] (6) The average Pd particle size was 11.0±1.2 nm, as measured by HAADF-STEM.

[0057] After 2 h of reaction, the glycerol conversion rate was 33.01%, the glycolaldehyde selectivity was 75.99%, and the carbon balance was 98%.

[0058] Example 3

[0059] (1) 0.10 g of Pd(NO3)2·2H2O was weighed and dissolved in 2.6 mL of deionized water, and then magnetically stirred at room temperature for 10 min to obtain a precursor solution;

[0060] (2) Slowly add 1.73 g of anatase TiO2 powder, continue stirring for 30 min until a uniform slurry is formed;

[0061] (3) Place the slurry in a 80°C water bath to evaporate dry, then transfer to a blast drying oven at 125°C and dry overnight;

[0062] (4) Place the dried product in a muffle furnace, heat to 600°C at a rate of 5°C / min, keep for 5 h, and then naturally cool to room temperature;

[0063] (5) Place the calcined product in a tube furnace, heat to 250°C at a rate of 1°C / min, reduce for 1 h under 10% H2 / Ar mixed gas (total flow rate 50 mL / min), and then store in argon after cooling, denoted as Pd / TiO2; p2

[0064] (6) The average Pd particle size is 22.5 ± 1.5 nm measured by HAADF-STEM.

[0065] After testing, the glycerol conversion rate is 36.52%, the ethanol aldehyde selectivity is 87.54%, the carbon balance is 95%, the generation rate is as high as 12.05 mmol·g -1 ·h-1, and the performance does not significantly decay after 8 cycles.

[0066] Comparative Example 1

[0067] (1) Weigh 0.025 g of Pd(NO3)2·2H2O (analytical pure) and 0.215 g of citric acid (analytical pure) into 2.6 mL of deionized water, magnetically stir for 10 min at room temperature, and obtain a precursor solution;

[0068] (2) Slowly add 1.73 g of anatase TiO2 powder, continue stirring for 30 min until a uniform slurry is formed;

[0069] (3) Place the slurry in a 80°C water bath to evaporate dry, then transfer to a blast drying oven at 125°C and dry overnight;

[0070] (4) Place the dried product in a muffle furnace, heat to 300°C at a rate of 5°C / min, keep for 5 h, and then naturally cool to room temperature;

[0071] (5) Place the calcined product in a tube furnace, heat to 250°C at a rate of 1°C / min, reduce for 1 h under 10% H2 / Ar mixed gas (total flow rate 50 mL / min), and then store in argon after cooling, denoted as Pd1 / TiO2;

[0072] (6) Confirm that Pd is dispersed in the form of a single atom by HAADF-STEM, and no metal clusters are observed.

[0073] ​The detection shows that the conversion rate of glycerol is 10.69%, the selectivity of glycolaldehyde is 45.26%, and the carbon balance is 97% after 2h reaction.

[0074] Comparative Example 2

[0075] The same as Example 3, except that the reduction is not performed, and the calcination product is directly used as the catalyst.

[0076] The detection shows that the conversion rate of glycerol is 15.23%, the selectivity of glycolaldehyde is 47.88%, and the carbon balance is 93% after 2h reaction.

[0077] Comparative Example 3

[0078] The same as Example 3, except that the anatase TiO2 powder is replaced by the rutile TiO2 powder.

[0079] The detection shows that the conversion rate of glycerol is 18.91%, the selectivity of glycolaldehyde is 55.45%, and the carbon balance is 97% after 2h reaction.

[0080] Comparative Example 4

[0081] The same as Example 3, except that the Pd(NO3)2·2H2O is replaced by Cu(NO3)2·3H2O, and the mass of Pd is kept consistent with the mass of Cu, and the prepared catalyst is recorded as Cu / TiO2.

[0082] The detection shows that the conversion rate of glycerol is 12.35, the selectivity of glycolaldehyde is 38.42, and the carbon balance is 94% after 2h reaction.

[0083] Comparative Example 5

[0084] The same as Example 3, except that the Pd(NO3)2·2H2O is replaced by Co(NO3)2·6H2O, and the mass of Pd is kept consistent with the mass of Co, and the prepared catalyst is recorded as Co / TiO2.

[0085] The detection shows that the conversion rate of glycerol is 14.78, the selectivity of glycolaldehyde is 42.15, and the carbon balance is 95% after 2h reaction.

[0086] Comparative Example 6

[0087] The same as Example 3, except that the Pd(NO3)2·2H2O is replaced by Ni(NO3)2·6H2O, and the mass of Pd is kept consistent with the mass of Ni, and the prepared catalyst is recorded as Ni / TiO2.

[0088] The detection shows that the conversion rate of glycerol is 10.92, the selectivity of glycolaldehyde is 35.87, and the carbon balance is 93% after 2h reaction.

Claims

1. Application of Pd / TiO2 photocatalyst in selective oxidation of glycerol to glycoaldehyde, characterized by: In the Pd / TiO2 photocatalyst, the particle size of Pd ranges from 0.5 to 25 nm.

2. The use according to claim 1, characterized in that: The particle size of the Pd is in the range of 10 to 25 nm.

3. The use according to claim 2, characterized in that: The particle size of the Pd is in the range of 20 to 25 nm.

4. The use according to any one of claims 1 to 3, characterized in that: In the Pd / TiO2 photocatalyst, the loading amount of Pd is 0.5-2 wt%.

5. The use according to any one of claims 1 to 3, characterized in that: The preparation process of the Pd / TiO2 photocatalyst is as follows: palladium nitrate or palladium nitrate and citric acid are dispersed in deionized water to obtain a palladium precursor solution; anatase phase TiO2 is then added, mixed thoroughly, and dried to obtain a solid precursor I; The solid precursor I is then calcined at 300-600° C. to obtain a solid precursor II; finally, the solid precursor II is reduced at 200-300° C. in a H2 / Ar atmosphere to obtain a Pd / TiO2 photocatalyst.

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