A Pd / TiO2 catalyst, its preparation method and application

Abstract

The application discloses a Pd / TiO2 catalyst and a preparation method and application thereof. The preparation method comprises the following steps: slowly adding tetrabutyl titanate into acetic acid, stirring to obtain a suspension, then transferring into an autoclave, placing into a drying box to age, obtaining a white mixed liquid, naturally cooling, centrifugally collecting the precipitate, washing, vacuum drying to obtain a white solid, then placing into a muffle furnace to calcine, obtaining flower-shaped nanometer ball TiO2 powder, then placing into a round-bottom flask, adding palladium acetylacetonate and ethanol, stirring to react to obtain a mixed liquid, rotary evaporation to obtain a light yellow powder solid, then placing into a muffle furnace to calcine, obtaining a catalyst precursor, then placing into a hydrogen tube furnace to reduce, and the Pd / TiO2 catalyst is obtained. The catalyst has a flower-shaped nanometer ball shape, contains high-dispersion and small-particle-size palladium nanoparticles, the titanium dioxide carrier contains oxygen defects, the oxygen vacancy concentration is high, and the catalyst has high selectivity and high conversion rate for a catalytic furfural decarbonylation reaction to prepare furan.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, specifically relating to a Pd / TiO2 catalyst, its preparation method, and its application. Background Technology

[0002] To reduce dependence on fossil fuels, biomass has become the only sustainable alternative and source for fuel and chemical synthesis. The selective conversion of renewable biomass-derived feedstocks plays a crucial role in the sustainable production of biofuels and fine chemicals, attracting widespread attention in fields such as green chemistry. Furfural is an important biomass chemical that can be obtained through acidic hydrolysis of hemicellulose and other abundant agricultural products. It can be used as an intermediate product to synthesize other high-value-added chemicals and materials. For example, catalytic conversion of furfural and its derivatives through hydrogenation and hydrogenolysis can yield valuable chemicals and fuels. Decarbonizing furfural into furan and then hydrogenating furan to tetrahydrofuran (THF) is a promising alternative to the industrial production of THF from fossil fuels.

[0003] The decarbonylation of furfural in both the gas and liquid phases has been extensively studied, and many catalysts for furfural decarbonylation have been reported. However, most of these are noble metal catalysts such as Pd / Pt. Furfural decarbonization requires highly active catalysts, and noble metals are widely used due to their high activity. Compared to the liquid phase, gas-phase furfural decarbonization is relatively simple, with easier contact between the catalyst and substrate. However, the temperature required for catalytic furfural decarbonization in the gas phase is excessively high, generally around 250℃. This can easily lead to carbon deposition, resulting in decreased catalyst activity, and can also cause substrate coupling and the formation of large molecular weight byproducts. Publication No. CN1095397C discloses a highly efficient supported noble metal catalyst for the gas-phase decarbonylation of furfural to produce furan. The catalyst uses an Al2O3-TiO2 composite oxide as a support, containing 0.4–0.7% P by weight, and also contains 0.5–2.0% K2O, Cs2O, MgO, CaO, or BaO by weight. This catalyst is prepared by an impregnation method. Under normal pressure, at 280°C, and with a furfural to hydrogen molar ratio of 0.5–2.0, the conversion rate can reach 80–97%, and the selectivity 85–92%. However, this patented catalyst has a high reaction temperature, a low furan yield, and is prone to deactivation. Summary of the Invention

[0004] To address the shortcomings of existing methods, this invention provides a Pd / TiO2 catalyst, its preparation method, and its applications.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a Pd / TiO2 catalyst includes the following steps:

[0007] S1. Tetrabutyl titanate is slowly added to acetic acid and stirred to obtain a suspension;

[0008] S2. Transfer the suspension obtained in step S1 to a high-pressure autoclave and place it in a drying oven for aging to obtain a white mixture.

[0009] S3. After the white mixture obtained in step S2 is cooled naturally, the precipitate is collected by centrifugation, washed, and dried under vacuum to obtain a white solid.

[0010] S4. Place the white solid obtained in step S3 into a muffle furnace and calcine it to obtain flower-shaped nanosphere TiO2 powder.

[0011] S5. Place the TiO2 powder obtained in step S4 into a round-bottom flask, add palladium acetylacetone and ethanol, and stir to react and obtain a mixture.

[0012] S6. The mixture obtained in step S5 is rotary evaporated to obtain a light yellow powder;

[0013] S7. Place the light yellow powder obtained in step S6 into a muffle furnace and calcine it at 150-250℃ for 1-3 hours to obtain the catalyst precursor.

[0014] S8. Place the catalyst precursor obtained in step S7 into a hydrogen tube furnace and reduce it at 150-250℃ for 1-3 hours to obtain the Pd / TiO2 catalyst.

[0015] Preferably, the volume ratio of tetrabutyl titanate to acetic acid in step S1 is 1:25-35.

[0016] Preferably, the ratio of TiO2 powder, palladium acetylacetone, and ethanol in step S5 is 150-250 mg: 7-10 mg: 10-30 mL.

[0017] Preferably, the aging temperature in step S2 is 160-200℃, and the time is 20-30h.

[0018] Preferably, the calcination temperature in step S4 is 400-500℃, and the time is 2-4 hours.

[0019] Preferably, the rotary evaporation temperature in step S6 is 50-70℃, and the time is 10-30 min.

[0020] Preferably, the heating rate of calcination in steps S4 and S7 is 3-10℃ / min, and the heating rate of reduction in step S8 is 3-10℃ / min.

[0021] A Pd / TiO2 catalyst with a flower-like nanosphere shape prepared by the above preparation method.

[0022] The application of a Pd / TiO2 catalyst prepared by the above method in the catalytic decarbonylation reaction of furfural to furan.

[0023] Preferably, the temperature for the furfural decarbonylation reaction to produce furan is 160-190℃, and the time is 8-16h.

[0024] The positive and beneficial effects of this invention are:

[0025] 1. The catalyst of this invention has a flower-like nanosphere shape and contains highly dispersed, small-particle-size palladium nanoparticles. The titanium dioxide support contains oxygen defects and has a high oxygen vacancy concentration, which endows it with high selectivity and high conversion rate for the catalytic decarbonylation reaction of furfural to furan. The palladium loading is low, but it exhibits high catalytic activity, which reduces the reaction cost. It can be widely used for the high-value conversion of biomass raw materials such as furanaldehyde and aldehydes. Moreover, the catalyst is easy to obtain and can be reused multiple times through recycling and separation, which is conducive to industrial promotion and application.

[0026] 2. The present invention has a low reaction temperature and mild reaction conditions for the decarbonylation of furfural to furan, exhibits high activity for the cleavage of C and D, high furfural conversion rate, high furan yield, and good selectivity for furan. Attached Figure Description

[0027] Figure 1 X-ray powder diffraction patterns of the prepared S-TiO2 (Example 1), P-TiO2 (Comparative Example 1), and C-TiO2 (Comparative Example 2) supports;

[0028] Figure 2 TEM and SEM images of the prepared S-TiO2 (Example 1), P-TiO2 (Comparative Example 1), and C-TiO2 (Comparative Example 2) supports;

[0029] Figure 3 X-ray powder diffraction patterns of the prepared S-Pd-TiO2 (Example 1), P-Pd-TiO2 (Comparative Example 1), and C-Pd-TiO2 (Comparative Example 2) catalysts;

[0030] Figure 4 TEM and SEM images of the prepared S-Pd-TiO2 (Example 1), P-Pd-TiO2 (Comparative Example 1), and C-Pd-TiO2 (Comparative Example 2) catalysts;

[0031] Figure 5 XPS 1s and EPR spectra of the prepared S-Pd-TiO2 (Example 1), P-Pd-TiO2 (Comparative Example 1), and C-Pd-TiO2 (Comparative Example 2) catalysts;

[0032] Figure 6The graph shows the results of five stability tests on the catalyst S-Pd-TiO2 (Example 1). Detailed Implementation

[0033] The present invention will be further described below with reference to some specific embodiments.

[0034] Example 1

[0035] A method for preparing a Pd / TiO2 catalyst includes the following steps:

[0036] S1. Slowly add 1 mL of tetrabutyl titanate to 30 mL of acetic acid and stir for 10 min to obtain a white suspension;

[0037] S2. Transfer the white suspension obtained in step S1 to a stainless steel autoclave lined with polytetrafluoroethylene and age it in a drying oven at 180°C for 24 hours.

[0038] S3. After the white mixture obtained in step S2 is cooled naturally, the precipitate is collected by centrifugation, washed three times with a mixture of ethanol and water, and then dried under vacuum at 100°C for 10 hours to obtain a white solid.

[0039] S4. The white solid obtained in step S3 is placed in a muffle furnace and calcined at 450°C for 3 hours to obtain flower-shaped nanosphere TiO2 powder, numbered S-TiO2. The calcination heating rate is 5°C / min.

[0040] S5. Take 200 mg of TiO2 powder obtained in step S4 and put it into a 100 mL round bottom flask. Add 8.6 mg of palladium acetylacetone and 20 mL of ethanol. Stir the reaction for 1 h to obtain a white mixture.

[0041] S6. Place the white mixture obtained in step S5 into a rotary evaporator and evaporate it at 60°C for 20 minutes to obtain a light yellow powder.

[0042] S7. The light yellow powder obtained in step S6 is placed in a muffle furnace and calcined at 200°C for 2 hours to obtain the catalyst precursor. The calcination heating rate is 5°C / min.

[0043] S8. The catalyst precursor obtained in step S7 is placed in a hydrogen tube furnace and reduced at 200℃ for 2 hours to obtain a Pd / TiO2 catalyst with flower-like nanosphere shape, numbered S-Pd-TiO2, with a reduction heating rate of 5℃ / min.

[0044] Example 2

[0045] A method for preparing a Pd / TiO2 catalyst includes the following steps:

[0046] S1. Slowly add 1 mL of tetrabutyl titanate to 30 mL of acetic acid and stir for 10 min to obtain a white suspension;

[0047] S2. Transfer the white suspension obtained in step S1 to a stainless steel autoclave lined with polytetrafluoroethylene and age it in a drying oven at 180°C for 24 hours.

[0048] S3. After the white mixture obtained in step S2 is cooled naturally, the precipitate is collected by centrifugation, washed three times with a mixture of ethanol and water, and then dried under vacuum at 100°C for 10 hours to obtain a white solid.

[0049] S4. The white solid obtained in step S3 is placed in a muffle furnace and calcined at 450°C for 3 hours to obtain flower-shaped nanosphere TiO2 powder, numbered S-TiO2. The calcination heating rate is 5°C / min.

[0050] S5. Take 200 mg of TiO2 powder obtained in step S4 and put it into a 100 mL round bottom flask. Add 8.6 mg of palladium acetylacetone and 20 mL of ethanol. Stir the reaction for 1 h to obtain a white mixture.

[0051] S6. Place the white mixture obtained in step S5 into a rotary evaporator and evaporate it at 60°C for 20 minutes to obtain a light yellow powder.

[0052] S7. The light yellow powder obtained in step S6 is placed in a muffle furnace and calcined at 200°C for 2 hours to obtain the catalyst precursor. The calcination heating rate is 5°C / min.

[0053] S8. The catalyst precursor obtained in step S7 is placed in a hydrogen tube furnace and reduced at 150°C for 2 hours to obtain a Pd / TiO2 catalyst with flower-like nanospheres, numbered S-Pd-TiO2-R150. The reduction heating rate is 5°C / min.

[0054] Example 3

[0055] A method for preparing a Pd / TiO2 catalyst includes the following steps:

[0056] S1. Slowly add 1 mL of tetrabutyl titanate to 30 mL of acetic acid and stir for 10 min to obtain a white suspension;

[0057] S2. Transfer the white suspension obtained in step S1 to a stainless steel autoclave lined with polytetrafluoroethylene and age it in a drying oven at 180°C for 24 hours.

[0058] S3. After the white mixture obtained in step S2 is cooled naturally, the precipitate is collected by centrifugation, washed three times with a mixture of ethanol and water, and then dried under vacuum at 100°C for 10 hours to obtain a white solid.

[0059] S4. The white solid obtained in step S3 is placed in a muffle furnace and calcined at 450°C for 3 hours to obtain flower-shaped nanosphere TiO2 powder, numbered S-TiO2. The calcination heating rate is 5°C / min.

[0060] S5. Take 200 mg of TiO2 powder obtained in step S4 and put it into a 100 mL round bottom flask. Add 8.6 mg of palladium acetylacetone and 20 mL of ethanol. Stir the reaction for 1 h to obtain a white mixture.

[0061] S6. Place the white mixture obtained in step S5 into a rotary evaporator and evaporate it at 60°C for 20 minutes to obtain a light yellow powder.

[0062] S7. The light yellow powder obtained in step S6 is placed in a muffle furnace and calcined at 200°C for 2 hours to obtain the catalyst precursor. The calcination heating rate is 5°C / min.

[0063] S8. The catalyst precursor obtained in step S7 is placed in a hydrogen tube furnace and reduced at 250°C for 2 hours to obtain a Pd / TiO2 catalyst with flower-like nanosphere shape, numbered S-Pd-TiO2-R250. The reduction heating rate is 5°C / min.

[0064] Example 4

[0065] A method for preparing a Pd / TiO2 catalyst includes the following steps:

[0066] S1. Slowly add 1 mL of tetrabutyl titanate to 30 mL of acetic acid and stir for 10 min to obtain a white suspension;

[0067] S2. Transfer the white suspension obtained in step S1 to a stainless steel autoclave lined with polytetrafluoroethylene and age it in a drying oven at 180°C for 24 hours.

[0068] S3. After the white mixture obtained in step S2 is cooled naturally, the precipitate is collected by centrifugation, washed three times with a mixture of ethanol and water, and then dried under vacuum at 100°C for 10 hours to obtain a white solid.

[0069] S4. The white solid obtained in step S3 is placed in a muffle furnace and calcined at 450°C for 3 hours to obtain flower-shaped nanosphere TiO2 powder, numbered S-TiO2. The calcination heating rate is 5°C / min.

[0070] S5. Take 200 mg of TiO2 powder obtained in step S4 and put it into a 100 mL round bottom flask. Add 8.6 mg of palladium acetylacetone and 20 mL of ethanol. Stir the reaction for 1 h to obtain a white mixture.

[0071] S6. Place the white mixture obtained in step S5 into a rotary evaporator and evaporate it at 60°C for 20 minutes to obtain a light yellow powder.

[0072] S7. The light yellow powder obtained in step S6 is placed in a muffle furnace and calcined at 150°C for 2 hours to obtain the catalyst precursor. The calcination heating rate is 5°C / min.

[0073] S8. The catalyst precursor obtained in step S7 is placed in a hydrogen tube furnace and reduced at 200℃ for 2 hours to obtain a Pd / TiO2 catalyst with flower-like nanosphere shape, numbered S-Pd-TiO2-D150. The reduction heating rate is 5℃ / min.

[0074] Example 5

[0075] A method for preparing a Pd / TiO2 catalyst includes the following steps:

[0076] S1. Slowly add 1 mL of tetrabutyl titanate to 30 mL of acetic acid and stir for 10 min to obtain a white suspension;

[0077] S2. Transfer the white suspension obtained in step S1 to a stainless steel autoclave lined with polytetrafluoroethylene and age it in a drying oven at 180°C for 24 hours.

[0078] S3. After the white mixture obtained in step S2 is cooled naturally, the precipitate is collected by centrifugation, washed three times with a mixture of ethanol and water, and then dried under vacuum at 100°C for 10 hours to obtain a white solid.

[0079] S4. The white solid obtained in step S3 is placed in a muffle furnace and calcined at 450°C for 3 hours to obtain flower-shaped nanosphere TiO2 powder, numbered S-TiO2. The calcination heating rate is 5°C / min.

[0080] S5. Take 200 mg of TiO2 powder obtained in step S4 and put it into a 100 mL round bottom flask. Add 8.6 mg of palladium acetylacetone and 20 mL of ethanol. Stir the reaction for 1 h to obtain a white mixture.

[0081] S6. Place the white mixture obtained in step S5 into a rotary evaporator and evaporate it at 60°C for 20 minutes to obtain a light yellow powder.

[0082] S7. The light yellow powder obtained in step S6 is placed in a muffle furnace and calcined at 250°C for 2 hours to obtain the catalyst precursor. The calcination heating rate is 5°C / min.

[0083] S8. The catalyst precursor obtained in step S7 is placed in a hydrogen tube furnace and reduced at 200℃ for 2 hours to obtain a Pd / TiO2 catalyst with flower-like nanosphere shape, numbered S-Pd-TiO2-D250. The reduction heating rate is 5℃ / min.

[0084] Example 6

[0085] A method for preparing a Pd / TiO2 catalyst includes the following steps:

[0086] S1. Slowly add 1 mL of tetrabutyl titanate to 30 mL of acetic acid and stir for 10 min to obtain a white suspension;

[0087] S2. Transfer the white suspension obtained in step S1 to a stainless steel autoclave lined with polytetrafluoroethylene and age it in a drying oven at 180°C for 24 hours.

[0088] S3. After the white mixture obtained in step S2 is cooled naturally, the precipitate is collected by centrifugation, washed three times with a mixture of ethanol and water, and then dried under vacuum at 100°C for 10 hours to obtain a white solid.

[0089] S4. The white solid obtained in step S3 is placed in a muffle furnace and calcined at 450°C for 3 hours to obtain flower-shaped nanosphere TiO2 powder, numbered S-TiO2. The calcination heating rate is 5°C / min.

[0090] S5. Take 200 mg of TiO2 powder obtained in step S4 and put it into a 100 mL round bottom flask. Add 7 mg of palladium acetylacetone and 20 mL of ethanol. Stir and react for 1 h to obtain a white mixture.

[0091] S6. Place the white mixture obtained in step S5 into a rotary evaporator and evaporate it at 60°C for 20 minutes to obtain a light yellow powder.

[0092] S7. The light yellow powder obtained in step S6 is placed in a muffle furnace and calcined at 200°C for 2 hours to obtain the catalyst precursor. The calcination heating rate is 5°C / min.

[0093] S8. The catalyst precursor obtained in step S7 is placed in a hydrogen tube furnace and reduced at 200℃ for 2 hours to obtain a Pd / TiO2 catalyst with flower-like nanosphere shape, numbered S-Pd-TiO2-Pd7. The reduction heating rate is 5℃ / min.

[0094] Example 7

[0095] A method for preparing a Pd / TiO2 catalyst includes the following steps:

[0096] S1. Slowly add 1 mL of tetrabutyl titanate to 30 mL of acetic acid and stir for 10 min to obtain a white suspension;

[0097] S2. Transfer the white suspension obtained in step S1 to a stainless steel autoclave lined with polytetrafluoroethylene and age it in a drying oven at 180°C for 24 hours.

[0098] S3. After the white mixture obtained in step S2 is cooled naturally, the precipitate is collected by centrifugation, washed three times with a mixture of ethanol and water, and then dried under vacuum at 100°C for 10 hours to obtain a white solid.

[0099] S4. The white solid obtained in step S3 is placed in a muffle furnace and calcined at 450°C for 3 hours to obtain flower-shaped nanosphere TiO2 powder, numbered S-TiO2. The calcination heating rate is 5°C / min.

[0100] S5. Take 200 mg of TiO2 powder obtained in step S4 and put it into a 100 mL round bottom flask. Add 10 mg of palladium acetylacetone and 20 mL of ethanol. Stir and react for 1 h to obtain a white mixture.

[0101] S6. Place the white mixture obtained in step S5 into a rotary evaporator and evaporate it at 60°C for 20 minutes to obtain a light yellow powder.

[0102] S7. The light yellow powder obtained in step S6 is placed in a muffle furnace and calcined at 200°C for 2 hours to obtain the catalyst precursor. The calcination heating rate is 5°C / min.

[0103] S8. The catalyst precursor obtained in step S7 is placed in a hydrogen tube furnace and reduced at 200℃ for 2 hours to obtain a Pd / TiO2 catalyst with flower-like nanosphere shape, numbered S-Pd-TiO2-Pd10. The reduction heating rate is 5℃ / min.

[0104] Comparative Example 1

[0105] This embodiment is basically the same as Example 1, and the similarities will not be repeated. The main difference is that in step S1, 25 mL of tetrabutyl titanate was slowly added to 3 mL of water, and the mixture was stirred for 30 min. This embodiment successfully prepared a blocky titanium dioxide supported catalyst, designated P-TiO2, and the target catalyst was designated P-Pd-TiO2.

[0106] Comparative Example 2

[0107] This embodiment is basically the same as Example 1, and the similarities will not be repeated. The main difference is that in step S1, 6.5 mL of tetrabutyl titanate was slowly added to 65 mL of water, and the mixture was stirred for 30 min. This embodiment successfully prepared a particulate catalyst. The resulting support was designated C-TiO2, and the target catalyst was designated C-Pd-TiO2.

[0108] Comparative Example 3

[0109] This embodiment is basically the same as Embodiment 1, and the similarities will not be repeated. The difference is that in step S5, nickel acetylacetone is added, and the resulting target catalyst is numbered Ni-TiO2.

[0110] Comparative Example 4

[0111] This embodiment is basically the same as Example 1, and the similarities will not be repeated. The difference is that in step S5, cobalt acetylacetone is added, and the resulting target catalyst is numbered Co-TiO2.

[0112] Comparative Example 5

[0113] This embodiment is basically the same as Example 1, and the similarities will not be repeated. The difference is that in step S5, 4.3 mg of palladium acetylacetone is added, and the resulting target catalyst is numbered S-Pd-TiO2-Pd4.3.

[0114] Comparative Example 6

[0115] This embodiment is basically the same as Example 1, and the similarities will not be repeated. The difference is that in step S5, 13 mg of palladium acetylacetone will be added, and the resulting target catalyst is numbered S-Pd-TiO2-Pd13.

[0116] The supports and catalysts prepared in Example 1 and Comparative Examples 1-2 of this invention were characterized structurally, as detailed below:

[0117] Figure 1X-ray powder diffraction patterns of the prepared S-TiO2 (Example 1), P-TiO2 (Comparative Example 1), and C-TiO2 (Comparative Example 2) supports. The XRD patterns of S-TiO2 (Example 1), P-TiO2 (Comparative Example 1), and C-TiO2 (Comparative Example 2) show diffraction peaks at 25.36°, 37.90°, 48.15°, 55.20°, 62.86°, 74.30°, and 81.02°, which correspond to the (101), (004), (200), (211), (204), (107), and (008) crystal planes of the TiO2 support, respectively. This indicates that the TiO2 structure was successfully fabricated. Compared with the peak shape and crystal plane of anatase, the peak shape and crystal plane are the same as those of anatase, indicating that the S-TiO2 (Example 1), P-TiO2 (Comparative Example 1), and C-TiO2 (Comparative Example 2) supports of this invention all belong to anatase TiO2.

[0118] Figure 2 The images show TEM and SEM images of S-TiO2 (Example 1), P-TiO2 (Comparative Example 1), and C-TiO2 (Comparative Example 2) supports. A, B, and C are SEM images of P-TiO2 (Comparative Example 1), S-TiO2 (Example 1), and C-TiO2 (Comparative Example 2), respectively. A1, B1, and C1 are TEM images of P-TiO2 (Comparative Example 1), S-TiO2 (Example 1), and C-TiO2 (Comparative Example 2), respectively. A2, B2, and C2 are magnified high-resolution TEM images of P-TiO2 (Comparative Example 1), S-TiO2 (Example 1), and C-TiO2 (Comparative Example 2), respectively. Figure 2 As can be seen from the AC SEM images and A1-C1 TEM images, three different morphologies of supports were successfully prepared: P-TiO2 (Comparative Example 1), S-TiO2 (Example 1), and C-TiO2 (Comparative Example 2) supports were blocky, flower-like nanospheres, and granular, respectively. The sizes of P-TiO2 (Comparative Example 1) and C-TiO2 (Comparative Example 2) were approximately 20 nm, while the size of S-TiO2 (Example 1) was approximately 30 nm. Furthermore, high-resolution TEM images ( Figure 2 A2, B2, and C2 all show clear lattice fringes with a spacing of approximately 0.35 nm, which match well with the (101) atomic plane of anatase titanium dioxide.

[0119] Figure 3 X-ray powder diffraction patterns of the prepared S-Pd-TiO2 (Example 1), P-Pd-TiO2 (Comparative Example 1), and C-Pd-TiO2 (Comparative Example 2) catalysts. Figure 1As can be seen, the three prepared catalysts correspond to the standard spectrum of anatase TiO2 (JCPDS Card No. 86-1157), indicating that the anatase TiO2 structure was successfully fabricated, and that the palladium supported on the support did not change the crystal structure of TiO2. C-Pd-TiO2 (Comparative Example 2) showed a weak Pd(111) peak at 40.1°, while S-Pd-TiO2 (Example 1) and P-Pd-TiO2 (Comparative Example 1) did not show a Pd(111) peak, indicating that the metal nanoparticles in S-Pd-TiO2 and P-Pd-TiO2 are smaller than 5 nm, which means that the palladium is highly dispersed, while the C-Pd-TiO2 (Comparative Example 2) catalyst has relatively poor dispersion.

[0120] Figure 4 The images show TEM and SEM images of the prepared S-Pd-TiO2 (Example 1), P-Pd-TiO2 (Comparative Example 1), and C-Pd-TiO2 (Comparative Example 2) catalysts. A, B, and C are SEM images of P-Pd-TiO2 (Comparative Example 1), S-Pd-TiO2 (Example 1), and C-Pd-TiO2 (Comparative Example 2), respectively. A1, B1, and C1 are TEM images of P-Pd-TiO2 (Comparative Example 1), S-Pd-TiO2 (Example 1), and C-Pd-TiO2 (Comparative Example 2), respectively. A2, B2, and C2 are magnified high-resolution TEM images of P-Pd-TiO2 (Comparative Example 1), S-Pd-TiO2 (Example 1), and C-Pd-TiO2 (Comparative Example 2), respectively. Figure 4 AC showed that three catalysts with different morphologies were successfully prepared: blocky, flower-like nanospheres, and particulates, corresponding to P-Pd-TiO2 (Comparative Example 1), S-Pd-TiO2 (Example 1), and C-Pd-TiO2 (Comparative Example 2) catalysts, respectively. Figure 2 SEM comparison showed that palladium loading on the support did not change the morphology of the support. Furthermore, the overall size of the P-Pd-TiO2 (Comparative Example 1) and C-Pd-TiO2 (Comparative Example 2) catalysts was approximately 20 nm, while the overall size of the S-Pd-TiO2 (Example 1) catalyst was approximately 30 nm. In addition, magnified high-resolution TEM images ( Figure 4 A2P-Pd-TiO2 (Comparative Example 1) Figure 4 B2S-Pd-TiO2 (Example 1) Figure 4 Both C2C-Pd-TiO2 (Comparative Example 2) and Pd-TiO2 showed clear lattice fringes with a spacing of approximately 0.35 nm, which matched well with the (101) atomic plane of anatase titanium dioxide. Another lattice fringe had a spacing of 0.23 nm, which matched well with the (111) atomic plane of palladium. From the TEM images ( Figure 4A1 P-Pd-TiO2 (Comparative Example 1), B1 S-Pd-TiO2 (Example 1), C1 C-Pd-TiO2 (Comparative Example 2) show that the palladium particle size distributions of the P-Pd-TiO2 (Comparative Example 1), S-Pd-TiO2 (Example 1), and C-Pd-TiO2 (Comparative Example 2) catalysts are 2.33, 1.56, and 4.64 nm, respectively. This indicates that the S-Pd-TiO2 (Example 1) catalyst has a higher dispersion than the other catalysts, exhibiting the best dispersion and smaller metal particles, while the C-Pd-TiO2 (Comparative Example 2) catalyst has the worst dispersion.

[0121] Figure 5 XPS O 1s and EPR spectra of the prepared S-Pd-TiO2 (Example 1), P-Pd-TiO2 (Comparative Example 1), and C-Pd-TiO2 (Comparative Example 2) catalysts were obtained. The XPS O 1s spectra of each catalyst showed three peaks at ~529.61 eV, ~531.81 eV, and ~533.21 eV, corresponding to lattice oxygen (lattice O), defect oxygen (defect O), and surface hydroxyl groups (hydroxyl O), respectively. The peak areas were normalized to the total O 1s spectral area, and the relative content of oxygen vacancies was calculated. The results showed that SP-TiO2 had the highest relative content of oxygen vacancies, following the order: S-Pd-TiO2 (23.54%) > P-Pd-TiO2 (15.2%) > C-Pd-TiO2 (11.34%). The EPR spectra showed that all catalysts exhibited a sharp peak at a g value of 2.004, indicating a strong signal. This signal represents the defect structure of oxygen vacancies. Among them, the peak signal intensity of the S-Pd-TiO2 catalyst was significantly higher than that of the P-Pd-TiO2 and C-Pd-TiO2 catalysts, indicating that the oxygen vacancy concentration in the S-Pd-TiO2 catalyst was higher than that in the P-Pd-TiO2 and C-Pd-TiO2 catalysts.

[0122] The catalysts prepared in Examples 1-7 and Comparative Examples 1-6 of this invention were subjected to performance tests, which are detailed below:

[0123] The prepared S-Pd-TiO2 (Example 1), P-Pd-TiO2 (Comparative Example 1), and C-Pd-TiO2 (Comparative Example 2) catalysts were used to catalyze the decarbonylation of furfural to prepare furan. The steps were as follows: furfural (100 mg), tridecane as an internal standard (100 mg), 1,4-dioxane (5 ml), and 50 mg of the corresponding catalyst were added to a 30 ml autoclave. Then, 0.3 MPa N2 was injected into the autoclave, and the mixture was magnetically stirred at 180 °C and 700 rpm for 16 h. After the reaction was completed, the autoclave was cooled with an ice bath, and the supernatant and solid catalyst were obtained by centrifugation. The supernatant was filtered, and the filtered liquid product was analyzed by gas chromatography. Based on the original furfural weight, the furfural conversion rate, the yield and selectivity of furan monomers during furfural pyrolysis were calculated. The solid catalyst was washed three times with 1,4-dioxane solvent, and then the same amounts of furfural, tridecane, catalyst and 1,4-dioxane solvent were added. The reaction was continued for 16 h under the conditions of 0.3 MPa N2, 180 °C and 700 rpm. This cycle was repeated 4 times.

[0124] Table 1 shows the performance tests of S-Pd-TiO2 (Example 1), P-Pd-TiO2 (Comparative Example 1), and C-Pd-TiO2 (Comparative Example 2) catalysts for the catalytic decarbonylation of furfural to prepare furan.

[0125] Table 1. Catalytic effects of the catalysts prepared in Example 1 and Comparative Examples 1-2 on the decarbonylation of furfural.

[0126]

[0127]

[0128] As shown in Table 1, the catalytic performance of the granular C-Pd-TiO2 catalyst in Comparative Example 2 and the blocky P-Pd-TiO2 catalyst in Comparative Example 1 is worse than that of the flower-shaped nanosphere S-Pd-TiO2 of this invention. The S-Pd-TiO2 catalyst achieves a 100% conversion rate of furfural, a 94% selectivity for furan formation, and a furan yield of up to 94%. Due to its excellent morphology, the S-Pd-TiO2 catalyst produces a small palladium particle size and good dispersibility. The titanium dioxide support contains oxygen defects and has a high oxygen vacancy concentration, which improves the furfural conversion rate and increases the furan yield and selectivity.

[0129] Table 2 shows the performance tests of S-Pd-TiO2 (Example 1), S-Pd-TiO2-R150 (Example 2), and S-Pd-TiO2-R250 (Example 3) catalysts for the catalytic decarbonylation of furfural to prepare furan.

[0130] Table 2. Catalytic effects of the catalysts prepared in Examples 1 and 2-3 on the decarbonylation of furfural.

[0131] Example 1 <![CDATA[S-Pd-TiO2]]> 100 94 94 Example 2 <![CDATA[S-Pd-TiO2-R150]]> 91 92 84 Example 3 <![CDATA[S-Pd-TiO2-R250]]> 98 94 92

[0132] As shown in Table 2, the catalyst exhibited the best conversion rate of furfural when the catalyst precursor in Example 1 was reduced at 200°C. When the reduction temperature was too low, the catalyst was not fully reduced, resulting in only a portion being reduced and affecting the yield. When the reduction temperature was too high, excessive reduction of the catalyst caused partial agglomeration, thus affecting catalytic performance and increasing reaction costs.

[0133] Table 3 shows the performance tests of S-Pd-TiO2 (Example 1), S-Pd-TiO2-D150 (Example 4), and S-Pd-TiO2-D250 (Example 5) catalysts for the catalytic decarbonylation of furfural to furan.

[0134] Table 3. Catalytic effects of the catalysts prepared in Examples 1 and 4-5 on the decarbonylation of furfural.

[0135] Example 1 <![CDATA[S-Pd-TiO2]]> 100 94 94 Example 4 <![CDATA[S-Pd-TiO2-D150]]> 86 90 77 Example 5 <![CDATA[S-Pd-TiO2-D250]]> 100 93 93

[0136] As shown in Table 3, when the calcination temperature of the pale yellow powder solid is too low, palladium precursor will still remain, which will affect the conversion rate of furfural catalyzed by the catalyst. However, if the calcination temperature is too high, the metal of the catalyst will form clusters, affecting the reaction and increasing the reaction cost. Appropriate calcination temperature is beneficial to the catalytic effect.

[0137] Table 4 shows the performance tests of S-Pd-TiO2 (Example 1), S-Pd-TiO2-Pd7 (Example 6), S-Pd-TiO2-Pd10 (Example 7), S-Pd-TiO2-Pd4.3 (Comparative Example 5), and S-Pd-TiO2-Pd13 (Comparative Example 6) catalysts for the catalytic decarbonylation of furfural to furan.

[0138] Table 4 shows the catalytic effects of the catalysts prepared in Examples 1, 6-7, and Comparative Examples 5-6 on the decarbonylation of furfural.

[0139] Example 1 8.6 100 94 94 Example 6 7 90 91 82 Example 7 10 85 90 77 Comparative Example 5 4.3 86 81 70 Comparative Example 6 13 54 75 40

[0140] As shown in Table 4, both excessive and insufficient palladium acetylacetone content will affect the yield of furan. This is because the palladium acetylacetone content affects the metal dispersion of the catalyst. The optimal palladium content is 8.6 mg. Excessive palladium content will lead to a decrease in palladium dispersion and palladium accumulation, while insufficient palladium content will reduce the number of palladium active sites on the catalyst, which is not conducive to the catalytic reaction of furfural.

[0141] Table 5 shows the performance tests of S-Pd-TiO2 (Example 1), Ni-TiO2 (Comparative Example 3), and Co-TiO2 (Comparative Example 4) catalysts for the catalytic decarbonylation of furfural to furan.

[0142] Table 5. Catalytic effects of the catalysts prepared in Example 1 and Comparative Examples 3-4 on the decarbonylation of furfural.

[0143] Example 1 <![CDATA[S-Pd-TiO2]]> 100 94 94 Comparative Example 3 <![CDATA[Ni-TiO2]]> 8.3 6.7 5.6 Comparative Example 4 <![CDATA[Co-TiO2]]> 12.3 6.1 7.5

[0144] As shown in Table 5, the S-Pd-TiO2 catalyst of this invention has a significantly higher catalytic effect on furfural decarbonylation than the non-precious metal Ni-TiO2 (Comparative Example 3) and Co-TiO2 (Comparative Example 4), indicating that there is a strong binding ability between the palladium and titanium dioxide support in the catalyst prepared by this invention, which makes the catalyst have a significant catalytic effect on furfural decarbonylation.

[0145] Figure 6 Five stability tests were conducted on the catalyst S-Pd-TiO2 in Example 1 of this invention. Figure 6 The paper demonstrates the catalytic decarbonylation of furfural using the S-Pd-TiO2 catalyst under optimal reaction conditions for four consecutive cycles. After each reaction, the catalyst was separated, washed with 1,4-dioxane, and then directly used in the next reaction. The selectivity for furan remained stable, while the conversion rate of furfural decreased slightly. After four cycles, the catalyst was calcined in a muffle furnace and reduced in a hydrogen tubular furnace before being used again, and the catalyst performance returned to the level of the first reaction. Therefore, the catalyst of this invention can be reused multiple times through recovery and separation, which is beneficial for industrial application.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a Pd / TiO2 catalyst, characterized in that, The steps include the following: S1. Tetrabutyl titanate is slowly added to acetic acid and stirred to obtain a suspension; S2. Transfer the suspension obtained in step S1 to a high-pressure autoclave and place it in a drying oven for aging to obtain a white mixture. S3. After the white mixture obtained in step S2 is cooled naturally, the precipitate is collected by centrifugation, washed, and dried under vacuum to obtain a white solid. S4. Place the white solid obtained in step S3 into a muffle furnace and calcine it to obtain flower-shaped nanosphere TiO2 powder. S5. Place the TiO2 powder obtained in step S4 into a round-bottom flask, add palladium acetylacetone and ethanol, and stir to react and obtain a mixture. S6. The mixture obtained in step S5 is rotary evaporated to obtain a light yellow powder; S7. Place the light yellow powder obtained in step S6 into a muffle furnace and calcine it at 150-250℃ for 1-3 hours to obtain the catalyst precursor. S8. Place the catalyst precursor obtained in step S7 into a hydrogen tube furnace and reduce it at 150-250℃ for 1-3 hours to obtain the Pd / TiO2 catalyst. In step S1, the volume ratio of tetrabutyl titanate to acetic acid is 1:25-35.

2. The method for preparing the Pd / TiO2 catalyst according to claim 1, characterized in that, In step S5, the ratio of TiO2 powder, palladium acetylacetone, and ethanol is 150-250 mg: 7-10 mg: 10-30 mL.

3. The method for preparing the Pd / TiO2 catalyst according to claim 1, characterized in that, The aging temperature in step S2 is 160-200℃, and the time is 20-30 h.

4. The method for preparing the Pd / TiO2 catalyst according to claim 1, characterized in that, The calcination temperature in step S4 is 400-500℃, and the time is 2-4 h.

5. The method for preparing the Pd / TiO2 catalyst according to claim 1, characterized in that, The rotary evaporation temperature in step S6 is 50-70℃, and the time is 10-30 min.

6. The method for preparing the Pd / TiO2 catalyst according to claim 1, characterized in that, The heating rate for calcination in steps S4 and S7 is 3-10℃ / min, and the heating rate for reduction in step S8 is 3-10℃ / min.

7. A Pd / TiO2 catalyst prepared by the preparation method according to any one of claims 1-6.

8. The application of a Pd / TiO2 catalyst prepared by the method according to any one of claims 1-6 in the catalytic decarbonylation reaction of furfural to furan.

9. The application according to claim 8, characterized in that, The temperature for the furfural decarbonylation reaction to produce furan is 160-190℃, and the time is 8-16h.

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