Catalyst for hydrogen production through partial oxidation of dimethyl ether as well as preparation method and application of catalyst

Abstract

The invention discloses a catalyst for hydrogen production through partial oxidation of dimethyl ether as well as a preparation method and application of the catalyst. According to the catalyst, TiO2-CeO2 serves as a carrier, an active component metal Pt is loaded, the molar ratio of Ti to Ce in the catalyst is 0.5-4, and the mass of Pt accounts for 0.05-0.2% of the mass of the carrier. The content of oxygen vacancy (Ov) is adjusted by changing the ratio of different Ti / Ce in the Pt / TiO2-CeO2 catalyst, and the Pt / TiO2-CeO2 catalyst disclosed by the invention has relatively small forbidden bandwidth (Ebg) and relatively high Ov concentration, and is excellent in catalytic performance.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen production by dimethyl ether reforming, and particularly relates to a catalyst for partial oxidation of dimethyl ether to hydrogen, a preparation method thereof, and an application thereof. Background Art

[0002] Energy is the driving force for social and economic development, and countries all over the world are actively developing renewable energy, including hydrogen energy, solar energy, and wind energy. Among them, hydrogen energy is regarded as the most promising option because of its high combustion energy and environmentally friendly combustion products.

[0003] Dimethyl ether (DME) is a by-product of ethanol dehydration to ethylene, and its current utilization rate is very low. DME has the characteristics of high hydrogen content and easy storage and transportation, and is regarded as a safe hydrogen carrier. Converting it to hydrogen has practical significance.

[0004] DME is easily decomposed into methane (CH 4 ), hydrogen (H 2 ), and carbon monoxide (CO) at high temperatures. In addition, under the oxidation of oxygen, DME is prone to deep oxidation, producing carbon dioxide (CO 2 ) and water (H 2 O). At the same time, reactions involving CH 4 reforming and steam reforming also occur. It is generally believed that a higher temperature can increase the DME conversion rate, but at the same time, it will also lead to an increase in the selectivity of CH 4 , mainly due to the cracking reaction caused by the cleavage of the carbon-oxygen (C-O) bond of DME. Summary of the Invention

[0005] The purpose of the present invention is to provide a catalyst for partial oxidation of dimethyl ether to hydrogen, a preparation method thereof, and an application thereof.

[0006] In order to solve the problems existing in the prior art, the technical solution adopted by the present invention is as follows:

[0007] In the first aspect, the present invention provides a catalyst for partial oxidation of dimethyl ether to hydrogen. The catalyst uses TiO 2 -CeO 2 as a carrier and loads the active component metal Pt. The molar ratio of Ti to Ce in the catalyst is 0.5-4, and the mass of Pt is 0.05-0.2% of the mass of the carrier.

[0008] Preferably, the TiO 2 -CeO 2 is prepared by the sol-gel method.

[0009] Preferably, the metal Pt is loaded onto the carrier TiO 2 -CeO 2 by vacuum impregnation.superior.

[0010] In a second aspect, the present invention provides a method for preparing a catalyst for producing hydrogen by partial oxidation of dimethyl ether as described in the first aspect, comprising the following steps:

[0011] (1) Under continuous stirring and heating, slowly add Pluronic F127 polymer to C 2 H 5 OH until completely dissolved;

[0012] (2) Add Ce(NO) to the solution obtained in step (1) 3 ) 2 6H 2 O, butyl titanate, glacial acetic acid, concentrated nitric acid, mix and age for 22-24 hours;

[0013] (3) allowing the mixture to gel naturally at 38-40° C. to obtain a sol-gel product;

[0014] (4) drying the obtained sol-gel product in an electric constant temperature blast drying oven at 78-82° C. for 11-13 h;

[0015] (5) After heating to 540-560°C at a rate of 1-2°C / min, calcining for 5-7h to obtain TiO 2 -CeO 2 ;

[0016] (6) H 2 PtCl 6 -6H 2 O solution and TiO 2 -CeO 2 Mix thoroughly and soak for 1-2 hours;

[0017] (7) Perform vacuum distillation at 58-62°C, and then dry the evaporated liquid at 98-102°C for 11-13h; this step can vaporize and remove volatile impurities at a lower temperature, and can also play a drying role. Too high a temperature may cause the catalyst structure to be damaged, and too low a temperature may result in poor impurity removal and insufficient drying.

[0018] (8) The obtained material was calcined at 440-460°C for 2-3h to obtain Pt / TiO 2 -CeO 2 This step can make TiO 2 and CeO 2 If the calcination temperature is too high, Pt will be sintered; if the calcination temperature is too low, TiO 2 and CeO 2 The crystallization is incomplete.

[0019] Furthermore, the solid-liquid ratio of the Pluronic F127 polymer to C 2 H 5 OH, Ce(NO 3 ) 2 ·6H 2 O, tetrabutyl titanate, glacial acetic acid, and concentrated nitric acid is 1-8:1-65:1-20:5-50:1-6:1-3.

[0020] Furthermore, the concentration of the H 2 PtCl 6 -6H 2 O solution is 0.01-0.1 g / mL, preferably 0.05 g / mL.

[0021] In a third aspect, the present invention provides the use of the DME partial oxidation hydrogen production catalyst described in the first aspect above in the photothermal catalytic DME partial oxidation hydrogen production reaction.

[0022] Furthermore, in the photothermal catalytic dimethyl ether partial oxidation hydrogen production reaction, the dosage of the dimethyl ether partial oxidation hydrogen production catalyst is 0.03 g, the feed ratio of dimethyl ether to oxygen is maintained at 2:1, the weight hourly space velocity (WHSV) is 134400 mL / (g·h), and the pressure is atmospheric pressure.

[0023] Furthermore, the temperature of the photothermal catalytic DME partial oxidation hydrogen production reaction is 300°C - 500°C.

[0024] The advantages and beneficial effects of the present invention are:

[0025] By using the sol-gel method to prepare a catalyst support TiO 2 -CeO 2 with a specific Ti / Ce ratio, and simultaneously loading a specific amount of metal Pt onto the TiO 2 -CeO 2 support by vacuum impregnation, the prepared Pt / TiO 2 -CeO 2 catalyst has a small E bg and a high O v concentration, and exhibits excellent catalytic performance. This is because the introduction of CeO 2 into TiO 2 increases the content of O v and promotes the progress of the reaction. The Pt / TiO 2 -CeO 2 catalyst of the present invention has a high O vThe concentration can preferentially activate the carbon-hydrogen (C-H) bond of DME, change the reaction path from cracking to dehydrogenation, and exhibit excellent dehydrogenation ability. In the present invention, by introducing more O on the carrier v and regulating E bg , the efficient conversion of DME at low temperature is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the XRD pattern of pure TiO 2 , pure CeO 2 , and the catalysts prepared in Examples 1, 2, 3, 4, and 7. In the figure: (a) is the XRD pattern of the catalysts with different Ti / Ce ratios, and (b) is the XRD pattern of the catalysts with different Pt loadings;

[0027] Figure 2 is the O 1s spectrum of the catalysts prepared in Examples 1, 4, and 7. In the figure: (a) is 0.05 wt% Pt / TiO 2 -CeO 2 -0.5, (b) is 0.05 wt% Pt / TiO 2 -CeO 2 -1, (c) is 0.05 wt% Pt / TiO 2 -CeO 2 -4;

[0028] Figure 3 is the ultraviolet-visible absorption spectrum of the catalysts with different carriers prepared in Examples 1, 4, 7, and Comparative Example 1;

[0029] Figure 4 is the Tauc plot of the catalysts with different carriers prepared in Examples 1, 4, 7, and Comparative Example 1;

[0030] In the figure: a is 0.05 wt% Pt / TiO 2 -CeO 2 -0.5, b is 0.05 wt% Pt / TiO 2 ,

[0031] c is 0.05 wt% Pt / TiO 2 -CeO 2 -1, d is; 0.05 wt% Pt / TiO 2 -CeO 2 -4;

[0032] Figure 5 is the valence band spectrum of the catalysts prepared in Examples 1, 4, and 7. In the figure:

[0033] (a) is 0.05 wt% Pt / TiO 2 -CeO 2-0.5, (b) is 0.05 wt% Pt / TiO 2 -CeO 2 -1, (c) is 0.05 wt% Pt / TiO 2 -CeO 2 -4;

[0034] Figure 6 are the H 2 -TPR curves of the catalysts prepared in Examples 1, 4, and 7;

[0035] Figure 7 are the Raman spectra of the catalysts prepared in Examples 1, 4, and 7;

[0036] Figure 8 is 0.05 wt% Pt / TiO 2 -CeO 2 -0.5 catalyst in DME / O 2 = 2, WHSV = 134000 mL / (g·h), atmospheric pressure, DME conversion and H 2 yield at different temperatures;

[0037] Figure 9 is for DME / O 2 = 2, WHSV = 134400 mL / (g·h), selectivity of carbon-containing products under atmospheric pressure. In the figure:

[0038] (a) is at different temperatures, (b) is at different Ti / Ce ratios, (c) is at different Pt loadings;

[0039] Figure 10 is for DME / O 2 = 2, 400 °C, WHSV = 134000 mL / (g·h), 1 atm, DME conversion and H 2 yield. In the figure: (a) is the DME conversion and H 2 yield at different Ti / Ce ratios when the Pt loading is 0.05 wt%,

[0040] (b) is the DME conversion and H 2 yield at different Pt loadings when the Ti / Ce ratio is 0.5. Detailed implementation manners

[0041] Next, the technical solutions in the embodiments of the present application will be clearly described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present application.

[0042] The experimental methods in the following examples, unless otherwise specified, are all conventional methods, and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial channels.

[0043] Example 1

[0044] This embodiment provides a catalyst for partial oxidation of dimethyl ether to produce hydrogen, and the preparation method thereof comprises the following steps:

[0045] (1) Under continuous stirring and heating, 3.2 g of Pluronic F127 polymer was gradually and slowly added to 60 mL of C 2 H 5 OH until completely dissolved.

[0046] (2) Add 2.17 g of Ce(NO) to the solution obtained in step (1). 3 ) 2 6H 2 O, 7 mL of butyl titanate, 5.6 mL of glacial acetic acid, and 2 mL of concentrated nitric acid (68%) were mixed and aged for 24 h.

[0047] (3) The mixture is allowed to gel naturally at 40°C. During this period, the state of the gel is carefully judged. If the gel has obviously cracked, the heating is stopped to obtain a sol-gel product.

[0048] (4) Dry the obtained sol-gel product in an electric constant temperature forced air drying oven at 80°C for 12 h.

[0049] (5) The dried sol-gel product was heated to 550°C at a heating rate of 1°C / min and calcined for 6 h to obtain a catalyst support with a Ti / Ce molar ratio of 0.5, denoted as TiO 2 -CeO 2 -0.5.

[0050] (6) Add 0.026 mL of 0.05 g / mL H 2 PtCl 6 -6H 2 O solution with 1g TiO 2 -CeO 2 -0.5, mix thoroughly, add to the eggplant-shaped bottle, turn on the rotary evaporator and soak for 1 hour.

[0051] (7) Turn on the circulating water pump to bring the system to a negative pressure state. After 0.5 h, turn on the water bath to perform vacuum distillation at 60 °C, and then evaporate the liquid. After the liquid in the eggplant-shaped bottle is evaporated to dryness, place the eggplant-shaped bottle in an oven at 100 °C and dry it for 12 h.

[0052] (8) After drying, the catalyst in the eggplant-shaped flask was taken out, ground, and then calcined in a muffle furnace at 450 °C for 3 h to prepare a catalyst with a Pt loading of 0.05% of the carrier mass, denoted as 0.05 wt% Pt / TiO 2 -CeO 2 -0.5。

[0053] Example 2

[0054] This example provides a DME partial oxidation hydrogen production catalyst. The difference between this example and Example 1 is only that: in step (6), 0.052 mL of H 2 PtCl 6 ·6H 2 O solution was fully mixed with 1 g of TiO 2 -CeO 2 -0.5 and impregnated for 1 h. The rest was the same as in Example 1. Finally, a catalyst with a Pt loading of 0.1 wt% of the carrier mass was prepared, denoted as 0.1 wt% Pt / TiO 2 -CeO 2 -0.5。

[0055] Example 3

[0056] This example provides a DME partial oxidation hydrogen production catalyst. The difference between this example and Example 1 is only that: in step (6), 0.104 mL of H 2 PtCl 6 ·6H 2 O solution was fully mixed with 1 g of TiO 2 -CeO 2 -0.5 and impregnated for 1 h. The rest was the same as in Example 1, and a catalyst with a Pt loading of 0.2 wt% of the carrier mass was prepared, denoted as 0.2 wt% Pt / TiO 2 -CeO 2 -0.5。

[0057] Example 4

[0058] This example provides a DME partial oxidation hydrogen production catalyst. The difference between this example and Example 1 is only that: in step (2), the dosage of Ce(NO 3 ) 2 ·6H 2 O was 8.71 g to obtain a catalyst support with a Ti / Ce molar ratio of 1, denoted as TiO 2 -CeO 2 -1, and the rest was the same as in Example 1. Finally, a catalyst with a Pt loading of 0.05 wt% of the carrier mass was prepared, denoted as 0.05 wt% Pt / TiO 2 -CeO 2 -1。

[0059] Example 5

[0060] This example provides a catalyst for hydrogen production by partial oxidation of DME. The difference between this example and Example 4 is only that: in step (6), 0.052 mL of H 2 PtCl 6 ·6H 2 O solution is fully mixed with 1 g of TiO 2 -CeO 2 -1 for 1 h. The rest are the same as in Example 4. Finally, a catalyst with a Pt loading of 0.1 wt% of the carrier mass is prepared, denoted as 0.1 wt% Pt / TiO 2 -CeO 2 -1.

[0061] Example 6

[0062] This example provides a catalyst for hydrogen production by partial oxidation of DME. The difference between this example and Example 4 is only that: in step (6), 0.104 mL of H 2 PtCl 6 ·6H 2 O solution is fully mixed with 1 g of TiO 2 -CeO 2 -1 for 1 h. The rest are the same as in Example 4. Finally, a catalyst with a Pt loading of 0.2 wt% of the carrier mass is prepared, denoted as 0.2 wt% Pt / TiO 2 -CeO 2 -1.

[0063] Example 7

[0064] This example provides a catalyst for hydrogen production by partial oxidation of DME. The difference between this example and Example 1 is only that: in step (2), the amount of Ce(NO 3 ) 2 ·6H 2 O used is 17.37 g, and a catalyst support with a Ti / Ce molar ratio of 4 is obtained, denoted as TiO 2 -CeO 2 -4, and the rest are the same as in Example 1. Finally, a catalyst with a Pt loading of 0.05 wt% of the carrier mass is prepared, denoted as 0.05 wt% Pt / TiO 2 -CeO 2 -4.

[0065] Example 8

[0066] This example provides a catalyst for hydrogen production by partial oxidation of DME. The difference between this example and Example 7 is only that: in step (6), 0.052 mL of H2 PtCl 6 ·6H 2 O solution was fully mixed with 1 g of TiO 2 -CeO 2 -4, and impregnated for 1 h. The rest was the same as in Example 7. Finally, a catalyst with a Pt loading of 0.1 wt% of the carrier mass was prepared, denoted as 0.1 wt% Pt / TiO 2 -CeO 2 -4.

[0067] Example 9

[0068] This example provides a DME partial oxidation hydrogen production catalyst. The difference between this example and Example 7 is only that: in step (6), 0.104 mL of H 2 PtCl 6 ·6H 2 O solution was fully mixed with 1 g of TiO 2 -CeO 2 -4, and impregnated for 1 h. The rest was the same as in Example 7. Finally, a catalyst with a Pt loading of 0.2 wt% of the carrier mass was prepared, denoted as 0.2 wt% Pt / TiO 2 -CeO 2 -4.

[0069] Comparative Example 1

[0070] This comparative example provides a DME partial oxidation hydrogen production catalyst. In this comparative example, the sol-gel method was used to prepare the catalyst support TiO 2 , and the metal Pt was loaded on TiO 2 by vacuum impregnation method. The specific preparation method includes the following steps:

[0071] (1) Weigh 33.0 g of hydrochloric acid (37 wt%) and mix it fully with 400 mLC 2 H 5 OH. Slowly add 20 g of Pluronic F127 polymer under stirring and heating conditions until it is completely dissolved.

[0072] (2) Then add 6.3 g of citric acid to the above solution to adjust the pH value to 0.75. After vigorously stirring at room temperature for 1 h, add 28.50 g of tetra-isopropyl titanate dropwise. After mixing, age for 24 h.

[0073] (3) Then let it gel naturally at 40 °C. During this period, pay attention to observing the gel state. If obvious cracks have occurred in the gel, stop heating to obtain the sol-gel product.

[0074] (4) Dry the obtained sol-gel product in an 80 °C electrothermal constant temperature blast drying oven for 12 h.

[0075] (5) The dried sol-gel product was heated to 550 °C at a heating rate of 1 °C / min and then calcined for 6 h to finally obtain TiO 2 material.

[0076] (6) 0.026 mL of an H 2 PtCl 6 ·6H 2 O solution with a concentration of 0.05 g / mL was mixed with 1 g of TiO 2 and then added to a eggplant-shaped flask. The rotary evaporator was turned on and allowed to impregnate for 1 h.

[0077] (7) The circulating water pump was turned on to make the system reach a negative pressure state. After 0.5 h, the water bath was turned on and vacuum distillation was carried out at 60 °C. Subsequently, the liquid was evaporated. After the liquid in the eggplant-shaped flask was completely evaporated, the eggplant-shaped flask was placed in an oven and dried at 100 °C for 12 h.

[0078] (8) After drying, the catalyst in the eggplant-shaped flask was taken out, ground, and then placed in a muffle furnace and calcined at 450 °C for 3 h. A catalyst with a Pt loading of 0.05 wt% of the carrier mass was prepared and denoted as: 0.05 wt% Pt / TiO 2 .

[0079] Experimental Example 1

[0080] 1 Catalyst Characterization

[0081] 1.1 X-ray powder diffraction (XRD)

[0082] Using a D / MAX-2500 diffractometer with a Cu K-ray source , X-ray diffraction (XRD) was performed to analyze the crystal structure of the catalyst. The operating parameters were set as follows: voltage 40 kV, current 30 mA, scanning angle (2θ) range 20 - 80°, and scanning rate 5° min -1 . The diffraction pattern was analyzed using JADE software.

[0083] 1.2 X-ray photoelectron spectroscopy (XPS)

[0084] The valence states of surface elements were detected using a Smartedx type X-ray photoelectron spectrometer (XPS) and a Gemini 300 Auger electron spectrometer (AES) from Carl Zeiss (ZEISS) of Japan. The radiation source used was Al K α , and the binding energy shift caused by the charging effect was calibrated by the energy of the C1s signal at 284.8 eV.

[0085] 1.3 Ultraviolet-visible absorption spectroscopy analysis (UV-vis)

[0086] The absorbance of the sample was measured using a Shimadzu UV-3600i Plus spectrophotometer (manufactured in Japan) in the wavelength range of 200 - 800 nm.

[0087] 1.4 Temperature-programmed reduction (H 2 -TPR)

[0088] Approximately 0.1 g of the sample with a particle size of 40 - 60 mesh was loaded into a U-tube, and the U-tube was connected to the instrument. First, it was purged with argon (Ar) at 750 °C for 1 h, then switched to O 2 / Ar (19.8 vol.% O 2 ) mixed gas and oxidized at 500 °C for 1 h, and then switched back to Ar and cooled to 50 °C. Subsequently, it was reduced with H 2 / N 2 (10 vol.% H 2 ) at a heating rate of 10 °C / min from 50 °C to 1000 °C to reduce the catalyst, and finally switched to Ar purge until room temperature.

[0089] 1.5 N 2 O titration

[0090] The dispersion of Pt active centers on the catalyst surface was measured using the N 2 O titration method. Before measurement, the catalyst was reduced at 500 °C using 10% H 2 / N 2 (30 mL·min -1 ) mixed gas. Subsequently, the surface Pt atoms were oxidized for 0.5 h using 10% N 2 O / N 2 (30 mL·min -1 ) mixed gas. After oxidation, it was purged with 10% H 2 / N 2 (30 mL·min -1 ) mixed gas, and the temperature of the catalyst was raised from 25 °C to 450 °C at a heating rate of 10 °C·min -1 to complete the reduction process. The number of exposed Pt atoms on the particle surface was measured, and the Pt dispersion was calculated using the following equation:

[0091] D Pt(％ ) = Pt 表面上暴露的Pt原子数量 / Pt 总Pt原子 .

[0092] 1.6 Raman spectroscopy

[0093] Raman spectroscopy analysis was performed using a Horiba LabRAM HR Evolution instrument (manufactured in Japan) to determine the chemical bond types of the catalyst and analyze its chemical composition.

[0094] 2 Catalyst Evaluation Process

[0095] 2.1 Experimental Procedure

[0096] The catalyst sample (0.03 g, 40 - 60 mesh) was uniformly mixed with an equal mass of quartz sand. After the catalyst was loaded into the fixed - bed photothermal atmospheric - pressure reactor, the airtightness of the device was checked. Subsequently, H 2 / Ar mixed gas (H 2 content was 10%) was introduced, and the temperature was raised to 500 °C for 1 h of dynamic reduction. Then, the system was purged with high - purity Ar (99.999%) for 10 minutes, and then a raw - material gas mixture containing DME and O 2 / Ar (O 2 content was 19.8%) was introduced. The gas flow rate was adjusted using a mass flow meter to keep the total flow rate of the O 2 / Ar mixed gas at 80 mL·min -1 (including 16 mL·min -1 of O 2 ) and the DME flow rate at 32 mL·min -1 . The reaction evaluation device was equipped with a xenon lamp (PLS - SXE300) as the light source, operating at an intensity of 1500 mW·cm -2 , and the power output was 300 W. The final products were analyzed online using a Shanghai Huaai GC - 9560 gas chromatograph, and the detected gases were quantified using the external - standard method.

[0097] 2.2 Calculation Method

[0098] The calculation methods for the conversion rate of DME, the yield of H 2 , and the selectivity of the main carbon - containing products are as follows:

[0099] DME conversion rate:

[0100] H 2 yield:

[0101] CO selectivity:

[0102] CO 2 selectivity:

[0103] CH 4 selectivity:

[0104] Among them, C x represents the concentration of each substance, F x,out represents the effluent rate of each substance, F x,inIndicates the inflow rate of each substance.

[0105] 3 Results

[0106] 3.1 Catalyst characterization results

[0107] (1) XRD characterization analysis

[0108] As Figure 1 shown, through XRD characterization, we studied the crystal structure of the catalyst. Figure 1 (a) and (b) show the diffraction patterns of the synthesized samples. Pure TiO 2 shows characteristic peaks at 2θ values of 25.8°, 36.9°, 37.8°, 38.6°, 48.1°, 53.9°, 55.1°, 62.1°, 62.7°, 68.8°, 70.3° and 75.3°. These peaks correspond to the (101), (103), (004), (112), (200), (105), (211), (204), (116), (220) and (215) crystal planes of anatase TiO 2 . Pure CeO 2 shows diffraction peaks at 2θ values of 28.6°, 33.1°, 47.5°, 56.4°, 58.8° and 68.9°. These peaks correspond to the (111), (200), (220), (311), (222) and (400) crystal planes of the cubic fluorite structure, thus confirming that CeO 2 is a single cubic phase. In the composite catalyst, the peaks of TiO 2 show a shift, and the overall peak shape is similar to that of pure CeO 2 .

[0109] The characteristic peaks of Pt were not detected in the XRD spectrum, attributed to the high dispersion of Pt metal, which was confirmed by N 2 O titration measurement, and the Pt dispersion was 24.29%. The dispersions of catalysts with different Ti / Ce ratios and different loadings are shown in Table 1:

[0110] Table 1 Dispersions of catalysts with different Ti / Ce ratios and different loadings

[0111] Sample Pt Dispersion (%) <![CDATA[0.05 wt% Pt / TiO 2 -CeO 2 -0.5]]> 24.30％ <![CDATA[0.05wt% Pt / TiO 2 -CeO 2 -1]]> 25.68％ <![CDATA[0.05wt% Pt / TiO 2 -CeO 2 -4]]> 25.23％ <![CDATA[0.1 wt% Pt / TiO 2 -CeO 2 -0.5]]> 23.72％ <![CDATA[0.2 wt% Pt / TiO 2 -CeO 2 -0.5]]> 24.59％

[0112] (2) XPS characterization analysis

[0113] XPS was used to measure the contents of different oxygen species in the catalyst. Figure 2The O1s XPS spectra of the catalysts under different pretreatment conditions are shown. These spectra are interpreted as two oxygen species with binding energies of 530.5 eV and 529.5 eV. The peaks in the range of 528-530 eV are attributed to the lattice oxygen (O lat ), while the peak in the range of 530-533 eV corresponds to O v .O v The presence of will cause the Fermi level of the catalyst to shift upward, thus reducing the bandwidth. The Advantage software was used to calculate O v Relative to O lat and O v Percentage of the total n(O v ) / n(O v +O lat ). The results show that 0.05wt% Pt / TiO 2 -CeO 2 -0.5 contains 15.4% O v , 0.05wt%Pt / TiO 2 -CeO 2 -1 contains 19.19% O v , while 0.05wt%Pt / TiO 2 -CeO 2 -4 contains 17.01% O v These findings indicate that the highest O v In addition, a slight shift to lower binding energy was observed in the spectra of the catalysts at Ti / Ce ratios of 0.5, 1, and 4. This shift suggests that an increase in the Ti / Ce ratio leads to a decrease in the oxygen binding energy of the catalyst, an increase in the electron binding energy, an increase in the electron density, and enhanced electronic excitation upon light irradiation.

[0114] (3) UV-vis characterization analysis

[0115] UV-vis was used to investigate the light absorption ability of the catalyst. Figure 3 There are two obvious absorption peaks. The absorption peak in the ultraviolet region, with a wavelength range of 250-400nm, is attributed to TiO 2 The electron-hole pairs generated by band gap excitation are separated. In this range, the most obvious absorption peak appears when the Ti / Ce ratio is 1, indicating that the catalyst has the strongest absorption of ultraviolet light. 2 There is no absorption in the visible light range. 2 The incorporation of a carrier extends the absorption band of the catalyst into the long visible light range, significantly improving its solar spectrum absorption capacity.

[0116] To clarify the effect of different Ti / Ce ratios on the band gap width of the catalyst, a Tauc plot was constructed using the Tauc formula (see Figure 4 ). Five points were selected to form an approximate line segment, and its R 2 value exceeded 0.999. The intersection of this line segment with its extension on the abscissa was determined as the E bg value. Finally, the E 2 values of 0.05 wt% Pt / TiO 2 -CeO 2 -0.5, 0.05 wt% Pt / TiO 2 -CeO 2 -1, and 0.05 wt% Pt / TiO 2 -CeO 2 -4 were determined to be 2.3 eV, 2.15 eV, and 2.22 eV, respectively (Table 2). By comparison, it was found that after introducing CeO bg on TiO 2 , the E 2 value decreased significantly. The decreased E bg value is beneficial to the separation and transfer of photo-generated electron-hole pairs, thereby enhancing the absorption of visible light.

[0117]

[0118] Table 2 VB, CB, and E bg of catalysts with the same Pt loading and different Ti / Ce ratios Ti / Ce Ti / Ce <![CDATA[VB / eV > <![CDATA E bg / eV > <![CDATA[CB / eV > 0.5 1.98 2.3 -0.32 1 2.14 2.15 -0.01 4 1.95 2.22 -0.27

[0119] (4) Characterization and analysis of the valence band (VB) spectrum of XPS

[0120] The VB spectra of the catalysts 0.05 wt% Pt / TiO 2 -CeO 2 -0.5, 0.05 wt% Pt / TiO 2 -CeO 2 -1, and 0.05 wt% Pt / TiO 2 -CeO 2 -4 were analyzed by XPS. As Figure 5 shown, the VB values of these catalysts were determined to be 1.98 eV, 2.14 eV, and 1.95 eV, respectively. Due to the different Ti / Ce ratios on the catalysts, the proportion of O v also changed. The state of oxygen atoms in the catalyst is an important part of regulating the band gap structure. Therefore, the differences in the VB values of the samples are due to O vCaused by the change in proportion. The state of oxygen atoms in the sample plays a crucial role in regulating the band gap structure. During the partial oxidation of DME to hydrogen, the photocatalytic reaction ability of the catalyst is determined by the VB value. The larger the VB value, the stronger the oxidation ability. Therefore, among the three Pt / TiO 2 -CeO 2 catalyst ratios, 0.05 wt% Pt / TiO 2 -CeO 2 -1 has the highest VB value and is presumed to have a strong oxidation ability.

[0121] (5) H 2 -TPR Characterization Analysis

[0122] To explore the redox properties of the catalyst and clarify the role of O lat in the reaction, we performed H 2 -TPR analysis on the catalysts prepared in Examples 1, 4, and 7 (see Figure 6 ). The TPR curve of a single TiO 2 showed a weak peak around 500 - 700 °C, which might be caused by the reduction of TiO 2 . CeO 2 showed an obvious two-step reduction process: several low-temperature reduction peaks appeared around 300 - 600 °C, which was attributed to the reduction of surface O v ; while the low-temperature reduction peak that appeared after 700 °C was related to the reduction of O 2 inside CeO v . For TiO 2 -CeO 2 , the reduction peak at 300 - 700 °C could be attributed to the reduction of O 2 on the surface of TiO 2 and CeO v . When the Ti / Ce ratio was 1, the bulk O 2 peak of CeO v became more obvious and clear after 700 °C, indicating that there was a large amount of bulk O 2 -CeO 2 in the catalyst. This finding was consistent with the XPS results. v .

[0123] (6) Raman Spectroscopy Characterization Analysis

[0124] To further verify the above hypothesis, we used Raman spectroscopy to analyze the catalysts 0.05 wt% Pt / TiO 2 -CeO 2 -0.5, 0.05 wt% Pt / TiO 2 -CeO 2-1 and 0.05 wt% Pt / TiO 2 -CeO 2 -4 were characterized. As Figure 7 shown, CeO 2 exhibited a distinct peak at approximately 464 cm -1 , which can be attributed to its cubic phase. TiO 2 and TiO 2 -CeO 2 catalysts showed a Raman peak at 145 cm -1 , corresponding to the E 2 mode of the anatase phase of TiO g . For the TiO 2 -CeO 2 catalyst, the characteristic peak associated with CeO -1 could be clearly identified at 464 cm 2 . Notably, the 0.05 wt% Pt / TiO 2 -CeO 2 -1 catalyst exhibited the most prominent E g peak area in terms of Ti-O vibration.

[0125] 3.2 Reaction performance evaluation

[0126] 3.2.1 Influence of different temperatures on reaction performance

[0127] Under specific conditions, the influence of reaction temperature on the performance of 0.05 wt% Pt / TiO 2 -CeO 2 -0.5 catalyst was investigated. In the experiment, the catalyst dosage was 0.03 g, the feed ratio of DME to oxygen was maintained at 2:1, the WHSV was 134400 mL / (g·h), and the experimental pressure was atmospheric pressure. In the temperature range of 300 - 500 °C, the pyrolysis and photothermal pyrolysis partial oxidation of DME to produce hydrogen were carried out. The unit of WHSV is mL / (g·h)

[0128] As Figure 8 shown, the reaction temperature had a significant impact on the reaction performance. Under pure thermal conditions, the conversion of DME slightly increased from 63.50% at 300 °C to 65.41% at 500 °C. In contrast, under photothermal conditions, the conversion of DME increased significantly from 64.96% to 75.54% in the same temperature range. These results indicate that the Pt / TiO 2 -CeO 2 catalyst has enhanced catalytic activity under visible light irradiation. Increasing the temperature intensifies the molecular motion of DME, thus promoting a faster reaction rate. Notably, under photothermal conditions, the conversion of DME and H 2The yields significantly exceeded those under pure thermal conditions at the same temperature. This enhancement is attributed to the excitation of photo-generated electrons in the TiO 2 -CeO 2 support. Meanwhile, the metal sites capture these photo-generated electrons, suppressing electron-hole recombination and thus improving the photothermal catalytic efficiency.

[0129] Figure 9 (a) shows the selectivity of 0.05 wt% Pt / TiO 2 -CeO 2 -0.5 towards carbonaceous products at different temperatures. As can be seen from Figure 9 (a), the CO selectivity of the photothermal catalytic system is significantly higher than that of the pure thermal system, indicating that more C-H bond cleavage of DME occurs, which is consistent with the result of the increased H 2 yield. Meanwhile, with the increase in temperature, the selectivity of CH 4 gradually increases, while the selectivity of CO generally shows a trend of increasing first and then decreasing. The oxidation performance of O v reaches the best state at 400 °C. The subsequent decrease in CO selectivity is due to the removal of oxygen atoms in O lat caused by the increase in temperature, resulting in an increase in the concentration of O v . Combining the CO / (CO + CO 2 ) ratios at different reaction temperatures in the two systems of thermal catalysis and photothermal catalysis in Table 3, it is found that this over-oxidized state of the catalyst at high temperature (500 °C) not only fails to promote electron-hole separation but instead becomes a recombination center of electron-hole, thus reducing the catalytic performance of the material. More CO is oxidized to CO 2 , resulting in a decrease in the CO / (CO + CO 2 ) ratio.

[0130] Table 3 CO / (CO + CO 2 values of 0.05 wt% Pt / TiO 2 -CeO 2 -0.5 catalyst at DME / O 2 = 2, 300 - 500 °C, WHSV = 134000 mL / (g·h), at atmospheric pressure.

[0131]

[0132] 3.2.2 Effect of different Ti / Ce ratios on the reaction performance when the Pt loading is 0.05 wt%

[0133] Figure 10 (a) shows the effect of the Ti / Ce ratio on the DME conversion and H 2Effect on the yield. In the photothermal system, as the Ti / Ce ratio increases, the DME conversion rate and H 2 yield initially show an upward trend and then a downward trend. In contrast, in the pure thermal system, although the DME conversion rate also shows a similar trend, the H 2 yield shows the opposite pattern, that is, it first decreases and then increases. In the thermocatalytic system, the correlation between the DME conversion rate and the O 2 content in the Pt / TiO 2 -CeO v catalyst indicates that the O v concentration plays a crucial role in the DME oxidation reaction.

[0134] The VB, E 2 and conduction band (CB) values of the 0.05 wt% Pt / TiO 2 -CeO 2 -0.5, 0.05 wt% Pt / TiO 2 -CeO 2 -1 and 0.05 wt% Pt / TiO 2 -CeO bg -4 catalysts were calculated based on the UV-Vis results (Table 2). Compared with pure TiO 2 (3.06 eV), it was found that the E 2 value decreased significantly after doping CeO 2 into TiO bg . The lower E bg promoted the separation and transition of photo-generated electrons and holes, enhancing the visible light absorption ability. During this reaction process, 0.05 wt% Pt / TiO 2 -CeO 2 -1 combined the highest O v concentration and the lowest E bg , achieving the best catalytic performance for the partial oxidation of DME to hydrogen.

[0135] Figure 9 (b) shows the variation of the selectivity of carbonaceous products with the Ti / Ce ratio. As can be seen from Figure 9 (b), in the photothermal system, the 0.05 wt% Pt / TiO 2 -CeO 2 -1 catalyst exhibits the lowest CH 4 selectivity, indicating that DME is more inclined to dehydrogenation reaction to produce H 2 , with the least cleavage of C-O bonds. Further combined with CO / (CO + CO 2 ) and O v / (O v + O lat) The trend of the values (Table 4) shows that the trends of CO / (CO + CO 2 ) and O v / (O v + O lat ) are consistent. Higher H 2 yield and CO selectivity both benefit from higher O v concentration, demonstrating the mechanism of regulating O v concentration and the reaction path by changing Ti / Ce.

[0136] Table 4 Under the conditions of DME / O 2 = 2, 400 °C, and WHSV = 134000 mL / (g·h), the O 2 - CeO 2 in the Pt / TiO v / (Ov + O lat ) and CO / (CO + CO 2 )

[0137]

[0138] Figure 10 (b) shows the effect of Pt loading on the catalyst performance. The same catalyst support TiO 2 - CeO 2 - 0.5 was selected for loading. As the Pt loading increased from 0.05 wt% to 0.2 wt%, the conversion of DME increased in both the photothermal and pure thermal systems. However, the yield of H 2 showed different trends: under photothermal conditions, the yield of H 2 first increased and then decreased, while in the pure thermal system, it continued to increase. This may be because the agglomeration of Pt in the high-temperature photothermal system weakened the dehydrogenation ability of the catalyst. Overall, the catalytic performance of the photothermal catalytic system is better than that of the pure thermal catalytic system. It should be noted that the increase in Pt loading generates more metal sites. In this way, more photogenerated electrons are attracted and captured, thereby suppressing the electron-hole recombination and improving the overall photothermal catalytic efficiency of DME.

[0139] Figure 9 (c) shows the selectivity of carbonaceous products at different Pt loadings. The same catalyst support TiO 2 - CeO 2 - 0.5 was selected for loading. Table 5 shows that in both the thermal catalytic and photocatalytic systems, as the Pt loading increased from 0.05 wt% to 0.2 wt%, the CO / (CO + CO 2 ) ratio initially showed an upward trend. This phenomenon is speculated to be due to the increase in the number of Pt catalysts, which reacts with more O vThe synergy promoted the reaction. Therefore, the catalyst exhibited enhanced oxidation performance during the reaction, resulting in a subsequent decrease in the CO / (CO + CO 2 ) ratio.

[0140] Table 5 0.05 wt% Pt / TiO 2 -CeO 2 (0.5), 0.1 wt% Pt / TiO 2 -CeO 2 (0.5), 0.2 wt% Pt / TiO 2 -CeO 2 (0.5) catalysts at DME / O 2 = 2, 400 °C, WHSV = 134000 mL / (g·h) for the value of CO / (CO + CO 2 )

[0141]

[0142] For photocatalysts, the light absorption ability is crucial for initiating photocatalytic redox reactions. When absorbing light energy, the photocatalyst can generate excited-state photoinduced electron-hole pairs on its surface. However, TiO 2 has a relatively wide intrinsic bandgap (3.0 eV for rutile and 3.2 eV for anatase). Therefore, only light with wavelengths less than 413 nm (rutile) and 388 nm (anatase) can excite the electrons in the VB to transition to the CB, thus generating photoinduced electron-hole pairs. The introduction of CeO 2 reduced the E bg value of the catalyst to 2.15 eV. According to the UV-Vis characterization results, the light absorption boundary extended to 615 nm, which helped the photoinduced electron transition and reduced the VB. In the partial oxidation of DME to hydrogen reaction, the photocatalytic ability of the catalyst is affected by the position of the VB. The more positive the VB, the stronger the oxidation ability. Further, the introduction of Pt in the catalyst and the synergy between Pt and O v promoted the efficient conversion of DME.

[0143] 4 Conclusions

[0144] In the Pt-Ce-Ti photothermal partial oxidation of DME to hydrogen system, the conversion rate of DME and the yield of H 2 significantly exceeded the conversion rate and yield in the pure thermal system at the same temperature. Further research found that in the same photothermal catalytic system, 0.05 wt% Pt / TiO 2 -CeO 2 -1 had both a high DME conversion rate and H 2 yield in the photothermal system, demonstrating the regulation of the catalyst E bg and Ov The concentration, and further optimize the action mechanism of the DME photothermal catalytic performance. At the same time, it is also proved that a small amount (0.05 wt%) of noble metal can also play an advantageous role in the photothermal dehydrogenation reaction system. This work provides a new idea for the design of efficient photothermal catalysts.

[0145] The embodiments of the present application have been described above in conjunction with the accompanying drawings. However, the present application is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present application, those of ordinary skill in the art can also make many forms without departing from the purpose of the present application and the scope protected by the claims, and all of them belong to the protection scope of the present application.

Claims

1. A catalyst for producing hydrogen by partial oxidation of dimethyl ether, characterized in that: The catalyst uses TiO2-CeO2 as a carrier and carries active component metal Pt. The molar ratio of Ti to Ce in the catalyst is 0.5-4, and the mass of Pt is 0.05-0.2% of the mass of the carrier.

2. A catalyst for producing hydrogen by partial oxidation of dimethyl ether according to claim 1, characterized in that: The TiO2-CeO2 is prepared by a sol-gel method.

3. The catalyst for producing hydrogen by partial oxidation of dimethyl ether according to claim 1, characterized in that: Metallic Pt was loaded onto the TiO2-CeO2 support by vacuum impregnation.

4. The method for preparing a catalyst for producing hydrogen by partial oxidation of dimethyl ether according to claim 1, characterized in that: The following steps are involved: (1) Pluronic F127 polymer was gradually and slowly added into C2H5OH under continuous stirring and heating until it was completely dissolved; (2) adding Ce(NO3)2·6H2O, butyl titanate, glacial acetic acid, and concentrated nitric acid to the solution obtained in step (1), mixing and aging for 22-24 hours; (3) allowing the mixture to gel naturally at 38-40° C. to obtain a sol-gel product; (4) drying the obtained sol-gel product in an electric constant temperature blast drying oven at 78-82° C. for 11-13 h; (5) heating the temperature to 540-560°C at a heating rate of 1-2°C / min, and calcining for 5-7h to obtain TiO2-CeO2; (6) Fully mix the H2PtCl6-6H2O solution and TiO2-CeO2 and immerse for 1-2 hours; (7) distilling under reduced pressure at 58-62°C, and then drying the evaporated liquid at 98-102°C for 11-13h; (8) The obtained material is calcined at 440-460°C for 2-3h to obtain Pt / TiO2-CeO2.

5. The preparation method according to claim 4, characterized in that: The solid-liquid ratio of the Pluronic F127 polymer to C2H5OH, Ce(NO3)2·6H2O, butyl titanate, glacial acetic acid and concentrated nitric acid is 1-8:1-65:1-20:5-50:1-6:1-3.

6. The preparation method according to claim 4, characterized in that: The concentration of H2PtCl6-6H2O solution is 0.01-01g / mL.

7. Use of the catalyst for producing hydrogen by partial oxidation of dimethyl ether according to any one of claims 1 to 3 in a photothermal catalytic reaction of producing hydrogen by partial oxidation of dimethyl ether.

8. The use according to claim 7, characterized in that: The amount of the dimethyl ether partial oxidation hydrogen production catalyst used in the photothermal catalytic dimethyl ether partial oxidation hydrogen production reaction is 0.03 g, the feed ratio of dimethyl ether to oxygen is maintained at 2:1, the mass space velocity is 134400 mL / (g·h), and the pressure is normal pressure.

9. The use according to claim 7, characterized in that: The temperature of the photothermal catalytic partial oxidation of dimethyl ether to produce hydrogen is 300-500°C.

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