High-activity Pt / gaCe-al2o3 catalyst, preparation method and application thereof

Abstract

The application discloses a high-activity Pt / GaCe-Al2O3 catalyst and a preparation method and application thereof. Firstly, an Al2O3 carrier doped with Ga and Ce is synthesized through a hydrothermal synthesis method; then, metal Pt is loaded on the synthesized GaCe-Al2O3 carrier through an impregnation method, so as to obtain the Pt / GaCe-Al2O3 catalyst with high dehydrogenation activity. The catalyst has a nanosheet structure and has strong adsorption performance on methylcyclohexane, and under the condition of 300 DEG C and normal pressure, the catalyst has excellent catalytic dehydrogenation activity and stability in a methylcyclohexane dehydrogenation reaction, and can realize an ultrahigh hydrogen release rate.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, specifically to a highly active Pt / GaCe-Al2O3 catalyst, its preparation method, and its application. Background Technology

[0002] Liquid organic hydrogen storage is based on the reversible reactions of hydrogenation and dehydrogenation of organic hydrides to store hydrogen. It features high hydrogen storage density, highly reversible hydrogenation-dehydrogenation processes, and is highly compatible with existing energy infrastructure, requiring minimal capital investment. Therefore, liquid organic hydrogen storage is considered an attractive hydrogen storage method. Methylcyclohexane (MCH) is considered an ideal liquid hydrogen storage material due to its low toxicity, high hydrogen cycle reversibility, and theoretical hydrogen storage capacity (~6.1 wt.%). However, methylcyclohexane dehydrogenation is a strongly endothermic reaction, typically requiring high reaction temperatures to achieve efficient hydrogen release rates, which also leads to short catalyst lifetimes. Therefore, developing a catalyst with a high hydrogen release rate and good stability to facilitate convenient hydrogen utilization is particularly important.

[0003] In catalyst preparation, Pt metal is widely used in catalytic dehydrogenation due to its strong CH bond activation ability and low C / C bond cleavage ability. Besides the active metal, the support is also an important component. γ-Al₂O₃, with its excellent mechanical and chemical properties, can effectively improve the metal-support interaction, enhance the dispersion of active components, and maintain the unique properties of the impregnated metal. Therefore, Pt / Al₂O₃ catalysts are the most commonly used dehydrogenation catalysts. However, the above catalysts have low catalytic dehydrogenation activity and are prone to deactivation, resulting in low purity of the produced hydrogen. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for preparing a highly active Pt / GaCe-Al2O3 catalyst, which enhances the dehydrogenation rate and stability of the single-metal Pt / Al2O3 catalyst by using a metal promoter.

[0005] A second objective of this invention is to provide a highly active Pt / GaCe-Al2O3 catalyst prepared by the above-described method.

[0006] A third objective of this invention is to provide the application of the aforementioned highly active Pt / GaCe-Al2O3 catalyst in catalytic dehydrogenation.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] One aspect of the present invention provides a method for preparing a highly active Pt / GaCe-Al2O3 catalyst, comprising the following steps:

[0009] (1) Aluminum salt, urea, cerium salt and gallium salt are mixed in water, and the resulting mixture is placed in a high-pressure reactor for hydrothermal reaction; after cooling to room temperature, the precipitate is washed, dried and calcined to obtain GaCe-Al2O3 support;

[0010] (2) The GaCe-Al2O3 support obtained in step (1) is added to an impregnation solution containing platinum precursor, ultrasonically mixed, and then vacuum impregnated for 12 h. After impregnation is completed, it is dried and calcined in an inert atmosphere to obtain Pt / GaCe-Al2O3 catalyst.

[0011] Preferably, the hydrothermal reaction in step (1) is carried out at a temperature of 100°C for 48 hours.

[0012] Preferably, the drying temperature in step (1) is 100°C and the time is 12h; the calcination temperature is 750°C and the time is 2h.

[0013] Preferably, the aluminum salt in step (1) is aluminum nitrate, the cerium salt is cerium nitrate, and the gallium salt is gallium nitrate.

[0014] Preferably, the impregnation solution in step (2) is one of deionized water, ethanol and acetone.

[0015] Preferably, the calcination temperature in step (2) is 500°C and the time is 2 hours.

[0016] Preferably, the platinum precursor in step (2) is chloroplatinic acid.

[0017] In another aspect, the present invention provides a highly active Pt / GaCe-Al2O3 catalyst, which is prepared by the above-described preparation method.

[0018] Preferably, the catalyst contains 0.5 wt.% Pt, 1.5 wt.% Ga, and 1.5 wt.% Ce.

[0019] The catalyst has a nanosheet structure and exhibits strong adsorption properties for methylcyclohexane.

[0020] In another aspect, the present invention also provides the application of the above-mentioned highly active Pt / GaCe-Al2O3 catalyst in the catalytic dehydrogenation of MCH.

[0021] The specific application steps include: the catalyst is tableted, pulverized, and sieved to obtain catalyst particles with a particle size of 40-60 mesh. 50 mg of catalyst diluted with quartz sand (total: 0.55 g) is added to a reaction tube (inner diameter = 8 mm), and the temperature is maintained at 300℃ and the pressure at 0.1 MPa. The flow rate of methylcyclohexane is controlled at 30 μL / min using a syringe pump and vaporized at 180℃. The carrier gas (Ar) flow rate is adjusted to 10-50 mL / min using a mass flow controller, and the mixture of methylcyclohexane and Ar is pumped into the reactor. The products are analyzed online using a gas chromatograph equipped with TCD and FID detectors.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) By hydrothermal synthesis, non-noble metals Ga and Ce were doped into Al2O3 support to synthesize GaCe-Al2O3, an excellent support with mesoporous nanosheet structure. This structure can ensure that the reactants can smoothly enter the pores to contact the active metal.

[0024] (2) A Pt / Ga1.5Ce1.5-Al2O3 catalyst was prepared by impregnating the GaCe-Al2O3 support with an ethanol-dissolved H2PtCl6·6H2O solution. It exhibited high efficiency in adsorbing methylcyclohexane and inhibiting carbon deposition, which improved the activity of the catalyst while maintaining an extremely low deactivation rate (0.09% / min).

[0025] (3) The above catalyst was applied to the dehydrogenation reaction of methylcyclohexane. The reaction was carried out in a continuous fixed-bed reactor. The selectivity of toluene was extremely high (~99.9%), and the hydrogen obtained was of high purity. There was no need to separate the gaseous products. Attached Figure Description

[0026] Figure 1 These are XRD patterns of catalysts with different amounts of additives prepared in Example 1 and Comparative Examples 1-4 of this invention;

[0027] Figure 2 This is a SEM image of the Pt / Ga1.5Ce1.5-Al2O3 catalyst prepared in Example 1 of this invention;

[0028] Figure 3 This is a TEM image of the Pt / Ga1.5Ce1.5-Al2O3 catalyst prepared in Example 1 of this invention;

[0029] Figure 4 These are MCH-TPD diagrams of catalysts with different amounts of additives prepared in Example 1 and Comparative Examples 1-4 of this invention;

[0030] Figure 5The effect of Ce addition on the dehydrogenation of methylcyclohexane;

[0031] Figure 6 The effect of Ga addition on the dehydrogenation of methylcyclohexane;

[0032] Figure 7 The effect of different impregnation solutions on the dehydrogenation of methylcyclohexane;

[0033] Figure 8 This is the effect of carrier gas flow rate on the dehydrogenation of methylcyclohexane. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0035] Example 1: Preparation of catalyst Pt / Ga1.5Ce1.5-Al2O3

[0036] I. Preparation of Ga1.5Ce1.5-Al2O3 support by hydrothermal synthesis

[0037] 6.44 g Al(NO3)3·9H2O, 9.28 g CO(NH2)2, 41.34 mg Ce(NO3)3·6H2O, and 48.60 mg Ga(NO3)3·xH2O were dissolved in 100 mL of deionized water. The resulting mixture was placed in a 200 mL Teflon-lined stainless steel autoclave and kept at 100 °C for 48 h. After cooling to room temperature, the precipitate was washed and filtered several times with deionized water, then dried at 100 °C for 12 h, and finally calcined in a muffle furnace at 750 °C for 2 h at a heating rate of 2 °C / min to obtain Ga1.5Ce1.5-Al2O3.

[0038] II. Synthesis of Pt / Ga1.5Ce1.5-Al2O3 catalyst by impregnation method

[0039] The 0.5 g support prepared above was added to an ethanol solution containing 6.67 mg H2PtCl6·6H2O and sonicated for 20 min. The mixed solution was then impregnated in a vacuum drying oven for 12 h. After impregnation, it was dried and calcined at 500 °C for 2 h in an inert atmosphere to obtain the Pt / Ga1.5Ce1.5-Al2O3 catalyst.

[0040] Comparative Example 1: Preparation of Pt / Al2O3 catalyst

[0041] The process was carried out according to the above hydrothermal synthesis method (the steps are the same as in Example 1). In the first step of dissolution, 6.44g of Al(NO3)3·9H2O and 9.28g of CO(NH2)2 were added respectively. Pt / Al2O3 was synthesized by the traditional impregnation method (the steps are the same as in Example 1).

[0042] Comparative Example 2: Preparation of Pt / Ce-Al2O3 catalysts with different Ce doping

[0043] The process was carried out using the hydrothermal synthesis method described above (steps are the same as in Example 1). In the first step of dissolution, 6.44 g of Al(NO3)3·9H2O, 9.28 g of CO(NH2)2, and 13.78 mg, 41.34 mg, 82.68 mg, and 275.60 mg of Ce(NO3)3·6H2O were added respectively. Pt / Ce0.5-Al2O3, Pt / Ce1.5-Al2O3, Pt / Ce3-Al2O3, and Pt / Ce10-Al2O3 were synthesized using the conventional impregnation method (steps are the same as in Example 1).

[0044] Comparative Example 3: Preparation of Pt / Ga1.5-Al2O3 catalyst

[0045] The process was carried out using the hydrothermal synthesis method described above (the steps are the same as in Example 1). In the first step of dissolution, 6.44 g of Al(NO3)3·9H2O, 9.28 g of CO(NH2)2 and 48.60 mg of Ga(NO3)3·xH2O were added respectively. Pt / Ga1.5-Al2O3 was synthesized using the conventional impregnation method (the steps are the same as in Example 1).

[0046] Comparative Example 4: Preparation of Pt / GaCe1.5-Al2O3 catalysts with different Ga doping

[0047] The process was carried out using the hydrothermal synthesis method described above (steps are the same as in Example 1). In the first step of dissolution, 6.44g Al(NO3)3·9H2O, 41.34mg Ce(NO3)3·6H2O, 9.28g CO(NH2)2, and 16.2mg and 97.20mg Ga(NO3)3·xH2O were added respectively. Pt / Ga0.5Ce1.5-Al2O3 and Pt / Ga3Ce1.5-Al2O3 were synthesized using the conventional impregnation method (steps are the same as in Example 1).

[0048] Table 1 Physical structural properties of catalysts

[0049]

[0050] a Specific surface area is calculated using the BET method.

[0051] b The total orifice volume was calculated at a relative pressure P / P0 = 0.99.

[0052] c The average aperture was calculated using the BJH method.

[0053] As shown in Table 1, the specific surface area, pore volume, and pore diameter of the Al2O3 support are 161 m², respectively. 2 / g, 0.77cm 3 After loading with Pt, the specific surface area and pore volume of the Pt / Al₂O₃ catalyst decreased relatively, which can be attributed to the collapse of some mesopores and the blockage of some small pores by metal clusters formed after recalcination. Furthermore, all catalysts exhibited mesoporous structures with pore sizes ranging from 6.70 to 8.15 nm, significantly larger than the dynamic pore size (0.70 nm) of toluene and MCH molecules. Therefore, the mesoporous structure of the catalysts facilitated the diffusion of reactant molecules.

[0054] Figure 1 These are the XRD patterns of different catalysts prepared in Example 1 and Comparative Examples 1-4; Figure 1 It can be seen that all samples exhibit clear characteristic diffraction peaks corresponding to γ-Al2O3 at 31.9°, 37.4°, 39.4°, 45.8°, and 66.9°. A small diffraction peak related to the (111) plane of the CeO2 cubic fluorite structure appears at 28.6° in Pt / Ga1.5Ce1.5-Al2O3, indicating that Ga... 3+ Ions enter the CeO2 lattice to form a solid solution structure, causing slight lattice contraction and increasing the 2θ value of the (111) peak. The diffraction peak of Pt was not detected, possibly due to its low content and high dispersion on the support.

[0055] Figure 2 This is a SEM image of the catalyst prepared in Example 1; by Figure 2 It can be seen that the catalysts all exhibit a nanosheet morphology.

[0056] Figure 3 The image shows a TEM image of the catalyst prepared in Example 1. When Ga or Ce is added, spherical particles of 5-10 nm in size are observed and are uniformly distributed on the catalyst surface.

[0057] Figure 4 The figures show the MCH-TPD diagrams for different catalysts prepared in Examples 1 and Comparative Examples 1-4. The Pt / Ga1.5Ce1.5-Al2O3 catalyst exhibits higher adsorption capacity due to its largest desorption peak. Furthermore, the order of MCH desorption peak temperature is: Pt / Ga1.5Ce1.5-Al2O3 (120℃) > Pt / Ce1.5-Al2O3 (109℃) > Pt / Ga1.5-Al2O3 (91℃) > Pt / Al2O3 (87℃). This indicates that the addition of the promoter metals Ga and Ce significantly enhances the catalyst's adsorption performance for MCH, thereby promoting the MCH dehydrogenation reaction.

[0058] Example 2: Application of Pt / GaCe-Al2O3 catalyst in the dehydrogenation of methylcyclohexane

[0059] All catalytic reactions were carried out in a micro-fixed bed.

[0060] All catalysts are processed by tableting, crushing, and sieving to produce catalyst particles with a particle size of 40-60 mesh.

[0061] In a typical experiment, 50 mg of catalyst diluted with quartz sand (total: 0.55 g) was added to a reaction tube (inner diameter = 8 mm), and the bed temperature was maintained at 300 °C and the pressure at 0.1 MPa. The MCH flow rate was controlled at 30 μL / min using a syringe pump and vaporized at 180 °C. The carrier gas (Ar) flow rate was adjusted to 30 mL / min using a mass flow controller, and the MCH and Ar mixture was pumped into the reactor together. The products were analyzed online using a gas chromatograph equipped with TCD and FID detectors. The hydrogen release rate is an important value reflecting the catalyst dehydrogenation efficiency, and the first-order deactivation rate is an important value reflecting the catalyst stability, calculated according to formulas 1-1 and 1-2 respectively.

[0062] hydrogen release rate

[0063] μ is the feed rate of MCH, in μL / min;

[0064] ρ is the density of MCH, in g / mL;

[0065] X represents the MCH rate, in %.

[0066] m is the mass of the catalyst, in grams;

[0067] M is the relative molecular mass of MCH, in g / mol;

[0068] W represents the platinum loading, in percent;

[0069] k d This represents the first-order inactivation rate;

[0070] t is the reaction time, in minutes.

[0071] Depend on Figure 5 It can be seen that, under the same reaction conditions, the initial conversion rate of the Pt / Al2O3 catalyst is 52%, and the hydrogen release rate is 963 mol / g. Pt The deactivation rate was 0.20% / min, and the toluene selectivity was ~99.6%. In contrast, the Pt / Ce1.5-Al2O3 catalyst had an initial conversion of 65% and a hydrogen release rate of 1561 mol / g. PtThe deactivation rate was 0.15% / min, while the catalyst exhibited the best hydrogen release rate and stability when Ce was added at 1.5 wt.%.

[0072] Depend on Figure 6 It can be seen that when the auxiliary metal Ga is further added, Pt / Ce1.5Ga1.5-Al2O3 exhibits the highest initial conversion rate (73%) and hydrogen release rate (1914 mol / g). Pt The deactivation rate exhibited a significant V-shaped change with increasing Ga content, with Pt / Ce1.5Ga1.5-Al2O3 showing the lowest deactivation rate (0.09% / min). The results indicate that the catalyst exhibits superior dehydrogenation activity and stability when 1.5 wt.% Ga, the promoter metal, is further added. This is likely because Ga ions are incorporated into the CeO2 lattice, improving the catalyst's adsorption performance for MCH and promoting the methylcyclohexane dehydrogenation reaction. Furthermore, the promoter metal reduces the accumulation of coke, thus more effectively exposing active sites and improving catalyst stability.

[0073] In summary, when both Ga and Ce are added at 1.5 wt.%, the catalyst exhibits a superior hydrogen release rate and catalytic effect.

[0074] Example 3: Effect of different impregnation solutions on the dehydrogenation of methylcyclohexane

[0075] The above-described hydrothermal synthesis method was followed (steps same as in Example 1). Using the traditional impregnation method, Pt / Ga1.5Ce1.5-Al2O3-deionized water, Pt / Ga1.5Ce1.5-Al2O3-ethanol, and Pt / Ga1.5Ce1.5-Al2O3-acetone were synthesized using one of the following impregnation solutions: deionized water, ethanol, and acetone (steps same as in Example 1).

[0076] Depend on Figure 7 It can be seen that, under the same reaction conditions, although the dehydrogenation activities of catalysts prepared with different impregnation solvents are similar, the stability of the catalysts varies significantly. When ethanol and acetone are used as impregnation solvents, the catalysts exhibit low deactivation rates, at 0.09% / min and 0.10% / min, respectively. However, when deionized water is used as the impregnation solution, the deactivation rate of the catalysts is as high as 0.13% / min. This may be because ethanol and acetone have low boiling points and strong diffusivity during impregnation, resulting in a more uniform distribution of the active components. However, compared with ketones, ethanol is non-toxic and inexpensive, therefore, ethanol is the optimal impregnation solution.

[0077] Example 4: Effect of carrier gas flow rate on the dehydrogenation of methylcyclohexane

[0078] Reaction conditions: 50 mg catalyst, methylcyclohexane = 30 μL / min, 300 °C, 0.1 MPa

[0079] The carrier gas flow rate has a significant impact on the dehydrogenation reaction. The flow rate determines the concentration and time of the MCH reaction, thus affecting the conversion rate of methylcyclohexane. Figure 8 It can be seen that when the carrier gas flow rate increases from 10 mL / min to 50 mL / min, the conversion rate of methylcyclohexane decreases with the increase of the carrier gas flow rate. This is because the relative concentration of methylcyclohexane and the decrease in reaction residence time reduce the contact between methylcyclohexane and the catalyst. Therefore, the conversion rate of methylcyclohexane decreases significantly with the increase of the carrier gas flow rate.

Claims

1. The application of a highly active Pt / GaCe-Al2O3 catalyst in the catalytic dehydrogenation of methylcyclohexane, characterized in that, The highly active Pt / GaCe-Al2O3 catalyst was prepared by the following steps: (1) Aluminum salt, urea, cerium salt and gallium salt are mixed in water, and the resulting mixture is placed in a high-pressure reactor for hydrothermal reaction; after cooling to room temperature, the precipitate is washed, dried and calcined to obtain GaCe-Al2O3 support; (2) The GaCe-Al2O3 support obtained in step (1) is added to the impregnation solution containing platinum precursor, ultrasonically mixed, and then vacuum impregnated for 12 h. After impregnation is completed, it is dried and calcined in an inert atmosphere to obtain Pt / GaCe-Al2O3 catalyst.

2. The application according to claim 1, characterized in that, The temperature of the hydrothermal reaction in step (1) is 100°C. o C, the time is 48 hours.

3. The application according to claim 1, characterized in that, The drying temperature in step (1) is 100°C. o C, the time is 12h; the calcination temperature is 750℃, the time is 2h.

4. The application according to claim 1, characterized in that, The aluminum salt in step (1) is aluminum nitrate, the cerium salt is cerium nitrate, and the gallium salt is gallium nitrate.

5. The application according to claim 1, characterized in that, The platinum precursor in step (2) is chloroplatinic acid, and the impregnation solution is one of deionized water, ethanol and acetone.

6. The application according to claim 1, characterized in that, The calcination temperature in step (2) is 500°C. o C, the time is 2 hours.

7. The application according to claim 1, characterized in that, The highly active Pt / GaCe-Al2O3 catalyst has a Pt loading of 0.5 wt.%, a Ga loading of 1.5 wt.%, and a Ce loading of 1.5 wt.%.

8. The application according to claim 1, characterized in that, The specific application steps include: Add catalyst particles with a particle size of 40-60 mesh, diluted with quartz sand, to the reaction tube, and then maintain the temperature at 300°C. o C, pressure maintained at 0.1 MPa; flow rate of methylcyclohexane controlled at 30 L / min and 180 o Under C conditions, the mixture of methylcyclohexane and carrier gas is vaporized, and the flow rate of the carrier gas is adjusted to 10-50 mL / min. The mixture of methylcyclohexane and carrier gas is then pumped into the reactor to obtain toluene and hydrogen.

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