A Ce-modified low-loading Pt Pt / gamma-Al2O3 catalyst, a preparation method and application thereof

Abstract

The application provides a Ce-modified low-loading Pt Pt / gamma-Al2O3 catalyst and a preparation method and application thereof, and belongs to the field of catalysts.The method comprises the following steps: S1, adding deionized water to Al(OH)3 powder, and then performing drying and extrusion into a strip to obtain a strip-shaped Al(OH)3; S2, performing first calcination on the strip-shaped Al(OH)3 to obtain a gamma-Al2O3 carrier with a set particle size; S3, immersing the gamma-Al2O3 carrier in a cerium nitrate aqueous solution, and then performing drying and second calcination to obtain a Ce-modified gamma-Al2O3 catalyst; and S4, immersing the Ce-modified gamma-Al2O3 catalyst in a chloroplatinic acid aqueous solution, and then performing drying and third calcination to obtain a Ce-modified Pt / gamma-Al2O3 catalyst. The method improves the catalytic performance of a fixed-bed catalyst in a reaction of preparing p-aminoanisole by catalytically hydrogenating p-nitroanisole.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a Ce-modified low-loading Pt Pt / gamma-Al2O3 catalyst and a preparation method and application thereof. BACKGROUND

[0002] Aromatic amino compounds are an important basic fine chemical raw material, widely used in dyes, pigments, pesticides, pharmaceuticals and fine chemicals, etc. fields, and have broad market prospects. There are many common synthesis methods for aromatic amino compounds. In the early stage, iron powder or sulfidic alkali was used to reduce aromatic nitro compounds to prepare aromatic amino compounds. This method produces a large amount of wastewater, which is harmful to the environment, and is gradually eliminated. In recent years, the reduction method using hydrazine hydrate or sodium borohydride as hydrogen source shows good catalytic performance in reducing aromatic nitro compounds, but the cost is too high, which is not conducive to large-scale production of aromatic amino compounds. The method of electrochemical reduction for reducing aromatic nitro compounds also shows excellent catalytic performance, but the method is relatively complex and unstable, and the requirements for conditions are also harsh, which is difficult to carry out large-scale production. As the most direct method for reducing aromatic nitro compounds, the catalytic hydrogenation method has the advantages of environmental friendliness, good selectivity and high yield, and becomes the ideal process for preparing aromatic amino compounds from aromatic nitro compounds in the industry.

[0003] The preparation of aromatic amino compounds from aromatic nitro compounds by hydrogenation is a typical reduction reaction, which often relies on catalysts. Researchers have studied many catalysts for the catalytic hydrogenation of aromatic nitro compounds, including non-noble metal (Cu, Ni, etc.) and noble metal (Pt, Pd, Ru, etc.) catalysts. Although the cost of non-noble metal catalysts is lower than that of noble metal catalysts, they are prone to deactivation due to their poor stability, and are mostly used in batch reactors for hydrogenation of aromatic nitro compounds, which has the problem of low efficiency. Noble metal catalysts have excellent stability and high selectivity, and are mostly used in the study of catalytic hydrogenation of nitrobenzene and its derivatives. Studies have shown that by modifying the carrier and uniformly dispersing 2.5% Pd particles on the surface of the carrier, the catalyst can achieve high selectivity for the reduction of p-nitroanisole to p-aminophenyl anisole under mild conditions of 0.1 MPa H2 flow and 30℃ reaction temperature. However, due to the influence of the -OCH3 substituent, the problem of low conversion of p-nitroanisole still exists. Considering that the noble metal loading of the noble metal catalysts used in the current research for catalytic hydrogenation of aromatic nitro compounds is relatively high, which greatly increases the cost and limits its widespread use, and there is no related prior art report on the continuous process of preparing p-aminophenyl anisole by hydrogenation of p-nitroanisole with a catalyst with low noble metal loading. SUMMARY

[0004] The application provides a Ce-modified low-loading Pt Pt / gamma-Al2O3 catalyst and a preparation method and application thereof, so as to solve the technical problem of how to improve the catalytic performance of a fixed-bed catalyst in a reaction of preparing p-aminoanisole by catalytic hydrogenation of p-nitroanisole.

[0005] In a first aspect, the application provides a preparation method of a Ce-modified low-loading Pt Pt / gamma-Al2O3 catalyst, which comprises the following steps:

[0006] S1, adding deionized water to Al(OH)3 powder, and then performing drying and extrusion into a strip to obtain a strip-shaped Al(OH)3;

[0007] S2, performing first calcination on the strip-shaped Al(OH)3 to obtain a gamma-Al2O3 carrier with a set particle size;

[0008] S3, immersing the gamma-Al2O3 carrier in a cerium nitrate aqueous solution, and then performing drying and second calcination to obtain a Ce-modified gamma-Al2O3 catalyst;

[0009] S4, immersing the Ce-modified gamma-Al2O3 catalyst in a chloroplatinic acid aqueous solution, and then performing drying and third calcination to obtain a Ce-modified Pt / gamma-Al2O3 catalyst.

[0010] Optionally, the set particle size is 250-425 mu m.

[0011] Optionally, the temperature of the first calcination is 800 DEG C, and the time of the first calcination is 3 h.

[0012] Optionally, the temperature of the second calcination is 800 DEG C, and the time of the second calcination is 3 h.

[0013] Optionally, the temperature of the third calcination is 450 DEG C, and the time of the third calcination is 3 h.

[0014] In a second aspect, the application provides a Ce-modified low-loading Pt Pt / gamma-Al2O3 catalyst prepared by the method in any one of the embodiments of the first aspect.

[0015] Optionally, the mass fraction of Pt in the Ce-modified gamma-Al2O3 catalyst is 0.02%.

[0016] Optionally, the mass fraction of Ce in the Ce-modified gamma-Al2O3 catalyst is 1-12%.

[0017] In a third aspect, the application provides an application of the Ce-modified low-loading Pt Pt / gamma-Al2O3 catalyst according to any one of the embodiments of the second aspect, which is used as a fixed-bed catalyst for a reaction of catalytic hydrogenation of p-nitroanisole to prepare p-aminoanisole.

[0018] Optionally, after 18 hours of continuous reaction, the conversion rate of p-nitroanisole on the Ce-modified low-loading Pt Pt / gamma-Al2O3 catalyst is ≥ 85%, and the yield of p-aminoanisole is ≥ 85%.

[0019] The above technical solution provided by the embodiments of the application has the following advantages compared with the prior art:

[0020] The embodiments of the application provide a preparation method of a Ce-modified low-loading Pt Pt / gamma-Al2O3 catalyst. The introduction of a certain amount of Ce can promote the dispersion of Pt particles and strengthen the interaction between the carrier and the metal Pt, thereby improving the reduction temperature of the catalyst. At the same time, with the increase of the amount of introduced Ce, the oxygen vacancy concentration on the surface of the catalyst can be increased, and the strong interaction between the metal and the carrier can be enhanced, which is beneficial to promoting the dispersion of the surface Pt particles, thereby improving the adsorption amount of CO and the catalytic performance of the catalyst. Therefore, the catalytic performance of the fixed-bed catalyst for the reaction of catalytic hydrogenation of p-nitroanisole to prepare p-aminoanisole is improved. BRIEF DESCRIPTION OF DRAWINGS

[0021] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the application and, together with the specification, serve to explain the principles of the application.

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the accompanying drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0023] Figure 1 A flowchart of a preparation method of a Ce-modified low-loading Pt Pt / gamma-Al2O3 catalyst provided by the embodiments of the application is shown in the figure.

[0024] Figure 2 XRD patterns of Pt / gamma-Al2O3 catalysts modified by different mass fractions of Ce provided by the application are shown in the figures.

[0025] Figure 3 Isothermal adsorption-desorption curves of Pt / gamma-Al2O3 catalysts modified by different mass fractions of Ce provided by the application are shown in the figures.

[0026] Figure 4 H2-TPR profiles of Pt / γ-Al2O3 modified with different mass fractions of Ce provided for the present application;

[0027] Figure 5 X-ray photoelectron spectrograms of Ce 3d(a) and O 1s(b) of Pt / γ-Al2O3 modified with different mass fractions of Ce provided for the present application;

[0028] Figure 6 Conversion rates of p-nitroanisole (a) and yield rates of p-aminophenyl ether (b) on the Pt / γ-Al2O3 catalyst modified with different mass fractions of Ce provided for the present application. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0030] Unless otherwise specified, various raw materials, reagents, instruments and equipment and the like used in the present application can be purchased from the market or can be prepared by existing methods.

[0031] Embodiment 1

[0032] Figure 1 A flowchart of a preparation method of a Ce-modified low-loading Pt Pt / γ-Al2O3 catalyst provided for the embodiments of the present application.

[0033] As shown in Figure 1 The present embodiment provides a preparation method of a Ce-modified low-loading Pt Pt / γ-Al2O3 catalyst, which comprises the following steps:

[0034] Step 1, weigh a certain amount of Al(OH)3 powder (chemically pure, purchased from the National Pharmaceutical Group Chemical Reagent Co., Ltd.) and add deionized water to stir thoroughly until mixed uniformly, then place in a 110℃ oven to dry for a certain period of time, take out and extrude into a strip, then place in the oven again for 3h, take out and place in a muffle furnace at 800℃ for 3h, take out and grind and sieve to obtain a γ-Al2O3 carrier with a particle size of 250-425μm;

[0035] Step 2, a certain amount of γ-Al2O3 carrier was impregnated in a measured cerium nitrate (analytical pure, Shanghai Maikelin Biotechnology Co., Ltd.) aqueous solution with the same volume, and then placed in a 110°C oven after standing at room temperature for 18h. After drying completely, it was placed in a muffle furnace at 800°C for 3h. Then it was impregnated in a measured chloroplatinic acid (analytical pure, National Pharmaceutical Group Chemical Reagent Co., Ltd.) aqueous solution with the same volume, and then placed in a muffle furnace at 450°C for 3h after drying as above. Thus, a Ce-modified Pt / γ-Al2O3 catalyst was obtained. The mass fraction of Pt element in the catalyst was 0.02%, and the mass fraction of Ce element was 1%. The Ce-modified Pt / γ-Al2O3 catalyst of Example 1 was named as Pt / 1Ce / γ-Al2O3 catalyst.

[0036] Example 2

[0037] Based on the disclosure of Example 1, the following modifications were made in this example:

[0038] The mass fraction of Pt element in the Ce-modified Pt / γ-Al2O3 catalyst was 0.02%, and the mass fraction of Ce element was 3%.

[0039] The Ce-modified Pt / γ-Al2O3 catalyst of Example 2 was named as Pt / 3Ce / γ-Al2O3 catalyst.

[0040] Example 3

[0041] Based on the disclosure of Example 1, the following modifications were made in this example:

[0042] The mass fraction of Pt element in the Ce-modified Pt / γ-Al2O3 catalyst was 0.02%, and the mass fraction of Ce element was 6%.

[0043] The Ce-modified Pt / γ-Al2O3 catalyst of Example 3 was named as Pt / 6Ce / γ-Al2O3 catalyst.

[0044] Example 4

[0045] Based on the disclosure of Example 1, the following modifications were made in this example:

[0046] The mass fraction of Pt element in the Ce-modified Pt / γ-Al2O3 catalyst was 0.02%, and the mass fraction of Ce element was 12%.

[0047] The Ce-modified Pt / γ-Al2O3 catalyst of Example 4 was named as Pt / 12Ce / γ-Al2O3 catalyst.

[0048] Comparative Example 1

[0049] This comparative example provides a Pt / γ-Al2O3 catalyst prepared in step 1 of Example 1.

[0050] The catalysts obtained in Examples 1 to 4 and Comparative Example 1 were characterized. The specific characterization method is as follows:

[0051] X-ray diffraction analysis (XRD) of the catalyst samples was performed on a Smart Lab X-ray diffractometer (Rigaku, Japan). The calcined catalyst samples were first reduced on an adsorption instrument at a temperature of 300°C and a high-purity H2 flow of 30 mL / min for 2 h. The samples were then ground into powder and placed on an X-ray diffractometer with a scanning angle of 10-80° and a flow rate of 20° min. -1 The instrument used a Cu target Kα line source, a tube current of 100 mA, and a tube voltage of 40 kV.

[0052] The specific surface area, pore volume, and pore size (BET) of the catalyst samples were measured using a Belsorp-II adsorption instrument (BEL, Japan). The calcined catalyst samples were first reduced on the adsorption instrument at 300°C under a 30 mL / min high-purity H₂ flow for 2 hours. Approximately 0.2 g of the sample was then vacuum pretreated at 300°C for 6 hours. Following this treatment, N₂ adsorption-desorption measurements were performed in liquid nitrogen at -196°C. The specific surface area was calculated using the BET equation, while the pore size and volume were calculated using the BJH equation.

[0053] The CO pulse adsorption analysis of the catalyst samples was performed on a TP-5000-II multi-purpose adsorption instrument (Tianjin Xianquan Company). The main steps were as follows: first, 0.5 g of sample was placed in the middle of the quartz tube of the instrument, then the temperature was raised to 300 °C and maintained for 2.5 h, during which time 30 mL min was used. -1 The high-purity H2 gas flow was continuously purged for 2 h, and after the purge was completed, the 30 mL·min -1 The He gas flow was purged again for 0.5 h, then cooled to 30 ° C and maintained, and finally 10 pulse injections of 100 μL of CO-He mixed gas (CO (10%)-He (90%)) were performed. The change in the tail gas flow after dehydration was detected by a thermal conductivity detector (TCD) and the pulse adsorption diagram was recorded.

[18] The CO adsorption capacity per unit mass of catalyst was calculated based on the peak area.

[0054] H2 temperature programmed reduction (H2-TPR) analysis of catalyst samples was performed on a TP-5000-II multi-purpose adsorption instrument (Tianjin Xianquan Company). The main steps were as follows: first, 0.2 g of the sample was placed in the middle of the quartz tube of the instrument, then the temperature was raised to 200 ℃ and maintained for 1 h, during which 30 mL·min -1 of high-purity N2gas flow was continuously purged, after the purge was completed, it was cooled to 30 ℃ and maintained, finally, 30 mL·min -1 of H2-N2mixed gas (H2(10%)-N2(90%)) was switched, the temperature was raised to 600 ℃ at a rate of 10 ℃·min -1 , the change in tail gas flow after dehydration was detected by a thermal conductivity detector (TCD) and the reduction curve was recorded, and the calibration was performed by injecting a known amount of H2.

[0055] X-ray photoelectron spectroscopy (XPS) analysis of catalyst samples was performed on a Kratoms axis supratm instrument (Japan Shimadzu Corporation). First, the reduced catalyst sample after calcination was subjected to reduction treatment on the adsorption instrument, and the reduction temperature was 300 ℃, 30 mL / min of high-purity H2gas flow was used for reduction for 2 h, and then X-ray photoelectron spectroscopy was determined. The incident radiation was monochromatic AlKα(1486.6 eV, 15 kV), and the charge correction standard was C1s(284.8 eV).

[0056] The characterization results of the catalysts obtained in Examples 1-4 and Comparative Example 1 are as follows:

[0057] Figure 2 XRD patterns of the Pt / γ-Al2O3 catalysts modified with different mass fractions of Ce provided in the present application;

[0058] In order to explore the influence of the introduction of different mass fractions of Ce on the phase structure of the Pt / γ-Al2O3 catalyst, XRD analysis was performed on the catalyst samples, and the results are shown in Figure 2 Figure 2 ​It can be seen that the catalysts of Pt / γ-Al2O3 and Pt / 1Ce / γ-Al2O3 both have the same characteristic diffraction peaks of γ-Al2O3 (PDF #10-0425) at 2θ = 37.6°, 39.4°, 45.8°, 67.0°, and the catalyst of Pt / 1Ce / γ-Al2O3 has no characteristic diffraction peaks of Ce, indicating that Ce is well dispersed on the surface of the carrier and has no effect on the crystal phase structure of γ-Al2O3; the catalysts of Pt / 3Ce / γ-Al2O3, Pt / 6Ce / γ-Al2O3 and Pt / 12Ce / γ-Al2O3 all have the characteristic diffraction peaks of γ-Al2O3 at 2θ = 37.6°, 39.4°, 45.8°, 67.0°, and the characteristic diffraction peaks of CeO2 (PDF #34-0394) at 2θ = 28.5°, 33.0°, 56.3°, and the intensity of the characteristic diffraction peaks of γ-Al2O3 of the catalyst samples gradually decreases at 2θ = 45.8°, 67.0°, and the intensity of the characteristic diffraction peaks of CeO2 of the catalyst samples gradually increases at 2θ = 28.5°, 33.0°, 47.4°, 56.3°, 76.6°, 79.0°. The results show that the introduction of Ce has no obvious effect on the crystal phase of the γ-Al2O3 carrier, but with the increase of the introduced Ce, the agglomeration of CeO2 fluorite structure gradually forms on the surface of the γ-Al2O3 carrier and exceeds the monolayer coverage of γ-Al2O3 on the surface of the carrier, resulting in the phenomenon of the decrease of the intensity of part of the characteristic diffraction peaks of γ-Al2O3 and the increase of the intensity of the characteristic diffraction peaks of CeO2.

[0059] The specific surface area, pore volume and average pore diameter of the Pt / γ-Al2O3 catalysts modified by different mass fractions of Ce are shown in Table 1.

[0060] Table 1 Textural properties of Pt / γ-Al2O3 catalysts modified by different mass fractions of Ce

[0061]

[0062] It can be seen from Table 1 that with the increase of the mass fraction of Ce, the specific surface area of the catalyst samples decreases from 197 to 154 m 2 ·g -1 , the pore volume decreases from 0.58 to 0.48 cm 3 ·g -1, the average pore size remained unchanged, all 13.91 nm. The results show that the introduction of Ce has a greater impact on the specific surface area, combined with XRD can be inferred that with the increase of the amount of Ce introduced, the CeO2 fluorite structure gradually increased on the surface of the γ-Al2O3 carrier, resulting in the shrinkage of the carrier surface, leading to a decrease in specific surface area, and a small amount of CeO2 into the carrier inside the pore volume decreased; while the average pore size remained unchanged, indicating that the introduction of Ce did not block the pores. In general, it is believed that the catalyst with a higher specific surface area shows better catalytic performance. Although the specific surface area of the Pt / γ-Al2O3 catalyst is the highest among all samples, the Pt / 6Ce / γ-Al2O3 catalyst with a lower specific surface area shows the best catalytic performance. This result shows that the specific surface area is not the key factor in determining the catalytic performance.

[0063] Figure 3 The isothermal adsorption-desorption curves of the different mass fraction Ce modified Pt / γ-Al2O3 catalysts provided in the present application are shown.

[0064] Figure 3 The nitrogen adsorption-desorption isotherms of all catalysts are shown. It can be seen from Figure 3 that all catalysts are Langmuir Ⅳ type adsorption-desorption isotherms, and the adsorption hysteresis loop is H1 type hysteresis loop, indicating that all catalysts are two-end-opened tubular pore size distribution uniform mesoporous materials, and the introduction of Ce does not affect the mesoporous structure of the catalyst.

[0065] The dispersion of noble metal Pt on the carrier is a key factor affecting the activity of the supported Pt-based catalyst, and the agglomeration of Pt particles on the carrier surface will lead to a decrease in catalyst activity and cause catalyst deactivation. Therefore, by CO pulse adsorption of different mass fraction Ce modified Pt / γ-Al2O3 catalysts, the CO adsorption amount of Pt on the catalyst was calculated, and the irreversible chemical adsorption amount of CO on the Pt-based catalyst was used to study the dispersion difference of Pt particles on the carrier surface, and the results are shown in Table 2. As shown in Table 2, the CO adsorption amount of the unreduced Pt / γ-Al2O3 and Pt / nCe / γ-Al2O3 catalysts is 0, and the reduced catalysts all have CO adsorption, indicating that only the zero-valent Pt particles on the surface of the catalyst can perform CO adsorption. Compared with the Pt / γ-Al2O3 catalyst, the CO adsorption amount of the Pt / nCe / γ-Al2O3 catalyst is increased, and the content of Ce from 0% to 6% shows a gradually increasing trend: from 2.0 μmol·g -1 to 4.2 μmol·g -1 , which may be due to the increase of the oxygen vacancy concentration on the carrier surface caused by the introduction of Ce, which promotes the dispersion of Pt particles and enhances the strong interaction between the metal and the carrier. While the introduction of 12Ce leads to a decrease in CO adsorption amount to 2.8 μmol·g-1 This may be due to excessive Ce introduction leading to catalyst surface active sites being covered, resulting in uneven Pt particle dispersion, causing partial Pt particle agglomeration, and greatly reducing CO adsorption. In summary, the introduction of Ce can promote the dispersion of Pt on the surface of the carrier, but excessive amounts of Ce introduction are not conducive to the dispersion of Pt.

[0066] Table 2 CO adsorption amount of Pt on the surface of Pt / γ-Al2O3 catalyst modified with different mass fractions of Ce

[0067] Catalyst Reduction conditions CO adsorption amount (pmol-g -1 )]]> Pt / gamma-Al203 Not reduced 0.0 Pt / nCe / γ-Al2O3 Not reduced 0.0 Pt / gamma-Al203 H2flow at 300°C for 2h 2.0 Pt / 1Ce / γ-Al2O3 H2flow at 300°C for 2h 2.9 Pt / 3Ce / γ-Al2O3 H2flow at 300°C for 2h 3.6 Pt / 6Ce / γ-Al2O3 H2flow at 300°C for 2h 4.2 Pt / 12Ce / γ-Al2O3 H2flow at 300°C for 2h 2.8

[0068] Figure 4 H2-TPR patterns of Pt / γ-Al2O3 modified with different mass fractions of Ce provided in the present application.

[0069] In order to investigate the effect of Ce introduction on the reduction performance of Pt / γ-Al2O3 catalyst, H2-TPR detection was performed on catalyst samples modified with different mass fractions of Ce, and the results are shown in Figure 4 From Figure 4 , it can be seen that in the temperature range of 100-600℃, the catalyst sample all has a clear reduction peak, which is the reduction peak of PtO x (x represents the number of oxygen elements). The reduction peak top temperature of the Pt / γ-Al2O3 catalyst is 269℃, and when the Ce mass fraction is increased to 6%, the reduction peak top temperature of the catalyst gradually increases to 395℃; and when the amount of Ce introduced is 12%, the reduction temperature of the catalyst slightly decreases to 385℃.

[0070] Table 3 H2 consumption of Pt / γ-Al2O3 catalyst modified with different mass fractions of Ce for reduction

[0071] Sample H2 consumption (pmol g -1 ​ Pt / gamma-Al203 30.3 Pt / 1Ce / γ-Al2O3 64.9 Pt / 3Ce / γ-Al2O3 91.1 Pt / 6Ce / γ-Al2O3 93.6 Pt / 12Ce / γ-Al2O3 126.5

[0072] From Table 3, it can be seen that the H2 consumption of the Pt / γ-Al2O3 catalyst is only 30.3 μmol·g -1 , and as the Ce mass fraction increases, the H2 consumption of the catalyst gradually increases: from 30.3 μmol·g -1 to a maximum of 126.5 μmol·g -1 . In summary, with the introduction of a certain amount of Ce, the interaction between the metal and the carrier in the catalyst is enhanced, promoting the dispersion and stability of Pt on the surface, resulting in a significant increase in the strength of the Pt-O bond, and the reduction of PtO xThe reduction activation energy of Ce increased, so the reduction peak temperature of the catalyst gradually increased, and the H2consumption gradually increased, but this may also be affected by the hydrogen overflow leading to the reduction of a small part of CeO2on the surface; but too much Ce introduction will lead to a decrease in the active center on the surface of the carrier, causing uneven dispersion of Pt particles and causing agglomeration, thereby slightly reducing the reduction temperature of the catalyst.

[0073] Figure 5 X-ray photoelectron spectroscopy of Ce 3d(a) and O 1s(b) of different mass fraction Ce modified Pt / γ-Al2O3 provided in the present application.

[0074] The surface electronic state and atomic concentration of Ce and O in the reduced different mass fraction Ce modified Pt / γ-Al2O3 catalyst were studied by XPS analysis. Figure 5 The Ce 3d(a) and O 1s(b) spectra of Pt / nCe / γ-Al2O3 catalyst are depicted. Figure 5 (a) shows that the two main regions of Ce 3d spectrum, 880-897 and 898-917 eV, are consistent with Ce 3d 5 / 2 (v) and Ce 3d 3 / 2 (u) respectively. The 3d peaks of Ce are decomposed into 10 peaks, and the v1, v3, u2 and u4 peaks are attributed to Ce 3+ , Ce 4+ including v2, v4, u1, u3, u5 and u6 peaks. The O 1s spectrum of the reduced catalyst is shown in Figure 5 (b), all catalysts show three clear peaks in the O 1s spectrum, respectively at 530, 530.9 and 531.8 eV. The first peak at 530 eV is attributed to lattice oxygen (O L =O 2- ); the second peak at 530.9±0.1 eV is attributed to surface oxygen defects or weakly adsorbed oxygen ions (O D =O2 2- or O - ); the third peak at 531.8±0.17 eV is attributed to oxygen species produced by surface hydroxyl (O H ). The valence state and relative content of Ce and O on the reduced Pt / nCe / γ-Al2O3 catalyst are summarized in Table 4, and the relative content is calculated by peak fitting and using the area under the fitting component.

[0075] Table 4 Valence state and relative content of surface atoms of Pt / γ-Al2O3 catalyst modified with different mass fraction Ce

[0076]

[0077] As shown in Table 4, as the mass fraction of Ce increases from 1% to 12%, the Ce content in the catalyst increases. 3+ The relative content of CeO2 increases linearly from 15.6% to 33.5%, reaching the maximum value of the sample. In addition, the migration of oxygen in ceria is mainly carried out through vacancy hopping, so CeO2 is also commonly used. 3+ and (Ce 3+ +Ce 4+ ) ratio to evaluate the formation of oxygen vacancies, so Ce 3+ and (Ce 3+ +Ce 4+ ) has a certain linear relationship with the oxygen vacancy concentration on the catalyst surface, and this relationship is also consistent with the O D / (O L +O D +O H ) ratio with Ce 3+ and (Ce 3+ +Ce 4+ ) ratio increases. This trend is also consistent with the catalytic performance of the catalyst. With the increase of Ce mass fraction, the oxygen vacancy concentration increases linearly, and the initial conversion rate of p-nitroanisole and the initial yield of p-aminoanisole gradually increase to 100% and 99%, respectively. However, the introduction of too much Ce is detrimental to the stability of the catalyst, indicating that the introduction of Ce is closely related to the catalytic performance.

[0078] Example 5

[0079] This example provides the use of a Ce-modified, low-Pt-loaded Pt / γ-Al2O3 catalyst as a fixed-bed catalyst for the catalytic hydrogenation of p-nitroanisole to produce p-aminoanisole. The specific application process is as follows:

[0080] The catalytic hydrogenation of p-nitroanisole to prepare p-aminoanisole was carried out in a continuous flow fixed-bed reactor (500 mm × 10 mm). The catalyst loading was 0.2 g (particle size 250-425 μm). Quartz sand was mixed to reduce the reaction heat and to disperse the catalyst evenly in the middle of the tube. Pure quartz sand was filled in the upper and lower sections. Before the reaction, a high-purity H2 flow (50 mL min-1) at 300°C and 0.5 MPa was used. -1 ) for 4 h, then cooled to 55 °C and pressurized to 1 MPa of high-purity H2 flow (50 mL min -1 ), a 10% mass fraction of p-nitroanisole (chemically pure, Sinopharm Chemical Reagent Co., Ltd.)-ethanol (chemically pure, Sinopharm Chemical Reagent Co., Ltd.) mixed solution was pumped into the tube by a double-plunger micropump. The mass space velocity of p-nitroanisole was 1.25 h -1The p-nitroanisole solution was mixed with a high-purity H₂ gas stream at the top of the reaction tube and then entered the catalyst bed. The reaction temperature was maintained at approximately 60°C by a temperature controller. The products were separated by a gas-liquid separator, and the liquid phase was quantitatively analyzed using the peak area normalization method on a GC-3900 gas chromatograph (Tengzhou Ruineng Analytical Instrument Co., Ltd.).

[0081] Figure 6 The conversion rate (a) of p-nitroanisole and the yield (b) of p-aminoanisole on Pt / γ-Al2O3 catalysts modified with different mass fractions of Ce provided in this application.

[0082] Depend on Figure 6 (a) and (b) show that after 18 hours of continuous reaction, the conversion rate of p-nitroanisole on the Pt / γ-Al2O3 catalyst is 71%, and the yield of p-aminoanisole is 67%; the conversion rate of p-nitroanisole on the Pt / 1Ce / γ-Al2O3 catalyst is 89%, and the yield of p-aminoanisole is 88%; the conversion rates of p-nitroanisole on the Pt / 3Ce / γ-Al2O3, Pt / 6Ce / γ-Al2O3 and Pt / 12Ce / γ-Al2O3 catalysts are all 100%, and the yields of p-aminoanisole are all 99%. After 54 hours of continuous reaction, the conversion rate of p-nitroanisole on the Pt / γ-Al2O3 catalyst was 58% and the yield was 56%; the conversion rate of p-nitroanisole on the Pt / 1Ce / γ-Al2O3 catalyst was 66% and the yield of p-aminoanisole was 65%; the conversion rate of p-nitroanisole on the Pt / 3Ce / γ-Al2O3 catalyst was 75% and the yield of p-aminoanisole was 74%; the conversion rate of p-nitroanisole on the Pt / 6Ce / γ-Al2O3 catalyst was 100% and the yield of p-aminoanisole was 99%; the conversion rate of p-nitroanisole on the Pt / 12Ce / γ-Al2O3 catalyst was 89% and the yield of p-aminoanisole was 87%. Experimental results show that compared to the Pt / γ-Al2O3 catalyst, the Ce-introduced Pt / γ-Al2O3 catalyst significantly improved both conversion and yield, indicating that the introduction of Ce enhances the catalytic performance and stability of the Pt / γ-Al2O3 catalyst. When the Ce mass fraction was 12%, the catalytic performance and stability of the catalyst showed a slight downward trend after 54 hours of reaction, indicating that excessive Ce incorporation is detrimental to the catalyst's catalytic performance and stability. When the Ce mass fraction was 6%, the catalyst exhibited the most excellent catalytic performance and stability, maintaining its activity over the 54 hours of continuous reaction, with the p-nitroanisole conversion remaining at 100% and the p-aminoanisole yield remaining stable at over 99%. However, the stability of this catalyst in the long-term continuous hydrogenation of p-nitroanisole to p-aminoanisole remains to be explored, as this was not possible due to limited experimental conditions and time.

[0083] In addition, one or more technical solutions in the embodiments of the present application have at least the following technical effects or advantages:

[0084] In the embodiments of the present application, as the amount of Ce introduced increases, CeO2 agglomeration is formed on the surface of the catalyst, affecting the crystal phase structure of the catalyst, reducing the specific surface area of the catalyst, and a small amount of CeO2 enters the interior of the catalyst, causing the pore volume to decrease slightly.

[0085] In the embodiments of the present application, a certain amount of Ce introduced can promote the dispersion of Pt particles and strengthen the interaction between the carrier and the metal Pt, thereby increasing the reduction temperature of the catalyst; however, excessive introduction can easily cover the active centers on the surface of the γ-Al2O3 carrier, causing uneven dispersion of part of the Pt particles and agglomeration, thereby slightly reducing the reduction temperature of the catalyst.

[0086] In the embodiments of the present application, as the amount of Ce introduced increases, the oxygen vacancy concentration on the surface of the catalyst can be increased, the strong interaction between the metal and the carrier is enhanced, which is beneficial to promoting the dispersion of the surface Pt particles, thereby increasing the adsorption amount of CO and the catalytic performance of the catalyst, but is not a decisive factor for the catalytic performance of the catalyst.

[0087] In the embodiments of the present application, compared with the Pt / γ-Al2O3 catalyst, the introduction of Ce can greatly improve the catalytic performance and stability of the catalyst. When the mass fraction of Ce is 6%, the catalyst exhibits the optimal conversion rate of p-nitroanisole and the yield of p-aminoanisole, and no obvious decrease is observed after 54 h of continuous reaction.

[0088] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is merely for the convenience and brevity, and should not be understood as a hard limitation on the scope of the present application; therefore, it should be considered that the described range has specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the described range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated in the present application, it refers to any cited number (fraction or integer) within the indicated range.

[0089] In addition, in the description of the present application, the terms "include", "contain" and the like mean "include but are not limited to". In the present text, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations.

[0090] The foregoing detailed description of the application has been presented for purposes of illustration and description. Various modifications and changes can be made to these embodiments without departing from the spirit and scope of the application. It is intended that the scope of the application should not be limited by the particular representative embodiments described above. Rather, the general scope of the application is to be determined by the appended claims and their equivalents.

Claims

1. Use of a Ce-modified low load Pt Pt / gamma-Al203 catalyst, characterized in that, The Ce-modified low-loading Pt Pt / gamma-Al2O3 catalyst is used as a fixed bed catalyst for a reaction of preparing p-aminoanisole by catalytic hydrogenation of p-nitroanisole; The preparation method of the Ce-modified low-loading Pt Pt / gamma-Al2O3 catalyst comprises the following steps: S1, adding deionized water to Al(OH)3 powder, and then drying and extruding into a strip to obtain a strip-shaped Al(OH)3; S2, performing first calcination on the strip-shaped Al(OH)3 to obtain a gamma-Al2O3 carrier with a set particle size; the temperature of the first calcination is 800 DEG C; S3, immersing the gamma-Al2O3 carrier in a cerium nitrate aqueous solution, and then drying and performing second calcination to obtain a Ce-modified gamma-Al2O3 catalyst; S4, immersing the Ce-modified gamma-Al2O3 catalyst in a chloroplatinic acid aqueous solution, and then drying and performing third calcination to obtain a Ce-modified Pt / gamma-Al2O3 catalyst; the mass fraction of Ce in the Ce-modified gamma-Al2O3 catalyst is 6%.

2. Use of a Ce-modified low load Pt Pt / gamma-Al203 catalyst according to claim 1, characterized in that, The set particle size is 250-425 mu m.

3. Use of the Ce-modified low-loaded Pt Pt / gamma-Al203 catalyst according to claim 1, characterized in that, The time of the first calcination is 3 h.

4. Use of the Ce-modified low-loaded Pt Pt / gamma-Al203 catalyst according to claim 1, characterized in that, The temperature of the second calcination is 800 DEG C, and the time of the second calcination is 3 h.

5. Use of the Ce-modified low-loaded Pt Pt / gamma-Al203 catalyst according to claim 1, characterized in that, The temperature of the third calcination is 450 DEG C, and the time of the third calcination is 3 h.

6. Use of the Ce-modified low load Pt Pt / gamma-Al203 catalyst according to claim 1, characterized in that, The mass fraction of Pt in the Ce-modified gamma-Al2O3 catalyst is 0.02%.

7. Use of the Ce-modified low-loaded Pt Pt / gamma-Al203 catalyst according to claim 1, characterized in that, After 18 h of continuous reaction, the conversion rate of p-nitroanisole on the Ce-modified Pt / gamma-Al2O3 catalyst is greater than or equal to 85%, and the yield of p-aminoanisole is greater than or equal to 85%.

Images