CN115999538B - Preparation method and application of acid-resistant metal catalyst - Google Patents

Abstract

The invention discloses a preparation method and application of an acid-resistant metal catalyst. The preparation method of the acid-resistant metal catalyst comprises the following steps: step 1, pretreatment of active carbon; step 2, preparing impregnating solution; step 3, preparing an immobilized catalyst; step 4, organic matter coating; step 5, carbonizing the catalyst precursor; and 6, functionalizing the catalyst. The invention provides an application of an acid-resistant metal catalyst prepared in synthesizing p-aminophenol from nitrobenzene. The catalyst has better acid resistance and stability, can have higher activity and higher selectivity of the para-aminophenol under relatively mild reaction conditions when being applied to the process for preparing the para-aminophenol by one-step hydrogenation rearrangement of nitrobenzene, and simultaneously removes the use of surfactants or other additives, improves the production conditions, reduces the production cost and improves the product quality.

Description

Preparation method and application of acid-resistant metal catalyst

Technical Field

The invention relates to a preparation method of an acid-resistant metal catalyst and application of the catalyst in preparing p-aminophenol by hydrogenating nitrobenzene.

Background Art

Para-aminophenol (PAP) is an extremely important fine organic chemical intermediate. It can be used in the pharmaceutical industry to synthesize paracetamol, clofibrate, etc., and in the dye industry to synthesize sulfur dyes, azo dyes, fur dyes, acid dyes, disperse dyes, etc. In addition to the above applications, para-aminophenol can also be directly used as an antioxidant and an additive for petroleum products.

At present, people have developed a variety of PAP preparation methods, such as: p-nitrophenol method, phenol method, p-nitrochlorobenzene method and nitrobenzene method, etc. Among them, the nitrobenzene method has strong competitiveness among various synthesis methods due to its many advantages such as low price of raw material nitrobenzene, low production cost, few production processes, simple process, etc. This method uses nitrobenzene as a raw material, generates an intermediate product phenylhydroxylamine (PHA) under the action of a hydrogenation catalyst, and then phenylhydroxylamine is catalyzed by protonic acids such as sulfuric acid and phosphoric acid to generate PAP through Bamberger rearrangement. However, due to the use of strong acids, the active components of the catalyst are easily lost, resulting in catalyst deactivation. In addition, metal ion residues are a problem that affects the quality of medicines. At the same time, in order to improve the selectivity of p-aminophenol, most patents choose to use surfactants or sulfides as additives, but this increases the difficulty of subsequent treatment and purification of p-aminophenol.

In view of the above problems, Komatsu et al. proposed that the synthesis of PAP can be achieved by replacing protonic acid with solid acid, but since the use of protonic acid is abandoned, the selectivity of the solid acid catalytic synthesis route is low. Chinese patent CN103553943A discloses a series of catalysts such as Pt/C, Pt-Sn/ _Al2O3 , Pd- _CaCO3 -PbO/ _{PbAC2 ,} etc., which react under carbon dioxide and water conditions, and the selectivity of p-aminophenol is about 5%-70%, but the carbon dioxide pressure required for the reaction is large, the reaction temperature is high, and the reaction time is long. Chinese patent CN1283612A discloses a supported Pt/γ-alumina-MEO catalyst, which is added with a surfactant under sulfuric acid conditions to carry out nitrobenzene catalytic reaction, and the selectivity of p-aminophenol can reach 70%, but the catalyst will be severely corroded under acidic conditions, resulting in a high content of metal impurities in the product, and due to the addition of a surfactant, the production cost is increased, making it difficult for the product to meet medical standards.

In view of the serious loss of metal components of the above-mentioned catalyst and the use of additives, the present invention provides a method for preparing an acid-resistant metal catalyst and its application in hydrogenating nitrobenzene to prepare p-aminophenol.

Summary of the invention

The primary purpose of the present invention is to provide a method for preparing an acid-resistant metal catalyst. The catalyst prepared by the method has good activity and long life under extreme conditions such as strong acid, and has the characteristics of high selectivity for p-aminophenol when applied to nitrobenzene hydrogenation to p-aminophenol without the need for additives.

The second object of the present invention is to provide the use of the acid-resistant metal catalyst in the preparation of p-aminophenol by hydrogenation of nitrobenzene.

To achieve the above object, the present invention adopts the following technical solution:

In a first aspect, the present invention provides a method for preparing an acid-resistant metal catalyst, comprising the following steps:

Step 1, activated carbon pretreatment:

Adding activated carbon to a 10-15wt% HCl solution, reflux at 80-90°C for 3-4h, cooling to room temperature, filtering and washing with deionized water until neutral, and drying to obtain pre-treated activated carbon;

Step 2, preparation of the impregnation solution:

Weigh NaNO ₃ and PdCl ₂ in a container, add concentrated hydrochloric acid, dilute with water to prepare a precious metal impregnation solution, wherein the concentrations of NaNO ₃ and PdCl ₂ are 0.05-0.1g/mL and 2-8mg/mL, and the amount of concentrated hydrochloric acid added is 20-30ml/100ml;

Step 3, preparation of immobilized catalyst:

Add the activated carbon treated in step 1 to the precious metal impregnation solution prepared in step 2, mix thoroughly, evaporate to dryness in a sand bath, continue heating to 250-300° C., and stop heating when no more nitrogen oxides are released, thereby obtaining a solid-supported catalyst;

Step 4, organic coating:

The solid-supported catalyst obtained in step 3 is added to solution A, and then 1-2 mol/L ammonium persulfate aqueous solution is added, and the mixture is stirred at 60-80°C for 8-10h, and then isocyanate is added. After the mixed solution gradually becomes gel-like, it is aged at 25-30°C for 24-30h, and then washed with ethanol and water, and dried at 60-70°C under vacuum for 10-12h to obtain a catalyst precursor; the solution A is an aqueous solution containing nitrobenzene and liquid acid, wherein the volume ratio of nitrobenzene, liquid acid and solution A is 4-10:15-20:50-120, and the feed ratio of the solid-supported catalyst to solution A and ammonium persulfate aqueous solution is calculated as 1g:80-200ml:25-60ml:0.02-0.07mol based on the feed ratio of the activated carbon treated in step 1 to solution A, ammonium persulfate aqueous solution and isocyanate contained therein;

Step 5, catalyst precursor carbonization:

The catalyst precursor obtained in step 4 is placed in a tube furnace, and the temperature is raised to 600-800° C. at a rate of 1-10° C./min under an inert atmosphere, and maintained for 3-6 hours to obtain a carbonized product;

Step 6, catalyst functionalization:

The carbonized product obtained in step 5 is added to a 10-12 wt% HNO ₃ aqueous solution and refluxed at 70-80° C. for 3-4 hours to obtain a final acid-resistant metal catalyst.

Preferably, the activated carbon in step 1 can be wood carbon or coconut shell carbon. The above activated carbons are all powdered microporous activated carbons, and the activated carbon parameters are: specific surface area of 1000-1500m ² /g, pore volume of 0.5-1.0cm ³ /g, and average pore size of 2-2.5nm.

Preferably, in step 1, the feed ratio of the activated carbon to the HCl solution is 1-2 g: 20-50 ml.

Preferably, in step 3, the feed ratio of the activated carbon treated in step 1 to the precious metal impregnation solution prepared in step 2 is 1 g: 15-20 ml.

Preferably, in step 4, the liquid acid may be one or both of formic acid and acetic acid.

Preferably, the isocyanate in step 4 is one of triphenylmethane triisocyanate, toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate.

Preferably, the inert atmosphere in step 5 may be one of nitrogen, argon and helium.

Preferably, in step 6, the feed ratio of the carbonized product to the nitric acid solution is 1 g: 25-30 ml, calculated based on the feed ratio of the activated carbon treated in step 1 to the nitric acid aqueous solution.

In a second aspect, the present invention provides the use of the prepared acid-resistant metal catalyst in the synthesis of p-aminophenol from nitrobenzene.

The application specifically includes the following operations:

Weigh nitrobenzene into a Hastelloy reaction kettle, add the acid-resistant metal catalyst and H ₂ SO ₄ solution prepared above, and inject 0.3-0.8MPa of H ₂ , react at 85-100°C and 800-1200r for 5-8h to generate p-aminophenol.

Preferably, the feed ratio of nitrobenzene, catalyst and H ₂ SO ₄ solution is 0.5-1 g: 0.01-0.03 g: 25-50 ml.

Preferably, the concentration of H ₂ SO ₄ solution is 10-15 wt %.

Compared with the prior art, the beneficial effects of the present invention are as follows: the catalyst of the present invention has good acid resistance and stability, and when applied to the process of preparing p-aminophenol by one-step hydrogenation rearrangement of nitrobenzene, it can have high activity and high selectivity for p-aminophenol under relatively mild reaction conditions, and at the same time eliminates the use of surfactants or other additives, improves production conditions, reduces production costs, and improves product quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a catalyst recycling result of Example 20;

FIG2 is a TEM image of the catalysts prepared in Example 1 and Comparative Example 1, wherein (a) is a TEM image of the catalyst in Example 1; (b) is a TEM image of the catalyst in Comparative Example 1;

Figure 3 is a TEM image of different catalysts, wherein (a) is a TEM image of the catalyst of Example 1; (b) is a TEM image of the catalyst of Comparative Example 2; (c) is a TEM image of the catalyst of Comparative Example 3; (d) is a TEM image of the catalyst of Comparative Example 2;

FIG. 4 is the Raman spectra of the catalysts prepared in Example 1 and Comparative Example 5.

DETAILED DESCRIPTION

The technical solution of the present invention is further described below through specific embodiments, but the protection scope of the present invention is not limited thereto:

The activated carbon used in the embodiment of the present invention is produced by Fujian Xinsen Carbon Industry Co., Ltd. The parameters of the activated carbon are shown in Table 1 below:

Table 1

The sources of the precious metal precursors used in the examples are: palladium chloride produced by Macklin, palladium chloride, Pd content 59-60%, item number P815731-5g.

Example 1

Step 1, weigh 1g coconut shell activated carbon and add it to 20ml 10wt% HCl solution, reflux at 80°C for 3h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 5g _NaNO3 and 0.2g _PdCl2 in a 100ml volumetric flask, add 20ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3, weigh 1 g of the activated carbon treated in step 1, add 20 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 250°C, and stop heating when no more nitrogen oxides are released. The immobilized catalyst is obtained.

Step 4, add the solid-supported catalyst obtained in step 3 to 100 ml of an aqueous solution containing 8 ml of nitrobenzene and 20 ml of formic acid, and then add 50 ml of a 1 mol/L ammonium persulfate aqueous solution. After stirring at 80° C. for 8 hours, add 0.02 mol of triphenylmethane triisocyanate, and after the mixed solution gradually becomes a gel, age at 30° C. for 24 hours, then wash with ethanol and water, and dry at 60° C. under vacuum for 10 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 600° C. at a rate of 1° C./min under an inert atmosphere and maintained at that temperature for 4 hours.

Step 6: Add the catalyst obtained in step 5 into 25 ml of 10 wt% HNO ₃ aqueous solution and reflux at 80° C. for 3 h to obtain the final catalyst.

Example 2

Step 1, weigh 1.2g of wood activated carbon and add it to 25ml of 12wt% HCl solution, reflux at 85°C for 3h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 6g _NaNO3 and 0.4g _PdCl2 in a 100ml volumetric flask, add 30ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3, weigh 0.5 g of the activated carbon treated in step 1, add 7.5 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 300° C., and stop heating when no more nitrogen oxides are released. The immobilized catalyst is obtained.

Step 4, add the solid-supported catalyst obtained in step 3 to 80 ml of an aqueous solution containing 6.4 ml of nitrobenzene and 18 ml of acetic acid, and then add 20 ml of a 1.5 mol/L ammonium persulfate solution. After stirring at 75°C for 10 hours, add 0.025 mol of triphenylmethane triisocyanate, and after the mixed solution gradually becomes a gel, age at 26°C for 24 hours, then wash with ethanol and water, and dry at 65°C under vacuum for 12 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 620° C. at a rate of 2° C./min under an inert atmosphere and maintained for 3 h.

Step 6: Add the catalyst obtained in step 5 into 15 ml of 10 wt% HNO ₃ aqueous solution and reflux at 80° C. for 3 h to obtain the final catalyst.

Example 3

Step 1, weigh 1.5g coconut shell activated carbon and add it to 30ml 11wt% HCl solution, reflux at 90°C for 4h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 8g _NaNO3 and 0.3g _PdCl2 in a 100ml volumetric flask, add 25ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3, weigh 0.8 g of the activated carbon treated in step 1, add 12.8 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 300° C., and stop heating when no more nitrogen oxides are released. The immobilized catalyst is obtained.

Step 4, add the solid-supported catalyst obtained in step 3 to 120 ml of an aqueous solution containing 9.6 ml of nitrobenzene and 17 ml of formic acid, and then add 48 ml of a 1 mol/L ammonium persulfate solution. After stirring at 70°C for 8.5 hours, add 0.025 mol of toluene diisocyanate, and after the mixed solution gradually becomes a gel, age at 27°C for 30 hours, then wash with ethanol and water, and dry at 62°C under vacuum for 12 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 650° C. at a rate of 3° C./min under an inert atmosphere and maintained for 3 h.

Step 6: Add the catalyst obtained in step 5 into 24 ml of 12 wt% HNO ₃ aqueous solution and reflux at 70° C. for 3 h to obtain the final catalyst.

Example 4

Step 1, weigh 2g coconut shell activated carbon and add it to 35ml 12wt% HCl solution, reflux at 85°C for 3h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 7g _NaNO3 and 0.5g _PdCl2 in a 100ml volumetric flask, add 26ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3, weigh 0.9 g of the activated carbon treated in step 1, add 16.2 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 280°C, and stop heating when no more nitrogen oxides are released. The immobilized catalyst is obtained.

Step 4, add the solid-supported catalyst obtained in step 3 to 90 ml of an aqueous solution containing 7.2 ml of nitrobenzene and 15 ml of acetic acid, and then add 45 ml of a 2 mol/L ammonium persulfate solution. After stirring at 60° C. for 9 hours, add 0.03 mol of diphenylmethane diisocyanate, and after the mixed solution gradually becomes a gel, age at 28° C. for 28 hours, then wash with ethanol and water, and dry at 70° C. under vacuum for 10 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 700° C. at a rate of 4° C./min under an inert atmosphere and maintained at that temperature for 4 h.

Step 6: Add the catalyst obtained in step 5 into 26 ml of 11 wt% HNO ₃ aqueous solution and reflux at 85° C. for 4 h to obtain the final catalyst.

Example 5

Step 1, weigh 1.5g of wood activated carbon and add it to 40ml of 13wt% HCl solution, reflux at 88°C for 3.5h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 9g _NaNO3 and 0.6g _PdCl2 in a 100ml volumetric flask, add 27ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3, weigh 0.6 g of the activated carbon treated in step 1, add 10.2 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 290° C., and stop heating when no more nitrogen oxides are released. The immobilized catalyst is obtained.

Step 4, add the solid-supported catalyst obtained in step 3 to 60 ml of an aqueous solution containing 4.8 ml of nitrobenzene, 7 ml of acetic acid, and 8 ml of formic acid, and then add 18 ml of a 1 mol/L ammonium persulfate solution. After stirring at 65°C for 9.5 hours, add 0.028 mol of isophorone diisocyanate, and after the mixed solution gradually becomes a gel, age at 25°C for 30 hours, then wash with ethanol and water, and dry at 65°C under vacuum for 12 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 800° C. at a rate of 5° C./min under an inert atmosphere and maintained at that temperature for 3 h.

Step 6: Add the catalyst obtained in step 5 into 18 ml of 10 wt% HNO ₃ aqueous solution and reflux at 75° C. for 4 h to obtain the final catalyst.

Example 6

Step 1, weigh 1.5g coconut shell activated carbon and add it to 30ml 11wt% HCl solution, reflux at 90°C for 4h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 10g _NaNO3 and 0.8g _PdCl2 in a 100ml volumetric flask, add 30ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3, weigh 0.8 g of the activated carbon treated in step 1, add 15.2 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 300° C., and stop heating when no more nitrogen oxides are released. The immobilized catalyst is obtained.

Step 4, add the solid-supported catalyst obtained in step 3 to 160 ml of an aqueous solution containing 9 ml of nitrobenzene, 9 ml of formic acid and 10 ml of acetic acid, and then add 20 ml of a 1.5 mol/L ammonium persulfate solution. After stirring at 78°C for 10 hours, add 0.027 mol of toluene diisocyanate, and after the mixed solution gradually becomes a gel, age at 30°C for 30 hours, then wash with ethanol and water, and dry at 60°C under vacuum for 12 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 600° C. at a rate of 3° C./min under an inert atmosphere and maintained at this temperature for 3 h.

Step 6: Add the catalyst obtained in step 5 into 20 ml of 12 wt% HNO ₃ aqueous solution and reflux at 70° C. for 3 h to obtain the final catalyst.

Example 7

Step 1, weigh 2g coconut shell activated carbon and add it to 45ml 14wt% HCl solution, reflux at 83°C for 3h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 5g _NaNO3 and 0.5g _PdCl2 in a 100ml volumetric flask, add 28ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3, weigh 0.8 g of the activated carbon treated in step 1, add 16 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 270°C, and stop heating when no more nitrogen oxides are released. The immobilized catalyst is obtained.

Step 4, add the solid-supported catalyst obtained in step 3 to 64 ml of aqueous solution containing 6 ml of nitrobenzene and 16 ml of acetic acid, and then add 36 ml of 2 mol/L ammonium persulfate solution. After stirring at 68°C for 9.8 hours, add 0.028 mol of dicyclohexylmethane diisocyanate, and after the mixed solution gradually becomes gel-like, age at 26°C for 25 hours, then wash with ethanol and water, and dry at 68°C under vacuum for 11 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 750° C. at a rate of 6° C./min under an inert atmosphere and maintained for 5 hours.

Step 6: Add the catalyst obtained in step 5 into 22 ml of 12 wt% HNO ₃ aqueous solution and reflux at 74° C. for 3.5 h to obtain the final catalyst.

Example 8

Step 1, weigh 1.3g of wood activated carbon and add it to 50ml of 15wt% HCl solution, reflux at 86°C for 3.6h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 8g _NaNO3 and 0.4g _PdCl2 in a 100ml volumetric flask, add 20ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3, weigh 0.3 g of the activated carbon treated in step 1, add 4.5 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 260° C., and stop heating when no more nitrogen oxides are released. The immobilized catalyst is obtained.

Step 4, add the solid-supported catalyst obtained in step 3 to 50 ml of an aqueous solution containing 4 ml of nitrobenzene and 15 ml of formic acid, and then add 18 ml of a 1 mol/L ammonium persulfate solution. After stirring at 75°C for 9 hours, add 0.021 mol of hexamethylene diisocyanate, and after the mixed solution gradually becomes a gel, age at 27°C for 28 hours, then wash with ethanol and water, and dry at 66°C under vacuum for 12 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 780° C. at a rate of 7° C./min under an inert atmosphere and maintained for 5.5 h.

Step 6: Add the catalyst obtained in step 5 into 9 ml of 11 wt% HNO ₃ aqueous solution and reflux at 78° C. for 4 h to obtain the final catalyst.

Example 9

Step 1, weigh 1.6g coconut shell activated carbon and add it to 20ml 12wt% HCl solution, reflux at 82°C for 3.8h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 6g _NaNO3 and 0.5g _PdCl2 in a 100ml volumetric flask, add 25ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3, weigh 1.5 g of the activated carbon treated in step 1, add 24 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 250° C., and stop heating when no more nitrogen oxides are released. The immobilized catalyst is obtained.

Step 4, add the solid-supported catalyst obtained in step 3 to 120 ml of an aqueous solution containing 8 ml of nitrobenzene and 19 ml of formic acid, and then add 55 ml of a 1.5 mol/L ammonium persulfate solution. After stirring at 60°C for 10 hours, add 0.03 mol of lysine diisocyanate, wait for the mixed solution to gradually become a gel, age at 28°C for 26 hours, then wash with ethanol and water, and dry at 69°C under vacuum for 11 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 790° C. at a rate of 8° C./min under an inert atmosphere and maintained for 6 hours.

Step 6: Add the catalyst obtained in step 5 into 40 ml of 10 wt% HNO ₃ aqueous solution and reflux at 80° C. for 3 h to obtain the final catalyst.

Example 10

Step 1, weigh 1.8g of wood activated carbon and add it to 25ml of 10wt% HCl solution, reflux at 84°C for 3h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 7g _NaNO3 and 0.3g _PdCl2 in a 100ml volumetric flask, add 26ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3, weigh 1 g of the activated carbon treated in step 1, add 18 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 300°C, and stop heating when no more nitrogen oxides are released. The immobilized catalyst is obtained.

Step 4, add the solid-supported catalyst obtained in step 3 to 90 ml of an aqueous solution containing 5 ml of nitrobenzene and 17 ml of formic acid, and then add 45 ml of a 1 mol/L ammonium persulfate solution. After stirring at 66°C for 9.5 hours, add 0.022 mol of toluene diisocyanate, and after the mixed solution gradually becomes a gel, age at 29°C for 24 hours, then wash with ethanol and water, and dry at 65°C under vacuum for 10 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 650° C. at a rate of 9° C./min under an inert atmosphere and maintained for 6 hours.

Step 6: Add the catalyst obtained in step 5 into 25 ml of 11 wt% HNO ₃ aqueous solution and reflux at 75° C. for 4 h to obtain the final catalyst.

Embodiment 11

Step 1, weigh 1.4g coconut shell activated carbon and add it to 35ml 11wt% HCl solution, reflux at 80°C for 3h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 10g _NaNO3 and 0.5g _PdCl2 in a 100ml volumetric flask, add 30ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3, weigh 0.7 g of the activated carbon treated in step 1, add 14 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 280°C, and stop heating when no more nitrogen oxides are released. The immobilized catalyst is obtained.

Step 4, add the solid-supported catalyst obtained in step 3 to 100 ml of an aqueous solution containing 8 ml of nitrobenzene, 8 ml of formic acid and 8 ml of acetic acid, and then add 35 ml of a 1 mol/L ammonium persulfate solution. After stirring at 75°C for 9 hours, add 0.024 mol of diphenylmethane diisocyanate, and after the mixed solution gradually becomes a gel, age at 30°C for 26 hours, then wash with ethanol and water, and vacuum dry at 70°C for 12 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 660° C. at a rate of 10° C./min under an inert atmosphere and maintained for 4.5 hours.

Step 6: Add the catalyst obtained in step 5 into 21 ml of 12 wt% HNO ₃ aqueous solution and reflux at 72° C. for 4 h to obtain the final catalyst.

Comparative Example 1

The preparation process of the comparative catalyst is similar to that of Example 1, except that no isocyanate is added in step 4 of the comparative catalyst. The carbon layer formed by the comparative catalyst is more imperfect than that of Example 1 and cannot protect the metal from corrosion in the acidic environment.

Further, the catalyst preparation process of this comparative example is:

Step 1, weigh 1g coconut shell activated carbon and add it to 20ml 10wt% HCl solution, reflux at 80°C for 3h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 5g _NaNO3 and 0.2g _PdCl2 in a 100ml volumetric flask, add 20ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3: Weigh 1 g of the activated carbon treated in step 1, add 20 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 300°C, and stop heating when no more nitrogen oxides are released. The immobilized catalyst is obtained.

Step 4: Add the solid-supported catalyst obtained in step 3 to 100 ml of an aqueous solution containing 8 ml of nitrobenzene and 20 ml of formic acid, and then add 50 ml of a 1 mol/L ammonium persulfate aqueous solution. Stir at 80° C. for 8 hours, filter, rinse with ethanol and deionized water, and vacuum dry at 60° C. for 10 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 600° C. at a rate of 1° C./min under an inert atmosphere and maintained at that temperature for 4 hours.

Step 6: Add the catalyst obtained in step 5 into 25 ml of 10 wt% HNO ₃ aqueous solution and reflux at 80° C. for 3 h to obtain the final catalyst.

Comparative Example 2

The catalyst preparation process of this comparative example is similar to that of Example 1, except that the supported catalyst is prepared by a deposition precipitation method in step 3 of this comparative example.

Further, the catalyst preparation process of this comparative example is:

Step 1, weigh 1g coconut shell activated carbon and add it to 20ml 10wt% HCl solution, reflux at 80°C for 3h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2. Weigh 5g _NaNO3 and 0.2g _PdCl2 into a 100ml volumetric flask, add 20ml concentrated hydrochloric acid, dilute with water to the scale to prepare the precious metal impregnation solution.

Step 3: weigh 1 g of the activated carbon treated in step 1, add 0.01 g of NaCl and 15 ml of deionized water, stir at 50°C for 30 min, then add 20 ml of the solution prepared in step 2, continue stirring at 50°C for 2 h, adjust the pH to 8, filter and wash to obtain the supported catalyst.

Step 4, add the supported catalyst obtained in step 3 to 100 ml of an aqueous solution containing 8 ml of nitrobenzene and 20 ml of formic acid, and then add 50 ml of a 1 mol/L ammonium persulfate aqueous solution. After stirring at 80° C. for 8 hours, add 0.02 mol of triphenylmethane triisocyanate, and after the mixed solution gradually becomes a gel, age at 30° C. for 24 hours, then wash with ethanol and water, and dry at 60° C. under vacuum for 10 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 600° C. at a rate of 1° C./min under an inert atmosphere and maintained at that temperature for 4 hours.

Step 6: Add the catalyst obtained in step 5 into 25 ml of 10 wt% HNO ₃ aqueous solution and reflux at 80° C. for 3 h to obtain the final catalyst.

Comparative Example 3

The preparation process of the catalyst in this comparative example is similar to that in Example 1, except that in step 2 of this comparative example, no NaNO ₃ is added when preparing the noble metal impregnation solution.

Further, the comparative example catalyst preparation process is:

Step 1, weigh 1g coconut shell activated carbon and add it to 20ml 10wt% HCl solution, reflux at 80°C for 3h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 0.2g _PdCl2 into a 100ml volumetric flask, add 20ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3, weigh 1 g of the activated carbon treated in step 1, add 20 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 300°C, and stop heating after maintaining 300°C for 30 minutes. The immobilized catalyst is obtained.

Step 4, add the solid-supported catalyst obtained in step 3 to 100 ml of an aqueous solution containing 8 ml of nitrobenzene and 20 ml of formic acid, and then add 50 ml of a 1 mol/L ammonium persulfate aqueous solution. After stirring at 80° C. for 8 hours, add 0.02 mol of triphenylmethane triisocyanate, and after the mixed solution gradually becomes a gel, age at 30° C. for 24 hours, then wash with ethanol and water, and dry at 60° C. under vacuum for 10 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 600° C. at a rate of 1° C./min under an inert atmosphere and maintained at this temperature for 3 h.

Step 6: Add the catalyst obtained in step 5 into 20 ml of 10 wt% HNO ₃ aqueous solution and reflux at 85° C. for 3 h to obtain the final catalyst.

Comparative Example 4

The preparation process of the catalyst in this comparative example is similar to that in Example 1, except that the activated carbon in this comparative example is not treated with HCl.

Further, the comparative example catalyst preparation process is:

Step 1, weigh 5g _NaNO3 and 0.2g _PdCl2 in a 100ml volumetric flask, add 20ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 2: weigh 1g coconut shell activated carbon and add 20ml of the solution prepared in step 1, evaporate to dryness in a sand bath, continue heating to 300°C, and stop heating when no more nitrogen oxides are released.

Step 3, add the solid-supported catalyst obtained in step 2 to 100 ml of an aqueous solution containing 8 ml of nitrobenzene and 20 ml of formic acid, and then add 50 ml of a 1 mol/L ammonium persulfate aqueous solution. After stirring at 80° C. for 8 hours, add 0.02 mol of triphenylmethane triisocyanate, and after the mixed solution gradually becomes a gel, age at 30° C. for 24 hours, then wash with ethanol and water, and dry at 60° C. under vacuum for 10 hours to obtain a catalyst precursor.

Step 4: The catalyst precursor obtained in step 3 is heated to 600° C. at a rate of 1° C./min under an inert atmosphere and maintained at that temperature for 4 hours.

Step 5: Add the catalyst obtained in step 4 into 25 ml of 10 wt% HNO ₃ aqueous solution and reflux at 80° C. for 3 h to obtain the final catalyst.

Comparative Example 5

The preparation process of the comparative catalyst is similar to that of Example 1, except that the catalyst obtained in step 5 of the comparative example is not further treated with nitric acid. The comparative catalyst has fewer surface defects than that of Example 1, and cannot provide active sites for chemical reactions, resulting in poor reaction activity.

Further, the comparative example catalyst preparation process is:

Step 1, weigh 1g coconut shell activated carbon and add it to 20ml 10wt% HCl solution, reflux at 80°C for 3h. After cooling to room temperature, filter and wash with deionized water until neutral, and dry for standby use.

Step 2, weigh 5g _NaNO3 and 0.2g _PdCl2 in a 100ml volumetric flask, add 20ml concentrated hydrochloric acid, dilute with water to the scale line, and prepare the precious metal impregnation solution.

Step 3, weigh 1 g of the activated carbon treated in step 1, add 20 ml of the solution prepared in step 2, evaporate to dryness in a sand bath, continue heating to 250°C, and stop heating when no more nitrogen oxides are released. The immobilized catalyst is obtained.

Step 4, add the solid-supported catalyst obtained in step 3 to 100 ml of an aqueous solution containing 8 ml of nitrobenzene and 20 ml of formic acid, and then add 50 ml of a 1 mol/L ammonium persulfate aqueous solution. After stirring at 80° C. for 8 hours, add 0.02 mol of triphenylmethane triisocyanate, and after the mixed solution gradually becomes a gel, age at 30° C. for 24 hours, then wash with ethanol and water, and dry at 60° C. under vacuum for 10 hours to obtain a catalyst precursor.

Step 5: The catalyst precursor obtained in step 4 is heated to 600° C. at a rate of 1° C./min under an inert atmosphere and maintained at that temperature for 4 hours to obtain the final catalyst.

Example 12

In order to test the acid resistance of the catalyst, the catalyst was acid-washed with 1.5MH ₂ SO ₄ aqueous solution, and the acid resistance of the catalyst was determined by testing the metal loss rate. The specific operation was as follows: the prepared catalyst was added to 50 ml of 1.5MH ₂ SO ₄ solution and stirred at room temperature for 8 hours, and the upper clear liquid was taken to detect the palladium content by AAS. The results are shown in Table 2.

Example 13

In order to test the activity of the catalyst, the conversion of nitrobenzene and the selectivity of p-aminophenol were compared in the reaction of nitrobenzene hydrogenation to p-aminophenol.

The specific operation is: weigh 0.5g nitrobenzene into a 100ml _Hastelloy reaction kettle, add 0.01g of the above-prepared catalyst, 25ml 10wt% _H2SO4 solution, and charge 0.3MPa _H2 , and react at 85℃ and 1200r for 5h. The specific results are shown in Table 2.

Table 2. Acid resistance and catalytic performance of catalysts

Examples 14-19

The synthesis process of p-aminophenol is similar to that of Example 12. The catalyst used is the catalyst prepared in Example 1. The difference is that the reaction temperature, the amount of catalyst and nitrobenzene, the hydrogen pressure, the acid concentration, the rotation speed, the reaction time and other conditions are changed to verify the activity of the catalyst. The specific reaction conditions and the reaction conversion rate and selectivity are shown in Table 3.

Table 3. Reaction conditions and reaction results

Embodiment 20

To test the stability of the catalyst, referring to Example 12, a cyclic application experiment was conducted under the conditions of 0.5 g nitrobenzene, 0.01 g catalyst prepared in Example 1, 25 ml 10 wt% H ₂ SO ₄ solution, 0.3 MPa H ₂ , 85° C., 1200 r, and reaction time of 5 h. The specific application results are shown in FIG1 .

Claims (10)

1. A preparation method of an acid-resistant metal catalyst is characterized in that: the preparation method comprises the following steps:

step 1, pretreatment of activated carbon:

Adding activated carbon into 10-15wt% HCl solution, refluxing for 3-4h at 80-90 ℃, cooling to room temperature, filtering with deionized water, washing to neutrality, and oven drying to obtain pretreated activated carbon;

Step 2, preparing an impregnating solution:

Weighing NaNO ₃ and PdCl ₂ in a container, adding concentrated hydrochloric acid, diluting with water to obtain a noble metal impregnation liquid, wherein the concentration of NaNO ₃ and PdCl ₂ is 0.05-0.1g/mL and 2-8mg/mL, and the adding amount of the concentrated hydrochloric acid is 20-30mL/100mL;

Step 3, preparation of the immobilized catalyst:

Adding the activated carbon treated in the step 1 into the noble metal impregnating solution prepared in the step 2, fully mixing, evaporating to dryness under the sand bath condition, continuously heating to 250-300 ℃, and stopping heating when no nitrogen oxides are released, thus obtaining the immobilized catalyst;

Step 4, organic matter coating:

Adding the immobilized catalyst obtained in the step 3 into the solution A, adding 1-2mol/L ammonium persulfate aqueous solution, stirring at 60-80 ℃ for 8-10 hours, adding isocyanate, aging at 25-30 ℃ for 24-30 hours after the mixed solution becomes gel gradually, washing with ethanol and water, and drying at 60-70 ℃ in vacuum for 10-12 hours to obtain a catalyst precursor; the solution A is an aqueous solution containing nitrobenzene and liquid acid, wherein the volume ratio of the nitrobenzene, the liquid acid and the solution A is 4-10:15-20:50-120, wherein the feeding ratio of the immobilized catalyst to the solution A and the ammonium persulfate aqueous solution is 1g:80-200ml:25-60ml:0.02-0.07mol;

step 5, carbonizing a catalyst precursor:

placing the catalyst precursor obtained in the step 4 into a tube furnace, heating to 600-800 ℃ at a speed of 1-10 ℃/min under inert atmosphere, and keeping for 3-6h to obtain a carbonized product;

step 6, catalyst functionalization:

adding the carbonized product obtained in the step 5 into 10-12wt% HNO ₃ water solution, and refluxing for 3-4 hours at 70-80 ℃ to obtain the final acid-resistant metal catalyst.

2. The method of manufacturing according to claim 1, wherein: in the step 1, the activated carbon is wood carbon or coconut shell carbon, the activated carbon is powdery microporous activated carbon, and the parameters of the activated carbon are as follows: the specific surface area is 1000-1500m ²/g, the pore volume is 0.5-1.0cm ³/g, and the average pore diameter is 2-2.5nm.

3. The method of manufacturing according to claim 1, wherein: in the step 1, the feeding ratio of the activated carbon to the HCl solution is 1-2g:20-50ml.

4. The method of manufacturing according to claim 1, wherein: in the step 3, the feeding ratio of the activated carbon treated in the step 1 to the noble metal impregnating solution prepared in the step 2 is 1g:15-20ml; in the step 6, the feeding ratio of the carbonized product to the nitric acid solution is 1g based on the feeding ratio of the activated carbon treated in the step 1 and the nitric acid aqueous solution contained in the carbonized product: 25-30ml.

5. The method of manufacturing according to claim 1, wherein: in the step 4, the liquid acid is one or two of formic acid and acetic acid.

6. The method of manufacturing according to claim 1, wherein: the isocyanate in the step 4 is one of triphenylmethane triisocyanate, toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate and lysine diisocyanate.

7. The use of the acid-resistant metal catalyst prepared by the preparation method according to claim 1 in synthesizing p-aminophenol from nitrobenzene.

8. The use according to claim 7, wherein: the application specifically comprises the following operations:

Weighing nitrobenzene, adding the prepared acid-resistant metal catalyst and H ₂SO₄ solution into a hastelloy reaction kettle, filling H ₂ with the pressure of 0.3-0.8MPa, and reacting for 5-8H at the temperature of 85-100 ℃ under the condition of 800-1200r to generate para-aminophenol.

9. The use according to claim 8, wherein: the concentration of H ₂SO₄ solution is 10-15wt%.

10. The use according to claim 8 or 9, wherein: the feeding ratio of nitrobenzene, catalyst and H ₂SO₄ solution is 0.5-1g:0.01-0.03g:25-50ml.