CN102407153A - Preparation method of nanogold catalyst for improving acidity of catalyst - Google Patents

Abstract

The invention belongs to the field of catalyst preparation, and relates to a preparation method of a nano-gold catalyst capable of increasing catalyst acidity. It is characterized in that nano-gold is supported on high-silica zeolite, and gold can strongly interact with silanol in high-silica zeolite to form a Si-O(H)-Au structure. Due to the polarization of Au, the Si-O(H)-Au bridging hydroxyl group has strong proton acidity. Said molecular sieve refers to high silica zeolite molecular sieve, especially S-1, ZSM-5, ZSM-8, ZSM-11, MCM-22, MCM-49, MCM-56, ITQ-2, and ZSM-12, β - Zeolite, Mordenite and TS-1 as supports. The method has the advantages of simple process, highly dispersed gold particles, significantly improved carrier acidity, and can obtain a metal-acid bifunctional molecular sieve catalyst with strong acidity. The obtained catalyst is used in many acid-catalyzed reactions such as aromatization, isomerization and alkylation, and has the characteristics of high activity, low reaction temperature and the like.

Description

A kind of preparation method of nanometer gold catalyst that increases catalyst acidity

technical field

The invention belongs to the field of catalyst preparation, and relates to a preparation method of a nano-gold catalyst capable of increasing catalyst acidity.

Background technique

The preparation and application of nano-gold catalysts is a major discovery in the field of catalysis. Gold has always been considered to be catalytically inert, but when it is loaded on an oxide support for high dispersion, it shows unique catalytic activity. Nano-gold catalysts have shown application prospects in the fields of catalyzing CO oxidation, ozonolysis, water gas shift reaction, reduction of _NOx , acetylene hydrochlorination, propylene epoxidation, fuel cells, petrochemical industry (Catal.Rev.-Sci. Eng, 1999, 41(3) 319-388).

The preparation methods of nano-gold catalysts are divided into two types: one is the co-precipitation method of the carrier and the gold precursor; the other is the impregnation method and the deposition precipitation method of loading the gold precursor on the pre-prepared carrier. The preparation method of early supported gold catalysts is commonly used impregnation method. The impregnation method is usually used to prepare catalysts with low content of active components and sufficient mechanical strength. The preparation process of the nano-gold catalyst by the method is as follows: first, the carrier is immersed in the gold-containing salt solution, and then dried, calcined and reduced, and the method is simple. Various metal or non-metal oxides and molecular sieves can be used as carriers in the impregnation method. Commonly used gold precursors for the preparation of nano-gold catalysts are auric acid chloride (HAuCl ₄ .3H ₂ O) and gold chloride (AuCl ₃ ) and gold complexes KAu(CN) ₂ and [Au(en) ₂ ]Cl ₃ ( en is ethylenediamine) and so on.

Co-precipitation method is an effective method for preparing high-loaded gold catalysts. The typical preparation process is: mixing the precursor salt solution of the carrier with the gold precursor salt solution, then precipitating with a precipitant, and then standing, filtering, and washing with water , drying and high-temperature roasting treatment. The advantage of the co-precipitation method is that the preparation is reproducible, but the disadvantage is that some gold particles will be buried inside the carrier, and the utilization rate of gold is low, so it is not suitable for carriers such as titanium oxide and zeolite molecular sieve. pH control is a technical difficulty when applying the precipitation method.

The deposition-precipitation method is also a commonly used preparation method for supported catalysts, which has the advantages of both the impregnation method and the precipitation method. The typical process of preparing gold catalysts by deposition-precipitation method is: adding metal or non-metal oxides and molecular sieves as carriers to the gold precursor solution, stirring continuously at a certain reaction temperature and adding a precipitant drop by drop to make the solution The reaction was carried out at a suitable pH value until the precipitation was complete. Then the solid is subjected to sedimentation, filtration, washing, drying, roasting or activation treatment.

In most cases, the supported gold catalysts prepared by various methods exist in the oxidation state of +3 after drying, and most of the gold atoms can become zero-valent after high-temperature heat treatment. In order to make the supported gold catalyst have high activity, it is the key to adopt a suitable preparation method to make the gold particles highly dispersed on the support.

Now, many patents have disclosed the preparation method of supported nano-gold catalyst. like:

Patent CN101530814A (2009) discloses a method for preparing a supported nano-gold catalyst. It is characterized in that: titanium-silicon molecular sieve with mesoporous-microporous composite structure is used as a carrier, the loading method is a deposition precipitation method, the loading is carried out under normal pressure, and chloroauric acid is used as a gold precursor.

Patent CN101237931A (2008) discloses a preparation method of supported gold catalyst. It is characterized in that: porous metal oxide is used as carrier, chloroauric acid is used as precursor, the loading method is conventional impregnation method, and the impregnation is carried out under normal pressure.

Patent CN101204655A (2008) discloses a preparation method of nano-gold catalyst. Its characteristics are: alumina, silicon oxide, ceramics, _TiO2 , etc. are used as carriers, chloroauric acid is used as the gold precursor, and the loading method is impregnation, and the impregnation is carried out under the condition of ultrasonic waves or the coexistence of ultrasonic waves and vacuum.

Patent CN1795985A (2006) discloses a method for preparing supported gold catalyst. It is characterized in that ferric nitrate is used as co-precipitation carrier, gold chlorate is used as precursor, sodium carbonate is used as precipitating agent, the loading method is co-precipitation method, and co-precipitation is carried out under normal pressure.

Patent CN1565727A (2005) discloses a preparation method of supported nano-gold catalyst. It is characterized in that oxides such as SiO ₂ , Al ₂ O ₃ , TiO ₂ are used as carriers, gold chlorate is used as a precursor, and the loading method is an impregnation method, and the impregnation is carried out under normal pressure in an equal-volume manner.

The following patents also disclose the preparation of supported gold catalysts.

The following patents are related to SiO _carrier loaded gold catalyst: CN101797514A (2010), CN101862660A (2010), CN101574654A (2009), US6821923 (2004), EP1044067B1 (2004), EP1027153B1 (2004), US64032093 (2004), US64032093 (2004), US64032093 (2004) .

涉及Al ₂ O ₃载体的负载金催化剂有以下专利：CN101618328A(2010)、US0010278A1(2010)、EP1309536B1(2010)、US0221849A1(2009)、US0088319A1(2009)、CN101147862A(2008)、CN101049561A(2007)、CN101036887A (2007), WO065138A1(2006), US7119225(2006), CN1827213A(2006), WO016298A1(2002), EP0909213B1(2001), EP0653401B1(1997).

The supported gold catalyst related to TiO _carrier has the following patents: CN101711982A (2010), EP1309536B1 (2010), CN101380575A (2009), WO076137A3R4 (2008), WO003450A1 (2006), US7119225 (2006), US68010623 (20A ), CN1349430A (2002).

The supported gold catalysts related to _ZrO2 carrier have the following patents: US0190347A1 (2007), WO0465145 (2006), US0276741A1 (2005), WO046255A1 (1999), US5895772 (1999).

In addition, the patent CN101683619A (2009) relates to a supported gold catalyst supported by Fe ₂ O ₃ .

Patent CN101722009A (2010) relates to a gold catalyst supported by CuO.

The supported gold catalyst related to the composite oxide carrier has the following patents: CN101822990A (2010), CN101822981A (2010), CN101612578A (2009), CN101376107A (2009), US02410381A1 (2008), US0193354A1 (2008), CN33A20105 (5624105) 2005), CN1698932A (2005), US0127353A1 (2004), US0060643A1 (2003), USP4839327, USP4837219.

There are also supported gold catalyst patents involving carbon supports: CN101631610A (2010), CN101648137A (2010), CN101785997A (2010), CN101804347A (2010), CN101829567A (2010).

However, the existing patents all use the atmospheric pressure method to prepare supported gold catalysts.

In addition, many published documents also relate to the preparation method of supported nano-gold catalysts. like:

Open literature Appl.Catal.A: Gen.291 (2005) 62, J.Catal.231 (2005) 105 and Geochem.Intern.11 (1985) 1656 have reported acidity (pH) on the preparation of loaded gold catalyst by deposition precipitation method effect, the carrier is TiO ₂ . The results show that pH has a great influence on the activity of nano-gold catalyst. This is mainly because, at different pH values, the degree of hydrolysis of the gold precursor compounds is different. As the pH value increases, the gold precursor compound [AuCl ₄ ] ^- gradually hydrolyzes to AuCl ₃ (H ₂ O), [AuCl ₃ (OH)] ^- , [AuCl ₂ (OH) ₂ ] ^- , [AuCl( OH) ₃ ] ^- and [Au(OH) ₄ ] ^- . The hydrolysis of different gold precursors is due to the difference in properties such as adsorption capacity, which affects the supported gold catalyst. The deposition precipitation method adopted in this publication is carried out under normal pressure conditions.

Publication Appl Catal A: Gen, 291 (2005) 162 reports a method for preparing a supported gold catalyst. Its technical features are: Y, β and mordenite are used as carriers, HAuCl ₄ is used as gold precursor, NaOH is used as precipitating agent, deposition and precipitation are adopted, and the operation is carried out under normal pressure.

Publication Appl Catal B: Env, 41 (2003) 83 reports a method for preparing a supported gold catalyst. Its technical features are: Y, β and mordenite are used as carriers, HAuCl ₄ is used as gold precursor, NaOH is used as precipitating agent, deposition and precipitation are adopted, and the operation is carried out under normal pressure.

Publication Appl. Catal. A: Gen. 240 (2003) 243 reports a method for preparing a supported gold catalyst. Its technical features are: Ti-MCM-41 is used as the carrier, NaOH is used as the precipitating agent, the deposition and precipitation method is adopted, and the operation is carried out under normal pressure.

Publication J.Catal.209(2002)331 reports a method for supporting gold catalysts. Its technical features are: Ti-MCM-48 is used as the carrier, NaOH is used as the precipitating agent, the deposition and precipitation method is adopted, and the operation is carried out under normal pressure.

Publication Appl. Cattal. A: Gen. 226 (2002) 1. Reported the chemical principle of preparing nano-gold catalyst by deposition precipitation method. The precipitant is urea, and _TiO2 is the carrier. This publication adopts _TiO2 as a carrier and urea as a precipitating agent, a deposition precipitation method, and the operation is carried out under normal pressure conditions.

Publication App. Catal. A: Gen. 190 (2000) 43 reports a method for preparing a supported gold catalyst. Its technical features are: Ti-MCM-41 is used as the carrier, NaOH is used as the precipitating agent, the deposition and precipitation method is adopted, and the operation is carried out under normal pressure.

In addition, the following publications also relate to the preparation method of supported gold catalysts: J.Catal, 2006, 237: 303-313; Catal.Today, 2006, 111 (1-2): 22-33; J.Phys.Chem , B: 2005, 109: 2321-2330; Catal. Lett, 2005, 99 (3-4): 235-239; J. PhysChem, B: 2005, 109: 3956-3965; Appl. Catal; B: Environ; 2005, 61: 201-207; Appl. Catal, A: Gen, 2005, 191: 222-229; Appl. Catal. A: Gen, 2004, 267: 191-201; Appl. Catal, A: Gen, 2004, 277:31-40; J.Am.Chem.Soc, 2004, 126:38-39; J.Catal, 2004, 226:156-170; J.Catal, 2003, 216(1-2):213-222 ; Catal. Lett, 2003, 86: 1-8; Oxid. Commun, 2003, 26 (4): 492; Appl. Catal, A: Gen, 2003, 246: 29-38; Appl. Catal, A: Gen, 2003, 243: 25-33; Appl. Catal. A: Gen., 2002, 226: 1-13; Appl. Catal, A: Gen, 226 (2002) 1; Chemical Progress 2002 (5): 360-367. J. Phys. Chem, J. Catal, 2002, 209: 331-340; B: 2002, 106(31): 7634-7642; Catal. Today, 2002, 74: 265-269; Gold Bull, 34 (2001) 4: 11; Appl. Catal, A: Gen, 2001, 215: 137-148; Appl. Catal, A: Gen, 2001, 209: 291-300; Catal. Today, 2001, 64(1): 69-81 ; Appl. Catal, B: Environ, 2001, 33: 217-222; Appl. Catal, A: Gen, 2001, 222: 427-437; .Phys.Chem, B: 2000, 104: 11153-11156; J. Catal, 2000, 191: 332-347; J. Catal, 2000, 191: 430-437; Ca tal. Rev-Sci. Eng, 1999, 41(3): 319-388; Catal. Today, 1999, 54: 31-38; Gold. Bull, 1998, 31: 105-106; Gold Bull, 31 (1998) 4: 111-118; J. Catal, 1998, 178: 566-575; Catal. Lett. (1997) 43(1-2): 51-54; Catal. Today, 36 (1997) 153; Catal. Today, 1996, 29: 443-447; Surf. Sci. Catal, 91 (1995) 227; "Preparation of catalysts V" Edit., 1991, Amsterdam, 695-704; J. Catal., 1989, 115: 301-309; Stud. Surf. Sci. Catal, 44 (1988) 33; Chem. Lett, 2 (1987) 405; J. Chem. Soc. Faraday Trans, 175 (1979) 385.

The above publications have adopted different methods and different oxides and zeolite molecular sieve carriers to prepare supported gold catalysts. However, the common feature of these methods is that the operation is carried out under normal pressure under load. The prepared catalyst is easy to agglomerate after calcining. When ZSM-5 is used as a carrier, only supported gold catalysts with gold particles of 40-50 nm can be obtained, and Au/ZSM-5 catalysts with smaller particles cannot be obtained.

The public literature Stud.Surf.Sci.Catal.84 (1994) 1059; J.Catal.152 (1995) 322, and J.Call.Inter.Sci.224 (2000) 366 have reported that AuCl ₃ is the gold precursor, Using dehydrated zeolite as a carrier, the method of introducing gold onto zeolite by mechanical mixing. The zeolites involved therein are NaY, Na-mordenite, Na-ZSM-5 and HZSM-5. The key point of this document is that the gold salt is highly dispersed on the zeolite during the vacuum heat treatment of the mechanical mixture, and the treatment temperature is 60-70°C.

Public documents Micro. Meso. Mater. 66 (2003) 15 and Catal. Lett. 72 (2001) 1 report a method of supporting gold. Its technical features are: A-type zeolite and ZSM-5 zeolite are used as carriers, the operation is carried out in a closed dark bottle, and AuCl ₃ is sublimated under vacuum and heating conditions, and then loaded on the corresponding carrier. The method actually uses chemical vapor deposition.

Although the above two documents support gold under negative pressure, the former adopts mechanical mixing method, while the latter adopts chemical vapor deposition method, the loading effect is not good, and the preparation repeatability is poor.

Solid acid is a versatile heterogeneous catalyst. Among solid acids, molecular sieves are considered to be the most promising solid acids for environmentally friendly catalysis because of their unique structures. The acid amount and acid strength of molecular sieves are very critical in the catalysis of molecular sieves. However, in the previous literature, although there are many related to molecular sieve solid acid, most of them are to reduce the acid amount and acid strength. There are very few people who increase the acid content and acid strength of molecular sieves.

The following patents and literature describe methods for increasing the acidity of molecular sieve or oxide catalysts:

Patent CN1354045 (2002.6.19) discloses a method for enhancing the acidity of molecular sieve catalysts. It is characterized in that it uses plasma technology to treat molecular sieve catalysts loaded with metal active components. The patent relates to Y-type molecular sieves, mordenite molecular sieves and HZSM-5 molecular sieves modified by transition metals such as Zn, Fe, and Mo. The above treatment can increase the acid content of the catalyst, especially the B acid content. But plasma processing technology involves high voltage electricity and consumes a lot of energy.

The published literature, Acta Catalytica Sinica 2002 (23) 5: 421-424, reported a method of treating ZSM-5 zeolite with alkaline steam to adjust its acidity and pore structure. The results showed that when HZSM-5 zeolite was treated with steam of 10% _NH3 , the amount of acid could be increased at appropriate temperature. But this method is unreliable and the effect is difficult to repeat.

Publication Catal.Lett.1995.(30)241-248 reported that heteropolyacid components (HPAs) were loaded on mesoporous molecular sieves to prepare acidic acid stronger than heteropolyacid, which was also comparable to concentrated sulfuric acid strong acidic catalyst. But this complex is unstable. The structure of the heteropolyacid component is easily destroyed at high temperature, and the acidity is completely lost. It is easy to lose in the environment with water, which also leads to the loss of acidity.

Open document Chem.Commun (2000) 2229-2230 has reported to use zirconium metaprasetic acid (Zr (OPr) ₄ ) as zirconium source, in hexane solution and MCM-41 molecular sieve stirring reflux, and constantly add water and carry out hydrolysis, then A method of making MCM-41 molecular sieve into a super acid material through sulfuric acid treatment. Also, this sulfate-promoted solid superacid is very unstable.

All in all, the preparation of supported gold catalysts in the past mainly adopts atmospheric pressure impregnation and atmospheric pressure deposition precipitation methods. Because gold is easy to agglomerate during roasting, people pay attention to the dispersion of gold particles. So far, it is not known that loading gold can increase the acidity of molecular sieves, let alone how to load gold to have this effect.

Contents of the invention

The invention provides a preparation method of a supported nano-gold catalyst for increasing the acidity of molecular sieves.

We have found through research that when nano-gold is loaded on high-silica zeolite, the gold can strongly interact with the silanol in the high-silica zeolite to form a Si-O(H)-Au structure. Due to the polarization of Au, the Si-O(H)-Au bridging hydroxyl group has strong proton acidity. Through research, it is further found that the loading method of Au plays a very important role in generating the above-mentioned acidic bridging hydroxyl groups. After sufficient negative pressure degassing and purification treatment on the molecular sieve, the gold precursor is loaded on the molecular sieve carrier by negative pressure deposition precipitation method. , which is most conducive to the formation of a strongly acidic Si-O(H)-Au structure. Said molecular sieve refers to high silica zeolite molecular sieve, especially S-1, ZSM-5, ZSM-8, ZSM-11, MCM-22, MCM-49, MCM-56, ITQ-2, and ZSM-12, β - Zeolite, Mordenite and TS-1 as supports. The said gold precursor mainly refers to HAuCl ₄ , and the precipitating agent can be urea. The use of negative pressure conditions is conducive to purifying the inner and outer surfaces and pores of the molecular sieve, allowing Au to enter the pores to achieve high dispersion and combine with the silanol on the inner and outer surfaces to form a Si-O(H)-Au structure.

The change of catalyst acid strength caused by gold loading can be measured by ammonia temperature programmed desorption (NH ₃ -TPD) device. The acidic hydroxyl formed by the interaction of Si-OH and gold can be characterized by pyridine adsorption infrared.

Technical scheme of the present invention is as follows:

The first step is to pretreat the high silica zeolite carrier.

(1). Roasting the high silica zeolite carrier. The calcination temperature is 300-700°C, preferably 400-600°C; the calcination time is 4-20 hours, preferably 3-8 hours. The silicon-aluminum ratio of the said high silica zeolite is 10～∞, such as ZSM-5, ZSM-8, ZSM-11, MCM-22, MCM-49, MCM-56, ITQ-2, ZSM-12, β- Zeolite, mordenite, TS-1 and pure silicalite or the above-mentioned zeolites treated by metal modification and other methods. The grain size of zeolite is between 5nm and 30μm.

The synthesis of the above carriers can be carried out using the formulas in published patents and literatures.如专利US3702886(1972)、US3941871(1976)、US4061724(1977)、US4166099(1979)、CN1086792A(1994)、CN1219571A(1999)、CN1056818C(2000)、CN100457622A(2001)、WO0138224A(2001)、CN1212892A(2002 )、CN1328960A(2002)、CN1088406C(2002)、CN1417116A(2003)、CN1530323A(2004)、CN1699173A(2005)、CN1686801A(2005)、CN100344375A(2005)、CN1715186A(2006)、CN101007637A(2007)、CN1307102C(2007 )、CN101279746A(2008)、CN101214971(2008)、CN101613114(2009)、CN101554592A(2009)、CN101559955A(2009)、CN101428818B(2010)、CN101993091A(2011)、CN101417810A(2009)、CN 101468800(2009)、CN 101519216 (2009)、CN101554592A(2009)、CN101618337A(2010)、US20100298598A1(2010)、CN101801848A(2010)、CN10204023A(2010)、CN101973560A(2011)、US7883686B2(2011)、WO2011061204A1(2011)、Microporous and Mesoporous Materials 31( 1999) 241-251, Journal of Materials Chemistry 12(2002) 369-373, Journal of Molecular Catalysis B: Enzymatic 22(2003) 119-133, Journal of Catalysis 255(2008) 68-78. Engineers familiar with the field can use the technical methods reported in the existing published documents and patents to synthesize the carrier.

(2) Ammonium exchange treatment: the calcined zeolite is subjected to ion exchange treatment with an ammonium salt solution at a suitable temperature. Then, it is washed with deionized water, dried and calcined to obtain hydrogen zeolite. The ammonium exchange process mainly controls the Na ⁺ content so that it cannot be higher than 1.0%, preferably lower than 0.8%. Described ammonium salt can be selected any one in ammonium nitrate, ammonium chloride, ammonium carbonate etc., and the concentration of ammonium salt solution is 0.05～1.0mol/L, and the liquid-solid volume ratio of catalyst and ammonium salt solution is 1: 1～ 20:1, preferably 3:1-10:1; exchange temperature is 20-80°C, preferably 20-60°C; exchange time is 0.2-100 hours, preferably 0.5-4 hours; exchange times 1-5 times. The drying temperature is 80-200°C, and the drying time is 1-100 hours; due to the strong complexing force between NH 3 and proton H ⁺ in NH ₄ ⁺ →NH ₃ +H ⁺ , the roasting process must be sufficient, so _the roasting temperature is selected as 300 ~700°C, preferably 400~600°C; calcination time is 4~20 hours, preferably 3~8 hours. The assay method of said ^Na content can adopt flame photometer, Inductively Coupled Plasma (ICP) to measure. Engineers familiar with this field can refer to the manual for Na ⁺ determination.

(3) Acid pore expansion treatment: the hydrogen-type zeolite is subjected to acid pore expansion treatment at a suitable acid concentration and temperature. Then it was washed with deionized water until neutral, then dried and calcined to obtain the carrier. Said acid can be any one of HCl, HNO ₃ , H ₂ SO ₄ or citric acid, preferably HNO ₃ and citric acid. Because the use of HCl will introduce Cl ^- , and H ₂ SO ₄ is difficult to decompose and difficult to remove. The acid concentration is 0.05-6mol/L, the liquid-solid volume ratio of the acid solution to the catalyst is 1:1-20:1, preferably 3:1-10:1; the acid pore expansion treatment time is 30min-100 hours, preferably 1-5 hours; the treatment temperature is 20-80°C. The drying temperature is 50-200°C, the drying time is 3-20 hours, the roasting temperature is 300-600°C, and the roasting time is 1-4 hours.

The purpose of acid reaming is to remove the amorphous impurities inside the HZSM-5 crystal nucleus and increase the diffusion rate of the pores. In fact, the hydrogen-type zeolite obtained after ammonium exchange can be directly used as a carrier. However, acid pore expansion is beneficial to improve the activity of the catalyst.

In the second step, a gold-loaded catalyst is prepared by a deposition precipitation method under a negative pressure condition.

(1). Loading gold by negative pressure deposition precipitation method: the pretreated hydrogen-type zeolite carrier is subjected to negative pressure degassing and purification treatment at a certain temperature. The treatment temperature is 20-90°C, the degassing time is 0.5-12 hours, and the negative pressure range is -0.01--0.1Mpa; then, under full stirring, maintain the temperature and negative pressure state, first contact the carrier with the gold precursor solution, Then add a precipitant to the mixture to carry gold through negative pressure deposition precipitation reaction, and the reaction time is 2 to 30 hours; although a higher vacuum degree is beneficial to purification, it will increase the cost of catalyst production.

(2). Carry out post-treatment to the gold-loaded precipitate: including solid-liquid separation, washing with deionized water until Cl ^- free and drying and roasting of solids. Among them, the drying temperature can be selected from 80 to 200°C, the drying time can be selected from 0.5 to 100 hours, the roasting temperature can be selected from 200°C to 600°C, the roasting time can be selected from 0.5 to 100 hours, and the roasting atmosphere can be selected from air, nitrogen, helium, argon and oxygen.

The acidity of the gold catalyst prepared by the above method can be characterized by ammonia temperature-programmed desorption (NH ₃ -TPD) and vibrational adsorption infrared methods. Among them, the conditions for ammonia temperature-programmed desorption (NH ₃ -TPD) are that 0.14 g of sample (40-60 mesh) is placed in a U-shaped quartz tube reactor with an inner diameter of 5 mm, and activated in a He atmosphere at 600 °C for 1 hours, then lowered to 150°C, injected NH ₃ to saturation, and purged with He gas to remove physically adsorbed NH ₃ , then programmed to heat up to 600°C at a rate of 15°C/min, during which the He gas flow rate was 20ml/ min, the desorbed _NH3 was analyzed by GC7890F gas chromatograph and detected by TCD.

The method for characterizing the hydroxyl group and acidity of the catalyst with infrared spectroscopy is as follows: the specific method is: the finely ground sample gold catalyst powder is pressed into a self-supporting sheet of about 10 mg, and the temperature is gradually raised to 300 ° C in the infrared cell and vacuumed to degas, Evacuated and desorbed under high vacuum (10 ^-3 Pa) for 4 hours, then lowered to room temperature, and tested pyridine infrared hydroxyl spectrum at room temperature. After obtaining the infrared hydroxyl spectrum, adsorb pyridine at room temperature for 0.5 hours, heat up and desorb, desorb at 150°C, 250°C, 300°C and 450°C respectively, then cool to room temperature and record the corresponding adsorption pyridine infrared hydroxyl spectrum and pyridine infrared spectrum picture.

The beneficial effect of the invention is that the loaded gold catalyst prepared by the method has the advantages of simple preparation method, highly dispersed gold particles, significantly improved acidity of the carrier, and the like. A highly acidic metal-acid bifunctional molecular sieve catalyst can be obtained.

Therefore, this catalyst is used in many acid-catalyzed reactions such as aromatization, isomerization and alkylation, and has the advantages of high activity and low reaction temperature.

Description of drawings

Fig. 1 is the ammonia temperature-programmed desorption (NH ₃ -TPD) spectrogram of the catalyst prepared in Example 1 of the present invention.

Fig. 2 is the pyridine adsorption infrared spectrum of the catalyst prepared in Example 1 of the present invention.

Detailed ways

The present invention will be further described below by examples, but the present invention is not limited by these examples.

Example 1:

Preparation of 0.1% Au/HZSM-5:

(1). Referring to the method disclosed in patent CN100364890C, ZSM-5 zeolite raw powder is synthesized, and the zeolite grain size is less than 50nm. Then calcined at 540° C. for 4 hours to obtain ZSM-5 zeolite.

(2). Ammonium exchange treatment: the calcined zeolite is subjected to ion exchange treatment with an ammonium salt solution at a suitable temperature. Then, it is washed with deionized water, dried and calcined to obtain hydrogen zeolite. Said ammonium salt is ammonium nitrate, the concentration of ammonium salt solution is 0.6mol/L, the liquid-solid volume ratio of ammonium salt solution and zeolite is 5:1, the exchange temperature is 30°C, the exchange time is 1 hour, and the exchange times are 2 times . The drying temperature is 110°C, the drying time is 12 hours, the firing temperature is 540°C, and the firing time is 6 hours. The Na ⁺ content after exchange is not higher than 0.5%.

(3). Acid pore expansion treatment: the hydrogen-type zeolite is subjected to acid pore expansion treatment at a suitable acid concentration and temperature. Then it is washed with deionized water until neutral, then dried and calcined to obtain the zeolite carrier. The acid is HNO ₃ . The acid concentration is 0.6 mol/L, the liquid-solid volume ratio of the acid solution to the zeolite is 5:1, the acid pore expansion treatment time is 24 hours, and the treatment temperature is 30°C. The drying temperature is 110°C, the drying time is 12 hours, the calcination temperature is 540°C, and the calcination time is 3 hours.

In fact, the hydrogen-type zeolite obtained after ammonium exchange can be directly used as a carrier. However, acid pore expansion is beneficial to improve the activity of the catalyst.

(4). Loading gold by negative pressure deposition precipitation method: the pretreated hydrogen-type zeolite carrier is subjected to negative pressure degassing and purification treatment at a certain temperature. Specifically, 5 g of the pretreated carrier is taken for negative pressure degassing treatment. The negative pressure degassing treatment temperature is 80°C, the degassing time is 5 hours, and the pressure is -0.05MPa. Then, under full stirring, maintaining the temperature and negative pressure state, the gold precursor solution is first used to contact the carrier, and then a precipitant is added to the mixture to carry gold through negative pressure deposition precipitation reaction. The gold precursor is HAuCl4, the concentration is 5～50mmol/L, the volume ratio of the gold precursor solution and the molecular sieve carrier is 1:1～1:10, and the described precipitation agent is urea, and the pH value of the solution is adjusted with urea to be 4～ 9. The specific method is to take _1.26ml of HAuCl4 solution with a concentration of 24.26mmol/L and add water to dilute it to 10ml, so that the volume ratio of the gold precursor solution and the carrier is 2:1; the pH value of the solution is adjusted to 8 with urea; The temperature was 80°C, the reaction time was 20 hours, and the reaction was stopped for 4 hours.

(5). Post-treatment of the gold-loaded solid: including solid-liquid separation, washing with deionized water until Cl ^- free, and drying and roasting of the solid. Wherein, the drying temperature is 100° C., and the drying time is 12 hours; the calcination temperature is 400° C., and the calcination time is 4 hours, and the calcination atmosphere is air. A supported Au/HZSM-5 zeolite molecular sieve catalyst A-1 with a particle diameter of less than 10 nm is obtained. The samples were characterized by NH ₃ -TPD and infrared spectroscopy. Spectrum shown in Figure 1 and Figure 2.

Example 2:

Repeat Example 1, but change the amount of chloroauric acid solution into 3.14ml and add water to dilute to 10ml, and the roasting temperature is 300°C. A 0.3% Au/HZSM-5 supported gold catalyst was obtained. Labeled: A-2.

Example 3:

Repeat Example 1, but change the vacuum to -0.01MPa, change the amount of chloroauric acid solution to 10.46ml, add water and dilute to 20ml, and obtain 1.0% Au/HZSM-5 supported gold catalyst. Labeled: A-3.

Example 4:

Repeat Example 1, but change the consumption of chloroauric acid solution into 20.93 μl, add water and dilute to 25ml, and the roasting temperature is 500°C. A 2.0% Au/HZSM-5 supported gold catalyst was obtained. Labeled: A-4.

Example 5:

Repeat Example 1, but change the degree of vacuum to -0.06MPa, the consumption of chloroauric acid solution is 41.86ml, add water and dilute to 50ml, and the roasting temperature is 600°C. A 3.0% Au/HZSM-5 supported gold catalyst was obtained. Labeled: A-5.

Embodiment 6:

Repeat Example 1, but change the firing temperature to 200°C, 300°C, 400°C, 500°C, and 600°C respectively, and the firing atmosphere is nitrogen. The supported gold catalysts calcined at different temperatures are obtained, and the catalysts are characterized by NH ₃ -TPD, and the acid content increases by 10-50%. The optimum calcination temperature is 300-600°C.

Embodiment 7:

Repeat Example 1, but synthesize large-grain ZSM-5 with a grain size of 5 μm as follows, and change the amount of urea precipitant to make the pH values 3, 5, 6, 8, 9 and 10, respectively. The method of synthesizing ZSM-5 zeolite is: first weigh a certain amount of industrial aluminum sulfate and dissolve it with deionized water, then add sulfuric acid to it, stir evenly, and use it as A solution; then weigh a certain amount of water glass and dilute it with water to form B solution. Then, under vigorous stirring, the A solution was slowly added dropwise to the B solution, and after the addition was completed, a certain amount of seed crystals were added (refer to the patent for the seed crystal synthesis method: ZL200510200328.9), and the stirring was continued for 2 hours to obtain a uniform gel. The molar composition of the gel is: SiO2/Al2O3=50; Na2O/SiO2=0.078; H2O/SiO2=900; the amount of seed crystal is 5% (mass percentage of SiO2 in the synthesis system). Put the obtained gel into a stainless steel crystallization kettle for crystallization. The crystallization temperature is 170°C, and the crystallization time is 18h. After the crystallization is completed, the mother liquor is removed by suction filtration and the filter cake is washed to neutrality, and dried at 110° C. to obtain Na-type ZSM-5 zeolite raw powder. The NH3-TPD characterization is carried out on the supported gold catalyst, and the acid content is increased by 10-55% compared with the parent body.

Embodiment 8:

Repeat Example 3, but change the reaction time to 0.5, 1, 2, 5, 10, 15, 20, 25, 30, 35 hours respectively to obtain 1.0Au/HZSM-5 catalysts with different reaction times. The results of NH3-TPD show that: the reaction time is too short, only a small amount of Au-O(H)-Si structure can be formed on the surface of the support. With the prolongation of time, the pH value gradually increased, and the number of gold particles generated increased, thus forming more Au-O(H)-Si structures on the surface of the carrier. The most suitable reaction time is 2 to 30 hours.

Embodiment 9:

Repeat Example 1, but change the degree of vacuum to -0.01MPa, -0.03MPa, -0.05MPa, -0.07MPa, -0.1MPa respectively. The supported gold catalysts under different vacuum degrees are obtained, and the catalysts are characterized by NH ₃ -TPD, and the acid content increases by 10-53%.

Example 10:

Repeat Example 1, but replace the carrier with HZSM-8 zeolite, ZSM-8 zeolite was synthesized by referring to the method disclosed in patent CN101703944A (2010), and then calcined at 540° C. for 4 hours. A 0.1% Au/HZSM-8 supported gold catalyst was obtained. Labeled: A-6.

Example 11:

Repeat Example 2, but replace the carrier with HZSM-11 zeolite, ZSM-11 zeolite was synthesized with reference to the method disclosed in patent CN1367758 (2002), and then calcined at 540° C. for 4 hours. At the same time, the firing temperature was changed to 400°C. A 0.3% Au/HZSM-11 supported gold catalyst was obtained. Marked: A-7.

Example 12:

Repeat Example 2, but replace the carrier with HZSM-12 zeolite, ZSM-12 zeolite was synthesized with reference to the method disclosed in patent CN1774398 (2006), and then calcined at 540° C. for 4 hours. At the same time, the firing temperature was changed to 400°C. A 0.3% Au/HZSM-12 supported gold catalyst was obtained. Marked: A-8.

Example 13:

Example 3 was repeated, but the carrier was replaced by MCM-22 zeolite, which was synthesized by referring to the method disclosed in patent CN1328960A (2002), and then calcined at 540° C. for 4 hours. At the same time, change the vacuum degree to -0.05MPa. A 1.0% Au/MCM-22 supported gold catalyst was obtained. Marked: A-9.

Example 14:

Example 4 was repeated, but the carrier was replaced by MCM-49 zeolite, which was synthesized by referring to the method disclosed in patent CN101468800 (2009), and then calcined at 540° C. for 4 hours. At the same time, change the vacuum degree to -0.06MPa. A 2.0% Au/MCM-49 supported gold catalyst was obtained. Marked: A-10.

Example 15:

Example 5 was repeated, but the carrier was replaced by MCM-56 zeolite, which was synthesized by referring to the method disclosed in patent CN101007637A (2007), and then calcined at 540° C. for 4 hours. At the same time, the degree of vacuum was changed to -0.05MPa, and the firing temperature was changed to 500°C. A 3.0% Au/MCM-56 supported gold catalyst was obtained. Marked: A-11.

Example 16:

Repeat Example 1, but replace the carrier with ITQ-2 zeolite, which was synthesized by referring to the method disclosed in patent CN101973560A (2011), and then calcined at 540°C for 4 hours. At the same time, the amount of chloroauric acid solution was changed to 15.70ml, and diluted with water to 20ml. A 1.5% Au/ITQ-2 supported gold catalyst was obtained. Marked: A-12.

Example 17:

Repeat Example 3, but the carrier is replaced by Hβ zeolite, Hβ zeolite is synthesized with reference to the method disclosed in patent CN1086792A (1994), and then calcined at 540° C. for 4 hours. At the same time, change the vacuum degree to -0.05MPa. A 1.0% Au/Hβ supported gold catalyst was obtained. Marked: A-13.

Example 18:

Repeat Example 1, but the carrier is replaced by S-1 zeolite, S-1 zeolite is synthesized with reference to the method disclosed in the open document Microporous and Mesoporous Materials, 1999 (28) 3: 387-393, and then calcined at 540 ° C for 4 hours. At the same time, change the vacuum degree to -0.045MPa, change the amount of chloroauric acid solution to 6.28ml, and add water to dilute to 10ml. A 0.5% Au/S-1 supported gold catalyst was obtained. Marked: A-14.

Example 19:

Example 18 was repeated, but the carrier was replaced by TS-1 zeolite, which was synthesized by referring to the method disclosed in patent CN100457622A (2001), and then calcined at 540° C. for 4 hours. A 0.5% Au/TS-1 supported gold catalyst was obtained. Marked: A-15.

Example 20:

Example 18 was repeated, but the carrier was replaced by ZSM-22 zeolite, which was synthesized by referring to the method disclosed in the patent US5783168A (1998), and then calcined at 540° C. for 4 hours. A 0.5% Au/ZSM-22 supported gold catalyst was obtained. Marked: A-16.

Example 21:

Repeat Example 4, but change the amount of precipitant so that the pH value is 7, the degree of vacuum is changed to -0.04MPa, and the calcination temperature is changed to 400°C. A 2.0% Au/HZSM-5 supported gold catalyst was obtained. Marked: A-17.

Example 22:

Repeat Example 21, but use the following method to synthesize strip-shaped ZSM-5 zeolite with a grain size of 10 μm, and change the amount of precipitant to make the pH value 5. The method for synthesizing the zeolite is as follows: weigh a certain amount of industrial aluminum sulfate and dissolve it with deionized water, then add sulfuric acid to it, stir evenly, and use it as A solution; then weigh a certain amount of water glass and dilute it with water to form B solution. Then, under vigorous stirring, the A solution and the measured absolute ethanol were slowly added dropwise to the B solution successively, and the stirring was continued for 2 hours after the addition, and the molar composition of the uniform gel obtained was: SiO ₂ /Al ₂ O ₃ = 60; Na ₂ O/SiO ₂ =0.1; Ethanol/SiO ₂ =1.5; H ₂ O/SiO ₂ =900; the seed crystal dosage is 5% (mass percentage of SiO ₂ in the synthesis system). Put the obtained gel into a stainless steel crystallization kettle for crystallization. The crystallization temperature is 170°C, and the crystallization time is 20h. After the crystallization is completed, the mother liquor is removed by suction filtration, the filter cake is washed to neutrality, and dried at 110° C. to obtain Na-type ZSM-5 zeolite molecular sieve powder. A 2.0% Au/HZSM-5 supported gold catalyst was obtained. Marked: A-18.

Example 23:

NH ₃ -TPD and infrared spectroscopy were performed on A2-A18 samples. The results showed that the acid strength of the above gold-supported catalysts was increased to varying degrees on the basis of the support, and the increase was protonic acid.

Claims (5)

1. a preparation method for increasing the nano-gold catalyst of catalyst acidity, is characterized in that comprising the steps: a. Pretreatment of high silica zeolite carrier (1) Roasting the high-silica zeolite carrier, the calcination temperature is 400-600°C; the calcination time is 3-8 hours; the silicon-aluminum ratio of the high-silica zeolite is greater than 10, and the grain size of the zeolite is 5nm-30μm; (2) Ammonium exchange treatment: the roasted zeolite is subjected to ion exchange treatment with 0.05-1.0mol/L ammonium nitrate, ammonium chloride or ammonium carbonate solution at 20-80°C, and the volume ratio of ammonium salt solution to zeolite liquid-solid is 3:1~10:1; the exchange time is 0.2~100 hours, the number of exchanges is 1~5 times, the Na ⁺ content is controlled to make it less than 1.0%; then it is washed with deionized water, and then dried and roasted Obtain hydrogen-type zeolite; drying temperature is 80-200°C, drying time is 1-100 hours; roasting temperature is 400-600°C, roasting time is 3-8 hours; (3) Acid pore expansion treatment: use HCl, HNO ₃ , H ₂ SO ₄ or citric acid solution to carry out acid pore expansion treatment on hydrogen-type zeolite; then wash with deionized water until neutral, then dry and roast to obtain the carrier; The acid concentration is 0.05-6mol/L, the liquid-solid volume ratio of the acid solution to the zeolite is 3:1-10:1, the acid pore expansion treatment time is 1-5 hours, the treatment temperature is 20-80°C; the drying temperature is 50- 200℃, the drying time is 3-20 hours; the calcination temperature is 300-600℃, the calcination time is 1-4 hours; b. Preparation of supported gold catalysts by deposition and precipitation under negative pressure conditions (1) Loading gold by negative pressure deposition precipitation method: the pretreated hydrogen-type zeolite carrier is subjected to negative pressure degassing and purification treatment, the treatment temperature is 20-90°C, the degassing time is 0.5-12 hours, and the negative pressure range is -0.01～-0.1MPa; then maintain the temperature and negative pressure under stirring, first contact the carrier with the gold precursor solution, and then add a precipitant to the mixture to load gold through negative pressure deposition precipitation reaction, the reaction time is 5 to 100 Hour; (2) Post-treatment of gold-loaded precipitates: including solid-liquid separation, washing with deionized water until Cl ^- free, drying and roasting of solids; drying temperature 80-200°C, drying time 0.5-100 hours; roasting The temperature is 300-700°C; the roasting time is 3-20 hours. 2. The method according to claim 1, characterized in that said high silica zeolite refers to ZSM-5, ZSM-8, ZSM-11, MCM-22, MCM-49, MCM-56, ITQ-2 , ZSM-12, β-zeolite, mordenite, TS-1 or pure silicalite. 3. The method according to claim 1 or 2, characterized in that the gold precursor is HAuCl ₄ , the concentration of HAuCl ₄ is 5-50 mmol/L, and the volume ratio of the gold precursor solution to the carrier is 1:1 ~10:1. 4. The method according to claim 1 or 2, characterized in that the precipitating agent is urea, and the pH value of the solution is adjusted to 4-9 with the precipitating agent. 5. The method according to claim 3, characterized in that the precipitating agent is urea, and the pH value of the solution is adjusted to 4-9 with the precipitating agent.

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