CN112387275B

CN112387275B - High-activity anti-sintering gold catalyst and preparation and application thereof

Info

Publication number: CN112387275B
Application number: CN201910754407.6A
Authority: CN
Inventors: 刘少峰; 王军虎
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2019-08-15
Filing date: 2019-08-15
Publication date: 2021-12-24
Anticipated expiration: 2039-08-15
Also published as: CN112387275A

Abstract

The invention relates to a method for inducing TiO by melamine under an oxidizing atmosphere₂A gold catalyst prepared by wrapping gold nanoparticles with a carrier and used for resisting sintering and a preparation method thereof. The catalyst has high catalytic activity and stability even after being calcined at 800 ℃ in air. Wherein the melamine functions to induce TiO in a high temperature oxidizing atmosphere₂The carrier wraps the gold particles to inhibit the growth of the gold particles; TiO 2₂Plays a role in enhancing the reaction active center of the gold catalyst. The preparation of the catalyst is relatively simple and practical, and the product has high activity and better anti-sintering performance, and the method has never been reported and has good industrial application prospect.

Description

High-activity anti-sintering gold catalyst and preparation and application thereof

Technical Field

The invention relates to the technical field of catalyst preparation and application, in particular to a gold catalyst with high activity and stronger sintering resistance and a preparation method thereof. Specifically, the following two steps are performed: 1) preparing a supported gold catalyst by a deposition-precipitation method; 2) the prepared catalyst is modified by melamine, and then is roasted by high-temperature nitrogen and then is roasted by high-temperature air to obtain the gold catalyst with high activity and sintering resistance. Compared with the reported activity and anti-sintering performance of a gold catalyst, the catalyst prepared by the method has a unique structure, higher activity and stronger anti-sintering performance. The invention provides a catalyst with high activity and sintering resistance and a preparation method thereof.

Background introduction

Gold, as a noble metal, has been of little use in the field of catalysis for a long time due to its relatively strong inertness. In the eighties of the last century, Haruta and Hutchings and the like find that the nano-gold catalyst has good catalytic activity on CO oxidation and acetylene hydrochlorination, and establish a milestone in the research history of the gold catalyst. After that, the research of gold in the field of catalysis has received increasing attention. So far, the nanogold catalyst has application in many reactions and shows unique and excellent catalytic performance, including CO oxidation, CO selective oxidation under a hydrogen-rich system, water vapor transformation, hydrogen peroxide synthesis, propylene epoxidation, hydrogenation reaction, selective hydrogenation reaction, catalytic combustion of alkane and the like. Although the supported gold catalyst has unique catalytic performance and potential application prospects in many reactions, the practical application of the gold catalyst is severely limited by the defects that gold nanoparticles in the catalyst are easy to sinter at high temperature and are easy to aggregate and inactivate under the reaction and the like.

At present, the improvement of the sintering resistance of the supported nano gold catalyst is mainly realized by the following strategies. For example, mixed carriers, i.e., carrier pre-modification, are used; covering a layer of porous carbon shell or porous oxide on the surface of the prepared gold catalyst to limit the growth of gold particles; limiting gold particles in the pore canal of the microporous or mesoporous material; enhancing the strong interaction between the metal carriers. Although these methods improve the stability of the catalyst to some extent, some problems still remain. For example, a shell layer confined to the surface of a gold particle may cover many gold active sites, and may also cause a decrease in catalyst activity and diffusion problems of reactant and product molecules. In addition, the pore size of the synthesized mesoporous material is difficult to control, so that the obtained gold particles have uneven size and still have poor activity at higher temperature. The Strong Interaction (Strong Metal-Support Interaction) between Metal carriers means that the carriers migrate to the surface of Metal particles in a reducing or oxidizing atmosphere, and a coating layer is formed on the surface of the Metal particles, thereby inhibiting the growth of the Metal particles. The current method for preparing the sintering-resistant Au catalyst is relatively less researched. This strategy can therefore be used to develop and study gold catalysts with high activity and resistance to sintering.

Disclosure of Invention

The invention aims to provide a gold catalyst with high activity and stronger sintering resistance and a preparation method thereof.

Gold is an active center; titanium dioxide is used as a carrier; the catalyst has high activity and better anti-sintering performance after being modified by melamine, wherein the melamine is mainly used for inducing to generate TiO under high-temperature oxidizing atmosphere_xThe shell layer wraps the gold nanoparticles so as to stabilize the function of the gold nanoparticles, and the function of the titanium dioxide is to improve the activity of the gold catalyst.

Researches show that a thin layer is arranged on the surface of the gold nanoparticle after roasting in a high-temperature oxidizing atmosphere, further analysis shows that the composition of the thin layer contains Ti, and shows that the Au nanoparticle is wrapped by titanium dioxide under the action of melamine, and the phenomenon is not reported before. The gold in the supported catalyst is activeThe carrier is TiO₂The gold nanoparticles are positioned on the carrier TiO₂Wherein the melamine functions to induce the formation of TiO under a high-temperature oxidizing atmosphere_xThe shell layer (the thickness of the shell layer is 0.75 +/-0.2 nm) wraps the gold nanoparticles to inhibit the growth of the gold particles; TiO 2₂Plays a role in enhancing the reaction active center of the gold catalyst. The catalyst modified by melamine still has good low-temperature activity and better anti-sintering performance after being roasted at 800 ℃.

In the gold catalyst with high activity and sintering resistance, the content of Au is 0.01-20 wt% (preferably 3.0-5.0 wt%);

the invention is realized by the following technical scheme;

preparing a catalyst:

carrying Au by a deposition-precipitation Method (D-P Method) in which a concentration of 1.5-3 mg is adjusted by using an alkaline solution having a concentration of 0.01-1 mol/L_AuAdjusting the pH value of a chloroauric acid solution to be 8-11, adding 1.0g of carrier, reacting at 60-100 ℃ for 0.5-3 hours, filtering, washing, and drying at 60-80 ℃ for 12-18 hours. The catalyst is roasted for 1 to 3 hours at the temperature of 60 to 300 ℃. Dissolving 0.05-0.2 g of melamine in 30-50 mL of water, adding 0.3-0.5 g of the catalyst, reacting at 50-80 ℃ for 12-48 hours, filtering, washing with ultrapure water, and drying at 60-80 ℃ for 12-18 hours. Roasting the catalyst for 1-6 hours at 400-700 ℃ in a nitrogen atmosphere; cooling to room temperature, and roasting at 600-800 ℃ for 2-4 hours.

The preparation method of the catalyst is simple, and the prepared catalyst has high activity and stronger anti-sintering performance (the lowest T50 can reach 20 ℃). The catalyst calcined at 800 ℃ still has good catalytic activity on CO oxidation reaction.

Drawings

FIG. 1 is a TEM and HRTEM image of example 39;

FIG. 2 is a TEM and HRTEM image of example 41;

FIG. 3.Au/TiO₂TEM and HRTEM images of-800.

Detailed Description

Comparative example 1

Standard Au/TiO₂WGC catalyst (Type A, world gold organization)

The actual content of gold is 1.47 wt%, and the catalyst is roasted for 3 hours at 600 ℃, 700 ℃ and 800 ℃ in the air atmosphere, and respectively recorded as Au/TiO₂-WGC-600、Au/TiO₂WGC-700 and Au/TiO₂-WGC-800。

Comparative example 2

Au/TiO₂

50mL (1.5 mg) of the solution was prepared_AumL) solution, adjusted to pH 10 with 0.5mol/L NaOH, 1.0g of TiO₂The carrier was added to the above solution and stirred in a water bath at 80 ℃ for 2 hours. Filtering, washing with ultrapure water, and drying at 60 ℃ for 12 hours. Roasting the sample at 600 ℃, 700 ℃ and 800 ℃ for 3 hours in air atmosphere, and respectively recording as Au/TiO₂-600、Au/TiO₂700 and Au/TiO₂-800。

Examples 1 to 18

1. Investigating the influence of each condition on the catalyst activity in the process of a deposition precipitation method

Carrying gold by a deposition precipitation method (D-P method), namely, carrying out gold loading by using an alkaline solution with the concentration of 0.01-1 mol/L to the concentration of 1.5-3 mg_AuAdjusting the pH of a/mL chloroauric acid solution to 8-11, and then adding 1.0g TiO₂Reacting the carrier at 60-100 ℃ for 0.5-3 hours, filtering, washing and drying at 60 ℃ for 12 hours.

And (3) melamine modification, namely roasting the sample at 250 ℃ for 2 hours in air, adding 0.3g of roasted catalyst into 50mL of ultrapure water containing 0.2g of melamine, reacting at 65 ℃ for 24 hours, filtering, washing with ultrapure water, and drying at 60 ℃ for 12 hours. The catalyst is roasted at 600 ℃ for 3 hours in a nitrogen atmosphere, cooled to room temperature and then roasted at 800 ℃ for 3 hours in the air.

In the activity test of the catalyst under each condition in the process of carrying gold by a deposition precipitation method, a CO oxidation reaction is taken as a probe reaction, and T is taken as₅₀The activities were compared for reference. T is₅₀Represents the reaction temperature, T, corresponding to a CO conversion of 50%₅₀The lower the reactivity, the higher. The reaction device is a fixed bed micro-reactor. The composition of the reaction gas was 1 v% CO +1 v% O₂+98 v% He, raw gasSpace velocity SV of 20L g_cat ^-1h^-1. The reaction raw material gas and the product gas were analyzed on-line by gas chromatography (Agilent6890N) equipped with a TDX-01 packed column.

TABLE 1 influence of the conditions during the preparation of the catalyst by the D-P method on the catalyst Activity

Note: the theoretical amount of gold in the catalyst was 5 wt%

As can be seen from Table 1, the activity was higher at a lower concentration of chloroauric acid, and the activity was lower at a higher concentration, probably because gold was not supported. The type and concentration of the alkaline solution will have some effect on the activity of the catalyst. In the D-P process, the PH is between 9 and 10, the reaction temperature is 80 to 90 ℃, and the activity of the catalyst is better if the reaction time is slightly longer.

Examples 19 to 38

2. Investigating the influence of each condition on the catalyst activity in the melamine modification process

Precipitation method (D-P method) gold supporting 50mL (1.5 mg)_Au/mL) chloroauric acid solution, adjusting the pH of the solution to 10 with 0.5mol/L sodium hydroxide, and then adding 1.0g TiO₂The carrier is added to the above solution. Stirring in 80 deg.C water bath for 2 hr, filtering, washing with ultrapure water, and drying at 60 deg.C for 12 hr.

And (2) modifying melamine, namely roasting the sample at the temperature of 60-300 ℃ for 2 hours, dissolving 0.05-0.2 g of melamine in 50mL of ultrapure water, adding 0.3-0.5 g of the catalyst, reacting at the temperature of 50-80 ℃ for 12-48 hours, filtering, washing with ultrapure water, and drying at the temperature of 60 ℃. Roasting the catalyst for 1-6 hours at 400-700 ℃ under nitrogen; after cooling to room temperature, the mixture was calcined at 800 ℃ for 3 hours in air.

When the activity of the catalyst is considered, the CO oxidation reaction is taken as a probe reaction, and T is taken as₅₀The activities were compared as reference. T is₅₀Representing the corresponding reaction temperature at 50% CO conversion. The reaction device is a fixed bed micro-reactor. The composition of the reaction gas was 1 v% CO +1 v% O₂+98 v% He, space velocity SV of raw material gas 20L g_cat ^-1h^-1. The reaction raw material gas and the product gas were analyzed on-line by gas chromatography (Agilent6890N) equipped with a TDX-01 packed column.

TABLE 2 influence of the conditions on the catalyst activity during the modification of Melamine

Note: the theoretical amount of gold in the catalyst was 5 wt%

It can be seen from Table 2 that the catalyst pre-calcination temperature has a great influence on the activity of the catalyst, possibly due to the surface hydroxyl groups, and the calcination temperature is slightly higher. The catalyst activity was highest with a melamine to catalyst dosage ratio of 2: 3. The reaction temperature is increased to improve the reaction activity. The reaction time is too short and too long, which is not favorable for improving the reaction activity, and the effect is best in 24-36 hours. The improvement of the nitrogen roasting temperature and the proper prolongation of the roasting time are beneficial to improving the reaction activity, and the gold nano-particles and TiO are possibly and enhanced₂The interaction between the carriers is relevant.

Examples 39 to 41

3. Investigating the influence of the roasting temperature on the activity and the anti-sintering performance of the catalyst, and comparing the influence with other catalysts

Gold was loaded by precipitation (D-P method) by using 50mL of 1.5mg sodium hydroxide solution with a concentration of 0.5mol/L_AuThe pH of the solution was adjusted to 10 with/mL chloroauric acid, and 1.0g TiO was added₂Adding the carrier into the solution, reacting in 80 ℃ water bath for 2 hours, filtering, washing with ultrapure water, and drying at 60 ℃ for 12 hours.

Modifying melamine, namely roasting for 2 hours at 250 ℃ in air; 0.2g of melamine was dissolved in 50mL of water, and 0.3g of the above catalyst was added to react at 65 ℃ for 24 hours, followed by filtration, washing with ultrapure water, and drying at 60 ℃. Roasting the catalyst for 3 hours at 600 ℃ under nitrogen; then, the mixture was baked at 600, 700, and 800 ℃ for 3 hours in an air atmosphere.

In the experiment for investigating the influence of roasting temperature on the activity and anti-sintering property of catalyst, the activity of catalyst is measuredCO oxidation reaction is used as a probe reaction, and T is used as₅₀Comparison of the activities as reference, T₅₀Representing the corresponding reaction temperature at 50% CO conversion. The reaction device is a fixed bed micro-reactor. The composition of the reaction gas was 1 v% CO +1 v% O₂+98 v% He, space velocity SV of raw material gas 20L g_cat ^-1h^-1The reaction raw material gas and the product gas were analyzed on-line by gas chromatography (Agilent6890N) equipped with a TDX-01 packed column.

Table 3 explores the effect of calcination temperature on catalyst activity

Note: the theoretical amount of gold in the catalyst was 5 wt%

It can be seen from Table 3 that the activity of the catalyst after calcination at 800 ℃ is higher than that after calcination at 600 ℃. In example 39, the size of the gold nanoparticles in the particle size distribution was 8.3. + -. 2.1nm (FIG. 1). The gold nanoparticles of examples 40-41 had a particle size distribution of 7.5. + -. 1.3 nm. FIG. 2 shows the electron microscope results of example 41, in which a layer of TiO was formed on the surface of the gold particles after firing at 800 deg.C_xA shell layer, wherein the thickness of the shell layer is 0.75 + -0.13 nm, and the surface of the gold particle is exposed and no shell layer is generated after the gold particle is baked at 600 ℃ (FIG. 1). Meanwhile, a layer of TiO is also arranged on the surface of the gold particles after being roasted at 700 DEG C_xThe thickness of the shell layer is 0.52 +/-0.09 nm. It is due to this TiO_xThe existence of the thin layer enables the catalyst to have better activity and stronger anti-sintering performance. And unmodified Au/TiO₂The activity of the catalyst after roasting is extremely poor, and the result of an electron microscope shows that Au particles are seriously sintered and grown (figure 3). FIG. 3 example Au/TiO₂The grain diameter of gold nanoparticles in-800 is 32.6 +/-5.6 nm. Same standard gold catalyst Au/TiO₂The activity after baking of WGC was also very poor, indicating that the two catalysts had poor sintering resistance. The method provides a method for preparing a gold catalyst with high activity and sintering resistance by using a wrapping strategy.

Claims

1. A high activity sintering resistant gold catalyst characterized by:

the catalyst is a supported catalyst with gold as an active center, the carrier is titanium dioxide, and the gold is supported on the carrier TiO in a manner that the surface of gold nanoparticles is wrapped by a titanium oxide shell layer₂A surface of (a); the content range of the noble metal gold in the catalyst is 0.05-20.0 wt%;

the grain diameter distribution of the gold nano-particles is 5.2-9.0 nm, and the thickness range of the coating layer is 0.43-0.95 nm.

2. The gold catalyst of claim 1, wherein:

the content range of the noble metal gold in the catalyst is 3.0-5.0 wt%.

3. The gold catalyst of claim 1, wherein:

4. A method of preparing a gold catalyst according to claim 1 or 2, characterized in that:

gold was supported on a titania support using a precipitation method: 1) the concentration is 1.5-3 mg_AuAdjusting the pH of the/mL chloroauric acid solution to 9-10 by using an alkaline solution with the concentration of 0.3-0.5 mol/L, then adding a titanium dioxide carrier according to a required proportion, and then adding the titanium dioxide carrier at 80-90 DEG C^oC, reacting for 2-3 hours, filtering, washing, and 60-80%^oC, drying for 12-18 hours; 2) the modification process of melamine comprises the following steps: the catalyst prepared by the deposition precipitation method is 250-300%^oC, roasting for 1-3 hours in air; dissolving 0.05-0.2 g of melamine in 30-50 mL of water, adding 0.3-0.5 g of the catalyst in 65-80^oC, reacting for 24-48 hours, filtering, washing, and 60-80%^oC, drying for 12-18 hours;

the dried catalyst is 600-700 deg.C^oRoasting for 3-6 hours in a nitrogen atmosphere; cooling to room temperature and cooling to 700-800 deg.c^oAnd C, roasting for 2-4 hours in an oxygen-containing atmosphere.

5. The method of claim 4, wherein:

gold was supported on a titania support using a precipitation method: 1) the concentration is 1.5-1.8 mg_AuAdjusting the pH of the/mL chloroauric acid solution to 9.5-10 by using an alkaline solution with the concentration of 0.4-0.5 mol/L, then adding a titanium dioxide carrier according to a required proportion, and then adding the titanium dioxide carrier at 80-82^oC, reacting for 2-2.5 hours, filtering, washing, 60-80^oC, drying for 12-18 hours;

2) the modification process of melamine comprises the following steps: the catalyst prepared by the deposition precipitation method is 250-270%^oC, roasting for 2-2.5 hours in air; dissolving 0.1-0.2 g of melamine in 30-50 mL of water, adding 0.3-0.34 g of the catalyst in 65-68 g of water^oC, reacting for 24-30 hours, filtering, washing, and 60-80%^oC, drying for 12-18 hours;

the dried catalyst is 600-630%^oRoasting for 3-3.5 hours in a nitrogen atmosphere; cooling to room temperature at 780-800 deg.C^oAnd C, roasting for 3-3.2 hours in an air atmosphere.

6. The method of claim 4, wherein:

the alkaline solution is one or more than two of NaOH solution, KOH solution, ammonia water or ammonium bicarbonate solution.

7. Use of a gold catalyst according to claim 1 or 2, characterized in that: the use of any of the high activity sintering resistant gold catalysts of claims 1 or 2 in catalyzing CO oxidation reactions.

8. Use of a gold catalyst according to claim 7, characterized in that: the catalytic CO oxidation reaction device is a fixed bed microreactor, and the reaction gas comprises 1-5 v% of CO and 1-5 v% of O₂+ 10-98 v% He, and the space velocity SV = 20-40L g of the raw material gas_cat ^-1 h^-1The reaction temperature is 25-400 deg.C^oC。