阅读说明：本技术 甘油制二羟基丙酮用金基双金属/ZnO-CuO催化剂及其制备方法 (Gold-based bimetallic/ZnO-CuO catalyst for preparing dihydroxyacetone from glycerol and preparation method thereof ) 是由 李殿卿 赵更强 何俊玲 贺宇飞 冯俊婷 于 2019-12-13 设计创作，主要内容包括：本发明提供了一种甘油制二羟基丙酮用金基双金属/ZnO-CuO催化剂及其制备方法。本发明采用共沉淀法制备具有较多氧缺陷的ZnO-CuO复合氧化物,以其为载体,采用沉淀沉积法负载双金属活性组分,经焙烧得到金基双金属/锌铜复合氧化物催化剂,表示为Au-M/ZnO-CuO。其中Au的负载量为0.5～5％,M代表贵金属Pd、Pt、Ag中的任意一种；Au：M的摩尔比为2～50:1。该催化剂中双金属Au-M以合金化状态存在,两种金属间的协同作用使得应用时具有更高的活性。该催化剂在甘油选择性氧化成二羟基丙酮过程中,在无碱和温和的条件下,甘油转化率高于70％,收率在50～70％。(The invention provides a gold-based bimetallic/ZnO-CuO catalyst for preparing dihydroxyacetone from glycerol and a preparation method thereof. The invention adopts a coprecipitation method to prepare ZnO-CuO composite oxide with more oxygen defects, takes the ZnO-CuO composite oxide as a carrier, adopts a precipitation deposition method to load bimetal active components, and obtains a gold-based bimetal/zinc-copper composite oxide catalyst, which is expressed as Au-M/ZnO-CuO, through roasting. Wherein the loading amount of Au is 0.5-5%, and M represents any one of noble metals Pd, Pt and Ag; au: the molar ratio of M is 2-50: 1. The bimetal Au-M in the catalyst exists in an alloying state, and the synergistic effect of the two metals enables the catalyst to have higher activity in application. In the process of selectively oxidizing glycerol into dihydroxyacetone, the catalyst has the glycerol conversion rate higher than 70% and the yield of 50-70% under the alkali-free and mild conditions.)

1. A preparation method of a gold-based bimetallic/ZnO-CuO catalyst for preparing dihydroxyacetone from glycerol comprises the following specific steps:

A. adding soluble copper salt and zinc salt into deionized water according to the molar ratio of 1: 5-5: 1, and performing ultrasonic dissolution to obtain a mixed salt solution, wherein the concentration of the copper salt and the concentration of the zinc salt are 0.05-0.50 mol/L; the copper salt and the zinc salt are hydrochloride, nitrate or sulfate of copper and zinc;

B. dropwise adding the alkali solution into the mixed salt solution to completely precipitate, wherein the dropwise adding time is 30-90 min; stirring at the rotating speed of 500-1000 r/min for 5-20 h after the dripping; filtering, centrifugally washing the filter cake to be neutral, drying at the temperature of 50-120 ℃ for 10-20 h, grinding to be 0.0374-0.0750 mm, heating to 400-700 ℃ in a muffle furnace at the heating rate of 2-20 ℃/min, and roasting for 3-7 h to obtain a ZnO-CuO composite oxide; the alkali solution is sodium hydroxide or sodium carbonate solution, and the concentration of the alkali solution is 0.5-1.5 mol/l;

C. adding soluble Au salt and M salt into deionized water to prepare a mixed double-metal salt solution, wherein the ratio of Au: the molar ratio of M is 2-50: 1, and the concentration of Au is 20.00-50.00 mmol/L; m is any one of Pd, Pt and Ag salts; the Au salt is chloroauric acid or sodium chloroaurate; the M salt is one of chloropalladic acid, sodium chloropalladate, palladium nitrate, silver nitrate and chloroplatinic acid;

D. adding a ZnO-CuO carrier into the noble metal solution according to the loading amount of Au in the catalyst being 0.5-5%, fully stirring, adding a precipitator, keeping the molar ratio of the precipitator to the bimetal at the constant temperature of 80-120 ℃ for 4-12 h, and stirring at the rotating speed of 500-900 r/min; cooling, filtering, centrifugally washing to neutrality, and drying at 60-90 ℃ for 6-12 h; grinding to 0.037-0.075 mm, heating to 200-400 ℃ at a heating rate of 2-5 ℃/min in a muffle furnace, and roasting for 4-8 h to obtain Au-M/ZnO-CuO; the precipitator is one of sodium hydroxide, potassium hydroxide and urea.

2. The method of claim 1, wherein the mixed double metal salt solution of step C contains Au: the molar ratio of M is 5-20: 1; and M is Pd.

3. The gold-based bimetallic/ZnO-CuO catalyst for preparing dihydroxyacetone from glycerol, which is prepared by the method according to claim 1, is represented as Au-M/ZnO-CuO, wherein the loading amount of Au is 0.5-5%, and M represents any one of noble metals Pd, Pt and Ag; wherein the ratio of Au: the molar ratio of M is 2-50: 1; ZnO-CuO is a composite oxide, and the molar ratio of ZnO to CuO is 1: 5-5: 1.

4. The gold-based bimetallic/ZnO-CuO catalyst for preparing dihydroxyacetone from glycerol according to claim 3, wherein M is Pd; au in the catalyst: the molar ratio of M is 5-20: 1.

Technical Field

The invention belongs to the field of catalyst preparation, and provides a gold-based bimetallic/ZnO-CuO catalyst and a preparation method thereof.

Background

Fossil resources have the disadvantages of non-renewable, limited reserves, high price, environmental pollution and the like, and the fossil resources are seriously deficient along with the exploitation of a large amount of people, and biomass resources have the advantages of renewability, wide sources, low price, green economy and the like and accord with the current strategy of green sustainable development. In the process of producing biodiesel in recent years, glycerin, which is one of its by-products, is in large excess and cannot be fully utilized, and the price of glycerin is continuously reduced. Glycerol is an organic molecule with multiple functional groups that can undergo a series of reactions to yield a very large number of commercially valuable products such as alkanes, glyceraldehydes, dihydroxyacetone, lactic acid, 1, 3-propanediol, and the like. The dihydroxyacetone which is one of the products is used as a medical intermediate, chemical raw materials and additives have wide application, large market demand and high price, but the dihydroxyacetone has low production efficiency and can not meet the market demand. At present, the method for realizing industrialization still utilizes biological fermentation, but the fermentation technical conditions are harsh, the time consumption is long, the yield is low, the occupied field causes environmental pollution to the surroundings, and the like.

In recent years, noble metal catalysts are increasingly widely used, and the preparation of dihydroxyacetone by oxidizing glycerol by using oxygen or air as an oxygen source has the advantages of economy, environmental protection, short time consumption, high yield and the like, so that the realization of industrialization is urgent. The noble metal Pt has good oxidation effect on the hydroxyl of the glycerol, and the patent CN200810061624.9 discloses that the Pt/C catalyst can oxidize the glycerol to obtain dihydroxyacetone, the glycerol conversion rate can be 53.38 percent under the condition that the reaction temperature is 60 ℃ and the reaction time is 6 hours, and the weight yield of the dihydroxyacetone is only 3.42 percent by weight. Hu et al in Ind.Eng.chem.Res.2010,49, 10876-10882 report that doping Bi, Sb, etc. in Pt catalyst can improve the oxidation capability of secondary hydroxyl, and the Pt-Bi/C catalyst can obtain 80% of glycerol conversion rate and 48% of dihydroxyacetone selectivity under the condition of acid reaction temperature of 80 ℃. Patent CN201510817848.8 discloses a method for producing 1, 3-dihydroxyacetone by catalytic oxidation of glycerol with a supported gold catalyst (ZnO, copper aluminum hydrotalcite, spinel are used as carriers), which can achieve 94.8% dihydroxyacetone selectivity with Au/spinel under high pressure, but the glycerol conversion rate is only 21.6%. Therefore, the efficiency of preparing dihydroxyacetone by adopting a glycerol catalysis method still has a certain distance from the realization of industrialization, and the development of a new catalyst to improve the yield of dihydroxyacetone is still the key point of research.

In summary, the metal catalysis method is more in line with the strategy of long-term development than biological fermentation, but at present, the method has great difficulty in ensuring high glycerol conversion rate and high dihydroxyacetone selectivity, so that the yield of dihydroxyacetone is low and the condition of industrialization cannot be met, and the preparation of a novel catalyst for efficiently realizing the oxidation of glycerol to dihydroxyacetone has very important significance. Therefore, the invention provides a high-performance catalyst for preparing dihydroxyacetone by glycerol oxidation and a preparation method thereof.

Disclosure of Invention

The invention aims to provide a gold-based bimetallic/zinc-copper composite oxide catalyst for preparing dihydroxyacetone from glycerol and a preparation method thereof. The catalyst is used in the reaction of preparing dihydroxyacetone by the directional oxidation of glycerol.

The gold-based bimetallic/ZnO-CuO catalyst for preparing dihydroxyacetone by glycerol is represented as Au-M/ZnO-CuO, wherein the loading amount of Au is 0.5-5%, M represents any one of noble metals Pd, Pt and Ag, and preferably Pd; wherein the ratio of Au: the molar ratio of M is 2-50: 1, preferably 5-20: 1; ZnO-CuO is a composite oxide, and the molar ratio of ZnO to CuO is 1: 5-5: 1. The catalyst is used in the reaction of preparing dihydroxyacetone by glycerol directional oxidation, and the yield reaches 70 percent.

The preparation method of the catalyst comprises the following specific steps:

A. adding soluble copper salt and zinc salt into deionized water according to the molar ratio of 1: 5-5: 1, and performing ultrasonic dissolution to obtain a mixed salt solution, wherein the concentration of the copper salt and the concentration of the zinc salt are 0.05-0.50 mol/L; the copper salt and the zinc salt are hydrochloride, nitrate or sulfate of copper and zinc;

B. dropwise adding the alkali solution into the mixed salt solution to completely precipitate, wherein the dropwise adding time is 30-90 min; stirring at the rotating speed of 500-1000 r/min for 5-20 h after the dripping; filtering, centrifugally washing the filter cake to be neutral, drying at the temperature of 50-120 ℃ for 10-20 h, grinding to be 0.0374-0.0750 mm, heating to 400-700 ℃ in a muffle furnace at the heating rate of 2-20 ℃/min, and roasting for 3-7 h to obtain a ZnO-CuO composite oxide; the alkali solution is sodium hydroxide or sodium carbonate solution, and the concentration of the alkali solution is 0.5-1.5 mol/l;

C. adding soluble Au salt and M salt into deionized water to prepare a mixed double-metal salt solution, wherein the ratio of Au: the molar ratio of M is 2: 1-50: 1, and the concentration of Au is 20.00-50.00 mmol/L; preferred Au: the molar ratio of M is 5: 1-20: 1; m is any one of Pd, Pt and Ag salts, preferably Pd; the Au salt is chloroauric acid or sodium chloroaurate; the M salt is one of chloropalladic acid, sodium chloropalladate, palladium nitrate, silver nitrate and chloroplatinic acid;

D. adding a ZnO-CuO carrier into the noble metal solution according to the loading amount of Au in the catalyst being 0.5-5%, fully stirring, adding a precipitator, keeping the molar ratio of the precipitator to the bimetal at the constant temperature of 80-120 ℃ for 4-12 h, and stirring at the rotating speed of 500-900 r/min; cooling, filtering, centrifugally washing to neutrality, and drying at 60-90 ℃ for 6-12 h; grinding to 0.037-0.075 mm, heating to 200-400 ℃ at a heating rate of 2-5 ℃/min in a muffle furnace, and roasting for 4-8 h to obtain Au-M/ZnO-CuO; the precipitator is one of sodium hydroxide, potassium hydroxide and urea.

Fig. 1 is an X-ray diffraction (XRD) spectrum of the ZnO — CuO support in example 2, which maintains the crystal structures of ZnO and CuO.

FIG. 2 is a High Resolution Transmission Electron Microscope (HRTEM) photograph and an active component particle size distribution diagram of the catalyst prepared in example 2, from which it can be seen that the active component particles are uniformly distributed and the average size of the particle size is 3.08 nm.

Fig. 3 shows Raman (Raman) spectrum studies of ZnO — CuO and CuO in example 2 and a ZnO carrier, and it can be seen from fig. 3 that CuO and ZnO strongly interact in the composite oxide carrier, and the presence of Cu destroys the regular Zn — O bond structure in ZnO.

FIG. 4 is an X-ray photoelectron spectroscopy (XPS) chart of O1s showing that oxygen vacancy defects of the ZnO-CuO composite oxide prepared in example 2 are significantly increased, and it is confirmed that the defects are adsorption-activated sites of secondary hydroxyl groups of glycerol, and CuO and ZnO carriers.

FIG. 5 is an HAADF-STEM diagram of the Au-Pd/ZnO-CuO catalyst of example 2, from which HAADF images it can be seen that the active particles show Au and Pd elements, and the lattice stripes of the particles have a spacing of 0.233nm, which corresponds to the distance between the 0.218nm plane of Pd (111) and the 0.236nm plane of Au (111), demonstrating the formation of an alloy between AuPd bimetals.

The invention has the beneficial effects that:

the invention adopts a coprecipitation method to prepare ZnO-CuO composite oxide, and takes the ZnO-CuO composite oxide as a carrier to prepare the Au-M/ZnO-CuO catalyst by a precipitation deposition method, wherein the Au-M exists in an alloying state, and the construction of the bimetallic alloy can fully play the synergistic effect between two metals. The prepared composite oxide ZnO-CuO has strong interaction to generate more oxygen defects than ZnO and CuO carriers, and the defects are active sites for the directional oxidation of secondary hydroxyl of glycerol under the alkali-free condition. In the process of selectively oxidizing the glycerol into the dihydroxyacetone, the yield of the dihydroxyacetone can reach 70 percent. Compared with a single metal Au catalyst, the catalytic activity of the catalyst is improved by 3.54 times. The catalyst using the composite oxide ZnO-CuO as the carrier has the activity improved by 25.7 times and 6.87 times compared with the catalyst using single-component CuO and ZnO as the carrier. The catalyst provided by the invention is simple to prepare and operate, the preparation process is green and environment-friendly, the catalyst is convenient to recover after being used, and the atom economy is obviously improved compared with that of the catalyst reported in the existing patent.

Description of the drawings:

FIG. 1 is an X-ray diffraction (XRD) spectrum of a ZnO-CuO support in example 2.

Fig. 2 is two characteristic diagrams of the catalyst prepared in example 2, wherein a is a transmission electron micrograph of metal particles and b is a particle size distribution of an active component.

FIG. 3 shows Raman (Raman) spectra of ZnO-CuO, CuO and ZnO carriers in example 2.

FIG. 4 is X-ray photoelectron spectroscopy (XPS) graphs of ZnO-CuO and CuO in example 2 and a ZnO carrier O1s, in which a is an O1s XPS graph of CuO, b is an O1s XPS graph of ZnO, and c is an O1s XPS graph of ZnO-CuO.

FIG. 5 is a HAADF-STEM diagram of the Au-Pd/ZnO-CuO catalyst prepared in example 2.

The specific implementation mode is as follows: