CN111250077A

CN111250077A - Composite metal oxide catalyst and application thereof

Info

Publication number: CN111250077A
Application number: CN202010128279.7A
Authority: CN
Inventors: 邵珊珊; 项贤亮; 刘成跃; 李小华
Original assignee: Jiangsu University
Current assignee: Jiangsu University
Priority date: 2020-02-28
Filing date: 2020-02-28
Publication date: 2020-06-09

Abstract

The invention relates to the field of preparing liquid fuel and chemical products by catalytic conversion of biomass, and discloses preparation and application of a composite metal oxide catalyst. The catalyst prepared by the method has high selectivity and high yield for ketonization of various biomass pyrolysis products, is cheap and efficient, and is suitable for large-scale production.

Description

Composite metal oxide catalyst and application thereof

Technical Field

The invention relates to the field of liquid fuel and chemical products prepared by catalytic conversion of biomass, in particular to a composite metal oxide catalyst and application thereof.

Background

In the world, people are urgently required to find a sustainable alternative energy source against various problems of fossil fuel depletion and environmental protection. Biomass energy, an inexhaustible source of energy, has gradually entered the human vision and can be converted into various forms of energy and high-value chemicals. Therefore, the rapid development of biomass energy sources has very important significance for the progress of the human society and the maintenance of civilized forms.

At present, two ways of thermochemical conversion and biochemical conversion are mainly used for utilizing biomass energy at home and abroad. Among other things, thermochemical conversion can gasify biomass to bio-oil or other high value chemicals under certain conditions. Due to the variety of biomass sources and process levels, the bio-oil derived therefrom is a complex mixture of various oxygenates in widely varying amounts, typically including furans, sugars, acids, aldehydes, phenols and other lower oxygenates, that must be further upgraded to form usable fuels or chemicals.

In recent years, researchers aim at the field of biomass thermochemical conversion, and different catalysts are added in the pyrolysis process, so that biomass is converted in different directions. The biomass directional pyrolysis for preparing the ketone substance is more beneficial to research on the biomass pyrolysis gas ketonization part by researchers of high-quality fuel oil conversion parts, and the highest yield of the ketone substance is about 23.5 percent and is far lower than the content of the ketonizable substance. The biomass pyrolysis gas is not converted into ketone substances completely, and a part of the biomass pyrolysis gas is also converted into other substances.

In patent CN107603649A, a method for preparing ketone-rich bio-oil and magnesium-rich activated carbon is described, which mainly uses seawater to modify biomass, and then directly pyrolyzes to obtain ketone-rich bio-oil and magnesium-rich activated carbon, wherein metal element (magnesium) in seawater is used as a catalyst. However, magnesium as a catalyst for biomass ketonization is still not sufficient, mainly the conversion is still below the theoretical value. Therefore, it is important to prepare a suitable catalyst.

The biomass pyrolysis gas contains a large amount of acid substances, and can be firstly combined with a metal oxide catalyst to generate carboxylate in the ketonization process of the acid substances, so that the pore channel structure is easily blocked, and the catalyst is coked and deactivated.

Disclosure of Invention

In order to solve the above problems, the present invention aims to provide a preparation and application of a composite metal oxide catalyst. The technical scheme provided by the invention is as follows:

a composite metal oxide catalyst is prepared through introducing the suspension of template agent chosen from sodium alginate, nano cellulose fibres, carbon nanotubes and hydrotalcite into the mixture of cerium salt and manganese salt, freeze drying to obtain gel microbeads, calcining and oxidizing.

The templating agent material selected for the test forms a templating agent suspension when dissolved in water, which suspension is negatively charged at neutral pH. Metal salts form metal cations when dissolved in water.

After the two suspensions and the metal salt solution are mixed, metal cations are attracted by negative charges to exchange ions, and the metal cations and the template agent are crosslinked to form gel microbeads.

In this process, the metal cation intercalates into the templating agent and is electrostatically charged, thus being an intercalation self-assembly process.

Preferably, the specific preparation method is as follows:

(1) taking a certain amount of template agent, adding water to prepare template agent suspension with a certain concentration, wherein the concentration of the template agent is not higher than 2 wt%;

(2) taking a certain amount of cerium salt and manganese salt, and adding water to prepare a mixed solution containing the cerium salt and the manganese salt, wherein the molar ratio of cerium to manganese is 1: 9-9: 1, and the total molar concentration of cerium and manganese is 5-15%;

(3) introducing the template suspension into a mixed solution of cerium salt and manganese salt, wherein the volume ratio of the template suspension to the mixed solution containing the cerium salt and the manganese salt is as follows: (1-5) 1;

(4) heating and stirring for 0.5-3 h at the temperature of 60-80 ℃;

(5) freeze-drying the solution remained in the step (4) at the freezing temperature of-5 to-15 ℃ to form gel beads;

(6) calcining the gel microspheres at the temperature of 500-600 ℃ for 4-6 h;

(7) grinding the calcined product in the step (6) to obtain the composite metal oxide catalyst.

Preferably, in the step (1), the template is selected from sodium alginate and cellulose nanofiber, and the cerium salt is selected from cerium chloride and cerium nitrate hexahydrate; the manganese salt is selected from manganese chloride or manganese nitrate tetrahydrate; in the step (2), the molar ratio of cerium to manganese is 7: 3-5: 5.

Preferably, the mass fractions of the sodium alginate and the cellulose nano-fiber in the template agent in the step (1) are both 1.0 wt%, the molar ratio of cerium ions to manganese ions in the step (2) is 6:4, and the total molar concentration of cerium and manganese is 10%.

Preferably, the heating temperature in the step (4) is 60 ℃ and the heating time is 1 h.

Preferably, the calcination temperature in the step (6) is 550 ℃ and the calcination time is 5 h.

Preferably, the particle size of the catalyst after grinding in step (7) is 40 to 120 meshes.

Preferably, the catalyst is applied to the pyrolysis product for directionally catalyzing and preparing the ketone substances.

Preferably, the specific method applied is as follows:

(1) putting the catalyst into a reactor, sealing the reactor, and introducing inert gas or N into the reactor₂；

(2) Heating to 300-380 ℃ and keeping the temperature for 0.5-3 h;

(3) when the temperature reaches a stable temperature, injecting a pyrolysis product which is 1-10 times of the mass of the catalyst into a reactor;

(4) collecting the condensed liquid, centrifuging, and filtering.

Preferably, the heat preservation temperature of the step (2) is 350 ℃, and the heat preservation time is 1 h.

The pyrolysis product is pyrolysis gas in the biomass low-temperature fast pyrolysis product, and mainly comprises oxygen-containing micromolecule substances such as acid, alcohol, aldehyde, ester and the like.

Has the advantages that:

(1) the composite metal oxide catalyst prepared by the intercalation self-assembly method presents ordered nano-sheet shapeStructure, and thus greater specific surface area, than the pure metal oxide CeO₂And MnO₂The larger specific surface area is about 45-100 m²The amount of active sites exposed outside the catalyst is effectively increased.

(2) The catalyst has better shape-selective capacity of the pore channel, and the macromolecular compound reacts on the surface of the catalyst, so that the problem that the bond-breaking catalyst is easy to block and inactivate the pore channel is solved, and the catalytic efficiency is improved.

(3) The composite cerium dioxide and manganese oxide effectively improve the oxygen vacancy of cerium dioxide crystals, effectively improve the flow of catalyst lattice oxygen, promote the adsorption, activation and transfer of oxygen and improve the conversion rate of directional ketonization.

(4) The composite metal oxide is amphoteric oxide and has excellent performance in the field of directional ketonization.

(5) The nano sheet structure catalyst prepared by the intercalation self-assembly method can change the type of the used metal oxide and prepare the composite metal oxide catalyst, and can screen out the catalyst which shows the best performance in the ketonization field by changing the molar ratio of the composite metal oxide catalyst.

Drawings

FIG. 1 is a flow chart of the preparation of a composite metal oxide catalyst

FIG. 2 shows catalytic ketonization conversion and selectivity of catalysts prepared from cerium oxide and manganese oxide in different proportions in examples 3-11

FIG. 3 SEM image of the product catalyst of example 6

FIG. 4 TEM image of the product catalyst of example 6

Detailed Description

The following detailed description of the embodiments of the present invention is provided, but it should be noted that the scope of the present invention is not limited by the embodiments, but is defined by the appended claims.

The pyrolysis gas model used in the examples was acetic acid with a purity of AR grade, the catalyst used raw materials were cerium nitrate hexahydrate with a purity of 99.5%, manganese nitrate tetrahydrate with a purity of 98%, sodium alginate with a purity of AR grade, and other raw materials were purchased from shanghai alatin biochemical company. The cellulose nanofiber is prepared in a laboratory by adopting cellulose and concentrated sulfuric acid to react. Gas chromatography mass spectrometry, Perkinelmer, USA. Catalyst characterization was performed in a professional characterization facility.

Example 1:

the preparation method of this example includes the following steps:

the preparation of the oriented ketonization composite metal oxide catalyst comprises the following steps as shown in figure 1:

(1) weighing 1.0 wt% of sodium alginate and 1.0 wt% of cellulose nano-fiber, placing the sodium alginate and the cellulose nano-fiber into a beaker, pouring distilled water into the beaker, and preparing a carbohydrate suspension as a template material;

(2) weighing 50g of cerium chloride and manganese chloride, putting the cerium chloride and the manganese chloride into a beaker, adding 500mL of deionized water, stirring to completely dissolve the cerium chloride and the manganese chloride, and preparing a mixed solution of the cerium chloride and the manganese chloride, wherein the molar ratio of the cerium ions to the manganese ions is 9:1, and the total molar concentration of the cerium chloride and the manganese chloride is 10%;

(3) introducing the template suspension into a mixed solution of cerium chloride and manganese chloride by using a pipette, wherein the volume ratio of the template suspension to the mixed solution containing cerium and manganese ions is 1: 1;

(4) magnetically stirring for 0.5h at 50 ℃ in an oil bath pan to uniformly diffuse cerium ions and manganese ions to the carbohydrate skeleton, and removing excessive water in the solution;

(5) freeze-drying the rest solution at-5 deg.C, and observing with naked eye to form gel microsphere;

(6) putting the gel microspheres into a muffle furnace for calcination at 500 ℃ for 4h, removing a carbohydrate framework in an air atmosphere, and oxidizing cerium ions and manganese ions;

(7) grinding the calcined product to obtain the composite metal oxide catalyst. The particle size of the grinded catalyst is 40-120 meshes.

The application of the oriented ketonization composite metal oxide catalyst comprises the following steps:

(1) mixing 1gCeO₂-MnO₂Loading the catalyst in a reactor, sealing the reactor, and introducing N into the reactor₂。

(2) And opening the temperature control box, heating to 300 ℃, and keeping the temperature for 0.5 h.

(3) After waiting for the temperature to stabilize, 10g of the pyrolysis product molding was pumped into the reactor by means of a micro-feed pump.

(4) Collecting the condensed liquid, placing the condensed liquid into a centrifuge for centrifugal treatment, and then filtering the liquid by using a filtering needle.

(5) And carrying out GC/MS analysis on the treated liquid to obtain the conversion rate and the yield of the ketone substances.

Example 2:

the catalyst was prepared in the same manner as in example 1 except that in the step (3) of the catalyst preparation method, the volume ratio of the template suspension to the cerium-containing manganese ion mixed solution was changed to 5: 1; changing the oil bath temperature to 80 ℃ and the time to 3h in the step (4); the freezing temperature in the step (5) is-15 ℃; in the step (6), the calcining temperature is changed to 600 ℃, and the time is changed to 6 hours. Finally, black catalyst particles were obtained.

The catalyst was used as in example 1, except that the temperature was changed to 380 ℃ and the holding time was 3 hours. Finally obtaining colorless transparent aqueous liquid.

Example 3:

the catalyst was prepared in the same manner as in example 1 except that the volume ratio of the template suspension to the cerium-manganese ion-containing mixed solution was changed to 3:1 in step (3); in the step (4) of the preparation method of the catalyst, the oil bath temperature is 60 ℃, and the time is changed to 1 h; the freezing temperature in the step (5) is-10 ℃, the calcining temperature in the step (6) is changed to 550 ℃, and the time is changed to 5 hours. Finally, black catalyst particles were obtained.

The catalyst was used as in example 1, except that the temperature was changed to 350 ℃ and the holding time was 1 hour. Finally obtaining colorless transparent aqueous liquid.

Example 4:

the preparation method was the same as in example 3 except that the molar ratio of cerium ions to manganese ions in the prepared cerium chloride and manganese chloride solutions was changed to 8: 2, the application process of the catalyst is the same as that of example 3.

Example 5:

the preparation method was the same as in example 3 except that the molar ratio of cerium ions to manganese ions in the prepared cerium chloride and manganese chloride solutions was changed to 7:3, the application process of the catalyst is the same as that of example 3.

Example 6:

the preparation method was the same as in example 3 except that the molar ratio of cerium ions to manganese ions in the prepared cerium chloride and manganese chloride solutions was changed to 6:4, the application process of the catalyst is the same as that of example 3. SEM and TEM images of the catalyst are shown in fig. 3 and 4, respectively. It can be seen that the resulting catalyst exhibits an ordered nano-platelet structure.

Example 7:

the preparation method was the same as in example 3 except that the molar ratio of cerium ions to manganese ions in the prepared cerium chloride and manganese chloride solutions was changed to 5:5, the application process of the catalyst is the same as that of example 3.

Example 8:

the preparation method was the same as in example 3 except that the molar ratio of cerium ions to manganese ions in the prepared cerium chloride and manganese chloride solutions was changed to 4: the procedure for the use of the catalyst was the same as in example 3.

Example 9:

the preparation method was the same as in example 3 except that the molar ratio of cerium ions to manganese ions in the prepared cerium chloride and manganese chloride solutions was changed to 3: the procedure for the application of the catalyst was the same as in example 3.

Example 10:

the preparation method was the same as in example 3 except that the molar ratio of cerium ions to manganese ions in the prepared cerium chloride and manganese chloride solutions was changed to 2: the application procedure of the catalyst is the same as in example 3.

Example 11:

the preparation method was the same as in example 3 except that the molar ratio of cerium ions to manganese ions in the prepared cerium chloride and manganese chloride solutions was changed to 1: the procedure for the use of the catalyst was the same as in example 3.

The following GC/MS analysis of the liquids obtained in examples 3 to 11 showed the conversion rate and yield of ketones in FIG. 2. The catalysts obtained in examples 3, 4, 5, 6, 7, 8, 9, 10 and 11 were compared for their catalytic performance with respect to cerium and manganese.

As can be seen from fig. 2, compared with pure cerium oxide and pure manganese oxide, the conversion of the composite metal oxide catalyst is increased by 20% to 40% for the ketonization of the pyrolysis product model, wherein when the molar ratio is 6: peak 86.7% is reached at 4, so the optimum molar ratio of the two metals should be in the range of 7:3 and 5:5, or more. In addition, whether pure cerium oxide or pure manganese oxide or composite metal oxide catalysts with different molar ratios are used, the selectivity of the biomass pyrolysis product model to the conversion of the ketone substances is always maintained at a high level and is slightly increased. Therefore, the composite metal oxide catalyst can effectively improve the utilization rate of raw materials in the field of oriented ketonization of biomass pyrolysis products.

As shown in table 1, it can be seen from table 1 that the specific surface areas of the catalysts prepared in examples 3 to 11, pure cerium oxide and pure manganese oxide were measured by using a BET specific surface area analyzer, and the specific surface areas of the composite metal oxide catalysts with different molar ratios were significantly improved compared to the pure metal oxide catalysts, when the molar ratio was 6: and reaches a maximum value at 4. The improvement of the specific surface area effectively increases the number of the active sites exposed outside the catalyst, and improves the catalytic performance of the catalyst.

TABLE 1 specific surface area of composite metal oxides of different molar ratios

Example 12:

the preparation method of the catalyst is changed into a common coprecipitation method, which comprises the following steps:

the molar ratio of cerium chloride to manganese chloride is 6:4, the raw materials are dissolved in deionized water, a certain amount of NaOH solution is added to enable the raw materials to react fully, then the mixed solution is heated and stirred, the precipitate is obtained through centrifugation, the precipitate is dried and then calcined to prepare the non-layered composite metal oxide catalyst, then the catalyst obtained through the coprecipitation method is applied to biomass pyrolysis, the application method is the same as that of example 3, and the ketone yield is 58.4%.

Comparing example 6 with example 12, the yield of ketones using the catalyst obtained in example 6 was 86.7%, while the yield of ketones in example 12 was only 58.4%. In addition, the layered composite metal oxide catalyst prepared in example 6 did not generate a large amount of carbon deposition after the reaction, and showed good anti-coking properties, while the catalyst prepared in example 12 was severely deactivated.

Example 13

The catalyst was prepared in the same manner as in example 1 except that the cerium salt in the step (2) of the catalyst preparation method was selected from cerium nitrate hexahydrate, the manganese salt was selected from manganese nitrate tetrahydrate, and other conditions were not changed to finally obtain black catalyst particles.

The application procedure of the catalyst was the same as in example 1, and a colorless and transparent aqueous liquid was finally obtained.

Although the embodiments of the present invention have been described in detail with reference to the examples, it should be noted that the scope of the present invention is not limited by the embodiments, but is defined by the claims. Those skilled in the art can appropriately modify the embodiments without departing from the technical spirit and scope of the present invention, and the modified embodiments are also clearly included in the scope of the present invention.

Claims

1. A composite metal oxide catalyst is characterized by being prepared by introducing a template suspension into a mixed solution containing cerium salt and manganese salt, freeze-drying to form gel beads, and calcining and oxidizing to form the composite metal oxide catalyst, wherein the template is one or a mixture of more of sodium alginate, cellulose nano-fiber, carbon nano-tube and hydrotalcite.

2. The catalyst according to claim 1, characterized in that the specific preparation method is as follows:

(1) adding water into the template to prepare template suspension, wherein the concentration of the template is not higher than 2 wt%;

(2) adding water into cerium salt and manganese salt to prepare a mixed solution containing the cerium salt and the manganese salt, wherein the molar ratio of cerium to manganese is 1: 9-9: 1, and the total molar concentration of cerium and manganese is 5-15%;

(3) introducing the template suspension into a mixed solution of cerium salt and manganese salt, wherein the volume ratio of the template suspension to the mixed solution containing the cerium salt and the manganese salt is as follows: 1-5: 1;

(4) heating and stirring for 0.5-3 h at the temperature of 60-80 ℃;

(6) calcining the gel microspheres at the temperature of 500-600 ℃ for 4-6 h;

3. The catalyst according to claim 2, wherein the template agent in step (1) is selected from sodium alginate and cellulose nanofibers, and the cerium salt in step (2) is selected from cerium chloride, cerium nitrate hexahydrate; the manganese salt is selected from manganese chloride or manganese nitrate tetrahydrate; in the step (2), the molar ratio of cerium to manganese is 7: 3-5: 5.

4. The preparation method of claim 3, wherein the mass fractions of the sodium alginate and the cellulose nano-fiber in the template agent in step (1) are both 1.0 wt%, the molar ratio of cerium to manganese in step (2) is 6:4, and the total molar concentration of cerium and manganese is 10%.

5. The catalyst according to claim 2, wherein the heating temperature in step (4) is 60 ℃ and the heating time is 1 h.

6. The catalyst of claim 2, wherein the calcination temperature in step (6) is 550 ℃ and the calcination time is 5 hours.

7. The catalyst of claim 2, wherein the particle size of the catalyst after grinding in step (7) is 40-120 mesh.

8. The use of the composite metal oxide catalyst of claim 1, wherein the catalyst is used for the directional catalytic preparation of ketones from pyrolysis products.

9. The application according to claim 8, wherein the specific method is as follows:

(2) Heating to 300-380 ℃ and keeping the temperature for 0.5-3 h;

(4) collecting the condensed liquid, centrifuging, and filtering.

10. The use according to claim 9, wherein the incubation temperature of step (2) is 350 ℃ and the incubation time is 1 h.