CN110026199B

CN110026199B - Lanthanum oxycarbonate modified aluminum oxide loaded nickel-based catalyst and preparation method thereof

Info

Publication number: CN110026199B
Application number: CN201910260585.3A
Authority: CN
Inventors: 巩金龙; 李康; 曾亮
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2019-04-02
Filing date: 2019-04-02
Publication date: 2022-01-28
Anticipated expiration: 2039-04-02
Also published as: CN110026199A

Abstract

The invention belongs to the technical field of supported catalysts, and discloses an alumina-supported nickel-based catalyst modified by lanthanum oxycarbonate and a preparation method thereof₂O₂CO₃Modified Al₂O₃Is a carrier and is loaded with an active component Ni; the catalyst is prepared by adopting a step-by-step isometric impregnation method: firstly, Al is impregnated in Al by an equal volume impregnation method₂O₃Upper load La₂O₂CO₃Then in CO₂Is roasted in the atmosphere of (A) to obtain La₂O₂CO₃Modified Al₂O₃A carrier; then loading Ni precursor in CO by using an equal volume impregnation method₂Is roasted in the atmosphere of (A) to obtain La₂O₂CO₃Modified Ni/Al₂O₃A catalyst. The catalyst of the invention is suitable for the reaction of preparing synthesis gas by reforming methane, and proves that La is used for preparing synthesis gas₂O₂CO₃Can be prepared by adjusting Ni and Al₂O₃The mutual action between the two components improves the reduction capability of Ni, increases the reduction degree and the active surface area of Ni, and improves the catalytic activity and the stability.

Description

Lanthanum oxycarbonate modified aluminum oxide loaded nickel-based catalyst and preparation method thereof

Technical Field

The invention belongs to the technical field of supported catalysts, and particularly relates to an alumina-supported nickel-based catalyst modified by lanthanum oxycarbonate and a preparation method thereof.

Background

As one of fossil fuels (petroleum, coal, natural gas), natural gas has the advantages of abundant and clean reserves, and the exploitation amount of natural gas is gradually increasing along with the breakthrough of shale gas exploitation technology. Therefore, how to efficiently convert and utilize natural gas has become a hot spot of research. The technology of shale gas exploitation in 2014 in China makes an important breakthrough and becomes a successive additionAfter canada and the united states, the third country that uses autonomous technical equipment for shale gas exploitation signed a 30 year natural gas ordering agreement with russia in the same year. Therefore, the proportion of natural gas in energy consumption in China is gradually increased, however, the utilization of natural gas in China is still in a relatively original low-level stage at present, most natural gas resources are used as fossil fuels for direct combustion, and therefore, the research on the technology capable of efficiently utilizing natural gas has great significance for future energy supply in China. Because the main component of natural gas is methane, the use of natural gas is essentially methane. However, the methane molecule has a highly symmetric tetrahedral configuration, its structure is very stable, and the C — H bond energy is as high as 438.8kJ/mol, which makes it difficult to synthesize the target product directly from methane. Therefore, the industry mostly uses an indirect conversion method, i.e. methane is firstly converted into synthesis gas, and then the target product is synthesized by the synthesis gas. At present, the widely studied technology for preparing synthesis gas from methane mainly comprises: methane Steam Reforming (SRM), methane dry gas reforming (DRM), methane Autothermal Reforming (ARM), methane Partial Oxidation (POM), and the like. Among them, DRM receives a wide attention because it has the following advantages: one, DRM may be employed with a CO-containing solution₂The natural gas with impurities is used as a raw material to produce the synthesis gas, so that an expensive gas separation process is avoided, and the investment and operation cost of equipment is reduced; II, H in the product synthesis gas₂: the theoretical ratio of CO is 1, and the synthesis gas with the ratio can be used for Fischer-Tropsch synthesis and can more selectively synthesize long-chain hydrocarbon and carbonyl oxygen-containing derivative. However, DRM, as a catalytic reaction process, has a bottleneck limiting industrialization, i.e., lack of a catalyst with high activity and long-term stability.

At present, catalysts used for DRM reactions are generally supported catalysts, in which common active components include two types of precious metals (Rh, Pt, Rh) and base metals (Ni, Co). The noble metal catalyst has high catalytic activity, carbon deposition tolerance, corrosion resistance and oxidation resistance. However, from the viewpoint of large-scale industrial application, Ni-based catalysts are the most interesting catalysts due to their high activity and low price. However, on the Ni-based catalyst, carbon deposition and sintering easily occur, and especially, severe carbon deposition of the catalyst is a main reason for limiting its industrial application. Therefore, how to improve the stability of the Ni-based catalyst is a problem that needs to be solved urgently.

In addition to the active metals, the properties of the support also have a significant effect on the performance of the catalyst. Al (Al)₂O₃As a carrier commonly used in industrial supported catalysts, the catalyst has the advantages of large specific surface area, good thermal stability and the like. Al (Al)₂O₃The base catalysts have a wide range of applications, from petrochemistry to automotive exhaust treatment, in addition, Al₂O₃Are themselves common acid catalysts for alcohol dehydration reactions. Wherein, Al is used₂O₃Ni/Al as carrier₂O₃The catalyst has been widely studied in DRM, and has advantages of large specific surface area, strong interaction with metal carrier, high metal dispersion degree and high catalytic activity, but due to Al₂O₃Is an acidic carrier and cannot provide activated CO₂And thus, the catalyst is deactivated by the generation of a large amount of carbon during DRM. To increase Ni/Al₂O₃The carbon deposition inhibiting performance of the catalyst is generally realized by adding an alkaline auxiliary agent to improve the CO activation of the catalyst₂Which inhibits carbon deposition, La is a more common basic promoter.

La₂O₃Has very good carbon deposition inhibiting performance, but has the problem of smaller specific surface area, so that La is adopted₂O₃Supported on a carrier with large specific surface area to improve La₂O₃Specific surface area of (2). After investigation, it was found that₂O₃Above, La₂O₃Tends to form a monolayer dispersed structure, and at low loading, La₂O₃Preferentially occupy unsaturated coordinated Al sites, and gradually form a monolayer dispersed structure along with the increase of the loading amount. In addition, the addition of La stabilizes Al₂O₃And the inhibition of high-temperature sintering of the catalyst, such as the application of the catalyst in high-temperature catalytic combustion reaction, is also one of the reasons for the La serving as a component in a three-way catalyst for treating automobile exhaust. Therefore, we hope to put La₂O₃Loaded to Al in the form of single-layer dispersion₂O₃On a support to increase La₂O₃Specific surface area of (2) while La₂O₃May be further covered with Al₂O₃Acid sites on the surface, so that La can be exerted simultaneously₂O₃And Al₂O₃Their advantages are high effect on improving their advantages and low cost. Gong et al [ Efficient hydrogen production from ethylene glycol step reforming over La-modified ordered mesoporous Ni-based catalysts. applied Catalysis B: Environmental,2016,181,321-]La modified Ni/Al was intensively studied₂O₃The catalyst is used for ethanol steam reforming reaction, and the addition of La is found to improve Ni and Al₂O₃The mutual action between the two components improves the reduction capability of Ni, increases the active surface area of Ni, improves the catalytic activity, and simultaneously, the addition of La improves the alkalinity of the catalyst and promotes CO₂The carbon deposition is suppressed. However, the optimum amount of La added is much lower than the monolayer loading, and when the amount of La added is too large, the activity of the catalyst is significantly reduced. The reason for the analysis is that La₂O₃At single layer loadings, Ni particles can be coated, resulting in a reduction in catalyst activity. Garbarino et Al [ A study of Ni/La-Al₂O₃catalysts:A competitive system for CO₂methanation.Applied Catalysis B:Environmental,2018,65,178-192.]The study also found that La is present in a single layer₂O₃Modified Al₂O₃On the support, Ni is still formed_xAl₂O_3+x。

Disclosure of Invention

The invention aims to solve the problem that La is used₂O₃Modified Ni/Al₂O₃The technical problem that Ni is easily covered and is difficult to reduce during the catalyst process is provided, and the nickel-based catalyst loaded on alumina modified by lanthanum oxycarbonate and the preparation method thereof are provided, and the nickel-based catalyst is designed in CO₂So that the firing is covered with La₂O₂CO₃Rather than La₂O₃Thereby preventing Ni from entering Al during firing₂O₃OfSurface layer La₂O₃The coated catalyst can improve the stability and the catalytic activity.

In order to solve the technical problems, the invention is realized by the following technical scheme:

a lanthanum oxycarbonate modified aluminum oxide loaded nickel-based catalyst is prepared by uniformly dispersing Ni nanoparticles in La₂O₂CO₃Modified Al₂O₃The surface of the carrier, based on the total mass of the catalyst, of the La in the catalyst₂O₂CO₃The loading amount of the Ni nano-particles is 20-25 wt.%, and the loading amount of the Ni nano-particles is 1-10 wt.%.

Furthermore, the particle size of the Ni nano-particles is 7.5-10.4 nm.

Further, the La₂O₂CO₃Modified Al₂O₃La in the support₂O₂CO₃Is in CO₂And roasting the obtained product in an atmosphere.

Further, the catalyst is prepared by a step-by-step equal volume impregnation method.

A preparation method of the lanthanum oxycarbonate modified aluminum oxide supported nickel-based catalyst comprises the following steps:

(1) according to La₂O₂CO₃The supported amount of the lanthanum nitrate is 20-25 wt.%, lanthanum nitrate hexahydrate is dissolved in deionized water to obtain a precursor solution of lanthanum nitrate, and then the obtained precursor solution of lanthanum nitrate is impregnated into Al₂O₃The above step (1);

(2) drying the sample obtained in the step (1) to dryness, and then adding CO₂Roasting for 4-6 hours at the temperature of 600-700 ℃ in the atmosphere to obtain La₂O₂CO₃Modified Al₂O₃A carrier;

(3) according to the load capacity of the Ni nano particles being 1-10 wt.%, nickel nitrate hexahydrate is dissolved in deionized water to prepare a precursor solution of nickel; la obtained in the step (2)₂O₂CO₃Modified Al₂O₃Soaking the carrier in the nickel precursor solution in the same volume, drying the sample to be dry, grinding the sample in CO₂Is roasted at 600-700 ℃ for 4-6H, and then at the same reaction temperature as the roasting temperature and 10-20 vol.% of H₂/N₂And reducing for 1-2 h under the atmosphere to obtain the target catalyst.

The invention has the beneficial effects that:

the invention is prepared by mixing La₂O₂CO₃Loaded on Al₂O₃Surface of (1) so that Al₂O₃The acid sites on the surface are covered, so that the basic sites on the surface of the catalyst are increased, and CO is promoted₂The activation of the catalyst inhibits the generation of carbon deposition in the reaction process;

(II) the invention is characterized in that La is added₂O₂CO₃Loaded on Al₂O₃The surface of the catalyst increases the specific surface area of La, improves the dispersion of Ni, reduces the particle size of Ni, increases the active surface area of Ni and further improves the catalytic reaction activity;

(III) the invention is realized by mixing La₂O₂CO₃Loaded on Al₂O₃Surface of La is avoided₂O₃Loaded on Al₂O₃On the surface, Ni is introduced into Al₂O₃Is La₂O₃The occurrence of such an adverse phenomenon as coating;

(IV) preparation method of the invention to obtain La₂O₂CO₃Modified Al₂O₃The carrier is impregnated in Al by an equal volume method₂O₃Loading La precursor on the substrate, and then passing through the catalyst in the presence of CO₂Is calcined in the atmosphere of (A) to obtain La₂O₂CO₃Modified Al₂O₃And (3) a carrier.

In conclusion, the catalyst prepared by the invention can be applied to the process of preparing synthetic gas by reforming methane dry gas and the like which require CO₂The reaction system for activating and eliminating the carbon deposition in time has excellent catalytic performance and thermal stability and long service life.

Drawings

FIG. 1 is La prepared as in example 2₂O₂CO₃Modified Ni/Al₂O₃The reactivity of the catalyst;

FIG. 2 is La prepared in example 1 and example 4₂O₂CO₃Modified Ni/Al₂O₃TEM images of the catalyst;

wherein (a) is a TEM image of the catalyst prepared in example 1 and (b) is a TEM image of the catalyst prepared in example 4;

FIG. 3 is La prepared in example 5₂O₂CO₃Modified Ni/Al₂O₃The catalyst was characterized by Raman spectroscopy after calcination and reduction.

Detailed Description

The present invention is further described in detail below by way of specific examples, which will enable one skilled in the art to more fully understand the present invention, but which are not intended to limit the invention in any way.

Example 1

According to La₂O₂CO₃The supported amount of the lanthanum nitrate is 20 wt.%, lanthanum nitrate hexahydrate is dissolved in deionized water to obtain a precursor solution of lanthanum nitrate, and then the obtained precursor solution of lanthanum nitrate is impregnated into Al₂O₃Drying the obtained sample, and then in CO₂Is roasted for 4 hours at the temperature of 650 ℃ in the atmosphere of (1) to obtain La₂O₂CO₃Modified Al₂O₃A carrier;

(II) according to La₂O₂CO₃Modified Ni/Al₂O₃The Ni loading in the catalyst was 5.5 wt.%, nickel nitrate hexahydrate (Ni (NO) was taken₃)₂·6H₂O) is dissolved in deionized water to prepare Ni precursor solution, and the prepared La is₂O₂CO₃Modified Al₂O₃Soaking a carrier in Ni precursor solution in the same volume, drying a sample to be dry, grinding the sample in CO₂Is roasted at 650 ℃ for 5h, and then is roasted at the same temperature as the roasting temperatureReaction temperature and 10 vol.% H₂/N₂Reducing for 1.5h under the atmosphere to obtain the target catalyst.

Example 2

La by the method of example 1₂O₂CO₃Modified Ni/Al₂O₃Preparation of the catalyst, distinguished by La in (A)₂O₂CO₃Was 21 wt.%, and the sample was then placed in CO₂Roasting for 5 hours at 670 ℃ in the atmosphere of (A) to obtain La₂O₂CO₃Modified Al₂O₃And (3) a carrier. The loading amount of Ni in the second step is 1 wt.%, the roasting condition is that the roasting is carried out for 4 hours at 650 ℃, and the reduction condition is that 20 vol% of H₂/N₂And reducing for 2h under the atmosphere.

Example 3

La by the method of example 1₂O₂CO₃Modified Ni/Al₂O₃Preparation of the catalyst, distinguished by La in (A)₂O₂CO₃Was 22.5 wt.%, and the sample was then placed in CO₂Is roasted for 6 hours at the temperature of 600 ℃ in the atmosphere of (A) to obtain La₂O₂CO₃Modified Al₂O₃And (3) a carrier. The loading amount of Ni in the second step is 1 wt.%, the roasting condition is that the roasting is carried out for 4 hours at 600 ℃, and the reduction condition is that 20 vol% of H₂/N₂And reducing for 2h under the atmosphere.

Example 4

La by the method of example 1₂O₂CO₃Modified Ni/Al₂O₃Preparation of the catalyst, distinguished by La in (A)₂O₂CO₃Was 24 wt.%, and the sample was then placed in CO₂Is roasted for 5.5 hours at the temperature of 650 ℃ in the atmosphere of (1) to obtain La₂O₂CO₃Modified Al₂O₃And (3) a carrier. The loading amount of Ni in the second step is 3 wt.%, the roasting condition is that the roasting is carried out for 4H at 670 ℃, and the reduction condition is 15 vol% of H₂/N₂Reducing for 1h under the atmosphere.

Example 5

La by the method of example 1₂O₂CO₃Modified Ni/Al₂O₃Preparation of the catalyst, distinguished by La in (A)₂O₂CO₃Was 25 wt.%, and the sample was then placed in CO₂Is roasted for 5 hours at the temperature of 700 ℃ in the atmosphere of (A) to obtain La₂O₂CO₃Modified Al₂O₃And (3) a carrier. The loading amount of Ni in the second step is 10 wt.%, the roasting condition is that the roasting is carried out for 6H at 700 ℃, and the reduction condition is that the reduction condition is 15 vol% of H₂/N₂Reducing for 1h under the atmosphere.

Discussion of results and data with respect to the above examples:

la prepared in the above-mentioned examples 1 to 5 of the present invention₂O₂CO₃Modified Ni/Al₂O₃Catalyst-based detailed examination of La₂O₂CO₃The influence of the modification on the catalyst structure and the reaction performance.

(I) La₂O₂CO₃Modified Ni/Al₂O₃Reaction performance of catalyst

Tabletting catalyst sample powder to 20-40 meshes, loading the prepared catalyst sample into a fixed bed reactor, controlling the bed temperature of the reactor to be 650 ℃, and controlling the volume space velocity of methane to be 36,000 mL.h^-1·gcat^-1Reaction gas is introduced for reaction, wherein the molar ratio of methane to carbon dioxide is 1:1, and the balance gas is nitrogen.

Catalyst activity in terms of methane conversion, carbon dioxide conversion and H in product₂Expressed as/CO, methane conversion, carbon dioxide conversion and H in the product₂the/CO is calculated by the following formula:

Y_i＝X_i×S_i×1OO％

the results of the activity test of example 2 are shown in fig. 1. It can be seen that the catalyst has higher activity and selectivity and exhibits better stability. La prepared for the remaining examples₂O₂CO₃Modified Ni/Al₂O₃The catalyst is also subjected to the same activity test, and the result shows that all the catalysts have good activity and stability.

(II) La₂O₂CO₃Modified Ni/Al₂O₃Structural analysis of catalyst

La prepared in example 1 and example 4₂O₂CO₃Modified Ni/Al₂O₃The catalyst was characterized by transmission electron microscopy, and the results are shown in FIG. 2. It can be seen that the Ni particles are very uniformly dispersed on the mesoporous lanthana support. And the particle size range of Ni is concentrated in 7.5-10.4 nm.

In order to analyze the presence of Ni on the catalyst, the catalyst prepared in example 5 was characterized by Raman spectroscopy after calcination and reduction, and the results are shown in fig. 3. It can be observed that for 5Ni/Al₂O₃Catalyst, after calcination, Ni is present in two forms: lattice Ni^[135](into Al)₂O₃Subsurface Ni) and NiAl₂O₄ ^[4,137]. After reduction, the Lattice Ni is reduced to metallic Ni, NiAl₂O₄It is difficult to be reduced. For 5Ni/La₂O₃-Al₂O₃Catalyst in the calcination ofThereafter, Ni exists in three forms: NiO^[138]Lattic Ni and NiAl₂O₄. Comparing the catalysts after reduction, it can be found that only NiO is reduced during the reduction process, and Lattice Ni and NiAl₂O₄Are difficult to reduce. In contrast, for 5Ni/La₂O₂CO₃-Al₂O₃The catalyst, after calcination, has Ni present predominantly as NiO, which is reduced to metallic Ni during the reduction process. This is consistent with our previous characterization analysis, i.e., for 5Ni/La₂O₃-Al₂O₃The catalyst has a great amount of Ni entering Al in the roasting process₂O₃In the crystal lattice to result in La being a monolayer₂O₃Coated to be difficult to be reduced, and for 5Ni/La₂O₂CO₃-Al₂O₃Catalyst, La₂O₂CO₃Can prevent Ni from entering Al₂O₃The subsurface layer of (2) prevents Ni from being coated, thereby improving the reduction degree of Ni.

Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are merely illustrative and not restrictive, and those skilled in the art can make various changes and modifications within the spirit and scope of the present invention without departing from the spirit and scope of the appended claims.

Claims

1. The lanthanum oxycarbonate modified aluminum oxide supported nickel-based catalyst is characterized in that Ni nanoparticles are uniformly dispersed in La₂O₂CO₃Modified Al₂O₃A carrier surface; based on the total mass of the catalyst, the La in the catalyst₂O₂CO₃The loading amount of the Ni nanoparticles is 20-25 wt.%, and the loading amount of the Ni nanoparticles is 1-10 wt.%; and is obtained by the following preparation process:

(1) push buttonShine La₂O₂CO₃The supported amount of the lanthanum nitrate is 20-25 wt.%, lanthanum nitrate hexahydrate is dissolved in deionized water to obtain a precursor solution of lanthanum nitrate, and then the obtained precursor solution of lanthanum nitrate is impregnated into Al₂O₃The above step (1);

2. The lanthanum oxycarbonate modified alumina supported nickel-based catalyst of claim 1, wherein the Ni nanoparticles have a particle size of 7.5-10.4 nm.

3. A method for preparing a lanthanum oxycarbonate modified alumina supported nickel-based catalyst according to any of claims 1-2, characterized in that it is carried out according to the following steps: