CN112295565A

CN112295565A - Multi-metal-doped perovskite catalyst, preparation method thereof and application of catalyst in catalytic pyrolysis of coal tar

Info

Publication number: CN112295565A
Application number: CN202011189345.8A
Authority: CN
Inventors: 崔馨; 曹景沛; 吴桐; 杨锐
Original assignee: China University of Mining and Technology CUMT
Current assignee: China University of Mining and Technology CUMT
Priority date: 2020-10-30
Filing date: 2020-10-30
Publication date: 2021-02-02

Abstract

The invention provides a multi-metal doped perovskite catalyst, a preparation method thereof and application thereof in catalytic pyrolysis of coal tar, wherein the catalyst is prepared by mixing, pre-calcining and calcining precursor materials, and one or more of La, Ni and Fe is doped at A, B site of the perovskite structure of the catalystSeveral kinds of the catalyst can be applied to the catalytic removal of coal pyrolysis tar. The preparation method of the catalyst is in LaFeO₃On the basis, the Ni element is added to improve the catalytic activity, the synthesis path of the catalyst is improved through low-temperature pre-calcination, the phenomenon of expansion and ejection of the catalyst is reduced, and the carbon deposition condition of the catalyst is well reduced when the prepared catalyst is applied.

Description

Multi-metal-doped perovskite catalyst, preparation method thereof and application of catalyst in catalytic pyrolysis of coal tar

Technical Field

The invention belongs to the technical field of preparation and catalysis of perovskite type catalysts, and particularly relates to a multi-metal doped perovskite type catalyst, a preparation method of the multi-metal doped perovskite type catalyst and application of the multi-metal doped perovskite type catalyst in catalytic pyrolysis of coal tar.

Background

Coking coal is a resource which is relatively short worldwide, in recent years, the continuous development of the iron and steel industry leads the demand of the coking coal supply to rise year by year, and the increasing environmental pressure of the iron and steel industry leads the application prospect of the coking coal to cover the shadow. Depending on the production of the traditional blast furnace process, the steel industry with high energy consumption and high emission faces huge challenges, and the development of a novel process which can get rid of coke dependence and change the energy structure of the steel industry becomes a problem to be solved urgently, so that the technology of non-blast furnace iron making is different from the military prominence. Among them, smelting reduction is one of the leading technologies in the metallurgical industry as a branch of an important non-blast furnace technology. The development and application of the method are fundamental changes of the traditional blast furnace ironmaking process, so the method has received wide attention once being put forward. The process flow can directly react the iron ore with the coal in a molten state to reduce the iron ore into molten iron, so that the iron-making process does not need a large amount of coal coke to reduce the iron ore during feeding, can directly reduce the iron-making by only supplying the coal with certain quality standard, and solves the problem of shortage of production raw materials. In the three relatively representative (COREX, Finex and Hismelt) smelting reduction iron-making processes, the COREX is firstly realized for industrial production and is also the most mature process. The COREX-3000 smelting reduction iron-making furnace is introduced into Lujing in Shanghai province of 2007 for the first time, and the project is the first domestic and the largest COREX smelting reduction clean smelting system all over the world. In COREX production, a smelting reduction iron-making process is completed in two reactors, and an upper pre-reduction shaft furnace reduces iron ore into sponge iron with the metallization rate of 92% -93%; the melting gasification furnace at the lower part melts the sponge iron into molten iron and simultaneously generates reducing coal gas. Lump ore, sintered ore, pellets or a mixture of these raw materials are charged into the upper reduction shaft through a closed hopper system, where they are reduced by a counter-current reducing gas to Direct Reduced Iron (DRI) having a degree of metallization of about 93%. The screw discharger transports DRI from the reduction shaft furnace to the lower melter gasifier where coal fed from another feed port is combusted to produce reducing gas and char, which, in addition to other metallurgical and slag reactions, is finally reduced and melted. Tapping and tapping are then carried out as on a conventional blast furnace.

However, although the COREX process has many advantages such as environmental friendliness and low requirement for raw materials, it has several obvious disadvantages: the operation rate is lower than that of the high furnace; only lump coal can be used; the tar precipitation amount is large; severe adhesion phenomenon, etc. The large tar precipitation amount can cause the tar to block the pipeline in the production process, and is a large potential safety hazard which must be solved. Generally, tar can be removed from the reaction system by physical, non-catalytic (e.g., pyrolysis) and catalytic methods. From the economic and technical points of view, the tar removal can be carried out by selecting a catalytic method, and the selection of a proper catalyst is a key problem in the tar removal process. At present, the catalysts used in a large number mainly include natural ore catalysts, alkali metal catalysts, transition metal catalysts, perovskite catalysts, molten salt catalysts and the like. Due to the advantages of simple manufacture, low cost, definite structure, high thermal stability and the like, the perovskite catalyst is introduced into the catalytic process of coal pyrolysis tar in the melting gasification furnace. The perovskite catalyst can catalyze and crack coal tar generated in the COREX production process, effectively reduce the precipitation amount of the tar, and solve the actual problem that the tar blocks a pipeline in the production process.

CN109317143A discloses a noble metal perovskite type catalyst for catalytic combustion and a preparation method thereof. The chemical composition of the catalyst is A_xM_yB_zO_δ. Wherein M is one or more of noble metals Pt, Pd, Rh, Ir and Ag. The catalyst is prepared by a sol-gel method, and the size of the noble metal in the catalyst is between 0.1 and 2 nm after the catalyst is roasted at 800-1200 ℃ for 100 hours without loss. The catalyst of the invention can be usedThe catalyst is used for catalytic combustion of hydrocarbons such as methane, propane, propylene, aromatic hydrocarbon and the like, and has the characteristics of simple preparation method, high activity and good stability. The method is mainly focused on ABO₃The perovskite structure of (a) is doped with an active noble metal to improve the catalyst activity, but the cost of the method is too high, and the practical production is difficult.

CN106732647A discloses a perovskite type methane combustion catalyst, a preparation method and application thereof, wherein the catalyst comprises an active component and a carrier, and the general formula of the active component is A_1-xA'_xB_1-yB'_yO₃Wherein A is a rare earth metal element, A 'is an alkaline earth metal element, B and B' represent transition metal elements, and the carrier is delta-Al₂O₃、θ-Al₂O₃Or alpha-Al₂O₃The alumina carrier can improve the loading capacity of the active component on the carrier, is beneficial to the uniform dispersion of the active component, prevents the active component from sintering and agglomerating, prolongs the service life of the catalyst, and has good activity, and the reaction of methane and oxygen on CO₂The catalyst has the advantages of high selectivity, low ignition temperature, high combustion efficiency, good mass transfer and heat transfer performance and the like. The research constructs a perovskite/alumina supported catalyst, and the structure and the preparation process of the spherical carrier are complex.

In summary, in the existing perovskite catalyst preparation process, active noble metal is often selected to be doped, or perovskite is selected to be loaded on a carrier for catalytic reaction, which leads to the problems of high cost, complex synthesis process and the like. In addition, the research on the catalytic effect of the single in-situ doped perovskite structure is probably significant for researching the catalytic reaction mechanism of the catalyst.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a multi-metal doped perovskite type catalyst, a preparation method thereof and application thereof in catalytic pyrolysis of coal pyrolysis tar. Common alkali metals and alkaline earth metals, namely La, Ni and Fe are selected and doped into the perovskite structure, and the sol-gel method is adopted to synthesize the single crystalThe perovskite catalyst is directly applied to the cracking catalysis of coal pyrolysis tar in the industrial production process. The scheme has simple preparation steps and low cost of raw materials and production process, and the simple catalyst composition is more intuitive when researching the reaction principle. The obtained catalyst has obvious effect in the reaction of catalytic pyrolysis of coal tar, and greatly improves H₂、CO、CO₂The yield of the gas is equal, the yield of tar is reduced, and the carbon deposition on the catalyst is obviously improved compared with the common commercial catalyst.

In order to solve the technical problems, the invention provides the following technical scheme: a multi-metal doped perovskite catalyst wherein: a, B sites of the perovskite structure of the catalyst are doped with one or more of metals La, Ni and Fe, wherein the molar ratio of La, Ni and Fe is 1: (1-x): x and x are 0.1-1.

As another aspect of the present invention, the present invention provides a method for preparing a multi-metal doped perovskite-type catalyst, comprising the steps of: (1) adding citric acid and glycol into precursors of La, Ni and Fe, and carrying out ultrasonic oscillation and stirring; (2) adjusting the pH value to be neutral, heating, stirring and drying to obtain a catalyst xerogel; (3) and precalcining the catalyst xerogel, then calcining, and cooling to obtain the perovskite catalyst.

Preferably, in the step (1), in the precursor of La, Ni and Fe, the molar ratio of the sum of La, Ni and Fe to citric acid is 1: 1.2.

preferably, in the step (3), the pre-calcination is performed by raising the temperature to 175-370 ℃ for 10 min.

Preferably, in the step (3), the calcination is carried out by heating to 800 ℃ for 3.5 h.

Preferably, in step (1), the precursor of La, Ni, Fe includes iron, nickel, lanthanum, ferrous sulfate, ferric nitrate, nickel nitrate, lanthanum nitrate, La₂O₃One or more of them.

Preferably, in the step (2), the drying temperature is higher than 105 ℃.

As another aspect of the present invention, the present invention provides a use of a multi-metal doped perovskite-type catalyst for catalytic pyrolysis of coal tar.

Preferably, the catalytic temperature of the tar is 700 ℃.

The invention has the beneficial effects that:

the invention takes nitrate as a precursor, prepares the perovskite catalyst by a sol-gel method, reduces the phenomenon of expansion and ejection of the catalyst by precalcination at a lower temperature, and adopts LaFeO as a precursor₃On the basis of the method, the Ni element is added, so that the catalytic activity is improved, the carbon deposition condition of the catalyst is reduced, the improvement of the synthesis path of the catalyst is realized, and the prepared perovskite catalyst is applied to the catalytic removal of coal pyrolysis tar. Compared with the prior art, the invention has the advantages that:

1) the raw materials are simple and easy to obtain, and the cost is low. Nitrate which is easy to dissolve in water is selected as a precursor to prepare the perovskite catalyst, and metals corresponding to the nitrate are common La, Ni and Fe. Nowadays, many metal catalysts select to add noble metals such as Pt, Pb, Rh and the like as active sites, which can improve the activity of the catalyst, but also can cause the cost of the catalyst to be greatly increased, and the catalyst is not required to be put into industrial production in large quantity. Compared with these noble metal catalysts, perovskites are less expensive to prepare and are a good choice for large-scale industrial application of catalysts.

2) The preparation process is simple, the cost is low, and the industrial application in a larger scale is convenient to carry out. The preparation process only comprises simple mechanical mixing and stirring, heating and calcining steps. It can be prepared in large quantities at a time as long as a sufficient amount of the catalyst raw material is provided.

3) The invention improves the preparation process of the catalyst. A pre-calcination step is added before the high-temperature calcination operation at 800 ℃. This is due to the fact that a certain amount of citric acid monohydrate is required to be added as a complexing agent during the catalyst preparation process, however, during the calcination process, the citric acid rapidly expands and increases in volume, overflowing the calcination vessel, and causing unnecessary product loss. The citric acid volatilizes in a gaseous state at a lower precalcination temperature, and the problem of citric acid expansion can be effectively reduced by the newly added precalcination process.

4) The perovskite catalyst prepared by the method has a good catalytic effect on pyrolysis coal tar at the catalytic temperature of 700 ℃. The XRD results show that the prepared catalysts all show good perovskite structures. The tar is produced by the first layer of the para-fen coal pyrolyzed at 900 ℃, and the tar reacts with the second layer of the catalyst bed layer at 700 ℃ to produce micromolecular gas products. The lattice oxygen in the perovskite crystal structure has good oxygen carrying capacity and plays a catalytic role in the reaction process. Comparison of 30% Ni-loaded Al under identical experimental conditions₂O₃Commercial catalysts, perovskite catalysts with Ni doping ratios of 0.4, 0.6 and 0.8 had higher gas yields. At the same N₂In the presence of a carrier gas, the sum of the oxidation states being passed through H₂/N₂The perovskite catalyst in a reduction state pre-reduced for 1 h at the temperature of 600 ℃ in the atmosphere has different catalytic effects. By comparing the total gas yield (fig. 4), the perovskite in the oxidized state has better catalytic performance, wherein the catalyst with the Ni doping ratio of 0.8 has the best catalytic effect. The two states of the catalyst have different catalytic reaction pathways: at 600 ℃, the LaNiFe perovskite is partially reduced to form Ni-Fe alloy, and Ni-Fe/LaNi_xFe_yO_3-δThe structure of the carrier loaded with active metal has a catalytic function as shown in figure 3; the perovskite in the oxidation state can directly play a catalytic role, the effect is not trivial, and the pre-reduction step and certain energy are saved.

5) The LaNiFe perovskite catalyst prepared by the invention is compared with Al loaded with 30% Ni₂O₃Commercial catalysts are significantly more resistant to carbon deposition. In an oxidation state catalyst experiment, the carbon deposition mass of each doping ratio of the perovskite catalyst is smaller than that of a commercial catalyst, the catalyst is not easy to inactivate, the working period of the catalyst can be prolonged in large-scale industrial application, and the cost is saved.

Drawings

FIG. 1 is a diagram of a pyrolysis experimental apparatus;

FIG. 2 is an XRD result of perovskite catalyst of each doping ratio, anXRD contrast with reduced catalyst, where (a) Ni 0.2; (b) 0.4 of Ni; (c) 0.6 of Ni; (d) 0.8 of Ni; (e) oxidized LaFeO₃And reduced 18.5% Ni;

FIG. 3 is XRD results before and after oxidation-reduction of a perovskite catalyst with a doping ratio of Ni 0.8;

FIG. 4 is a graph comparing gas yields for various examples;

FIG. 5 is a comparison graph of carbon balances of various examples of oxidized (a) and reduced (b) catalysts;

FIG. 6 shows Ni/Al₂O₃Commercial catalyst (a) and LaFeO₃The perovskite catalyst (b) is compared before and after the reaction, and the left side of the graph is in the pre-reaction catalyst state, and the right side is in the post-reaction catalyst state.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

Example 1

A multi-metal doped perovskite catalyst for preparing 0.04 mol LaFeO₃A catalyst comprising, by mass: fe (NO)₃)₃ 16.16 g， La₂O₃6.52 g and citric acid monohydrate 20.17 g.

The preparation method comprises the following steps:

step 1, 16.16 g Fe (NO) is weighed out separately₃)₃，6.52 g La₂O₃Pouring 20.17 g of citric acid monohydrate into a beaker, adding a small amount of deionized water to dissolve the citric acid monohydrate, fully stirring to mix the citric acid monohydrate and the deionized water, then dropwise adding a small amount of glycol solution, and then placing the mixed solution into an ultrasonic oscillator to oscillate for 30 min to obtain a transparent mixed solution;

step 2, placing the mixed solution in a constant-temperature magnetic stirring instrument, stirring for 30 min at 40 ℃, taking out, adjusting the pH value of the solution to about 7 by using ammonia water, observing that the solution turns turbid from transparent to transparent, and then stirring for 30 min at 80 ℃;

step 3, putting the mixed solution into an electronic blast drying oven at 120 ℃ for drying all nightDrying, evaporating water to obtain semi-viscous dry catalyst gel, placing the dry gel in a horizontal tubular furnace, wrapping with tinfoil to prevent the catalyst from spraying out, heating to about 370 ℃ for preliminary preburning for 10 min, observing that citric acid volatilizes in a gas form, taking out the catalyst to obviously expand and turn into grey black, placing in a muffle furnace, heating to 800 ℃ for formal calcination for 3.5 h, taking out a sample after the time is up, and naturally cooling in the air to obtain the LaNiFeO₃A perovskite catalyst.

The prepared LaNiFeO₃The perovskite is used as a catalyst for catalytic removal of coal pyrolysis tar. The specific experimental setup is shown in fig. 1, and the steps are as follows: weighing 1 g of fenjie coal, placing in a storage ball, and weighing 5 cm³The catalyst is placed on a middle section distribution sealing plate of a quartz tube reactor with the length of 1m and the inner diameter of 46 mm, the tail end of the quartz tube is connected with three cold traps, 70 mL of deionized water is filled in each cold trap for collecting liquid tar products, the cold traps are soaked in a low-temperature environment, the outlet of each cold trap is connected with a wet-type flowmeter for recording the volume of gas collected in the reaction process, and the outlet of the flowmeter is connected with a gas bag for collecting gas products. In the pyrolysis experiment, 300 mL/min of nitrogen is used as carrier gas, and the pyrolysis mode is rapid pyrolysis. The pyrolysis furnace is controlled by three sections of temperature, after the pipeline connection is finished, the quartz tube is placed in the hearth, the furnace temperature of the upper section is set to be 900 ℃, the section is a pyrolysis section, the furnace temperature of the middle section is set to be 700 ℃, and the section is a catalysis section. And when the furnace temperature of the upper section reaches the set temperature, continuously feeding for 10 min by virtue of the storage balls on the side surfaces, and reacting for 15 min after the feeding is finished. The tar is produced by the first layer of the para-fen coal pyrolyzed at 900 ℃, and the tar reacts with the second layer of the catalyst bed layer at 700 ℃ to produce micromolecular gas products. The gas product carries tar into a cold trap, the tar is condensed and collected by deionized water in the cold trap, and the remaining gas is collected by an air bag at the tail end. The gas yield was approximately 24.08 mmol_gas/g_coal。

In the process of preparing the perovskite catalyst by a general sol-gel method, a certain amount of citric acid monohydrate is required to be added as a complexing agent, but the citric acid can rapidly expand at about 175 ℃ in the calcining process and overflow a calcining container, so that unnecessary product loss is caused. Therefore, the citric acid is expected to slowly volatilize in a gaseous form when the precalcination is carried out at a lower temperature, and the volume expansion of the catalyst can not occur when the formal calcination is carried out after the citric acid is completely volatilized. After the volatilization temperature of the citric acid is determined to be about 175 ℃, the catalyst is heated and calcined near the temperature section, the temperature is gradually increased, the optimal temperature for completely volatilizing the citric acid is found, and the pre-calcination process can be stopped after the citric acid is completely volatilized.

The perovskite is used as a catalyst with better thermal stability, the applied catalytic temperature is generally higher, but the promotion effect of the temperature on tar cracking under the high-temperature condition is also considered, so through a large number of experiments, the catalytic temperature effect is best when 700 ℃ is selected as the catalytic temperature in the experiment. In the present study, a KQ-500DE type digital ultrasonic cleaner manufactured by ultrasonic instruments ltd of kunshan was used. The power supply voltage is 220V, the capacity is 22.5L, the ultrasonic frequency is 40KHz, the ultrasonic input power is 500W, the total input power is 1300W, and 100% power is adopted during experiments. During the drying of the gel, which was originally employed at 105 ℃, the water content of the liquid mixture was evaporated to form a xerogel. However, after several experiments it was found that when the amount of catalyst is made larger, the drying time required at 105 ℃ is 18-24 hours, much longer than 12 hours. Therefore, the drying temperature is increased to reduce the drying time, but considering that the decomposition temperature of the nitrate precursor is generally not high, after the drying temperature is increased step by step in multiple attempts, the drying time is effectively reduced by 120 ℃, so that the efficiency is improved.

Example 2

Preparation of 0.04 mol LaNi of multi-metal doped perovskite catalyst_0.2Fe_0.8O₃A catalyst comprising, by mass: fe (NO)₃)₃•6H₂O 12.93 g，La₂O₃ 6.52 g，Ni(NO₃)₂•6H₂O2.33 g and citric acid monohydrate 20.17 g.

The preparation method comprises the following steps:

step 1, 12.93 g Fe (NO) are weighed out separately₃)₃•6H₂O，6.52 g La₂O₃，2.33 g Ni(NO₃)₂•6H₂O, pouring 20.17 g of citric acid monohydrate into a beaker, adding a small amount of deionized water to dissolve the citric acid monohydrate, fully stirring to mix the citric acid monohydrate and the deionized water, then dropwise adding a small amount of glycol solution, and then placing the mixed solution into an ultrasonic oscillator to oscillate for 30 min;

step 2, placing the mixed solution in a constant-temperature magnetic stirring instrument, stirring for 30 min at 40 ℃, taking out, adjusting the pH value of the solution to about 7 by using ammonia water, and stirring the solution for 30 min at 80 ℃;

and 3, placing the mixed solution in an electronic blast drying oven at 120 ℃ for drying overnight, evaporating water to obtain semi-viscous catalyst dried gel, placing the dried gel in a horizontal tubular furnace, heating to about 370 ℃ for preliminary presintering for 10 min, placing the dried gel in a muffle furnace, heating to 800 ℃ for formal calcination for 3.5 h, taking out a sample after the time is up, and naturally cooling in the air to obtain LaNi_0.2Fe_0.8O₃A perovskite catalyst.

The prepared LaNi_0.2Fe_0.8O₃The perovskite is used as a catalyst for catalytic removal of coal pyrolysis tar. The experimental setup and procedure were the same as in example 1. The gas yield was approximately 24.11 mmol_gas/g_coal。

Example 3

Preparation of 0.04 mol LaNi of multi-metal doped perovskite catalyst_0.4Fe_0.6O₃A catalyst comprising, by mass: fe (NO)₃)₃•6H₂O 9.70 g，La₂O₃ 6.52 g，Ni(NO₃)₂•6H₂O4.65 g and citric acid monohydrate 20.17 g.

The preparation method comprises the following steps:

step 1, respectively weighing 9.70 g Fe (NO)₃)₃•6H₂O，6.52 g La₂O₃，4.65 g Ni(NO₃)₂•6H₂O, 20.17 g citric acid monohydrate was poured into a beaker, dissolved by adding a small amount of deionized water, mixed by stirring thoroughly, and thenDropwise adding a small amount of glycol solution, and then placing the mixed solution into an ultrasonic oscillator to oscillate for 30 min;

and 3, placing the mixed solution in an electronic blast drying oven at 120 ℃ for drying overnight, evaporating water to obtain semi-viscous catalyst dried gel, placing the dried gel in a horizontal tubular furnace, heating to about 370 ℃ for preliminary presintering for 10 min, placing the dried gel in a muffle furnace, heating to 800 ℃ for formal calcination for 3.5 h, taking out a sample after the time is up, and naturally cooling in the air to obtain LaNi_0.4Fe_0.6O₃A perovskite catalyst.

The prepared LaNi_0.4Fe_0.6O₃The perovskite is used as a catalyst for catalytic removal of coal pyrolysis tar. The experimental setup and procedure were the same as in example 1. The gas yield was about 33.34 mmol_gas/g_coal。

Example 4

Preparation of 0.04 mol LaNi of multi-metal doped perovskite catalyst_0.6Fe_0.4O₃A catalyst comprising, by mass: fe (NO)₃)₃•9H₂O 6.46 g，La₂O₃ 6.52 g Ni(NO₃)₂•6H₂O6.98 g and citric acid monohydrate 20.17 g.

The preparation method comprises the following steps:

step 1, 6.46 g Fe (NO) is weighed out separately₃)₃•9H₂O，6.52 g La₂O₃，6.98 g Ni(NO₃)₂•6H₂O, pouring 20.17 g of citric acid monohydrate into a beaker, adding a small amount of deionized water to dissolve the citric acid monohydrate, fully stirring to mix the citric acid monohydrate and the deionized water, then dropwise adding a small amount of glycol solution, and then placing the mixed solution into an ultrasonic oscillator to oscillate for 30 min;

and 3, placing the mixed solution in an electronic blast drying oven at 120 ℃ for drying overnight, evaporating water to obtain semi-viscous catalyst dried gel, placing the dried gel in a horizontal tubular furnace, heating to about 370 ℃ for preliminary presintering for 10 min, placing the dried gel in a muffle furnace, heating to 800 ℃ for formal calcination for 3.5 h, taking out a sample after the time is up, and naturally cooling in the air to obtain LaNi_0.6Fe_0.4O₃A perovskite catalyst.

The prepared LaNi_0.6Fe_0.4O₃The perovskite is used as a catalyst for catalytic removal of coal pyrolysis tar. The experimental setup and procedure were the same as in example 1. The gas yield was about 33.37 mmol_gas/g_coal。

Example 5

Preparation of 0.04 mol LaNi of multi-metal doped perovskite catalyst_0.8Fe_0.2O₃A catalyst comprising, by mass: fe (NO)₃)₃•9H₂O 3.23 g，La₂O₃ 6.52 g，Ni(NO₃)₂•6H₂9.31 g of O and 20.17 g of citric acid monohydrate.

The preparation method comprises the following steps:

step 1, 3.23 g Fe (NO) was weighed out separately₃)₃•9H₂O，6.52 g La₂O₃，9.31 g Ni(NO₃)₂•6H₂O, pouring 20.17 g of citric acid monohydrate into a beaker, adding a small amount of deionized water to dissolve the citric acid monohydrate, fully stirring to mix the citric acid monohydrate and the deionized water, then dropwise adding a small amount of glycol solution, and then placing the mixed solution into an ultrasonic oscillator to oscillate for 30 min;

step 3, placing the mixed solution in an electronic forced air drying oven at 120 ℃ for drying overnight, evaporating water to obtain semi-viscous catalyst xerogel,putting the xerogel into a horizontal tubular furnace, heating to about 370 ℃ for preliminary presintering for 10 min, putting into a muffle furnace, heating to 800 ℃ for formal calcination for 3.5 h, taking out the sample after the time is up, and naturally cooling in the air to obtain LaNi_0.8Fe_0.2O₃A perovskite catalyst.

The prepared LaNi_0.8Fe_0.2O₃The perovskite is used as a catalyst for catalytic removal of coal pyrolysis tar. The experimental setup and procedure were the same as in example 1. The gas yield was about 34.84 mmol_gas/g_coal。

In the scope of the examples, LaNi prepared in example 5_0.8Fe_0.2O₃The perovskite catalyst has the best catalytic removal effect on coal pyrolysis tar. Under the action of the catalyst in the oxidized state, as can be seen from the gas yield of fig. 4, the catalytic effect of the catalyst gradually increases with the increase in the amount of Ni doping, with the best effect at a doping ratio of 0.8. Comparing the carbon equilibrium distribution of fig. 5a, the higher the Ni content in the catalyst, the lower the tar content in the product, and the carbon in the product is transferred to the gas. As can be seen from FIG. 6b, in LaFeO not doped with Ni₃In a perovskite catalysis experiment, the carbon deposition phenomenon of the catalyst is serious, and after the Ni element is doped, the carbon deposition phenomenon is improved due to the interaction of Ni and Fe.

Example 6

A pre-reduced multi-metal doped perovskite catalyst is prepared by preparing 0.04 mol LaNi_0.2Fe_0.8O₃A catalyst comprising, by mass: fe (NO)₃)₃•6H₂O 12.93 g，La₂O₃ 6.52 g，Ni(NO₃)₂•6H₂O2.33 g and citric acid monohydrate 20.17 g.

The preparation method comprises the following steps:

step 1, 12.93 g Fe (NO) are weighed out separately₃)₃•6H₂O，6.52 g La₂O₃，2.33 g Ni(NO₃)₂•6H₂O, 20.17 g citric acid monohydrate was poured into a beaker, dissolved by adding a small amount of deionized water, and stirred well to allow it to standMixing, then dropwise adding a small amount of glycol solution, and then placing the mixed solution in an ultrasonic oscillator to oscillate for 30 min;

The prepared LaNi_0.2Fe_0.8O₃The perovskite is pre-reduced and then used as a catalyst for catalytic removal of coal pyrolysis tar. The specific experimental setup is shown in fig. 1, and the steps are as follows: weighing 1 g of fenjie coal, placing in a storage ball, and weighing 5 cm³The catalyst is arranged on a cloth sealing plate at the middle section of the quartz tube reactor. The cold trap was filled with 70 mL of deionized water to collect the liquid tar product. The pyrolysis experiment used 300 mL/min of nitrogen as the carrier gas. After the pipeline connection is finished, the quartz tube is placed into a hearth of the pyrolysis furnace, a pre-reduction temperature rise program is set, and the furnace temperatures of the upper section and the middle section are set to be 600 ℃. After the furnace temperature reaches the set temperature, adding N₂The flow is adjusted to 60 mL/min, the flow of the hydrogen generator is adjusted to 60 mL/min, and H is opened₂And (4) a valve, starting the pre-reduction process and continuing for 1 h. After the pre-reduction is finished, H is closed₂Valve, regulation N₂The flow rate is 300 mL/min, the furnace temperature of the upper section is set to be 900 ℃, and the furnace temperature of the lower section of the middle section is set to be 700 ℃. And when the furnace temperature reaches the set temperature, starting continuous feeding through the material storage balls on the side surface for 10 min, and reacting for 15 min after the feeding is finished. The gas product carries tar into a cold trap, the tar is condensed and collected by deionized water in the cold trap, and the remaining gas is collected by an air bag at the tail end. The gas yield was about 23.8 mmol_gas/g_coal。

Example 7

A pre-reduced multi-metal doped perovskite catalyst is prepared by preparing 0.04 mol LaNi_0.4Fe_0.6O₃A catalyst comprising, by mass: fe (NO)₃)₃•6H₂O 9.70 g，La₂O₃ 6.52 g，Ni(NO₃)₂•6H₂O4.65 g and citric acid monohydrate 20.17 g.

The preparation method comprises the following steps:

step 1, respectively weighing 9.70 g Fe (NO)₃)₃•6H₂O，6.52 g La₂O₃，4.65 g Ni(NO₃)₂•6H₂O, pouring 20.17 g of citric acid monohydrate into a beaker, adding a small amount of deionized water to dissolve the citric acid monohydrate, fully stirring to mix the citric acid monohydrate and the deionized water, then dropwise adding a small amount of glycol solution, and then placing the mixed solution into an ultrasonic oscillator to oscillate for 30 min;

The prepared LaNi_0.4Fe_0.6O₃The perovskite is pre-reduced and then used as a catalyst for catalytic removal of coal pyrolysis tar. The experimental setup and procedure were the same as in example 6. The gas yield was about 30.83 mmol_gas/g_coal。

Example 8

A pre-reduced multi-metal doped perovskite catalyst is prepared by preparing 0.04 mol LaNi_0.6Fe_0.4O₃Catalyst comprisingThe components by mass: fe (NO)₃)₃•9H₂O 6.46 g，La₂O₃ 6.52 g Ni(NO₃)₂•6H₂O6.98 g and citric acid monohydrate 20.17 g.

The preparation method comprises the following steps:

The prepared LaNi_0.6Fe_0.4O₃The perovskite is pre-reduced and then used as a catalyst for catalytic removal of coal pyrolysis tar. The experimental setup and procedure were the same as in example 6. The gas yield was about 32.65 mmol_gas/g_coal。

Example 9

A pre-reduced multi-metal doped perovskite catalyst is prepared by preparing 0.04 mol LaNi_0.8Fe_0.2O₃A catalyst comprising, by mass: fe (NO)₃)₃•9H₂O 3.23 g，La₂O₃ 6.52 g，Ni(NO₃)₂•6H₂O9.31 g, citric acid monohydrate 20.17g。

The preparation method comprises the following steps:

and 3, placing the mixed solution in an electronic blast drying oven at 120 ℃ for drying overnight, evaporating water to obtain semi-viscous catalyst dried gel, placing the dried gel in a horizontal tubular furnace, heating to about 370 ℃ for preliminary presintering for 10 min, placing the dried gel in a muffle furnace, heating to 800 ℃ for formal calcination for 3.5 h, taking out a sample after the time is up, and naturally cooling in the air to obtain LaNi_0.8Fe_0.2O₃A perovskite catalyst.

The prepared LaNi_0.8Fe_0.2O₃The perovskite is pre-reduced and then used as a catalyst for catalytic removal of coal pyrolysis tar. The experimental setup and procedure were the same as in example 6. The gas yield was about 34.44 mmol_gas/g_coal。

Example 10

A pre-reduced multi-metal doped perovskite catalyst is prepared by preparing 0.02 mol of 18.5% Ni/LaFeO₃A catalyst comprising, by mass: fe (NO)₃)₃•6H₂O 8.08 g，La₂O₃ 3.26 g，Ni(NO₃)₂•6H₂O3.36 g and citric acid monohydrate 10.08 g.

The preparation method comprises the following steps:

step 1, weighing 8.08 g Fe (NO) respectively₃)₃，3.26 g La₂O₃10.08 g lemon monohydratePouring acid into a beaker, adding a small amount of deionized water to dissolve the acid, fully stirring the acid and the deionized water to mix the acid and the deionized water, then dropwise adding a small amount of glycol solution, and placing the mixed solution into an ultrasonic oscillator to oscillate for 30 min;

and 3, placing the mixed solution in an electronic forced air drying oven at 120 ℃ for drying overnight, evaporating water to obtain semi-viscous catalyst dried gel, placing the dried gel in a horizontal tubular furnace, heating to about 370 ℃ for preliminary presintering for 10 min, placing the dried gel in a muffle furnace, heating to 800 ℃ for formal calcination for 3.5 h, taking out a sample after the time is up, and naturally cooling in the air to obtain LaNiFeO₃A perovskite catalyst support.

Step 4, weigh 3.36 g Ni (NO)₃)₂•6H₂And mixing O and the perovskite carrier, placing the mixture in a beaker, adding deionized water to dissolve the mixture, uniformly stirring the mixture, and placing the mixture in an ultrasonic oscillator to perform ultrasonic oscillation for 30 min. Stirring for 12 hr in a magnetic stirrer, and drying the mixed solution in a 105 deg.C air-blast constant temperature drying oven until water is completely evaporated to obtain powder of 18.5% Ni/LaFeO prepared by wet impregnation method₃A catalyst.

The prepared 18.5 percent Ni/LaFeO₃The perovskite is pre-reduced and then used as a catalyst for catalytic removal of coal pyrolysis tar. The experimental setup and procedure were the same as in example 6. The gas yield was about 34.76 mmol_gas/g_coal。

As shown in fig. 2, the catalysts synthesized in each example have a pure perovskite structure. The intensity of the peak may reflect the crystallinity and grain size of the perovskite. With the increase of Ni doping ratio, the strength of the strongest characteristic peak at about 27 degrees in an XRD pattern is reduced to a certain degree, mainly by LaFeO₃The substitution of Fe for Ni in the structure, and the addition of a second B-site metal also influences LaFeO₃Original intact crystal structure and reduced crystallinity of perovskite. After reduction, some dominance in the XRD pattern of the perovskiteThe different XRD patterns between oxidized and reduced perovskites indicate that the reduction process destroys the pure perovskite structure, as the position of the characteristic peaks is shifted to lower angles, as well as the intensity of some peaks. La can be observed in the XRD patterns of all the reduced perovskites in FIGS. a-d₂O₃The doped Ni and Fe in the perovskite structure are converted into metal particles, such as Ni simple substance (panel b) and Ni-Fe alloy (panel c-e). These metal particles correspond to a characteristic peak at 42 DEG, and the reduction process can be seen to convert the original pure perovskite into an active metal supported perovskite (LaNi) with an uncertain doping ratio_1-xFe_xO₃）。

As shown in FIG. 4, LaFeO₃And the gas yield of the catalyst with the Ni doping ratio of 0.2 was 24mmol/g_coalAnd 24.1mmol/g_coalThis is the lowest of all the perovskite oxides, because of the lower Ni content in both catalysts. Ni/Al loaded with 20% Ni₂O₃Commercial catalyst ratio LaFeO₃And Ni 0.2 has a higher gas yield but a lower gas yield than Ni 0.4, Ni 0.6 and Ni 0.8 catalysts. The gas yield increased with increasing Ni content, and Ni 0.8 showed the highest gas yield, about 34.8 mmol/g_coal. According to the data shown in FIG. 4, higher Ni content can improve in-situ LaNi doping_1-xFe_xO₃Catalytic activity of the perovskite. Ni 0.8 in the oxidized state also shows the highest H₂Yield, 20.9 mmol/g_coalThis is almost 1.4 times that of commercial catalysts. Ni 0.8 in the oxidized state and commercial catalysts showed the highest carbon oxide yields, both exceeding 11 mmol/g_coal。Ni/Al₂O₃And the higher Ni content of Ni 0.8 can promote the decomposition of methane into H₂And results in less hydrocarbons (methane) in the gaseous product, while H₂More.

As further shown in FIG. 4, all reduced perovskite catalysts showed lower overall gas yields than their oxidation states, but H₂The yield is slightly improved compared with the prior art. H for reducing Ni 0.2₂Yield and CO yield increased by 14.2% and 13.5%, respectively. And alsoThe gas yield reduction of the original perovskite is mainly due to hydrocarbons and CO₂Reduced Ni 0.2 hydrocarbon yield by 52%, reduced Ni 0.8 and CO of commercial catalysts₂The yield is reduced by 92%. For commercial catalysts, CO can be reduced by carbon deposited on their surface₂To generate CO; for perovskite catalysts, LaNi_1-xFe_xO₃The perovskite can directly promote CO at higher temperature₂The reduction, gas yield results show that the in situ doped oxidation state Ni 0.8 catalyst has the best activity. Therefore, the effect of Ni addition on the activity of the perovskite catalyst was investigated by using an 18.5% Ni catalyst containing Ni in the catalytic reaction, which is the same as the Ni 0.8 catalyst. Reduced 18.5% Ni showed lower CO than reduced Ni 0.8₂Content and higher hydrocarbon content, but the severe carbon deposition of the 18.5% Ni catalyst still limits its useful life.

Comparative example 1

Purchased 30% Ni Al₂O₃Commercial catalysts, i.e. Ni/Al₂O₃A commercial catalyst. Large granular commercial catalysts were ground to a powder prior to the experiment.

Prepared Ni/Al₂O₃The catalyst is used for catalytic removal of coal pyrolysis tar. Weighing 1 g of fenjie coal, placing in a storage ball, and weighing 5 cm³The catalyst is placed on a distribution sealing plate at the middle section of a quartz tube reactor, the tail end of the quartz tube is connected with three cold traps, and each cold trap is filled with 70 mL of deionized water for collecting liquid tar products. In the pyrolysis experiment, 300 mL/min of nitrogen is used as carrier gas, and the pyrolysis mode is rapid pyrolysis. The pyrolysis furnace is controlled in three sections, the quartz tube is placed into the hearth after the pipeline connection is finished, the furnace temperature of the upper section is set to be 900 ℃, and the furnace temperature of the middle section is set to be 700 ℃. And when the furnace temperature of the upper section reaches the set temperature, continuously feeding for 10 min by virtue of the storage balls on the side surfaces, and reacting for 15 min after the feeding is finished. The tar is produced by the first layer of the para-fen coal pyrolyzed at 900 ℃, and the tar reacts with the second layer of the catalyst bed layer at 700 ℃ to produce micromolecular gas products. Gas product carrying tarAnd (4) entering a cold trap, condensing and collecting tar by deionized water in the cold trap, and collecting the residual gas by a tail gas bag. The gas yield was approximately 26.52 mmol_gas/g_coal。

Comparative examples of examples 1 to 5, Ni/Al used in comparative example 1₂O₃The catalytic effect of the commercial catalyst participating in the catalytic reaction in the oxidation state is better than that of a perovskite catalyst (LaFeO) with low Ni doping ratio₃And LaNi_0.2Fe_0.8O₃) (ii) a Perovskite catalyst (LaNi) with higher doping ratio than Ni_0.4Fe_0.6O₃，LaNi_0.6Fe_0.4O₃And LaNi_0.8Fe_0.2O₃) In contrast, the gas yield decreased more. The greatest disadvantage of this commercial catalyst is seen in the carbon balance results, which are associated with more severe catalyst carbon deposition problems than all perovskite catalysts, and with higher yields of liquid product tar. This is because Al is supported on₂O₃The Ni metal on the surface of the carrier can be agglomerated in the catalytic reaction process, so that tar or other carbon-containing products are deposited on the surface of the catalyst, and the activity of the catalyst is reduced.

Comparative example 2

Purchased 30% Ni Al₂O₃Commercial catalysts, i.e. Ni/Al₂O₃A commercial catalyst.

Large granular commercial catalysts were ground to a powder prior to the experiment.

Mixing Ni with Al₂O₃The catalyst is used for catalytic removal of coal pyrolysis tar after pre-reduction, and specifically refers to example 6. The gas yield was about 35.58 mmol_gas/g_coal。

As shown in FIG. 6, the commercial catalyst and LaFeO before the reaction₃The catalyst is gray and yellow respectively, and the color is obviously deepened after the reaction. This is due to carbon deposition on the catalyst surface during the reaction. According to the data of carbon distribution in the product, the carbon deposition phenomenon of the two catalysts is serious and can be directly observed through appearance. As example 6-implementationComparative example of example 10, Ni/Al used in comparative example 2₂O₃After the commercial catalyst is subjected to pre-reduction, the activity is greatly improved compared with the activity participating in the catalytic reaction in an oxidation state, the total gas yield is improved by about 34%, the tar yield is reduced, and the serious carbon deposition condition (figure 6 b) participating in the reaction in the oxidation state is also improved. Compared with other perovskite type catalysts subjected to pre-reduction, Ni/Al₂O₃Commercial catalyst and LaNi with best catalytic effect_0.8Fe_0.2O₃The gas yield of the catalyst was essentially equivalent. However, when the perovskite catalyst with each doping ratio compares the catalytic activity of the oxidation state and the reduction state, the catalytic activity is not obviously improved like that of a commercial catalyst after the pre-reduction treatment, and the gas yield is reduced to a certain extent. LaNi in the oxidized state_xFe_1-xO₃The perovskite catalyst has better catalytic effect, does not need pre-reduction treatment, has simpler working procedures and has more advantages when being applied to industrial production.

As shown in fig. 5 (a), Ni 0.8 in the oxidized state exhibited the best catalytic performance, with 23.5% of the carbon in the coal sample being converted to carbon-containing gas. The gas conversion of the commercial catalyst in the oxidized state reached 20.3%, but was still below 21.7% of that of the oxidized Ni 0.4 and Ni 0.6. According to the TOC results, about 0.3% of the carbon in the coal is converted to tar by the commercial catalyst. While the reaction product of Ni 0.8 had a tar content of 0.05%, which is the smallest of all oxidation state catalysts. About 13.8% of the carbon in the coal is converted to C over the commercial catalyst in the oxidized state_dep(including carbon deposits on the catalyst and on the reactor walls). The proportion of Cdep in the oxidized perovskite catalyst decreases with increasing Ni content. Carbon deposition in the oxidation state Ni 0.8 is the lightest, with Cdep being about 10.9%. And LaFeO in the oxidized state₃Most severe carbon deposition of C_depThe content was 17.2%. As shown in fig. 5 (b), the gas conversion of reduced Ni 0.8 was about 18.8%, while the gas conversion of the reduced commercial catalyst was reduced by 49.0% compared to its oxidation state. After reduction, the tar yield of the commercial catalyst decreased by 32.4%; but is reducedThe tar yield of Ni 0.8 of (2) was 3.6 times that of Ni 0.8 in the oxidized state. Reduced commercial catalyst C_depThe increase is 8.1%; reduced Ni 0.4, Ni 0.6 and Ni 0.8C_dep(about 15% -17%) increased by nearly 40% compared to the oxidation state. The gas conversion of the reduced 18.5% Ni catalyst was only 84% of the oxidation state Ni 0.8. And tar yield and C of the reduced 18.5% Ni catalyst_dep4.7 times and 1.3 times respectively the oxidation state Ni 0.8. The carbon distribution results show that Ni 0.8 in the oxidation state showed the highest gas yield, the lowest tar yield and the lowest C among all catalysts_dep。

Reduction Process for increasing H for Metal Supported catalysts (e.g., 20% Ni Supported commercial catalyst and 18.5% Ni catalyst)₂Production, reduction of tar yield and C_depAre advantageous. However, for in situ doped perovskite catalysts, the reduction process will reduce gas conversion and increase tar yield and C_dep. The above results indicate that pre-reduction is not a suitable method for improving in situ doping of perovskite catalysts.

The invention discloses a multi-metal doped perovskite catalyst and application of a preparation method thereof in catalytic pyrolysis of coal tar.A metal-doped nitrate is used as a precursor, the precursor is mixed by adopting a sol-gel method, different A, B-site metal ions are introduced into a perovskite structure, La is selected as an A-site metal, Fe is selected as a B-site metal, and LaFeO is prepared by the sol-gel method₃The perovskite catalyst is introduced with active metal Ni with different doping ratios at the B site to realize ABO₃Modification of perovskite catalyst and prepared LaNi_1-xFe_xO₃The catalyst is applied to the removal of tar products in the coal pyrolysis process. The invention utilizes the novel perovskite catalyst to catalyze and crack the coal tar generated in the blast furnace ironmaking process, and has simple preparation process and low cost. Different metal elements are introduced at the A, B th site to form a special perovskite crystal form, so that the catalyst has a good catalytic effect on the cracking and removal of coal tar, has good thermal stability, is easy to regenerate, and is beneficial to large-scale industrial application

It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.

Claims

1. A multi-metal doped perovskite catalyst characterized by: a, B sites of the perovskite structure of the catalyst are doped with one or more of metals La, Ni and Fe, wherein the molar ratio of La, Ni and Fe is 1: (1-x): x and x are 0.1-1.

2. A method of preparing a multi-metal doped perovskite catalyst as claimed in claim 1, characterized in that: comprises the following steps of (a) carrying out,

(1) adding citric acid and glycol into precursors of La, Ni and Fe, and carrying out ultrasonic oscillation and stirring;

(2) adjusting the pH value to be neutral, heating, stirring and drying to obtain a catalyst xerogel;

(3) and precalcining the catalyst xerogel, then calcining, and cooling to obtain the perovskite catalyst.

3. The method of preparing a multi-metal doped perovskite catalyst as claimed in claim 2, wherein: in the step (1), in the precursors of the metals La, Ni and Fe, the molar ratio of the sum of the molar quantities of the metals La, Ni and Fe to the citric acid is 1: 1.2.

4. the method of preparing a multi-metal doped perovskite catalyst as claimed in claim 2, wherein: in the step (3), the pre-calcination is performed by raising the temperature to 175-.

5. A process for the preparation of a multi-metal doped perovskite catalyst as claimed in any one of claims 2 to 4, wherein: in the step (3), the calcination is carried out by heating to 800 ℃ for 3.5 h.

6. A process for the preparation of a multi-metal doped perovskite catalyst as claimed in any one of claims 2 to 4, wherein: in the step (1), the precursors of the metals La, Ni and Fe include iron, nickel, lanthanum, ferrous sulfate, ferric nitrate, nickel nitrate, lanthanum nitrate and La₂O₃One or more of them.

7. A process for the preparation of a multi-metal doped perovskite catalyst as claimed in any one of claims 2 to 4, wherein: in the step (2), the drying temperature is higher than 105 ℃.

8. Use of the multi-metal doped perovskite catalyst of claim 1 for catalytic pyrolysis of coal pyrolysis tar.

9. Use of a multi-metal doped perovskite catalyst according to claim 8 for catalytic pyrolysis of coal tar, wherein: the catalytic temperature of the tar was 700 ℃.