CN115178254B

CN115178254B - Non-toxic, high-activity and high-stability rare earth base NH 3 SCR catalyst and preparation technology thereof

Info

Publication number: CN115178254B
Application number: CN202211022705.4A
Authority: CN
Inventors: 李渊; 王旭超
Original assignee: Tianjin Polytechnic University
Current assignee: Tianjin Polytechnic University
Priority date: 2022-08-26
Filing date: 2022-08-26
Publication date: 2024-03-19
Anticipated expiration: 2042-08-26
Also published as: CN115178254A

Abstract

The invention provides a non-toxic, high-activity and high-stability rare earth based ammonia-selective catalytic reduction (NH 3-SCR) catalyst and a preparation method thereof, belonging to rare earth based NH ₃ -technical field of SCR catalytic materials. The invention aims to provide rare earth based NH which is environment-friendly and has better denitration performance ₃ -SCR catalyst and method of preparing the same. The method comprises the following specific steps: reacting zirconium salt solution with inorganic acid or inorganic acid salt solution at a certain temperature, regulating pH value with alkaline solution, adding transition metal salt solution containing cerium salt, regulating pH value with alkaline solution, maintaining temperature at a certain temperature, stirring for a period of time, vacuum filtering, drying, and calcining to obtain rare earth base NH ₃ -an SCR catalyst. Rare earth based NH obtained by the present invention ₃ SCR catalyst, when the air speed is higher than or equal to 220000h ^‑1 When the catalyst is used, the conversion rate of NO of the catalyst is more than 90% in the temperature range of 290-530 ℃.

Description

Non-toxic, high-activity and high-stability rare earth base NH 3 SCR catalyst and preparation technology thereof

Technical Field

The present invention relates to rare earth based ammonia-selective catalytic reduction (NH) ₃ -SCR) catalytic material, in particular to a cerium-zirconium-based NH ₃ -SCR denitration catalyst and preparation thereof.

Background

In recent years, economy and science and technology have been rapidly developed, but environmental pollution problems are coming to the end, and environmental problems have become a focus of attention. The air pollution is prominent in the environmental pollution, and nitrogen oxides (NO _X ) Is one of main pollutants of air pollution, and NO _X Is also one of the important influencing factors for acid rain, photochemical smog and greenhouse effect, so the NO _X Is a serious test. NH has been ₃ SCR technology is globally recognized for NO removal _X The most efficient method, NH ₃ The SCR denitration technology is to use NH ₃ As a reducing agent, NOx is reduced to N under the action of a catalyst ₂ 。

At present, the denitration catalyst mainly comprises four major types of noble metal catalysts, molecular sieve catalysts, bifunctional catalysts and metal oxide catalysts, wherein the vanadium-based catalysts in the metal oxide catalysts have better activity in denitration catalysis, and the application in industry is wider. But due to the narrower temperature window of the vanadium-based catalyst, poor N at high temperature ₂ The selectivity, the volatility and the toxicity of vanadium have not been able to meet the requirements of increasingly strict emission regulations, and therefore, novel non-vanadium-based NH with high activity, no toxicity and high stability has been developed ₃ SCR catalysts are of great importance. Such as Mn-based catalysts, fe-based catalysts, and Ce-based catalysts, in which CeO ₂ The catalyst has large storage capacity, excellent oxygen storage capacity and oxidation-reduction property, and is widely applied to the field of environmental catalysis. But pure CeO ₂ NH of (C) ₃ SCR activity is low, so that other metal and mineral acid solutions are usually introduced to improve the pure CeO ₂ NH of (C) ₃ -SCR activity. Yi et al (Yi T, zhang Y, li J, et al, programme effect of H) ₃ P-O ₄ on ceria catalyst for selective catalytic reduction of NO by NH ₃ [J]Chinese Journal of Catalysis,2016, 37 (2): 300-307.) to find phosphorylated CeO ₂ Catalyst vs. unphosphorylated CeO ₂ The catalyst has better NH ₃ SCR activity, the phosphoric acid is believed to increase its acid strength and thus its NH ₃ -SCR activity. Han et al (Han Z, li X, wang X, et al Insight into the promoting effect of support pretrea tment with sulfate acid on selective catalytic reduction performance of CeO) ₂ /ZrO ₂ catalysts[J]Journal of Colloid and Interface Scienee,2022, 608: 2718-2729.) ZrO by sulfuric acid treatment ₂ CeO preparation by carrier ₂ /ZrO ₂ The catalyst has good NH ₃ SCR Activity, han et al used several common mineral acids (HCl, HNO) ₃ ，H ₃ PO ₄ ，H ₂ SO ₄ ) To treat ZrO ₂ The carrier, the result shows that H is used ₂ SO ₄ Treated CeO ₂ /ZrO ₂ The catalyst has the bestNH of (C) ₃ -SCR activity. In patent (Zhou Shemin et al, application publication No. CN 103638939A) a cerium sulfate as the catalyst active component was disclosed, and it was found that a certain catalytic activity was also exhibited as a soluble sulfate, but the activity was not high. In patent (Yu Lin et al, application publication No. CN 110548503A), in order to improve the catalytic activity of cerium-based catalysts, manganese oxide is introduced, and vanadium oxide is used as an active component, and although the low-temperature catalytic activity of the catalyst is improved and the temperature window is widened, the volatility and toxicity of vanadium cannot meet the requirements of increasingly strict emission regulations, so that the application in practical denitration is limited. Although many researches are carried out on rare earth based denitration catalysts by the former, the existing rare earth based denitration catalysts are not completely free from the use of metal vanadium, or are low in activity and poor in stability, and cannot meet the requirements of industrial use, so that the existing rare earth based denitration catalysts are less applied to industrial denitration. The invention provides a rare earth-based denitration catalyst with no toxicity, high activity and high stability and a preparation technology thereof, and has a good application prospect.

The invention provides an environment-friendly rare earth-based catalyst with better denitration performance and a preparation method thereof, wherein the rare earth-based catalyst is prepared by using NH ₃ In the SCR reaction, when the air speed is higher than or equal to 220000h ^-1 When the NO conversion rate is over 90 percent in the temperature range of 290-530 ℃, the specific surface area is not less than 131m ² Per gram, pore volume is not less than 0.34cm ³ And/g, the pore diameter range is 3-20 nm.

Disclosure of Invention

The invention aims to provide rare earth based NH which is environment-friendly and has better denitration performance ₃ SCR catalyst, method for its production, NH ₃ There is still better catalytic activity and heat resistance in the SCR reaction. The invention has reasonable design and is simple and easy to implement.

The present invention relates to a composite comprising cerium, zirconium and a mixture of transition metal elements other than cerium.

The rare earth group NH of the invention ₃ The preparation method of the SCR catalyst comprises the following steps:

(1) Preparing a salt solution containing cerium, zirconium and transition metal elements other than cerium, wherein the concentration of cerium oxide is 5.0wt% to 60.0wt%, the concentration of zirconium oxide is 5.0wt% to 90.0wt%, the concentration of transition metal element oxide other than cerium is 1wt% to 20wt%, and the concentration of inorganic acid radical is 0.5wt% to 10.0wt%;

(2) Mixing the zirconium salt solution prepared in the step (1) with inorganic acid in quantitative deionized water;

(3) Heating the mixed solution in the step (2) to more than 40 ℃ under the stirring state, and after stabilizing for a period of time, regulating the pH value of the mixed solution by using an alkaline solution to ensure that the pH value of the mixed solution is more than 5.0;

(4) Adding the cerium salt solution and the transition metal salt solution except cerium into the solution obtained in the step (3), stirring the mixture while adding, regulating the pH value to be neutral or alkaline by using an alkali solution after stirring the mixture for a period of time, slowly dropwise adding the mixture, and stirring the mixture while adding;

(5) The solution prepared in the step (4) is stirred for a certain time in a heat preservation way and then filtered to obtain rare earth based NH ₃ -SCR catalyst precursor:

(6) Drying and roasting the precursor prepared in the step (5).

The cerium salt solution in the step (1) may be one or a mixture of several kinds of soluble cerium salts such as cerium nitrate, cerous nitrate, cerium chloride, cerium sulfate and the like, and the zirconium salt solution may be one or a mixture of several kinds of soluble zirconium salts such as zirconium nitrate, zirconium oxychloride, zirconium nitrate, zirconium sulfate, zirconium phosphate, zirconium oxide and the like, wherein the salt solution contains the oxide concentration of 0.1-50 wt%.

The mass ratio of the zirconium salt solution (calculated by weight of oxide) to the inorganic acid (calculated by 100%) in the step (2) is 1:0.2-1, and the inorganic acid solution is one or a mixture of two of sulfuric acid and phosphoric acid.

The alkaline solution in the step (3) is ammonia water, hydroxide of alkali metal or alkaline earth metal and anions which can form precipitation with zirconium ions, cerium ions and other doped transition metal ions, such as one or more of carbonate or bicarbonate; the pH value range adjustment can be carried out in a segmented way, for example, the pH value is adjusted to be 2-3, and the pH value is adjusted to be more than 5 after a period of reaction.

The salt solution of cerium and the transition metal element other than cerium in the above step (4) may be added at one time or may be added in steps or in divided portions, and the pH value is in the range of 7 to 14, preferably 8 to 9.

The heat-insulating temperature in the step (5) is 50-100 ℃, preferably 50-70 ℃.

The roasting temperature in the step (6) is 400-600 ℃, the temperature is programmed to be 400-600 ℃, the heating rate is preferably 2 ℃/min, and the roasting time is 0.5-12h, preferably 3-6h.

The invention has the advantages of easily obtained raw materials, simple preparation process, easily controlled experimental conditions, no harm to the environment and environmental protection, and is an environment-friendly rare earth based NH ₃ -SCR catalyst and has better denitration performance.

The invention provides a rare earth based NH ₃ The preparation method of the SCR denitration catalyst has scientific and reasonable design, is simple and easy to operate, and prepares NH through the invention ₃ SCR catalyst with better NH ₃ SCR catalytic Activity and Heat resistance, in rare-earth based NH ₃ The SCR catalysis field has better application prospect.

Drawings

FIG. 1 is the XRD patterns of examples 1-5 and comparative example 1.

Fig. 2 is an isothermal desorption profile of example 2.

FIG. 3 is a pore size distribution diagram of example 2.

FIG. 4 is NH of examples 1-5 and comparative example 1 ₃ -SCR denitration performance evaluation graph.

FIG. 5 is NH of example 2, comparative example 1, comparative example 2 ₃ -SCR denitration performance evaluation graph.

FIG. 6 is NH of example 2 and comparative example 3 ₃ -SCR denitration performance evaluation graph.

FIG. 7 is NH of example 2 and comparative example 4 ₃ -SCR denitration performance evaluation graph.

FIG. 8 is NH of example 6 and comparative example 5 ₃ -SCR denitration performance evaluation graph.

FIG. 9 is NH of example 2 and comparative example 2 ₃ -TPD curve.

Detailed Description

The present invention will be further described with reference to examples.

Example 1

Firstly, the weight proportion of cerium oxide and zirconium oxide is as follows: 50wt% cerium oxide: 50wt% zirconia was formulated into a solution.

Preparing a solution:

70.44g of a zirconium oxychloride solution (containing 17.74wt% of zirconia) was prepared, 35.22g of zirconium oxychloride was dissolved in 35.22g of deionized water, 67.4g of a zirconium nitrate solution (containing 18.54wt% of ceria) was prepared, and 33.7g of cerium nitrate was dissolved in 33.7g of deionized water.

52.7g of sulfuric acid (8 wt%) and 70.44g of the zirconium oxychloride solution were added to 416.6g of deionized water and stirred uniformly, and the solution was heated to 60℃in a water bath under stirring and stabilized for 3 hours.

Preparing ammonia water with the concentration of 6.375wt%, regulating the pH value of the solution with ammonia water under the water bath condition of 60 ℃ to ensure that the pH value of the solution is more than 5, and then continuing to keep the water bath for 2 hours under the stirring state.

67.4g of cerium nitrate was added to the above solution, the pH value of the solution was adjusted to 8-9 with ammonia water, and the solution was stirred at 60℃in a water bath for 1 hour.

Filtering the solution, drying in a 100 ℃ oven for 2-4h, heating to 600 ℃ in a transfer muffle furnace by adopting a temperature programming mode, heating at a speed of 2 ℃/min, and roasting for 6h to obtain rare earth base NH ₃ -an SCR denitration catalyst.

Example 2

Preparing a solution:

70.44g of the zirconium oxychloride solution and 70.2g of sulfuric acid (8 wt%) were added to 416.6g of deionized water and stirred uniformly, the solution was heated to 60 ℃ in a water bath under stirring, and the solution was stabilized for 3 hours.

Example 3

Preparing a solution:

70.44g of the zirconium oxychloride solution and 78.86g of sulfuric acid (8 wt%) were added to 416.6g of deionized water and stirred uniformly, the solution was heated to 60 ℃ in a water bath under stirring, and the solution was stabilized for 3 hours.

67.4g of cerium nitrate solution was added to the above solution, the pH of the solution was adjusted to 8-9 with ammonia water, and the solution was stirred at 60℃in a water bath for 1 hour.

Filtering the solution, drying in a 100 ℃ oven for 2-4 hours, and heating to a temperature in a transfer muffle furnace by adopting a temperature programming modeHeating at 600 deg.c and 2 deg.c/min for 6 hr to obtain rare earth base NH ₃ -an SCR denitration catalyst.

Example 4

Preparing a solution:

70.44g of the zirconium oxychloride solution and 87.51g of sulfuric acid (8 wt%) were added to 416.6g of deionized water and stirred uniformly, the solution was heated to 60 ℃ in a water bath under stirring, and the solution was stabilized for 3 hours.

Example 5

Preparing a solution:

67.4g of cerium nitrate solution was added to the above solution, the pH of the solution was adjusted to 8-9 with ammonia water, and the mixture was stirred at 60℃in a water bath for 1 hour.

Example 6

The denitration catalyst obtained in example 2 was placed in a tube furnace, and the catalyst was purified by heating in a furnace with a water vapor content of 10vol% of N ₂ Roasting for 6 hours at 600 ℃ in atmosphere to obtain the rare earth-based denitration catalyst after hydrothermal aging treatment.

Example 7

Firstly, the weight proportion of cerium oxide, zirconium oxide and manganese oxide is as follows: 45wt% cerium oxide: 45wt% zirconia: 10wt% manganese oxide was formulated into a solution.

Preparing a solution:

70.44g of zirconium oxychloride solution (containing 17.74wt% of zirconia) was prepared, 35.22g of zirconium oxychloride was dissolved in 35.22g of deionized water, 67.4g of cerium nitrate (containing 18.54wt% of ceria) was prepared, 33.7g of cerium nitrate was dissolved in 33.7g of deionized water, 11.69g of manganese nitrate solution (containing 21.38wt% of manganese oxide) was prepared, and 5.845g of manganese nitrate was dissolved in 5.845g of deionized water.

70.44g of the zirconium oxychloride solution and 115.83g of sulfuric acid (8 wt%) are added into 458.3g of deionized water and stirred uniformly, the solution is heated to 60 ℃ in a water bath under stirring, and the solution is stabilized for 3 hours.

67.4g of cerium nitrate solution and 11.69g of manganese nitrate solution are added into the above solution, the pH value of the solution is adjusted to 8-9 by ammonia water, and the solution is stirred for 1h at the water bath temperature of 60 ℃.

Comparative example 1

Preparing a solution:

70.44g of zirconium oxychloride solution (containing 17.74wt% of zirconia) was prepared, 35.22g of zirconium oxychloride was dissolved in 35.22g of deionized water, 67.4g of cerium nitrate (containing 18.54wt% of ceria) was prepared, and 33.7g of cerium nitrate was dissolved in 33.7g of deionized water.

70.44g of the zirconium oxychloride solution, 67.4g of the cerium nitrate solution, were taken and added to 416.6g of deionized water, and the solution was heated to 60℃in a water bath with stirring, and was stabilized for 3 hours.

Preparing ammonia water with the concentration of 6.375wt%, regulating the pH value of the solution to 8-9 by using the ammonia water under the water bath condition of 60 ℃, and then continuously preserving the heat in the water bath for 2h under the stirring state.

Comparative example 2

4g of the comparative example 1 was taken, dried and ground to a powder, added to 20ml of sulfuric acid (0.5M) solution, and soaked for 3 hours.

Washing the solution with deionized water for several times, filtering, drying in a 100 ℃ oven for 2-4h, heating to 600 ℃ in a transfer muffle furnace by adopting a temperature programming mode, heating at a speed of 2 ℃/min, and roasting for 6h to obtain rare upper base NH ₃ -an SCR denitration catalyst.

Comparative example 3

Commercial vanadium molybdenum titanium NH ₃ -an SCR denitration catalyst.

Comparative example 4

Commercial vanadium tungsten titanium NH ₃ SCR denitration catalyst

Comparative example 5

The commercial vanadium tungsten titanium denitration catalyst of comparative example 4 was placed in a tube furnace, and was purified in a reactor having a water vapor content of 10vol% of N ₂ Roasting for 6 hours at 600 ℃ in atmosphere to obtain vanadium-tungsten-titanium NH after hydrothermal aging treatment ₃ -an SCR denitration catalyst.

NH ₃ -SCR denitration catalyst performance detection:

NH is carried out on the samples respectively ₃ SCR denitration activity test, wherein the reaction gas is NH ₃ (500ppm)、NO(500ppm)、10Vol％O ₂ 、5Vol％CO ₂ 、5Vol％H ₂ O，N ₂ As an equilibrium, the reaction temperature is 100-550 ℃, ghsv=220000h ^-1 。

Specific denitration performance is shown in table 1.

As can be seen from Table 1, in NH ₃ The out-of-stock activity temperature window of the example in the SCR out-of-stock performance test results is significantly higher than that of the comparative example, in particular example 2 shows better NH ₃ SCR denitration performance, high catalytic activity and wide denitration activity temperature window.

TABLE 1

The specific surface area, pore volume, pore diameter of the catalysts of examples 1-4 and comparative examples 1-2 and the sulfur contents of examples 2, 5 and comparative example 1 are shown in Table 2 below.

The specific surface area was calculated by the BET method and the pore volume and pore diameter were measured by the BJH method in Table 2.

TABLE 2

Example	Specific surface area (m) ² /g)	Pore volume (cm) ³ /g)	Aperture (nm)	Sulfur content (%)
					Example 1	78.8076	0.0722	3.8858	-
Example 2	131.7161	0.3402	11.3669	2.0524
					Example 3	67.0718	0.0652	3.8884	-
Example 4	13.0823	0.0548	16.7555	-
					Example 5	16.3471	0.0981	24.0043	2.5365
Comparative example 1	75.7095	0.0719	3.6539	2.9293
					Comparative example 2	67.1769	0.0714	4.2515	-

As is clear from Table 2, the catalyst of the above example, in which the fresh specific surface area of example 2 reaches 131m, can be obtained by adjusting the ratio of zirconium salt to sulfuric acid ² According to the preparation method, the specific surface area of the catalyst can be increased by adjusting the acid amount, so that the NH of the catalyst is further increased ₃ -SCR denitration activity.

The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Those skilled in the art will appreciate that various modifications, adaptations, and alternatives may be made without departing from the spirit and principles of the invention and are within the scope of the appended claims.

Claims

1. Non-toxic, high-activity and high-stability rare earth-based ammonia-selective catalytic reduction (NH) ₃ -SCR) catalyst, characterized in that: the rare earth group NH ₃ -a method for preparing an SCR catalyst comprising the steps of:

(1) The weight proportion of cerium oxide and zirconium oxide is as follows: 50wt% cerium oxide: 50wt% zirconia formulation solution;

(2) Preparing a solution: 35.22g of zirconium oxychloride is dissolved in 35.22g of deionized water to prepare 70.44g of zirconium oxychloride solution with the concentration of 17.74wt% of zirconia, 33.7g of cerium nitrate is dissolved in 33.7g of deionized water to prepare 67.4g of cerium nitrate solution with the concentration of 18.54wt% of ceria;

(3) Adding 70.44g of the zirconium oxychloride solution and 70.2g of 8wt% sulfuric acid into 416.6g of deionized water, uniformly stirring, heating the solution to 60 ℃ in a water bath under a stirring state, and stabilizing for 3 hours;

(4) Preparing ammonia water with the concentration of 6.375 weight percent, regulating the pH value of the solution by using the ammonia water under the water bath condition of 60 ℃ to ensure that the pH value of the solution is more than 5, and then continuing to keep the water bath for 2 hours under the stirring state;

(5) Adding 67.4g of cerium nitrate into the solution, regulating the pH value of the solution to 8-9 by ammonia water, and carrying out heat preservation and stirring for 1h at the water bath temperature of 60 ℃;

(6) Filtering the solution, drying in a 100 ℃ oven for 2-4h, heating to 600 ℃ in a transfer muffle furnace by adopting a temperature programming mode, heating at a speed of 2 ℃/min, and roasting for 6h to obtain rare earth base NH ₃ -an SCR denitration catalyst;

the compound has 131.71m after 6 hours roasting at 600 DEG C ² BET specific surface area per gram, pore volume of 0.34cm ³ Per g, pore diameter 11.37nm, sulfur content 2.05%.