CN108855051A - A kind of synthetic method of the two-dimentional Mn oxide for low temperature SCR denitration - Google Patents

Abstract

A two-dimensional manganese oxide for low-temperature SCR denitrification and a synthesis method thereof, belonging to the fields of pollution control and environmental catalysis. The synthesis steps are as follows: a certain concentration of surfactants containing one or more of sodium dodecylsulfonate, sodium dodecylsulfate, sodium dodecylbenzenesulfonate and sodium cetylsulfate The aqueous solution is heated in a water bath at a certain temperature; the metal ion precursor solution of potassium manganate or potassium permanganate assisted by ultrasonic dissolution is quickly poured into the above-mentioned surfactant solution, and the acid solution is added dropwise to the mixed solution at the same time, React for a certain period of time at a certain water bath temperature, and then obtain two-dimensional manganese oxides after filtering, washing, drying and roasting. The catalyst of the invention can realize SCR denitrification at relatively low temperature, the denitrification efficiency is greater than 80% when the reaction temperature is 100°C, the denitrification efficiency can reach more than 90% at 150-250°C, and the _N2 selectivity is greater than 90%. The catalyst of the invention presents a two-dimensional structure, has good water and sulfur resistance, and the synthesis method is convenient in operation, simple in process, and easy to realize industrial production.

Description

A kind of synthesis method of two-dimensional manganese oxide for low-temperature SCR denitrification

technical field

The invention relates to a two-dimensional manganese oxide used for low-temperature SCR denitrification and a synthesis method thereof. The material is applied to the removal of nitrogen oxides (NOx) in low-temperature flue gas of industrial kilns, sintered pellets, coking industry, glass industry, etc. The invention belongs to the field of flue gas denitrification and the field of environmental catalysis.

Background technique

With the development of the world economy, the problem of environmental pollution is becoming more and more prominent in industrial production. In the process of rapid economic development, countries around the world mostly used the consumption of natural resources to promote economic development. my country mainly uses fossil fuels such as coal, oil, and natural gas to generate power, and at the same time it brings about an increasingly severe environment. question. The combustion of fossil fuels inevitably produces a large amount of environmental pollutants. As one of the main air pollutants, nitrogen oxides (NO _x , NO, NO ₂ ) can cause acid rain, photochemical smog, ozone layer destruction and climate change, as well as damage to human body. damage to health. NO is a colorless and odorless gas, which is easy to combine with heme to cause blood hypoxia and cause central nervous paralysis; NO ₂ is more toxic than NO, and it is extremely harmful to the human body after inhalation. The hazards of NO _x are mainly: (1 )NO _x decomposes under sunlight to produce oxygen atoms, causing a series of chain reactions to generate photochemical smog with O ₃ and PAN as main components. Photochemical smog is foggy and has extremely low visibility, which increases the probability of traffic accidents. At the same time, photochemical smog has a strong poisonous effect on human eyes and respiratory tract; (2) it is easy to form haze weather, and NO _x in coal-fired smoke is Precursor of nitrate in atmospheric particulate matter PM2.5; (3) NO _x can react with O ₃ to change O ₃ into O ₂ , which has a destructive effect on the ozone layer. Therefore, the problems caused by NOx need to be solved urgently.

Currently, NOx removal methods mainly include selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR) technologies. Since selective non-catalytic reduction (SNCR) does not require a catalyst during the treatment process, in order to achieve higher chemical reaction activity, this technology needs to remove NOx at a higher temperature, which is very sensitive to temperature conditions. The ideal temperature is between 850°C and 1100°C. Different reactors require different temperature windows. When the reaction temperature is lower than the temperature window, due to the limitation of the residence time, the chemical reaction is often insufficient, resulting in a low reduction rate of NO. At the same time, the increase of NH ₃ that does not participate in the reaction will also cause the escape of ammonia gas, and this The NOx removal rate of the technology can only reach 70%. SCR is currently the most effective and widely used flue gas denitrification technology in the world. Most of the catalysts used are vanadium-based materials. The working temperature window of this type of catalyst is 300-400°C. Concentrations of _SO2 can cause catalyst poisoning and deactivation. In order to solve the above problems, the NH ₃ -SCR device is placed after the dust removal and desulfurization process to reduce the influence of dust and SO ₂ on the catalyst. At this time, the temperature of the flue gas will drop below 200 ° C, so the development of a low temperature has High activity SCR catalyst has important practical significance. Manganese oxides have become a research hotspot for low-temperature SCR catalysts because of their multiple valence states and easy redox reactions. According to the current research results, although Mn-based catalysts have good low-temperature catalytic activity, they have poor water and sulfur resistance. Therefore, it is of practical significance to develop catalysts with good sulfur and water resistance.

Two-dimensional materials have a special lamellar structure, showing the characteristics of large specific surface area, size effect of nanomaterials, strong planar conductivity, and large electronic conductivity. According to research, the catalyst with this structure is not conducive to the deposition of sulfate on its surface in the NH ₃ -SCR reaction system. Compared with traditional catalysts, it has better water resistance and sulfur resistance. Chinese patent CN105561982A discloses a γ-MnO ₂ nanosheet low-temperature SCR flue gas denitrification catalyst. The conversion rate of the catalyst to NO can reach more than 90% within the temperature window of 130°C to 250°C, but its low-temperature activity is poor. When the reaction temperature is 90°C, the highest catalytic activity is only 50%.

Chinese patent CN104289227A discloses a Mn, Co, Ce, Ti four-component NH ₃ -SCR supported catalyst for low-temperature flue gas denitrification and its preparation method. After roasting, a multi-component composite metal oxide is formed. The prepared The specific surface area of the catalyst is 115.38cm·g ^-1 . But the anti-sulfur effect of the catalyst is not good. Chinese patent CN201510961222.4 discloses a preparation method of rGO-loaded petal _- like MoS2 heterostructure for improving the efficiency of photocatalytic degradation of organic dyes. It is synthesized by a one-step hydrothermal reaction and annealed to increase the degree of crystallization, forming a heterogeneous composite structure in which petal _- like MoS2 clusters and rGO are intertwined. The material can be significantly increased by using the large specific surface area of two-dimensional materials. The adsorption of organic pollutants, and its heterogeneous interface can promote the rapid transfer of photogenerated electrons to graphene sheets, leaving oxidative photogenerated holes in the valence band of MoS ₂ to participate in the degradation of organic pollutants, greatly improving the Photocatalytic properties.

Contents of the invention

Aiming at the current low-temperature SCR denitrification catalysts, such as small specific surface area and poor water and sulfur resistance, the present invention provides a two-dimensional manganese oxide for low-temperature SCR denitrification and its synthesis method. The catalyst has high NOx conversion rate, stability and resistance at <200°C, and is suitable for low-temperature SCR denitrification.

A method for synthesizing two-dimensional manganese oxide for low-temperature SCR denitrification, characterized in that: the microscopic appearance of the two-dimensional manganese oxide is in the shape of a two-dimensional layer, and the synthesis method is a one-step reduction method of a surfactant.

A two-dimensional manganese oxide synthesis method for low-temperature SCR denitrification as described above is characterized in that: the synthesis steps are as follows: (1) prepare a surfactant aqueous solution A of a certain concentration, and place it in a water bath heating at a certain temperature; (2) configure a certain concentration of manganate aqueous solution B, and use ultrasonic treatment to assist dissolution; (3) quickly add solution B to solution A, and dropwise add a certain concentration of acid solution at the same time, after the addition is completed, solution C is obtained; (4) solution After C reacts for a certain period of time at the water bath temperature described in (1), filter, wash and extract the solid particles D formed in the above process; (5) place the dried solid particles D at a certain temperature to roast for a certain period of time, that is A two-dimensional manganese oxide catalyst was obtained.

Further, the surfactant includes one or more of sodium dodecylsulfonate, sodium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium cetyl sulfate; The manganate radical precursor includes one or more of potassium permanganate and potassium manganate; the acid solution includes one or more of sulfuric acid, hydrochloric acid, and nitric acid.

Further, the molar concentration of the surfactant solution A is 0.15-0.75 mol/L; the molar concentration of the manganate aqueous solution B is 0.01-0.15 mol/L; the molar concentration of the acid solution is 0.5 ~1.5mol/L.

Further, the water bath heating temperature of the solutions A and C is 65-95°C; the water bath heating time of the solution C is 1-5 hours; the calcination temperature of the solid particle D is 80-450°C, and the calcination The time is 2 to 6 hours.

Compared with the prior art, the present invention mainly has the following effects after adopting the above synthesis scheme: the present invention successfully synthesizes a two-dimensional manganese oxide for low-temperature SCR denitrification, which has a relatively large specific surface area, and its preparation method operates Convenient and simple process; the prepared catalyst is applied in the NH ₃ -SCR reaction system, and at a lower reaction temperature window (100-250°C), it can achieve better NOx removal effect, and the N ₂ selectivity can reach 90 % above, and has good water and sulfur resistance. The catalyst material prepared by this method has a special structure, which makes good use of the advantages of two-dimensional materials, and is suitable for nitrogen oxides (NOx) in low-temperature flue gas such as industrial kilns, sintered pellets, coking industries, and glass kilns. removal.

Description of drawings

Fig. 1 is the SEM figure of the catalyst prepared by embodiment 1 (Fig. 1a), embodiment 2 (Fig. 1b), embodiment 3 (Fig. 1c) of the present invention;

Fig. 2 is the TEM figure of the catalyst prepared by embodiment 1 (Fig. 2a), embodiment 2 (Fig. 2b), embodiment 3 (Fig. 2c) of the present invention;

Fig. 3 is the XRD figure of the catalyst prepared by the embodiment of the present invention 1, embodiment 2, embodiment 3;

Fig. 4 is the catalyst prepared by the embodiment of the present invention 3 (Fig. 4a) and the precipitation method preparation catalyst (Fig. 4b) and the citric acid method preparation catalyst (4c) water and sulfur resistance data diagram;

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. These examples are only for illustrating the present invention and are not intended to limit the scope of the present invention.

Example 1

(1) Accurately weigh 5g of sodium dodecylsulfonate and dissolve it in 200ml of deionized water to form solution A, and place it at a water bath temperature of 65°C;

(2) Accurately weigh 0.3g potassium manganate and dissolve it in a certain amount of deionized water to form a 0.03mol/L B solution, and dissolve it with the aid of ultrasound;

(3) quickly join the B solution in the step (2) in the A solution of the step (1), and dropwise add 10 ml of hydrochloric acid while stirring to obtain a mixed solution C;

(4) Place the solution C obtained in step (3) at the temperature of the water bath described in step (1) to react for a period of time, then filter and wash the solid particles D formed in the above process;

(5) Put the dried solid particle D in a muffle furnace at a temperature of 80° C. for 2 h to obtain two-dimensional manganese oxide.

Example 2

(1) Accurately weigh 7g of sodium lauryl sulfate and dissolve it in 300ml of deionized water to form solution A, and place it at a water bath temperature of 80°C;

(2) Accurately weigh 0.2022g potassium manganate and dissolve it in a certain amount of deionized water to form a 0.06mol/L B solution, and dissolve it with the aid of ultrasound;

(3) The B solution in the step (2) is quickly added in the A solution of the step (1), and the nitric acid of 13ml is added dropwise while stirring to obtain a mixed solution C;

(4) Place the solution C obtained in step (3) at the temperature of the water bath described in step (1) to react for a period of time, then filter and wash the solid particles D formed in the above process;

(5) Put the dried solid particles D in a muffle furnace at a temperature of 200° C. for 4 hours and roast them to obtain a two-dimensional manganese oxide.

Example 3

(1) Accurately weigh 3.8g of sodium dodecylbenzenesulfonate and dissolve it in 350ml of deionized water to form solution A, and place it at a water bath temperature of 90°C;

(2) Accurately weigh 0.1680g potassium permanganate and dissolve it in a certain amount of deionized water to form a 0.1mol/L B solution, and dissolve with ultrasonic assistance;

(3) quickly join the B solution in the step (2) in the A solution of the step (1), and drop the sulfuric acid of 9ml while stirring simultaneously, obtain the mixed solution C;

(4) Place the solution C obtained in step (3) at the temperature of the water bath described in step (1) to react for a period of time, then filter and wash the solid particles D formed in the above process;

(5) Put the dried solid particles D in a muffle furnace at a temperature of 400° C. for 6 hours to obtain two-dimensional manganese oxide. Test the water resistance and sulfur resistance of the catalyst obtained in this example, and the resistance of the catalyst can be expressed by the conversion rate of NOx. Accompanying drawing 4 (a) shows that preparation MnO Catalyst resists 8% H ₂ O and 150ppm SO ₂ test conditions at 150 ℃, nitrogen oxide removal rate only drops 16% in ₆ hours test time, illustrates this The catalyst has good resistance to water and sulfur.

Catalyst performance test

The catalyst activity test is carried out by placing it in a quartz tube-type fixed-bed reactor. The catalyst is placed in the middle of the reactor. The reaction temperature is controlled by a tube-type electric furnace through a voltage regulator, and the reaction temperature is controlled by a program temperature controller. The coking flue gas is simulated by the cylinder gas, the gas flow is controlled by the mass flow meter, the reaction space velocity is 32000h ^-1 , the reaction gas is composed of NO, NH ₃ , O ₂ , N ₂ , and the gas concentration of the inlet and outlet before and after the catalyst treatment is tested. Carry out the calculation of NOx removal rate and _N2 selectivity, and carry out the water resistance and sulfur resistance test. The denitrification efficiency of the manganese oxide catalyst prepared in the preferred embodiment of the present invention is greater than 80% when the reaction temperature is 100°C, the denitrification efficiency at 150-250°C can reach more than 90%, and the _N2 selectivity is greater than 90%

The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (5)

1. A synthetic method for a two-dimensional manganese oxide used for low-temperature SCR denitrification, characterized in that: the microscopic appearance of the described manganese oxide is a two-dimensional laminar shape; the synthetic method is a surfactant one-step reduction method. 2. The synthetic method of the two-dimensional manganese oxide of low-temperature SCR denitrification according to claim 1, characterized in that: the synthetic steps are as follows: (1) configure a certain concentration of surfactant aqueous solution A, and place it in a water bath at a certain temperature for heating (2) configure manganate aqueous solution B with a certain concentration, and use ultrasonic treatment to assist dissolution; (3) quickly add solution B to solution A, and dropwise add a certain concentration of acid solution at the same time, after the addition is completed, solution C is obtained; (4 ) Solution C reacts at the water bath temperature described in (1) for a certain period of time, then filters, washes and extracts the solid particles D formed in the above process; (5) roasting the dried solid particles D at a certain temperature for a certain period of time , that is, a two-dimensional manganese oxide for low-temperature SCR denitrification. 3. the synthetic method of the two-dimensional manganese oxide of low-temperature SCR denitrification according to claim 2, is characterized in that: described tensio-active agent comprises sodium dodecylsulfonate, sodium lauryl sulfate, lauryl sodium One or more of sodium alkylbenzenesulfonate and cetyl sodium sulfate; the manganate precursor includes one or more of potassium manganate and potassium permanganate; the acid solution includes sulfuric acid , hydrochloric acid, nitric acid or one or more. 4. The method for synthesizing two-dimensional manganese oxides for low-temperature SCR denitrification according to claim 2, characterized in that: the molar concentration of the surfactant solution A is 0.15-0.75mol/L; The molar concentration of the aqueous solution B is 0.01-0.15 mol/L; the molar concentration of the acid solution is 0.5-1.5 mol/L. 5. The synthesis method of two-dimensional manganese oxide for low-temperature SCR denitrification according to claim 2, characterized in that: the heating temperature of the water bath for the solution A and the solution C is 65-95°C; the water bath for the solution C The heating time is 1-5 hours; the calcination temperature of the solid particle D is 80-450° C., and the calcination time is 2-6 hours.