CN115779916B - Catalyst, method for reducing nitrogen oxides and application of catalyst - Google Patents

Abstract

The invention relates to a catalyst, which comprises a carrier, wherein the carrier consists of 20-80% of alumina and 80-20% of titanium oxide; and, taking the carrier as 100%, further comprising the following elements: 0.2-4.5% Ni;2.5-6.5% Co and 0.5-2.0% Mo; and wherein the Ni, co and Mo contents satisfy the following relation: 0.3 +.Mo (Co+Ni)/NiCo +.4.0, and a method for reducing NO _x using the above catalyst. The catalyst does not contain noble metals, and has good catalytic activity for reducing NOx; the reduction method based on the catalyst can solve the problem of high cost of H ₂ -selective catalytic reduction technology.

Description

Catalyst, method for reducing nitrogen oxides and application of catalyst

Technical Field

The present invention belongs to the technical field of catalysts, and in particular relates to a catalyst, a method for reducing NO _x and application of the catalyst.

Background technique

Nitrogen oxides (NOx ₎ are one of the main pollutants that cause acid rain, photochemical smog and greenhouse effect. According to statistics, about 60% of _NOx in China's air pollutants comes from fossil fuels. Therefore, reducing nitrogen oxide emissions is one of the effective means of air pollution control.

Using the Selective Catalytic Reduction (SCR) method to treat exhaust gas can effectively reduce the emission of nitrogen oxides. Among them, the selective catalytic reduction ( _H2 -SCR) technology using _H2 as a reducing agent has the advantages of clean process, no secondary pollution, and good economy. At present, the catalyst used in _H2 -SCR technology is mainly a precious metal catalyst.

However, the precious metal catalyst uses precious metals as raw materials and is very expensive, which leads to the problem of high cost in H ₂ -SCR technology.

Summary of the invention

In order to solve the problems in the prior art and provide a new solution for reducing nitrogen oxide emissions, the present invention provides a catalyst comprising

a carrier composed of 20-80% alumina and 20-80% titania; and

Taking the carrier as 100%, the following elements are also included:

0.2-4.5% Ni;

2.5-6.5% Co; and

0.5-2.0% Mo;

And the contents of Ni, Co and Mo satisfy the following relationship:

0.3≦Mo(Co+Ni)/NiCo≦4.0.

At the same _time , the present invention also provides a method for reducing _NOx , wherein _{NOx is a substance selected from NO, N2O, NO2, N2O3 , N2O4 , N2O5 or} a mixture thereof, and the method comprises reacting _NOx with _{H2 ,} characterized in that the reaction is carried out in the presence of the aforementioned catalyst of the present invention.

The present invention also provides the use of the above catalyst in reducing NOx, especially in reducing NO.

The catalyst of the present invention does not contain precious metals and has good catalytic activity for reducing _NOx ; the reduction method based on the catalyst can solve the problem of high cost of _H2 -SCR technology.

Detailed ways

In the present invention, unless otherwise specified, all component contents are based on weight.

In the present invention, unless otherwise specified, all operations are carried out at room temperature and normal pressure.

The present invention provides a catalyst, comprising

a carrier composed of 20-80% alumina and 20-80% titania; and

Taking the carrier as 100%, the following elements are also included:

0.2-4.5% Ni;

2.5-6.5% Co; and

0.5-2.0% Mo;

And the contents of Ni, Co and Mo (based on values excluding %, for example, Ni is calculated as a value between 0.2-4.5, the same below) satisfy the following relationship:

0.3≦Mo(Co+Ni)/NiCo≦4.0.

In a preferred embodiment of the present invention, the catalyst of the present invention comprises

a carrier composed of 40-45% alumina and 55-60% titania; and

Taking the carrier as 100%, the following elements are also included:

0.9-1.1% Ni;

4.8-5.2% Co; and

1.5-1.75% Mo;

And the contents of Ni, Co and Mo satisfy the following relationship:

1.9≦Mo(Co+Ni)/NiCo≦2.0.

In a further preferred embodiment of the present invention, the catalyst of the present invention consists of the following components:

a carrier composed of 40-45% gamma-alumina and 55-60% titania; and

Taking the carrier as 100%, the following elements:

0.9-1.1% Ni;

4.8-5.2% Co; and

1.5-1.75% Mo;

And the contents of Ni, Co and Mo satisfy the following relationship:

1.9≦Mo(Co+Ni)/NiCo≦2.0.

In a further preferred embodiment of the present invention, the catalyst of the present invention consists of the following components:

a carrier composed of 41-43% gamma-alumina and 57-59% titania; and

Taking the carrier as 100%, the following elements:

0.95-1.05% Ni;

4.9-5.1% Co; and

1.60-1.65% Mo;

And the contents of Ni, Co and Mo satisfy the following relationship:

1.9≦Mo(Co+Ni)/NiCo≦2.0.

In the present invention, the carrier is a mixture of titanium oxide TiO ₂ and aluminum oxide Al ₂ O ₃ , and commercially available titanium oxide and aluminum oxide can be used, preferably in the form of micro-spherical particles. Preferably, the titanium oxide TiO ₂ has an anatase structure, and the Al ₂ O ₃ is micro-spherical γ-Al ₂ O ₃ .

In a preferred embodiment, the weight ratio of the TiO ₂ and the γ-Al ₂ O ₃ is TiO ₂ :γ-Al ₂ O ₃ =(1-4):1, preferably (1.2-1.6):1, and more preferably (1.30-1.35):1.

The catalyst of the present invention can be prepared by a common impregnation method. For example, it can be prepared as follows: an aqueous solution of a metal salt of each active component is mixed with a mixture of carrier titanium oxide and aluminum oxide, and if necessary, heating and stirring are performed; after drying, the temperature is lowered; and then roasting is performed to obtain the catalyst.

When the aqueous solution of the metal salt of each active component is mixed with the carrier titanium oxide and aluminum oxide, the total volume of the solution and the total volume of the carrier mixture are preferably (1-2.5):1, preferably (1-2):1. Mixing can be carried out at room temperature, or at 20-60°C, preferably at 25-50°C, optionally under heating and stirring conditions, for 0.1-2 hours, preferably 0.2-1.5 hours. Then stand for 2-24 hours, preferably stand for 6-16 hours, more preferably stand for 10-15 hours. The drying temperature is 60-130°C, preferably 65-90°C, and the drying is 1-8 hours, preferably 3.5-6.5 hours. The calcination temperature is 380-650°C, preferably 400-630°C, especially 580-620°C; the calcination time is 1.5-8 hours, preferably 3.5-6.0 hours.

The metal salt of each active component can be a water-soluble salt of each metal, especially a nitrate of each metal.

When preparing the catalyst, preferably, the carrier uses the 40-60 mesh portion. Preferably, the prepared catalyst uses the 40-60 mesh portion.

In the method for reducing _NOx of the present invention, _NOx is a substance selected from NO, _N2O , _NO2 , _{N2O3 , N2O4 , N2O5 or} a mixture thereof, and in particular, _NOx is NO. The method comprises reacting _{NOx with H2} , and the reaction is carried out in the presence of the catalyst of the present invention.

In the method of the present invention, the catalyst can be used in a fixed bed manner, and the reaction process can be carried out in a tubular reactor. The product can be detected by any known method, such as using an online chromatograph, a nitrogen and oxygen analyzer, etc.

In a preferred embodiment of the method of the present invention, the catalyst is reduced at 400-500°C for 0.5-3 hours, wherein the reducing gas comprises a mixture of _H2 and _N2 , wherein the volume percentage of _H2 is 1-20%. Subsequently, NOx is reduced. In a further embodiment, the reaction of _NOx with _H2 is carried out at 270-300°C, in particular at 290-300°C. Preferably, in the reaction of _NOx with _H2 , the reaction gas comprises _H2 / _NOx , wherein the volume ratio of _H2 / _NOx is 1-5, preferably 2-3.5, _H2 and _NOx account for 0.05-1.5% of the gas volume, preferably 0.1-1.2%, and the rest is an inert gas, such as nitrogen, argon, etc. Preferably, the catalyst is a 40-60 mesh catalyst.

In the present invention, all devices or equipment used may be conventional devices or equipment known in the art, and may be purchased or obtained by methods disclosed in literature.

It goes without saying that the various catalysts of the present invention described above, i.e., the catalysts in the broadest range and the catalysts in each preferred embodiment, can be used in the method of reducing NOx of the present invention, constituting corresponding wide-range methods and various preferred methods, and combined with the method characteristics of the present invention itself, forming a further preferred method.

The present invention also provides the use of the above catalyst in reducing NOx, especially in reducing NO.

By using the catalyst of the present invention to catalytically reduce NO _x , the use of expensive catalysts containing precious metals is avoided, thereby solving the problem of high cost of H ₂ -SCR technology.

The present invention will be described in further detail below in conjunction with embodiments.

The following examples are only used to explain the present invention, but not to limit the present invention.

I. Catalyst Preparation Example

In the following preparation examples, the catalyst was selected from the part between 20-40 mesh.

Comparative Example 1

44.59 g of nickel nitrate (Ni(NO ₃ ) ₂ ·6H ₂ O, molecular weight 290.80) and 13.12 g of cerium nitrate (Ce(NO ₃ ) ₃ ·6H ₂ O, molecular weight 434.23) were weighed and dissolved in 200 mL of water to prepare a first mixed metal salt solution. Then 100 g of carrier TiO ₂ was placed in the first mixed metal salt solution and stirred for 1 hour, and allowed to stand for 4 hours. Thereafter, the water was evaporated under vacuum at 70° C. with strong stirring to obtain a first catalyst precursor. The first catalyst precursor was calcined at 800° C. for 2 hours to obtain a first catalyst.

Based on 100 g of the carrier mass, the Ni loading of the first catalyst was 9.00% (loading=active component mass/carrier mass, the same below), and the Ce loading was 4.23%.

Comparative Example 2

29.64g of cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O, molecular weight 291.03) and 30.89g of ammonium heptamolybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O, molecular weight 1235.86) were weighed and dissolved in 200mL of water to prepare a second mixed metal salt solution. Then 100g of the second carrier γ-Al ₂ O ₃ was placed in the second mixed metal salt solution and stirred for 1 hour, and then allowed to stand for 12 hours. Thereafter, the water was evaporated under vacuum at 70°C with strong stirring to obtain a second catalyst precursor. The second catalyst precursor was calcined at 500°C for 5 hours to obtain a second catalyst.

Based on the mass of the support, the second catalyst has a Co loading of 6% and a Mo loading of 16.79%.

Example 3

29.63g of cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O), 2.48g of nickel nitrate (Ni(NO ₃ ) ₂ ·6H ₂ O) and 3.22g of ammonium heptamolybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O) were weighed and dissolved in 200mL of water to prepare a third mixed metal salt solution. Then 100g of the third carrier (including 80g of TiO ₂ and 20g of γ-Al ₂ O ₃ ) was placed in the third mixed metal salt solution and stirred for 1 hour, and then allowed to stand for 24 hours. Thereafter, the water was evaporated under vacuum at 70°C with strong stirring to obtain a third catalyst precursor. The third catalyst precursor was calcined at 400°C for 6 hours to obtain a third catalyst.

Based on the mass of the support, the third catalyst has a Co loading of 6.00%, a Ni loading of 0.5%, and a Mo loading of 1.75%.

Example 4

14.81g of cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O), 19.82g of nickel nitrate (Ni(NO ₃ ) ₂ ·6H ₂ O) and 1.20g of ammonium heptamolybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O) were weighed and dissolved in 200mL of water to prepare a fourth mixed metal salt solution. Then 100g of the fourth carrier (including 60g of TiO ₂ and 40g of γ-Al ₂ O ₃ ) was placed in the fourth mixed metal salt solution and stirred for 1 hour, and then allowed to stand for 12 hours. Thereafter, the water was evaporated under vacuum at 70°C with strong stirring to obtain a fourth catalyst precursor. The fourth catalyst precursor was calcined at 600°C for 4 hours to obtain a fourth catalyst.

Based on the mass of the support, the fourth catalyst has a Ni loading of 4.00%, a Co loading of 3.00%, and a Mo loading of 0.65%.

Comparative Example 5

Weigh 19.82g of nickel nitrate (Ni(NO ₃ ) ₂ ·6H ₂ O) and 2.75g of iron nitrate

(Fe(NO ₃ ) ₃ ·9H ₂ O, molecular weight is 403.85) and 2.94g cerium nitrate (Ce(NO ₃ ) ₃ ·6H ₂ O) are dissolved in 200mL water to prepare a fifth mixed metal salt solution. Then 100g of the fifth carrier (including 75g TiO ₂ and 25g γ-Al ₂ O ₃ ) is placed in the fifth mixed metal salt solution and stirred for 1 hour, and then allowed to stand for 12 hours. After that, the water is evaporated under vacuum at 70°C with strong stirring to obtain a fifth catalyst precursor. The fifth catalyst precursor is calcined at 600°C for 4 hours to obtain a fifth catalyst.

Based on the weight of the support, the fifth catalyst has a Ni loading of 4.00%, a Fe loading of 0.38%, and a Ce loading of 0.95%.

Example 6

24.70g of cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O), 4.96g of nickel nitrate (Ni(NO ₃ ) ₂ ·6H ₂ O) and 3.0g of ammonium heptamolybdate ((NH ₄ ) ₆ Mo ₇ O ₂₄ ·4H ₂ O) were weighed and dissolved in 200mL of water to prepare a sixth mixed metal salt solution. Then 100g of the sixth carrier (including 57.15g of TiO ₂ and 42.85g of γ-Al ₂ O ₃ ) was placed in the sixth mixed metal salt solution and stirred for 1 hour, and then allowed to stand for 12 hours. Thereafter, the water was evaporated under vacuum at 70°C with strong stirring to obtain a sixth catalyst precursor. The sixth catalyst precursor was calcined at 600°C for 4 hours to obtain a sixth catalyst.

Based on the weight of the support, the sixth catalyst has a Co loading of 5.00%, a Ni loading of 1%, and a Mo loading of 1.63%.

Comparative Example 7

4.94g of cobalt nitrate (Co(NO ₃ ) ₂ ·6H ₂ O), 14.86g of nickel nitrate (Ni(NO ₃ ) ₂ ·6H ₂ O) and 6.87g of iron nitrate (Fe(NO ₃ ) ₃ ·9H ₂ O) were weighed and dissolved in 200mL of water to prepare the seventh mixed metal salt solution. Then 100g of the seventh carrier (including 80g of TiO ₂ and 20g of γ-Al ₂ O ₃ ) was placed in the seventh mixed metal salt solution and stirred for 1 hour, and then allowed to stand for 12 hours. Thereafter, the water was evaporated under vacuum at 70°C with strong stirring to obtain the seventh catalyst precursor. The seventh catalyst precursor was calcined at 500°C for 5 hours to obtain the seventh catalyst.

Based on the weight of the support, the seventh catalyst has a Co loading of 1.00%, a Ni loading of 3.00%, and a Fe loading of 0.95%.

The catalyst compositions of Examples 1-7 are summarized in Table 1.

Table 1 Catalyst composition (wt.%, γ-Al ₂ O ₃ +TiO ₂ is 100%)

Example Comparison 1 Comparison 2 3 4 Contrast 5 6 Contrast 7 γ-Al ₂ O ₃ 100 20 40 25 42.85 20 _TiO2 100 80 60 75 57.15 80 Ni 9 0.5 4 4 1 3 Co 6 6.0 3 5 1 Mo 16.79 1.75 0.65 1.63 Fe 0.38 0.95 Ce 4.23 0.95 Mo(Ni+Co) /NiCo 3.79 0.379 1.956

II. Catalyst activity test

When evaluating the denitration catalytic activity of the catalyst of the present invention, a PJ-05TDC fixed bed reactor system of Beijing Shishi Jiaqi Zhiyuan Technology Development Co., Ltd. was used, in which a quartz tube reactor (inner diameter 8 mm) was used, and the catalyst was filled in the middle of the reactor in the form of a fixed bed, and both ends of the reactor were filled with 40-60 mesh quartz sand.

1. Catalyst pre-reduction

First, the catalyst was pre-reduced, and the total gas flow rate was 50 mL/min. 0.4 g (20-40 mesh) of catalyst was heated (10°C/min) to 450°C in a H ₂ /Ar (8% H ₂ , volume percentage) gas flow and kept at a constant temperature for 40 min. A gas mass spectrometer was used to measure and record the signal changes of hydrogen. A stable hydrogen signal means that the pre-reduction is completed. After stopping heating and cooling to room temperature, the H ₂ /Ar mixed gas was switched to Ar gas, purged for 10 min, and then used for standby.

2.H ₂ -SCR denitrification reaction

After completing the pre-reduction and cooling to room temperature, switch to one of the following reaction gases, with a total gas flow rate of 80 mL/min; program the temperature from room temperature to 500°C at a heating rate of 4°C/min.

Reaction gas composition (volume percentage):

Reaction gas 1: 0.06% NO, 0.12% H ₂ , the rest Ar;

Reaction gas 2: 0.06% NO, 0.12% H ₂ , 0.02% SO ₂ , and the remainder Ar.

A 42i-HL nitrogen oxide analyzer (Thermo Electron, USA) was used to detect the NO concentration in the exhaust gas in real time.

The catalytic performance of the denitration catalyst was analyzed based on T ₅₀ and T _90. T ₅₀ and T ₉₀ respectively represent the reaction temperatures (°C) corresponding to NO removal rates of 50% and 90%. The lower the reaction temperature, the better the catalyst activity.

The results are summarized in Table 2, where the catalyst numbers correspond to the example numbers, and the catalyst specific surface areas are measured by nitrogen adsorption method; the columns where SO ₂ = 0 and SO ₂ = 0.02% correspond to the reaction results of reaction gas 1 and reaction gas 2, respectively.

Table 2 Catalyst activity test results

As shown in Table 2, the catalysts of Examples 3, 4 and 6 exhibited good catalytic activities.

Claims (7)

1. A method for reducing _NOx , wherein _NOx is a substance selected from NO, _N2O , _NO2 , _{N2O3 , N2O4 , N2O5} or a mixture thereof, the method comprising reacting _NOx with _H2 , characterized in _that the reaction _is carried out in the presence of the following catalyst: A catalyst for reducing _NOx , comprising a carrier composed of 40-45% alumina and 55-60% titania; and Taking the carrier as 100%, the following elements are also included: 0.9-1.1% Ni; 4.8-5.2% Co; and 1.5-1.75% Mo; All component contents are by weight; And the contents of Ni, Co and Mo satisfy the following relationship: 1.9≦Mo(Co+Ni)/NiCo≦2.0. 2. The method for reducing NO _x according to claim 1, characterized in that the catalyst consists of the following components: a carrier composed of 40-45% gamma-alumina and 55-60% titania; and Taking the carrier as 100%, the following elements are also included: 0.9-1.1% Ni; 4.8-5.2% Co; and 1.5-1.75% Mo; All component contents are by weight; And the contents of Ni, Co and Mo satisfy the following relationship: 1.9≦Mo(Co+Ni)/NiCo≦2.0. 3. The method for reducing _NOx according to claim 2, characterized in that the catalyst consists of the following components: a carrier composed of 41-43% gamma-alumina and 57-59% titania; and Taking the carrier as 100%, the following elements are also included: 0.95-1.05% Ni; 4.9-5.1% Co; and 1.60-1.65% Mo; All component contents are by weight; And the contents of Ni, Co and Mo satisfy the following relationship: 1.9≦Mo(Co+Ni)/NiCo≦2.0. 4. The method for reducing _NOx according to any one of claims 1-3, characterized in that it comprises reducing the catalyst at 400-500°C for 0.5-3 hours, wherein the reducing gas comprises _H2 and _N2 , and the volume percentage of _H2 is 1-20%. 5. The method for reducing _NOx according to any one of claims 1 to 3, characterized in that the reaction of _NOx with _H2 is carried out at 290-300°C. 6. The method for reducing _NOx according to any one of claims 1-3, characterized in that, in the reaction of _NOx with _H2 , the reaction gas comprises _H2 and _NOx , wherein the volume ratio of _H2 / _NOx is 1-5; _H2 and _NOx account for 0.1-1.2% of the volume of the reaction gas, and the rest is inert gas. 7. The method for reducing _NOx according to any one of claims 1 to 3, characterized in that the _NOx is NO.