Transition metal doped cerium and titanium compound oxide catalyst for selective catalytic reduction of nitric oxide by ammonia

Abstract

The invention relates to a transition metal doped cerium and titanium compound oxide catalyst for selective catalytic reduction of nitric oxide by ammonia, and a preparation method thereof. The catalyst in the invention is a transition metal (iron, tungsten and molybdenum) doped cerium and titanium compound oxide catalyst. The preparation method of the catalyst is a co-precipitation method, which comprises the following steps of: preparing mixed solution from cerium salt, titanium salt and salt corresponding to one or more transition metals of iron, tungsten and molybdenum, and continuously stirring for 3 to 15 hours at the temperature of between 50 and 150 DEG C by using one of ammonia water, sodium hydroxide, sodium carbonate, ammonium bicarbonate or urea; and filtering, washing, baking and calcining. In the invention, the adopted raw materials are non-toxic and harmless, the preparation method is simple and easy, the prepared catalyst has the characteristics of high catalytic activity, excellent N2 generation selectivity, broad operation temperature window, high space velocity reaction condition adaptability and the like, and is suitable for mobile sources represented by tail gas of diesel vehicles, as well as stationary source nitric oxide catalytic purification device represented by flue gas of coal fired power plants.

Description

technical field

[0001] The invention is applied in the technical field of environmental catalysis, and relates to a transition metal (tungsten, molybdenum, iron) doped cerium-titanium composite oxide catalyst used for catalytic purification of nitrogen oxides in stationary source flue gas and diesel vehicle exhaust. Background technique

[0002] Currently, NH for industrial applications 3 Selective Catalytic Reduction of NO x (NH 3 -SCR) catalyst is mainly WO 3 or MoO 3 Doped V 2 o 5 / TiO 2 system. The catalyst system has been widely used in stationary source flue gas denitrification, and has also been used in diesel vehicle exhaust NO x catalytic elimination. However, there are still some problems in this catalyst system, such as: it contains toxic substance V, if it falls off during use, it has great biological toxicity when it enters the environment; the operating temperature window is narrow, and a large amount of greenhouse gas N is generated at high temperatur...

Examples

Embodiment 1-3

[0013] Use cerium nitrate hexahydrate, ammonium tungstate and titanium sulfate as cerium salt, tungsten salt and titanium salt respectively, prepare a solution with a Ce / W / Ti molar ratio of 0.2 / 0.1 / 1.0 and mix well, add excess urea to the solution Solution, and continuously stirred at 90°C for 12h, then suction filtered and washed, put the filter cake in an oven and dried overnight at 100°C, and finally roasted in the air at 500°C in a muffle furnace for 5h to obtain a powder catalyst. The prepared catalyst was pressed into tablets, crushed, sieved, and 40-60 meshes were taken for later use, which was called catalyst A. With other conditions unchanged, ammonium tungstate was changed to ammonium molybdate and iron nitrate to prepare catalysts B and C respectively.

Embodiment 4-6

[0015] Use cerium nitrate hexahydrate, ammonium tungstate and titanium sulfate as cerium salt, tungsten salt and titanium salt respectively, prepare a solution with a Ce / W / Ti molar ratio of 0.2 / 0.2 / 1.0 and mix well, add excess urea to the solution Solution, and continuously stirred at 90°C for 12h, then suction filtered and washed, put the filter cake in an oven and dried overnight at 100°C, and finally roasted in the air at 500°C in a muffle furnace for 5h to obtain a powder catalyst. The prepared catalyst was pressed into tablets, crushed, sieved, and 40-60 meshes were taken for later use, called catalyst D. Catalysts E and F were prepared respectively by changing the Ce / W / Ti molar ratio to 0.2 / 0.3 / 1.0 and 0.2 / 0.5 / 1.0 while other conditions remained unchanged.

Embodiment 7

[0017] With the catalyst A, B, C, D, E and F that embodiment 1-6 makes, carry out NH on self-made miniature fixed-bed reactor 3 Selective Catalytic Reduction of NO x The investigation of reactivity. The consumption of catalyst is 0.12ml, and the composition of reaction gas mixture is: [NO]=[NH 3 ]=500ppm, [O 2 ] = 5%, N 2 As balance gas, the total gas flow rate is 500ml / min, and the space velocity is 250,000h -1 , The reaction temperature is 150-450°C. NO and NH 3 and by-product N 2 O, NO 2 All were measured using an infrared gas cell. The reaction results are shown in Table 1.

[0018] Table 1 Evaluation results of catalyst activity

[0019]

[0020] Catalyst D with the best activity is at 250,000h -1 Under space velocity conditions, more than 100% NO can be achieved in the temperature range of 250-450°C x conversion rate, and at N 2 Selectivity is 100%.

technical field

[0001] The invention is applied in the technical field of environmental catalysis, and relates to a transition metal (tungsten, molybdenum, iron) doped cerium-titanium composite oxide catalyst used for catalytic purification of nitrogen oxides in stationary source flue gas and diesel vehicle exhaust. Background technique

[0002] Currently, NH for industrial applications 3 Selective Catalytic Reduction of NO x (NH 3 -SCR) catalyst is mainly WO 3 or MoO 3 Doped V 2 o 5 / TiO 2 system. The catalyst system has been widely used in stationary source flue gas denitrification, and has also been used in diesel vehicle exhaust NO x catalytic elimination. However, there are still some problems in this catalyst system, such as: it contains toxic substance V, if it falls off during use, it has great biological toxicity when it enters the environment; the operating temperature window is narrow, and a large amount of greenhouse gas N is generated at high temperatur...

Examples

Embodiment 1-3

[0013] Use cerium nitrate hexahydrate, ammonium tungstate and titanium sulfate as cerium salt, tungsten salt and titanium salt respectively, prepare a solution with a Ce / W / Ti molar ratio of 0.2 / 0.1 / 1.0 and mix well, add excess urea to the solution Solution, and continuously stirred at 90°C for 12h, then suction filtered and washed, put the filter cake in an oven and dried overnight at 100°C, and finally roasted in the air at 500°C in a muffle furnace for 5h to obtain a powder catalyst. The prepared catalyst was pressed into tablets, crushed, sieved, and 40-60 meshes were taken for later use, which was called catalyst A. With other conditions unchanged, ammonium tungstate was changed to ammonium molybdate and iron nitrate to prepare catalysts B and C respectively.

Embodiment 4-6

[0015] Use cerium nitrate hexahydrate, ammonium tungstate and titanium sulfate as cerium salt, tungsten salt and titanium salt respectively, prepare a solution with a Ce / W / Ti molar ratio of 0.2 / 0.2 / 1.0 and mix well, add excess urea to the solution Solution, and continuously stirred at 90°C for 12h, then suction filtered and washed, put the filter cake in an oven and dried overnight at 100°C, and finally roasted in the air at 500°C in a muffle furnace for 5h to obtain a powder catalyst. The prepared catalyst was pressed into tablets, crushed, sieved, and 40-60 meshes were taken for later use, called catalyst D. Catalysts E and F were prepared respectively by changing the Ce / W / Ti molar ratio to 0.2 / 0.3 / 1.0 and 0.2 / 0.5 / 1.0 while other conditions remained unchanged.

Embodiment 7

[0017] With the catalyst A, B, C, D, E and F that embodiment 1-6 makes, carry out NH on self-made miniature fixed-bed reactor 3 Selective Catalytic Reduction of NO x The investigation of reactivity. The consumption of catalyst is 0.12ml, and the composition of reaction gas mixture is: [NO]=[NH 3 ]=500ppm, [O 2 ] = 5%, N 2 As balance gas, the total gas flow rate is 500ml / min, and the space velocity is 250,000h -1 , The reaction temperature is 150-450°C. NO and NH 3 and by-product N 2 O, NO 2 All were measured using an infrared gas cell. The reaction results are shown in Table 1.

[0018] Table 1 Evaluation results of catalyst activity

[0019]

[0020] Catalyst D with the best activity is at 250,000h -1 Under space velocity conditions, more than 100% NO can be achieved in the temperature range of 250-450°C x conversion rate, and at N 2 Selectivity is 100%.

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