CN102179243A - Catalyst for selective catalytic reduction of nitrogen oxide in moderate/low temperature environment - Google Patents

Abstract

The invention belongs to the field of end gas decontamination of diesel cars, and in particular relates to a MnOx-Wo3/TiO3 catalyst for selective catalytic reduction of nitrogen oxide, which is used for treating NOx in the end gas of diesel cars in moderate/low temperature environment (120-300 DEG C) and prepared by an immersion method. The catalyst adopts a common metal oxide MnOx as an active component, the raw materials are low-cost and easily obtained, the use condition is simple, and the catalyst can be mass produced. The catalyst disclosed by the invention can be used for catalyzing ammonia selective reduction nitric oxides to be harmless nitrogen and water in the low temperature environment of 120 DEG C, and the high conversion rate of the catalyst can be kept at about 300 DEG C.

Description

The catalyst of selective catalyst reduction of nitrogen oxides under the middle low temperature environment

Technical field

The invention belongs to the diesel car tail gas refining field, be specifically related in a kind of processing under the low temperature environment NO in (120 ℃～300 ℃) exhaust gas from diesel vehicle _xThe catalyst of selective catalyst reduction of nitrogen oxides.

Background technology

Motor-vehicle tail-gas was one of the most serious pollution sources in recent years, in the big city because a large amount of buses and diesel-powered trucks of using, pollute very serious, research report according to internal authority mechanism shows, in 150 big cities, the world, Beijing of China, Shanghai, Guangzhou, Xi'an, Shenyang five big city air pollutions come top 10, carry out the research of diesel engine vent gas purification techniques and become to need badly with Study of Catalyst work.The emission of exhaust gas from diesel vehicle mainly is NO _x(mainly being NO) and soot (PM), the discharging of CO and HC is starkly lower than gasoline engine, so Exhaust Control for Diesel Engine focus on PM and NO _xControl.For NO under the excess oxygen _xRemove ammine selectivity catalytic reduction method (NH ₃-SCR) be considered to one of effective method.

External practicability the SCR technology with V ₂O ₅-WO ₃/ TiO ₂Catalyst is a catalyst system and catalyzing, has good NO in 300 ℃～400 ℃ temperature range _xClean-up effect.But still there are some problems in actual applications in this technology: the one, and the catalyst cost is higher; The 2nd, vanadic anhydride itself is exactly a kind of noxious material; The 3rd, the catalyst temperature active window is narrower, when temperature is lower than 300 ℃, NO _xConversion ratio obviously descends, even less than 50%.For MnO _x-TiO ₂Catalyst system and catalyzing has good NO in low temperature range _xConversion ratio, but when temperature surpasses 200 ℃, catalyst can be because heat endurance be not good and sintering etc. is former thereby cause NO _xConversion ratio descends.Tungsten oxide can improve the heat endurance of catalyst as important transition metal oxide, and can provide extra catalytic active center ( The acid position), help NH ₃-SCR reaction.Therefore, we are with WO ₃Be incorporated into MnO _x-TiO ₂Catalyst system and catalyzing is to MnO _x-WO ₃/ TiO ₂Catalyst has carried out the research in a dark step.

Summary of the invention

The objective of the invention is to overcome the deficiency of above-mentioned two kinds of catalyst, seek and a kind ofly can in middle low temperature range, (120 ℃～300 ℃) have higher NO _xThe NH of conversion ratio ₃-SCR catalysts.This catalyst can be widely used in gently, heavy-duty diesel oil car engine and other small-sized universal engine tail gas catalytic purification.

The present invention uses infusion process to make MnO _x-WO ₃/ TiO ₂Catalyst, its step is as follows:

(1) particle size range had the TiO of single anatase phase at 30～40nm ₂Powder mixes stirring at normal temperatures with deionized water, makes TiO ₂Slurries, TiO ₂Mass concentration be 4～10%;

(2) with tungstic acid hydrate ammonia (traditional Chinese medicines group produces, analyze pure, molecular formula: H ₄₀N ₁₀O ₄₁W ₁₂YH ₂O) be dissolved in the oxalic acid solution, heating is stirred to tungstic acid hydrate ammonia and all dissolves, and then the solution that obtains is joined the TiO of step (1) ₂In the slurries, tungstic acid hydrate ammonium and TiO ₂Mol ratio be 0.007～0.009: 1, continue to stir after 2～5 hours and obtain mixed solution;

(3) mixed solution is continued stir in 85～95 ℃ water-bath, become thickly until mixed solution, take out to be positioned in the baking oven then and under 120～130 ℃ of temperature conditions, dry, make WO ₃/ TiO ₂The catalyst precursor;

(4) with WO ₃/ TiO ₂The catalyst precursor is ground to 80 orders～100 orders;

(5) WO after will grinding ₃/ TiO ₂450～550 ℃ of calcinings 3～6 hours under excess oxygen of catalyst precursor are treated that Muffle furnace naturally cools to take out after the room temperature to be ground to 80 orders～100 orders;

(6) with mass concentration be 50～65% Mn (NO ₃) ₂Solution dilutes according to 1: 4～8 volume ratio with deionized water, adds the WO in the step (5) ₃/ TiO ₂Stirred 2～4 hours Mn (NO behind the catalyst precursor powder again ₃) ₂With TiO ₂Mass ratio be 0.4～3: 1; The mixed liquor of above-mentioned steps is continued to stir in 85～95 ℃ water-bath, become thickly until mixed liquor, take out to be positioned in the baking oven then and under 120～130 ℃ of temperature conditions, dry, make MnO _x-WO ₃/ TiO ₂Catalyst precursor (X=3 or X=4);

(7) with MnO _x-WO ₃/ TiO ₂The catalyst precursor is ground to 80 orders～100 orders;

(8) MnO after will grinding _x-WO ₃/ TiO ₂450～550 ℃ of calcinings 3～6 hours under excess oxygen of catalyst precursor are treated that Muffle furnace naturally cools to take out after the room temperature to be ground to 80 orders～100 orders, thereby are made MnO _x-WO ₃/ TiO ₂Catalyst.

Preparation process of the present invention is simple, and is easy to operate.Compare with existing technology, the present invention has following advantage:

(1) catalyst of the present invention is selected common metal oxide MnO for use _xBe active constituent, raw material is cheap is easy to get in preparation, and service condition is simple, can produce in batches;

(2) catalyst of the present invention can the catalysis ammonia selective reducing nitrogen oxide be harmless nitrogen G﹠W just under 120 ℃ cryogenic conditions, and this high conversion can be remained to about 300 ℃.

Description of drawings

Fig. 1: different MnO _xThe MnO of content _x-WO ₃/ TiO ₂The XRD spectra of catalyst.From XRD spectra as can be seen, TiO in four general lines ₂Have only single Detitanium-ore-type crystalline phase diffraction maximum, use among the figure

Mark; Also all detected WO in four spectral lines simultaneously ₃Characteristic diffraction peak, mark with " ◇ " among the figure; And MnO ₂Characteristic diffraction peak (marking) with " " only at MnO _x(0.4)-WO ₃(0.1)/TiO ₂, MnO _x(0.6)-WO ₃(0.1)/TiO ₂Detect in two kinds of pairing XRD spectral lines of catalyst, at MnO _x(0.1)-WO ₃(0.1)/TiO ₂, MnO _x(0.2)-WO ₃(0.1)/TiO ₂Two kinds of corresponding XRD spectral lines of catalyst but do not detect, and the oxide that manganese is described is at WO ₃(0.1)/TiO ₂Apparent height disperses.

Fig. 2: different MnO _xThe MnO of content _x-WO ₃/ TiO ₂The ESEM picture of catalyst.As can be seen, sintering phenomenon does not all take place in catalyst, and particle size distribution is even from four width of cloth SEM pictures.

The specific embodiment

In order to be illustrated more clearly in the present invention, enumerate following examples, but it there is not any restriction to scope of the present invention.

Embodiment 1～4:

Take by weighing the 8g particle size range has single anatase phase at 30～40nm TiO ₂Powder mixes stirring with the 40ml deionized water, makes TiO ₂Fully mix with water, obtain TiO ₂Slurries.Take by weighing 2.54g tungstic acid hydrate ammonia and be dissolved in the solution that 30ml contains 5g oxalic acid, heating all joins TiO after the dissolving until tungstic acid hydrate ammonia ₂In the slurries, continue to stir 2 hours, in 90 ℃ water-bath, continue to stir evaporate to dryness then, become the taking-up of thick back until mixed liquor and be positioned over 120 ℃ of oven dry in the baking oven, be ground to 80 orders～100 orders, 500 ℃ of calcinings 5 hours under air conditions are then treated that Muffle furnace naturally cools to take out after the room temperature to be ground to 80 orders～100 orders, obtain 10.34g WO ₃/ TiO ₂Carrier, wherein WO ₃With TiO ₂Mol ratio be 0.1: 1, be expressed as WO ₃(0.1)/TiO ₂

The mass concentration that takes by weighing 3.58g then is 50% Mn (NO ₃) ₂Solution is with the dilution of 80ml deionized water, then with 10.34g WO ₃(0.1)/TiO ₂Carrier adds wherein, continue to stir 2 hours, in 90 ℃ water-bath, continue to stir evaporate to dryness then, become the taking-up of thick back until mixed liquor and be positioned over 120 ℃ of oven dry in the baking oven, be ground to 80 orders～100 orders, 500 ℃ of calcinings 5 hours under air conditions are then treated that Muffle furnace naturally cools to take out after the room temperature to grind, and obtain 11g MnO _X(0.1)-WO ₃(0.1)/TiO ₂Catalyst.Change the consumption of nitrate, make to use the same method, obtain catalyst MnO respectively _X(0.2)-WO ₃(0.1)/TiO ₂, MnO _X(0.4)-WO ₃(0.1)/TiO ₂And MnO _X(0.6)-WO ₃(0.1)/TiO ₂The each component raw material uses and sees Table 1.In this example, X=3 or X=4.The catalyst of 0.5ml embodiment 1～4 preparation is positioned over respectively in the quartz tube type fixed bed reactors reacts, experiment condition is as follows:

Reaction condition is NO:500ppm, NH ₃: 500ppm, O ₂: 2% (volumetric concentration), N ₂Be balance gas, total tolerance 400ml/min, reaction velocity (GHSV) is 40000h ^-1The reaction temperature interval uses flue gas analyzer (KM9106 Quintox Kane International Limited) every 20 ℃ of real-time NO of record from 80 ℃ to 300 ℃ _x(NO and NO ₂) concentration, use infrared gas analyser (QGS-08C, north, Beijing is divided) to measure NH ₃Concentration, experimental result sees Table 2.

Table 1: raw material use amount

		TiO 2	Tungstic acid hydrate ammonia	50％Mn(NO 3) 2
					Embodiment 1	Mn?O x(0.1)-WO 3(0.1)/TiO 2	8g	2.54g	3.58g
Embodiment 2	Mn?O x(0.2)-WO 3(0.1)/TiO 2	8g	2.54g	7.16g
					Embodiment 3	Mn?O x(0.4)-WO 3(0.1)/TiO 2	8g	2.54g	14.42g
Embodiment 4	Mn?O x(0.6)-WO 3(0.1)/TiO 2	8g	2.54g	21.48g

Table 2: the activity of catalyst nitrogen oxides reduction under the differential responses temperature

From above table as can be seen the catalyst the embodiment 1 in 120～300 ℃ temperature range, be 74.9% to the average removal efficiency of nitrogen oxide, catalyst among the embodiment 2 is 98.74% to the average removal efficiency of nitrogen oxide in 120～300 ℃ temperature range, catalyst among the embodiment 3 is 94.53% to the average removal efficiency of nitrogen oxide in 120～300 ℃ temperature range, and the catalyst among the embodiment 4 is 86.2% to the average removal efficiency of nitrogen oxide in 120～300 ℃ temperature range.

Claims (4)

1. the catalyst of selective catalyst reduction of nitrogen oxides under the low temperature environment in a kind, it is prepared by following steps:

1) particle size range had the TiO of single anatase phase at 30～40nm ₂Powder mixes stirring at normal temperatures with deionized water, makes TiO ₂Slurries;

2) tungstic acid hydrate ammonia is dissolved in the oxalic acid solution, heating is stirred to tungstic acid hydrate ammonia and all dissolves, and then the solution that obtains is joined the TiO of step 1) ₂In the slurries, continue stirring and obtain mixed solution after 2～5 hours;

3) mixed solution is continued stir in 85～95 ℃ water-bath, become thickly until mixed solution, take out to be positioned in the baking oven then and under 120～130 ℃ of temperature conditions, dry, make WO ₃/ TiO ₂The catalyst precursor;

4) with WO ₃/ TiO ₂The catalyst precursor is ground to 80 orders～100 orders;

5) WO after will grinding ₃/ TiO ₂450～550 ℃ of calcinings 3～6 hours under excess oxygen of catalyst precursor are treated that Muffle furnace naturally cools to take out after the room temperature to be ground to 80 orders～100 orders;

6) with mass concentration be 50～65% Mn (NO ₃) ₂Solution dilutes according to 1: 4～8 volume ratio with deionized water, adds the WO in the step 5) ₃/ TiO ₂Stirred again 2～4 hours behind the catalyst precursor powder; The mixed liquor of above-mentioned steps is continued to stir in 85～95 ℃ water-bath, become thickly until mixed liquor, take out to be positioned in the baking oven then and under 120～130 ℃ of temperature conditions, dry, make MnO _x-WO ₃/ TiO ₂Catalyst precursor, wherein X=3 or X=4;

7) with MnO _x-WO ₃/ TiO ₂The catalyst precursor is ground to 80 orders～100 orders;

8) MnO after will grinding _x-WO ₃/ TiO ₂450～550 ℃ of calcinings 3～6 hours under excess oxygen of catalyst precursor are treated that Muffle furnace naturally cools to take out after the room temperature to be ground to 80 orders～100 orders, thereby are made MnO _x-WO ₃/ TiO ₂Catalyst.

2. the catalyst of selective catalyst reduction of nitrogen oxides is characterised in that: TiO in the step 1) altogether under a kind of middle low temperature environment as claimed in claim 1 ₂Mass concentration be 4～10%.

3. the catalyst of selective catalyst reduction of nitrogen oxides is characterised in that: step 2 altogether under a kind of middle low temperature environment as claimed in claim 1) middle tungstic acid hydrate ammonium and TiO ₂Mol ratio be 0.007～0.009: 1.

4. the catalyst of selective catalyst reduction of nitrogen oxides is characterised in that: Mn (NO in the step 6) altogether under a kind of middle low temperature environment as claimed in claim 1 ₃) ₂With TiO ₂Mass ratio be 0.4～3: 1.

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