CN101462049B - Preparation method of high-dispersion manganese-cerium composite oxides - Google Patents

Abstract

The invention discloses manganese-cerium composite oxide, which is prepared in one step through the oxidation reduction-precipitation process among Mn<VII>, Mn<II> and Ce<III> ions, wherein components, namely MnO2 and CeO2 of the manganese-cerium composite oxide have high dispersion on a near molecular scale, the mol ratio of Mn to Ce is randomly adjusted, and the composite oxide has good oxidation reduction and oxygen affinity. As a catalyst carrier of reactions of formaldehyde oxidation at room temperature and low-temperature selective catalytic reduction of nitrogen oxide, the use of the composite oxide can ensure that a catalyst has higher activity, and the stability of the composite oxide is more superior to those of other carriers.

Description

A kind of preparation method of high-dispersion manganese-cerium composite oxides

Technical field

The present invention relates to a kind of manganese-cerium composite oxide with polymolecularity and good oxidation reproducibility, can do reaction such as complete catalytic oxidation (as room temperature oxidation of formaldehyde, VOCs catalytic combustion, VOCs wet oxidation) and middle low temperature NOx SCR etc. catalyst or catalyst carrier.

Background technology

As a kind of special catalyst or catalyst carrier, manganese-cerium composite oxide obtains having carried out science and application study widely in decades at home and abroad.According to known at present, manganese-cerium composite oxide has the performance of excellence in reactions such as catalytic combustion and wet oxidation.Compare other material, the use of manganese cerium combined oxidation can significantly improve the activity of catalyst in above-mentioned reaction, reduce the consumption of expensive active component such as noble metal, obtains more permanent service life simultaneously.In addition, research shows that also manganese-cerium composite oxide has good catalytic performance equally in low temperature NH3-SCR (Selective Catalytic reduction of NOx by ammonia) reaction.It has been generally acknowledged that the outstanding catalytic performance of the manganese-cerium composite oxide character such as oxidation-reduction quality special with it has confidential relation.In manganese-cerium composite oxide, manganese is with the form high degree of dispersion of higher oxidation number (AON), and its reversible redox cycle in surface has guaranteed that catalyst has good stable simultaneously.

The performance of manganese-cerium composite oxide is subjected to the material impact of factors such as its preparation method, auxiliary agent.Existing preparation method commonly used has sol-gal process and coprecipitation etc.But these methods are difficult to control on the one hand on production technology, can't fairly largely prepare, and the manganese cerium oxide can't be accomplished even high degree of dispersion in the resulting on the other hand manganese-cerium composite oxide, thereby makes its performance receive certain limitation.With the coprecipitation is example, Ce (OH) ₃And Ce (OH) ₄Solubility product be approximately 1.6 * 10 ^-20With 2.5 * 10 ^-47, and Mn (OH) ₂Solubility product 1.5 * 10 ^-13, this shows that the manganese cerium is difficult to precipitate simultaneously in coprecipitation, thereby causes the inhomogeneous of its distribution.Patent CN 101028595A adopts manganese nitrate titration potassium permanganate and ammonium ceric nitrate (Ce ^IV) method prepare manganese-cerium composite oxide.The shortcoming of this method is, manganese nitrate and the potassium permanganate generation Mn oxide that is swift in response, but the Ce that manganese nitrate and the reaction of sour cerium ammonium then generate ^IIIAnd remaining Ce ^IVThen need to regulate higher pH value and just can precipitate, can't reach the high degree of dispersion of manganese and cerium by follow-up dropping KOH.

Summary of the invention

The object of the present invention is to provide a kind of manganese cerium on nearly molecular scale high degree of dispersion, have the good oxidation reproducibility, the oxygen affinity is closed the manganese-cerium composite oxide of high stability, as the good catalyst or the catalyst carrier of reactions such as catalytic oxidation, SCR.

Another object of the present invention provides a kind of method that repeatably prepares above-mentioned catalyst.

The objective of the invention is to be achieved through the following technical solutions:

Under suitable PH condition, Mn ^VIIWith Mn ^IIGenerate MnO by redox reaction ₂Precipitation, Mn simultaneously ^VIIWith Ce ^IIIThen reaction generates MnO ₂And CeO ₂Precipitation

Above-mentioned being reflected in the solution evenly taken place simultaneously, therefore can reach MnO as much as possible ₂And CeO ₂Homogeneous precipitation, realize the high degree of dispersion of manganese cerium in its composite oxides.

The technology of the present invention effect:

Manganese-cerium composite oxide preparation technology gentleness, repeatable high, manganese cerium component height evenly disperses in the products obtained therefrom, has good oxidation-reduction quality and O ₂Affinity, stable in properties.Behind this composite oxides supported precious metal or the transition metal oxide, during as catalyst for reaction such as oxidation of formaldehyde room temperature or selective catalyst reduction of nitrogen oxides, has excellent reactivity and stability.

Description of drawings

The XRD diffracting spectrum of Fig. 1 manganese-cerium composite oxide and predecessor thereof.

The activity of room temperature catalytic oxidation formaldehyde behind Fig. 2 manganese-cerium composite oxide carried noble metal Pt.Test condition: contain formaldehyde air mass flow 3L/min, the about 25ppm of concentration of formaldehyde, room temperature, relative humidity 60%, air speed is about 400,000h ^-1

Fig. 3 manganese-cerium composite oxide is at NH ₃Activity among the low-temperature selective catalytic reduction NOx.Test condition: NOx 500ppm, NH ₃500ppm, O ₂8%, H ₂O5%, SO ₂0.1ppm, air speed 50,000h ^-1

The specific embodiment

Embodiment 1:

Prepare manganese-cerium composite oxide according to following technology

1) according to required manganese cerium proportioning, configuration concentration is that potassium permanganate, manganese acetate, cerous nitrate solution and the concentration of 0.1mol/L is the potassium hydroxide solution of 0.2mol/L;

2) in 50 ℃ under intense agitation, above-mentioned solution is dripped, mixes, and continue to stir 1 hour dropwising the back;

3) the gained sediment with 50 ℃ of hot washes, suction filtration after, in 110 ℃ the oven dry 8h, the gained predecessor is designated as S ₁Continuation is with S ₁Predecessor was 500 ℃ of roastings 2 hours, and the gained manganese-cerium composite oxide is designated as S ₂

From S ₁And S ₂In get respectively that an amount of sample is that BET analyzes, Raman spectrum analysis and XRD analysis (Fig. 1).The BET analysis result shows, predecessor S ₁The about 198m of specific area ²/ g, sample S after the roasting ₂Specific surface still remains on 130m ²About/g.And S ₁And S ₂Diffracting spectrum, comparatively obvious variation does not take place in the crystalline structure of manganese-cerium composite oxide before and after the roasting, wide and weak diffraction maximum shows and is typical long-range disordered structure on this composite oxides microcosmic.The Raman spectral results then shows, CeO in the manganese-cerium composite oxide ₂And MnO ₂Particle diameter near 2～4nm.

Embodiment 2:

Preparing manganese cerium ratio according to the step among the embodiment 1 is 1: 1 manganese-cerium composite oxide.Based on 0.25wt%Pt content, with dinitroso diammonia platinum solution impregnation manganese-cerium composite oxide,, carry out activation in 2 hours after 450 ℃ of roastings in 110 ℃ of oven dry, obtain the manganese-cerium composite oxide Pt/MnCeOx. of supporting Pt

Getting 0.3g Pt/MnCeOx places quartzy fixed catalytic reaction bed to carry out the active assessment of room temperature formaldehyde through catalytic oxidation.Reaction temperature is 22 ℃, relative humidity 60%, and air mass flow 3L/min, it is about 400 to amount to air speed, 000h ^-1Adopt common activated carbon (AC2) and dilatation activated carbon (AC1) sample as a comparison simultaneously.Experimental result as shown in Figure 2.As seen from Figure 2, though activated carbon has the ability of certain elimination formaldehyde, it mainly relies on absorption, and reaches capacity very soon, and activated carbon is not with oxidation of formaldehyde Cheng Shui and carbon dioxide, and catalytic bed is imported and exported CO ₂Concentration does not change.Formaldehyde through Pt/MnCeOx has then obviously been changed into CO by Catalytic Oxygen ₂: when using the Pt/MnCeOx catalyst in the reaction bed, be accompanied by the decline of concentration of formaldehyde, outlet CO ₂Concentration is apparently higher than import, and its formaldehyde once reaches more than 50% by conversion ratio.

Embodiment 3:

Preparing manganese cerium ratio according to the step among the embodiment 1 is 3: 1 manganese-cerium composite oxide.Getting 0.3g MnCeOx places quartzy fixed catalytic reaction bed to carry out low temperature NH ₃Selective Catalytic Reduction of NO x (NH ₃-SCR) active assessment.Reaction temperature is 50 ℃～200 ℃, NOx 500ppm, NH ₃500ppm, O ₂8%, H ₂O 5%, SO ₂0.1ppm, air speed 50,000h ^-1Experimental result as shown in Figure 3.As seen from Figure 3, MnCeOx is to NH ₃-SCR has good low temperature active.The NOx conversion ratio more than 70% can be reached near 60 ℃, and nearly 100% ground of NOx N can be changed into more than 80 ℃ ₂

Claims (6)

1. the preparation method of a manganese-cerium composite oxide is characterized in that: the component of described manganese-cerium composite oxide is the MnO that nearly molecular scale disperses ₂And CeO ₂, the Mn/Ce mol ratio is adjustable arbitrarily, and described manganese-cerium composite oxide adopts redox-precipitation method preparation, and its idiographic flow is as follows:

(i) with soluble M n ^VIISalt, Ce ^IIIAnd Mn ^IISalt is made into the aqueous solution of concentration at 0.05mol/L～0.5mol/L;

(ii) KOH is made into the aqueous solution of concentration at 0.2mol/L～2mol/L;

(iii) under 30～80 ℃ of intense agitation, use Ce ^III, Mn ^IISalting liquid and potassium hydroxide solution are with proper speed titration Mn ^VIISolution, the control reactant liquor is in suitable pH value scope, and the pH value scope that titration is fit to is 6～10;

(iv) step will contain sedimentary mother liquor and continue to stir 0.5～8h at 30～80 ℃ after (iii) titration is finished;

(vi) with after gained sediment suction filtration, the washing, in 110 ℃ of dried overnight;

(vii) the gained predecessor is MnO ₂With CeO ₂Composite oxides.

2. the preparation method of manganese-cerium composite oxide according to claim 1 is characterized in that: with described MnO ₂With CeO ₂Composite oxides at 200～700 ℃ of roasting temperature 2～6h, dewater, activate and change the purpose of crystal formation to reach.

3. the preparation method of manganese-cerium composite oxide according to claim 1 and 2 is characterized in that: soluble M n ^VIISalt is a kind of in sodium permanganate or the potassium permanganate.

4. the preparation method of manganese-cerium composite oxide according to claim 1 and 2 is characterized in that: solubility Ce ^IIISalt is a kind of in cerous acetate or the cerous nitrate.

5. the preparation method of manganese-cerium composite oxide according to claim 1 and 2 is characterized in that: soluble M n ^IISalt is a kind of in manganese acetate, manganese sulfate or the manganese nitrate.

6. the preparation method of manganese-cerium composite oxide according to claim 1, it is characterized in that: the content of described Mn/Ce is tried to achieve by following equation:

3molMn ^VII＝2mol?Mn? ^II+molCe ^III

$\frac{{\mathrm{molMn}}^{\mathrm{VII}}+{\mathrm{molMn}}^{\mathrm{II}}}{{\mathrm{molCe}}^{\mathrm{III}}}\mathrm{Mn}/\mathrm{Ce}$

molMn ^VII+mol?Mn? ^II+molCe ^III＝1

Wherein, molMn ^VII, molMn ^II, molCe ^IIIExpression prepares 1 mole of Mn that manganese-cerium composite oxide is required respectively ^VII, Mn ^IIAnd Ce ^IIIThe molal quantity of salt.

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