CN100386147C - Catalyst for transforming No into N2 and its prepn process - Google Patents

Abstract

The present invention provides a catalyst with a gamma-Al2O3 carrier and for the selective reduction of NO by propylene under a rich oxygen condition, and a preparation method thereof. The catalyst comprises the gamma-Al2O3 carrier and 1 to 5 wt% of Cu 2+ as active components, and is characterized in that the carrier is modified with SO4 <2->. The preparation method comprises the major steps: firstly, the carrier gamma-Al2 O3 is modified with SO4 <2->, soaked in a La 3+ solution, dried, calcined, soaked in a Cu 2+ solution, dried and calcined. The catalyst of the present invention has the advantages of NO conversion rate reaching over 83 %, hydrothermal stability and wide operating temperature range, and provides a feasible way for the manufacture of oxygen-rich tail gas NO purifiers in vehicles.

Description

A kind of NO is converted into N 2Catalysts and its preparation method

Technical field

The present invention relates to the catalyst of a kind of selecting reduction of NO by propylene (nitric oxide), relate to a kind of catalyst in particular at propylene in oxygen-rich condition selective reduction NO.

The invention still further relates to above-mentioned Preparation of catalysts method.

Background technology

Because lean burn technology can significantly improve the utilization rate of fuel on the one hand, save the energy, can reduce emission of harmful substances such as CO, HC in the tail gas significantly on the other hand, so the design and the application of lean-burn gasoline engine, Diesel engine are continuous ascendant trend in the world from the nineties.Yet the lean-burn process unavoidably can produce more nitrogen oxide (NO _x, wherein NO accounts for more than 90%), cause NO _xPollution to atmosphere is serious day by day, directly endangers people's healthy and ecological environment.Therefore, eliminate NO _xPollution become current global urgent task, the catalyst development that NO is converted into non-toxic gas becomes at present the focus of catalyst research in the world.

Hydro carbons selective reduction NO Study of Catalyst is one of current direction under the excess oxygen.That is developed at present mainly concentrates on molecular sieve catalyst and metal oxide catalyst, because metal oxide catalyst has better hydrothermal stability than molecule sieve catalyst, so more favored.Al wherein ₂O ₃The catalyst of load copper has the lower advantage of optimum activity temperature to hydro carbons selective reduction NO under the excess oxygen, and cheap and easy to get, thereby causes extensive studies interest.Yet prepared so far Al ₂O ₃The activity of copper-loading catalyst is still lower, fails to obtain practical application.For example: " SCI " the 25th volume the 1st phase (in January, 2004) " Cu/Al under the excess oxygen ₂O ₃C on the catalyst ₃H ₆The research of selective reduction NO " (author: Zhang Changbin, He Hong, Yu Yunbo, Zhang Runduo, 136-139 page or leaf) introduced Al ₂O ₃Copper-loading catalyst has been reported the Cu/Al that adopts immersion process for preparing to the research method of propylene in oxygen-rich condition selective reduction NO catalytic activity ₂O ₃The NO maximum conversion rate only has an appointment 40% on the catalyst." environmental science " the 25th volume the 4th phase (in July, 2004) " Ag, Co and Cu/Al under the excess oxygen ₂O ₃The research of Selective Catalytic Reduction of NO " (author: Cui Xiangyu, Hao Jiming, Fourier are new, Li Junhua, Zhu Tianle, Liu Zhiming, the 18-22 page or leaf) also have similar report, the Cu/Al that promptly adopted immersion process for preparing ₂O ₃Catalyst, the NO maximum conversion rate is less than 40% on this catalyst.

The inventor takes Al through conscientiously research ₂O ₃Carry out the method for modification, the conversion ratio of NO on the catalyst that makes is increased substantially, demonstrate good catalytic activity and hydrothermal stability.

Summary of the invention

The purpose of this invention is to provide a kind of effective catalyst that under excess oxygen, the reaction of selecting reduction of NO by propylene is had high catalytic activity and hydrothermal stability.

Another object of the present invention provides a kind of aforementioned Preparation of catalysts method.

For achieving the above object, catalyst provided by the invention is with γ-Al ₂O ₃Be carrier, with Cu ²⁺Being active component, is benchmark with the vehicle weight, Cu ²⁺Content is 1-5%, and this catalyst carrier is to be matrix with the boehmite, makes γ-Al through 500 ℃ of roastings 5 hours ₂O ₃, then by per 100 gram γ-Al ₂O ₃Add 20-40 gram SO ₄ ^2-Ratio, with γ-Al ₂O ₃Be added to (the NH that concentration is 0.5mol/L ₄) ₂SO ₄In the solution, slowly stirred 1-3 hour down in 40-80 ℃, suction filtration, oven dry, grinding is sieved, and then at 300-500 ℃ of following roasting 1-3 hour, makes SO ₄ ^2-γ-the Al of modification ₂O ₃, use Cu at last again ²⁺Solution impregnation, dry, roasting.

Described catalyst activity component Cu ²⁺Optimum content be 3%.

With the vehicle weight is benchmark, and described catalyst contains the auxiliary agent La of 1-3% ³⁺, auxiliary agent La ³⁺Optimum content be 2%;

The present invention also provides a kind of method for preparing catalyst of the present invention, and this method comprises the steps:

(1) preparation γ-Al ₂O ₃: with boehmite roasting 5 hours under 500 ℃ of conditions;

(2) preparation SO ₄ ^2-γ-the Al of modification ₂O ₃: by per 100 gram γ-Al ₂O ₃Add 20-40 gram SO ₄ ^2-Ratio γ-Al that (1) is made ₂O ₃Be added to (the NH that concentration is 0.5mol/L ₄) ₂SO ₄In the solution, slowly stirred 1-3 hour down in 40-80 ℃, suction filtration, oven dry, grinding is sieved, and then at 300-500 ℃ of following roasting 1-3 hour, makes SO ₄ ^2-γ-the Al of modification ₂O ₃

(3) make catalyst: the SO that (2) are made ₄ ^2-γ-the Al of modification ₂O ₃Use Cu ²⁺Solution incipient impregnation 12-24 hour, the oven dry back made catalyst and (is abbreviated as Cu/SO in 400-600 ℃ of roasting 1-3 hour ₄ ^2-/ Al ₂O ₃).

Described step (3) preparation SO ₄ ^2-γ-the Al of modification ₂O ₃After, use La earlier ³⁺Solution incipient impregnation 12-24 hour is dried the back in 400-600 ℃ of roasting 1-3 hour, and then is carried out (3) described step process.

Described step (3) SO ₄ ^2-γ-Al after the modification ₂O ₃La (NO with 0.3mol/L ₃) ₃Solution floods, 80 ℃ of dryings 6 hours, in the air atmosphere in 500 ℃ of roastings 2 hours.

Described step (3) adopts the Cu (NO of 0.62mol/L ₃) ₂The solution incipient impregnation, the time is 12-24 hour, then in 80 ℃ of dryings, the time is 6 hours, again in air atmosphere in 500 ℃ of roastings, the time is 2 hours, heating rate is 5 ℃ of per minutes.

Catalyst of the present invention is under the situation of water steam not, and the conversion ratio of NO was the highest when reaction temperature was 300 ℃, can reach more than 83%; Under the situation that has 10% steam to exist in the reaction mixture gas, the conversion ratio of NO still reaches about 80% in the time of 300 ℃, shows that catalyst of the present invention has fabulous catalytic activity and hydrothermal stability.

Below in conjunction with embodiment the present invention is done further detailed description:

Of the present invention NO is converted into N ₂γ-Al ₂O ₃The activity of copper-loading catalyst and study on the stability carry out in fixed bed continuous-flow reaction system, and reaction unit is made with quartz ampoule (diameter 8mm), and reaction bed temperature is controlled by thermocouple.Reacted product adopts GC9790 gas chromatograph and online each components contents of detection gaseous mixture of FGA-4100 five component automobile exhaust analyzers via six-way valve.Packed column is 5A molecular sieve and Porapak-N.The former is used for detecting N ₂, CO, O ₂And NO, the latter is used for detecting C ₃H ₆, CO ₂And N ₂O.Initial concentration and N with NO ₂Generation be calculated as follows the conversion ratio of NO, with the activity of the conversion ratio evaluate catalysts of NO.

$C_{\mathrm{NO}}=\frac{2\left[N_2\right]}{{\left[\mathrm{NO}\right]}_0}\&times;100\%$

Reaction condition: temperature 200-600 ℃, air speed 20000h ^-1, catalyst is the 60-80 order, and loading amount is 0.3g, and each component of reactor feed gas is controlled separately flow with mass flowmenter and is mixed to blender, and it is as follows that control mixes the back gas composition: NO, 2000ppm; C ₃H ₆, 1200ppm; O ₂, 2.0%, do carrier gas with high-purity He.When the investigation water vapour influences catalytic activity, add 10% water vapour, by adjusting the He throughput, it is constant to keep air speed and other each reactive component concentration.

The specific embodiment

Example 1:Cu/Al ₂O ₃Catalyst is to the changing effect of NO

γ-Al ₂O ₃The preparation of copper-loading catalyst:

1. with boehmite roasting 5 hours under 500 ℃ of conditions;

2. use the Cu (NO of 0.62mol/L ₃) ₂Solution impregnation γ-Al ₂O ₃24 hours, make Cu ²⁺Load capacity be 3%, in 80 ℃ of dryings 6 hours, in air atmosphere, 500 ℃ of roastings 2 hours, heating rate was 5 ℃ of per minutes, makes γ-Al ₂O ₃Copper-loading catalyst (is abbreviated as Cu/Al ₂O ₃).

Utilize the Cu/Al of the cupric 3% of method for preparing ₂O ₃Catalyst is 100-600 ℃ in reaction temperature, and air speed is 20000h ^-1, react under the catalyst loading amount 0.3g.In helium atmosphere, heat up before the reaction, heating rate is 10 ℃ of per minutes, and under 500 ℃ of temperature, catalyst was carried out activation processing 2 hours with hydrogen, switch to helium then, naturally cooling, when temperature is reduced to 90 ℃, switch unstripped gas and react NO conversion data such as table 1 under each reaction temperature.

Table 1 NO is at Cu/Al ₂O ₃Conversion results on the catalyst

Reaction temperature (℃)	NO conversion ratio (%)
		200	3.19
250	18.65
		300	50.45
350	36.43
		400	25.83
450	16.62
		500	4.47
550	0
		600	0

As can be seen from Table 1: when reaction temperature was 300 ℃, the conversion ratio of NO reached maximum, was 50.45%, and the rising with reaction temperature then descends.When reaction temperature was 400 ℃, the NO conversion ratio was 25.83%; When reaction temperature was 500 ℃, the NO conversion ratio was 4.47%.

Example 2:Cu/SO ₄ ^2-/ Al ₂O ₃Catalyst is to the changing effect of NO

Press the γ-Al of example 1 preparation ₂O ₃Be added to (the NH that concentration is 0.5mol/L ₄) ₂SO ₄In the solution, slowly stirred 60 minutes down in 60 ℃, suction filtration, 80 ℃ of oven dry down, grinding is sieved, and then 400 ℃ of following roastings 2 hours, makes SO ₄ ^2-γ-the Al of modification ₂O ₃, press Cu in the method load of example 1 then ²⁺, obtain SO ₄ ^2-Modification γ-Al ₂O ₃Copper-loading catalyst (is abbreviated as Cu/SO ₄ ^2-/ Al ₂O ₃).

The conversion reaction conditions of NO is with example 1, reaction result such as table 2

Table 2 NO is at Cu/SO ₄ ^2-/ Al ₂O ₃Conversion results on the catalyst

Reaction temperature (℃)	NO conversion ratio (%)
		200	5.10
250	26.74
		300	79.88
350	62.92
		400	48.98
450	41.20
		500	24.60
550	21.24
		600	16.42

Can be seen that by table 2 when reaction temperature was 300 ℃, the conversion ratio of NO reached maximum, be 79.88%, and the rising with reaction temperature then descends.When reaction temperature was 400 ℃, the NO conversion ratio was 48.98%; When reaction temperature was 500 ℃, the NO conversion ratio still remained 24.60%.This shows, adopt SO ₄ ^2-To γ-Al ₂O ₃Modification can make catalyst that the catalytic activity of the conversion reaction of NO is increased substantially.

Example 3:Cu/La/SO ₄ ^2-/ Al ₂O ₃Catalyst is to the changing effect of NO

Press the SO of example 2 preparations ₄ ^2-Modification γ-Al ₂O ₃Catalyst is with the La (NO of 0.3mol/L ₃) ₃Solution floods, and makes La ³⁺Load capacity be 2%, 80 ℃ of drying 6 hours, in the air atmosphere in 500 ℃ of roastings 2 hours, and then with the Cu (NO of 0.62mol/L ₃) ₂Solution floods, and makes Cu ²⁺Load capacity be 3%, 80 ℃ of drying 6 hours, in 500 ℃ of following roastings 2 hours, can obtain the SO that contains the auxiliary agent lanthanum of the present invention in the air atmosphere ₄ ^2-Modification on Al ₂O ₃Copper-loading catalyst (is abbreviated as Cu/La/SO ₄ ^2-/ Al ₂O ₃).

The conversion reaction conditions of NO is with example 1, reaction result such as table 3.

Table 3 NO is at Cu/La/SO ₄ ^2-/ Al ₂O ₃Conversion results on the catalyst

Reaction temperature (℃)	NO conversion ratio (%)
		200	6.63
250	28.27
		300	83.72
350	67.57
		400	55.58
450	48.03
		500	30.86
550	24.27
		600	19.76

As can be seen from Table 3, when reaction temperature was 300 ℃, the conversion ratio of NO reached maximum, was 83.72%, and the rising with reaction temperature then descends.When reaction temperature was 400 ℃, the NO conversion ratio was 55.58%; When reaction temperature was 500 ℃, the NO conversion ratio still remained 30.86%.This shows that auxiliary agent La can make catalyst that the catalytic activity of the conversion reaction of NO is further improved, and widens operating temperature range.

Example 4:Cu/La/SO ₄ ^2-/ Al ₂O ₃Catalyst in the presence of steam to the changing effect of NO

For investigating the wet-hot aging performance of catalyst, utilize the Cu/La/SO of example 3 methods preparation ₄ ^2-/ Al ₂O ₃Catalyst is 100-600 ℃ in reaction temperature, and air speed is 20000h ^-1, catalyst loading amount 0.3g reacts under the 10% steam existence condition in the reaction mixture gas.In helium atmosphere, heat up before the reaction, heating rate is 10 ℃ of per minutes, and under 500 ℃ of temperature, catalyst was carried out activation processing 2 hours with hydrogen, then switch to helium, naturally cooling, when temperature is reduced to 90 ℃, switch unstripped gas and react NO conversion data such as table 4 under each reaction temperature.

NO was at Cu/La/SO under table 4 steam existed ₄ ^2-/ Al ₂O ₃Conversion results on the catalyst

Reaction temperature (℃)	NO conversion ratio (%)
		200	1.96
250	22.95
		300	80.20
350	65.62
		400	53.53
450	45.20
		500	28.68
550	22.36
		600	17.82

As can be seen from Table 4, Cu/La/SO ₄ ^2-/ Al ₂O ₃Catalyst has hydrothermal stability preferably, and the maximum conversion of NO has only descended 3.52%.

Example 5: the Cu/La/SO of different sintering temperature preparations ₄ ^2-/ Al ₂O ₃Changing effect to NO

Prepared Catalysts Cu/La/SO by example 3 ₄ ^2-/ Al ₂O ₃Method, just sintering temperature is changed to 400 ℃ and 600 ℃, prepare the Cu/La/SO of different sintering temperatures respectively ₄ ^2-/ Al ₂O ₃, and with the same NO conversion reaction conditions of example 3 under, measure its catalytic activity, result such as table 5 to the NO conversion reaction.

Table 5 NO is at the Cu/La/SO of different sintering temperature preparations ₄ ^2-/ Al ₂O ₃Conversion results on the catalyst

As can be seen from Table 5, when reaction temperature was 300 ℃, the conversion ratio of NO reached maximum, was respectively 82.12% and 82.26%, and the rising with reaction temperature then descends.When reaction temperature was 500 ℃, the NO conversion ratio was respectively 26.49% and 26.32%.This shows, at 400 ℃ and 600 ℃ of Cu/La/SO that roasting makes ₄ ^2-/ Al ₂O ₃Catalytic activity make not as 500 ℃ of roastings.

Example 6: the Cu/La/SO of different roasting time preparations ₄ ^2-/ Al ₂O ₃Changing effect to NO

Prepared Catalysts Cu/La/SO by example 3 ₄ ^2-/ Al ₂O ₃Method, just roasting time was changed to 1 hour and 3 hours, prepare the Cu/La/SO of different roasting time respectively ₄ ^2-/ Al ₂O ₃, and with the same NO conversion reaction conditions of example 3 under, measure its catalytic activity, result such as table 6 to the NO conversion reaction.

Table 6 NO is at the Cu/La/SO of different roasting time preparations ₄ ^2-/ Al ₂O ₃Conversion results on the catalyst

As can be seen from Table 6, when reaction temperature was 300 ℃, the conversion ratio of NO reached maximum, was respectively 81.86% and 82.67%, and the rising with reaction temperature then descends.When reaction temperature was 500 ℃, the NO conversion ratio was respectively 26.12% and 27.78%.This shows, be 1 hour and the Cu/La/SO that made under the condition in 3 hours in roasting time ₄ ^2-/ Al ₂O ₃Catalytic activity be to make in 2 hours not as roasting time.

Example 7: different Cu ²⁺The Cu/La/SO of load capacity ₄ ^2-/ Al ₂O ₃Changing effect to NO

Prepared Catalysts Cu/La/SO by example 3 ₄ ^2-/ Al ₂O ₃Method, just Cu ²⁺Load capacity change to 2% and 4%, prepare different Cu respectively ²⁺The Cu/La/SO of load capacity ₄ ^2-/ Al ₂O ₃, and with the same NO conversion reaction conditions of example 3 under, measure its catalytic activity, result such as table 7 to the NO conversion reaction.

Table 7 NO is at different Cu ²⁺The Cu/La/SO of load capacity ₄ ^2-/ Al ₂O ₃Conversion results on the catalyst

As can be seen from Table 7, when reaction temperature was 300 ℃, the conversion ratio of NO reached maximum, was respectively 82.66% and 83.30%, and the rising with reaction temperature then descends.When reaction temperature was 500 ℃, the NO conversion ratio was respectively 29.76% and 30.36%.This shows Cu ²⁺Load capacity is 2% and 4% Cu/La/SO ₄ ^2-/ Al ₂O ₃Catalytic activity not as Cu ²⁺Load capacity is 3%.

Example 8 Different L a ³⁺The Cu/La/SO of load capacity ₄ ^2-/ Al ₂O ₃Changing effect to NO

Prepared Catalysts Cu/La/SO by example 3 ₄ ^2-/ Al ₂O ₃Method, just La ³⁺Load capacity change to 1% and 3%, prepare Different L a respectively ³⁺The Cu/La/SO of load capacity ₄ ^2-/ Al ₂O ₃, and with the same NO conversion reaction conditions of example 3 under, measure its catalytic activity, result such as table 8 to the NO conversion reaction.

Table 8 NO is at Different L a ³⁺The Cu/La/SO of load capacity ₄ ^2-/ Al ₂O ₃Conversion results on the catalyst

As can be seen from Table 8, when reaction temperature was 300 ℃, the conversion ratio of NO reached maximum, was respectively 82.08% and 82.52%, and the rising with reaction temperature then descends.When reaction temperature was 500 ℃, the NO conversion ratio was respectively 26.11% and 26.36%.This shows La ³⁺Load capacity is 1% and 3% Cu/La/SO ₄ ^2-/ Al ₂O ₃Catalytic activity not as La ³⁺Load capacity is 2%.

Example 9: different SO ₄ ^2-The Cu/La/SO of pickup preparation ₄ ^2-/ Al ₂O ₃Changing effect to NO

Prepared Catalysts Cu/La/SO by example 3 ₄ ^2-/ Al ₂O ₃Method, just SO ₄ ^2-Pickup change to 20% and 40%, prepare different SO respectively ₄ ^2-The Cu/La/SO of pickup ₄ ^2-/ Al ₂O ₃, and with the same NO conversion reaction conditions of example 3 under, measure its catalytic activity, result such as table 9 to the NO conversion reaction.

Table 9 NO is at different SO ₄ ^2-The Cu/La/SO of pickup preparation ₄ ^2-/ Al ₂O ₃Conversion results on the catalyst

As can be seen from Table 9, when reaction temperature was 300 ℃, the conversion ratio of NO reached maximum, was respectively 79.29% and 79.41%, and the rising with reaction temperature then descends.When reaction temperature was 500 ℃, the NO conversion ratio was respectively 23.12% and 24.35%.This shows SO ₄ ^2-Pickup is the Cu/La/SO that makes under 20% and 40% condition ₄ ^2-/ Al ₂O ₃Catalytic activity not as SO ₄ ^2-Pickup is 30% to make.

Claims (10)

1. one kind is converted into N with NO ₂Catalyst, comprise carrier γ-Al ₂O ₃, active component Cu ²⁺, be benchmark with the vehicle weight, Cu ²⁺Content is 1-5%, it is characterized in that:

A. described γ-Al ₂O ₃Made in 5 hours by boehmite roasting under 500 ℃ of conditions, and adopt SO ₄ ^2-Modification: by per 100 gram γ-Al ₂O ₃Add 20-40 gram SO ₄ ^2-Ratio, with γ-Al ₂O ₃Be added to (the NH that concentration is 0.5mol/L ₄) ₂SO ₄In the solution, slowly stirred 1-3 hour down in 40-80 ℃, suction filtration, oven dry, grinding is sieved, and then at 300-500 ℃ of following roasting 1-3 hour, makes SO ₄ ^2-γ-the Al of modification ₂O ₃

B. the SO that makes through step a ₄ ^2-γ-the Al of modification ₂O ₃, use Cu ²⁺Solution incipient impregnation 12-24 hour, the oven dry back made described catalyst in 400-600 ℃ of roasting 1-3 hour.

2. catalyst according to claim 1 is characterized in that: with the vehicle weight benchmark, and described active component Cu ²⁺Content be 3%.

3. catalyst according to claim 1 is characterized in that: described catalyst also contains auxiliary agent La ³⁺, be benchmark with the vehicle weight, auxiliary agent La ³⁺Content be 1-3%, step b replaces with: the SO that makes through step a ₄ ^2-γ-the Al of modification ₂O ₃Use La earlier ³⁺Solution incipient impregnation 12-24 hour is dried the back in 400-600 ℃ of roasting 1-3 hour, and then is used Cu ²⁺Solution incipient impregnation 12-24 hour, the oven dry back made catalyst in 400-600 ℃ of roasting 1-3 hour.

4. catalyst according to claim 3 is characterized in that: with the vehicle weight benchmark, and described auxiliary agent La ³⁺Content is 2%.

5. catalyst according to claim 1 is characterized in that: with the vehicle weight benchmark, and SO ₄ ^2-Content is 30%.

6. method for preparing the described catalyst of claim 1 in turn includes the following steps:

(1) preparation γ-Al ₂O ₃: with boehmite roasting 5 hours under 500 ℃ of conditions;

(2) preparation SO ₄ ^2-γ-the Al of modification ₂O ₃: by per 100 gram γ-Al ₂O ₃Add 20-40 gram SO ₄ ^2-Ratio, γ-Al that (1) is made ₂O ₃Be added to (the NH that concentration is 0.5mol/L ₄) ₂SO ₄In the solution, slowly stirred 1-3 hour down in 40-80 ℃, suction filtration, oven dry, grinding is sieved, and then at 300-500 ℃ of following roasting 1-3 hour, makes SO ₄ ^2-γ-the Al of modification ₂O ₃

(3) make catalyst: the SO that (2) are made ₄ ^2-Modification γ-Al ₂O ₃Use Cu ²⁺Solution incipient impregnation 12-24 hour, the oven dry back made catalyst in 400-600 ℃ of roasting 1-3 hour.

7. method according to claim 6 is characterized in that: step (3) replaces with: the SO that (2) are made ₄ ^2-Modification γ-Al ₂O ₃Use La earlier ³⁺Solution incipient impregnation 12-24 hour is dried the back in 400-600 ℃ of roasting 1-3 hour, and then is used Cu ²⁺Solution incipient impregnation 12-24 hour, the oven dry back made catalyst in 400-600 ℃ of roasting 1-3 hour.

8. method according to claim 7 is characterized in that: SO ₄ ^2-γ-the Al of modification ₂O ₃La (NO with 0.3mol/L ₃) ₃Solution floods, 80 ℃ of dryings 6 hours, in the air atmosphere in 500 ℃ of roastings 2 hours.

9. method according to claim 6 is characterized in that: described step (3) adopts the Cu (NO of 0.62mol/L ₃) ₂The solution incipient impregnation, the time is 12-24 hour.

10. method according to claim 9 is characterized in that: described step (3) baking temperature is 80 ℃, 6 hours time; Sintering temperature is 500 ℃, and the time is 2 hours, and heating rate is 5 ℃ of per minutes.