CN101371987B - Catalyst of CO selective methanation for reformed gas rich in hydrogen and preparation method thereof - Google Patents

Abstract

The invention discloses a catalyst Ni-Ru-B-ZrO2 which is used for the selective methanation of CO in hydrogen-rich reformed gases and is characterized in that the catalyst comprises the compositions by weight percentage of 53.1-71.3 percent of ZrO2, 20.2-33.1 percent of Ni, 1.6-7.3 percent of Ru and 4.4-7.1 percent of B. The invention also discloses the preparation method of the catalyst. Steps of chemical reduction and chemical sedimentation are used to be coupled mutually. Ni and Ru are uniformly mixed with Zr(OH)2 in the form of Ni-B alloy and Ru-B alloy. Through the air drying at 70 to 100 DEG C and the hydrogen activation treatment, the catalyst Ni-Ru-B-ZrO2 in mixed form of crystal state and amorphous state is obtained. When the catalyst is applied to the selective methanation of COin the hydrogen-rich reformed gases, the exit concentration of CO can be lowered below 22ppm. Simultaneously, extremely low methanation rate of CO2 can be maintained.

Description

The Catalysts and its preparation method that is used for hydrogen-rich reformed gas CO selective methanation

Technical field

The present invention relates to a kind of Catalysts and its preparation method that is used for hydrogen-rich reformed gas CO selective methanation.

Background technology

Proton Exchange Membrane Fuel Cells (PEMFC) is because of the advantage that has high efficiency, low pollutes, operating temperature is low, startup is fast, power density is high, current one of the most competitive power source that has become the instead of gasoline internal-combustion engines vehicle power becomes the research focus of countries in the world.PEMFC adopts hydrogen-rich reformed gas as unstripped gas, and reformation gas generally all contains 0.8～1.2% CO, because the anode Pt electrode catalyst of PEMFC is to the CO sensitivity, a small amount of CO just is easy to make its poisoning, the serious battery performance that reduces, therefore a small amount of CO in the reformation gas must be removed, make its concentration reduce to the tolerance level of fuel cell Pt electrode (50ppm is following).CO selective oxidation method becomes the research focus in the hydrogen-rich gas, is considered to more effective CO removal method usually, and this reaction system needs extra bubbling air or pure oxygen as oxidant, but because H ₂Be to be easy to be oxidized to water, so this has proposed great challenge to selection of catalysts, simultaneously, if with air as oxidant, bring inert gas N inevitably into ₂Thereby, diluted H in the hydrogen-rich gas ₂Concentration, and then influence the performance of PEMFC.

Adopt the selective methanation method, technological process is simple relatively, and methanation 1molCO need consume 3mol hydrogen (seeing reaction equation Eq.1) in theory, but for the reformation gas that contains a small amount of CO, consumes H ₂Total amount in fact only account for H ₂A total amount part seldom.Owing to have CO in the methanation reaction system ₂Methanation (seeing reaction equation Eq.2) and CO ₂The competitive reaction of hydrosphere transformation (seeing reaction equation Eq.3), so the key of methanation method is selection of catalysts, i.e. the strict CO of inhibition when keeping the basic all methanations of CO ₂Methanation reaction and CO ₂Water gas shift reaction.The catalyst of research adopts the preparation of dip loading method mostly at present, and carrier has ZrO ₂(or the ZrO of Co modification ₂), Al ₂O ₃, SiO ₂, MgO and zeolite molecular sieve etc., active component is that Ni and Ru are main, studies show that the Ni/ZrO of low nickel-content ₂Catalyst, Ru/Al ₂O ₃And Ru/Co modification ZrO ₂Demonstrate preferable performance, but reaction temperature need be at 240～300 ℃, obviously, the cryogenic property of these catalyst reaches unsatisfactory to the methanation selectivity of CO.

CO+3H ₂→CH ₄+H ₂O， Eq.1

CO ₂+4H ₂→CH ₄+2H ₂O， Eq.2

Amorphous alloy is the new material that a class has shortrange order, long-range disordered structure characteristics, and it is formed by chaotic accumulation of cluster of ordered structure, belongs to metastable state on thermodynamics.Because amorphous alloy has particular structure, show unique excellent performance as catalysis material." amorphous state Ni alloy catalyst is used for the research of low temperature methanation reaction " (Wu Hao, Pan Zhiyong, Zong Baoning, Shen Shikong. the chemical industry progress, 2005,24 (3): 299～302) introduced a kind of skeleton Ni catalyst that adopts the SRNA-4 amorphous form of high-temperature fusion quench preparation, through being used for low temperature CO and CO after the alkali extracting activation ₂The time methanation reaction, the result shows, just can make CO and CO down at 160～200 ℃ ₂The methanation that produces higher degree transforms.Adopt KBH ₄Some binary or the ternary amorphous alloy catalyst such as the Ni-B of chemical reduction method preparation, Co-B, though catalyst such as Ru-B, Fe-Co-B, Ni-Ru-B have shown quite high activity and selectivity in the low temperature hydrogenation reaction, but thermally-stabilised extreme difference, temperature higher position slightly may cause it that crystallization behavior takes place, and makes its active serious reduction even disappearance.

Summary of the invention

The objective of the invention is to provides a kind of catalyst that is used for hydrogen-rich reformed gas CO selective methanation at existing catalyst activity, selectivity and the not high enough defective of stability.

Another object of the present invention provides a kind of above-mentioned Preparation of catalysts method.

A kind of catalyst n i-Ru-B-ZrO that is used for hydrogen-rich reformed gas CO selective methanation ₂, each component of catalyst and mass percent are: ZrO ₂: 53.1～71.3%, Ni:20.2～33.1%, Ru:1.6～7.3%, B:4.4～7.1% exists with the amorphous state form before the catalyst activation fully, exists with crystalline state and amorphous state mixed form after 250～300 ℃ hydrogen activation.

The above-mentioned catalyst n i-Ru-B-ZrO that is used for hydrogen-rich reformed gas CO selective methanation ₂, can prepare with the following method: NaOH solution and KBH ₄Solution mix, with ZrOCl ₂Solution, NiCl ₂Solution and RuCl ₃Solution mixes, under stirring condition with NaOH and KBH ₄Mixed solution slowly be added drop-wise to ZrOCl ₂, NiCl ₂, RuCl ₃Mixed solution in, control NaOH and ZrOCl ₂Mol ratio is 2.0:1, KBH ₄With (Ni ²⁺+ Ru ³⁺) mol ratio be 1.8～2.4:1, reaction temperature is a room temperature, react after 20～40 minutes the black precipitate filtration, the washing that obtain are obtained the complex catalyst precursor thing, with complex catalyst precursor thing under 70～100 ℃ air atmosphere condition dry 18-24 hour, the contained hydroxide of complex catalyst precursor thing is slowly dewatered form the Ni-Ru-B-ZrO that oxide can obtain complete amorphous state form ₂Catalyst.

Further, Ni ²⁺With Ru ³⁺Mol ratio be 5.7～28.0:1, Zr and (Ni ²⁺+ Ru ³⁺) mol ratio be 0.7～1.5:1.

Further, initially the concentration of each solution is respectively: ZrOCl ₂Solution concentration is 0.2mol/L, NiCl ₂Solution concentration is 0.5mol/L, RuCl ₃Solution concentration is 0.19mol/L; KBH ₄Solution concentration is 1.0mol/L, and the NaOH solution concentration is 1.0mol/L.

With amorphous state Ni-Ru-B-ZrO of the present invention ₂Catalyst is ground to Powdered, and activation processing is 2～3 hours under 250～300 ℃ of hydrogen atmosphere conditions, obtains containing the Ni-Ru-B-ZrO of crystalline state and amorphous state mixed form ₂Catalyst.When Ni:Ru=6.5:1, it is best that catalyst performance reaches.Air speed (

) be 12000h ^-1, reaction temperature can make the concentration of CO from 1.08% be reduced to and be lower than 22ppm in 210～250 ℃ of temperature ranges, can keep CO simultaneously ₂Conversion ratio is lower than 1.34%.The CO exit concentration falls and reaches to 7ppm under 230 ℃ of temperature, and the methanation selectivity of CO reaches 99.83%, and CO ₂Conversion ratio only be 0.17%.

In view of the superior function of amorphous alloy material catalyst, the present invention adopts KBH ₄The method of electronation and chemical precipitation coupling has prepared a kind of amorphous catalyst Ni-Ru-B-ZrO of containing metal oxide ₂This catalyst has not only overcome the defective that contains B amorphous alloy catalyst poor heat stability, and a small amount of CO selective methanation reaction in the hydrogen-rich reformed gas had good low temperature active and selectivity, and has the temperature applicable range (210～250 ℃) of broad.

Description of drawings

Fig. 1 is the x-ray diffraction pattern of Ni-Ru-B-ZrO2 catalyst, and curve a is the Ni-Ru-B-ZrO of embodiment 1 preparation among the figure ₂The x-ray diffraction pattern of catalyst behind 80 ℃ of dry 18h, curve b are the Ni-Ru-B-ZrO of embodiment 1 preparation ₂Catalyst is behind 80 ℃ of dry 18h, again through the x-ray diffraction pattern of 300 ℃ of hydrogen treat 3h.

The specific embodiment

Catalyst of the present invention is seated in the fixed bed reaction system, investigates catalyst a small amount of CO in the hydrogen-rich gas is carried out selective methanation activity and selectivity, reactor is quartz glass tube (d=8mm), and product is by HP4890D gas chromatograph and CO, CO ₂Infrared radiation detection apparatus (detection range CO:1～500ppm, CO ₂: 0.1～30%) exit concentration and the CO of online detection CO ₂Exit concentration.CO conversion ratio (X _CO), CO ₂Conversion ratio (

) and CO methanation selectivity (S _CO) computational methods as follows:

$X_{\mathrm{CO}}=\frac{F_{\mathrm{CO}}^i-F_{\mathrm{CO}}^o}{F_{\mathrm{CO}}^i}\×100\%$

$X_{{\mathrm{CO}}_2}=\frac{F_{{\mathrm{CO}}_2}^i-F_{{\mathrm{CO}}_2}^o}{F_{{\mathrm{CO}}_2}^i}\×100\%$

$S_{\mathrm{CO}}=\frac{X_{\mathrm{CO}}}{X_{\mathrm{CO}}+X_{{\mathrm{CO}}_2}}\×100\%$

In the formula:

Inlet flow rate (ml/min) for CO;

Rate of discharge (ml/min) for CO;

Be CO ₂Inlet flow rate (ml/min);

Be CO ₂Rate of discharge (ml/min).

Reaction condition is 190～250 ℃ of temperature, and air speed is 12000h ^-1, each component percent by volume of hydrogen-rich reformed gas is: CO, 1.08%; CO ₂, 23.68%; N ₂, 1.57%; H ₂O, 0.52%, H ₂, 73.15%.

Embodiment 1

With concentration is the ZrOCl of 0.2mol/L ₂The NiCl of solution, 0.5mol/L ₂The RuCl of solution and 0.19mol/L ₃Solution is pressed Ni ²⁺With Ru ³⁺Mol ratio be 8.6:1, Zr:(Ni ²⁺And Ru ³⁺) mol ratio is that the 1:1 ratio is mixed and forms solution A; Concentration is the KBH of 1.0mol/L ₄Form solution B with the NaOH mixed solution of 1.0mol/L, press NaOH and ZrOCl ₂Mol ratio is 2:1, KBH ₄With (Ni ²⁺And Ru ³⁺) mol ratio be the ratio of 2.2:1, under stirring condition, mixed solution B slowly is added drop-wise to mixed solution A, reaction temperature is a room temperature.Solution B dropwises, continue that reaction after 30 minutes is filtered the black precipitate that obtains and cyclic washing to remove Cl ^-,, make the contained zirconium hydroxide of the catalyst formation zirconia that slowly dewaters with the black precipitate after the washing under 80 ℃ exposed air conditions dry 18 hours.Dried black precipitate is ground to the Powdered Ni-Ru-B-ZrO that can obtain complete amorphous form ₂Catalyst.The mass percent of each component of catalyst is: Ni:26.8%; Ru:5.3%, B:5.9%, ZrO ₂: 62.0%.The catalyst of amorphous state form after handling activation in 3 hours under 300 ℃ of hydrogen atmosphere conditions, is obtained containing the Ni-Ru-B-ZrO of crystalline state and amorphous state mixed form ₂Catalyst.Catalyst is seen accompanying drawing 1 at 300 ℃ of forward and backward X-ray diffracting spectrums of hydrogen atmosphere activation.

Embodiment 2-6

Adopt the identical method of embodiment 1, by the different Zr of modulation ²⁺With (Ni ²⁺+ Ru ³⁺) technological parameter of mol ratio prepares catalyst, in 20 minutes reaction time, with the dry 24h under 70 ℃ of conditions of the black precipitate after the overanxious washing, each constituent mass mark of the catalyst of gained sees Table 1.

The different Zr of table 1 and (Ni+Ru) each constituent mass mark of catalyst of mol ratio

The selective methanation that above-mentioned catalyst is used for a small amount of CO of hydrogen-rich reformed gas after handling 3h under 250 ℃ the hydrogen atmosphere reacts, and catalyst amount is 0.6g (V=0.5mL), the results are shown in Table 2.

By table 2 as seen, when Zr when (Ni+Ru) mol ratio is 1.1:1, catalyst shows best activity and selectivity, makes the inlet concentration of CO from 1.08% be reduced to 9ppm under 220 ℃ of temperature, conversion ratio reaches 99.92%, has kept CO simultaneously ₂Conversion ratio is 2.34% reduced levels, is 97.71% to CO methanation selectivity.

The catalyst activity of the different Zr of table 2 and (Ni+Ru) mol ratio and selectivity ratios are

Example 7-10

Adopt the identical step of embodiment 1, and keep Zr ²⁺With (Ni ²⁺+ Ru ³⁺) mol ratio is the ratio of 1.1:1, difference is control KBH ₄With (Ni ²⁺+ Ru ³⁺) mol ratio between 1.8～2.4:1, the reaction time is 30 minutes, with the washing after black precipitate dry 21h under 85 ℃ of temperature, each constituent mass mark of the catalyst of preparing with this understanding sees Table 3.

Table 3 different B and (Ni+Ru) each constituent mass mark of catalyst of mol ratio

The selective methanation that above-mentioned catalyst is used for a small amount of CO of hydrogen-rich reformed gas after handling 2.5h under 280 ℃ the hydrogen atmosphere reacts, and catalyst amount is 0.6g (V=0.5mL), and evaluation result sees Table 4.

The catalyst activity of table 4 different B and (Ni+Ru) mol ratio and selectivity ratios are

Find out by table 4, when B when (Ni+Ru) mol ratio is lower than 2.2, catalyst activity and selectivity are lower; After B and (Ni+Ru) mol ratio are greater than 2.2, catalyst performance is kept stable substantially, so B is 2.2 o'clock with (Ni+Ru) mol ratio, it is best that activity of such catalysts and selectivity reach, under 220～230 ℃ temperature, make the inlet concentration of CO from 1.08% be reduced to 10ppm, conversion ratio reaches 99.91%, keeps CO simultaneously ₂Conversion ratio be lower than 2%, the methanation selectivity of CO is reached 98.21%.

Example 11-15

Adopt the identical method of embodiment 1, keep Zr ²⁺With (Ni ²⁺+ Ru ³⁺) mol ratio is 1.1:1, KBH ₄With (Ni ²⁺+ Ru ³⁺) mol ratio at the constant rate of 2.2:1, modulation Ni ²⁺With Ru ³⁺Mol ratio, the reaction time is 40 minutes, with the washing after black precipitate dry 18h under 100 ℃ of temperature, each constituent mass mark of the catalyst of preparing sees Table 5.

Each constituent mass mark of the catalyst of table 5 different Ni and Ru mol ratio

The selective methanation that above-mentioned catalyst is used for a small amount of CO of hydrogen-rich reformed gas after handling 2h under 300 ℃ the hydrogen atmosphere reacts, and catalyst amount is 0.6g (V=0.5mL), the results are shown in Table 6.

The catalyst activity of table 6 different Ni and Ru mol ratio and selectivity ratios are

Find out by table 6, the mol ratio of Ni and Ru has bigger influence to catalyst performance, increase with the Ru addition, activity of such catalysts and selectivity all are greatly improved, and wherein the mol ratio of Ni and Ru is when 5.7～8:4, and catalyst shows preferable performance, catalyst performance reaches best when Ni:Ru=6.5:1, in 210～250 ℃ of temperature ranges, the concentration of CO from 1.08% is reduced to is lower than 22ppm, can keep CO simultaneously ₂Conversion ratio is lower than 1.34%, and the CO exit concentration falls and reaches to 7ppm CO under 230 ℃ of temperature ₂Conversion ratio be 0.17%, the methanation selectivity of CO is reached 99.83%.

Claims (7)

1. catalyst n i-Ru-B-ZrO who is used for hydrogen-rich reformed gas CO selective methanation ₂, it is characterized in that each constituent mass percentage of catalyst is: ZrO ₂: 53.1～71.3%, Ni:20.2～33.1%, Ru:1.6～7.3%, B:4.4～7.1%, described Preparation of catalysts method comprises the steps: NaOH solution and KBH ₄Solution mix, with ZrOCl ₂Solution, NiCl ₂Solution and RuCl ₃Solution mixes, wherein ZrOCl ₂, NiCl ₂, RuCl ₃Mixed solution in Zr and (Ni ²⁺+ Ru ³⁺) mol ratio be 0.7～1.5: 1, Ni ²⁺With Ru ³⁺Mol ratio be 5.7～28.0: 1; Under stirring condition with NaOH and KBH ₄Mixed solution slowly be added drop-wise to ZrOCl ₂, NiCl ₂, RuCl ₃Mixed solution, control NaOH and ZrOCl ₂Mol ratio is 2: 1, KBH ₄With (Ni ²⁺+ Ru ³⁺) mol ratio be 1.8～2.4: 1; Reaction temperature is a room temperature, reacts after 20～40 minutes the black precipitate that obtains filtered and washing, and then under 70～100 ℃ air atmosphere condition dry 18～24 hours, can obtain the Ni-Ru-B-ZrO that exists with the amorphous state form fully ₂Catalyst.

2. catalyst n i-Ru-B-ZrO according to claim 1 ₂, it is characterized in that Zr and (Ni ²⁺+ Ru ³⁺) mol ratio be 1.1: 1.

3. catalyst n i-Ru-B-ZrO according to claim 2 ₂, it is characterized in that Ni ²⁺With Ru ³⁺Mol ratio be 5.7～8.4: 1.

4. catalyst n i-Ru-B-ZrO according to claim 3 ₂, it is characterized in that Ni ²⁺With Ru ³⁺Mol ratio be 6.5: 1.

5. catalyst n i-Ru-B-ZrO according to claim 1 ₂, it is characterized in that catalyst exists with crystalline state and amorphous state mixed form after 250～300 ℃ hydrogen activation processing.

6. catalyst n i-Ru-B-ZrO according to claim 1 ₂, it is characterized in that the KBH that is adopted ₄Solution concentration is 1.0mol/L, and the NaOH solution concentration is 1.0mol/L, ZrOCl ₂Solution concentration 0.2mol/L, NiCl ₂Solution concentration is 0.5mol/L, RuCl ₃Solution concentration is 0.19mol/L.

7. catalyst n i-Ru-B-ZrO according to claim 1 ₂, it is characterized in that each constituent mass percentage of catalyst is: ZrO ₂: 62.3～63.8%, Ni:24.3～24.9%, Ru:5.1～7.3%, B:6.1～6.2%.

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