CN105983427A - Apatite loaded platinum catalyst as well as preparation method and application thereof - Google Patents

Abstract

The invention relates to a catalyst for a carbon monoxide water gas shift (WGS) reaction, in particular to preparation of hydroxyapatite (HAP) and halogen-substituted apatite (FAP, ClAP and BrAP) by virtue of a co-precipitation method. Platinum is introduced by virtue of a dipping method. The carrying capacity of the platinum in the catalyst is 0.3-5% of the total mass of the catalyst. The regulation and control of the activity of the catalyst can be realized by controlling Ca/P of a carrier. The catalyst prepared by the method is used for performing a water gas shift reaction in a typical reformed gas, has high activity and selectivity and good high-temperature stability, and shows higher activity compared with that of a catalyst in which a noble metal is loaded to a reducible rare earth oxide carrier (CeO2) under the same noble metal carrying capacity.

Description

A kind of apatite supported platinum catalyst and its preparation and application

technical field

The invention relates to a water vapor shift reaction catalyst, in particular to an apatite-loaded platinum catalyst used for carbon monoxide water vapor shift (WGS) reaction and its preparation and application.

Background technique

The development of my country's economy has caused more and more serious environmental pollution, and environmental problems have become an important issue restricting my country's economic development. Fuel cells (such as PEMFC) are an ideal power generation mode, with outstanding advantages such as high energy conversion rate and non-polluting products. With the development of fuel cell technology, how to provide a cheap and practical hydrogen source for fuel cells has become one of the obstacles that currently limit their large-scale applications. Fuel reformed gas contains H ₂ , CO, CO ₂ and a small amount of converted fuel. The CO concentration must be below 100ppm in the _H2 feed gas for low temperature fuel cells such as PEMFC. The water-steam shift reaction is an effective method for eliminating CO in reformed gas. CO is converted into CO by water reaction, and an equimolar amount of H ₂ is obtained.

The palladium membrane reactor that couples H ₂ separation and water vapor shift reaction can not only produce high-purity H ₂ , but also reduce equipment investment. In order to prevent the hydrogen embrittlement of the palladium membrane, the operating temperature of the palladium membrane reactor should be higher than 350 degrees. At present, the main WGS reaction catalysts used in industry mainly include iron-based high-slew catalysts, copper-based low-slew catalysts, and cobalt-molybdenum-based sulfur-resistant wide-temperature catalysts. However, these catalysts are not suitable for use in palladium membrane reactor systems due to their disadvantages such as harsh reduction conditions, narrow use temperature, easy poisoning, and easy spontaneous combustion when exposed to air. Therefore, the development of water vapor shift catalysts with high activity, good thermal stability and high stability has become one of the keys for water vapor shift palladium membrane reactors. In this field, the noble metal (Pt, Au, Pd, etc.)/reducible support (CeO ₂ , La ₂ O ₃ , etc.) system has attracted extensive attention from scientists all over the world. But many noble metal/reducible supported catalysts are not stable enough in reformed gas (Zalc, JM; Sokolovskii, DG; DGJCatal.2002,209,169.), In addition, due to expensive noble metals and rare earth elements (CeO ₂ , La ₂ O ₃ ), its practical application is also limited. As a cheap and environmentally friendly material, hydroxyapatite has also received some attention as a catalyst. Au loaded onto hydroxyapatite for water vapor shift is only applied to 320 degrees, while Ru loaded onto hydroxyapatite for water vapor shift has serious methanation side reactions (A.Venugopal, MS Scurrell, Applied Catalysis A:General2003, 245, 137.).

Contents of the invention

The object of the present invention is to provide a noble metal/apatite catalyst with low cost and good catalytic activity and its preparation and application. When the catalyst is used for water vapor shift reaction, it has high activity and good stability.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A kind of catalyst for carbon monoxide water vapor shift (WGS) reaction, described catalyst is composed of platinum/apatite; Platinum loading is: mass fraction 0.01%-10%; Carrier apatite is hydroxyapatite (HAP, Ca _10-Z (HPO ₄ ) _Z (PO ₄ ) _6-Z (OH) _2-Z ), fluoride-substituted hydroxyapatite (FAP, Ca _10-Z (HPO ₄ ) _Z (PO ₄ ) _6-Z F _2-Z ), chloride-substituted hydroxyapatite (ClAP, Ca _10-Z (HPO ₄ ) _Z (PO ₄ ) _6-Z Cl _2-Z ), or bromide-substituted hydroxyapatite (BrAP , Ca _10-Z (HPO ₄ ) _Z (PO ₄ ) _6-Z Br _2-Z ), wherein the Ca/P molar ratio range is: 1.5≤Ca/P≤1.93.

In the catalyst, the platinum content is preferably 0.3%-5% (mass fraction). The preparation of the catalyst: put hydroxyapatite or halogen-substituted hydroxyapatite solid in a certain amount of H ₂ PtCl ₆ or In PdCl ₂ aqueous solution, immerse at room temperature for 10-24h, dry, and bake at 400-600°C for 2-4 hours to obtain a catalyst in which Pt or Pd is supported on apatite.

The main steps of the preparation of the carrier hydroxyapatite are: dissolving calcium nitrate and diammonium hydrogen phosphate in a certain amount of water respectively, adding concentrated ammonia water to adjust the pH value of the solution, and dripping the diammonium hydrogen phosphate solution under the condition of stirring Add to calcium nitrate solution, stir at 80-95°C for 2-4h, precipitate at room temperature, age, wash and dry, and roast at 400-600°C for 2-4 hours to obtain carrier hydroxyapatite.

The main steps for the preparation of the halogen-substituted hydroxyapatite of the carrier are: dissolving calcium nitrate and diammonium hydrogen phosphate in a certain amount of water respectively, adding ammonium fluoride, ammonium chloride or ammonium bromide to the diammonium hydrogen phosphate In the solution, add concentrated ammonia water to adjust the pH value of the solution, add the mixed solution of diammonium hydrogen phosphate and ammonium fluoride, ammonium chloride or ammonium bromide dropwise to the calcium nitrate solution under the condition of stirring, at 80-95 ℃ Stir for 2-4 hours, age the precipitate at room temperature, wash and dry, and bake at 400-600° C. for 2-4 hours to obtain carrier halogen-substituted hydroxyapatite.

The application of the catalyst of the invention in the water vapor shift reaction.

The present invention has the following advantages:

1. The present invention adopts precipitation method and impregnation method to prepare catalyst. The operation process is simple, the conditions are mild, and the repeatability is good;

2. The catalyst involved in the present invention does not need rare earth elements such as Ce and La, and instead adopts cheap Ca and P, which reduces the cost of the catalyst;

3. The catalyst prepared by the present invention is used for the water vapor shift reaction, even at high temperature (450° C.), there is no side reaction such as methanation;

4. _The catalyst prepared by the present invention shows higher catalytic activity than Pt/CeO2 catalyst for water vapor shift reaction at high temperature;

5. The catalyst prepared by the present invention does not require any oxidation or reduction pretreatment before use;

6. The catalyst involved in the present invention has the characteristics of environmental friendliness (hydroxyapatite is a typical biological material), and the catalyst has good stability;

The above advantages make the catalyst prepared by the present invention a catalyst with industrial application prospects.

Description of drawings

Figure 1 is a comparative diagram of the catalytic activity of 1%Pt/HAP-X in 5%CO-20%H2O-75%He.

Fig. 2 is a comparison chart of catalytic activity of 1%Pt/CeO ₂ , 1%Pt/HAP-1.75, 1%Pt/FAP and 1%Pt/ClAP in 5%CO-20%H2O-75%He.

Fig. 3 is a graph showing the stability experiment results of 1% Pt/CeO ₂ and 1% Pt/HAP-1.75 in 15% CO-5% CO ₂ -30% H ₂ O-40% H ₂ -10N ₂ .

detailed description

The technical details of the present invention are described in detail by the following examples and experimental examples. It should be noted that the given examples and experimental examples are only used to further illustrate the technical characteristics of the present invention, rather than to limit the present invention.

Comparative example 1

Prepare a ₁ % Pt/CeO2 catalyst (the number in front of Pt indicates the mass percentage of Pt in the catalyst).

The Ce(NO ₃ ) ₃ ·4H ₂ O was placed in a muffle furnace and calcined at 450° C. for 4 hours to obtain CeO ₂ powder. Take 1g of CeO ₂ powder and add it to 1.365ml of 0.02g/ml H ₂ PtCl ₆ aqueous solution, evaporate in a 60°C water bath until most of the water evaporates to dryness, immerse at room temperature for 24 hours, dry in a 60°C oven for 12 hours, and dry at 450°C The 1% Pt/CeO ₂ catalyst was obtained by calcining in air in a muffle furnace for 4 hours.

Example 1

Prepare 1% Pt/HAP-X (the number in front of Pt represents the mass percentage of Pt in the catalyst), where X is the molar ratio of Ca/P in the catalyst obtained according to the following preparation method. For example, HAP-1.76 means that the molar ratio of Ca/P in the catalyst is 1.76.

Weigh 7.87g Ca(NO ₃ ) ₂ ·4H ₂ O and dissolve it in 100ml distilled water, weigh 2.64g (NH ₄ ) ₂ HPO ₄ and dissolve it in 100ml distilled water, stir to dissolve completely, use commercially available 25%- Adjust the pH value of the solution to 10.5 with 28% ammonia water, and slowly add the (NH ₄ ) ₂ HPO ₄ solution dropwise to the Ca(NO ₃ ) ₂ ·4H ₂ O solution with a constant flow pump under stirring. After the end, transfer the mixed solution to a 90°C water bath, continue to stir, take it out after 2 hours, put it at room temperature for aging for 6 hours, wash and filter the precipitate, dry it in an oven at 60°C for 12 hours, and roast it in air in a muffle furnace at 500°C for 4 hours. hours, the carrier HAP-1.76 was obtained. After grinding 1g of HAP-1.76, it was added to 1.365ml of 0.02g/ml H ₂ PtCl ₆ aqueous solution, immersed at room temperature for 24 hours, dried in an oven at 60°C for 12 hours, and calcined in air in a muffle furnace at 500°C for 4 hours to obtain 1% Pt/HAP-X catalyst.

Example 2

1%Pt/FAP and 1%Pt/ClAP were prepared, where FAP stands for fluoride ion substituted hydroxyapatite and ClAP stands for chloride ion substituted hydroxyapatite.

Weigh 7.87g Ca(NO ₃ ) ₂ ·4H ₂ O in 100ml distilled water, weigh 2.64g (NH ₄ ) ₂ HPO ₄ and 0.247g NH ₄ F or 0.357g NH ₄ Cl in 100ml distilled water, stir Dissolve it completely, adjust the pH value of the solution to 10 with commercially available 25%-28% ammonia water, and slowly add the (NH ₄ ) ₂ HPO ₄ solution to the Ca(NO ₃ ) Dissolve in ₂ ·4H ₂ O, after the dropwise addition, transfer the mixed solution to a 90°C water bath, continue to stir, take it out after 2 hours, put it at room temperature for 6 hours, wash and filter the precipitate, and dry it in an oven at 60°C 12 hours, calcination in muffle furnace at 500°C for 4 hours in air to obtain carrier FAP or ClAP. Grind 1g of FAP or ClAP, add it to 1.365ml of 0.02g/ml H ₂ PtCl ₆ aqueous solution, immerse at room temperature for 24 hours, dry in 60°C oven for 12 hours, and bake in air in muffle furnace at 500°C for 4 hours, respectively 1% Pt/FAP and 1% Pt/ClAP catalysts were obtained.

Example 3

The Ca/P molar ratio of the catalyst was changed by Ca(NO ₃ ) ₂ modification.

Dissolve 0.12g Ca(NO ₃ ) ₂ ·4H2O in 1ml H ₂ O, add 0.5g HAP-1.58, stir evenly, impregnate at room temperature for 24 hours, dry in oven at 60°C for 12 hours, bake in air at 500°C muffle furnace for 4 hours , to obtain HAP-1.74.

Application example 1

Application of catalysts 1%Pt/HAP-1.76, 1%Pt/HAP-1.75, 1%Pt/HAP-1.68, 1%Pt/HAP-1.58, 1%Pt/HAP-1.74.

Catalyst pellets, crushed to a size of 40-60 mesh, take 75mg of catalyst particles and dilute with 100mg of quartz sand of the same mesh, place in a quartz reactor with an inner diameter of 8mm, heat up to 250°C under _N2 or He, and pass through 5 %CO-20%H ₂ O-75%He (V/V) reaction gas, the total gas flow rate is 187.5ml/min, and the mass space velocity GHSV=150,000ml/g/h. The reaction temperature was gradually increased to 450°C, and the reactivity of the catalyst at different temperatures was investigated. The experimental results are shown in Figure 1.

With the increase of the Ca/P molar ratio in the catalyst, the reactivity gradually increased, and there was no change in the reactivity when the Ca/P molar ratio was further increased.

Application example 2

Catalyst Application 1%Pt/CeO ₂ , 1%Pt/HAP-1.75, 1%Pt/FAP and 1%Pt/ClAP

Catalyst pellets, crushed to a size of 40-60 mesh, take 75mg of catalyst particles and dilute with 100mg of quartz sand of the same mesh, place in a quartz reactor with an inner diameter of 8mm, heat up to 250°C under _N2 or He, and pass through 5 %CO-20%H ₂ O-75%He reaction gas, total gas flow rate is 187.5ml/min, mass space velocity GHSV=150,000ml/g/h. The reaction temperature was gradually increased to 450°C, and the reactivity of the catalyst at different temperatures was investigated. The experimental results are shown in Figure 2.

At 250 °C, the ₁ %Pt/CeO2 catalyst had the highest reactivity, but as the temperature increased, the 1%Pt/HAP-1.75 and 1%Pt/ClAP catalysts outperformed the ₁ %Pt/CeO2 catalyst, and The 1%Pt/HAP-1.75 and 1%Pt/ClAP catalysts exhibited the same reactivity in all temperature ranges.

Application example 3

Evaluation of Catalyst Stability 1%Pt/CeO ₂ and 1%Pt/HAP-1.75

Catalyst pellets, crushed to 40-60 mesh size, take 100mg of catalyst particles, put them in a quartz reactor with an inner diameter of 8mm, heat up to 400°C under _N2 , and feed typical reformed gas, the composition is: 15% CO -5%CO ₂ -30%H ₂ O-40%H ₂ -10N ₂ , the total gas flow rate is 150ml/min, and the mass space velocity is: GHSV=90,000ml/g/h. The reaction was carried out for 100 hours to check the stability of the catalyst. The experimental results are shown in Figure 3.

The catalytic activity of 1%Pt/HAP-1.75 and 1%Pt/CeO ₂ catalysts decreased slightly at the beginning of the reaction, and reached a steady state after about 30 hours. During the entire 100-hour evaluation process, 1%Pt/HAP The activity of -1.75 is consistently higher than that of ₁ %Pt/CeO2 and shows a stability comparable to that of the ₁ %Pt/CeO2 catalyst.

The reaction product was analyzed online by gas chromatography, and the CO conversion rate was calculated using the following formula.

Conversion rate (%) = (CO concentration in raw material - CO concentration in product) / CO concentration in raw material

Conclusion: From application example 1, it can be seen that with the increase of Ca/P molar ratio, the reaction activity gradually increases, which is reflected in the increase of CO conversion rate. It can be seen from Application Example 2 that the activities of 1%Pt/HAP-1.75 and 1%Pt/ClAP catalysts are basically similar, and both are more than 1%Pt/CeO ₂ catalysts. It can be seen from Application Example 3 that the 1%Pt/HAP-1.75 catalyst exhibits good stability in typical reformed gas.

Analysis explanation: the catalyst prepared by the present invention shows good catalytic activity in typical reformed gas, and its catalytic activity is higher than that of the rare earth oxide (CeO ₂ ) supported catalyst. The catalyst does not use rare earth elements, but instead uses cheap Ca and P, making the cost of the catalyst lower _than that of the Pt/CeO2 catalyst. The catalyst showed good high temperature stability in application.

Claims (8)

1. an apatite load platinum catalyst, it is characterised in that: platinum is carried on apatite and carries On body, in catalyst, the mass loading amount of platinum is 0.01%-10%.

Catalyst the most according to claim 1, it is characterised in that: carrier apatite is hydroxyl Base apatite (HAP, Ca_10-Z(HPO₄)_Z(PO₄)_6-Z(OH)_2-Z, 0 < z≤1), fluorion takes Hydroxyapatite (FAP, the Ca in generation_10-Z(HPO₄)_Z(PO₄)_6-ZF_2-Z, 0 ＜ z≤1), chloride ion Substituted hydroxyapatite (ClAP, Ca_10-Z(HPO₄)_Z(PO₄)_6-ZCl_2-Z, 0 ＜ z≤1) or Person's bromide ion substituted hydroxyapatite (BrAP, Ca_10-Z(HPO₄)_Z(PO₄)_6-ZBr_2-Z, 0 ＜ z ≤ 1) one or two or more kinds in, in apatite, Ca/P molar ratio range is: 1.5≤Ca/P ≤1.93。

Catalyst the most according to claim 1 or claim 2, it is characterised in that: platinum is at catalyst Middle load capacity is mass fraction 0.3%-5%, and in apatite, Ca/P molar ratio range is: 1.58≤ Ca/P≤1.8。

4. the preparation method of the arbitrary described catalyst of claim 1-3, it is characterised in that:

By hydroxyapatite, the substituted hydroxyapatite of fluorion, chloride ion substituted hydroxyl phosphorus One or two or more kinds in lime stone or bromide ion substituted hydroxyapatite solid is placed in H₂PtCl₆In aqueous solution, at room temperature dipping 10-24 hour, it is dried, 400-600 DEG C of roasting Burn 2-4 hour, obtain the catalyst that Pt is carried on apatite.

5. the preparation method of catalyst as claimed in claim 4, it is characterised in that: wherein, Prepared by carrier hydroxyapatite mainly comprises the following steps: calcium nitrate and diammonium phosphate are dissolved in respectively In water, it is separately added into the pH value 9-11 of strong aqua ammonia regulation solution, calcium nitrate solution molar concentration 0.05mol/L to 4mol/L (usually 0.33mol/L), ammonium dibasic phosphate solution molar concentration 0.05mol/L to 3mol/L (usually 0.20mol/L), by phosphoric acid under conditions of stirring Hydrogen two ammonium salt solution is added drop-wise in calcium nitrate solution, controls to rub by needed for calcium nitrate and diammonium phosphate That ratio 1.5 to 2.0, stirs 2-4 hour at 80-95 DEG C, precipitates aged at room temperature, and washing is dry Dry, 400-600 DEG C of roasting 2-4 hour, obtain carrier hydroxyapatite.

6. the preparation method of catalyst as claimed in claim 4, it is characterised in that: wherein, The hydroxyapatite (one or two or more kinds in FAP, ClAP, BrAP) of carrier halogen substiuted Mainly comprising the following steps of preparation: by the most soluble in water to calcium nitrate and diammonium phosphate, by ammonium fluoride, One or two or more kinds in ammonium chloride or ammonium bromide joins in ammonium dibasic phosphate solution, point Not Jia Ru strong aqua ammonia regulation solution pH value=9-11, calcium nitrate solution molar concentration 0.05mol/L To 4mol/L (usually 0.33mol/L), ammonium dibasic phosphate solution molar concentration 0.05mol/L arrives 3mol/L (usually 0.20mol/L), the one in ammonium fluoride, ammonium chloride or ammonium bromide Or more than two kinds in solution, molar concentration 0.0167mol/L to 1mol/L is (usually 0.667mol/L), under conditions of stirring by diammonium phosphate and ammonium fluoride, ammonium chloride or The mixed solution of one or two or more kinds in ammonium bromide is added drop-wise in calcium nitrate solution, controls to press Molar ratio 1.5 to 2.0 needed for calcium nitrate and diammonium phosphate, stirs 2-4h at 80-95 DEG C, Precipitation aged at room temperature, washing is dried, and 400-600 DEG C of roasting 2-4 hour obtains carrier halogen Substituted hydroxyapatite.

7. according to the preparation method of described catalyst arbitrary in claim 5 or 6, its feature It is: the Ca/P ratio of carrier apatite can be by carrying out modulation with calcium salt modification；Particularly as follows: The Ca/P mol ratio of target as required, by hydroxyapatite, the substituted hydroxyl of fluorion The substituted hydroxyapatite of apatite, chloride ion or bromide ion substituted hydroxyapatite solid Being placed in calcium saline solution, aqueous solution Ca ion molar concentration is 0.5mol/L to 5mol/L (usually 2mol/L), at room temperature dipping 10-24 hour, be dried, at 400-600 DEG C Roasting 2-4 hour；Calcium salt is Ca (NO₃)₂、CaCl₂In one or two kinds.

8. the arbitrary described catalyst of the claim 1-3 application in water gas shift reation.