WO2016124161A1 - Pt/α-moc1-x supported catalyst, and synthesis and uses thereof - Google Patents

Abstract

Disclosed are a Pt/α-MoC_1-x supported catalyst, and synthesis and uses thereof. Dissolving a platinum precursor salt in water, immersing same onto an MoO₃ support, and stirring till dry; placing the solid in a vacuum drying chamber to heat till dry in a temperature between 40℃ and 60℃; placing in a muffle furnace for heating under a temperature program to 400℃ and 500℃, maintaining at the highest temperature for a period of time, and obtaining Pt-MoO₃; carbonizing the obtained solid in a carbonized atmosphere of a certain ratio to obtain the Pt/α-MoC_1-x catalyst. The Pt/α-MoC_1-x supported catalyst is a good catalyst for producing hydrogen using methanol by means of low temperature (150℃ to 190℃) water-phase reformation. The catalytic activity is better than platinum supported on an oxide and platinum supported on non-pure MoC. The invention has relatively high stability in simulations close to a real system.

Description

Pt/α-MoC1-x supported catalyst and its synthesis and application

This application claims priority to Chinese Patent Application No. 201510053793.8, entitled "Pt/α-MoC _1-x Supported Catalyst and Its Synthesis and Application", filed on February 2, 2015. The content is incorporated herein by reference.

Technical field

The invention belongs to the field of catalysis, relates to a Pt/α-MoC _1-x supported catalyst and its synthesis and application, in particular to a Pt/α-MoC _1- catalyst with a water phase stability and low-temperature high-efficiency reforming methanol hydrogen production catalyst. The synthesis method and application of _x .

Background technique

The use of waste gas and solid particles generated by fossil energy far exceeds the automatic purification capability of the environment. The development of clean energy is not only the fundamental solution to energy problems, but also the key to solving environmental problems. Hydrogen energy is recognized as a clean, high calorific value energy source. The most effective form of hydrogen energy utilization is a hydrogen fuel cell. Compared to the combustion reaction of an internal combustion engine, a hydrogen fuel cell efficiently converts chemical energy into electrical energy, and the utilization rate is increased by 40% to 50%. However, the hydrogen storage technology is backward. At present, whether it is storing hydrogen in the form of gas or storing hydrogen in the form of liquid, there are problems of excessive pressure, large volume and low safety factor. If hydrogen is stored in a liquid fuel (methanol, formic acid, ammonia) in a chemical form, and the stored hydrogen is released in situ for use in a fuel cell by a certain catalytic reaction, this method can effectively solve the fuel cell storage. The problem of hydrogen is difficult to promote the development of hydrogen fuel cells.

Methanol is the most promising hydrogen storage liquid material. Because methanol can be industrialized on a large scale, its output value exceeds fossil energy. At the same time, methanol has a high H/C ratio and has a strong hydrogen storage capacity. In addition, methanol does not contain CC bonds and easily releases hydrogen. And fewer by-products. At present, the hydrogen production method of methanol is through steam reforming and liquid phase reforming of methanol which is studied in reforming and reforming. The current research on water vapor reforming mainly focuses on Cu-based catalysts and noble metal (group VIII) catalysts: Cu-based catalysts have a reaction temperature of 250-300 ° C, and the reaction activity is high, but the catalyst is easily oxidized by water, and when the reaction is stopped, reforming is carried out. Gas condensation (H ₂ O and CH ₃ OH) will cause the catalyst to live 40% or more of activity; noble metal catalysts generally use oxide as a carrier, but methanol is more susceptible to decomposition reactions on oxide-supported noble metal catalysis. , resulting in CO content exceeding 50% or even higher, CO content far exceeds the tolerance of fuel cells (<100 °C for low-temperature hydrogen fuel cells, CO content should be less than 50ppm, 100-200 °C for high-temperature hydrogen fuel cells, CO The content should be less than 5%). The steam reforming not only needs to vaporize the reactants through the gasifier, but because of the high CO content, the hydrogen is purified by vapor migration (WGS) or Prox. The whole set of equipment is complicated and complicated. Liquid phase methanol reforming directly reacts methanol and water in a solution, without the need to vaporize the reactants, and the reaction in the liquid phase can greatly reduce the CO content, thus eliminating the purification of the generated hydrogen. This makes the liquid phase reforming of methanol and the hydrogen fuel cell integrated device more compact and simple. However, the conventional Cu-based catalyst cannot be stably present in the liquid phase, and the oxide-supported noble metal catalyst has extremely low activity and does not meet the requirements for use.

Summary of the invention

The object of the present invention is to provide a synthesis of a Pt/α-MoC _1-x supported catalyst and its application in liquid phase reforming of methanol, which is prepared by the present invention at a liquid phase reforming reaction temperature (170 to 210 ° C). The Pt-(MoC)-based catalyst which is stable in existence has good methanol liquid phase reforming performance.

The inventors found during the study that the carbide-supported noble metal Pt Pt-(MoC)-based catalyst exhibited superior liquid-phase methanol reforming activity compared to the oxide-supported Pt Pt-(A _x O _y ) catalyst. . It was found that in various types of carbides (pure α phase is recorded as α-MoC _1-x , pure β phase is recorded as β-Mo ₂ C, αβ mixed phase is recorded as MoC _x ), and α-MoC _1-x carrier is expressed. The highest catalytic activity. Through temperature programmed surface reaction (TPSR) and temperature programmed methanol desorption (TPD), it was found that the "-OH" produced by H ₂ O dissociation facilitates the "-CH" cleavage in CH ₃ OH, thereby promoting the reforming of methanol. Low temperature occurs and the formation of CO is suppressed. However, other oxidizing carriers cannot decompose water at a low temperature of 170 to 210 ° C, and methanol decomposition reaction mainly occurs. Therefore, the uniform dispersion of Pt on pure α-MoC _1-x carrier (Pt/α-MoC _1-x ) is the key to low-temperature high-performance liquid methanol reforming.

In order to achieve the above object, the present invention adopts the following technical solutions:

A method for synthesizing a Pt/α-MoC _1-x supported catalyst, comprising the steps of:

1) dissolving the platinum precursor salt in water;

2) adding the platinum precursor salt solution obtained in the step 1) to the MoO ₃ solid, and stirring to dryness;

3) further drying the solid obtained in step 2), and then heating to 400-500 ° C, at a maximum temperature for a certain period of time, to obtain a Pt-MoO ₃ solid;

4) The Pt-MoO ₃ solid obtained in the step 3) is carbonized in a carbonization atmosphere containing both a carbon source and a hydrogen source to obtain a Pt/α-MoC _1-x supported catalyst.

In the above step 1), the platinum precursor salt is generally a water-soluble platinum salt, for example, one selected from the group consisting of potassium chloroplatinate, sodium chloroplatinate, chloroplatinic acid and the like. The concentration of the finally formed platinum precursor salt solution is 0.05-0.3M.

In step 2), the solid MoO ₃ may be obtained by various preparation methods of different sizes, different specific surface areas of MoO _3. By adjusting the amount of platinum precursor salt added, different Pt:Mo molar ratios can be obtained, wherein the Pt element content (molar number) should not exceed the Mo element content (moles).

In step 3), the temperature is programmed in the tube furnace, the temperature of the program temperature is 3~10 °C/min, and the time reserved at the highest temperature is 2-6 hours. Different heating rates and different constant temperature times will affect the size of Pt and Dispersion.

In step 2), the mixture is stirred to dryness at a temperature of 20-40 ° C, and dried in a vacuum drying oven at 40-60 ° C in step 3).

The carbonization atmosphere in step 4) includes CH ₄ /H ₂ or C ₂ H ₆ /H ₂ , and the volume ratio of the carbon source to the hydrogen source is between 10 and 30%, preferably 20% by volume, and the rate of carbonization is 1 to 10 ° C / min, the maximum temperature of carbonization is 600 ~ 900 ° C.

The preparation of Pt/α-MoC _1-x at different temperatures using different carbonization atmospheres affects the crystallinity and Pt size and dispersion of the Pt/α-MoC _1-x carrier.

The present invention provides a Pt/α-MoC _1-x supported catalyst synthesized by the above method.

Further, the carrier α-MoC _1-x of the above Pt/α-MoC _1-x supported catalyst is a pure α phase, and the weight percentage of Pt is 0.5 to 15%.

Further, in the above Pt/α-MoC _1-x supported catalyst, Pt is distributed in a layered form on the α-MoC _1-x carrier.

The invention also provides the use of the above Pt/α-MoC _1-x supported catalyst for efficient reforming of methanol at low temperature (150-210 ° C) in an aqueous phase.

As used herein, the expression "Pt/α-MoC _1-x supported catalyst" refers to a catalyst in which Pt is supported on an α-MoC _1-x support, wherein x is from 0 to 0.5. The technical advantages of the present invention are:

1. Developed a good catalyst Pt/α-MoC _{1-x for the} efficient reforming of methanol in aqueous phase. Its activity under 190 °C reaction condition is much better than other precious metal catalysts supported by molybdenum carbide support, far superior to oxide. Supported precious metal catalyst. It is worth mentioning that at this rate of high activity hydrogen production, the selectivity of CO is less than 0.1%. The catalyst overcomes the weakness of the low hydrogen production activity of the supported precious metal catalyst with high CO selectivity.

2. The α-MoC _{1-x is} stably present in the aqueous phase and has the characteristics of low temperature dissociation water, which improves the coverage of “-OH” on the catalyst surface. “-OH” is beneficial to the “-CH” cleavage of Pt catalyzed methanol. Thereby, the methanol reforming reaction is promoted and the methanol decomposition reaction is inhibited.

Therefore, the present invention has wide application prospects in the Pt-(MoC)-based catalyst for the efficient reforming of methanol aqueous phase or the catalytic reaction of molybdenum carbide in the aqueous phase.

DRAWINGS

In order to more clearly illustrate the embodiments of the present invention and the prior art, the following description of the embodiments and the drawings used in the prior art will be briefly described. It is obvious that the drawings in the following description are only Some embodiments of the invention may also be used to obtain other figures from these figures without departing from the art.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an XRD pattern of various Pt-(MoC)-based catalysts synthesized in different supports in Examples 1, 2, 3, 4 and Comparative Example 1.

2 is a transmission electron micrograph of Pt/α-MoC _1-x in Example 1.

Figure 3 is a graph showing the reactivity data of Pt/?-MoC _1-x in Example 1 obtained by optimizing the methanol to water concentration ratio.

Fig. 4 is a graph showing activity evaluation data of Pt/α-MoC _1-x in Example 1.

Figure 5 is a graph of temperature-programmed surface reaction (TPSR) of various Pt-(MoC)-based catalysts synthesized in different carriers in Example 1 and Comparative Examples 1, 2, wherein (a) corresponds to Example 1, and (b) corresponds to the comparative example. 1, (c) corresponds to Comparative Example 2.

detailed description

The present invention will be further described in detail below with reference to the accompanying drawings. It is apparent that the described embodiments are only a part of the embodiments of the invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention in any way.

Example ₁ Synthesis of Pt/α-MoC _1-x (100% α) Catalyst (MoO ₃ 200 nm)

Dissolve 1 g of platinum precursor salt chloroplatinic acid hexahydrate in 10 mL of water, impregnate H ₂ PtCl ₆ solution onto MoO ₃ support, stir to dryness at room temperature, then dry in a vacuum oven at 60 ° C, then place the catalyst Calcination in a muffle furnace, temperature programmed to 500 ° C and retained for 120 min. Finally carbonized in a 20% CH ₄ /H ₂ atmosphere, programmed to 700 ° C and retained for 120 min.

The morphology of the Pt/α-MoC _1-x supported catalyst synthesized in this example was observed using a dark field scanning transmission mode of a transmission electron microscope, and the bulk phase structure was observed by an X-ray diffractometer (XRD).

The XRD sample preparation method was as follows: The above carbonized catalyst was passivated with a passivation gas of 0.5% O ₂ /Ar for 8 h, and was ground for use in an XRD test.

The transmission electron microscope sample preparation method is as follows: the obtained catalyst is placed in a glove box, and the ground solid is introduced into an oxygen-free anhydrous ethanol to be dispersed, and a plurality of droplets are dispersed and added to an ultrathin carbon film for transmission electron microscope. Above, after air drying, it is sent to a transmission electron microscope for testing.

The XRD pattern is shown in Figure 1 (a), and the Pt/α-MoC _1-x vector is pure α-MoC _1-x (100% α). The electron micrograph is shown in Fig. 2. Pt is mostly distributed in a layered form on the α-MoC _1-x carrier, about 2 nm, and can be determined to be epitaxial growth by lattice alignment.

The synthesis method can control the loading of different Pt/α-MoC _1-x by the calcination procedure, and the Pt wt% obtained by the experimental method is 2.2%.

The Pt-(MoC)-based catalyst synthesized in this embodiment can be controlled by changing the form of the precursor. The composition of the phase of the carrier MoC.

Example 2 Synthesis of Pt/MoC _x (70% α)

Dissolve 1 g of platinum precursor salt chloroplatinic acid hexahydrate in 10 mL of water, impregnate H ₂ PtCl ₆ solution onto MoO ₃ carrier, stir to dryness at room temperature, and then dry at 60 ° C in a vacuum drying oven at 20% CH ₄ The carbonization procedure in the atmosphere of /H ₂ was ramped to 700 ° C and retained for 120 min. The XRD pattern is shown in Figure 1(b).

Example 3 Synthesis of Pt/MoC _x (45% α)

Take 1g of ammonium heptamolybdate dissolved in 10mL deionized water, stir until completely dissolved, dissolve 1kg of platinum precursor salt chloroplatinic acid hexahydrate in 10mL water, add chloroplatinic acid aqueous solution to ammonium molybdate solution, stir for 2h to precipitate Completely, it was evaporated to dryness in an oil bath at 100 ° C, ground in an oven at 60 ° C for 3 h, and the catalyst was carbonized in an atmosphere of 20% CH ₄ /H ₂ , and the temperature was programmed to 700 ° C for 120 min. The XRD pattern is shown in Figure 1(d).

Example 4 Synthesis of Pt/Mo ₂ C (100% β)

1 g of ammonium heptamolybdate was dissolved in a muffle furnace, and the temperature was programmed to 500 ° C and left for 240 min to obtain 0.8 g of MoO ₃ . The MoO ₃ was carbonized in an atmosphere of 20% CH ₄ /H ₂ , programmed to a temperature of 700 ° C and retained for 120 min to obtain β-Mo ₂ C, which was passivated with a passivation gas of 0.5% O ₂ /Ar for 8 h.

Dissolve 1 g of platinum precursor salt chloroplatinic acid hexahydrate in 10 mL of water, add chloroplatinic acid aqueous solution to the ground β-Mo ₂ C, stir to dryness, place in a vacuum oven at 60 ° C for 3 h, and then place the catalyst in Carbonization was carried out in an atmosphere of 20% CH ₄ /H ₂ , and the temperature was programmed to 700 ° C for 120 min. The XRD pattern is shown in Figure 1(e).

Comparative Example 1 Synthesis of Pt/α-MoC _1-x (100%α) Catalyst (ammonium heptamolybdate)

Take 1g of ammonium heptamolybdate dissolved in 10mL deionized water, stir until completely dissolved, dissolve 1kg of platinum precursor salt chloroplatinic acid hexahydrate in 10mL water, add chloroplatinic acid aqueous solution to ammonium molybdate solution, stir for 2h to precipitate Completely, evaporate to dryness in a 100 ° C oil bath, grind and place in an oven at 60 ° C for 3 h, then place the catalyst in a muffle furnace for calcination, and program temperature to 500 ° C for 120 min. The catalyst was again carbonized in an atmosphere of 20% CH ₄ /H ₂ and was warmed to 700 ° C for 120 min. For the synthesis method, see Ma, Y., et al., International Journal of Hydrogen Energy, 2014. 39(1): p. 258-266. The XRD pattern is shown in Figure 1(c). As seen from the XRD pattern, in the catalyst prepared in Comparative Example 1, Pt was not distributed in a layered form on the support but in the form of dispersed nanoparticles.

Comparative Example 2 Pt/Al ₂ O ₃

1 g of the platinum precursor salt chloroplatinic acid hexahydrate was dissolved in 10 mL of water, and the platinum precursor salt was added to 0.8 g of Al ₂ O ₃ (equal volume impregnation volume 800 μL), stirred to dryness and placed in an oven at 60 ° C for 3 h, then The catalyst was calcined in a muffle furnace and programmed to 500 ° C for 120 min. The catalyst was again reduced in an H ₂ atmosphere, programmed to 500 ° C and held at 500 ° C for 120 min.

Comparative Example 3 Pt/TiO ₂

1 g of platinum precursor salt chloroplatinic acid hexahydrate was dissolved in 10 mL of water, and a platinum precursor salt was added to 0.8 g of TiO ₂ (an equal volume of impregnation volume of 700 μL), stirred to dryness and placed in an oven at 60 ° C for 3 h, and then the catalyst was It was calcined in a muffle furnace and programmed to 500 ° C for 120 min. The catalyst was again reduced to 500 ° C in an atmosphere of H ₂ and held at 500 ° C for 120 min.

Comparative Example 4 Pt-Mo ₂ C/C

Dissolve 0.92 g of ammonium heptamolybdate in 30 mL of hot water, dissolve 1 g of platinum precursor salt chloroplatinic acid hexahydrate in 10 mL of water, add platinum solution to 2.5 g of treated activated carbon, stir at room temperature for 12 h, then irradiate with infrared light. The mixture was stirred and dried to a gel state, dried in an oven at 60 ° C, and finally baked at a constant temperature of 120 ° C to obtain a catalyst precursor. The precursor was reduced in a tube furnace, programmed to 400 ° C for 1 h, and then programmed to 700 ° C for 180 min.

For its synthesis, see Li, J., et al., Energy & Environmental Science, 2014.7(1): p.393.

The supported catalyst prepared above is used in an aqueous methanol reforming reaction under the following conditions: a closed system reaction, 5 mL of methanol and 45 mL of water are added to the reaction system, n (methanol): n (water) = 1:20, at 2 MPa. N ₂ (10% Ar is an internal standard) protective gas reaction, the reaction temperature was 190 ° C, the reaction was carried out for 10 h, and the gas phase product was detected by gas chromatography after being lowered to room temperature.

Wherein, for the Pt/α-MoC _1-x supported catalyst prepared in Example 1, after adjusting the reaction conditions n (methanol): n (water) concentration, in n (methanol): n (water) = 1: At 3 o'clock, the reactivity was the highest, as shown in Figure 3. Meanwhile, since the Pt/α-MoC _1-x supported catalyst prepared in Example 1 has high activity, and the reaction system is a closed system, excessive generation of H ₂ suppresses the reactivity, so that a catalyst having a high activity is required to be shorter. The time (eg 1 h) was used to evaluate the catalytic activity, see Table 1 Entry 2 ^a .

The reaction performance of each catalyst is shown in Table 1 below.

Table 1. Comparison of the reaction performance of aqueous phase methanol reforming (190 °C) of Pt-(MoC) based catalysts and other catalysts

It can be seen that the catalytic activity of the present invention at 190 ° C is significantly higher than other molybdenum carbide based catalysts and oxide supported Pt catalysts. At the same time, the catalyst of the invention not only has a relatively high hydrogen production rate and a low CO selectivity (less than 0.1%, as shown in Fig. 3), but is far lower than the CO tolerance of the high temperature hydrogen fuel cell, overcoming the oxide carrier loading. Pt catalyst has low catalytic activity and high CO selectivity; its near-real system simulation data shows the stability of catalysis during heating and cooling. The weakness of the conventional Cu catalyst and water deactivation which cannot be used multiple times is overcome, and the activity of the Cu-based catalyst at 250 ° C is approached at 190 ° C.

The temperature-programmed surface reaction (TPSR) patterns of various Pt-(MoC)-based catalysts synthesized in different carriers in Example 1 and Comparative Examples 1 and 2 are shown in Figures 5(a), (b) and (c), respectively. The reaction procedure is 30-500 ° C, 5 ° C / mon, mass spectrometry detection m / z is 2, 28, 16, 44, etc., TPSR mainly shows that Pt-MoC system catalyst (a) (b) at low temperature 115 ° C The -CH and -OH bonds can be broken, and hydrogen and CO _{2 are} produced to undergo methanol reforming reaction. However, the conventional catalyst (c) needs to undergo -CH bond cleavage at 180 ° C, and no H ₂ O -OH bond cleavage occurs. Methanol decomposition mainly occurs, although H ₂ is produced but a large amount of CO is generated at the same time, which is not suitable for use with a fuel cell.

In short, this is a promising catalyst for the integration of methanol reforming and hydrogen fuel cells.

The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalents, improvements, etc., which are made within the spirit and principles of the present invention, should be included in the present invention. Within the scope of protection.

Claims (11)

1. A method for synthesizing a Pt/α-MoC _1-x supported catalyst, comprising the steps of:

   1) dissolving the platinum precursor salt in water;

   2) adding the platinum precursor salt solution obtained in the step 1) to the MoO ₃ solid, and stirring to dryness;

   3) further drying the solid obtained in step 2), and then heating to 400-500 ° C, at a maximum temperature for a certain period of time, to obtain a Pt-MoO ₃ solid;

   4) The Pt-MoO ₃ solid obtained in the step 3) is carbonized in a carbonization atmosphere containing both a carbon source and a hydrogen source to obtain a Pt/α-MoC _1-x supported catalyst.
2. The method for synthesizing a Pt/α-MoC _1-x supported catalyst according to claim 1, wherein in the step 1), the platinum precursor salt is selected from the group consisting of potassium chloroplatinate and sodium chloroplatinate. Or chloroplatinic acid, the final concentration of the platinum precursor salt solution formed is 0.05-0.3M.
3. The method for synthesizing a Pt/α-MoC _1-x supported catalyst according to claim 1 or 2, wherein in step 2), different Pt:Mo moles are obtained by adjusting the amount of the platinum precursor salt added. The ratio of the number of moles of the Pt element does not exceed the number of moles of the Mo element.
4. The method for synthesizing a Pt/α-MoC _1-x supported catalyst according to any one of claims 1 to 3, wherein in step 3), the temperature is programmed in the tube furnace, and the temperature of the program is 3 ~10 ° C / min, the time reserved at the highest temperature 2 ~ 6h.
5. The method for synthesizing a Pt/α-MoC _1-x supported catalyst according to any one of claims 1 to 4, wherein in step 2), stirring is carried out at a temperature of 20-40 ° C, step 3 In the vacuum drying oven, drying at 40-60 ° C.
6. The method for synthesizing a Pt/α-MoC _1-x supported catalyst according to any one of claims 1 to 5, wherein in the step 4), the carbonization atmosphere comprises CH ₄ /H ₂ or C ₂ H ₆ /H ₂ , the volume ratio of the carbon source to the hydrogen source is between 10 and 30%; the rate of carbonization programming is 1 to 10 ° C / min, and the maximum temperature of carbonization is 600 to 900 ° C.
7. A Pt/α-MoC _1-x supported catalyst synthesized by the synthesis method according to any one of claims 1 to 6.
8. A Pt/α-MoC _1-x supported catalyst characterized in that Pt is distributed in a layered form on the α-MoC _1-x support in the Pt/α-MoC _1-x supported catalyst.
9. The Pt/α-MoC _1-x supported catalyst according to claim 7 or 8, wherein the carrier α-MoC _1-x of the Pt/α-MoC _1-x supported catalyst is a pure α phase. The weight percentage of Pt is 0.5 to 15%.
10. The Pt/α-MoC _1-x supported catalyst according to claim 7, wherein Pt is distributed in a layered form to α-MoC _1-x in said Pt/α-MoC _1-x supported catalyst. On the carrier.
11. The use of the Pt/α-MoC _1-x supported catalyst according to any one of claims 7 to 10 for efficiently reforming methanol at a low temperature in an aqueous phase, wherein the low temperature means 150 to 210 °C.

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