SULFUR-FREE PLATINUM CATALYST FOR HYDROGEN PRODUCTION

Abstract

This disclosure provides systems and methods related to a Pt/TiO.sub.2 catalyst. In one aspect water with a platinum precursor dissolved therein is mixed with TiO.sub.2 nanoparticles. The TiO.sub.2 nanoparticles with the platinum precursor disposed thereon are heat treated in air to form platinum oxide nanoparticles disposed on the TiO.sub.2 nanoparticles. The TiO.sub.2 nanoparticles are deposited on a TiO.sub.2 substrate to form a structure. The structure is reduced to form platinum nanoparticles disposed on the TiO.sub.2 nanoparticles, including: heat treating the structure at about 375 C. to 450 C. with hydrogen being present; cooling the structure from about 375 C. to 450 C. to about 350 C. at about 2 C./minute with hydrogen being present; and cooling the structure from about 350 C. to room temperature at about 1 C./minute to 5 C./minute with hydrogen being present. After the reduction operation, the structure is heat treated in an atmosphere including methylcyclohexane.

Claims

1. A method comprising: mixing water with a platinum precursor dissolved therein with TiO.sub.2 nanoparticles; heat treating the TiO.sub.2 nanoparticles with the platinum precursor disposed thereon in air to form platinum oxide nanoparticles disposed on the TiO.sub.2 nanoparticles; depositing the TiO.sub.2 nanoparticles on a TiO.sub.2 substrate to form a structure; and reducing the structure to form platinum nanoparticles disposed on the TiO.sub.2 nanoparticles, including heat treating the structure at about 375 C. to 450 C. with hydrogen being present, cooling the structure from about 375 C. to 450 C. to about 350 C. at about 2 C./minute with hydrogen being present, and cooling the structure from about 350 C. to room temperature at about 1 C./minute to 5 C./minute with hydrogen being present; and after the reducing, heat treating the structure in an atmosphere including methylcyclohexane (MCH).

2. The method of claim 1, wherein the platinum precursor is chloroplatinic acid (H.sub.2PtCl.sub.6).

3. The method of claim 1, wherein the mixing is dropwise mixing of the water with the TiO.sub.2 nanoparticles.

4. The method of claim 1, wherein the mixing is performed by incipient wet impregnation.

5. The method of claim 1, wherein the TiO.sub.2 nanoparticles have dimensions of about 15 nanometers to 25 nanometers.

6. The method of claim 1, wherein heat treating the TiO.sub.2 nanoparticles with the platinum precursor disposed thereon is performed at about 400 C. to 500 C. for about 2 hours to 4 hours.

7. The method of claim 1, further comprising: after heat treating TiO.sub.2 nanoparticles with the platinum precursor disposed, cooling the TiO.sub.2 nanoparticles to room temperature at about 1 C./minute to 5 C./minute.

8. The method of claim 1, wherein the structure is heated to about 375 C. to 450 C. at about 10 C./minute with hydrogen being present during the reducing, and wherein the structure is held at about 375 C. to 450 C. for about 1 hour.

9. The method of claim 1, wherein after reducing the structure, at least some of the platinum nanoparticles are embedded in the TiO.sub.2 nanoparticles.

10. The method of claim 1, wherein reducing the structure forms a TiO.sub.2x overlayer on surfaces of the platinum nanoparticles.

11. The method of claim 1, wherein the platinum nanoparticles have dimensions of about 1 nanometer to 2 nanometers.

12. The method of claim 1, wherein the platinum nanoparticles do not include sulfur.

13. The method of claim 1, wherein the TiO.sub.2 nanoparticles and the TiO.sub.2 substrate do not include sulfur.

14. The method of claim 1, wherein the heat treating after the reducing is at about 300 C. to 400 C. for about 20 hours to 30 hours.

15. A method comprising: mixing water with a platinum precursor dissolved therein with TiO.sub.2 nanoparticles; heat treating the TiO.sub.2 nanoparticles with the platinum precursor disposed thereon in air to form platinum oxide nanoparticles disposed on the TiO.sub.2 nanoparticles; depositing the TiO.sub.2 nanoparticles on a TiO.sub.2 substrate to form a structure; reducing the structure to form platinum nanoparticles disposed on the TiO.sub.2 nanoparticles, including heating the structure to about 375 C. to 450 C. at about 10 C./minute with hydrogen being present, heat treating the structure at about 375 C. to 450 C. for about 1 hour with hydrogen being present, cooling the structure from about 375 C. to 450 C. to about 350 C. at about 2 C./minute with hydrogen being present, and cooling the structure from about 350 C. to room temperature at about 1 C./minute to 5 C./minute with hydrogen being present; and after the reducing, heat treating the structure in an atmosphere including methylcyclohexane (MCH), the platinum nanoparticles, the TiO.sub.2 nanoparticles, and the TiO.sub.2 substrate substantially not including sulfur.

16. The method of claim 1, wherein reducing the structure forms a TiO.sub.2-x overlayer on surfaces of the platinum nanoparticles.

17. The method of claim 1, wherein the heat treating after the reducing is at about 300 C. to 400 C. for about 20 hours to 30 hours.

18. A method comprising: mixing water with a platinum precursor dissolved therein with TiO.sub.2 nanoparticles; heat treating the TiO.sub.2 nanoparticles with the platinum precursor disposed thereon in air to form platinum oxide nanoparticles disposed on the TiO.sub.2 nanoparticles; depositing the TiO.sub.2 nanoparticles on a TiO.sub.2 substrate to form a structure; reducing the structure to form platinum nanoparticles disposed on the TiO.sub.2 nanoparticles, including heat treating the structure at about 375 C. to 450 C. with hydrogen being present, cooling the structure from about 375 C. to 450 C. to about 350 C. at about 2 C./minute with hydrogen being present, and cooling the structure from about 350 C. to room temperature at about 1 C./minute to 5 C./minute with hydrogen being present, the reducing the structure forming a TiO.sub.2x overlayer on surfaces of the platinum nanoparticles; and after the reducing, heat treating the structure in an atmosphere including methylcyclohexane (MCH).

19. The method of claim 1, wherein the platinum nanoparticles, the TiO.sub.2 nanoparticles, and the TiO.sub.2 substrate do not include sulfur.

20. The method of claim 1, wherein the heat treating after the reducing is at about 300 C. to 400 C. for about 20 hours to 30 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 shows an example of a flow diagram illustrating a manufacturing process for a sulfur-free platinum catalyst.

[0015] FIG. 2 shows an example of a graph of the dibenzyltoluene (HO-DBT) hydrogenation degree performance of the Pt/TiO.sub.2 catalysts described herein.

DETAILED DESCRIPTION

[0016] Reference will now be made in detail to some specific examples of the invention including the best modes contemplated by the inventors for carrying out the invention. Examples of these specific embodiments are illustrated in the accompanying drawings. While the invention is described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to the described embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

[0017] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. Particular example embodiments of the present invention may be implemented without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.

[0018] Various techniques and mechanisms of the present invention will sometimes be described in singular form for clarity. However, it should be noted that some embodiments include multiple iterations of a technique or multiple instantiations of a mechanism unless noted otherwise.

[0019] The terms about or approximate and the like are synonymous and are used to indicate that the value modified by the term has an understood range associated with it, where the range can be 20%, 15%, 10%, 5%, or 1%. The terms substantially and the like are used to indicate that a value is close to a targeted value, where close can mean, for example, the value is within 80% of the targeted value, within 85% of the targeted value, within 90% of the targeted value, within 95% of the targeted value, or within 99% of the targeted value.

[0020] As used herein, dispose means to place (things) at proper distances apart and in proper positions with regard to each other, to place suitably, adjust; to place or arrange in a particular order.

[0021] FIG. 1 shows an example of a flow diagram illustrating a manufacturing process for a sulfur-free platinum catalyst. Starting at block 105 of the method 100 shown in FIG. 1, water with a platinum precursor dissolved therein is mixed with TiO.sub.2 nanoparticles. In some embodiments, the mixing is dropwise mixing of the water with TiO.sub.2 nanoparticles.

[0022] In some embodiments, the mixing is performed by incipient wet impregnation. In some embodiments, incipient wet impregnation does not generate any waste water pollution. For example, a small volume of water is used to dissolve the platinum precursor. In some embodiments, the platinum precursor solution is mixed with TiO.sub.2 nanoparticles and only the pores of the TiO.sub.2 nanoparticles get filled with precursor solution. The mixing at block 105 results in TiO.sub.2 nanoparticles with the platinum precursor disposed thereon. In some embodiments, the water is then be evaporated from the TiO.sub.2 nanoparticles.

[0023] In some embodiments, the platinum precursor is or comprises chloroplatinic acid (H.sub.2PtCl.sub.6). In some embodiments, the TiO.sub.2 nanoparticles have dimensions of about 15 nanometers to 25 nanometers, or about 20 nanometers.

[0024] At block 110, the TiO.sub.2 nanoparticles with the platinum precursor disposed thereon are heat treated in air to form platinum oxide nanoparticles disposed on the TiO.sub.2 nanoparticles. In some embodiments, the heat treating is performed at about 400 C. to 500 C. for about 2 hours to 4 hours. In some embodiments, the heat treating is performed at about 450 C. for about 3 hours. In some embodiments, the method 100 further comprises after the heat treating, cooling the TiO.sub.2 nanoparticles with the platinum precursor disposed thereon to room temperature at about 1 C./minute to 5 C./minute.

[0025] At block 115, the TiO.sub.2 nanoparticles are deposited on a TiO.sub.2 substrate to form a structure.

[0026] At block 120, the structure is reduced to form platinum nanoparticles disposed on the TiO.sub.2 nanoparticles that are disposed on the TiO.sub.2 substrate. This reduction operation includes heat treating the structure to about 375 C. to 450 C., or at about 400 C., with hydrogen being present, cooling the structure from about 375 C. to 450 C. to about 350 C. at about 2 C./minute with hydrogen being present, and cooling the structure from about 350 C. to room temperature at about 1 C./minute to 5 C./minute with hydrogen being present. Note that with hydrogen being present indicates that hydrogen is in a furnace containing the structure or hydrogen is flowing around the structure during the reduction operation.

[0027] In some embodiments, the structure is heated to about 375 C. to 450 C. at about 10 C./minute with hydrogen being present during the reduction operation. In some embodiments, the structure is held at about 375 C. to 450 C. for about 1 hour.

[0028] In some embodiments, after reducing the structure, at least some of the platinum nanoparticles are embedded or half-embedded in the TiO.sub.2 nanoparticles. In some embodiments, reducing the structure forms a TiO.sub.2x overlayer on surfaces of the platinum nanoparticles. In some embodiments, the TiO.sub.2x overlayer partially encapsulates the platinum nanoparticles.

[0029] In some embodiments, the reduction operation forms a strong metal-support interaction between platinum nanoparticles and TiO.sub.2. For example, a platinum nanoparticle partly covered by a reduced TiO.sub.x overlayer may exhibit unique electronic properties.

[0030] In some embodiments, the platinum nanoparticles have dimensions of about 1 nanometer to 2 nanometers, or about 1.5 nanometers. In some embodiments, the platinum nanoparticles do not include or substantially do not include sulfur. In some embodiments, the TiO.sub.2 nanoparticles and the TiO.sub.2 substrate do not include or substantially do not include sulfur.

[0031] In some embodiments, the TiO.sub.2 (i.e., both the nanoparticles and the substrate) is partially reduced to TiO.sub.x (0<x<2) when reducing the structure. That is, a portion of the Ti.sup.4+ is reduced to Ti.sup.3+. In some embodiments, the Ti.sup.3+/(Ti.sup.3++Ti.sup.4+) ratio at the surface of the nanoparticles and the substrate is about 10% to 20%.

[0032] At block 125, the structure is heat treated in an atmosphere including methylcyclohexane (MCH). In some embodiments, this heat treatment is performed at about 300 C. to 400 C., or at about 450 C., for about 20 hours to 30 hours. This heat treatment may be referred to as a catalyst induction period. In some embodiments, the liquid hourly space velocity (LHSV) of MCH flow during this heat treatment is about 2 h.sup.1 to 5 h.sup.1. In some embodiments, the MCH is mixed with an inert gas (e.g., argon) during this heat treatment.

[0033] In some embodiments, the heat treatment at block 125 creates electron deficient platinum nanoparticles. The electron deficient platinum nanoparticles are due to electrons associated with the platinum nanoparticles being more attracted to the TiO.sub.2. The electron deficient platinum nanoparticles catalyze the MCH dehydrogenation reaction more efficiently than metallic platinum.

[0034] In some embodiments, the method 100 shown in FIG. 1 generates a Pt nanoparticle covered by a TiO.sub.x overlayer with net structure or TiO.sub.x overlayer islands. The Pt electronic structure is modified by the reduced TiO.sub.x overlayer through electron transfer. The Pt/TiO.sub.2 catalyst is a semi-core-shell structure, with Pt nanoparticles of about 1.5 nm half-embedded in TiO.sub.2 particles. The Pt nanoparticles in the Pt/TiO.sub.2 catalyst exhibit a high electron deficiency.

[0035] From the mechanistic viewpoint, the stabilization of Pt nanoparticles by a TiO.sub.x overlayer and the electron-deficient property of Pt nanoparticles is important in achieving H.sub.2 production from MCH dehydrogenation. First, Pt nanoparticles are immobilized on the TiO.sub.2 surface so that the Pt nanoparticles cannot move during catalysis. Second, electron-deficient Pt nanoparticles facilitate the desorption of toluene and other products, which helps to prevent coke formation that would deactivate catalysts.

[0036] Advantages of the embodiments described herein include: [0037] No pre-sulfidation of the catalysts. In the process for fabricating the Pt/TiO.sub.2 catalyst, neither the support nor the Pt species receives a pre-sulfidation treatment. [0038] No H.sub.2 cofeeding during dehydrogenation of MCH. The Pt/TiO.sub.2 catalyst can actively, selectively, and durably dehydrogenate MCH for H.sub.2 production without H.sub.2 cofeeding. [0039] No addition of a second metal species. The Pt/TiO.sub.2 catalyst is fabricated without additional noble metals. [0040] Industrial feasibility. The Pt/TiO.sub.2 catalyst fabrication processes described herein are amenable to one-pot methods, which hold potential in commercial production by lowering capital expenditure.

[0041] The following examples are intended to be examples of the embodiments disclosed herein, and are not intended to be limiting.

Example

[0042] Without the pre-sulfidation of the Pt species, the Pt/TiO.sub.2 catalyst with a Pt weight loading of about 1% exhibited MCH dehydrogenation performance in the absence of H.sub.2 cofeeding. Reaction conditions were as follows: catalyst mass=100 mg; temperature=350 C.; liquid hourly space velocity=5 h.sup.1; and pressure: 0.1 MPa. No catalyst deactivation was observed over about 500 h. MCH conversion of about 91% and toluene selectivity of about 100% were obtained.

Example

[0043] In a scaled up catalytic test, H.sub.2 production from MCH dehydrogenation could be achieved. Reaction conditions were as follows: catalyst mass=4 g; temperature=350 C.; liquid hourly space velocity=5 h.sup.1; and pressure: 0.1 MPa. No deactivation was detected over about 150 h. The Pt/TiO.sub.2 catalyst could also be used for toluene re-hydrogenation and DBT hydrogenation.

Example

[0044] FIG. 2 shows an example of a graph of the dibenzyltoluene (HO-DBT) hydrogenation performance of the Pt/TiO.sub.2 catalysts described herein. As shown in FIG. 2, the catalyst enabled greater than 99% hydrogenation degree of HO-DBT to perhydro-dibenzyl toluene (H18-DBT) within 8 hours of a hydrogenation process.

CONCLUSION

[0045] A catalyst comprising Pt nanoparticles disposed on and/or embedded in titanium dioxide (Pt/TiO.sub.2) was synthesized by the tuning metal-oxide interface. Pt nanoparticles (e.g., particle size of about 1 nm) are stabilized by a TiO.sub.x overlayer and are electron deficient. The Pt/TiO.sub.2 catalyst with its geometric and electronic properties exhibits active, selective, and durable MCH dehydrogenation performance in the absence of H.sub.2 cofeeding.

[0046] In the foregoing specification, the invention has been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of invention.