NANO-ENGINEERED CATALYSTS FOR DRY REFORMING OF METHANE

Abstract

Catalysts and processing useful in the dry reforming of methane (DRM) are provided. Catalyst are composed of nickel (Ni) nanoparticles supported on a hollow fiber substrate, such as an -Al.sub.2O.sub.3 hollow fiber. The nickel (Ni) nanoparticles can be deposited onto the hollow fiber substrate support by atomic layer deposition. If desired, one or more layers of an overcoat of a promoter can be applied to increase catalyst performance such as in the reforming of methane.

Claims

1. A catalyst comprising nickel (Ni) nanoparticles supported on a hollow fiber substrate.

2. The catalyst of claim 1 wherein the hollow fiber substrate comprises alumina.

3. The catalyst of claim 1 wherein the hollow fiber substrate comprises -Al.sub.2O.sub.3.

4. The catalyst of claim 1 wherein the nickel (Ni) nanoparticles are 2-6 nm in size.

5. The catalyst of claim 1 wherein the nickel (Ni) nanoparticles are deposited onto the hollow fiber substrate by atomic layer deposition.

6. The catalyst of claim 1 additionally comprising an overcoat of a promoter to increase catalyst performance in reforming of methane, wherein the promoter is selected from the group consisting of Al.sub.2O.sub.3, CeO.sub.2, CaO and La.sub.2O.sub.3.

7. The catalyst of claim 1 additionally comprising an alumina ALD overcoat as a promoter to increase catalyst performance in reforming of methane.

8. The catalyst of claim 7 comprising multiple cycles of Al.sub.2O.sub.3 ALD overcoat.

9. The catalyst of claim 1 wherein the nickel (Ni) nanoparticles are nanoparticles selected from the group consisting of Ni+Co bimetallic nanoparticles, Ni+Pt bimetallic nanoparticles, and only nickel nanoparticles.

10. The catalyst of claim 1 wherein the nickel (Ni) nanoparticles are neat nickel nanoparticles.

11. A process for reforming methane, the process comprising: contacting methane and carbon dioxide in the presence of the catalyst of claim 1.

12. A process for dry reforming methane, the process comprising: introducing methane and carbon dioxide into a reactor containing a packed bed of a plurality of hollow fiber substrate supports carrying nickel (Ni) nanoparticles.

13. The process of claim 12 wherein the hollow fiber substrate support comprise -Al.sub.2O.sub.3.

14. The process of claim 12 wherein the nickel (Ni) nanoparticles are 2-6 nm in size.

15. The process of claim 12 wherein the nickel (Ni) nanoparticles are deposited onto -Al.sub.2O.sub.3 hollow fiber substrate supports by atomic layer deposition.

16. The process of claim 15 wherein the -Al.sub.2O.sub.3 hollow fiber supports carrying nickel (Ni) nanoparticles include an overcoat of a promoter to increase catalyst performance in reforming of methane, wherein the promoter is selected from the group consisting of Al.sub.2O.sub.3, CeO.sub.2, CaO and La.sub.2O.sub.3.

17. The process of claim 12 wherein the -Al.sub.2O.sub.3 hollow fiber supports carrying nickel (Ni) nanoparticles include an alumina ALD overcoat as a promoter to increase catalyst performance in reforming of methane.

18. The process of claim 12 wherein the dry reforming produces syngas having H.sub.2/CO ratio of no more than 0.95.

19. The process of claim 12 wherein the dry reforming produces syngas having H.sub.2/CO ratio in a range of 0.7 to 0.95.

20. The process of claim 12 wherein the nickel (Ni) nanoparticles are nanoparticles selected from the group consisting of Ni+Co bimetallic nanoparticles, Ni+Pt bimetallic nanoparticles, and only nickel nanoparticles.

21. The process of claim 12 wherein the nickel (Ni) nanoparticles are neat nickel nanoparticles.

22. A method for producing a catalyst for dry reforming methane, the method comprising: depositing nickel (Ni) nanoparticles onto a hollow fiber substrate support by atomic layer deposition.

23. The method of claim 22 wherein the nickel (Ni) nanoparticles are 2-6 nm in size.

24. The method of claim 22 wherein the hollow fiber substrate support comprises -Al.sub.2O.sub.3.

25. The method of claim 24 additionally comprising applying by atomic layer deposition at least one layer of a metal oxide coating over the nickel (Ni) nanoparticles on the -Al.sub.2O.sub.3 hollow fiber substrate support, the metal oxide coating increasing catalyst performance in reforming of methane.

26. The method of claim 22 wherein the nickel (Ni) nanoparticles are neat nickel nanoparticles.

Description

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

[0013] Objects and features of this invention will be better understood from the following description taken in conjunction with the drawings, wherein:

[0014] FIG. 1 is a chart showing a projected global syngas market for 2025.

[0015] FIG. 2a is a TEM image showing 2-3 nm ALD deposited Ni nanoparticles on 20-30 nm silica particles.

[0016] FIG. 2b is a TEM image showing 3-4 nm ALD-deposited Ni nanoparticles on 50-100 nm -alumina particles.

[0017] FIG. 2c is a TEM image showing Ni nanoparticles deposited on nonporous -alumina nanoparticles by ALD.

[0018] FIG. 3 is a TEM image showing Ni nanoparticles synthesized by a conventional liquid phase method.

DETAILED DESCRIPTION

[0019] As identified above, in accordance with one aspect of the subject development, a new nickel (Ni) nanoparticle catalyst, supported on a hollow fiber substrate is provided.

[0020] Though -Al.sub.2O.sub.3 has been widely used as support for Ni-based catalysts, it is not suitable for the industrial DRM process due to phase transformation when the temperature is higher than 770 C., which also accompanies with a decrease in surface area. Among different phases of Al.sub.2O.sub.3, -Al.sub.2O.sub.3 is the most stable phase. The better thermal and mechanical stability of -Al.sub.2O.sub.3, as compared to other phases of Al.sub.2O.sub.3, makes it more suitable for industrial application and -Al.sub.2O.sub.3 has been employed to prepare industrial packed bed catalyst support.

[0021] In one embodiment, such a catalyst material in accordance with the subject development can desirably be synthesized by atomic layer deposition (ALD). For example, in the ALD process, a NiAl.sub.2O.sub.4 spinel is formed when Ni nanoparticles are deposited on alpha-alumina substrates, such as can act to inhibit sintering of the Ni nanoparticles.

[0022] A coat or coatings of one or more promoters, such as of Al.sub.2O.sub.3, CeO.sub.2, CaO and La.sub.2O.sub.3, for example, can be employed such as to increase catalyst performance such as by further improving the interaction between the Ni nanoparticles and the hollow fiber substrate supports. In one embodiment, such a promoter coating produced or synthesized by atomic layer deposition (ALD) is desirably employed. In one particular embodiment, Al.sub.2O.sub.3 ALD films, can be employed to further improve the interaction between the Ni nanoparticles and the hollow fiber support. Different cycles (e.g., 2, 5, and 10) of promoter, e.g., Al.sub.2O.sub.3 ALD, films have been applied on the hollow fiber supported Ni catalysts. For example, both catalyst activity and stability were improved with the deposition of the Al.sub.2O.sub.3 ALD overcoat films. Among the ALD coated catalysts, the catalysts with 5 cycles of Al.sub.2O.sub.3 ALD exhibited the best performance, e.g., catalyst activity and stability, in the reforming of methane. Those skilled in the art and guided by the teachings herein provided will understand and appreciate that the broader practice of the invention is not necessarily limited by the method or technique by which the metal oxide promoter, if present, is prepared as, for example, the metal oxide promoters can be prepared by alternative methods such as liquid phase impregnation, for example.

[0023] Table 1, below, identifies H.sub.2/CO ratios for the common state-of-the-art syngas production technologies of methane steam reforming reaction, partial oxidation of biomass, and underground coal gasification, as well as for dry reforming of methane in accordance with the invention.

TABLE-US-00001 TABLE 1 H.sub.2/CO ratios of syngas production technologies. Technology H.sub.2/CO ratio Methane steam reforming >3 Partial oxidation of biomass 1.0 Underground coal gasification 2 Dry reforming of methane (this invention) 0.70-0.95

[0024] In contrast with the H.sub.2/CO ratios for the common state-of-the-art syngas production technologies of methane steam reforming reaction, partial oxidation of biomass, and underground coal gasification, of >3, 1.0, and 2, respectively, the projected H.sub.2/CO ratio of dry reforming using the invention technology is 0.70-0.95, which H.sub.2/CO ratio is more favorable for C.sub.5+ hydrocarbon production.

[0025] It is envisioned that, at full scale, the subject technology can utilize CO.sub.2 captured from a coal-fired power plant (550 MWe), at approximately 11,000 tons of CO.sub.2/day, which can produce 790 million standard cubic feet of syngas/day using the dry reforming technology. Please note that this is simply estimated by the chemical reaction equation (CO.sub.2+CH.sub.4.fwdarw.2H.sub.2+2CO). The global syngas market is estimated to reach 6.010.sup.11 m.sup.3 by 2020. If this amount of syngas is produced by the subject technology, approximately 3.010.sup.8 ton CO.sub.2 will be consumed per year. This is the equivalent to the total CO.sub.2 emission from 420 coal-fired power plants (each with 550 MWe (net) capacity). Moreover, technologies for syngas conversion to valuable fuels and chemicals, such as transportation fuels, are currently being developed. Thus, if the economics of syngas conversion processes improve, the market for syngas will increase substantially.

[0026] In accordance with one embodiment of the subject development, highly dispersed Ni nanoparticles are deposited on high specific surface -alumina hollow fibers, along with a catalyst promoter film deposited on Ni/alumina catalysts by ALD. The subject development features at least the following advantages/improvements over current technologies: [0027] 1) The subject nano-engineered catalyst desirably can improve catalytic activity and stability [0028] Our studies have shown that the nano-engineered catalyst possessed: [0029] Higher activity than conventional catalysts (Table 2) due to highly dispersed 2-4 nm Ni nanoparticles compared to 10-30 nm Ni particles prepared by traditional methods (see FIGS. 2a and 2b). FIG. 2c is a TEM image showing Ni nanoparticles deposited on nonporous G-alumina nanoparticles by ALD; [0030] High stability due to a strong bonding between the nickel nanoparticles and substrates since the nickel particles were chemically bonded to the substrate during the ALD process; and [0031] The high thermal stability maintained high dispersion of Ni nanoparticles, which could inhibit coke formation.

TABLE-US-00002 TABLE 2 Comparison of activity for nono-engineered and conventional catalysis. CH4 reforming rate (L .Math. h.sup.1gNi.sup.1) Catalyst 850 C. 800 C. 750 C. Nano-engineered catalyst 1,840 1,740 1,320 prepared by ALD Conventional catalyst 1,700 1,150 480 prepared by incipient

[0032] FIG. 3 is a TEM image showing Ni nanoparticles synthesized by a conventional liquid phase method. [0033] 2) Novel geometric hollow fiber shape to increase the geometrical surface area [0034] The -Al.sub.2O.sub.3 hollow fibers provide high thermal stability and mechanical strength for the catalyst as well as the following advantages over conventional substrates: [0035] High Packing Density: The specific area per unit volume for the alumina hollow fibers is as high as 3,000 m.sup.2/m.sup.3. This provides a high packing density for catalytic dry reforming applications. [0036] Low Pressure Drop: Whether the direct use of CO.sub.2 in flue gas (13-15 vol. %) or the use of high-purity CO.sub.2 (>95 vol. %) captured from flue gas using a CO.sub.2 capture system, the pressure is low. With CO.sub.2 compression being costly, a low pressure drop through the reactor is desirable. For the hollow fiber with a length of 60 inches (typical length for a hollow fiber module), the calculated pressure drop for the flow of dry reforming reactants is less than 0.2 psi when operating with our pressure-driven transport configuration at the design flow conditions. [0037] 3) Desired H.sub.2/CO ratio for follow-up Fischer-Tropsch synthesis to produce C.sub.5+ hydrocarbons [0038] The syngas produced in accordance with processing of the subject development has a H.sub.2/CO ratio of 0.7 to 0.95, whereas the benchmark technology steam reforming delivers a H.sub.2/CO of about 3. This can be particularly significant in conjunction with applications such as Fischer-Tropsch fuel synthesis that produce high yield C.sub.5+ hydrocarbons, wherein the preferred H.sub.2/CO ratio is 0.8.

[0039] Ni nanoparticles used in the practice of the subject development may, in accordance with one preferred embodiment, desirably and preferably be 2-6 nm in size. In another preferred embodiment, Ni nanoparticles used in the practice of the subject development are desirably and preferably 2-4 nm in size.

[0040] While in the foregoing detailed description this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.