Nanoporous cerium oxide with interconnected pores for catalysis and a cost-effective method of preparing thereof

Abstract

Provided herein are a method of making a nanoporous cerium oxide material which can be used for heterogeneous catalysis. The method may include mixing a cerium nitrate solution and an amine solution to form a mixture and stirring the mixture thus forming a nanoporous cerium oxide precipitate. Further, the molar ratio of cerium nitrate and the amine ranges from 2:1 to 5:1.

Claims

1. A method of making nanoporous cerium oxide, comprising mixing a cerium nitrate solution and an amine solution to form a mixture and stirring the mixture thus forming a nanoporous cerium oxide precipitate; wherein the molar ratio of cerium nitrate and the amine ranges from 2:1 to 5:1.

2. The method of claim 1, further comprising dissolving cerium nitrate or a hydrate thereof in a mixture of alcohol and deionized water of a ratio about 1:1 by weight or by volume to obtain the cerium nitrate solution.

3. The method of claim 2, wherein in the alcohol is selected from the group consisting of isopropyl alcohol and ethyl alcohol.

4. The method of claim 3, wherein the alcohol is isopropyl alcohol.

5. The method of claim 3, wherein the alcohol is ethyl alcohol.

6. The method of claim 1, further comprising dissolving an amine in an alcohol to obtain the amine solution.

7. The method of claim 6, wherein in the alcohol is selected from the group consisting of isopropyl alcohol and ethyl alcohol.

8. The method of claim 1, further comprising washing the precipitate with a mixture of alcohol and water to remove residual amine; drying the precipitate; and calcining the precipitate.

9. The method of claim 8, wherein in the alcohol is selected from the group consisting of isopropyl alcohol and ethyl alcohol.

10. The method of claim 8, wherein the precipitate is dried at about 60 C. under vacuum for about 24 hours.

11. The method of claim 8, wherein cerium oxide precipitate is calcined at a temperature ranging from about 500 C. to about 600 C.

12. The method of claim 1, wherein the hydrate of cerium nitrate is cerium nitrate hexahydrate.

13. The method of claim 1, wherein the amine is selected from the group consisting of cyclohexalamine and polyethyleneimine.

14. The method of claim 1, wherein the amine is cyclohexalamine.

15. The method of claim 1, wherein the amine is polyethyleneimine.

16. The method of claim 1, wherein the mixture is stirring at a temperature ranging from 40 C. to 70 C.

17. The method of claim 1, wherein the mixture is stirred for about 4 hours to about 96 hours.

18. The method of claim 1, wherein the concentration of the amine in the amine solution is ranging from about 5% to about 20% by weight or by volume.

19. The method of claim 1, wherein the concentration of the amine solution is about 10% by weight or by volume.

20. The method of claim 1, wherein the ratio of cerium nitrate and amine and the reaction temperature are adjusted so that the pore sizes of the nanoporous cerium oxide is within the range of about 100 nm to about 400 nm and the pores are spaced substantially evenly at a distance of about 500 nm to about 1000 nm.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows a magnified image of a whole grain of cerium oxide showing the presence of pores in the entire grain.

(2) FIG. 2 shows magnified SEM images of cerium oxide showing pore distribution on the internal and external surfaces.

(3) FIG. 3 shows magnified SEM image of porous cerium oxide showing the arrangement nanopores along parallel lines.

DETAILED DESCRIPTION

(4) It is understood that, with regard to this description and the appended claims, any reference to any aspect of this invention made in the singular includes the plural and vice versa unless it is expressly stated or unambiguously clear from the context that such is not intended.

(5) As used herein, any term of approximation such as, without limitation, near, about, approximately, substantially, essentially, and the like, mean that the word or phrase modified by the term of approximation need not be exactly that which is written but may vary from that written description to some extent. The extent to which the description may vary will depend on how great a change can be instituted and have one of ordinary skill in the art recognize the modified version as still having the properties, characteristics and capabilities of the word or phrase unmodified by the term of approximation. In general, but with the preceding discussion in mind, a numerical value herein that is modified by a word of approximation may vary from the stated value by up to 10%, unless expressly stated otherwise.

(6) In one aspect of the present invention disclosed herein, provided is a method of making nanoporous cerium oxide, comprising

(7) mixing a cerium nitrate solution and an amine solution to form a mixture and stirring the mixture thereby forming a nanoporuous cerium oxide precipitate;

(8) wherein the molar ratio of cerium nitrate and the amine ranges from 2:1 to 5:1.

(9) In some embodiments, the method further comprises dissolving cerium nitrate or hydrate thereof in a mixture of 1:1 alcohol and deionized water to obtain the cerium nitrate solution. In some embodiments, the alcohol is selected from the group consisting of isopropyl alcohol and ethyl alcohol. In some embodiments, the alcohol is isopropyl alcohol. In some embodiments, the alcohol is ethyl alcohol.

(10) In some embodiments, the method further comprises dissolving an amine in an alcohol to obtain the amine solution. In some embodiments, the alcohol is selected from the group consisting of isopropyl alcohol and ethyl alcohol. In some embodiments, the alcohol is isopropyl alcohol. In some embodiments, the alcohol is ethyl alcohol.

(11) In some embodiments, the method further comprises washing the precipitate with a mixture of alcohol and water to remove residual amine; drying the precipitate; and calcining the dried precipitate.

(12) In some embodiments, the alcohol is selected from the group consisting of isopropyl alcohol and ethyl alcohol. In some embodiments, the alcohol is isopropyl alcohol. In some embodiments, the alcohol is ethyl alcohol.

(13) In some embodiments, cerium nitrate hexahydrate is used.

(14) In some embodiments, the amine is selected from the group consisting of cyclohexalamine and polyethyleneimine. In some embodiments, the amine is cyclohexalamine. In some embodiments, the amine is polyethyleneimine.

(15) In some embodiments, the mixture of cerium nitrate solution and an amine solution is stirring at a temperature ranging from about 40 C. to about 70 C. In some embodiments, the mixture is stirred for about 4 hours to about 96 hours.

(16) In some embodiments, the cerium oxide precipitate is dried at about 60 C. under vacuum for about 24 hours.

(17) In some embodiments, the dried cerium oxide precipitate is calcined at a temperature ranging from about 500 C. to about 600 C.

(18) In some embodiments, the concentration of the amine in the amine solution is ranging from about 5% to about 20% by weight or by volume. In some embodiments, the concentration of the amine in the amine solution is about 10% by weight or by volume.

(19) In some embodiments, the ratio of cerium nitrate and amine and the reaction temperature are adjusted so that the pore sizes of the nanoporous cerium oxide is within the range of about 100 nm to about 400 nm and the pores are spaced evenly or substantially evenly at a distance of about 500 nm to about 1000 nm.

(20) In one aspect of the present invention disclosed herein, provided is nanoporous cerium oxide produced by the method disclosed herein.

(21) In one aspect of the present invention disclosed herein, provided is nanoporous cerium oxide having the following characteristics:

(22) the nanoporous cerium oxide has a plurality of pores in the diameter range of about 100 to about 400 nm and evenly or substantially evenly spaced at a distance of about 500 nm to about 1000 nm,

(23) the pores are present on the internal and external surfaces of cerium oxide grain and the internal and external pores are interconnected,

(24) the pores on the external surface of the nanoporous cerium oxide are uniform diameter and are present along evenly or substantially evenly spaced parallel line; and

(25) the pores are present on the entire external surface of the nanoporous cerium oxide grain.

(26) The present invention disclosed herein relates to producing porous cerium oxide catalyst having plurality of pores arranged along parallel lines, consisting of interconnecting pores on the external and internal surfaces. Specifically this invention relates to the production of porous cerium oxide having plurality of pores in the diameter range of about 100 nm to about 400 nm arranged along parallel lines via a cost-effective single-step precipitation process.

(27) The present invention disclosed herein provides a cerium oxide material for heterogeneous catalysis having uniform pores in the diameter range of about 100 nm to about 400 nm throughout the internal and external surfaces of the grain. Plurality of pores are arranged roughly along parallel lines, present on the internal and external surfaces of the grain, and interconnected through narrow constrictions. The method of preparing aforesaid oxide comprises of a cost-effective single step precipitation reaction between a cerium compound and amines. The porous oxide disclosed here is useful for applications including heterogeneous catalysis for emission control, desalination, ultrafiltration, hyperfiltration, and templated growth of nanowires and device containing thereof.

(28) The present invention disclosed herein provide a novel cerium oxide catalyst containing pores throughout the grain and arranged in evenly or substantially evenly spaced parallel lines. The catalyst has pores on the internal and external surfaces and the pores are interconnected through narrow constrictions. The pore size can be controlled by a simple process of adjusting the ratio of precursor cerium salt and amine, and the reaction temperature. The cerium oxide catalyst that is produced through a novel cost-effective single-step precipitation process.

(29) The present invention disclosed herein has several main features. One feature of the present invention is that a single step liquid-phase reaction is used herein for producing nanoporous cerium oxide.

(30) Another feature is that by adjusting the ratio of cerium salt and amine, and the reaction temperature, the pore sizes can be controlled in the range of about 100 nm to about 400 nm and are spaced evenly at a distance of about 500 nm to about 1000 nm.

(31) Another feature of the present invention is that it requires only commonly available cerium salt and uses low-cost solvents in a conventional stirred reactor.

(32) An advantage of the present invention is that no need of steam or its mixture is necessary to produce the porous cerium oxide.

(33) Another feature of the present invention is that the pores are created in the internal and external surfaces of cerium oxide grain and the internal and external pores are interconnected through constrictions.

(34) Another feature of the present invention is that the pores on the external surface are uniform diameter and are present along roughly evenly spaced parallel lines.

(35) Another feature of the invention is that pores are present on the entire external surface of the grain.

(36) The present invention has utility in production of nanoporous cerium oxide catalyst cost effectively. The present invention relates to the production of nanoporous cerium oxide catalyst using cost effective precipitation route. Non-porous cerium oxide effected on porous body has been used as catalyst for reducing the post-combustion emissions from internal combustion engines. Porous cerium oxide disclosed in the present invention has high density of uniform pores, which is useful in a range of applications including emission control, heterogeneous catalysis, templated growth of nanowires, desalination, and filtration.

(37) Emissions from internal combustion engines of automobiles contain environmentally noxious gases including carbon monoxide, nitrogen oxides and hydrocarbons. Bulk cerium oxide alone or used with other metal oxides is an important catalyst for treating exhaust emissions globally. Nanoporous cerium oxides having good density of uniform pores increases the efficiency of the catalytic conversion of carbon monoxide, nitrogen oxides and hydrocarbons. A cost-effective preparation method disclosed in this invention would be very important for OEMs developing automobiles exhaust system for the bulk production of highly efficient exhaust catalysts.

Examples and Experiments

(38) The nanoporous cerium oxide of the present invention was produced by a single-step precipitation method. In typical preparation procedure, cerium nitrate is dissolved in 1:1 alcohol-deionized water under continuous magnetic stirring. In another vessel, a solution of an amine is prepared in alcohol. The amine and cerium nitrate solutions are mixed and heated on a hot plate. The precipitated nanoporous oxide is washed with alcohol-water mixture to remove the residual amines and calcined.

Example 1

(39) 1.86 ml of cyclohexylamine was mixed with 20 ml of isopropyl alcohol. In another vessel cerium nitrate hexahydrate was dissolved in 60 ml of solution containing 50:50 (by volume) deionized water and isopropyl alcohol (30 ml). The amount of cerium nitrate hexahydrate used was to maintain a molar ratio range of 2:1 to 5:1 with the cyclohexylamine. The cyclohexylamine solution was poured into the cerium nitrate solution and the solution was stirred for 4 hours to 96 hours on a hot plate at temperature range of 0 C.-70 C. Afterwards, the precipitate formed was washed with 100 mL of isopropyl alcohol-water mixture, filtered off, and dried in the oven at 60 C. under vacuum for 24 hours. The dried cerium oxide precipitate was calcined at 500 C.-600 C.

Example 2

(40) In a variant of the process of Example 1, polyethyleneimine was used instead of cyclohexylamine to produce the nanoporous cerium oxide.

(41) The SEM (scanning electron microscope) images of final product are shown in the FIGS. 1-3. FIG. 1 shows a magnified (2500 times) image of a whole grain of cerium oxide showing the presence of pores in the entire grain. FIG. 2 shows magnified SEM images of cerium oxide showing pore distribution on the internal and external surfaces. FIG. 3 shows magnified (50,000 times) SEM image of porous cerium oxide showing the arrangement nanopores along parallel lines.

Example 3

(42) In another variant of the process of Example 1, ethyl alcohol was used instead of isopropyl alcohol.

Example 4

(43) In another variant of the process of Example 1, the amount of cerium nitrate used is 1.16 g to 2.95 g.