Cerium manganese catalyst, preparation method therefor and use thereof

Abstract

A cerium manganese catalyst for ozone decomposition, which is mainly a composite oxide of Mn.sub.2O.sub.3 and CeO.sub.2 with the chemical constitution of CeMn.sub.aO.sub.x, a being a natural number selected from 6 to 15. A method for preparing a catalyst comprises: mixing a solution containing a cerium source and a manganese source with excessive urea, reacting to obtain a precipitate, washing the precipitate to neutral, drying, and roasting to obtain the cerium manganese catalyst.

Claims

1. A method for preparing a cerium-manganese catalyst for ozone decomposition at a high space velocity within a wide temperature range: mixing a solution consisting of a cerium source and a manganese source with excess urea, carrying out a reaction to obtain a precipitate, washing the precipitate to a neutral pH, drying, and calcining to obtain the cerium-manganese catalyst, wherein the cerium-manganese catalyst has a following chemical composition: CeMn.sub.aO.sub.x, wherein a in CeMn.sub.aO.sub.x is a natural number selected from 9 to 15, and the cerium-manganese catalyst is mainly a composite oxide of Mn.sub.2O.sub.3 and CeO.sub.2, wherein the cerium-manganese catalyst is in a form of particles, wherein when the cerium-manganese catalyst is used for ozone decomposition, a temperature range is −10° C. to 100° C., a space velocity is up to 2,000,000 h.sup.−1, a humidity is not more than 90%, a decomposition efficiency is above 80%, and the cerium-manganese catalyst gives a decomposition rate of 99% of ozone of 4 ppm after 70 h of use.

2. The preparation method according to claim 1, wherein a molar ratio of cerium in the cerium source to manganese in the manganese source is 1:(6-15).

3. The preparation method according to claim 1, wherein a temperature of the reaction is 60° C. to 100° C.

4. The preparation method according to claim 1, wherein the cerium source is selected from one or a mixture of at least two of cerium nitrate, cerium sulfate, cerium acetate or cerium chloride.

5. The preparation method according to claim 1, wherein the manganese source is selected from one or a mixture of at least two of manganese nitrate, manganese sulfate, manganese acetate or manganese chloride.

6. The preparation method according to claim 1, wherein a period for the reaction is 8 to 24 hours.

7. The preparation method according to claim 1, wherein the washing the precipitate to a neutral pH is performed with water.

8. The preparation method according to claim 1, wherein a temperature for the drying is 90° C. to 150° C.

9. The preparation method according to claim 1, wherein a temperature for the calcining is 300° C. to 700° C.

10. The preparation method according to claim 1, further comprising: mixing a solution containing a cerium source and a manganese source with urea, wherein a concentration of the cerium source and a concentration of the manganese source in the solution containing the cerium source and the manganese source are 0.01 to 0.05 mol/L and 0.1 to 0.5 mol/L respectively, and a solid-to-liquid ratio of the urea to the solution containing the cerium source and the manganese source is 0.15 to 0.3 g/L; stirring an obtained mixture at a speed of 400 to 800 r/min for 8 to 24 hours at 60° C. to 100° C. to obtain a precipitate; and washing the precipitate with water to a neutral pH, drying the washed precipitate at 90° C. to 150° C. for 8 to 24 hours, and calcining the dried precipitate at 300° C. to 700° C. for 1.5 to 5 hours to obtain the cerium-manganese catalyst.

11. The preparation method according to claim 1, wherein a concentration of the cerium source is 0.01 to 0.05 mol/L.

12. The preparation method according to claim 1, wherein a concentration of the manganese source is 0.1 to 0.5 mol/L.

13. The preparation method according to claim 1, wherein a solid-to-liquid ratio of the urea to the solution containing the cerium source and the manganese source is 0.15 to 0.3 g/L.

14. The preparation method according to claim 1, wherein the reaction comprises stirring at a speed of 400 to 800 r/min.

15. The preparation method according to claim 1, wherein a period for the drying is 8 to 24 hours.

16. The preparation method according to claim 1, wherein a period for the calcining is 1.5 to 5 hours.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is an XRD pattern of a cerium-manganese catalyst provided by Example 3.

(2) FIG. 2 is an SEM picture of the cerium-manganese catalyst provided by Example 3.

(3) FIG. 3 is a TEM picture of the cerium-manganese catalyst provided by Example 3, where the scale dimension represents 0.1 μm.

DETAILED DESCRIPTION

(4) Technical solutions of the present application are further described below through specific implementations in conjunction with the drawings.

EXAMPLE 1

(5) A method for preparing a cerium-manganese catalyst:

(6) A solution containing a cerium source (cerium nitrate) and a manganese source (manganese nitrate) (a molar ratio of Ce:Mn=1:6) was mixed with excess urea, where a concentration of the cerium source and a concentration of the manganese source in the solution containing the cerium source and the manganese source were 0.03 mol/L and 0.18 mol/L respectively, and a solid-to-liquid ratio of the urea to the solution containing the cerium source and the manganese source was 0.20 g/L. An obtained mixture was stirred for 12 h at 80° C. to obtain a precipitate. The precipitate was washed with water to a neutral pH, the washed precipitate was dried at 120° C., and the dried precipitate was calcined at 600° C. to obtain the cerium-manganese catalyst, marked as CeMn.sub.6O.sub.x-600.

EXAMPLE 2

(7) A method for preparing the cerium-manganese catalyst as in Example 1, except that the molar ratio of Ce:Mn was 1:8. The resultant cerium-manganese catalyst was marked as CeMn.sub.8O.sub.x-600.

EXAMPLE 3

(8) A method for preparing the cerium-manganese catalyst as in Example 1, except that the molar ratio of Ce:Mn was 1:10. The resultant cerium manganese catalyst was marked as CeMn.sub.10O.sub.x-600.

EXAMPLE 4

(9) A method for preparing the cerium-manganese catalyst as in Example 1, except that the molar ratio of Ce:Mn was 1:15. The resultant cerium-manganese catalyst was marked as CeMn.sub.15O.sub.x-600.

EXAMPLE 5

(10) A method for preparing the cerium-manganese catalyst as in Example 3, except that the calcining temperature was 300° C. The resultant cerium-manganese catalyst was marked as CeMn.sub.10O.sub.x-300.

EXAMPLE 6

(11) A method for preparing the cerium-manganese catalyst as in Example 3, except that the calcining temperature was 400° C. The resultant cerium-manganese catalyst was marked as CeMn.sub.10O.sub.x-400.

EXAMPLE 7

(12) A method for preparing the cerium-manganese catalyst as in Example 3, except that the calcining temperature was 500° C. The resultant cerium-manganese catalyst was marked as CeMn.sub.10O.sub.x-500.

EXAMPLE 8

(13) A method for preparing the cerium-manganese catalyst as in Example 3, except that the calcining temperature was 700° C. The resultant cerium-manganese catalyst was marked as CeMn.sub.10O.sub.x-700.

(14) The catalysts obtained in Examples 1 to 8 were subjected to the performance test, and the specific test conditions and test results are shown in Table 1 below.

(15) TABLE-US-00001 TABLE 1 Ozone O.sub.3 concen- Temper space con- tration ature Relative velocity version No. Catalyst (ppm) (° C.) humidity (h.sup.−1) rate 1 CeMn.sub.6O.sub.x-600 40 30 65% 600,000 98% 2 CeMn.sub.8O.sub.x-600 40 35 70% 600,000 98% 3 CeMn.sub.10O.sub.x-600.sup.  40 30 65% 800,000   99.5% 4 CeMn.sub.15O.sub.x-600.sup.  40 35 90% 600,000 99% 5 CeMn.sub.10O.sub.x-300.sup.  40 50 60% 700,000 80% 6 CeMn.sub.10O.sub.x-400.sup.  10 50 50% 700,000 80% 7 CeMn.sub.10O.sub.x-500.sup.  20 30 70% 700,000 99% 8 CeMn.sub.10O.sub.x-700.sup.  30 30 70% 700,000 85% 9 CeMn.sub.8O.sub.x-600 40 30 65% 1000,000 90% 10 CeMn.sub.10O.sub.x-600.sup.  40 50 65% 1000,000 95% 11 CeMn.sub.15O.sub.x-600.sup.  40 100 65% 1000,000 100%  12 CeMn.sub.10O.sub.x-600.sup.  4 −10 <20%   2000,000 99% 13 CeMn.sub.10O.sub.x-600.sup.  0.1 0 60% 2000,000 99%

(16) It can be seen that the cerium-manganese catalyst can efficiently decompose ozone in the conditions of a wide temperature range and high space velocity, where the temperature range can be scaled to −10° C. to 100° C., the space velocity can be up to 2000,000 h.sup.−1, and the humidity range can be scaled to below 90%, and the ozone decomposition rate is not less than 80%, up to 100%; in addition, the test shows that the catalytic activity of the catalyst can be maintained for more than 70 hours (the catalyst still gives a decomposition rate of 99% of ozone of 4ppm after 70 h of use).

(17) Furthermore, once any one or a combination of at least two of the reaction temperature, stirring period or drying temperature in the preparation method described in Example 3 was adjusted such that the reaction temperature became 60° C., 65° C., 72° C., 84° C. or 100° C., the stirring period became 8 h, 8.5 h, 9.5 h, 10.2 h, 15.6 h, 20.0 h h or 24.0 h, and the drying temperature became 90° C., 95° C., 100° C., 105° C., 110° C., 125° C., 130° C., 145° C. or 150° C., the prepared cerium-manganese catalyst allows efficient ozone decomposition under the conditions of wide temperature range and high space velocity, where the temperature range can be scaled to −10° C. to 100° C., the space velocity can be up to 2000,000 h.sup.−1, and the humidity range can be scaled to below 90%, and the ozone decomposition rate is not less than 80%, up to 99%; in addition, the test shows that the catalytic activity of the catalyst can be maintained for more than 70 hours (the catalyst still gives a decomposition rate of 99% of ozone of 4ppm after 70 h of use).

(18) In case the concentrations of the cerium source and the manganese source, the molar ratio of the cerium source and the manganese source, and the amount of the urea added (always in excess) in the preparation method described in Example 3 were adjusted such that the concentration of the cerium source was any value between 0.01 and 0.05 mol/L, such as 0.02 mol/L, 0.03 mol/L, 0.04 mol/L, etc., that the concentration of the manganese source was any value between 0.1 and 0.5 mol/L, such as 0.1 mol/L, 0.02 mol/L, 0.3 mol/L, 0.4 mol/L, etc., and that the molar ratio of cerium in the cerium source to manganese in the manganese source was any value between 1:(6-15), such as 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, etc., and that the solid-to-liquid ratio of the urea and the solution containing the cerium source and the manganese source was 0.15 to 0.3 g/L, such as 0.18 g/L, 0.19 g/L, 0.23 g/L, 0.25 g/L, 0.27 g/L, etc., the prepared cerium manganese catalyst allows efficient ozone decompositon under the conditions of wide temperature range and high space velocity, where the temperature range can be scaled to −10° C. to 100° C., the space velocity can be up to 2000,000 h.sup.−1, and the humidity range can be scaled to below 90%, and the ozone decomposition rate is not less than 80%, up to 99%; in addition, the test shows that the catalytic activity of the catalyst can be maintained for more than 70 hours (the catalyst still gives a decomposition rate of 99% of ozone of 4ppm after 70 h of use).

(19) In case the cerium source in Example 3 is replaced with one or a mixture of at least two of cerium sulfate, cerium acetate or cerium chloride, or the manganese source in Example 3 is replaced with one or a mixture of at least two of manganese sulfate, manganese acetate or manganese chloride, the performance of the obtained cerium-manganese catalyst will not be affected.

(20) It is found after testing that in case the calcining temperature reaches above 420° C. during the preparation of a cerium-manganese catalyst, the obtained catalyst, when used for ozone decomposition under the conditions of the temperature range of −10° C. to 100° C. and the space velocity of 2000,000 h.sup.−1, presents an ozone decomposition rate of more than 85%.

COMPARATIVE EXAMPLE 1

(21) A method for preparing a catalyst as in Example 3, except that the urea was replaced with Na.sub.2CO.sub.3 in a same amount.

COMPARATIVE EXAMPLE 2

(22) A method for preparing a catalyst as in Example 3, except that the urea was replaced with aqueous ammonia in a same amount.

COMPARATIVE EXAMPLE 3

(23) A method for preparing a catalyst as in Example 3, except that the urea was replaced with NaOH in a same amount.

COMPARATIVE EXAMPLE 4

(24) A method for preparing a catalyst as in Example 3, except that the amount of added urea was ½ of the molar quantity of urea required for fully precipitating Ce and Mn.

(25) The catalysts obtained in Comparative examples 1 to 4 were tested for their catalytic activity according to the test conditions numbered 3, 5-8, 10, 12 and 13 in Table 1, to obtain an ozone decomposition rate of up to 60% and a minimum of 12%.

(26) It can be seen from Comparative examples 1 to 4 that the use of urea has a great influence on the catalyst performance, and in case the urea was replaced with any other material, the above cerium manganese catalyst with excellent performance cannot be obtained.

(27) The applicant has stated that the above are only specific embodiments of the present application and that the scope of the present application is not limited thereto.