Catalyst For Carbon Monoxide Oxidation and Process For The Preparation Thereof

Abstract

The present invention provides a catalyst and a process for the selective oxidation of carbon monoxide (CO) to produce carbon dioxide gas (CO.sub.2). The process provides a process which selectively oxidizes CO to CO.sub.2 in presence of excess hydrogen. The process provides a selective oxidation of CO to CO.sub.2 gas over Cu/CeO.sub.2 catalyst between temperature range 40 C. to 90 C. at atmospheric pressure in presence of excess H.sub.2, H.sub.2O and CO.sub.2. The process provides a CO conversion up to 100% without deactivation till 100 h.

Claims

1. A nanocrystalline CuCe oxide catalyst comprises CuO in the range of 5-10 wt % and CeO.sub.2 in the range of 95-90 wt % wherein 2 to 5 nm Cu nanoparticles are present on 10-20 nm CeO.sub.2 nanoparticles.

2. A process for the preparation of nanocrystalline CuCe oxide catalyst comprising the steps of: i. precipitating CuCl.sub.2, Ce salt with 20 to 25% NH.sub.3 solution followed by adjusting pH in the range of 7 to 8 to obtain solution; ii. adding cetyltrimethylammonium bromide (CTAB), Polyvinylpyrrolidone (PVP) in the solution as obtained in step (i) followed by stirring for period in the range of 1 to 2 h at room temperature in the range of 20 to 30 C. to obtain substance; iii. heating the substance as obtained in step (ii) at temperature in the range of 170 to 180 C. in a autoclave for period in the range of 20 to 25 h followed by cooling at room temperature in the range of 20 to 30 C., washing and dried for period in the range of 10 to 12 hr at temperature in the range of 90 to 100 C. to obtain solid; iv. calcining the solid as obtained in step (iii) at temperature in the range of 500 to 550 C. for period in the range of 4-8 hours to obtain nanocrystalline CuCe oxide catalyst.

3. The process as claimed in claim 2, wherein the Ce salt used in step (a) is cerium chloride heptahydrate.

4. The process as claimed in claim 2, wherein wt % ratio of Cu and Ce is in the range of 5:95 to 10:90.

5. The catalyst as claimed in claim 1, wherein said catalyst is useful for activation of carbon monoxide to obtain carbon dioxide gas, wherein the said process comprising the steps of: i. passing O.sub.2:CO:He:H.sub.2:H.sub.2O:CO.sub.2 mixture in a molar ratio ranging between 3:6:91:0:0:0 to 3:6:11:50:10:20 (mol %) to in a reactor at atmospheric pressure in the presence of nanocrystalline CuCe oxide catalyst at a temperature ranging between 40-100 C. for a period ranging between 1-100 hrs at a gas hourly space velocity (GSHV) ranging between 3000-20000 mlg.sup.1 h.sup.1 to obtain carbon dioxide gas.

6. The process as claimed in claim 5, wherein the process is carried out at temperature in the range 30 to 100 C.

7. The process as claimed in claim 5, wherein conversion of carbon monoxide is in the range of 1-100%.

8. The process as claimed in claim 5, wherein the O.sub.2/CO ratio obtained in the range of 1:2.

9. The process as claimed in claim 5, wherein gas hourly space velocity (GHSV, feed/g.sub.catalyst/hour) is preferably in the range of 3500 to 18000 ml g.sup.1 h.sup.1.

10. The process as claimed in claim 5, wherein conversion of methane is in the range of 1 to 100%.

Description

BRIEF DESCRIPTION OF DRAWING

[0034] FIG. 1 X-ray Diffraction (XRD) of 5% CuCeO.sub.2

[0035] FIG. 2 Scanning Electron Microscope (SEM) image of 5% CuCeO.sub.2

[0036] FIG. 3 Low magnification Transmission Electron Microscope (TEM) image of 5% CuCeO.sub.2

[0037] FIG. 4 High magnification TEM image of 5% CuCeO.sub.2

[0038] FIG. 5 Mapping of O in 5% CuCeO.sub.2

[0039] FIG. 6 Mapping of Ce in 5% CuCeO.sub.2

[0040] FIG. 7 Mapping of Cu in 5% CuCeO.sub.2

[0041] FIG. 8 Energy Dispersive X-ray analysis (EDAX) of Cu in 5% CuCeO.sub.2.

[0042] FIG. 9 Effect of temperature on conversion of carbon monoxide and oxidation of carbon monoxide at 65 C. in presence of hydrogen

[0043] FIG. 10 Effect of temperature on conversion of carbon monoxide and oxidation of carbon monoxide in presence of hydrogen, carbon dioxide and water vapour

[0044] FIG. 11 Effect of time on conversion of carbon monoxide and oxidation of carbon monoxide in presence of hydrogen, carbon dioxide and water vapour

DETAILED DESCRIPTION OF THE INVENTION

[0045] Present invention provides CuCe oxide catalyst having formula CuOCeO.sub.2 comprises CuO in the range of 5-10 wt % and CeO.sub.2 in the range of 90-95 wt % and a process for the preparation thereof.

[0046] The present invention provides a process for the preparation of nanocrystalline CuCe oxide comprising the steps of: [0047] i. Synthesis of CuCeO.sub.2 oxide was carried out using precipitation of CuCl.sub.2, CeCl.sub.3.7H.sub.2O with 25% NH.sub.3 solution where CuCl.sub.2 and CeCl.sub.3.7H.sub.2O was used as the precursor of Cu and Ce. [0048] ii. The pH of the mixture was adjusted at 8. [0049] iii. After adding NH.sub.3 solution, cetyltrimethylammonium bromide (CTAB), Polyvinylpyrrolidone (PVP) were added. [0050] iv. The mixed solution was stirred for 1-2 h at room temperature (i.e. 20 to 30 C.). [0051] v. The substance was transferred to a Teflon lined stainless steel autoclave and heated at 180 C. for 20-25 h. The solid obtained was calcined at 550 C. for a time period in the range of 4-8 hours to obtain CuCe oxide.

[0052] The weight ratio of Cu to CeO.sub.2 varied in the range between 5-10%.

[0053] The present invention provides CuCe oxide catalyst for selective oxidation of carbon monoxide with oxygen to obtain carbon dioxide gas, wherein the said process is carried out in the presence or absence of hydrogen.

[0054] The present invention provides a process for selective oxidation of carbon monoxide with oxygen using CuCe oxide catalyst in the absence of hydrogen comprises: [0055] i. passing O.sub.2:CO:He mixture with a molar ratio of 1:2:18 in a reactor at atmospheric pressure in the presence of nanocrystalline CuCe oxide catalyst at a temperature ranging between 40-100 C. for a period ranging between 1-100 h at a gas hourly space velocity (GHSV) ranging between 3000-20000 mlg.sup.1 h.sup.1 to obtain carbon dioxide gas.

[0056] The present invention provides a process for selective oxidation of carbon monoxide with oxygen using CuCe oxide catalyst in the presence of hydrogen comprises: [0057] i. passing O.sub.2:CO:He:H.sub.2:H.sub.2O:CO.sub.2 mixture with a molar ratio of 3:6:91:0:0:0 to 3:6:11:50:10:20 (mol %) to in a reactor at atmospheric pressure in the presence of nanocrystalline CuCe oxide catalyst at a temperature ranging between 40-100 C. for a period ranging between 1-100 hrs at a gas hourly space velocity (GSHV) ranging between 3000-20000 mlg.sup.1 h.sup.1 to obtain carbon dioxide gas.

[0058] The selective oxidation of carbon monoxide was carried out in a fixed-bed down flow reactor at atmospheric pressure for 1-100 h to get carbon dioxide.

[0059] The reaction temperature is preferably in the range 30-100 C.

[0060] The gas hourly space velocity (GHSV, feed/g.sub.catalyst/hour) is preferably in the range 3000 to 20000 ml g-1 h-1 more preferably in the range 3500 to 18000 ml g.sup.1 h.sup.1.

[0061] The carbon monoxide conversion is obtained up to 100%.

[0062] The reaction time used is preferably in the range 1-100 h.

[0063] The conversion of methane is in the range of 1 to 100%.

[0064] The O.sub.2/CO ratio obtained in the range of 1:2.

General Procedure for the Selective Oxidation of Carbon Monoxide to Carbon Dioxide

[0065] The selective oxidation of carbon monoxide was carried out in a fixed-bed down flow reactor at atmospheric pressure. Typically 300 to 500 mg of previously reduced (reduced at 450 C. with 20% H.sub.2 balance He for 1-3 hr.) catalyst was placed in between two quartz wool plugged in the centre of the 6 mm quartz reactor. The reaction was carried out with the freshly prepared catalyst at different temperatures ranging 40-100 C. The gas hourly space velocity (GHSV) was varied between 3000 to 20000 ml g.sup.1 h.sup.1 with a molar ratio of O.sub.2:CO:He of 1:2:18. The reaction products were analyzed using an online gas chromatography (Thermo Scientific TRACE GC 700) fitted with a TCD detector using column Unibeads-C (for analyzing H.sub.2, CO.sub.2 and CO).

[0066] The following examples are given by way of illustration of working of the invention in actual practice and should not be constructed to limit the scope of the present invention in any way.

Example 1: Preparation of 5% Cu on Cerium Oxide Support

[0067] Cu nanoparticles on cerium oxide support were prepared hydrothermally. All chemicals were used without further purification. Catalyst synthesis was carried out under ambient conditions. In a typical preparation method, 0.5289 g CuCl.sub.2 and 10.2823 g CeCl.sub.3.7 H.sub.2O were dissolved in 150 ml by stirring that gave a light blue solution. The pH of the solution was measured by pH Meter, which was standardised for pH measurement before use. The ammonia solution was added drop by drop gradually until the pH of the solution was 8. Then alcoholic solution of CTAB (50% aqueous alcohol) was added in that mixture under vigorous stirring condition (2000 rpm) for half an hour to form gel. Then alcoholic solution of Polyvinylpyrrolidone (PVP) was added under stirring condition. Stirring was continued for 2 h. All the reagents were used maintain the ratio Cu:CTAB:PVP:H.sub.2O=0.25:0.1875:0.0937:150. The resulting mixture was treated hydrothermally in a Teflon lined stainless steel autoclave (1000 ml capacity) at 180 C. for 24 h and then cooled it to room temperature (25 C.). The obtained material was successively washed with distilled water and dried overnight (12 hr) at 100 C. At last the dried material was calcined at 550 C. in presence of air for 6 h. The material was characterized by XRD, SEM and TEM.

[0068] The XRD pattern of the 5% CuCeO.sub.2 is shown in FIG. 1. XRD depicts the presence of CeO.sub.2 in the sample. Cu nanoparticle was not shown because of very small size. The morphology of the material (5% CuCeO.sub.2) was characterized by SEM. The typical image of the 5% CuCeO.sub.2 is shown in FIG. 2. From the TEM image it is clear that the particles are almost spherical in shape. The typical TEM images of the 5% CuCeO.sub.2 are shown in FIG. 3-4, which indicate that 5-10 nm Cu nanoparticles are present on 10-20 nm CeO.sub.2 nanoparticles. FIG. 3 is the TEM images at low magnification and FIG. 4 is the image of the 5% CuCeO.sub.2 at very high magnification. The dispersion of the Cu particles on CeO.sub.2 support was analyzed by taking the elemental mapping of oxygen, Ce and Cu using SEM as shown in FIG. 5-7 and the mapping confirms that Cu is highly dispersed on CeO.sub.2.

Example 2: Preparation of 10% Cu on Cerium Oxide Support

[0069] Cu nanoparticles on cerium oxide support were prepared hydrothermally. All chemicals were used without further purification. Catalyst synthesis was carried out under ambient conditions. In a typical preparation method, 1.0579 g CuCl.sub.2 and 9.7412 g CeCl.sub.3.7H.sub.2O were dissolved in 150 ml by stirring that gave a light blue solution. The pH of the solution was measured by pH Meter, which was standardised for pH measurement before use. The ammonia solution was added drop by drop gradually until the pH of the solution was 8. Then alcoholic solution of CTAB (50% aqueous alcohol) was added in that mixture under vigorous stirring condition (2000 rpm) for half an hour to form gel. Then alcoholic solution of PVP was added under stirring condition. Stirring was continued for 2 h. All the reagents were used maintain the ratio Cu:CTAB:PVP:H.sub.2O=0.5:0.375:0.1875:150. The resulting mixture was treated hydrothermally in a Teflon lined stainless steel autoclave (1000 ml capacity) at 180 C. for 24 h and then cooled it to room temperature (30 C.). The obtained material was successively washed with distilled water and dried overnight (12 hr) at 100 C. At last the dried material was calcined at 550 C. in presence of air for 6 h.

Example 3

[0070] The example describes the effect of time on conversion. The product analysis presented in Table-1.

Process Conditions

Catalyst: 0.50 g

[0071] Cu:CeO.sub.2 weight ratio in the catalyst=5:95.
Process pressure: 1 atm.
Process temperature: 50 C.
Gas hourly space velocity (GHSV): 7500 ml g.sup.1 h.sup.1
Reaction time: 100 h

O.SUB.2.:CO:He=5:10:85 (mol %)

[0072]

TABLE-US-00001 TABLE 1 Effect of time on conversion of carbon monoxide and oxidation of carbon monoxide Temperature GHSV Carbon monoxide Hour ( C.) (mlg.sup.1h.sup.1) Conversion (%) (h) 47 7500 100 10 47 7500 100 20 47 7500 100 40 47 7500 100 60 47 7500 100 80 47 7500 100 100

Example 4

[0073] The example describes the effect of gas hourly space velocity (GHSV) conversion. The product analysis presented in Table-2.

Process Conditions

Catalyst: 0.50 g

[0074] Cu:CeO.sub.2 weight ratio in the catalyst=5:95.
Process pressure: 1 atm.
Process temperature: 50 C.
Gas hourly space velocity (GHSV): 3750 ml g.sup.1 h.sup.1 to 10000 ml g.sup.1 h.sup.1
Reaction time: 100 h

O.SUB.2.:CO:He=5:10:85 (mol %)

[0075]

TABLE-US-00002 TABLE 2 Effect of space velocity on conversion of carbon monoxide and oxidation of carbon monoxide Temperature Carbon monoxide Hour ( C.) GHSV (mlg.sup.1h.sup.1) Conversion (%) (h) 50 7500 100 100 50 10000 95 100 50 3750 100 100

Example 5

[0076] The example describes the effect of time on conversion. The product analysis presented in Table-3.

Process Conditions

Catalyst: 0.50 g

[0077] Cu:CeO.sub.2 weight ratio in the catalyst=5:95.
Process pressure: 1 atm.
Process temperature: 65 C.
Gas hourly space velocity (GHSV): 15000 ml g.sup.1 h.sup.1
Reaction time: 100 h
O.sub.2:CO:He:H.sub.2=3:6:41:50 (mol %)

TABLE-US-00003 TABLE 3 Effect of time on conversion of carbon monoxide and selective oxidation of carbon monoxide at 65 C. in presence of hydrogen Temperature Carbon monoxide Hour ( C.) GHSV (mlg.sup.1h.sup.1) Conversion (%) (h) 65 15000 100 10 65 15000 100 20 65 15000 100 40 65 15000 100 60 65 15000 100 80 65 15000 100 100

[0078] The process produces very high conversion at low temperature which is also a major advantage of this process.

[0079] The catalyst shows no deactivation up to 100 h time on stream at 65 C.

[0080] The catalyst is used in very low amounts.

Example 6

[0081] The example describes the effect of temperature on conversion. The product analysis presented in Table-4.

Process Conditions

Catalyst: 0.50 g

[0082] Cu:CeO.sub.2 weight ratio in the catalyst=5:95.
Process pressure: 1 atm.
Process temperature: 40 C. to 65 C.
Gas hourly space velocity (GHSV): 15000 ml g.sup.1 h.sup.1
Reaction time: 10 h
O.sub.2:CO:He:H.sub.2=3:6:41:50 (mol %)

TABLE-US-00004 TABLE 4 Effect of temperature on conversion of carbon monoxide and oxidation of carbon monoxide at 65 C. in presence of hydrogen Temperature Carbon monoxide Hour ( C.) GHSV (mlg.sup.1h.sup.1) Conversion (%) (h) 40 15000 50 10 45 15000 55 10 50 15000 65 10 55 15000 80 10 60 15000 95 10 65 15000 100 10

Example-7

[0083] The example describes the effect of temperature on conversion. The product analysis presented in Table 5.

Process Conditions:

Catalyst: 0.50 g

[0084] Cu:CeO.sub.2 weight ratio in the catalyst=5:95.
Process pressure: 1 atm.
Process temperature: 65 C. to 100 C.
Gas hourly space velocity (GHSV): 15000 ml g.sup.1 h.sup.1
Reaction time: 10 h
O.sub.2:CO:He:H.sub.2:H.sub.2O:CO.sub.2=3:6:11:50:10:20 (mol %)

TABLE-US-00005 TABLE 5 Effect of temperature on conversion of carbon monoxide and oxidation of carbon monoxide in presence of hydrogen, carbon dioxide and water vapour Temperature Carbon monoxide Hour ( C.) GHSV (mlg.sup.1h.sup.1) Conversion (%) (h) 65 18000 50 10 70 18000 55 10 75 18000 65 10 80 18000 80 10 85 18000 85 10 90 18000 90 10 100 18000 100 10

Example 8

[0085] The example describes the effect of time on conversion. The product analysis presented in Table-6.

Process Conditions:

Catalyst: 0.50 g

[0086] Cu:CeO.sub.2 weight ratio in the catalyst=5:95.
Process pressure: 1 atm.
Process temperature: 100 C.
Gas hourly space velocity (GHSV): 15000 ml g.sup.1 h.sup.1
Reaction time: 100 h
O.sub.2:CO:He:H.sub.2:H.sub.2O:CO.sub.2=3:6:11:50:10:20 (mol %)

TABLE-US-00006 TABLE 6 Effect of time on conversion of carbon monoxide and oxidation of carbon monoxide in presence of hydrogen, carbon dioxide and water vapour Temperature Carbon monoxide Hour ( C.) GHSV (mlg.sup.1h.sup.1) Conversion (%) (h) 100 18000 100 10 100 18000 100 20 100 18000 100 40 100 18000 100 60 100 18000 100 80 100 18000 100 100

Advantages of the Present Invention

[0087] The main advantages of the present invention are: [0088] The process of the present invention is to oxidize carbon monoxide to carbon dioxide gas through preferential oxidation of carbon monoxide in a single step with a single catalyst. [0089] The process provides not only good conversion but also selectivity of carbon dioxide gas. [0090] The process of the present invention is to oxidize carbon monoxide to carbon dioxide gas selectively in presence of excess hydrogen, carbon dioxide and water vapour in low temperature 100 C. [0091] The process removes carbon monoxide gas from fuel cell to produce carbon dioxide gas which increases the lifetime of the Pt-electrode of the PEM fuel cell. This becomes the major advantages of this process. [0092] The process does not produce any by-products which is also a major advantage of this process. [0093] The catalyst shows no deactivation up to 100 h time on stream at 100 C. in presence of excess hydrogen, carbon dioxide and water vapor. [0094] The catalyst is used in very low amounts.