Claims:1. A supported bimetallic catalyst system for preparing carbon nanotubes, said catalyst system comprising
- a first transition metal or its oxide;
- a second transition metal; and
- at least one support selected from the group consisting of Mg(OR)2 and MgCl2,
wherein R is ethyl.
2. The catalyst system as claimed in claim 1, wherein said first transition metal and said second transition metal is at least one independently selected from the group consisting of nickel, molybdenum, iron, and cobalt.
3. The catalyst system as claimed in claim 1, wherein the weight ratio of said first transition metal or its oxide, and said second transition metal is in the range of 5:0.1 to 5:0.3.
4. The catalyst system as claimed in claim 1, wherein the weight ratio of said first transition metal or its oxide, and said support is in the range of 10:1 to 3:1.
5. A process for preparing a supported bimetallic catalyst system, said process comprising the following steps:
a. mixing predetermined amounts of a first transition metal salt, a second transition metal salt, a support and water to obtain a first mixture;
b. adding a predetermined amount of an organic compound to obtain a second mixture;
c. heating said second mixture at a temperature in the range of 70 to 110 °C for a time period in the range of 30 minutes to 180 minutes to obtain a heated mass;
d. drying said heated mass to obtain a dried mass;
e. grinding said dried mass to obtain a powder; and
f. heating said powder at a temperature in the range of 600 to 800 °C to obtain the supported bimetallic catalyst system,
wherein, said support is at least one selected from the group consisting of Mg(OR)2 and MgCl2, wherein R is ethyl.

6. The process as claimed in claim 5, wherein said organic compound is citric acid.
7. The process as claimed in claim 5, wherein the weight ratio of said organic compound to said support is in the range of 6:1 .
8. A process for preparing carbon nanotubes using a supported bimetallic catalyst system, said process comprising the following steps:
a. mixing predetermined amounts of said supported bimetallic catalyst system and a polyolefin to obtain a first mixture;
b. heating said first mixture at a temperature in the range of 750 to 950 °C for a time period in the range of 5 minutes to 15 minutes to obtain a second mixture;
c. cooling said second mixture to obtain a cooled mixture; and
d. purifying said cooled mixture to obtain carbon nanotubes,
wherein said carbon nanotubes are multiwalled, having diameter in the range of 15 to 20 nm; and purity of at least 96%; and
wherein said supported bimetallic catalyst syatem comprises a first tansition metal or its oxide; a second transition metal; and at least one support selected from the group consisting of Mg(OR)2 and MgCl2, wherein R is ethyl.
9. The process as claimed in claim 8, wherein said step ‘d’ of purifying said cooled mixture comprises the following steps:
i. adding concentrated nitric acid to said cooled mixture and sonicating to obtain a third mixture;
ii. diluting said third mixture with water followed by filtering to obtain a solid;
iii. washing said solid with water to attain neutral pH and to obtain amorphous carbon;
iv. oxidizing said amorphous carbon at a temperature in the range of 300 to 500 °C for a time period in the range of 30 minutes to 180 minutes to obtain carbon nanotubes.
10. The process as claimed in claim 8, wherein the weight ratio of said supported bimetallic catalyst system to said polyolefin is in the range of 1:30 to 1:50.
, Description:FIELD
The present disclosure relates to a supported bimetallic catalyst system for preparing carbon nanotubes and a process for preparation thereof.
BACKGROUND
Carbon nanotubes (CNTs) exhibit unique properties, which are advantageous for many applications. Carbon nanotubes can be conventionally synthesized from different carbon sources. The methods for synthesizing carbon nanotubes include arc discharge, laser vaporization, chemical vapor deposition, and catalytic decomposition of carbon.
Catalytic decomposition of carbon is a promising method for the production of carbon nanotubes on a large scale.
Synthesis of CNTs using polymers as a carbon source is known in the art. Such a process offers the advantage of resource saving and environmental protection due to its potential application of a large amount of virtually non-degradable polymer as a carbon source, instead of incineration and landfilling. However, catalytic decomposition of polymers does not provide CNTs of the desired quality and purity.
Therefore, there is felt a need to provide a catalyst system that can produce carbon nanotubes of the desired quality and purity.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to provide a supported bimetallic catalyst for preparing carbon nanotubes.
Another object of the present disclosure is to provide a process for preparing a supported bimetallic catalyst system.
Still another object of the present disclosure is to provide a process for preparing carbon nanotubes.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure envisages a supported bimetallic catalyst system for preparing carbon nanotubes. The supported bimetallic catalyst system comprises a first transition metal or its oxide, a second transition metal, and at least one support selected from the group consisting of Mg(OR)2 and MgCl2, wherein R is ethyl.
The first transition metal and the second transition metal can be at least one independently selected from the group consisting of nickel, molybdenum, iron, and cobalt.
The weight ratio of the amount of the first transition metal or its oxide, and the amount of the second transition metal can be in the range of 5:0.1 to 5:0.3. The weight ratio of the amount of the first transition metal or its oxide, and the amount of the support can be in the range of 10:1 to 3:1.
In accordance with another aspect of the present disclosure, there is provided a process for preparing the supported bimetallic catalyst, the process comprises mixing predetermined amounts of a first tansition metal salt, a second transition metal salt, at least one support and water to obtain a first mixture. A predetermined amount of an organic compound is added to the first mixture to obtain a second mixture. The second mixture is heated at a temperature in the range of 70 to 110 °C for a time period in the range of 30 minutes to 180 minutes to obtain a heated mass. The heated mass is dried to obtain a dried mass. The dried mass is grounded to obtain a powder. The powder is heated at a temperature in the range of 600 to 800 °C for a time period in the range of 60 minutes to 180 minutes, to obtain the supported bimetallic catalyst system.
The organic compound can be citric acid.
The weight ratio of the amount of the organic compound to the amount of the support is in the range of 6:1.
In accordance with a still another aspect of the present disclosure, there is provided a process for preparing carbon nanotubes using the supported bimetallic catalyst system. The process comprises mixing predetermined amounts of the supported bimetallic catalyst system and a polyolefin to obtain a first mixture. The first mixture is heated at a temperature in the range of 750 to 950 °C for a time period in the range of 5 minutes to 15 minutes to obtain a second mixture. The second mixture is cooled to obtain a cooled mixture, which is purified to obtain multiwalled carbon nanotubes.
The diameter of the carbon nanotubes obtained by using the process of the present disclosure can be in the range of 15 to 20 nm; and the purity can be at least 96%.
Further, the step of purification of the cooled mixture comprises adding concentrated nitric acid to the cooled mixture and sonicating to obtain a third mixture. The third mixture is diluted with demineralized water followed by filtration to obtain a solid. The solid is washed with water to attain neutral pH, and produce amorphous carbon. The amorphous carbon is oxidized at a temperature in the range of 300 to 500 °C for a time period in the range of 30 minutes to 120 minutes to obtain multiwalled carbon nanotubes.
The weight ratio of the amount of the supported bimetallic catalyst to the amount of the polymer can be in the range of 1: 30 to 1: 50.
DETAILED DESCRIPTION
The carbon nanotubes exhibit unique peroperties, which make them advantageous for many applications. Carbon nanotubes can be conventionally synthesized from different carbon sources. The catalytic decomposition of polymers does not provide CNTs of the desired quality and purity. Therefore, there is a need to provide an efficient catalytic decomposition method for preparing carbon nanotubes having desired properties and purity.
In accordance with one aspect of the present disclosure, there is provided a supported bimetallic catalyst system. The supported bimetallic catalyst system of the present disclosure is used for the preparation of carbon nanotubes from a polymer or its waste. The catalyst system of the present disclosure comprises a first transition metal or its oxide, a second transition metal, and at least one support.
The first transition metal and the second transition metal can be at least one independently selected from the group consisting of nickel, molybdenum, zirconium and cobalt.
In accordance with one embodiment of the present disclosure, the first transition metal can be nickel.
In accordance with another embodiment of the present disclosure, the oxide of the first transition metal can be nickel oxide.
In accordance with one embodiment of the present disclosure, the second transition metal can be molybdenum.
The support of the catalyst system of the present disclosure can be at least one selected from the group consisting of Mg(OR)2 and MgCl2, wherein R is ethyl.
The weight ratio of said first transition metal or its oxide, and said second transition metal can be in the range of 5:0.1 to 5:0.3.
The weight ratio of said first transition metal or its oxide, and said support can be in the range of 10:1 to 3:1.
In accordance with one embodiment of the present disclosure, the proportion of the first transition metal or its oxide, the second transition metal and the support can be 5:0.2:1.
The specific combination of the first transition metal or its oxide, the second transition metal and the support controls the morphology of the final catalyst to yield CNTs of the desired quality and purity.
In accordance with another aspect of the present disclosure, there is provided a process for preparing the supported bimetallic catalyst system. The process comprises the following steps:
Predetermined amounts of a first transition metal salt, a second transition metal salt, a support and water are mixed together to obtain a first mixture.
Next, a predetermined amount of an organic compound is mixed with the first mixture to obtain a second mixture.
The so obtained second mixture is heated at a temperature in the range of 70 to 110 °C for a time period in the range of 30 minutes to 180 minutes to obtain a heated mass, which is viscous in nature.
The heated mass is dried to obtain a dried mass, followed by grinding the dried mass to obtain a powder.
The so obtained powder is heated at temperature in the range of 600 to 800 °C for a time period in the range of 60 minutes to 180 minutes, to obtain the supported bimetallic catalyst system.
The organic compound can be citric acid. The organic compound used while preparing the catalyst system of the present disclosure acts as a combustion agent and helps to make the catalyst system fluffy. In one embodiment, the heating of the powder can be carried out in a muffle furnace.
The weight ratio of the amount of the organic compound to the amount of the support is in the range of 6:1.
In accordance with a still another aspect of the present disclosure, there is provided a process for preparing carbon nanotubes using a supported bimetallic catalyst system of the present disclosure. The process comprises the following steps:
Initially, predetermined amounts of the supported bimetallic catalyst system and a polyolefin are mixed together to obtain a first mixture.
The so obtained first mixture is heated at a temperature in the range of 750 to 950 °C for a time period in the range of 5 minutes to 15 minutes to obtain a second mixture.
The second mixture is further cooled to obtain a cooled mixture.
Next, the cooled mixture is purified to obtain multiwalled carbon nanotubes.
The polymer obtained during preparation of carbon nanotubes can be polyethylene or its waste.
The diameter of multiwalled carbon nanotubes obtained using the process of the present disclosure can be in the range of 15 to 20 nm.
The carbon nanotubes obtained by the process of the present disclosure can have the purity of at least 96%.
Conventionally, the process of growing carbon nanotubes is carried out in an inert atmosphere. The process of the present disclosure for preparing carbon nanotubes comprises pyrolysis of the polymer in the presence of the supported bimetallic catalyst system. The pyrolysis of the polymer is carried out at such a temperature that the pyrolysis vapors create the inert atmosphere.
Typically, the heating of the polymer is carried out in a muffle furnace, wherein the polymer is placed in a crucible. The initial heating of the polymer generates hydrocarbon vapours, which removes air from the crucible, thereby making inert atmosphere.
The process for preparing carbon nanotubes using the supported bimetallic catalyst system comprises a step of purification of the cooled mixture to obtain multiwalled carbon nanotubes. The step of purifying the cooled mixture can be carried out as follows.
Concentrated nitric acid is added to the cooled mixture and sonicated to obtain a third mixture. The step of sonication allows removal of the particles of the supported bimetallic catalyst from the cooled mixture.
The third mixture is diluted with demineralized water. The resultant mixture is filtered to obtain a solid and filtrate. The filtrate is discarded and the solid is washed with demineralized water to attain a neutral pH, and obtain amorphous carbon.
The amorphous carbon is oxidized at a temperature in the range of 600 to 800 °C for a time period in the range of 30 minutes to 180 minutes to obtain multiwalled carbon nanotubes.
The oxidation of amorphous carbon by heating can be carried out in a muffle furnace.
The weight ratio of the amount of the supported bimetallic catalyst to the amount of polyolefin can be in the range of 1:30 to 1:50.
The carbon nanotubes obtained by using the process of the present disclosure and by employing the supported bimetallic catalyst system of the present disclosure has high purity . The process for producing carbon nanotubes is economical, as it utilizes polymer waste for the production of carbon nanotubes.
The use of the supported bimetallic catalyst system of the present disclosure, for the production of carbon nanotubes controls the morphology and the yield of carbon nanotubes.
The carbon nanotubes obtained by using the process of the present disclosure can be multiwalled carbon nanotubes having high surface area, having diameter in the range of 15 to 20 nm.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and are not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
Experiment 1: Synthesis of a supported bimetallic catalyst system
A vessel containing 20 mL of deionised water was charged with 2.0 g Ni(NO3)2.6H2O, 0.048 g (NH4)6Mo7O24.4H2O, and 0.16 g Mg(OR)2 of 99.9 % purity to obtain a first mixture. Next, 2 g of citric acid was added to the first mixture to obtain a second mixture, which was heated at 90 °C for 1 hour. Heating of the second mixture resulted in formation of green coloured heated mass, which was then evaporated on a hot plate to form a viscous mass. The viscous mass was dried in an oven at 120 °C for 10 hours to obatin a dried mass. The dried mass was ground to fine powder and combusted in a muffle furnace at 700 °C for 2 hours to obtain a supported bimetallic catalyst system.
Experiment 2: Preparation of carbon nanotubes using a supported bimetallic catalyst system
The catalyst system as obtained in experiment 1 and polypropylene resins were mixed together to obtain a mixture, which was kept in a muffle furnace at 850 °C. The mixture was placed in a silica crucible in the muffle furnace. The heating was continued for 10 minutes. The crucible was removed from furnace after 10 minutes and cooled to room temperature to obtain a cooled mixture, which was then purified to obtain multiwalled carbon nanotubes.
Purification of cooled mixture:
17 mL Concentrated nitric acid was added to 1.5 g of cooled mixture (as obtained above), which was then sonicated at room temperature. The sonicated mixture was diluted with 35 mL of demineralized water followed by filtering to obtain a solid. The solid was further washed with 300 mL of demineralized water to attain neutral pH and to obtain amorphous carbon. The amorphous carbon was oxidized at 400 °C for 90 minutes to obtain multiwalled carbon nanotubes.

TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a supported bimetallic catalyst that
- is used for converting the polymer or its waste into high value CNTs;
- controls the morphology and the yield of carbon nanotubes; and
- produces carbon nanotubes having high purity.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.