WO2016005896A2

WO2016005896A2 - Dehydrogenation catalyst composite and a process for the preparation thereof

Info

Publication number: WO2016005896A2
Application number: PCT/IB2015/055126
Authority: WO
Inventors: Sharad Vasudeorao Lande; Sita Rama Murthy Veera Venkata Satya Bhaskara Katravulapalli; Sreedharan Unnikrishnan; Nagesh Sharma; Shashank Dattatraya Vaidya; Raksh Vir Jasra
Original assignee: Reliance Industries Ltd
Current assignee: Reliance Industries Ltd
Priority date: 2014-07-08
Filing date: 2015-07-07
Publication date: 2016-01-14
Anticipated expiration: 2017-01-08
Also published as: EP3166913A2; WO2016005896A3

Abstract

The present disclosure relates to a dehydrogenation catalyst composite and a process for the preparation thereof. The catalyst composite of the present disclosure comprises at least one nano-sized Group VIII metal component, at least one group IV component, at least one group V component, at least one alkaline earth metal component, at least one alkali metal component, at least one group VI component and a support having an inner core comprising alpha alumina and an outer layer comprising a mixture of gamma alumina, delta alumina and theta alumina. The dehydrogenation catalyst composite may optionally contain a halogen component. The group V metal component is used as a promoter to improve the Group VIII metal dispersion in the dehydrogenation catalyst composite.

Description

DEHYDROGENATION CATALYST COMPOSITE AND A PROCESS FOR THE PREPARATION THEREOF

FIELD

The present disclosure relates to catalyst composition. BACKGROUND

Dehydrogenation of saturated hydrocarbons or alkanes, specifically C2-C2₀ alkanes, is an important chemical process through which a number of useful unsaturated hydrocarbons are manufactured. These unsaturated hydrocarbons are the olefinic monomers; such as ethylene, propylene, butenes, butadiene, styrene and straight chain mono-olefins of carbon number range C6-C20, which find extensive applications in the production of a variety of plastics, synthetic rubber and detergents. Further, dehydrogenation of naphthenes and alkanes are the most important reactions during the catalytic reforming processes, practiced worldwide, for the production of aromatics (BTX) and high octane gasoline.

The conventional dehydrogenation catalyst composite employed for alkanes has platinum and tin metals on alumina support. The platinum and tin metal based alumina supported dehydrogenation catalyst composite gets deactivated mainly due to coke deposition resulting in reduced stability and activity of the catalyst.

Accordingly, there is felt a need to provide a catalyst composite for dehydrogenation of alkanes that has high stability and high activity.

OBJECTS

Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows. It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.

An object of the present disclosure is to provide a dehydrogenation catalyst composite having high activity.

Another object of the present disclosure is to provide a dehydrogenation catalyst composite having high stability.

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

In accordance with one aspect of the present disclosure, there is provided a dehydrogenation catalyst composite for hydrocarbons comprising at least one nano-sized Group VIII metal component, at least one group IV component, at least one group V component, at least one alkaline earth metal component, at least one alkali metal component, at least one group VI component and a support having an inner core comprising alpha alumina and an outer layer comprising a mixture of gamma alumina, delta alumina and theta alumina. The dehydrogenation catalyst composite may optionally contain a halogen component.

In accordance with another aspect of the present disclosure, there is provided a process for the preparation of the dehydrogenation catalyst composite of the present disclosure.

The group V metal component is used as a promoter to improve the Group VIII metal dispersion in the dehydrogenation catalyst composite. Higher metal dispersion leads to higher activity and stability of the dehydrogenation catalyst composite. The group V component also diminishes the amount of coke formed on the catalyst metal active sites.

The dehydrogenation catalyst composite, characterized by an X-ray diffraction patterns having peaks expressed as 2Θ at about 25.63°, 35.21°, 37.83°, 43.41°, 52.61°,57.56°, 66.59°,67.25° and 76.97°.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The dehydrogenation catalyst composite and a process for the preparation thereof will now be described with the help of the accompanying drawings, in which:

Figure -1 depicts the X-ray diffraction pattern of the dehydrogenation catalyst composite of the present disclosure.

DETAILED DESCRIPTION

The disclosure will now be described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

The present disclosure provides a dehydrogenation catalyst composite and a process for the preparation thereof. The catalyst composite of the present disclosure exhibits high activity and stability during dehydrogenation of alkanes.

In accordance with one aspect of the present invention, there is provided a dehydrogenation catalyst composite for hydrocarbons comprising:

- at least one nano-sized Group VIII metal component selected from the group consisting of platinum, nickel and palladium;

- at least one group IV-A metal component selected from the group consisting of tin and germanium;

- at least one group V metal component selected from the group consisting of niobium and tantalum;

- at least one alkaline earth metal component selected from the group consisting of magnesium, calcium and barium;

- at least one alkali metal component consisting of sodium, lithium and potassium;

- at least one group VI-A metal component selected from the group consisting of sulfur, selenium and tellurium; and

- a support having an inner core and an outer layer; wherein the inner core is at least one selected from the group consisting of alpha alumina, alumina, silica, oxide of magnesium and oxide of calcium; and the outer layer comprises a mixture of gamma alumina, delta alumina and theta alumina.

In accordance with one embodiment of the present disclosure, the group VIII metal component is platinum.

In accordance with one embodiment of the present disclosure, the group IV- A metal is tin.

In accordance with one embodiment of the present disclosure, the group V metal component is niobium.

In accordance with one embodiment of the present disclosure, the alkaline earth metal component is magnesium.

In accordance with one embodiment of the present disclosure, the alkali metal component is sodium.

In accordance with one embodiment of the present disclosure, the group VI- A metal component is sulfur.

In accordance with one embodiment of the present disclosure, the inner core is alpha alumina.

The active component of the dehydrogenation catalyst composite is group VIII metal component such as Platinum, which catalyzes the dehydrogenation reaction of alkanes. The average particle size of the group VIII metal component in dehydrogenation catalyst composite is crucial. A lower particle size of the group VIII metal leads to higher dispersion which affords higher activity to the dehydrogenation catalyst composite. It was found that the group V metal component such as Niobium as a promoter increases the platinum metal dispersion percentage.

The dehydrogenation catalyst composite gets deactivated primarily because of coke deposition on active Platinum sites. It was found that the presence of group V metal component such as niobium increases the fraction of bare metallic Platinum surface after coke deposition during the dehydrogenation. The amount of the Group VIII metal component in the dehydrogenation catalyst composite ranges from 0.01% to 5% of the total weight of the dehydrogenation catalyst composite.

The amount of the Group IV-A metal component in the dehydrogenation catalyst composite ranges from 0.01% to 15% of the total weight of the dehydrogenation catalyst composite.

The amount of the Group V metal component in the dehydrogenation catalyst composite ranges from 0.01% to 5% of the total weight of the dehydrogenation catalyst composite.

The amount of the alkaline earth metal component in the dehydrogenation catalyst composite ranges from 0.01% to 10% of the total weight of the dehydrogenation catalyst composite.

The amount of the alkali metal component in the dehydrogenation catalyst composite ranges from 0.01% to 10% of the total weight of the dehydrogenation catalyst composite.

The amount of the group VI-A component in the dehydrogenation catalyst composite ranges from 0.01 to 15% of the total weight of the dehydrogenation catalyst composite.

The amount of delta alumina in the outer core of the support ranges from 1 % to 10 % with respect to the weight of the total alumina present in the outer core.

The dehydrogenation catalyst composite optionally comprises at least one halogen component selected from the group consisting of fluorine, chlorine, bromine and iodine; preferably chlorine.

The amount of the halogen in the dehydrogenation catalyst composite ranges from 0.01 to 1% of the total weight of the dehydrogenation catalyst composite.

The dehydrogenation catalyst composite of the present invention exhibits an X- ray powder diffraction pattern as shown in Figure 1. The Group VIII metal component and the Group V metal component is distributed uniformly on the outer layer of the support.

The Group IVA component is distributed uniformly on the outer layer of the support. The Group IVA component is present partly in elemental state, with or without chemical interaction with Group VIII component. The Group IVA component may exist wholly in oxide state, with or without interaction with the support, when the support is gamma alumina.

In accordance with another aspect of the present invention, there is provided a process for the preparation of the dehydrogenation catalyst composite of the present disclosure. The process for the preparation of the dehydrogenation catalyst composite comprises the following steps:

i) preparing a spheroidal support comprising an inner core and an outer layer; wherein the inner core is at least one selected from the group consisting of alpha alumina, alumina, silica, oxide of magnesium and oxide of calcium; and the outer layer comprises a mixture of gamma alumina, delta alumina and theta alumina; ;

ii) subjecting the spheroidal support to a first impregnation step with at least one alkaline earth metal component using an alkaline earth metal component precursor to obtain an alkaline earth metal impregnated support;

iii) drying and calcining the alkaline earth metal impregnated support at a temperature ranging from 500 °C to 700 °C for a time period ranging from 1 hour to 10 hours;

iv) subjecting the alkaline earth metal impregnated support with a second impregnation step with at least one group V metal component using a group V metal component precursor to obtain a group V metal impregnated support; v) drying and calcining the group V metal impregnated support at a temperature ranging from 500 °C to 700 °C for a time period ranging from 1 hour to 10 hours;

vi) subjecting the group V metal impregnated support with a third impregnation step with a mixture containing at least one group VIII metal component, at least one group IV-A metal component, at least one group VI-A metal component, at least one alkali metal component and optionally at least one halogen component, using respective precursors of each component, to obtain a wet composite;

vii) drying and calcining the wet composite; and

viii) reducing the dried and calcined wet composite by treatment with a stream of reducing gas to obtain the dehydrogenation catalyst composite.

The process step of preparing a spheroidal support comprises; selecting an inner core sphere of average diameter ranging from 1.0 nm to 1.4 nm; coating the inner core sphere with activated alumina powder and a binder to obtain a coated core having an average diameter size in the range of 1.8 nm to 2.2 nm; hydrating the coated core; and heating the hydrated core in the presence of air to obtain spheroidal alumina support having a mixture of gamma, delta and theta alumina in the outer layer.

The binder is at least one selected from a group consisting of water, ethanol and ethyl acetate.

The hydrated core is heated at a temperature ranging from 800 °C to 900 °C for a time period of 1 hour to 10 hours.

In one embodiment of the present disclosure, the Group VIII component is platinum. Platinum is impregnated in the support by using chloroplatinic acid salt as precursor employing a technique selected from the group consisting of 'wet impregnation', 'co-gelling with the support' and 'chemical vapour deposition' . In one embodiment of the present disclosure, the alkaline earth metal component is magnesium and magnesium nitrate is the precursor for magnesium during the first impregnation.

In one embodiment of the present disclosure, the group V metal is niobium and niobium chloride is the precursor for niobium during the second impregnation.

In one embodiment of the present disclosure, the alkali metal component is sodium and sodium chloride is the precursor for sodium during the third impregnation.

In one embodiment of the present disclosure, the Group IV-A component is tin and aqueous solution of stannous chloride is the precursor during the third impregnation.

In one embodiment of the present disclosure, the group VI-A element is sulfur and the precursor for sulfur is at least one selected from the group consisting of thioglycolic acid and thiomalic acid.

In one embodiment of the present disclosure, the halogen component is chlorine and HC1 solution is the precursor of chlorine during the third impregnation.

The halogen component is impregnated together with or before the addition of the group VIII component.

The alkaline earth metal precursor, magnesium nitrate converts the gamma alumina in the outer layer of the support to magnesium oxide and magnesium aluminate.

The alkaline earth metal and alkali metal components are present as oxides or in combined form with the support material or with the other components.

The support is substantially refractory in the hydrocarbon reaction medium.

The treatment with a stream of gas under chemically reducing conditions is performed either in-situ or off-site.

The treatment with a stream of gas under chemically reducing conditions is performed off-site followed by purging with high purity inert gas stream at elevated temperature of more than 300 °C, at high gas hourly space velocity (GHSV) of 100-10000 h^"1 followed by cooling in the same inert gas stream for blanketing.

The dehydrogenation catalyst composite is characterized by X-ray diffraction pattern having peaks expressed as 2Θ at about 25.63°, 35.21°, 37.83°, 43.41°, 52.61°, 57.56°, 66.59°, 67.25° and 76.97°.

In one embodiment of the present disclosure said treatment is carried out at GHSV in the range of 2000-5000 h ¹.

It was found out that optimum results are obtained for the dehydrogenation of alkane using the dehydrogenation catalyst composite of the present disclosure, using the process parameters given in Table 1.

Table- 1: Optimized process parameters

Further, the dispersion of the active component of dehydrogenation catalyst composite of the present disclosure was measured by hydrogen chemisorption method. The hydrogen chemisorption method evaluates the number of active sites that can be reached or that can interact with a fluid phase. The evaluation is based on a chemical reaction between hydrogen gas and the active sites of platinum metal dispersion on the support. It was found that an improved dispersion of active component is accomplished by employing the wet impregnation method. The improved dispersion of the active component of the dehydrogenation catalyst composite of the present disclosure was found to be not less than 68% of surface area of the support surface. The present disclosure is further described in light of the following examples which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure.

Example 1

Preparation of catalyst support

Inert alpha alumina core sphere of average diameter 1.2 nm were used as core. The particles were grown by coating activated alumina powder and binder in rotating pan till it attained average diameter 1.8 nm. The particles were hydrated followed by drying and heating at 850 °C in the presence of air for 6 hours. Activated alumina gave phase mixture of delta and theta alumina.

Example-2

Preparation of catalyst composite of dehydrogenation catalyst

The spheroidal coated alumina support prepared in example 1 was coated with the catalyst composite material of the composition mentioned in table 2. The coating was carried out employing a three-step impregnation adopting incipient wetness technique.

Table -2

In the first step of impregnation, a solution of MgN0₃ was used to impregnate the support by wet impregnation. The impregnated support was dried and calcined at 640 °C for 4h. In the second step of impregnation, a solution of NbCls was employed to impregnate the magnesium impregnated support by wet impregnation followed by drying and calcination. The third impregnation was carried out with a solution containing the salt solutions of Pt, Sn, S, Na; and optionally CI to obtain a wet catalyst composite. The precursors used are H2PtCl₆, SnCi₂, TMA, NaCl, and HC1 respectively. The wet catalyst composite was dried and calcined.

Example 3:

Activity and stability of novel dehydrogenation catalyst composite

Bromine number for the dehydrogenation of alkane using the novel catalyst as prepared in accordance with example 1 and 2 was found out. The comparative bromine numbers of these catalysts are provided in Table 3.

Table -3

*Catalyst A - catalyst comprising platinum, tin, sodium, magnesium and also comprising chloride compounds and sulfur component like thiomalic acid.

*Catalyst B - Catalyst of the Invention comprising platinum, tin, sodium, magnesium, niobium and also comprising chloride compounds and sulfur component like thiomalic acid.

It was found out the catalyst of the present invention (catalyst B) showed a better bromine number activity and stability compared to catalyst A, which lacks niobium. The addition of niobium in the dehydrogenation catalyst composite has led to increased activity and stability.

In catalyst B, niobium is used as promoter to improve the metal dispersion. The role of niobium is (I) modifying the platinum metal dispersion; (II) diminishing the amount of coke formed on the dehydrogenation catalyst composite (not only the supports, but also the active metal sites); and (III) increasing the fraction of bare metallic Pt surface after coke deposition.

Platinum is a highly active element that catalyzes dehydrogenation of alkanes. High dispersion is necessary to achieve higher activity and selectivity to dehydrogenation. Example 4:

Effect group V element on active metal dispersion

Hydrogen chemisorption at 150 °C was used for the determination of dispersion and average crystallite size of the platinum particles supported on alumina in catalyst A and catalyst B. The metal dispersion and average crystallite size for catalyst A and catalyst B are given in the table 4.

Table- 4

The size of metal particles depends upon the method of catalyst preparation and promoters. The Pt dispersion in catalyst B is higher due to the presence of niobium as promoter and adoption of novel catalyst preparation process.

The average crystallite of size platinum metal in catalyst B (1.37 nm) is lower than that in catalyst A (1.62 nm). The lower average metal crystallite size in catalyst B corresponds to a higher metal dispersion. Thus, the number of active Pt sites available on the surface of catalyst B is higher than catalyst B, which corresponds to good activity, selectivity and stability for dehydrogenation reactions.

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE

The dehydrogenation catalyst composite of the present disclosure described herein above has several technical advantages including but not limited to the realization of: The dehydrogenation catalyst composite of the present disclosure has higher activity and higher stability.

The process of the present disclosure is more economical.

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 disclosure to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.

While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments 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.

Claims

1. A dehydrogenation catalyst composite for hydrocarbons comprising:

(a) at least one nano-sized Group VIII metal component selected from the group consisting of platinum, nickel and palladium;

(b) at least one group IV-A metal component selected from the group consisting of tin and germanium;

(c) at least one group V metal component selected from the group consisting of niobium and tantalum;

(d) at least one alkaline earth metal component selected from the group consisting of magnesium, calcium and barium;

(e) at least one alkali metal component consisting of sodium, lithium and potassium;

(f) at least one group VI-A metal component selected from the group consisting of sulfur, selenium and tellurium; and

(g) a support having an inner core and an outer layer; wherein the inner core is at least one selected from the group consisting of alpha alumina, alumina, silica, oxide of magnesium and oxide of calcium; and the outer layer comprises a mixture of gamma alumina, delta alumina and theta alumina.

2. The dehydrogenation catalyst composite as claimed in claim 1, wherein the Group VIII metal component is platinum; the group IV-A metal component is tin; the group V metal component is niobium; the alkaline earth metal component is magnesium; the alkali metal component is sodium; the group VI-A metal component is sulfur and the inner core is alpha alumina.

3. The dehydrogenation catalyst composite as claimed in claim 1, wherein the amount of the Group VIII metal component in the dehydrogenation catalyst composite ranges from 0.01% to 5% of the total weight of the dehydrogenation catalyst composite.

4. The dehydrogenation catalyst composite as claimed in claim 1, wherein the amount of the Group IV-A metal component in the dehydrogenation catalyst composite ranges from 0.01% to 15% of the total weight of the dehydrogenation catalyst composite.

5. The dehydrogenation catalyst composite as claimed in claim 1, wherein the amount of the Group V metal component in the dehydrogenation catalyst composite ranges from 0.01% to 5% of the total weight of the dehydrogenation catalyst composite.

6. The dehydrogenation catalyst composite as claimed in claim 1, wherein the amount of the alkaline earth metal component in the dehydrogenation catalyst composite ranges from 0.01% to 10% of the total weight of the dehydrogenation catalyst composite.

7. The dehydrogenation catalyst composite as claimed in claim 1, wherein the amount of the alkali metal component in the dehydrogenation catalyst composite ranges from 0.01% to 10% of the total weight of the dehydrogenation catalyst composite.

8. The dehydrogenation catalyst composite as claimed in claim 1, wherein the amount of the group VI-A metal component in the dehydrogenation catalyst composite ranges from 0.01 to 15% of the total weight of the dehydrogenation catalyst composite.

9. The dehydrogenation catalyst composite as claimed in claim 1, wherein the amount of delta alumina in the outer layer of the support ranges from 1 % to 10 % of the total alumina present in the outer layer.

10. The dehydrogenation catalyst composite as claimed in claim 1, wherein the dehydrogenation catalyst composite optionally comprises at least one halogen component selected from the group consisting of fluorine, chlorine, bromine and iodine.

11. The dehydrogenation catalyst composite as claimed in claim 10, wherein the amount of the halogen in the dehydrogenation catalyst composite ranges from 0.01 to 1% of the total weight of the dehydrogenation catalyst composite.

12. The dehydrogenation catalyst composite as claimed in claim 1, wherein the Group VIII metal component and the Group V metal component are distributed on the outer layer of the support.

13. A process for the preparation of the dehydrogenation catalyst composite as claimed in claim 1 ; said process comprises the following steps:

i) preparing a spheroidal support comprising an inner core and an outer layer; wherein the inner core is at least one selected from the group consisting of alpha alumina, alumina, silica, oxide of magnesium and oxide of calcium; and the outer layer comprises a mixture of gamma alumina, delta alumina and theta alumina;

ii) subjecting the spheroidal support to a first impregnation step with at least one alkaline earth metal component using an alkaline earth metal component precursor to obtain an alkaline earth metal impregnated support; iii) drying and calcining the alkaline earth metal impregnated support at a temperature ranging from 500 °C to 700 °C for a time period ranging from 1 hour to 10 hours;

iv) subjecting the alkaline earth metal impregnated support with a second impregnation step with at least one group V metal component using a group V metal component precursor to obtain a group V metal impregnated support;

v) drying and calcining the group V metal impregnated support at a temperature ranging from 500 °C to 700 °C for a time period ranging from 1 hour to 10 hours;

vii) drying and calcining the wet composite; and

14. The process as claimed in claim 13, wherein the method step of preparing a spheroidal support comprises; selecting an inner core sphere of average diameter ranging from 1.0 nm to 1.4 nm; coating the inner core sphere with activated alumina powder and a binder to obtain a coated core having an average diameter size in the range of 1.8 nm to 2.2 nm; hydrating the coated core; and heating the hydrated core in the presence of air to obtain spheroidal alumina support containing a mixture of gamma, delta and theta alumina in the outer layer.

15. The process as claimed in claim 14, wherein the hydrated core is heated at a temperature ranging from 800 °C to 900 °C for a time period of 1 hour to 10 hours.

16. The process as claimed in claim 13, wherein the alkaline earth metal component is magnesium and magnesium nitrate is the precursor for magnesium during the first impregnation.

17. The process as claimed in claim 13, wherein the group V metal component is niobium and niobium chloride is the precursor for niobium during the second impregnation.

18. The process as claimed in claim 13, wherein the Group VIII metal component is platinum and chloroplatinic acid salt is the precursor of platinum during the third impregnation.

19. The process as claimed in claim 13, wherein the alkali metal component is sodium and sodium chloride is the precursor for sodium during the third impregnation.

20. The process as claimed in claim 13, wherein the group VI- A metal component is sulfur and the precursor for sulfur during the third impregnation is at least one selected from the group consisting of thioglycolic acid and thiomalic acid.

21. The process as claimed in claim 13, wherein the Group IV- A metal component is tin and aqueous stannous chloride solution is the precursor of tin during the third impregnation.

22. The process as claimed in claim 13, wherein the halogen component is chlorine and HC1 solution is the precursor of chlorine during the third impregnation.

23. The process as claimed in claim 13, wherein said support is substantially refractory in the hydrocarbon reaction medium.

24. The process as claimed in claim 13, wherein the treatment with a stream of gas under chemically reducing conditions is performed either in-situ or off- site.

25. The process as claimed in claim 13, wherein the treatment with a stream of gas under chemically reducing conditions is performed by

(a) purging with high purity inert gas stream at elevated temperature in the range of 300 °C - 500 °C at high gas hourly space velocity (GHSV) of 100-10000 h^"1; and

(b) cooling under the same inert gas stream.

26. A process for dehydrogenation of an alkane; said process comprising subjecting the alkane to dehydrogenation in the presence of a dehydrogenation catalyst composite as claimed in claim 1.

27. The process as claimed in claim 26, wherein said dehydrogenation is carried out at temperature in the range of 400 °C to 800 °C; at a pressure in the range of 0.1- 100 kg/cm ; and liquid hourly space velocity in the range of 1 to 100

28. The process as claimed in claim 26, wherein said alkane is at least on selected from C₂- C20 hydrocarbons.

29. A dehydrogenation catalyst composite, characterized by X-ray diffraction pattern having peaks expressed as 2Θ at about 25.63°, 35.21°, 37.83°, 43.41°, 52.61°,57.56°, 66.59°,67.25° and 76.97°.