Description:FIELD OF THE INVENTION The present invention relates to a catalyst system for isomerization of endo to exo- THDCPD (tetrahydrodicyclopentadiene) comprising desilicated HY zeolites and a process of preparing thereof. More particularly, the invention relates to a catalyst system for isomerization of endo to exo-THDCPD comprising desilicated HY zeolites with Si/Al ratio ranging from 5.1 to 60 and a process of preparing thereof. This invention also relates to modification of zeolites. BACKGROUND OF THE INVENTION The high calorific value liquid fuel finds applications in spacecraft, rockets, ramjets, and turbofans. Primarily, the performance of the engine is influenced by two crucial factors: density and volumetric energy of aviation fuels. Indeed, the fuel tanks for military missions and space travel must be as compact as feasible to accommodate electronics and other components. Therefore, high-density fuel is produced and used to address properties such as higher density and volumetric net heat of combustion (NHOC) compared to conventional aviation fuel. Furthermore, it also provides high propulsion energy which helps in increasing the flight range and payload of missiles and aircraft. Till now, various high density liquid fuels (HED fuel) have been synthesized. However, one of the most commonly applied HED fuels is JP-10. In comparison with aviation kerosene, JP-10 fuel possesses superior properties such as high-density (0.94 g/cm3), high volumetric heat (39.6 MJ/L), low freezing point (-79°C) and high flash point (54°C). The energy it provides can be greater than that offered by distilled kerosene (such as Jet-A). JP-10 is a single-component and chemically known as exo-tetrahydrodicyclopentadiene (exo-THDCPD) commonly referred to as JP-10. It consists of 96.5 wt.% exo-THDCPD, 2.5 wt.% endo-THDCPD, and 1 wt. % adamantane. Generally, it has been synthesized in two steps, firstly the hydrogenation of dicyclopentadiene (DCPD) followed by isomerization of the hydrogenated product. DCPD is also obtained as a byproduct on the steam cracking of naphtha, and it is also widely available as the hydrocarbon. Nevertheless, hydrogenation of DCPD consists of predominantly endo-isomer (solid, endo-THDCPD), which is necessary to isomerize in the exo-isomer (liquid exo-THDCPD). Both the isomers have similar physicochemical properties and high volumetric energy content, except for major differences between freezing points (exo-isomers, -79°C and endo-isomer, 77°C). Therefore, isomerization of endo to exo-THDCPD is indeed essential. Several methods have been reported for the preparation of JP-10 fuel using AlCl3, ionic liquids, and sulfuric acid. Comparatively, AlCl3 exhibits higher isomerization activity. Since AlCl3 is Lewis’s acid liquid phase catalyst it may enhance contact time with endo THDCPD molecules, and thus offer good yield and endo isomer selectivity. All of these techniques, however, have a number of drawbacks, including the inability to regenerate the catalyst, widespread corrosion, and post-treatment procedures like incineration to remove the waste AlCl3, which has negative environmental and biological impact. Furthermore, handling of huge amount of acids/AlCl3 is another safety concern and low production efficiency. Besides, AlCl3 requires additional solvent (DCM) to conduct an isomerization reaction. Separation of DCM is also a time-consuming process. Thus, there is a requirement of an effective solid phase catalyst which is regenerable. Heterogeneous solid acid zeolites have been reported for the isomerization of endo to exo-THDCPD due to their lower operational cost and ease of recovery as well as reusability. In the Isomerization process two factors are very important: activity and shape selective pore dimension. The dimension of endo-THDCPD is 0.67nm*0.65 nm. So, HY types of zeolites (0.74nm*0.74 nm) are the best candidates for the reactant to diffuse into the pores. However, moderate acidity is required for isomerization of endo to exo-THDCPD, and strong acidity leads to side reactions, degradation and coke formation. Also, strong acidity increases the yield of adamantane (ADM) and decreases the selectivity of exo-isomers. Acidic strength also plays important role in isomerization reaction than the number of acidic sites. Zhang et al. reported the synthesis route for JP-10 using fluorine modified HY zeolites in autoclave at 195°C, atmospheric pressure in 4h and the conversion of endo-THDCPD is 96% with exo-THDCPD selectivity is 94%. Since this reaction system required a high temperature of 195°C it led to forming adamantane of 2.32 wt. % and coke formation. Moreover, it is tough to separate adamantane from reaction mixture. Removing adamantane from a solvent can be challenging depending on the specific solvent and the conditions. Adamantane is a highly hydrophobic, cage-like hydrocarbon molecule that can be particularly resistant to dissolution or removal in certain solvents. Adamantane is the most stable isomer of C10H16 and is sublime in nature. However, it is not easy to separate in the system of the final product, adamantane should contain less than 1% by weight. Khan et al investigated the synthesis of JP-10 using Ni-MCM-41 catalyst in autoclave at 150°C, 30 bar H2 pressure in 11h with 85% of exo-THDCPD yield. Although, MCM-41 is a relatively expensive mesoporous material as comparison to zeolites and use of metal content (Ni) is another issue. In another study, acidic Ionic liquid (ILs) are also used to catalyzed isomerization of endo to exo-THDCPD. Wang et al. investigated IL composed of several 1-alkyl-3-methylimidazolium chlorides ([RMIM]Cl) and different metal chlorides and analyzed ([BMIM]Cl)/AlCl3 displays good performance as compared to zeolites catalyst. This catalyst system shows excellent conversion and selectivity with 98%. Huang et al performed isomerization of endo to exo-THDCPD using supported ILs and combining the advantages of high activity and easy separation. However, scaling up ionic liquid to an industrial level and the handling problems that come with it will be a drawback. Moreover, acidic strength is more important than the number of acidic sites. Additionally, operational parameters like temperature, pressure, and time considerably affect the reaction performance. Reaction pressure has a high impact on conversion and selectivity. Higher temperature >150°C and more, might lead to oligomerization (polymer of double bond). In view of the above, there is a requirement of developing a catalytic system for the producing JP-10 (exo-THDCPD) synthesis in batch mode at milder process condition. OBJECTIVES OF THE INVENTION The objective of the present invention is to develop a catalytic system for JP-10 (exo-THDCPD) synthesis in batch mode at milder process condition. In this regard, various catalysts were formulated and evaluated for the isomerization reaction for the maximizing yield of JP-10 production in batch mode under mild condition with ADM yield