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Catalytic performance of Pt impregnated parent and desilicated nano-crystalline zeolites, ZSM-5 and Beta for n-hexane isomerization was studied. Difference in channel systems of the zeolites and absence/presence of mesopores therein were found to be reflected in product distributions. ZSM-5 was desilicated by NaOH and zeolite Beta with tetramethylammonium hydroxide (TMAOH.) Desilication was found to afford comparable catalytic performance to that of the parent counterpart at reaction temperature lower by 25°C. Observed product distributions could be substantiated with characterizations such as ammonia TPD, surface area determination and SEM. Desilicated zeolite Beta was seen to be less prone to coking as deduced from the TGA study. Location of Pt with reference to proton sites within the channels and that inside the pores viz a viz external surface also have been discussed briefly.

The effects of variation in Si/Al ratio (25 and 100) and crystallization temperature (80 °C to 180 °C, at an interval of 20 K) on crystal size of zeolite beta were studied. Products obtained at different synthesis parameters were characterized by powder X-ray diffraction, IR spectroscopy, thermal analysis, scanning electron microscopy and nitrogen adsorption. Increase in crystal size with crystallization temperature and Si/Al molar ratio was observed. Crystal morphology at 140 °C was spherical whereas at 180 °C it was of irregular shape.

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Hydroisomerization of n-hexane simultaneously proceeding with benzene saturation over platinum impregnated nano-crystalline zeolite beta (Si/Al = 25) at 1.0 MPa and 573-673 K was studied. The feed contained 30 wt% benzene. The synthesized catalyst was characterized by various techniques, e.g., powder X-ray diffraction, IR spectroscopy, thermal analysis, scanning electron microscopy and nitrogen adsorption. At the operating conditions used, total saturation of benzene with 95% selectivity to cyclohexane (CH) and methylcyclopentane (MCP) was observed. n-Hexane conversion increased with temperature whether benzene was present or not during the reaction. However, in the presence of benzene, n-hexane conversions as well as isomer selectivities were observed to be lower. This was attributed to reduced availability of acid sites by predominating benzene adsorption. Formation of carbenium ion on an acid site is questioned and plausible mechanism has been suggested.

Zeolite Beta crystals in nanometer size (about 44 nm) were hydrothermally synthesized and its catalytic activities with and without Pt impregnation were studied for 1-hexene isomerization in presence of different carrier gases, namely, hydrogen, nitrogen and carbon dioxide and also in the absence of carrier gas at reaction temperatures of 473-573 K and 0.1 MPa. General observation for all the cases was that with reaction temperature, hexene conversion increased, however, total isomer selectivity dropped. With temperature skeletal isomerization increased at the cost of double bond shift isomerization. Observed product distribution has been explained on the basis of zeolite structure and crystal size. Catalyst performed better in nitrogen than in hydrogen or carbon dioxide as carrier gas. Nevertheless, catalyst life was shorter with nitrogen as carrier gas than that with hydrogen.

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