We report here the results of our computational studies on porous catalysts to bring out the catalytic role played by nanostructures. We present two typical case studies where the molecular dynamic (MD) and quantum chemical (QC) techniques have revealed the important structural aspects involved in the functioning of nanostructured microporous materials. The central role played by the exchanged metal cations of zeolite A in the molecular sieving of nitrogen and oxygen was studied by MD calculations. The results indicated that the mobility of the exchanged cations which are dependent on temperature causes the separation of nitrogen and oxygen molecules. The real time visualization of the dynamic behavior of the exchanged cations during the MD process aids the understanding of this intriguing process occurring inside the micropores of the zeolites. The controlled pore opening of hydrated VPI-5 molecular sieve by careful removal of water leads to a large one dimensional channel. The possibility of anchoring organometallics, namely porphyrins with 'enzyme-like' active sites were studied using QC calculations. The analysis of the 3-d contours of electron density and molecular electrostatic potential maps corresponding to various porphyrin systems and the cluster models representing VPI-5 framework brought out the probable locations for porphyrins inside VPI-5.