The instant disclosure provides a composition for fluid catalytic cracking of petroleum based feedstock into useful short chain olefins. The composition comprising: 76-86% of a non-zeolitic material; and 2-30% of at least one zeolite material, the percentage being based on weight of the catalyst composition, wherein one of the zeolites has been modified with 0.1-2.5 wt % metal. The said catalyst was found to be selective in enhancing the usable propylene gas content, while reducing the undesirable dry gas content of the cracked olefinic products. The present disclosure also provides a process for the preparation of the composition. The present disclosure also provides an apparatus (100) and process (200) for fluid catalytic cracking to obtain light olefins. The apparatus comprises a second riser (33) that includes a lower dense riser (2) and upper dilute riser (3). Further, the lower dense riser (2) has a diameter that is 1.1 to 2 times that of the upper dilute riser (3).