The present invention relates to preparation of catalyst for production of olefinic hydrocarbons by dehydrogenation of their corresponding paraffins, particularly propylene from propane, comprising a metal oxide or combination of metal oxides utilizing spent catalyst from Fluid Catalytic Cracking (FCC)/Resid Fluid Catalytic Cracking (RFCC) processes. The metal oxides are possibly from transition metal group, particularly from groups VB, VIB, VIII, and Lanthanide series, and at least one metal from alkali group. The catalyst support used is spent catalyst or modified spent catalyst or combination thereof. The said catalyst can be used for both non-oxidative Propane Dehydrogenation (PDH) and Oxidative Propane Dehydrogenation (OPDH) process in the presence of CO2.