Abstract: An active highly acidic microporous solid catalyst comprising sulphated metal oxide and at least one of carbon molecular sieve and/or heteropoly acid and having pore volume in the range of 0.1-0.2 m3/g and pore size distribution in the range of 25-40 Å for use in acid catalized organic reactions which occur in the microporous range of the catalysts such as nitration of aromatic compounds, cyclization of terpenoids and more particularly relates to the preparation of modified sulphated zirconia catalysts. The invention also covers the process for producing the abovesaid solid catalyst and its use in producing isopulegol-rich in 1-isopulegol isomer from d-citronellal and in process for mononitration of aromatic compounds C6H4R1R2 wherein R1=—CH3, —C2H5, —Cl, —Br or —I and R2—H or —CH3.