The major aspects of aromatic hydrogenation are the production of aromatic-free diesel fuels. Health risks and diesel quality depend on the aromatic compounds that have insisted legislators to improve the quality of the diesel fuel and to reduce the aromatic content in the diesel. In diesel fuel, aromatic compounds are also responsible for particle emissions in exhaust gases. The major concern related to exhaust gases are particle emissions such as CO, SOx and NOx. This book represents the study on metal catalysts for liquid phase hydrogenation of aromatics in a high pressure catalytic reactor and kinetic study of the hydrogenation of aromatic compounds. The hydrogenation of benzene, toluene, naphthalene and mixtures of these on a synthesized platinum and nickel catalysts in a fixed bed reactor is discussed. The oil refinery industry today faces increasing production demands for diesel fuels, but the fuel specifications are being tightened day by day. Intensive study toward more efficient hydroprocessing reactor is therefore required. Hydrogenation of diesel fuel also comprises the removal of heteroatoms (S, N, O) and aromatic compounds. Aromatic compounds are converted to saturated hydrocarbons through hydrogenation reaction over metal catalysts in a continuous catalytic fixed bed reactor at high temperature and pressure. Regulations today allow total aromatics contents to 36 wt % in the U.S. and polyaromatics contents to 11 wt % in the EU. Stringent limitations are, however, forthcoming. The World Fuels Charter, issued by engine and vehicle manufacturers, specifies higher qualities for diesel fuel of the future. Among these qualities are total contents of aromatics and polyaromatics as low as 15 and 2 wt %, respectively.