The present invention is directed to the removal of nitrogen and sulfur containing impurities from high molecular weight petroleum feedstock obtained from fluid cracking catalyst or distillation zone of a petroleum treatment plant. The present process comprises first treating C.sub.12 and higher hydrocarbon petroleum feedstock having nitrogen and sulfur containing compounds therein with a porous, particulate adsorbent comprising a silica matrix having an effective amount of metal atoms therein to cause the adsorbent to have Lewis acidity of at least 500 .mu.mol/g and then treating the resultant feedstock to catalytic hydrodesulfurization to produce a hydrocarbon fuel having low sulfur and nitrogen content.