A method to improve NOx reduction in diesel engine exhausts by selective catalytic reduction using reductants comprising hydrocarbons, comprising passing the exhaust gases through a series of zones, said zones comprising a first zone in which a first catalyst is located that promotes HC SCR, to yield a first product gas; a second zone through which the first product gas is passed and in which a second catalyst is located that promotes the H2-promoted HC SCR reaction to produce a second product gas and a third zone through which the second product gas is passed and in which a third catalyst is located that promotes CO/H2 SCR to yield a final, NOx-depleted, exhaust gas, and admixing a reformate gas comprising CO and H2 with one or more of the exhaust gases, the first product gas and the second product gas. The use of the series of catalysts offers a sound alternative to urea-based SCR, without requiring a source and storage of urea.