Emissions of nitrogen oxides in exhaust from gas turbine systems are reduced, in accordance with the invention, by introducing, into the combustor, a supplementary gaseous stream comprising dihydrogen, carbon monoxide and carbon dioxide, and a stream of gaseous fuel and/or mixtures thereof, with a source of dioxygen to form a combustible gaseous mixture; combusting the mixture to produce heat and a combustion product stream; and driving a turbine with the combustion product stream to produce an exhaust stream and to generate mechanical power. Supplementary gaseous streams are, advantageously, formed by a process for hydroshifting dimethyl ether, i.e. formed by a process which comprises passing a feed stream which includes dimethyl ether and steam to a hydroshifting, reaction zone including an essentially alkali metal-free catalytic composition substantially composed of copper or nickel in elemental form. This process produces a hydroshifted product stream which is, advantageously, relatively rich in dihydrogen, carbon monoxide, and carbon dioxide.