A system, includes an emissions reduction system, including a catalyst system comprising an oxidation catalyst assembly and a selective catalytic reduction catalyst assembly. The system includes a diesel particulate fuel assembly, a first and a second sensor upstream of the catalyst system configured to measure emissions of the exhaust flow of the gas engine and a gas turbine before flowing into the catalyst system to generate a first and a second signal. A third sensor is downstream of the catalyst system to measure emissions of the catalyst system to generate a third signal, and a fourth and a fifth sensor disposed upstream and downstream of the DPF assembly to measure a change in pressure to generate a fourth signal and a controller to generate a first control signal to control an amount of reductant based on at least the first, second, and third signals.