In at least one embodiment of the present invention, a method of recovering energy from a FCC unit having a reactor and a regenerator for overall CO2 reduction is provided. The method comprises cooling syngas to a predetermined low temperature to define cooled syngas. A turbo-expander including a first compressor is provided. The turbo-expander train is configured to combust and expand gas to drive the first compressor. The cooled syngas is compressed with the first compressor to define compressed syngas. A first stream of gas comprising CO2 and a second stream of gas comprising CO are separated from the compressed syngas. O2 and the first and second streams of gas are introduced to the turbo-expander train. The first stream of gas is expanded and the second stream of gas is combusted and expanded with the O2 to recover energy, driving the first compressor and producing the syngas.