In at least one embodiment of the present invention, a method of heating a FCC unit having a regenerator and a reactor having overall CO.sub.2 reduction is provided. The method comprises compressing syngas to define compressed syngas. Separating a first stream of gas comprising CO.sub.2 from the compressed syngas. A second stream of gas comprising O.sub.2 is expanded with the first stream of gas to produce a feed gas. The feed gas is introduced to the regenerator at gasification conditions to burn coke from coke heavy spent catalyst advanced from the reactor, producing syngas and heat for operating the reactor at reaction temperatures.