1. A system comprising: a catalyst light-off circuit configured to selectively generate a first signal based on an engine coolant temperature and an estimated exhaust enthalpy; a setpoint circuit configured to selectively initiate a catalyst light-off period in response to receiving the first signal and that generates a desired exhaust enthalpy; a first model predictive control (MPC) circuit configured to: predict an exhaust enthalpy based on a model of an engine and multiple sets of possible target values; generate a respective cost for each of the sets of possible target values based on differences between the predicted exhaust enthalpy and the desired exhaust enthalpy; and select a set of possible target values from the multiple sets of possible target values based on the respective costs; and an actuator circuit configured to adjust an actuator of the engine based on at least one of the target values from the selected set of possible target values.