1. A method for controlling a process of the type utilizing a catalyst, the method including the steps of: defining a state space model for the process, the state space model including a catalyst state comprising a hidden catalyst property; defining a set of input variables for the state space model, wherein the input variables are empirically measurable properties of the process; defining a set of output variables for the state space model, wherein the output variables are empirically measurable properties of the process; measuring a set of input values corresponding to the set of input variables; measuring a set of output values corresponding to the set of output variables; and estimating the hidden catalyst property based on the input values, the output values, and the state space model.