Abstract In catalyst development, a targeted reaction often is inhibited by a strongly adsorbed species. To help develop mitigation means, it is important to quantitatively relate the inhibition dynamics to catalyst properties. The present study develops a combined modeling and experimental approach to address this problem. A general mathematical model consisting of three nonlinear partial differential equations is reduced to quadratures or two first-order ordinary differential equations. The result is a simple parameter estimation method, which is used for kinetic characterization of an unsupported CoMo sulfide catalyst for desulfurizing 4,6-diethyldibenzothiophene with 3-ethylcarbazole as the inhibitor. The active site densities and adsorption-reaction rate constants are determined from modeling of transient response experiments. The unsupported CoMo catalyst has a higher hydrodesulfurization turnover frequency than a commercial sulfided Co z Mo/Al 2O 3–SiO 2 catalyst in the absence of 3-ethylcarbazole. However, the unsupported CoMo sulfide is about three times less resilient to 3-ethylcarbazole inhibition than the Co z Mo/Al 2O 3–SiO 2 catalyst.