A dynamic model is developed to describe two parallel reactions between one gaseous and two non-volatile components on partially wetted catalysts with a time-dependent welting efficiency. This simulates the performance of catalytic particles in a trickle-bed reactor operating in the pulsing-flow regime. The periodically varying external surface coverage results in periodically varying mass transfer rates to the surface of the particle. No a priori assumption is made about a rate limiting reactant. The results show the effect of interface and intraparticle mass transfer resistances as well as of the wetting efficiency and the frequency with which it varies on catalyst performance. It is shown that the wetting efficiency, the location of the wetted zones and the frequency need to be specified in order to determine the time-averaged effectiveness factors. For the same time-averaged wetting efficiency, pulse-flow can significantly enhance catalyst performance. Conditions are determined under which the effectiveness factors are maximized. The model is applied to a typical HDS process of heavy gas oil.