The highest-temperature step in iodine–sulfur and hybrid–sulfur thermochemical cycles for hydrogen generation is the sulfuric acid decomposition reaction. To efficiently utilize solar energy directly to operate this step, the development of a catalytic solar receiver reactor is essential. A cavity-type reactor coupled to a solar dish and a numerical analysis of the reactor predicting the reaction conversion as a function of the solar absorption coefficient is presented in this study. The catalytic receiver reactor consists of a double-walled quartz cylindrical tube to form the cavity and a flat quartz plate window for entry of the concentrated solar radiation. Two catalysts, Fe_1.8Cr_0.2O₃ and Fe₂O₃/SiO₂, are tested in the solar catalytic receiver reactor and SO₂ yields of ≈40% and 38% are observed, respectively. Numerical analysis of the reactor is performed and a reaction conversion–absorption coefficient correlation is established. For the catalytic packed bed assuming absorption coefficient of 0.65, a steady-state temperature of 1212 K is achieved, accomplishing an approximate theoretical efficiency of ≈56%. The numerical analysis suggests that by utilizing a material of construction with high absorption coefficient, significantly enhanced sulfuric acid decomposition can be achieved by the cavity-type solar receiver reactor.