The aim of this study is to describe the flow as well as the heat and mass transfer of twin laminar jet impinging a flat catalytic sample. The Navier–Stokes and energy equations are solved by numerical simulations. When the flow reaches a steady state, a passive scalar transport equation is added to account for mass transfer on the impinging plate. The computed flows for a range of Reynolds number (3.3–100), jet-to-jet distance (2. 4$R$ − 6.2$R$) and two temperature gradients between the sample and the jet injection (0 and 300 K), are analyzed. The jet-to-jet interactions are specially described in the case where a fountain flow resulting from the wall-jets colliding is observed. Described interactions are classified in a topological diagram according to the Reynolds number and the normalized jet spacing for the isothermal case as well as in the presence of temperature gradient. The heat and mass transfer description is further conditioned on the flow characteristics as identified by the topological diagram. It is observed that the average Nusselt number on the sample is the lowest when the fountain flow is blocked by the impinging jet shear layer interaction. Mass transfer on the sample is then described by the ratio of the mass flux orthogonal and parallel to the injection line within the boundary layer on the sample. The ratio is lower than 1 when the flow is blocked. This study points out the importance of the presence of a fountain flow on heat and mass transfer quantities in the flow surrounding the catalytic sample.