An aftertreatment module may include a housing with an inlet port and an outlet port. A selective catalytic reduction catalyst may be disposed between the inlet port and the outlet port. A diffuser plate may be disposed downstream of the inlet port and upstream of the selective catalytic reduction catalysts. The diffuser plate may include a first section including a first degree of porosity and a second section including a second degree of porosity. The first degree of porosity may be greater than the second degree of porosity.