A catalyst retainer includes an inner particle retention device having apertures and a first non-apertured section; and an outer particle retention device having apertures and a second non-apertured section. The inner and the outer particle retention devices are spaced apart to define a particle retaining space of the retainer. The first non-apertured section and the second non-apertured section define a blanked-off section of the particle retaining space, and the blanked-off section is spaced from an end of the particle retaining space. The catalyst retainer also includes a louver with at least a portion located between the blanked-off section and the end of the particle retaining space. The louver extends into the particle retaining space at an angle with respect to an inner surface of the inner particle retention device. The louver introduces the fluid to the top catalyst free surface in a more uniform manner and hence prevents particle movement and attrition.