A silencer and catalytic converter apparatus includes a housing and a frame assembly arranged in the housing. The frame assembly may receive at least one catalyst panel and support the catalyst panel to occupy an area of a flow passage between upstream and downstream chamber sections of the housing. A blocking panel may be supported by the frame assembly to obstruct a remaining area of the flow passage so that fluid flowing between the upstream and downstream chamber sections is directed to flow through the catalyst panel. The blocking panel may be adjustable to accommodate catalyst panels of different sizes.