is there any patch for catia v5 to upgrade the rendering ability and improve it?
The intention of CATIA V5 isn´t rendering, Photostudio and Realtime-Rendering are the "top products". Some years ago the quality of those have been incredible, but today it is like you said ... different.
There is no upgrade, so use a different, specialiced software like keyshot.
The Dassault product "3Dvia composer" has really great visual effects, it is a single solution and will be a part of V6.