In this work, we demonstrate the fine structural tuning of metal-metal oxide heterostructure with regards to the individual tuning of the various core and shell components from shell thickness to metal core constitution. Furthermore, we deliberately engineered spatially confined and clustered Au nanoparticles in the core of a porous shell structure without the assistance of template or linker. Our findings unambiguously highlight that whilst it is important to incorporate metal nanoparticles into metal oxide for higher photocatalytic performance through enhanced light absorption and charge separation, the "whereabout" and clustering of Au nanoparticles affect the photocatalytic performance. Furthermore, we also prove the enhanced and prolonged catalytic activity of spatially confined metal cores over conventional surface loaded metal particles, which originates from the structural stability and optimized contact interface for heterojunction-induced charge transfer. The present well-controlled synthetic route can offer a facile and valuable way to tune and probe specific structure in relation to nanoscale light-matter manipulation and solar-to-chemical energy conversion studies.