Harnessing surface plasmon- of metal) nanostructuresto ptomote catalytic organic synthesis holds great promise in, solar-to-Chemical energy Conversion: High conversion 'efficiency relies not only on broadening the absorption spectrum but on coupling the harvested,energy into chemical reactions. Such coupling undergoes hot electron transfer and-photothermal,conversion during the decay of surface plasmon;, however, the two plasmonic effects are unfortunately entangleckmaking-Aeir inditdual roles still under debate, Here, we report that in a,model system of bituetallic Au-Pd core shell nanostructures the two effects- can be.disentangled through tailoring the,shell thickness a("atomictevel precision. As demonsttated by our ultrafast absorption spectroscoPy. characterizations, the achieved tunability of the two effects in a triode' reaction of "Pd-catalyzed organic hydrogenation offers a knob for enhancing energy Coupling. In addition, the two intrinsic plasmonic modes at 400--/00 ancI700-100() nm in the bar-shaped nanostructures allow for utilizing "photons td-a-large extent in full Solar spectrum. This work establishes a paradigmatic guidance toward designihg plasmonic-catalytic nanomaterials for enhanced solar-to-chemical energy conversion.