Plasmonic nanomaterials, featured with high optical cross-section resulted from the induction of the collective oscillation of free electrons in metallic nanostructures, known as localized surface plasmon resonance, by the alternative electromagnetic wave in light, is emerging as a new promising photocatalyst. Hot carriers derived from the non-radiative decay of LSPR are capable in activating chemical bond, in an intrinsically different mechanism from the conventional thermal-driven means, and provide the possibility in achieving chemical transformation in milder conditions with sustainable energy. When further combined with catalytically active materials in a synergic way to form the antenna-reactor complexes, the versatility and efficiency of plasmonic photocatalysts are greatly boosted. In this thesis, I will present four plasmonic photocatalysts, classified into two categories, for three reactions to show the stepwise understanding of the structure-property-function relationship in plasmonic photocatalysts and subsequent improvement in the design of photocatalysts. The first part, including chapters 3 and 4, involves applying monometallic plasmonic nanomaterials in H2 activation. Au and Al nanomaterials, though being inert towards H2 activation if driven thermally, are demonstrated to be active in hydrogen dissociation under light excitation. They both exhibit linear intensity dependence in photocatalytic H2-D2 exchange reaction and H-H bond activated by the electronic transition of initial hot carriers is proposed to be the dominated mechanism. In contrast, Cu nanoparticles exhibit an S-shape intensity dependence in photocatalytic H2-D2 exchange reaction with a more-than-1 external quantum yield of light-to-chemical conversion. The hot carrier multiplication resulted from thermalization of hot carriers through electron-electron scattering plays a crucial role in the Cu system. The rate-determining step (RDS) is believed to be associative desorption of HD, different from the dissociative adsorption of H2/D2 on Au and Al surface, making the transition barrier of hot carriers low and the thermalized hot carriers effective. Next, I designed a new antenna-reactor structure, surface alloy, to incorporate materials with the favorable electronic structure for activation of specific molecules into plasmonic nanomaterials with intent to achieve better usage of hot carriers. Cu-Ru surface alloy was prepared and shows highly efficient photocatalytic activity towards ammonia decomposition reaction, making it feasible for studying the effect of plasmon-mediated hot carriers on the activation barrier of chemical reactions. By carefully tuning the loading ratio of Cu and Ru, I further synthesized single-atom-alloy plasmonic photocatalyst composed of a Cu core antenna with atomically dispersed Ru sites reactor on the surface. This antenna-reactor complex exhibits outstanding coke resistance in methane dry reforming reaction under illumination. Both of the hot carriers and single-atom structure were demonstrated to be essential for the observed stability. This thesis increases the knowledge in the mechanism of hot-carrier-mediated chemical reaction and guides the design of new generation of plasmonic photocatalysts.