Visible light-driven catalytic processes have the potential to influence the energetics or rates of specific elementary steps on a catalyst surface without influencing others, an effect not achievable under equilibrium heating. This unique capability could enhance catalyst efficiency and selectivity towards a desired product. Although photochemistry has been extensively studied on single crystals for individual elementary steps, and on nanoparticles in the context of complete catalytic reactions, there is very limited quantitative understanding on how visible photon fluxes influence single elementary steps on metal nanoparticles. This dissertation addresses that gap. In this dissertation I explore the effects of visible photon exposure on CO desorption on Pt and Pd nanoparticles, as well as the kinetics of CO desorption and oxidation rates on Pt nanoparticles. These studies provide insights into photon-induced, bond-selective interactions at the metal adsorbate interface. Through a combination of experimental and theoretical approaches, this work highlights how photon activation impacts CO reactivity on metals surfaces, laying the groundwork for future photon driven catalytic processes. Using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) I investigated CO desorption kinetics on 1-2 nm Pt and Pd nanoparticles supported on γ-Al₂O₃ under dark and visible photon exposure conditions. Temperature programmed desorption (TPD) measurements revealed that visible photon flux, particularly at 440 nm, significantly enhanced the rate of CO desorption from Pt nanoparticles, aligning with the excitation energy for the interfacial electronic transition within the Pt-CO bond. In contrast, similar photon exposure had no measurable effect on CO desorption rates from Pd after accounting for photon induced heating. Complementary density functional theory (DFT) calculations further elucidate differences in photon adsorbate interactions between Pt and Pd. These findings demonstrate the specificity with which photons can facilitate chemical reactions on metal nanoparticle surfaces, illustrating how photon flux can steer catalytic processes in ways not achievable through thermal activation. In the second part of this work, I developed a kinetic model to describe CO photo-desorption from Pt surfaces, utilizing CO temperature-programmed desorption (TPD) measurements on Pt nanoparticles under both light and dark conditions to assess model accuracy, as well as extract valuable parameters such as quantum yield normalized by Pt absorbance (Ptabs*QY). The CO photo-desorption model comprises two terms, a thermal desorption component, based on a Temkin model that accounts for changes in apparent activation energy as a function of CO coverage, and a visible photon-driven desorption component. The Temkin thermal desorption model provided a good fit of the thermal TPD data with low uncertainties for activation energies of ~130-160 kJ/mol, consistent with literature. The term accounting for photon induced desorption assumes a first order dependence on photon flux and on CO coverage and includes for the potential of temperature effects through an Arrhenius dependence with an activation barrier, Ephoto. The best model fits produced values of Pt¬¬abs*QY ~ 0.02-0.1 (maximum for 440 nm photons) and Ephoto = ~20-25 kJ/mol. The predicted Pt¬¬abs*QY values from the model are in agreement with previous measurements of QY in photocatalysis on Pt nanoparticle surfaces. Further, the Ephoto is consistent with the energy of a CO vibrational quanta (~ 2100 cm-1 = 25 kJ/mol), which is suggestive that thermal energy promotes photochemistry by increasing the proportion of molecules in excited vibrational states. The model provides valuable insights into the interplay between thermal and photon-induced desorption processes during CO TPD experiments under visible photon exposure, demonstrating how temperature and photon flux together impact CO reactivity on Pt surfaces. Lastly, I investigated the effects of 440 nm photons on CO oxidation over 1-2 nm Pt nanoparticles, demonstrating that this wavelength significantly decreases the apparent activation energy (Eapp) for the reaction. The CO oxidation reaction was conducted under conditions where CO desorption is a rate limiting step (the surface is saturated in CO). This indicates that 440 nm light promotes the rate of CO desorption from the Pt surface, freeing up active sites for O2 adsorption, which then reacts with CO to form CO2, increasing the reaction rate and lowering the Eapp. This finding aligns with other studies in this dissertation, where an increase in Eapp corresponds with a rise in QY, which enhances CO desorption and frees up active sites. I observed a decrease Eapp with increasing photon flux, with a decrease of 32 kJ/mol at 2.2x10^22 photons*m^(-2)*s^(-1). This finding aligns with previous reports showing that visible photon exposure increases reaction rates by promoting CO desorption from Pt surface and highlights the potential for photon driven catalysis to influence reaction kinetics in ways that are not possible through thermal energy alone.