(Invited) Transient Absorption Spectroscopy of Au/CeO2 Powder

Abstract

CeO2 is one of the most studied metal oxide catalysts due to its redox and oxygen transport properties. Transitions occur between the O2p - Ce5d (ca. 6 eV) and the O2p - Ce4f (ca. 3.5 eV) in addition to defect states that can be present between the O2p and Ce4f levels [1],[2]. Very few studies have been conducted by transient absorption spectroscopy (TAS) to probe into the generated charge carrier dynamics[3],[4] to date. The system Au (nanoparticles) / CeO2 has been studied extensively in catalysis because of many reactions such as CO oxidation and ethanol reforming [5],[6]. Because of the plasmonic nature of Au nanoparticles, the interface Au/CeO2 and consequently the charge carriers lifetime and concentration are poised to be affected. In this work, we have studied by pump-probe TAS the lifetime of excited electrons for a series of Au/CeO2 particles (1-4 Au wt. %). Upon excitation with a 480 nm light (2.55 eV), TAS signal in the 700-900 nm range (1.75-1.35 eV) was observed for both CeO2 alone and Au/CeO2. This signal is tentatively attributed to defects states between Ce4f and O2p. Excitation with a 300nm light (4.2 eV) resulted in the appearance of a strong signal in the 400-500 nm (3.1-2.5) in addition to the 700-900 nm. The 3.1-2.5 eV signal might be originating from the Ce4f-O2p recombination process. The presence of gold nanoparticle was found to increase the lifetime of this signal, and this might be linked to an electric field effect. Work in progress in order to extract kinetic information related to the charge lifetime in both regions and further probe into gold plasmon-CeO2 effects. [1] El Khalifi, M.; Picaud, F.; Bizia, M.; Anal. Methods, 2016, 8, 5045–5052. [2] Castletona, C.W.M.; Kullgren, J.; Hermansson, K.; J. Chem. Phys., 2007, 127, 244704, 1-11. [3] Singh, P.; Srivatsa, K.M.K.; Jewariya, M.; Optical Mater., 2016, 58, 1-4. [4] Pettinger, N. W.; Williams, R.E.A.; Chen, J.; Kohler, B.; Phys. Chem. Chem. Phys., 2017, 19, 3523-3531. [5] Zhang, S.; Li, X.-S.;Chen, B., Zhu, X.; Shi, C.; Ai-Min Zhu, A.-M.; ACS Catal., 2014, 4, 3481–3489. [6] Sheng, P.-Y.; Bowmaker, G.A.; Idriss, H.; Appl. Catal. A, 2004, 261, 171-181.