This article reports the use of innovative diagnostics to monitor toluene adsorption and oxidation on CeO2 surface under non-thermal plasma (NTP) exposure. Two plasma-catalytic configurations are explored, namely: post-plasma catalysis (PPC) and in-plasma catalysis (IPC). Since heterogeneous processes are pointed out as key steps of the plasma-catalyst coupling, the catalyst surface has been monitored by two complementary in situ diagnostics: (i) diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and (ii) transmission fourier transform infrared spectroscopy using Sorbent track (ST) device. Dielectric barrier discharges (DBD) are used in both PPC and IPC configurations to induce adsorbed toluene oxidation. Toluene in dry air is first adsorbed on the selected catalytic surface: ceria (CeO2). Subsequently, the plasma is switched on. During the experiment, the ceria surface is monitored by infrared to study toluene adsorption and oxidation mechanisms. The adsorption capacity of toluene on ceria is, respectively, measured in the configurations of PPC and IPC by DRIFTS and ST. The oxidation of toluene by plasma follows a first-order reaction regardless of plasma configuration and injected power and IPC is more effective for the toluene removal than PPC. Intermediates of toluene (benzyl alcohol, benzaldehyde and benzoic acid) are also identified on the surface and their respective temporal evolutions as a function of the plasma exposure are studied.ppap201600114-gra-0001