Rh/Ce0.9Pr0.1O2 active phase has been loaded on γ-Al2O3 particles and successfully tested for N2O decomposition in simulated nitric acid plants conditions. Reaction mechanisms have been studied by in situ DRIFTS-MS experiments. Display omitted ► A γ-Al2O3 particles-supported Rh/Ce0.9Pr0.1O2 catalyst has been prepared and characterised. ► N2O decomposition in simulated nitric acid plant conditions has been successfully performed. ► Ceria–alumina interaction slightly hinders rhodium–ceria interaction. ► Among inhibitors in nitric acid plant gasses (H2O, NOx and O2) NOx is the strongest and O2 the weakest. A supported catalyst composed by the active phase Rh/Ce0.9Pr0.1O2 loaded on γ-Al2O3 particles was prepared and characterised by SEM, TEM, XRD, Raman spectroscopy, N2 adsorption at −196°C, H2-TPR and XPS. The catalytic decomposition of N2O was studied in simulated nitric acid plant streams (in the presence of O2, H2O and/or NOx) both in a fix-bed reactor and by in situ DRIFTS-MS experiments. The supported catalyst is able to decompose N2O from around 350–400°C in the presence of O2, H2O and/or NOx, and this temperature would be enough to decompose N2O in a nitric acid production plant after the expansion turbine, avoiding the use of an additional energy input. Among O2, H2O and NOx, NOx is the strongest inhibitor and O2 the weakest. The inhibiting effect of O2 is attributed to its reversible chemisorption on catalyst active sites, while the effect of H2O and NOx is mainly related with their irreversible chemisorption. The inhibition of H2O is not as high as that of NOx because the product of H2O chemisorption (Ce–OH surface groups) is suitable for N2O chemisorption and decomposition, while the surface nitrogen species created upon NOx chemisorption are not.