In-Situ UV/vis and Transient Isotopic Analysis of the Role of Oxidizing Agent in the Oxidative Dehydrogenation of Propane over Silica-Supported Vanadia Catalysts

In-situ UV/vis spectroscopy in combination with transient isotopic analysis was applied for elucidating the governing factors, which determine the superior performance of N 2 O as compared to O 2 in the oxidative dehydrogenation of propane (ODP) over VO x /MCM-41, VO x /MCM-48, and VO x /SiO 2 catalytic materials. Characterization studies applying in-situ steady-state UV/vis spectroscopy evidenced higher reduction degree of surface VO x species at 773 K in a C 3 H 8 −N 2 O (C 3 H 8 /N 2 O = 1/1) feed than in a C 3 H 8 −O 2 (C 3 H 8 /O 2 = 2/1) flow at controlled conversions of propane (<5%) and oxidizing agent (<10%). The in-situ UV/vis method in a transient mode enabled to distinguish the ability of O 2 and N 2 O for reoxidation of reduced VO x species; N 2 O reoxidizes reduced VO x species slower than O 2 . This property of N 2 O is very essential for suppressing nonselective consecutive propene oxidation to CO x (mainly to CO). Additionally, the results of transient isotopic experiments in the temporal analysis of products reactor revealed that adsorbed (nonlattice) oxygen species are formed upon O 2 activation over reduced VO x species and participate in CO 2 and CO formation. It is suggested that these nonselective species do not originate from N 2 O.