Cr/ZSM-5 catalysts with 0.5–2.6 wt % Cr loadings and zeolites with 15–140 Si/Al ratios were characterized with in situ UV–vis, IR, and Raman spectroscopies, including operando Raman measurements under reaction conditions in methane conversion at 773–1123 K with a simultaneous online analysis of reaction products. DFT calculations with cluster and periodic models were performed with DMol3, Gaussian 09, and VASP software packages. Isolated Cr(VI) dioxo and Cr(III) mono-oxo structures on framework Al anchoring sites were identified as the dominant species under most conditions. In the absence of gas-phase O2 (under Ar flow) at 773 K, the Cr(VI) dioxo species on framework Al anchoring sites autoreduce, and the Cr(III) mono-oxo species remain the only observable surface Cr oxide structures. For ZSM-5 zeolites with a relatively low concentration of framework Al atoms (Si/Al ≥ 25), exposure to gas-phase O2 at 773 K forces surface Cr oxide species to migrate from framework Al anchoring sites to Si sites on the ex...