Methane conversion into valuable aromatic products represents a highly desirable route for conversion of natural gas into liquid fuels and chemical feedstocks. Cr and Mo catalysts supported on ZSM-5 are actively studied for methane dehydroaromatization with benzene as the main product. Cr-based catalysts are usually less active than Mo/ZSM-5. However, addition of Cr to Mo/ZSM-5 can improve both activity and benzene selectivity. The current study is the first investigation of the initial structure of Cr and Mo/ZSM-5 with operandoRaman spectroscopy, UV-vis measurements and density functional theory (DFT) calculations.UV-vis spectra exhibit two main oxide species with isolated M (Mo or Cr) atom. DFT calculations suggest that both of these species are M(=O)2 dioxo nanostructures that are bridge-bonded to zeolite framework oxygen, but located on different Al framework sites: single Al sites and two Al sites. The dioxo structure [Cr(=O)2]2+ on two Al sites in an Al-Si-Si-Al arrangement is shown in Fig. 1. Calculated vibrational frequencies for the symmetric stretch of the two dioxo Cr and Mo models match the corresponding Raman band pairs in Fig. 2. 

Spectroscopic and computational study of supported Cr and Mo oxides on ZSM-5 for methane dehydroaromatization (DHA)

248th National Meeting (2014)

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