Journal Article Research Support, Non-U.S. Gov't X-ray absorption spectroscopy CoMoS structure Comparative Study Evaluation Study FEL Johann geometry Research Support, N.I.H., Extramural Research Support, U.S. Gov't, Non-P.H.S. Research Support, U.S. Gov't, P.H.S. Rowland circle Validation Study X-ray FEL X-ray emission spectrometers X-ray emission spectroscopy X-ray free-electron lasers XES XRS atomic precision coordinated network copper nanoclusters crystal analyzers dissipative self‐assembly focusing hard X-ray emission spectroscopy heterogeneous catalysis hydrodesulfurization (HDS) catalyst systems hydrotreating catalysts photon-in photon-out spectroscopy methods