Activation of CO and surface carbon species for conversion of syngas to light olefins on ZnCrO x -Al2O3 catalysts

As an effective part of the bifunctional catalyst for conversion of syngas to light olefins, ZnCrO_x-Al₂O₃ mixed oxides were studied using surface sensitive techniques of X-ray photoelectron spectroscopy (XPS) and high-sensitivity low-energy ion scattering spectroscopy (HS-LEIS), as well as in situ Fourier Transform infrared spectroscopy (FTIR) and temperature-programmed desorption (TPD). Reducing and oxidizing treatments induce significant changes of the top-surface compositions as observed by HS-LEIS. After CO/H₂ treatment, an obvious amount of dissociated carbon and oxygen-containing carbon species were evidenced on the surface by XPS and HS-LEIS. The oxygen-containing carbon species include bicarbonate, carbonate and formate, and can be efficiently removed under H₂. Formate species may be formed by hydrogenation of the carbonate and bicarbonate species, and can be removed to regenerate the active sites for CO dissociation. TPD results under H₂ atmosphere show the production of methane, ethane and methanol for the surface pre-treating in CO at 300 °C.