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

Abstract As an effective part of the bifunctional catalyst for conversion of syngas to light olefins, ZnCrOx-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.