Tuning the properties of the cobalt-zeolite nanocomposite catalyst by potassium: Switching between dehydration and dehydrogenation of ethanol

Abstract

In this work, we offer an understanding of the potassium impact on the performance of the cobalt-zeolite catalysts in the ethanol steam reforming process (ESR) conditions. The catalytic behavior of the undoped and K-doped cobalt-containing materials (10 wt% of cobalt) is discussed concerning their structure and surface properties. The 2K/CoY and 4K/CoY samples, where potassium was introduced on the HY support together with cobalt phase upon incipient wetness impregnation (IWI method), were faced with the Co(K)Y sample with K+ in the ion-exchange positions (IE method), where cobalt was introduced on the surface of KY support by IWI method. The chemical and phase composition, texture, morphology, and reducibility of the catalysts were comprehensively evaluated by the ICP, XRD, low-temperature N2 adsorption, STEM/EDX, and H2-TPR methods, respectively. The catalysts’ active sites nature was assessed in the quantitative pyridine and CO adsorption FT-IR studies. A detailed description of the surface properties of the materials was faced with their catalytic interaction with the ethanol–water mixture at 500 °C. The in situ FT-IR reaction studies supported the catalytic results. Undoped CoY catalyst exhibited 100% ethanol conversion, whereas its selectivity to H2, CO2, CO, and C2H4, reached values in the range of 55–60%, 25–30%, 0–5%, and 65–70%, respectively, pointing the dehydration path as the main one. The presence of potassium altered the reaction mechanism, what reflected in the decrease of ethanol conversion to 75–80% for Co(K)Y sample and 15–30%, and 5–10%, respectively for 2K/CoY and 4K/CoY samples. Undesired C2H4 production was reduced to 40% for the potassium-exchanged sample and did not occur for both, 2K/CoY and 4K/CoY, IWI-prepared samples. The coke species of various chemical nature were identified over the deactivated catalysts with the use of Raman, UV–VIS, and XPS spectroscopic methods and thermogravimetric analysis method.