One-step catalytic conversion of syngas to aromatics over ZrO₂ catalyst

A series of ZrO₂ nanoparticles with different particle sizes and different crystalline phases were prepared using coprecipitation and hydrothermal methods. Their physico-chemical properties were characterized by N₂ physisorption, XRD, TEM, Raman spectroscopy, XPS, and NH₃-TPD techniques. The catalytic performances for syngas conversion were tested at 400 ℃, 3 MPa, gas hourly space velocity (GHSV) of 500 mL/(g_cat·h), and H₂/CO/Ar (volume ratio)=5:5:1. It was found that syngas can be directly converted into hydrocarbons over ZrO₂ nanoparticles. The hydrocarbon products are mainly composed of isomerized olefins, cyclenes, and aromatics. The selectivity of C₅₊ hydrocarbons is up to 48%. Moreover, the aromatic concentration in C₅₊ ranges from 30% to 53% depending on ZrO₂ structures. It is also found that the monoclinic ZrO₂ shows higher activity than the tetragonal one. Monoclinic ZrO₂ with larger specific surface area and acid amount show highest CO conversion as well as the yield of target products, but the monoclinic ZrO₂ with lager particle size has the higher acid surface density and results in the higher aromatic selectivity. Consequently, acidity is the key factor for CO conversion. And high acid surface density promotes the formation of aromatics but acid amount affects the activity.