Hydrothermal liquefaction of biomass is a promising technology for production of biofuels. In this work, the catalytic effect of a nanocrystalline zirconia catalyst on hydrothermal liquefaction of dried distiller's grains with solubles (DDGS) was investigated using a stop-flow reactor system. Additionally, the catalytic effects originating from the reactor wall were also studied by means of an inert gold liner to isolate the reaction from the X22 reactor alloy. DDGS was converted into a crude bio-oil at a fixed reaction temperature (350 degrees C), pressure (250 bar) and reaction time (15 min). The oil was characterized in terms of yield, char content, ash content, elemental composition, chemical composition and heating value. Neither the ZrO2 catalyst nor the reactor wall was found to have any significant effects on the yields and properties of the produced bio-oil. Consequently, ZrO2 appears to be a poor catalyst for hydrothermal liquefaction of biomass. The X22 alloy is found to be highly suitable for construction of hydrothermal liquefaction reactors. (C) 2014 Elsevier Ltd. All rights reserved.