Fresh fluid catalytic cracking (FCC) catalysts and ZSM-5 additives were hydrothermally treated with 100% steam at 732 degrees C (1350 degrees F) and 788 degrees C (1450 degrees F) for 4 h in a fluidized bed reactor. The catalytic pyrolysis of hybrid poplar wood with fresh and steam treated catalysts was conducted in a 50 mm bench scale bubbling fluidized bed reactor at 475 degrees C and a weight hourly space velocity (WHSV) of 2 h(-1). BET surface area measurements showed a reduction of 24% and 34% in the surface area of the FCC catalyst after steam treatment at 732 degrees C and 788 degrees C respectively. The non-phosphorus based ZSM-5 additive lost about 15% of its surface area after mild steaming at 732 degrees C. However, the phosphorus impregnated ZSM-5 additive was not affected at both steaming conditions. The hydrothermal treatment of the catalysts influenced the catalytic product distribution and the quality of the bio-oil. The steamed FCC catalyst produced higher organic liquid and gas yields and lower formation of coke and water. The viscosity and the density of the bio-oils produced from the steamed FCC catalyst were lower than those produced with the fresh FCC catalyst. In the case of the ZSM-5 additives, the steam treatment affected only the organic liquid and gas yields. The organic liquid yield increased and the gas yield decreased. Steaming of the ZSM-5 additive did not show any effect on the char/coke yield as was seen with the FCC catalyst due to the lower tendency of ZSM-5 to form coke. The GC analysis of the product gases suggested that steam treatment influenced the catalyst selectivity in the formation of CO, CO2, H-2, CH4 and C-2-C-5 hydrocarbons. The C-13 NMR analysis of the bio-oil showed generally that steaming of the FCC catalyst increased the selectivity for the production of aromatic hydrocarbons. (C) 2012 Elsevier B.V. All rights reserved.