Co-modified HZSM-5 zeolite catalysts were prepared by ion exchange with Co(CH3COO)(2) solution, and incipient wetness impregnation with aqueous solutions of Co(NO3)(2) and Co(CH3COO)(2), respectively. The catalysts were characterized by N-2-adsorption, NH3-TPD, FrIR and adsorption of m- and p-cresol. The catalytic performance for the synthesis of pyridine and picolines from aldehyde-ammonia condensation was tested. It shows that Co disperses in the zeolite pores for the ion exchanged samples, while Co deposits mainly on the external surface for the samples prepared by impregnation of Co(CH3COO)(2), which results in a narrowing of the pore mouth. NH3-TPD and pyridine-FrIR measurements indicate that the total acidity and the Lewis acidity of the catalysts increased with the decrease of Bronsted acidity among the samples. The samples prepared by impregnation with Co(CH3COO)(2) have the highest yield of the desired products among all the samples tested. This is attributed to the change of surface acidity and the reduction of the pore-mouth of the zeolite. (C) 2007 Elsevier B.V. All rights reserved.