In a coal-fired thermal power plant, ash particles laden in flue gas adhere on de-NO_x catalyst surface, and ash coverage causes the degradation of de-NO_x catalyst. Therefore, in this study, effect of the flow in a honeycomb rectangular channel, which represents a single channel of de-NO_x catalyst, on the adhesion characteristics of particles to the wall was investigated by applying a direct numerical simulation (DNS). Results show that the adhesion of particles is strongly affected by the flow. The particle adhesion is enhanced by turbulence near the inlet of channel, whereas suppressed due to the attenuation of turbulence in the downstream region. The particle adhesion also depends on particle diameter. Small particles adhere on the wall only in the upstream region, whereas large particles adhere all the way down to outlet, nevertheless flow transients to laminar. This is due to the fact that large particles keep the inertial force even in the downstream region. Moreover, the cross sectional position of particle adhesion also depends on both flow stagnation near the corner and a secondary flow which is driven on the plane normal to the streamwise direction.