A systematic study on the influence of geometrical parameters (pitch and wall thickness) of commercial high-dust honeycomb SCR-DeNOx catalysts on DeNOx-activity, mercury oxidation and SO2/SO3-conversion is described. All catalysts had an identical chemical composition of 0.6 wt.% V2O5. The study was conducted in a laboratory micro reactor and a technical scale bench reactor and focuses on the effect of different honeycomb geometrical parameters on the reactions at the catalysts. The combined variation of pitch and wall thickness showed lower DeNOx-activity at catalysts with larger channel openings. This indicates mass transfer limitations when the flow regimes are developed in the catalyst's channels due to the relatively fast reaction kinetics of the DeNOx-reaction. Results showed that the SO2/SO3-conversion is linearly dependent on catalysts wall thickness. Mercury oxidation increased slightly linear with increasing wall thickness of the catalyst, indicating that the reaction takes also place in the catalysts bulk because of its slow chemical reaction kinetics in contrast to DeNOx-reaction being controlled by diffusion. The importance of flue gas HCl-concentration on mercury oxidation was pointed out. Additionally, research on the co-influence of DeNOx-reaction and SO2/SO3-conversion was performed. A strong inhibition of SO2/SO3-conversion by flue gas ammonia was shown. However, DeNOx-activity is enhanced by conditioning with SO2 due to superior acidity of active sites. Summarising the results, due to the drawback of elevated SO2/SO3-conversion, higher risk of channel blocking and material costs, increasing wall thickness cannot be considered a reasonable strategy to enhance mercury oxidation by SCR catalysts. (C) 2013 Elsevier B.V. All rights reserved.