The chemical composition of raw materials for a TiO2- based honeycomb extruded for De-NOx via selective catalytic reduction (SCR) was optimized in terms of catalytic activity and extrusion formability. The catalytic activity of powder mixtures containing TiO2, 10 w/o of WO3, 1-2 w/o of V2O5 and 1, 3 and 5 w/o of SO3 were examined. Various combinations of catalytic materials in the form of either oxide power or precursor dissolvable in an oxalic acid solution were attempted in order to differentiate the effect of homogeneity of catalytic materials while mixing with TiO2 powder. V2O5 powder or ammonium metavanadate (AMV), and WO3 powder or ammonium metatungstate hydrate (AMT) dissolved in an oxalic acid solution were used as sources of V2O5 and WO3, respectively. The powder mixture containing 1 w/o V2O5 and 10 w/o WO3 obtained from AMV and AMT dissolved in an oxalic acid solution, exhibited more than 90% of De-NOx activity at temperatures above 300 oC, attributed to the homogeneous dispersion of V2O5 in TiO2 particles due to the complete solubility of AMV in oxalic acid. Increasing the V2O5 content from 1 w/o to 2 w/o, and adding 1 w/o of SO3 in the form of H2SO4, while maintaining the WO3 content at 10 w/o, consequently with a chemical composition of TiO2/10 w/o WO3/2 w/o V2O5/1 w/o SO3, showed nearly 100% NOx reduction in the temperature range of 250 oC to 400 oC. Based on this composition of a catalytic powder mixture, the additives for extrusion forming such as inorganic binder, water, MC, and PEG were also optimized as 8, 40, 3.5 and 3.5 parts, respectively, with respect to the weight of the catalytic powder mixture. The processing developed in this study was applied in manufacturing a large scale commercial SCR honeycomb catalyst with 150 mm × 150 mm × 1,000 mm dimensions.

Keywords: De-NOx SCR, Honeycomb extrusion, Catalytic activity, Optimum SCR composition.