Novel carbon based catalysts for the reduction of NO: Influence of support precursors and active phase loading

Carbon-supported catalysts in the form of powder, briquettes and monolitos have been prepared. Powder and briquette samples have been obtained using a Spanish low-rank coal as raw material for carbon support through a pyrolysis process whereas monoliths were prepared by coating cordierite monoliths with a blend of two polymers. Vanadium was chosen as active element and impregnated by equilibrium adsorption from 1 to 8 wt% on the surface of as-prepared supports. All samples were tested in the selective catalytic reduction of NO with NH3 as reducing agent at low temperature (150 °C), demonstrating a considerable efficiency which was enhanced mainly by oxidation treatments and an increase of vanadium loading up to vanadium agglomerates formation. The nature of carbon precursor determines the porosity development and surface chemistry of supports, what results in a different dispersion and fixation of active phase. An enhancement of NO efficiency is achieved by increasing microporosity and the amount of surface oxygen groups in pyrolysed coal whereas in polymer blend, mesoporosity and just a certain amount of surface oxygen groups should be promoted. An excess in vanadium loading decreases NO reduction efficiency because of a pore blockage and the formation of vanadium agglomeration what makes to expose a lower vanadium surface to the reactants.