Zeolite Co-MOR on cordierite honeycomb for the selective catalytic reduction of NO with CH4

M.A. ULLA; R. MALLADA; L. GUTIERREZ; J. CORONAS; E. MIRÓ; J. SANTAMARÍA.

Lahnstein (Alemania)

Congreso; 6th International Congress on Catalysis in Membrane Reactor; 2004

Zeolite membranes have been widely used for separation and in some cases also as a catalytic membrane reactor. Usually, zeolite layers have been deposited on tubular and flat supports in order to obtain a selective layer for transport and/or catalytic activity. In this work a zeolite layer has been synthesised onto the channels of a cordierite monolithic support. This kind of support is thermally resistant and provides good flow features for exhaust gas catalytic treatment. The selected zeolite was mordenite ion-exchanged with cobalt, due to its activity in the selective catalytic reduction (SCR) of nitrogen oxides. The MOR layer on this substrate was obtained by hydrothermal synthesis without template, after seeding with commercial mordenite crystals the surface of the monolith. Hydrothermal synthesis of MOR took place in a Teflon-lined autoclave at 175°C for 24h, using a gel with the molar composition: H2O:SiO2:Na2O:Al2O3 = 80:1:0.38:0.025. Cobalt exchange was done using a Co(CH3COO)2 solution. The amount of incorporated Co was analysed by atomic absorption spectroscopy (AAS), and it was 3% by weight referred to zeolite. The MOR layer on cordierite substrates was characterized by scanning electron microscopy (SEM) and X-Ray diffraction (XRD). Characterization results showed pure and well crystallised mordenite. The crystals were growing having their c-axis perpendicular to the surface of the support, and were highly accessible to the reacting gas. MOR layer thickness ranges from 40 to 100 mm. Co/Al ratio of 0.65 was measured, this ratio would induce the formation of Co oxide clusters. After the interpretation of the NO temperature programme reduction we can conclude that the Co in the clusters is not accessible for NO adsorption. The SCR of NO with CH4 in excess of oxygen was performed in a continuous flow system under atmospheric pressure at temperatures between 350 and 550°C. The experimental results showed that the conversion of NO to nitrogen increases as temperature goes up to a value of 52% at 450ºC, after this point NO conversion decreases and methane conversion reaches a 100% at 500ºC. These results are similar to those observed in the Co-MOR powder.