Selective Catalytic Reduction of NOx over Zeolite-Coated Cordierite-Based Ceramic Foams: Water Deactivation

The reactors used for Selective Catalytic Reduction (SCR) of NOx require low pressure drop structured catalyst packing. Structured packings, such as ceramic foams, are gaining increasing interest for application in low pressure drop reactors, membrane reactors and catalytic distillation units. In this work, cobalt ion exchanged mordenite (Co-HMOR)-coated cordierite-based foams produced by the replication method were evaluated for catalytic reduction of NOx with methane. The addition of 0.3 wt.% Pd to 2 wt.% Co-HMOR leads to a material that can convert 50 % NOx to N2 at 450 °C in a reaction mixture containing 2000 ppm CH4, 1000 ppm NOx, 5 % O2 and balance helium, at GHSV=17000 h-1. Although in an early stage of development, an efficient coating procedure was explored and different ways of exchange of Co and Pd cations into mordenite (Si/Al=10) were studied. Additions of 2 wt.% fumed silica enhanced adhesion of the zeolite onto the ceramic foam. Pd-exchanged Co-HMOR showed to be very sensitive to steam. A 50 % decrease in NOx conversion to N2 was observed after Pd/Co-HMOR samples were exposed at 450 °C to a reaction mixture containing 2 vol% H2O. Although further research is needed to ascertain the mechanism of this deactivation behaviour, agglomeration of Pd forming PdO particles is envisaged.