Environmental application of natural microporous aluminosilicates: NOx reduction by propane over modified clinoptilolite zeolite

Synthetic exchanged zeolites have proved to be active catalysts for the selective catalytic reduction (SCR) NOx by hydrocarbons as reductors in the presence of O2. The abundance and potentiality of argentine zeolite mineral resources encouraged us to analyze the possibitity of taking advantage of these minerals as starting materials for catalyts preparation. In this sense, clinoptilolite-rich tuffaceous material was selected. Clinoptilolite (named CLI), belonging to the heulandite-type zeolite (HEU), was treated with Co(II) and Co(II)-Rh(III) solutions to obtain the monometallic and bimetallic zeolite systems, precursors of the catalysts. The mineral, the precursors and the catalysts were characterized by means of several techniques such as XRD, XRF, FTIR and DRS spectroscopies, thermal studies (DTGA, TPR), SEM-EDAX microscopy and textural analysis. The steps of the chemical treatment were carried out, in part, in solution, involving the mineral transformation into the NH4-CLI, Co(II)-CLI and Co-Rh-CLI precursor phases. Catalysts were obtained by thermal treatment at 500ºC. TPR measurements provided information about the interactions and characteristics of the active metals with the aluminosilicate framework of the catalysts. Two types of catalysts were evaluated for the NOx reduction reaction using propane in O2 presence: 0.5%(w/w)Co-CLI and 0.25%(w/w)Rh--0.5%(w/w)Co-CLI respectively. The performance of catalysts obtained from natural zeolites revealed that they were active for the reaction, despite the very low metallic content.