Co-Rh modified natural zeolites as new catalytic materials to remove propane and naphthalene from emission sources

MARÍA SILVIA LEGUIZAMÓN APARICIO; MARÍA E. CANAFOGLIA; MARCO A. OCSACHOQUE; ILEANA DANIELA LICK; IRMA LÍA BOTTO

Open Chemistry

DeGruter

Año: 2016 vol. 14 p. 335 - 342

Natural zeolites as raw materials to prepare catalytic precursors for the oxidation reaction of linear and poly-aromatic hydrocarbons are reported in this work. The process consisted in the formation of mono and bi-metallic species containing Co and Co- Rh active species on natural zeolite tuffs. The technique included the transformation of clinoptilolite zeolite and a mixture of mordenite-clinoptilolite mineral species in acid-zeolites that were supplementary treated with solutions of Co(II) and Rh(III) salts. Catalysts are obtained by thermal treatment of metal-precursors at 500ºC, analyzing by different physico-chemical techniques the effect and stability of active species as well as zeolite lattices. Modified zeolites were used as catalysts for hydrocarbon oxidation in emissions sources. So, two model molecules (propane and naphthalene) are selected to prove the catalytic behavior. Comparatively, Rh-zeolites are the most active catalysts for propane conversion, which occurred at temperatures lower than those observed for the oxidation without catalyst and even for other catalytic systems. In this case, the formation of mixed oxides seems to be conditioned by surface properties. It could be also suggested that the Rh incorporation in non active phases affected the effectiveness of the system. On the other hand and by using bimetallic materials the NO presence increases the activity. So, to reach 50 % activity without NO the sequence is RhCli-Mor >RhCli ≈ RhCoCli > RhCli-Mor whereas, equivalent activity in NO presence for bi-metallic catalysts is observed at lower temperature (between 30-50ºC). Unlike the propane oxidation, bimetallic systems affect markedly the naphthalene combustion temperature. Whereas in absence of catalysts a conversion of 50% and 100 % is reached at 430ºC and 485ºC respectively, it is interesting to observe that for RhCoCli-Mor and RhCoCli catalyst the 100 % conversion is/was reached at 250ºC, suggesting a different mechanism for linear and poly-aromatic hydrocarbons. Efficiency of catalysts is supported on the basis of physicochemical properties. Results, together with a low cost of raw materials and simplicity of activation by means of a soft chemical modification are very promising factors to reduce the negative effect of volatile linear and particularly poly-aromatic hydrocarbon emissions.