Influence of temperature and volume ratio of Cu:Ni exchange solutions on the chemical properties of the guest metals in prepared CuNi–mordenite materials: Evidence of direct competition between copper and nickel ions

Abstract

Mordenite-type zeolites with a SiO2/Al2O3 ratio of 13 in sodium form were subjected to ion exchange using 0.1 N solutions of Ni(NO3)2 and CuSO4, or mixtures thereof with variable ratio of components at two different temperatures, 20 and 90 °C, varying the volume of Cu:Ni ratio in solution. The diffraction patterns revealed the preservation of the zeolite structure after the ion exchange process. Further ICP–AES measurements showed that the ions exchanged percentage depended on the volume ratio of the components added to the exchange solution. The electronic and chemical states of the species in zeolite were studied by diffuse UV–Vis spectroscopy, TPD–NO, and TPR–H2 methods. According to the UV–Vis DRS spectra, absorption increased in the charge transference region (200–350 nm) as the ion exchange temperature increased from 20 to 90 °C. On the other hand, evidence for changes in the chemical state was obtained from TPR and TPD–NO profiles. In the TPR experiments, we observed differences in reductivity with increasing ion exchange temperature. Meanwhile by TPD–NO experiments, all materials showed a capacity to desorb NO molecule at low temperature (<350 °C) and changes in the types of present species as was related with the variation in the ion-exchange temperature. The composition and properties of the Ni:Cu/mordenite bimetallic system were affected by the ion–exchange temperature and the volume ratio of Cu:Ni metal solutions.