Synthesis and characterization of metal oxides loaded-HZSM-5 and their implication for selective conversion of isopropanol

A series of HZSM-5 catalysts containing Co(II), Ni(II) and Cu(II) were prepared by using the incipient wetness impregnation method. They were characterized by X-ray diffractometry (XRD), Fourier transform infra-red (FTIR) spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and pore structure analysis by nitrogen adsorption at −196 °C. The zeolitic samples have been tested as catalysts for the isopropanol conversion at 150–275 °C. A significant structural collapse associated with disilication and dealumination of HZSM-5 took place upon treatment with Co(II), giving rise to Co3O4, Co2SiO4 and α-cristobalite silica crystalline multi phases. This fact is in fair agreement with the XPS spectra of this sample, thus the Co 2p3/2 signal at 779.7 eV revealed the enrichment of Co(II) cations as oxide-like clusters in the outer layers of the crystals. The relevant components are absent in the XPS and XRD spectra of Ni/ and Cu/HZSM-5, so we assume that the extent of incorporation of Ni(II) and Cu(II) into the interconnecting pore system of HZSM-5 is almost complete. Cu/and Ni/HZSM-5 only exhibited IR bands at 3755 and 3735 cm−1 ascribed to terminal silanol groups, respectively, due to the influence of the compensating cation. HZSM-5 and Cu/HZSM-5 have been proven to be the most active catalysts in isopropanol conversion, while Co/HZSM-5 is the least active one. Ni/and Cu/HZSM-5 gave 91% and 58% yields to acetone at 150 °C, respectively, while Co/HZSM-5 and HZSM-5 led to 13% and 0.3%, respectively. HZSM-5 acted only as an active dehydration catalyst converting isopropanol to propylene. In contrast, Cu/and Ni/HZSM-5 served as dehydration and dehydrogenation catalysts yielding propylene as well as acetone, although at high isopropanol conversion only propylene is obtained.