Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

PP-V-17DEHYDROGENATION/DEHYDRATION OF ISOPROPANOL OVERBIMETALLIC COPPER-METAL (m = Ni, Co, Fe) CATALYSTSSaadi A.Faculty of chemistry, USTHB University, Algiers, 1 Centre de Recherche Scientifique etTechnique en Analyses Physico-Chimiques (C.R.AP.C). BP 248, 16004 Algiers, Algeria.2 Laboratoire de Chimie du Gaz Naturel, Faculté de Chimie, BP 32, 16111, El Alia,U.S.T.H.B., Bab Ezzouar 16111, Algiers, AlgeriaThe replacement of copper-chromite systems with more environmentally benign coppercatalysts, such as silica supported Cu, is of current interest because of the prohibition ofchromite disposal in landfills by the EPA. Cu is highly selective for alcohol dehydrogenationbut suffers from low activity and a propensity to sinter; thus, the addition of a second metalmay not only increase dehydrogenation activity and catalyst lifetime and still maintain highselectivity, but also facilitate reduction of the Cu precursor to metallic Cu. The bimetallic Cu-Ni/SiO 2 , Cu-Co/SiO 2 and Cu-Fe/SiO 2 catalysts investigated here were prepared by theaddition of Ni, Co, and Fe to a prereduced Cu/SiO 2 catalyst and then characterized by theirBET specific area, X-ray diffraction (XRD), Infra-Red spectroscopy (XPS), and temperatureprogrammed reduction (TPR). Dehydrogenation and/or dehydration of isopropanol to acetoneand/or propylene respectively over a family of silica-supported Cu, and bimetallic Cu–Ni,Cu–Co, Cu–Fe catalysts revealed that Ni (99%), Co (99,3%) and Fe (98.8%) were moreactive than copper monometallic and that all catalysts were 100% selective to acetone whensupported on a high-temperature treated silica possessing weak acidic surface groups. Incontrast, a silica support with a surface rich in acidic, oxygen containing functional groupsallowed a dehydration pathway to form propylene. The different studies have providedevidence of the dissociative adsorption of isopropanol and the formation of isopropoxidespecies which decompose at high temperature to acetone and/or propylene. A Langmuir–Hinshelwood mechanism assuming that removal of the first hydrogen atom from the hydroxylgroup was rate-determining fit the data well, provided physically and thermodynamicallymeaningful rate parameters, and explained the decrease in apparent energy (Eapp) at highertemperatures. In addition to hydrogen and acetone, which produced small rate inhibitions,inclusion of isopropanol (IPA) in the site balance was supported by in situ diffuse-reflectanceinfrared spectra. The heats of adsorption for IPA, H 2 , and acetone obtained from theadsorption equilibrium constants in the rate expression were consistent with values reportedby surface science and adsorption studies.489