Supported chromia catalysts for oxidation of organic compounds - The stateof chromia phase and catalytic performance

A series of 13 bulk transition metals oxides frequently used as components of full oxidation catalysts was tested in air oxidation of n-butane and eth ylacetate (EA). Co3O4 Cr2O3 CuO and MnO2,displayed the best activity, about one order of magnitude higher than the others. Chromia displayed the highe st CO2 productivity. The activity and CO2 selectivity of Cr2O3 catalyst dep osited on mineral supports (SiO2, Al2O3, MCM-41) depended strongly on the s upports nature, texture and chromia loading. XPS, EDAX, XRD, FTIR and TPR-T PO measurements displayed two forms of Cr3+-oxide on silica-supported catal ysts: bulk alpha-Cr2O3 nanocrystals of 10-20 nm and a monolayer of chromia surface species chemically bonded to the support: -Si-O-Cr=O. The chromia n anocrystals detected by XRD displayed higher activity and selectivity in co mplete EA oxidation due to higher redox mobility of chromium cations on the ir surface compared with grafted chromium silicate species. The optimized C r2O3/SiO2 catalyst showed high efficiency in wet oxidation of amino-3-phosp honopropionic acid, comparable with the best catalysts reported in the lite rature. (C) 2000 Elsevier Science B.V. All rights reserved.