CrOx/SiO2 catalysts prepared using chromium recovered from tanning sewage

Catalysts at different Cr loading (x, in the range 0.18-3.8 wt% Cr) were prepared by (i) impregnation of SiO2 Aerosil directly with the waste water (SCx(I) samples); or (ii) mixing Aerosil with chromium oxo-hydroxides, precipitated from the waste water to eliminate the sulphate and sodium ions (SCx(II) and SCx(III) samples). Preparations (II) and (III) only differ for the accuracy in sulphate and sodium ions elimination. Catalyst surface characterization was performed by FT-IR spectroscopy using CO, adsorbed at room temperature, as test molecule, and by UV-Vis-NIR DR spectroscopy. Their activity towards ethylene polymerization were tested by FT-IR spectroscopy, monitoring the time dependence of the CH2 stretching modes intensity. The obtained results were compared with those obtained for simplified Phillips catalysts with comparable chromium contents, SCx(R). SCx(I) catalysts were not active in the ethylene polymerization, while the SCx(II) and SCx(III) ones showed lower activity (1/10 at maximum) compared to that of simplified Phillips catalysts with comparable chromium contents. SCx(II) and SCx(III) catalysts were active in the isobutane dehydrogenation reaction and showed activity in the range of those of standard catalysts, while SCx(I) ones showed activity at 873 K, but very low at the usual temperatures (773-823 K). (C) 1997 Elsevier Science B.V.