Alumina Foam Coated with Nanostructured Chromia Aerogel:  Efficient Catalytic Material for Complete Combustion of Chlorinated VOC

ABSTRACT Commercial volatile organic compound (VOC) combustion catalysts, including V−W−Ti−O, Mn−Al−O, and Mn−W−Al−O, that operate well below 600 K produce only dehydrochlorination of 2-chloropropane to HCl and propylene. Catalytic materials based on chromia aerogel, prepared in this study, yielded complete combustion with about 90% selectivity to CO2 at mild conditions. α-Al2O3 ceramic foam was coated with chromia aerogel consisting of 1−2 nm CrOOH nanocrystals with surface area of 670 m2/g. The layer thickness changed from 15 to 80 μm corresponding to CrOOH loading of 4.5−21.5 wt % with the total surface area of 40−105 m2/g. The chromia-loaded foams were packed in a tubular reactor and tested with a mixture of 1000 ppmv 2-chloropropane (2-CP) in air at 450−550 K and GHSV = 60 000 h-1. Ceramic foam containing 7.7 wt % CrOOH yielded essentially complete conversion of 2-CP to mainly CO2/H2O/HCl at 550 K. Actually, those results were obtained despite apparent bypassing at high chromia loading indicated by the analysis of three catalysts tested in this study. Increasing chromia loading from 7.7 to 21.5 wt % little increased the apparent rate constant. This is further reflected by the relatively low apparent activation energy of 14 kcal/mol calculated from the measured values. The measured pressure drop was low, as expected, in general agreement with the predictions of a literature correlation developed for various foams. The results of this study demonstrate the significant potential of ceramic foams. For high-loaded catalytic systems further work is needed to create the right configuration of the foam.