Environmental Catalysis: Gas Phase Hydrodechlorination of Chlorophenols

This proposal sets out a fundamental study that is focused on probing the link between catalytic hydrodechlorination activity/selectivity and catalyst structure. Previous work by the PI has established that nano-dispersed nickel on amorphous silica in the presence of hydrogen is highly efficient in the dechlorination of concentrated chlorinated gas streams; the chlorine that is removed is solely in the form of HCl that is easy to trap. The existing catalyst activity/selectivity database will be extended in a strategic fashion, focusing on the treatment of chlorinated phenols as model reactants; the latter represents a class of commercially significant and highly toxic industrial waste. Preliminary results have revealed that chlorobenzene and chlorophenol hydrodechlorination over Ni/SiO2 is structure sensitive in that larger Ni particles (in the range 1-4 nm) exhibit higher specific dechlorination rates but are more susceptible to deactivation. The issue of catalyst decay will be addressed through a comprehensive program of catalyst characterization before and after reaction. This will involve bulk structural studies (x-ray diffraction), high-resolution transmission electron microscopy (TEM), analytical TEM including EDX and EELS, surface area/porosity measurements, chemisorption/TPD/TPO studies and x-ray photoelectron spectroscopy to probe changes in Ni electronic structure. Moreover, the nature of the reactant(s)/product(s) interaction with the catalyst surface will be probed using spectroscopic (FTIR-DRIFT) and chromatographic techniques. The presence of chlorinated aromatics in industrial effluent is now established as a major source of environmental pollution. This work may form the basis for a more efficient pollution prevention method. The PI has previously worked with both graduate and undergraduate students in an international context. In this project he will also work with chemistry students and provide training in engineering research.