Catalytic purification of waste gases containing VOC mixtures with Ce/Zr solid solutions

This study has been undertaken to investigate the efficiency of ceria, zirconia, and CexZr1−xO2 mixed oxides as catalysts for the vapour-phase destruction in air of single model VOCs (n-hexane, 1,2-dichloroethane and trichloroethylene) and non-chlorinated VOC/chlorinated VOC binary mixtures. Considering all catalyst compositions examined for the individual destruction of these compounds, activity for complete oxidation decreased in the following order: n-hexane < 1,2-dichloroethane < trichloroethylene. The compositions with the best performance for chlorinated VOCs abatement (Ce0.5Zr0.5O2 and Ce0.15Zr0.85O2) were different than that with the best performance for n-hexane oxidation (CeO2). Concerning chlorinated VOCs conversion, it was observed that notable improvements in catalyst activity of CeO2 could be achieved through structural doping with Zr ions. Mixed oxides exhibited promoted redox and acid properties, which resulted catalytically relevant for the oxidation of 1,2-dichloroethane and trichloroethylene. In contrast, the combustion of n-hexane was essentially controlled by surface oxygen species, which were more abundant on CeO2. Attainment of high n-hexane conversions with CeO2 was also attributed in part to the hydrophobicity of the support and the reduced interaction with carbon dioxide.Significant ‘mixture effects’ on both activity and selectivity were noticed when a given chlorinated feed was decomposed in the presence of n-hexane. On one hand, each VOC decreased the reactivity of the other relative to that of the pure compound resulting in higher operating temperatures to achieve adequate destruction. Competitive adsorption played an important role in the reciprocal inhibition effects detected with all catalysts. On the other hand, the selectivity to HCl was noticeably enhanced when n-hexane was co-fed, probably due to the increased presence of water generated as an oxidation product.