文摘
The main scope of this work is to evaluate the catalytic stability of two Ce/Zr mixed oxides, namely Ce0.5Zr0.5O2 and Ce0.15Zr0.85O2, in the gas-phase oxidation of 1,2-dichloroethane as a model reaction for chlorinated VOC abatement. In order to simulate an accelerated Cl-poisoning of the catalysts the samples were submitted to a chlorination step with an aqueous solution of HCl at room temperature followed by calcination or by reduction and calcination at mild temperature (550 °C). For comparative purposes pure CeO2 and ZrO2 catalysts were also investigated. It was found that chlorination led to remarkable changes in surface area, acidity and redox properties, as revealed by EDX, N2-physisorption, XRD, Raman spectroscopy, adsorption of pyridine followed by IR, NH3-TPD, H2-TPR and oxygen storage capacity. Interestingly, the balance between negative (significant decrease in surface area, and lower overall acidity and reducibility) and positive (promoted redox properties due to the formation of stable CeOCl patches and generation of new acid sites related to Cl− ions adsorbed on Ce4+ and Zr4+ cations) changes introduced by chlorine incorporation appeared to be effectively counterbalanced. As a result the catalytic behaviour of chlorinated samples was not markedly affected when compared with the corresponding parent samples. Hence, a slightly lower activity was found for CeO2 and Ce0.5Zr0.5O2 while catalytic conversion was somewhat promoted for Ce0.15Zr0.85O2 and ZrO2. Anyway, after chlorination both Ce0.5Zr0.5O2 and Ce0.15Zr0.85O2 exhibited an adequate catalytic performance not only in terms of low-temperature conversion, but also of stability during extended periods of time on stream.
