Study Of Ir/ZrO₂, M/OMS-2 Catalysts For CH₄, CO And VOCs Complete Oxidation

Catalytic combustion of volatile organic compounds (VOCs), CH4 and CO is the main way for reducing emissions of pollutants. CH4 and CO oxidation are widely studied to evaluate catalytic performances of catalysts. In this work, Ir/ZrO2, Ir/CeO2 and a series of Co, Cu and Fe oxide catalysts supported on OMS-2 were prepared using an impregnation method. These catalysts were tested for oxidation of CH4, CO and VOCs. The detailed results are as follows:1. Catalytic combustion of methane over Ir/ZrO2 catalystsZrO2 supports were prepared by precipitation method, and a series of Ir/ZrO2 catalysts were prepared by an impregnation method and their catalytic performance for CH4 catalytic combustion were tested. The catalyst structure and Ir species in the catalyst were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and H2 temperature programmed reaction (H2-TPR) techniques. The results showed that Ir existed in the form of IrO2 in the Ir/ZrO2 catalysts. The apparent activity of Ir/ZrO2 catalysts for CH4 combustion increased with Ir loading, and the catalysts showed high activities as well as good stability. With low Ir loading (≤1%), turnover frequency (TOF) for CH4 combustion increased with Ir particle size, however, it remained constant with high Ir loading (≥1%).2. Ir/CeO2 catalysts for CO catalytic oxidationA series of Ir/CeO2 catalysts were prepared by an impregnation method, and they were tested for CO oxidation. It was found that the activity of Ir/CeO2 catalysts for CO catalytic oxidation rose first and then declined with Ir loading. The catalysts showed the highest activity when Ir content is 1%. Ir existed in the form of IrO2 in the Ir/CeO2 catalysts. IrO2 was high dispersed with low Ir loading (≤1%), and existed as crystalline phase with high Ir loading (>1%). Ir particle size increased gradually with Ir loading, but specific rate and turnover frequency (TOF) declined gradually. It indicated that the catalyst with small particle size had a higher CO reactivity. It was also found that for CO oxidation, the activity of Ir catalyst with metal state was higher than that of with oxidation state.3. Oxidation of volatile organic compounds (VOCs) over manganese oxide octahedral molecular sieves (OMS-2) supported Co, Cu and Fe oxide catalystsA manganese oxide octahedral molecular sieve (OMS-2) was synthesized using KMnO4 and MnS04 as precursors by a reflux method. Co/OMS-2, Cu/OMS-2 and Fe/OMS-2 catalysts were prepared using a impregnation method and tested for catalytic combustion of toluene and ethyl acetate. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) results showed that the synthesized OMS-2 molecular sieves were nano-rods, with the cryptomelane-type structure. Hydrogen temperature program reduction (H2-TPR) results indicated that the supported Co, Cu and Fe oxide catalysts have lower reduction temperatures. The activity test results showed that the catalytic activity of the catalysts for ethyl acetate was much higher than that for toluene. The addition of a small amount of Co, Cu and Fe oxides (1-2%) to OMS-2 was favorable for the catalytic combustion of ethyl acetate and toluene. However, due to excessive loading, the surface of OMS-2 was covered and the catalytic activity decreased. The activity order of the catalysts was Fe/OMS-2> Cu/OMS-2> Co/OMS-2> OMS-2. The highest activity was obtained over Fel/OMS-2 catalyst, with a complete oxidation of ethyl acetate and toluene at 175℃and 220℃respectively.