| Summary: | 博士 === 國立交通大學 === 環境工程所 === 91 === An evaluation of physicochemical characteristic of vanadia-titania catalyst for NO removal by selective catalytic reduction (SCR) process was conducted in this study. The intrinsic rate constant, effective rate constant and characteristic time were obtained using a mathematical model employing the effective factor method to describe physical and chemical characteristic of SCR reaction. The result showed that the physical enhancement was obvious by increasing pore radius that resulted in a higher effective diffusivity. One the contrast, decreasing pore radius that resulted in lower effective diffusivity and reduced the NO removal efficiency although it has higher surface area.
The effects of operating parameters (moisture, vanadia content, working temperature) on the roles of Bronsted and Lewis acids acting in the SCR reaction were specified by the observed NO removals and the spectra of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results indicated that H2O competed with NH3 molecules to be adsorbed on the pure titania catalyst that contained only Lewis acid sites. But competition did not occur over vanadia-based catalyst. Both Bronsted and Lewis acid sites appeared on vanadia-based catalyst in the presence of H2O. But a lower catalytic activity was observed and this may be due to less reaction sites are available as compared to that under dry conditions where only Lewis acid sites were found. It is concluded that surface acid sites are varied according to different operation conditions. Lewis acidity was dominant under the condition of low vanadia content and in the absence of H2O molecules. It is also less irrelevant to temperature. In contrast, Bronsted acidity was dominant under the condition of high vanadia content and with the presence of H2O molecules. It is also highly affected by temperature.
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