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Pristine CeO2 is not active for the selective catalytic reduction of NOx with NH3 (NH3-SCR) and the SCR activity is nearly totally lost due to the introduction of K. However, sulfation treatment of CeO2 leads to significantly improved SCR activity and remarkable resistance towards K poisoning. In-situ DRIFTS results revealed that the addition of K seldom affects the adsorption of NH3 over sulfated CeO2, whereas the adsorption of NH3 becomes very weak in the case of K-doped CeO2. The noticeably improved Brønsted acid sites due to the sulfation are responsible for the enhanced alkali resistance of sulfated CeO2 catalyst.