酸性质对磷钨酸改性CeO_2上NH_3选择性催化还原NO性能影响

分别制备了磷钨酸、磷酸、偏钨酸铵及磷酸+偏钨酸铵改性的CeO_2催化剂,用于NO的NH3选择性催化还原反应(NH3-SCR),对酸改性的作用进行了研究。结果表明,不同酸改性后的CeO_2催化剂均含有弱酸和中强酸位,但酸量差别明显,依次为:磷钨酸/CeO_2偏钨酸铵/CeO_2磷酸+偏钨酸铵/CeO_2磷酸/CeO_2。由于磷钨酸改性的CeO_2催化剂中P与W之间相互作用,导致磷钨酸/CeO_2催化剂表面弱酸及中强酸含量较多,Ce物种和O物种相对活跃,有利于NH3的吸附、活化和NH3-SCR反应的进行;因此,磷钨酸改性的CeO_2催化剂活性最佳,在225-450℃下NO转化率高于90%。

Effect of acid property on selective catalytic reduction of NO with ammonia over photungstic acid modified CeO2 catalyst

A series of CeO₂ catalysts was modified with different acids including phosphotungstic acid (P-W), phosphate acid (P), partial ammonium tungstate (W), and phosphate acid plus partial ammonium tungstate (P+W); the effect of acid modification on the performance of CeO₂ catalyst in the selective catalytic reduction of NO with ammonia (NH₃-SCR) was then investigated. The results indicated that the CeO₂ catalyst after acid modification possesses abundant surface acid sites of weak-medium strength and the acid quantity of various catalysts follows the order of P-W/CeO₂ >W/CeO₂ >P+W/CeO₂ >P/CeO₂. Due to the interaction between P and W species, the P-W/CeO₂ catalyst modified with phosphotungstic acid exhibits high amount of weak-medium surface acid sites and active Ce and O species, which may promote the adsorption and activation of NH₃ and then enhance its catalytic activity in the NH₃-SCR of NO; over the P-W/CeO₂ catalyst, the conversion of NO keeps above 90% at 225-450℃.