富氧条件下Cu/Al2O3催化剂上C3H6选择性还原NO的研究

以Cu/Al2O3为催化剂,对富氧条件下C3H6为还原剂选择性催化还原NO反应进行了研究.活性评价结果表明,与高活性的Ag/Al2O3催化剂相比,Cu/Al2O3催化剂选择性还原NO的活性较低,NO的最高转化率仅为40%.在所考察的温度范围(473～723K)内,红外谱图中不存在有机含氮化合物(R—ONO和R—NO2)的特征振动吸收峰.作为反应中间体—NCO的前驱体,有机含氮化合物在Cu/Al2O3催化剂表面难以生成是造成催化剂选择性还原NO活性低的直接原因.在Cu/Al2O3催化剂上,NO2吸附能够优先发生,并以NO3-物种的形式覆盖在大部分催化剂表面.动态原位红外光谱实验发现,这种NO3-表面物种与C3H6的反应性较差,使生成有机含氮化合物的关键反应难以发生,但此时的催化剂表面有利于C3H6和O2的完全氧化反应,这是导致Cu/Al2O3催化剂选择性较低的根本原因.

Research of Selective Catalystic Reduction of NO with Propene over Catalyst Cu/Al2O3 in Excess Oxygen

The selective catalytic reduction (SCR) of NO with propylene was investigated over Cu/Al2O3 catalyst by using fixed-bed reactor and in situ FTIR and compared with Ag/Al2O3 which has a relative high activity in C3H6-SCR of NO. The highest conversion of NO is only 40% at about 650 K, when the catalyst was exposed to a gas mixture of NO/C3H6/O2/N2=0.08%/0.171 4%/10%/balance with W/F=0.018 g·s/mL. Surface R—NO2 and R—ONO species, which were observed on Ag/Al2O3 catalyst as the precursor of —NCO species, can hardly be found on Cu/Al2O3 catalyst surface in FTIR spectra under the same condition. This results in the low activity of Cu/Al2O3 catalyst for NO reduction. Through dynamic FTIR experiment, it was found that NO3- species, which are dominant surface species over Cu/Al2O3 catalyst, have a low activity with C3H6, so that the reaction producing R—NO2 and R—ONO is very difficult to take place.