无模板法合成的Phi分子筛在NO选择性催化还原中的应用

氮氧化物(NO_x)是大气中的一种主要污染物。采用具有菱沸石结构(CHA)的铜基分子筛作为催化剂,通过选择性催化还原(SCR)技术可有效去除NO_x。采用一种经济环保的制备方法,在不使用模板剂的条件下水热合成一种具有结构缺陷的低硅铝比CHA型分子筛(Phi,Si/Al=4.7)。结果表明,经Cu离子交换制备的Cu/Phi具有最丰富的表面酸性与孤立态Cu²⁺,表现出较好的低温活性、较宽的工作温度窗口以及良好的水热稳定性。Na或Mg的存在降低了Cu/Phi的表面酸性及孤立态Cu²⁺的含量,水热老化后的Na,Cu/Phi和Mg,Cu/Phi均呈现出不同程度的骨架坍塌,相应导致了催化剂失活。

Phi zeolite synthesized by template-free method for selective catalytic reduction of NO

Nitrogen oxide (NO_x) is one of the major air pollutants. Using a copper-based zeolite with a chabazite structure (CHA) as a catalyst, the selective catalytic reduction (SCR) technology can effectively remove NO_x. This work introduces a low silica CHA type zeolite with structural defects (zeolite Phi, with Si/Al of 4.7). The zeolite Phi is synthesized through a hydrothermal method without adding any template, which is low-cost and environment-friendly. The Cu-exchanged Phi is abundant of surface acidity and isolated Cu²⁺, showing a superior low-temperature activity, a wide work temperature window and a good hydrothermal stability. The presence of Na or Mg decreases the surface acidity and isolated Cu²⁺. The hydrothermally aged Na,Cu/Phi and Mg,Cu/Phi present different levels of framework collapse, which correspondingly induces catalyst deactivation.