有序介孔CuFe_(2)O_(4)同时催化去除碳烟与NOx

Simultaneous Catalytic Removal of Soot and NO by Ordered Mesoporous CuFe_(2)O_(4)

采用纳米复刻(浇筑)法制备一系列介孔CuFe_(2)O_(4).通过X射线衍射(XRD)、 N_(2)物理吸附、透射电镜(TEM)等研究了不同制备条件对有序介孔CuFe_(2)O_(4)结构形成的影响.研究发现,作为对比,柠檬酸法仅能合成普通的四方相CuFe_(2)O_(4)纳米颗粒,但是硬模板法则能合成出高温淬火才能形成的立方晶相介孔结构CuFe_(2)O_(4).进一步研究了该催化剂同时催化去除碳烟和氮氧化合物(NO_(x))的性能,研究发现,与柠檬酸法合成的普通CuFe_(2)O_(4)催化剂相比,介孔结构CuFe_(2)O_(4)不仅大幅降低了碳烟起燃温度(324降低到278℃),而且将N_(2)的最高产率从5.9%提升到了92.2%.基于原位漫反射红外(in-situ DRIFTS)的机理分析研究表明,合成过程中采用NaOH除去硬模板的过程中会在介孔CuFe_(2)O_(4)表面造成大量残留的钠盐,这种高分散的钠物种促进了NO_(x)的吸附并转化为硝酸盐物种,从而促进碳烟氧化以及NO_(x)转化.但是与表面Na修饰的CuFe_(2)O_(4)相比,体相Na掺杂的CuFe_(2)O_(4)虽然具有更好的有序介孔结构,但是其氧化性能下降,进一步也导致了NO_(x)的催化还原性能的下降.

A series of mesoporous CuFe_(2)O_(4) was prepared by nanocasting method. The effects of different synthesis conditions on the formation of ordered mesoporous CuFe_(2)O_(4) have been investigated by X-ray diffraction(XRD), N_(2) physical adsorption, and transmission electron microscopy(TEM). CuFe_(2)O_(4) with tetragonal structure was synthesized by the citrate acid method, but mesoporous CuFe_(2)O_(4) with cubic crystal phase structure which can be formed only under high-temperature quenching condition, was synthesized by the nanocasting method. The performance of simultaneous catalytic removal of soot and nitrogen oxides(NO_(x)) by a series of CuFe_(2)O_(4) catalysts was further evaluated. Compared with the CuFe_(2)O_(4) nanoparticles synthesized by the citrate acid method, mesoporous CuFe_(2)O_(4) not only reduced the soot ignition temperature from 324.6 to 278.2 ℃ but also significantly increased the maximum N_(2) yield from 5.92% to 92.24%. Mechanism analysis based on in-situ DRIFTS showed that removing the hard template by NaOH during the synthesis process would cause a large amount of residual sodium salt on the surface of the mesoporous CuFe_(2)O_(4). Highly dispersed sodium species promoted the adsorption of NO_(x) on the surface of mesoporous CuFe_(2)O_(4) and conversion of NO_(x) into nitrate species, thus facilitated soot oxidation and NO_(x) conversion. However, compared with CuFe_(2)O_(4) modified with Na, Na-doped CuFe_(2)O_(4) showed a better ordered mesoporous structure, but its oxidation performance was reduced coupling with a worse catalytic reduction performance of NO_(x).