摘要
采用等容浸渍法制备了三种类型的Cu/SiO_2,催化剂(铜担载量都为3.3Wt%).将其制备因素与XRD、SEM、XPS等表征手段所得结果相关联,得出氨具有分散硅胶表面铜组分的作用、有无氨介入催化剂制备过程可导致截然不同的表面CuO分散状态.有氨介入时所得催化剂表面孤立Cu^(2+)(二硅氧基钳合—Cu^(2+)与具有一定分散程度的CuO共存、氨介入方式及所用铜盐不同,二种状态的铜组分在载体表面所占的比例不同.用硝酸铜为原料,先浸铜盐后浸氨的方式所得催化剂表面绝大部分为孤立Cu^(2+);而浸铜盐后不浸氨的催化剂表面绝大部分为CuO.在制得的5个催化剂中,表面上明显有CuO存在的4个催化剂,CuO似乎都分布于载体外表面,即形成近似于“蛋壳形”的分布.
Three kinds of Cu/SiO2catalysts (5 catalysts in total, the copper loading is 3. 3 wt%) were prepared by the iso-volumetric impregnation method and characterized by XRD, SEM and XPS. XRD profiles reveals that CuO is detected as the only copper phases on four catalysts except N-5. However, for N-5, XPS results show that the binding energy of Cu2p3/2 is 936. 4 eV which agrees with that of isolated Cu2+ in literature. Its colour and DRS spectrum are the same as the Cu/SiO2 catalyst prepared by ion exchange. Thus it is possible to conclude that the isolated Cu2+ (two siloxyl on the surface of silica coordinates with one Cu2+) is absolutely the major surface copper species. SEM images show that CuO particles on N-l to N-3 are in the size of 0. 3-0. 5 μm, but CuO particle sizes on N-4 catalyst are up to 3-5 μm. The difference in the CuO particle sizes of these four catalysts can be attributed to using or not using of ammonia in the procedure of catalyst preparation. Piled up CuO particles (3 - 5 μm) are formed on the surface of silica if it is prepared just by impregnation of copper nitrate aquous solution without ammonia treatment (N-4). CuO(0. 3-0. 5 μm) and isolated Cu2+co-exist on the surface of support if the catalyst is prepared by impregnation of tetra-ammonia copper nitrate complex solution (N-3). Mainly isolated Cu2+ exist on the silica surface if the catalyst is produced by impregnation of copper nitrate aquous solution followed by impregnation of ammonia aqua (N-5). On the catalysts prepared from copper chloride(N-l , N-2), CuO(0. 3 - 0. 5 μm) and isolated copper ions coexist on support no matter what ammonia treatment was adapted, in contrast to the case of copper nitrate. In summary, ammonia gives a dispersive effect on Cu/SiO2catalyst preparation.
XPS measurement of surface component of N- 2 to N- 5 catalysts was carried out in two ways: directly from the pellets of catalyst and from the disc sample prepared by powdering and pressing of the catalyst pellets. It can be seen that, surface coppe
出处
《分子催化》
EI
CAS
CSCD
1993年第3期178-185,共8页
Journal of Molecular Catalysis(China)
关键词
催化剂
制备
表征
铜
二氧化硅
Cu/SiO2, Catalyst preparation, Characterization, Ammonia dispersive effect.
