碱土金属化合物在氧化锆上的分散与碱性

The Basicity and Dispersion State of Alkaline Earth Metal Compounds on the Surface of ZrO_2

研究了碱土金属化合物在ＺｒＯ２ 表面上的分散状况及碱性． 结果表明，碱土金属硝酸盐分解成为氧化物的难度随着原子序数的增大而增加． Ｍｇ（ＮＯ３）２ 在５５０ ℃时就可以直接分解为ＭｇＯ．Ｃａ（ＮＯ３）２ 和Ｓｒ（ＮＯ３）２ 不能单独分解成ＣａＯ和ＳｒＯ， 但当负载在ＺｒＯ２ 载体上时，就可以在载体表面分解成ＣａＯ和ＳｒＯ， 只是由于负载量不同其存在的形式各不相同．ＣａＯ含量较少时，ＣａＯ与ＺｒＯ２ 形成固溶体而不是以ＣａＯ 的形式分散在ＺｒＯ２ 的表面；ＣａＯ含量较多时，生成ＣａＺｒＯ３ ．ＳｒＯ含量较少时，以ＳｒＯ 的形式分散在ＺｒＯ２ 的表面上； 含量较多时，有ＳｒＺｒＯ３ 生成．Ｂａ（ＮＯ３）２ 即使有载体ＺｒＯ２ 存在时也不能分解成ＢａＯ， 而是以Ｂａ（ＮＯ２）２ 的形式分散于ＺｒＯ２ 表面．ＣＯ２ＴＰＤ 实验表明，与纯ＺｒＯ２ 相比，负载样品的碱位分布范围较宽，碱的强度与数量都有很大提高．

The basicity and dispersion state of alkaline earth metal compounds on the surface of ZrO 2 were investigated. The results show that the decomposition of alkaline earth metal nitrates become more difficult as the atomic number increases. Mg(NO 3) 2 can decompose directly to MgO at 550 ℃; Ca(NO 3) 2 and Sr(NO 3) 2 can not decompose directly to respective oxide at 550 ℃, but can decompose after being supported on the surface of ZrO 2. When the content of CaO is low, the resultant is a solid solution of CaO and ZrO 2; a new compound CaZrO 3 shows up with increasing content of CaO. For the system of Sr/ZrO 2, SrO can disperse on the surface of ZrO 2 at low loading, and SrZrO 3 appears when the content of SrO increases. Ba(NO 3) 2 cannot decompose to BaO even in the existence of the support, but to Ba(NO 2) 2 and the latter disperses on the surface of ZrO 2 as a monolayer. CO 2 TPD test shows that ZrO 2 supported alkaline earth metal samples present a wider distribution and a larger amount of basic sites compared with pure ZrO 2, and that the strength of basic sites is also increased a lot, especially for Ca/ZrO 2.