CuO／γ－Al_2O_3中热稳定助剂作用的探讨

Effects and Mechanism of Thermal Stabilizers in Cuo/Al_2O_3 Catalysts

用等量共浸法和分浸法制备了含Ｃａ、Ｓｒ、Ｂａ、Ｍｇ、Ｚｒ和Ｌａ助剂的ＣｕＯ／γ－Ａｌ_２Ｏ_３催化剂（ＣｕＯ／Ａｌ_２Ｏ_３＝８ｗｔ％，Ｍ／Ｃｕ（原子比）＝０．１５，Ｌａ／Ｃｕ＝０．３５）．用ＸＲＤ和ＸＰＳ等考察了在高温７５０℃、９５０℃和１０５０℃老化后的相结构和ＣＯ氧化活性，实验表明所有助剂均有不同程度的抗烧结和抗相变作用。其中Ｌａ、Ｃａ和Ｚｒ的效果最好。分浸法比共浸法好。在９５０℃老化后，ＣｕＡｌ_２Ｏ_４和α－Ａｌ_２Ｏ_３同步产生；随老化温度增高，ＣＯ氧化活性有所下降。分浸法制备的含Ｚｒ样品在９５０℃老化后活性最高。从γ－Ａｌ_２Ｏ_３缺陷尖晶石特征及高温脱结构水过程，探讨了助剂抑制α－Ａｌ_２Ｏ_３生成的原因。

A series of stabilizers Ca, Sr, Ba, Mg, La and Zr to retard thermal and thermo-chemical degradation of CuO/Al_2O_3 catalyst are studied at high temperature. The composition of the catalyst sample is 8 wt% CuO/Al_2O_3. The atomic ratios for all the promoters to Cu, M/Cu, are 0. 15 with the exception of La/Cu which is 0. 35. XRD, XPs and DTA, combined with the CO oxidation activity are measured for the fresh samples calcined at 750℃ for 2h and the samples aged at 950 ℃ and 1050℃ for 2 h respectively. It is found that all the stabillze rs possess the ability of resisting the sintering of CuO/Al_2O_3 and retard the phase transition of γ-Al_2O_3 to different extents. La, Zr and Ca exhibit distinctive function among the promoters. Both the CuAl_2O_4 and α-Al_2O_3 are produced when the samples are aged at 950℃. The new phases La_2Al_(24.4)O(31.6) and BaAl_2O_(19) are detected in the samples containing La or Ba when the samples are aged at 1050℃. The CO oxidation activity of CO is reduced only to some extent, although the aging temperature is as high as 1050℃. The activity is the lowest for the sample containing La. The mechanism of inhibiting α-Al_2O_3 formation is analysed on the basis of crystalline structure characteristics of γ-Al_2O_3 and α-Al_2O_3 and the process of γ-Al_2O_3 dehydration. A good promoter for thermal stability should be highly stable in itself, with high melting point, high formation enthalpy, only one oxidation state, ionic radius much larger than Al￣(3+), and a high positive charge.