环己酮肟在改性氧化锆催化剂上的Beckmann重排反应 Ⅴ.活化焙烧温度对B_2O_3/ZrO_2催化剂的影响

Vapor-Phase Beckmann Rearrangement of Cyclohexanone Oxime on Modified Zirconia Catalysts Ⅴ. Effect of Catalyst Activation Temperature on B_2O_3/ZrO_2

采用BET ,XRD ,TG DTA ,FT IR ,XPS和NH3 TPD等分析手段 ,研究了活化焙烧温度 (5 0 0～ 80 0℃ )对B2 O3 /ZrO2 催化剂织构 /结构、表面性质和环己酮肟气相重排反应的影响 .催化剂活化焙烧温度升高促进了ZrO2 向单斜晶相转化 ,同时活性组分氧化硼由以BO4为主要结构单元的物种转变为以BO3 为基本结构单元的B2 O3 ,导致催化剂比表面积、孔体积以及表面酸量减小 ,ZrO2 与B2 O3 之间的相互作用减弱 .70 0℃活化焙烧的催化剂表面拥有最大比例的中强酸中心 ,而且Beckmann反应的活性稳定性最高 .这些结果表明 ,活化焙烧温度对B2 O3 /ZrO2 催化剂上气相重排反应的影响主要是通过改变催化剂中B原子的配位状态和表面酸性实现的 .

By means of BET, XRD, TG DTA, FT IR, XPS, NH 3 TPD techniques, the effects of catalyst activation temperature (CAT: 500～800 ℃) on the texture/structure and surface properties of 15 8% B 2O 3/ZrO 2, prepared by impregnation of ZrO(OH) 2 with boric acid solution, were studied. When the CAT was not higher than 600 ℃, the catalyst appears as an amorphous mixture of B 2O 3 ZrO 2, in which tetrahedral BO 4 units are incorporated into the network of amorphous zirconia. With the increase of CAT, the B 2O 3 component with trigonal BO 3 as the structure unit increased while the specific surface area, pore volume and acid amount of the catalyst decreased. Also, the interaction between ZrO 2 and B 2O 3 was weakened with increasing CAT. The increment of CAT led to phase transformation of the ZrO 2 support to tetragonal phase at 700 ℃ and to monoclinic phase at 800 ℃. The maximum percentage of medium strong acid sites was obtained with CAT=700 ℃. The B 2O 3/ZrO 2 catalyst activated at 700 ℃ also exhibited higher stability than other catalysts for the vapor phase Beckmann rearrangement of cyclohexanone oxime. Variations of BO 3 units in the catalyst and of caprolactam selectivity versus CAT showed that the B 2O 3 component with BO 3 as the structure unit is mainly responsible for the selective synthesis of caprolactam.