摘要
以Cu(NO3 ) 2 ,Zn(NO3 ) 2 和Al(NO3 ) 3 为原料 ,以NaOH为沉淀剂 ,利用共沉淀法合成了含铜三元类水滑石化合物CuZnAl HTLcs .从不同Cu/Zn/Al比的混合原料溶液的滴定曲线入手 ,详细探讨了溶液 pH值、原料加入方式、组分配比及水热处理条件对类水滑石合成的影响 ,利用XRD ,ICP及比表面积测定对合成物进行了表征 ,并以苯酚羟基化为探针反应评价了催化剂的催化性能 .结果表明 ,在体系pH =5 .0～ 6 .2 ,(Cu +Zn) /Al摩尔比 =2 .0 ,Cu/Zn摩尔比≤ 1.0及室温条件下共沉淀后 ,于 10 0℃水热处理 3h ,即可得到晶相单一和结晶度高的CuZnAl HTLcs.变化 pH法合成的样品的相对结晶度为10 0 %,低过饱和法为 76 .5 %,高过饱和法为 75 .9%.合成的CuZnAl HTLcs中Cu2 + 的含量均比原料液中Cu2 + 的含量有所增加 ,这可能是由于在 pH =5 8时Cu2 + 对Al(OH) 3 的同晶取代能力比Zn2 + 强 .随着CuZnAl HTLcs中Cu含量的增加 ,催化剂对苯酚羟化反应的催化活性逐渐增大 .
CuZnAl-hydrotalcite-like compounds (CuZnAl-HTLcs) were prepared by coprecipitation with Cu(NO 3) 2, Zn(NO 3) 2, Al(NO 3) 3, and NaOH. Based on the titration of the mixed salt solutions with different Cu/Zn/Al molar ratios, the effects of pH, precipitation way, Cu/Zn/Al molar ratio, temperature and time of the hydrothermal treatment on the preparation of CuZnAl-HTLcs were studied. The samples were characterized by XRD, ICP, and measurement of specific surface area, and used to catalyze phenol hydroxylation. The results showed that unique CuZnAl-HTLcs with high crystallinity can be prepared by precipitating a solution of (Cu+Zn)/Al molar ratio of 2.0 and Cu/Zn molar ratio ≤1.0 at pH=5.0～6.2 and then hydrothermal treatment at 100 ℃ for 3 h. The relative crystallinity of the sample obtained in the way of variable pH method is 100%, and those of the samples prepared by precipitation at low supersaturation and at high supersaturation are 76.5% and 75.9%, respectively. The Cu content in CuZnAl-HTLcs was higher than that in the mixed salt solution. This is because Cu 2+ has a greater ability to replace Al 3+ in Al(OH) 3 than Zn 2+. CuZnAl-HTLcs with high Cu content showed higher catalytic activity for the phenol hydroxylation, which implied that the Cu-Zn collaboration in the catalysis process is important.
出处
《催化学报》
SCIE
EI
CAS
CSCD
北大核心
2003年第8期569-573,共5页
基金
山西省自然科学基金资助项目 (2 0 0 0 10 15 )
关键词
铜
锌
铝
类水滑石
阴离子粘土
苯酚
羟基化
copper, zinc, aluminum, hydrotalcite-like compound, anionic clay, phenol, hydroxylation
