制备溶液pH对C uO-ZnO/Al_2O_3催化剂前体物相及其CO水汽变换反应活性的影响

Influence of Precipitation pH on Phase Composition of Catalyst(CuO-ZnO/Al_2O_3) Precursors and Activity of Catalyst in CO Water Gas Reaction

用X射线衍射、微分热重分析、程序升温还原、N2吸附、N2O滴定及常压微反活性评价技术考察了制备溶液pH对CuO-ZnO/A l2O3催化剂前体物相、催化剂物性参数及CO水汽变换反应活性的影响。实验结果表明,催化剂前体中主要存在3种物相:Cu2CO3(OH)2、(Cu,Zn)2CO3(OH)2和(Cu,Zn)6A l2(OH)16CO3.4H2O。随着pH的升高,Cu2CO3(OH)2和(Cu,Zn)2CO3(OH)2的含量先增加后减少,而(Cu,Zn)6A l2(OH)16CO3.4H2O的含量则随着pH的升高单调上升。焙烧后的试样中形成的CuO-ZnO固溶体越多,CO水汽变换反应活性越高。实验结果表明,CO水汽变换反应是一个结构敏感型反应。

Effect of precipitation pH on phase composition of catalyst （ CuO - ZnO/Al2O3 ） precursors was studied by means of X - ray diffraction, differential thermogravimetry, temperature pregrammed reduction, N2 adsorption and N2O titration. Activity of catalyst for CO water gas reaction（WGR） was evaluated in a differential fixed - bed reactor under atmospheric pressure. Precursors of catalysts were prepared by cocurrent coprecipitation. It was found that Cu2CO3 （ OH ） 2, （ Cu, Zn ） 2CO3 （ OH ） 2 and （ Cu, Zn ） 6Al2 （ OH ） 16 CO3 · 4H2O were main phases of catalyst precursors. At lower pH, CuECO3 （OH）2 and （Cu, Zn ）2CO3 （OH）2 were main phases of precursors and their contents decreased with continuous raising of pH,but amount of（ Cu ,Zn）6Al2 （OH）16CO3 · 4H2O increased monotonously with raising of precipitation pH. CuO - ZnO solid solution formed during calcination and its amount was direct proportional to catalytic activity in WGR. Activity of catalysts firstly rose with increasing of precipitation pH, then dropped after reaching a maximum at pH = 8. Pure CuAl2 O4 hardly had any catalytic activity for WGR. No correlation had been observed between WGR activity and specific surface area of copper metal. That suggested WGR was a structure - sensitive reaction.