沉淀pH对CuO/ZnO/Al_2O_3系催化剂前体性质的影响

用并流共沉淀方法制备了一系列CuO／ZnO／Al2O3催化剂前体及催化剂,用XRD,TG-DTG,TPR及微反活性评价等技术考察了沉淀pH对催化剂前体物相组成及焙烧后物相中CuO-ZnO间的作用情况。研究表明,沉淀pH主要对催化剂前体的物相组成有重要影响,在不同的沉淀pH下,前体中的物相组成不同。在pH为7的情况下,前体中存在碱式硝酸铜Cu2(NO3)(OH)3、碱式碳酸铜Cu2CO3(OH)2、类碱式碳酸锌(Zn,Cu)5(CO3)2(OH)6及类孔雀石(Cu,Zn)2CO3(OH)2等多种物相;在pH为8-9时,前体中主要存在(Cu,Zn)2CO3(OH)2和(Zn,Cu)5(CO3)2(OH)6两种物相,且其结晶度较低,在此范围内催化剂的活性最好,TPR实验表明,此时催化剂中形成了较多的CuO-ZnO固溶体。实验结果表明,(Cu,Zn)2CO3(OH)2和(Zn,Cu)5(CO3)2(OH)6两种物相对提高催化剂的活性至关重要。

Influence of pH on Properties of CuO/ZnO/Al2O3 Catalyst Precursors

fluence of pH on precursors of CuO/ZnO/Al2O3 catalysts was studied by means of XRD,TG-DTG and TPR techniques. Initial catalytic activity were tested in a differential fixed-bed reactor. The catalyst precursors were prepared by co-current co-precipitation method. Precipitation pH had a key effect on phase and composition of the catalyst precursors. When pH = 7, the precursor contained Cu2 (NO3) (OH)3, amorphous Cu2CO3(OH)2(georgeite), (Cu, Zn)2CO3 (OH)2 (rosasite) and(Zn,Cu)5 (CO3)2 (OH)6 (aurichalcite). As pH increased,the phase of Cu2(NO3)(OH)3 disappeared and the amount of (Cu,Zn)2CO3(OH)2 and (Zn,Cu)5-(CO3)2(OH)6 increased. The phases (Cu,Zn)2CO3(OH)2 and (Cu,Zn)5(CO3)2 (OH)6 in precursors were of vital importance to enhancing the catalyst activity. The CuO - ZnO solid - solution originated from the decomposition of (Zn,Cu)5(CO3)2(OH)6 was higher in catalytic activity than the one alternatively originated from (Cu,Zn)2CO3(OH)2.