浸渍液pH对镍物种存在状态及催化剂加氢催化性能的影响

Effects of impregnating pH value on Ni existing states and catalytic performance of hydrogenation catalyst

以HZSM-5为载体,硝酸调节浸渍液的pH,采用等体积浸渍法制备含Ni质量分数0.5%的Ni/HZSM-5催化剂,结合XRD、TEM、BET、NH_3-TPD及H_2-TPR等表征手段,考察浸渍液pH对Ni物种存在状态及催化剂加氢催化性能的影响。结果表明,pH为2.5时,Ni物种以3种形式存在,载体外表面较大颗粒(8 nm)和较小颗粒[(1～2)nm]的Ni以及孔道内部较难还原的一小部分Ni,由于Ni分布较分散,3-羟基丙醛(3-HPA)转化率较高;随着浸渍液pH逐渐增大至5.6,Ni物种逐渐趋向于以单一颗粒(3 nm)形式存在于载体外表面,有效活性位少,3-HPA转化活性降低。

Ni/HZSM-5 catalysts with 5wt% Ni were prepared by incipient wetness impregnation method, and the pH value of the impregnating solution was adjusted with nitric acid. The physico-chemical proper- ties of the samples were characterized by XRD, TEM, BET, NH3-TPD and H2-TPR. The hydrogenation reaction of 3-hydroxypropionaldehyde （3-HPA） to 1,3-propanediol （ l, 3-PDO） was carried out in a fixedbed reactor under the condition of n（ H2 ） ： n（3-HPA） =7.0 ,space velocity 4.5 h -1,50 ℃ and 5.0 MPa. The results showed that when the pH value was 2.5, Ni species existed in three states ： the larger particles （8 nm） and the smaller particles [ （ 1 - 2） nm ] in the outer surface of HZSM-5, and a small part of Ni reduced difficult in the internal pore. 3-HPA conversion was higher due to the effect of Ni distribution more dispersed;As the pH value increased to 5.6, Ni species gradually tended to exist in the form of single particles （3 nm） in the outer surface of the carrier. The effective active site was less and 3-HPA conversion was decreased.