镧钡掺杂量对氧化铝孔结构的影响

Influence of La/Ba doping content on pore structure of alumina

采用纯γ-氧化铝,制备含镧/钡质量分数为5%、10%、20%、30%的系列改性氧化铝,样品分别在550、950、1050、1200℃条件下进行煅烧,采用比表面积、孔容、孔径、XRD表征老化前后的改性氧化铝孔结构,研究不同镧/钡含量对改性氧化铝孔结构特征的影响。BET和XRD结果表明,镧、钡在高温时产生的大量铝酸盐结构可抑制γ-A l2O3相转变,有利于保持γ-Al2O3相结构稳定性和孔结构稳定性,同时较高镧/钡含量也会导致改性氧化铝比表面积降低、孔容、孔径下降,尤其是1 200℃高温区表现更为明显,对活性金属分散存在负面影响。综合考虑孔结构和衰减率因素认为,2.5%La2.5%Ba/Al2O3具有最好的表面活性和孔结构稳定性。

A series of modified alumina with different mass fractions { 5 %, 10% ,20% , and 30% ） of La/Ba were prepared by γ-Al2O3- All samples were calcined at 550,950,1 050, and 1 200℃respectively. Pore structure of all samples were characterized by BET, pore volume, pore diameter, and XRD before and after aging. Influence of La/Ba doping contents on pore structure of modified Al2O3 was studied. Results of BET and XRD demonstrated that La/Ba can form large amount of aluminate structure to inhibit γ-Al2O3 phase tranfer at high temperature and is good for maintaining stability for both phase structure and pore structure of γ-Al2O3. Meanwhile, higher La/Ba content can decreased the surface area, pore volume, and pore diameter, and is not good for precious metals dispersing, especially at 1 200 ℃. Comprehensively considering pore structure and loss rate,2.5% La2.5% Ba/Al2O3 has the optimal surface activity and pore structure stability.