Effect of lanthanum species on the physicochemical properties of La/SAPO-11 molecular sieve

La/SAPO-11 was synthesized via one-pot method. Lanthanum ions protect framework from distortion under the severe thermal (600 degrees C, 4 h) and hydrothermal (800 degrees C, 4 h) conditions. A higher retention of Bronsted acid sites (45.5%) is obtained after hydrothermal treatment. Lanthanum ions enhance the depolymerization of phosphorus species and interaction with phosphorus and aluminum species. In the coexistence of silicon and lanthanum ions, lanthanum ions could not incorporate into zeolite framework. LaPO4 preserves framework structure from steam attack. In addition, [La(OH)(2)](+) ions compensate structure tensions and increase the bond strength of Al-O inhibiting the desilication reaction during the thermal treatment. The hydrolyzed species of Si (4Al) and Si (3Al) can be recovered by dehydroxylation. In the cracking reaction of n-dodecane, La/SAPO-11 molecular sieve possessing moderate acid sites enhance isomerization reaction (increasing iso-paraffin by 9.5%) and inhibit cracking. The narrow pore has restriction for di-molecular reactions (e.g., hydrogen transfer reaction). (C) 2017 Elsevier Inc. All rights reserved.