Substituting effect of Ce3+ on the AlPO-11 molecular sieve

Abstract

Substituted AlPO-11 molecular sieve with Ce³⁺ was first prepared. The substitution was verified by characterization techniques and density functional theory. The results showed that both Al³⁺ and P⁵⁺ sites could be substituted. Cerium–oxygen tetrahedron was formed when Al³⁺ sites were replaced via isomorphous substitution. As for substituting the P⁵⁺ sites, Ce³⁺ coordinated with two or three oxygen atoms to form surface defects. Brønsted and Lewis acid sites appeared from the charge compensation and structure defects, respectively. The defective surface with higher interface energy resulted in particle aggregation and oriented growth. CeAPO-11 possesses a superior hydrothermal stability, which enables its application in a steam atmosphere with severely high temperatures. It was added as the bi-functional promoter (isomerization and dehydrogenation) to a fluid catalytic cracking catalyst. The results showed that CeAPO-11 increased the reaction conversion and the selectivity of aromatics and cycloparaffins.