Octahedron-based redox molecular sieves M-PKU-1 (M = Cr, Fe): A novel dual-centered solid acid catalyst for heterogeneously catalyzed Strecker reaction

Cr-PKU-1, an octahedron-based redox molecular sieve, was found to be an efficient, environmentally benign and easily recoverable catalyst for the heterogeneously-catalyzed Strecker reaction under the mild conditions. This material was evidenced to be a dual-centered solid acid with a large density of Bronsted acid (borate hydroxyl groups, B-OH) and Lewis acid sites (Cr3+), and therefore showed much higher catalytic activity than mono central solid acid in the formation of alpha-aminonitriles. Although commonly considered as Lewis acid centers, electron-deficient boron atoms (tri-coordinated BO3) in Cr-PKU-1 failed to exhibit the desired catalytic activity in the present investigations probably due to steric hindrance against the large organic substrates. A plausible mechanism about two-centered catalysis in Strecker reaction were proposed based on the comprehensive and sufficient analysis. This work illustrates for the first time the possible application in the Strecker reaction using the dual-centered redox molecular sieve, and highlights their potential ability to address the various functions involved in the reaction mechanism.