Aluminum Complexes as Models for Broensted Acid Sites in Zeolites: Structure and Energetics of [Al(OH)4]-, [Al(H2O)6]3+, and Intermediate Monomeric Species [Al(OH)x(H2O)n-x·mH2O]3-x Obtained by Hydrolysis

摘要: Using ab initio quantum mechanical methods, we examined cluster models for the transformation of aluminum sites in zeolites from tetrahedral to octahedral coordination. We investigated relative stability tetracoordinated, pentacoordinated, and hexacoordinated at different degrees ligand protonation using monomeric hydroxy−aquo complexes form [Al(OH)x(H2O)n-x]3-x. For n = 4 5, also having water second coordination sphere, i.e., [Al(OH)x(H2O)n-x·mH2O]3-x, + m 6. A shift preference tetra- hexacoordination occurred when net charge on a complex was equal or greater than +1. Hydrogen bonds were found be very important stabilizing pentacoordinated species, especially highly protonated complexes. Trends bond lengths, angles, orientations identified as functions number charge.