Density functional study on models of interaction between phosphorus species and HZSM-5

The DMol3 calculations, based on density functional theory (DFT), have been employed to investigate the interactions between phosphorus species and HZSM-5 zeolite. The possible initial conformations designed by five proposed models were optimized at the generalized gradient approximation (GGA) level, with BLYP/DND methods. The results suggest that group is not included in the proposed model. Phosphorus species aggregation does not occur prior to the neutralization of all the Brönsted sites. Proposed model cannot contain next-nearest-neighboring (NNN) Al pairs. Stabilization effect of phosphorus on steamed HZSM-5 zeolites may be assigned to the shortening of overall bond lengths and increasing of geometric mean electronegativity. Dealuminated species may neutralize the Brönsted acid sites and stabilize the framework of steamed zeolites to result in retention of partial tetrahedral aluminum.