RESUMO
Physical adsorption of methane in purely siliceous molecular sieves prepared by a recently discovered synthetic pathway using 2D zeolites as nanoscale building blocks has been investigated by means of combined experimental and theoretical approaches. The DFT/CC-based method has been tested on ADOR zeolites of the UTL family and a few experimentally well-characterized siliceous zeolites. Excellent agreement between theoretical and experimental heats of adsorption has been found for OKO, PCR, MFI, CHA and AEI zeolites. The observed discrepancy for the UTL germanosilicate (2 kJ mol-1) has been plausibly explained using a simple model of D4R defects. The proposed methodology can be used as a reliable characterization tool for newly synthesized silica nanomaterials.
RESUMO
The inter-layer interactions and the possible arrangements of MWW-type layers were investigated computationally at the non-local density functional theory level. Powder XRD patterns were simulated for structures obtained computationally and compared with experimental data. The MCM-22P material corresponds to the layers bound with relatively strong hydrogen bonds between surface silanol groups that is an energetically preferred structure in the presence of a structure directing agent (hexamethyleneimine). The powder XRD pattern of MCM-56 is best matched for relatively disordered (in the ab plane) MWW layers that are partially condensed. The appearance of the powder XRD pattern in the 2θ range of 7.5-10° depends on the extent of interlayer condensation. The combination of density functional investigation of interactions between MWW layers together with simulation of powder XRD patterns brings atomistic insight into the inter-layer arrangement and better understanding of the effects responsible for the differences between various layered materials of the MWW family.