Dispersible exfoliated zeolite nanosheets and their application as a selective membrane.

Thin zeolite films are attractive for a wide range of applications, including molecular sieve membranes, catalytic membrane reactors, permeation barriers, and low-dielectric-constant materials. Synthesis of thin zeolite films using high-aspect-ratio zeolite nanosheets is desirable because of the packing and processing advantages of the nanosheets over isotropic zeolite nanoparticles. Attempts to obtain a dispersed suspension of zeolite nanosheets via exfoliation of their lamellar precursors have been hampered because of their structure deterioration and morphological damage (fragmentation, curling, and aggregation). We demonstrated the synthesis and structure determination of highly crystalline nanosheets of zeolite frameworks MWW and MFI. The purity and morphological integrity of these nanosheets allow them to pack well on porous supports, facilitating the fabrication of molecular sieve membranes.

DFT study of deNO(x) reactions in the gas phase: mimicking the reaction mechanism over BaNaY zeolites.

Neutral and ionic pathways for aci-nitromethane decomposition were studied in the gas phase, and the Gibbs free energy surfaces were constructed at 473 K. The pathways studied were based on proposed mechanisms of NO(x) reduction by acetaldehyde over BaNaY zeolites. Density functional theory at the B3LYP/6-311++G(d,p) level of theory was used, and 29 stable intermediates and 39 transition states were identified and quantified. Plausible pathways involving unimolecular decomposition or NO(2) addition were both explored. The rate constants for all elementary steps were estimated using transition state theory, and kinetic modeling was carried out to identify the dominant reaction channel. For the ionic routes, one of the NO(2) addition pathways dominated at typical NO(2) concentrations. For the neutral routes, one of the unimolecular decomposition routes was dominant. A solvation model was then included to mimic the environment of the BaNaY zeolite catalyst in a simplified manner. While inclusion of solvation effects stabilized the ionic species significantly, the dominant reaction channels in both the neutral and ionic systems were not altered. Our results show that the addition of NO(2) facilitates the decomposition of aci-anion nitromethane.