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Abstract: A cesium-exchanged mordenite zeolite was tested as a hydrocarbon trap for cold-start automotive applications using a modified temperature programmed desorption (TPD) procedure. In the modified TPD procedure, a step increase in feed concentration was performed simultaneously with the start of the temperature ramp to more closely mimic cold start conditions. The feed stream contained mixtures of toluene, propane, and water. The cesium-exchanged mordenite trapped propane under these dynamic conditions, demonstrated improved propane trapping when toluene was coadsorbed, and retained its trapping capacity after nearly 40h of hydrothermal treatment. [Copyright &y& Elsevier]

The extraframework locations of many metal cations in pentasil zeolites, such as ferrierite, are not known, but new infrared bands in the 800–1000 cm−1 region are experimentally observed upon exchange. To investigate the origin of these bands and to better understand cation siting, density functional theory calculations were performed on ferrierite cluster models for seven divalent metals: magnesium, manganese, iron, cobalt, nickel, copper, and zinc. The calculated properties, such as the metal–zeolite binding energy, follow a U-shaped trend with respect to the number of metal d electrons. The calculated infrared bands are consistent with the occupation of the B and G ferrierite sites by the metal cations. However, a definitive assignment of the published experimental infrared bands to particular extraframework sites was not possible. Despite this limitation, all seven metals were shown to perturb the ferrierite framework similarly. All of the cations coordinate to four framework oxygen atoms and the framework T–O bonds associated with these oxygen atoms are elongated by the metal. This elongation is shown to be proportional to the wavenumber of the infrared bands. [Copyright &y& Elsevier]

Abstract: Quantum chemical calculations were employed to develop a better understanding of the adsorption properties of BaNaY interacting with molecules relevant to deNO x catalysis. First, various basis sets and levels of theory were tested for barium-containing species and gas-phase reactions, and it was shown that the choice of the basis set for barium is critical. Density functional theory (DFT) with the B3LYP functional and SDD as the basis set was selected based on its combination of relative accuracy and speed. This level of theory was then used to calculate energies, geometries, and frequencies for acetaldehyde, acetic acid, nitromethane, and water adsorbed and in the gas phase. The predicted properties were compared to experiment where available and reasonable agreement was found. To study the effect of the zeolite framework on the adsorption properties, the size of the zeolite cluster was increased from 6T to 36T to 96T using the embedded ONIOM method. Inclusion of van der Waals interactions with increasing cluster size only changed the adsorption enthalpy by a small amount for all of the adsorbates studied. It was found that the interaction between the empty 6s orbital of Ba and the lone pair orbital of the oxygen atom in the adsorbed state, revealed by natural bond orbital analysis, correlates with the adsorption enthalpy and the gas-phase charge of the oxygen atom that interacts with Ba. [Copyright &y& Elsevier]

Highlights: [•] The geometric properties of over 137,000 hypothetical MOFs were analyzed. [•] The hypothetical MOFs have diverse geometrical properties. [•] Only 6 different framework nets appear in this database of hypothetical MOFs. [•] Energy minimization provides insights to MOF construction algorithms. [Copyright &y& Elsevier]

Several zeolites with varying pore dimensionality have been investigated as hydrocarbon (HC) traps by studying the temperature programmed desorption of propane and toluene mixtures. In one-dimensional (1-D) zeolites, the diffusive motion of propane is blocked by the more-strongly adsorbed toluene thus raising the desorption temperature of propane above its single-component desorption temperature. In the 1-D zeolite EUO, propane is trapped within the pores by the toluene and is only able to desorb to the gas phase once toluene begins to desorb. This leads to an increase in the propane desorption temperature of 35 °C over the single-component value. In the 1-D zeolite mordenite, propane desorbs in the presence of toluene at an intermediate temperature that is 100 °C larger than the single component case. Toluene then desorbs at an even higher temperature. It is suggested that propane undergoes an activated process of passing toluene within the 1-D pores that requires the intermediate temperatures. This HC trapping is not observed in the three-dimensional pore zeolites ZSM-5 or Y. Propane in the binary mixture with toluene in these zeolites desorbs at the same temperature as in the single component cases, suggesting that propane is able to diffuse around the more-strongly adsorbed toluene due to the connectivity of the pores. Therefore, it is the one-dimensionality of the zeolites that allows the trapping of propane to higher temperatures in the presence of the more-strongly adsorbing toluene. This phenomenon may find application in reducing cold start HC emissions from automotive exhaust. [Copyright &y& Elsevier]