Understanding the role of sodium during adsorption. A force field for alkanes in sodium exchanged faujasites

We have developed a united atom force field able to accurately describe the adsorption properties of linear alkanes in the sodium form of FAU-type zeolites. This force field successfully reproduces experimental adsorption properties of n-alkanes over a wide range of sodium cation densities, temperatures, and pressures. The force field reproduces the sodium positions in dehydrated FAU-type zeolites known from crystallography, and it predicts how the sodium cations redistribute when n-alkanes adsorb. The cations in the sodalite cages are significantly more sensitive to the n-alkane loading than those in the supercages. We provide a simple expression that adequately describes the n-alkane Henry coefficient and adsorption enthalpy as a function of sodium density and temperature at low coverage. This expression affords an adequate substitute for complex configurational-bias Monte Carlo simulations. The applicability of the force field is by no means limited to low pressure and pure adsorbates, for it also successfully reproduces the adsorption from binary mixtures at high pressure

Improving the selectivity to 4-tert-butylresorcinol by adjusting the surface chemistry of heteropolyacid-based alkylation catalysts

Keggin tungstophosphoric acid (H3PW12O40, HPW) was immobilized onto Santa Barbara Amorphous (SBA-15) type silica to obtain selective catalysts for the resorcinol tert-butylation with methyl-tert-butyl ether. The challenge was to enhance the reaction selectivity to the mono-alkylated product i.e. 4-tert-butylresorcinol at the expenses of other more thermodynamically favored products as the 4,6-di-tert-butylresorcinol. Using HPW@SBA15 catalysts, remarkable selectivity to 4-tert-butylresorcinol was obtained, up to 42% (at 20% of resorcinol conversion). Our finding is that the change in the product distribution was dependent on the catalyst surface chemistry: 4TBR selectivity can be increased adjusting the fraction of Brønsted acid sites versus Lewis ones at the catalyst surface

Synthesis of MTT zeolite catalysts with surface Al depletion

MTT zeolite crystals with siliceous layer on their external surface were synthesized using a two step hydrothermal procedure in which cores prepared from an aluminosilicate gel were transferred into a siliceous gel for farther crystal growth. The thickness of the siliceous shell was varied by varying the proportion of the two gels. The samples were characterized using physicochemical methods (XRD, XPS, 27Al MAS NMR, SEM, N2 adsorption). The zeolites were converted into bifunctional catalysts and evaluated in hydroisomerization of decane