Theoretical Study on the Nitration of Methane by Acyl Nitrate Catalyzed by H-ZSM5 Zeolite

Abstract

A theoretical study on the nitration of methane by acyl nitrate catalyzed by HZSM-5 zeolite is reported. The zeolite was represented by a "double ring" 20T cluster. The calculations were performed at the DFT/X3LYP/6-31G** and MP2/6-31G** levels. The first step of the mechanism involves the protonation of the acyl nitrate by the zeolite and the formation of a nitronium-like ion. The reaction proceeds through a concerted step with the attack of the methane molecule by the nitronium-like ion and the simultaneous transfer of a proton from the methane molecule to the zeolite, thus reconstructing the acidic site. The activation energies for the first and second steps of this reaction are, respectively, 14.09 and 10.14 kcal/mol at X3LYP/6-31G** level and 16.68 and 13.85 kcal/mol at the MP2/6-31G**.

Effect of the Zeolite Cavity on the Mechanism of Dehydrogenation of Light Alkanes over Gallium-Containing Zeolites

“…Therefore, theoretical studies on the catalytic behavior of zeolites of chemical interest, like HZSM-5, HY and US-HY, must still rely on cluster-model type of calculations. Some studies using a T20 cluster without gallium species have already been reported. − In these studies, reagents, intermediates, and transition states have been described incorporating cavity effects with no geometrical restrictions applied during the calculations.…”

How to find an optimum cluster size through topological site properties: MoSxmodel clusters

“…Ranging from very small model clusters to describe active sites, employed in the pioneering works, 1,2 to the increasingly larger, thus more realistic ones, 3,4 there is always the challenge to find the smallest size which both accurately represents properties of the surface and demands affordable computational efforts.…”