The mechanism of dimethyl ether formation from methanol catalyzed by zeolitic protons

Here we show that two parallel reaction pathways for the production of dimethyl ether are possible. The first proceeds via two distinct steps, similar to that proposed by Kubelkova et al. The second path, as proposed by Bandiera and Naccache, involves the simultaneous adsorption and reaction of two methanol molecules with formation of DME and water in one step. The results presented are based on density functional theory (DFT) calculations, as implemented in the DGauss program. All discussed structures herein were obtained including nonlocal exchange and correlation correction due to Becke and Perdew, respectively, in a self-consistent manner. We conclude that DME is formed according to an association mechanism without formation of an intermediate methoxy species. The reaction mechanism is of the SN2 (backside) type, similar as expected in the homogeneous phase.