Effects of amine organic groups as lattice in ZSM-5 on the hydrolysis of dimethyl ether

• We studied catalytic activity of amine doped ZSM-5 for dimethyl ether hydrolysis.
• The reaction has two possible stepwise and concerted channels.
• The reaction favors to proceed via the concerted channel at all active centers.
• The undoped center shows the best catalytic performance.
• The demethylation step is energetically favorable over amine-doped center.

The effects of doping amine to ZSM-5 on its catalytic activity for hydrolysis of dimethyl ether (DME) have been studied theoretically using Density Functional Theory with the embedded cluster ONIOM(M06/6-31G(d,p):UFF) model. Doping by amine to ZSM-5 yields two new active centers, namely the protonated Z[NH2] and non-protonated Z[NH] amine sites in addition to the normal Brønsted acid Z[OH] site. The reaction has two possible stepwise and concerted channels. The stepwise channel consists of two elementary steps; (i) the demethylation followed by (ii) the hydrolysis while the concerted channel involves in the demethylation and hydrolysis in a single step. We found that the reaction favors to proceed via the concerted channel at all three active centers. The results predict that the Z[OH] shows the best catalytic performance for the studied reaction. The Z[NH2] is not catalytically active due to the activation barriers are extremely high for both stepwise and concerted pathways. The demethylation step is energetically favorable over the Z[NH] site, however, the product methylamonium surface intermediate is too stable to be further converted to methanol.

The energy profiles for the concerted channel of the DME hydrolysis over the three active centers.Figure optionsDownload high-quality image (167 K)Download as PowerPoint slide