Deoxygenation mechanism of methyl butyrate on HZSM-5: A density functional theory study

HZSM-5 zeolite modification and catalytic reaction mechanism in the reaction of cyclohexene hydration

This study investigated a three-phase (liquid–liquid–solid) reaction system of cyclohexene hydration where the catalyst was hydrophilic at the bottom of the water phase.

A DFT Study for Catalytic Deoxygenation of Methyl Butyrate on a Lewis Acid Site of ZSM-5 Zeolite

The catalytic deoxygenation mechanism of fatty acid esters on a Lewis acid site of ZSM-5 zeolite was elucidated via density functional theory (DFT) by using a methyl butyrate (MB) as the model compound for fatty acid esters. The configurations of the initial reactant, transition states, and products together with the activation barrier of each elementary reaction were determined. The activation barrier of different initial cracking reactions decreases in the order of α-C–C > β-C–C > α-C–O > β-C–O. The best reaction path for catalytic deoxygenation of methyl butyrate over Lewis acid site is CH3CH2CH2C(OCH3)=O⋯Lewis → CH3CH2⋯Lewis⋯C(=CH2)OCH3 → CH2=CH2 + CH3COOCH3 + Lewis. The oxygen of methyl butyrate is mainly removed as CO2, methyl acetate, formaldehyde, and butyraldehyde, while ethylene, propylene, and butane are the main hydrocarbon products. In addition, the group generated by cracking of methyl butyrate form a bond with the Lewis acid site, promoting the transformation between a Lewis acid and a Brønsted acid. The corresponding intermediates have a high single point energy, but the poor stability leads to further deoxygenation and cracking reactions. This work provides a theoretical basis for the modification in the number of Brønsted acid and Lewis acid sites in the ZSM-5 zeolite.

Removal of H2S to produce hydrogen in the presence of CO on a transition metal-doped ZSM-12 catalyst: a DFT mechanistic study

Hydrogen sulfide (H₂S) leads to corrosion in transport lines and poisoning of many catalysts. Meanwhile, H₂S is an inexhaustible potential source of hydrogen, which is a very valuable chemical reagent and an environmentally friendly energy product. Therefore, removal of H₂S and producing hydrogen gas using potential catalysts has been intensively studied, according to the equation: H₂S(g) + CO(g) → COS(g) + H₂(g). In this study, hydrogen sulfide (H₂S) decomposition in the presence of CO over transition metal-doped ZSM-12 clusters (TM-ZSM-12) has been investigated based on DFT calculations at the B3LYP-D3/6-31G(d,p) level. The calculation results reveal that the proposed reaction mechanism is controlled by 4 key steps, (i) hydrogen dissociation (E_a1 = +0.04 eV for the 1st hydrogen and E_a2 = +0.22 eV for the 2nd hydrogen), (ii) COS desorption (the rate-determining step of this H₂S removal process, E_des = +1.18 eV), (iii) hydrogen diffusion to the transition metal with an energy barrier (E_a3) of +0.62 eV, and (iv) the H₂ formation step (E_a4 = +0.94 eV). Our results indicate that in the presence of CO, the Cu-ZSM-12 cluster has a potential application as a highly active catalyst for H₂S removal together with hydrogen production.