Conversion of Dimethyl Ether to Light Olefins on Rh–Mg/HZSM-5: The Role of Rhodium As a Modifier

The authors study the effect a second modifying metal (Rh) has on the acidic and catalytic properties of Mg/НZSM-5 in the conversion of dimethyl ether to light olefins. The state of the active components (Mg, Rh) on the zeolite surface is analyzed. It is shown that introducing rhodium into Mg/НZSM-5 considerably improves the on-stream stability of the catalyst, while the selectivity toward light olefins is preserved at a level of 75 wt %. It is found that different oxocationic or oxide species of magnesium form on the zeolite surface in a monometallic Mg/HZSM-5 sample. Introducing rhodium contributes to the stabilization of magnesium mostly in the form of Mg²⁺ cations, while the Lewis acidic properties of magnesium cations are diminished. The combination of these factors contributes to the slowing down of the catalyst deactivation.