Conversion of dimethyl ether to light olefins on Rh-Mg/HZSM-5: role of Rh as a modifier

The influence of the second modifying metal (Rh) on the acid and catalytic properties of Mg/HZSM-5 in conversion of dimethyl ether to light olefins and the state of active components (Mg, Rh) on the zeolite surface are studied. It is shown that when it is introduced into Mg/HZSM-5, rhodium significantly increases stability of the catalyst operation while maintaining the selectivity for light olefins at the level of 75 wt. %. It is found that various oxocationic or oxide forms of magnesium are formed on the zeolite surface in the monometallic sample of Mg/HZSM-5, and introduction of rhodium contributes to stabilization of magnesium mainly in the form of Mg2+ cations while the strength of Lewis acid properties of magnesium cations decreases, which all together makes catalyst deactivation slow down.