Selective synthesis of para-xylene and light olefins from CO2/H2 in the presence of toluene

Abstract

Catalytic hydrogenation of CO₂ with renewable H₂ into valuable chemicals such as para-xylene and light olefins (C₂⁼–C₄⁼), which are important raw materials for the production of various commodities, is highly attractive. Herein we report that an oxide–zeolite (OXZEO) composite catalyst composed of ZnCrO_x-ZSM-5 enables the selective synthesis of para-xylene and light olefins from CO₂/H₂ in the presence of toluene. The product selectivities depend strongly on the acidity and location of acid sites of the zeolite function. By modifying ZSM-5 with silica, the external acid sites are shielded, and the pore openings are narrowed, which enhances significantly the formation of para-xylene. By modifying the zeolite with phosphorus, light olefins are co-produced due to the weakened acidity. As a result, the para-xylene fraction in xylene isomers reaches 82.8%, and the light olefin fraction in aliphatic hydrocarbons is as high as 75.8% when CO₂ conversion is 20.9% and toluene conversion is 10.6%. Furthermore, the catalyst exhibits a good stability within a 100 h test. This provides a potential route for utilization of centralized greenhouse gas for synthesis of value-added chemicals.