High-yield synthesis of BTEX over Na–FeAlOx/Zn–HZSM-5@SiO2 by direct CO2 conversion and identification of surface intermediates

Abstract

We present a tandem catalyst consisting of Na-promoted bifunctional FeAlOx (Na–FeAlOx) and Zn-doped HZSM-5, the outer surface of which was coated with a SiO2 layer (Zn–HZSM-5@SiO2). This tandem catalyst afforded a high BTEX space–time yield of 4.0 mmol g–1 h–1 with a CO2 conversion of 45.2%. The selectivities toward BTEX were tuned by controlling the nature, density, and distribution of the Brønsted acid sites of the zeolites, in addition to adjusting the proximity between the Fe-based and zeolitic active sites. In situ operando experiments revealed the role of Zn–HZSM-5@SiO2 not only in dehydroaromatization, but also in CO2 adsorption, reverse water–gas shift reactions, and C–C coupling reactions. The findings of this study are promising for designing a tandem catalyst to directly convert CO2 to BTEX in high yields, and also provide novel insights into the reaction intermediates for this tandem catalyst.