Designing a bifunctional ZrCuOx/HZSM-5 catalyst for selective methylation of toluene with carbon dioxide to para-xylene

• A bifunctional catalyst ZrCuOx/HZSM-5 is effective for toluene methylation with CO 2. • A maximum xylene selectivity of 84.79% was obtained at conversions of toluene and CO 2 of 45.94% and 31.99%, respectively. • CO in the stack gas can be recycled to further improve the conversion and product yield. • A core–shell ZrCuO x @HZSM-5 configuration can improve catalytic stability. Direct synthesis of valuable aromatics, such as xylene from CO 2 hydrogenation is of highly interest for carbon emission reduction and reutilization, but it remains a challenge due to the poor product yield limited by low CO 2 conversion. On the other hand, toluene methylation with methanol suffers from low methylation efficiency due to severe side reactions of methanol. Herein, a tandem catalysis that combines CO 2 methanol synthesis and toluene methylation using CO 2 /H 2 mixture as C1 source with a Zr-modified CuO/HZSM-5 bifunctional catalyst has been evaluated. Introducing Zr provided abundant sites for CO 2 adsorption, more oxygen defects and surface area, thus enhancing the conversion of CO 2 and toluene. The competitive adsorption of CO 2 and toluene on ZrCuO x caused the phase transition of bulk CuO, and further catalytic deactivation. This issue was successfully solved by configuring a core (metal)-shell (zeolite) like composite catalyst to minimize the exposure of toluene on ZrCuO x surface. Toluene conversion rate can reach 45.94% when CO 2 conversion is 31.99%, and the yield of xylene can reach 0.6 g g cat −1 ⋅h −1 . The selective of high value product para-xylene in xylene isomers can get higher than 90 % by silicon coating modification.