Advanced 3D Hollow-Out ZnZrO@C Combined with Hierarchical Zeolite for Highly Active and Selective CO Hydrogenation to Aromatics

Herein, we explore a facile "defect-mediated outward contraction" strategy to fabricate three-dimensional (3D) hollow-out ZnZrO@C (HO-ZnZrO@C) materials by carbonizing local defect-engineered multivariate UiO-66(ZnZr) (MTV-UiO-66(ZnZr)). The defects mainly result from geo- metrical substitution of distinct Zn secondary building units for Zr counterparts on MTV-UiO-66 crystals. The as-synthesized HO-ZnZrO@C catalyst possesses rich surface oxygen vacancies on ultrafine ZnZrO nanoparticles, which are confined in robust 3D hierarchical carbon frameworks with open and successive channels. The HO-ZnZrO@C and hierarchical H-ZSM-5 tandem catalyst prepared by powder mixing not only affords a selectivity of aromatics up to 73.1% but also suppresses the CH4 selectivity down to 3.4% at a CO conversion of 35.2%. Particularly, we achieve a record-high space-time yield of 0.302 g g(oxide)(-1) h(-1) for methanol-mediated COx hydrogenation to aromatics with high catalytic stability. The 2,6-di-tert-butyl-pyridine adsorption FT-IR results indicate that the powder mixing mode between HO-ZnZrO@C and H-ZSM-5 decreases the number of external Bronsted acid sites on H-ZSM-5, which is beneficial for selective hydrogenation of intermediates to aromatics. Our strategy might open up an avenue for the rational design of highly open hierarchical nanostructures with targeted functionalities for various advanced applications.