Pd–WOx heterostructures immobilized by MOFs-derived carbon cage for formic acid dehydrogenation

Abstract

Formic acid (FA), a major product formed in biomass processing and CO2 reduction, has attracted considerable attention as a promising renewable liquid-phase hydrogen carrier. Designing highly efficient catalysts for FA dehydrogenation is a key challenge for fuel cell-based hydrogen economy. Herein, Pd-WOx nano-heterostructures (2.9 nm in diameter) anchored on ZIF-8 @ZIF-67 core-hell MOFs-derived nitrogen-doped porous carbon cage (NPCC) are fabricated for the first time through a phosphate mediation approach. Strong adsorption and dispersion of Pd2+ in the phosphate-modified NPCC are essential for the synthesis of highly dispersed ultrafine Pd nanoparticles. The alkaline solution produced during the subsequent reduction process of metal ions can remove the phosphate. The obtained Pd-WOx/(P)NPCC catalyst presents an extraordinarily catalytic performance (TOF, 2877 h–1 at 303 K and 6135 h–1 at 323 K) with a 100% H2 selectivity and conversion toward FA dehydrogenation. The superior performance of Pd–WOx/(P)NPCC is likely due to the strong interaction effect between Pd-WOx and NPCC; unique structures of Pd-WOx nano-heterostructures; and NPCC with hollow and large surface area and abundant surface defects. Kinetic isotope effect (KIE) measurements demonstrated that cleavage of CH bond is the rate-determining step for HCOOH dehydrogenation. This study provides new insights into a facile and controllable synthesis strategy of inexpensive and efficient catalysts for high-efficiency dehydrogenation of liquid-phase hydrogen carrier.