Positive Effects of K+ Ions on Three-Dimensional Mesoporous Ag/Co3O4 Catalyst for HCHO Oxidation

Three-dimensional (3D) ordered mesoporous Ag/Co3O4 and K-Ag/Co3O4 catalysts were successfully prepared on the basis of 3D-Co3O4. All catalysts possess 3D mesoporous structures, which are not affected due to Ag and K addition. Ag nanoparticles, uniformly dispersed and supported on the polycrystalline wall of K-Ag/Co3O4, provide sufficient active sites for HCHO oxidation reaction. 1.7% K-Ag/Co3O4 has turnover frequencies (TOFs) of 0.22 s(-1) at 60 degrees C and 2.62 s(-1) at 100 degrees C, and its HCHO conversion at room temperature is 55% (HCHO 100 ppm and GHSV 30000 h(-1)). The addition of K+ ions obviously promotes the catalytic performance for HCHO oxidation due to surface OH- species provided by K+ ions and more abundant Ag(111) active faces, Co3+ cations and surface lattice oxygen (O2-) species generated by stronger interaction between Ag and Co and anion lattice defects. Ag(111) faces, Co3+ ions, and O2- are active species. Combined with TOFs, at low temperature (<80 degrees C), the HCHO catalytic activity on K-Ag/Co3O4 catalyst largely depends on the surface OH- species at the perimeter of the Ag(111) facets; at relatively high temperature (>80 degrees C), the surface OH- species are consumed and replaced quickly, and their supplement relies on the migration of O2- species from 3D-Co3O4 support. The pathway of reaction for HCHO oxidation on the K-Ag/Co3O4 follows the HCHO -> CHOO- + OH- CO2 + H2O route.