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

Abstract

Three-dimensional (3D) ordered mesoporous Ag/Co 3 O 4 and K–Ag/Co 3 O 4 catalysts were successfully prepared on the basis of 3D-Co 3 O 4 . 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/Co 3 O 4, provide sufficient active sites for HCHO oxidation reaction. 1.7% K–Ag/Co 3 O 4 has turnover frequencies (TOFs) of 0.22 s –1 at 60 °C and 2.62 s –1 at 100 °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, Co 3+ cations and surface lattice oxygen (O 2– ) species generated by stronger interaction between Ag and Co and anion lattice defects. Ag(111) faces, Co 3+ ions, and O 2– are active species. Combined with TOFs, at low temperature (<80 °C), the HCHO catalytic activity on K–Ag/Co 3 O 4 catalyst largely depends on the surface OH – species at the perimeter of the Ag(111) facets; at relatively high temperature (>80 °C), the surface OH – species are consumed and replaced quickly, and their supplement relies on the migration of O 2– species from 3D-Co 3 O 4 support. The pathway of reaction for HCHO oxidation on the K–Ag/Co 3 O 4 follows the HCHO → CHOO – + OH – → CO 2 + H 2 O route.