A Novel Redox Precipitation to Synthesize Au-Doped α-MnO₂ with High Dispersion toward Low-Temperature Oxidation of Formaldehyde

Abstract

A novel method of redox precipitation was applied for the first time to synthesize a Au-doped α-MnO catalyst with high dispersion of the Au species. Au nanoparticles (NPs) can be downsized into approximate single atoms by this method, thereby realizing highly efficient utilization of Au element as well as satisfying low-temperature oxidation of formaldehyde (HCHO). Under catalysis of the optimal 0.25% Au/α-MnO catalyst, a polluted stream containing 500 ppm HCHO can be completely cleaned at 75 °C with the condition of a weight hourly space velocity (WHSV) of 60000 mL/(g h). Meanwhile, the catalyst retains good activity for removal of low-concentration HCHO (about 1 ppm) at ambient temperature with a high WHSV, and exhibits a high tolerance to water and long-term stability. Our characterization of Au/α-MnO and catalytic performance tests clearly demonstrate that the proper amount of Au doping facilitates formation of surface vacancy oxygen, lattice oxygen, and charged Au species as an active site, which are all beneficial to catalytic oxidation of HCHO. The oxidation of HCHO over Au-doped α-MnO catalyst obeys the Mars-van Krevelen mechanism as evidenced by in situ diffuse reflectance infrared Fourier transform spectroscopy.

3D Gold‐Modified Cerium and Cobalt Oxide Catalyst on a Graphene Aerogel for Highly Efficient Catalytic Formaldehyde Oxidation

“…Oxide‐supported noble metal catalysts are reasonably efficient at HCHO removal . Various oxide‐supported noble metals have been used as catalysts for HCHO oxidation, such as Pd/CeO 2 , Au/MnO 2 , Au/TiO 2 , Au/Co 3 O 4 ‐CeO 2 , Pd‐Mn/Al 2 O 3 , Ag/SiO 2 , and Au/ZrO 2 . Some transition metal oxides (Fe 2 O 3 , Co 3 O 4 , and MnO 2 ) and rare earth or composite oxides (CeO 2 and LaFeO 3 ) have also been investigated for catalytic oxidation of HCHO .…”

Single-atom site catalysts for environmental catalysis

“…Thus, methods of eliminating HCHO are vital for the environment and human health, and catalytic oxidation of HCHO is an efficient and promising approach to solve these issues. Note that the majority of studies have currently focused on K [136], Na [57], Ag [49], Au [137] and Pt [138][139][140] based SACs for HCHO catalytic oxidation.…”

“…Supported Au catalysts have been regarded as excellent catalysts for catalytic oxidations since Haruta et al discovered its excellent CO oxidation activity at temperatures far below 0 o C [142]. Jia and coworkers successfully synthesized Au1/MnO2 and Au1/CeO2 SAC by redox etching precipitation and noticed that these materials could trap Au atoms in in-situ generated holes over metal oxides supports during redox reactions between the supports and H2O2 [137,143]. Besides, the synergy between Au atoms and metal oxides supports could liberate more surface oxygen vacancies, promoting the activation of oxygen species and improving low-temperature catalytic oxidation activity of HCHO.…”

“…This, in turn, enhanced electron transfer between the active atoms and oxygen species, and improved the activation of oxygen. By contrast to conventional and metal-assisted MvK mechanisms, OH-assisted MvK and L-H synergy MvK have been proposed for HCHO oxidation over Au1/CeO2 and Au1/MnO2, respectively [137,143]. For Au1/CeO2, HCHO was firstly activated by the surficial OH group and then oxidized by lattice oxygen following OH groupassisted MvK mechanism [143].…”

“…For Au1/CeO2, HCHO was firstly activated by the surficial OH group and then oxidized by lattice oxygen following OH groupassisted MvK mechanism [143]. However, two mechanistic routes (L-H and MvK) occurred simultaneously over Au1/MnO2, activating HCHO through by lattice oxygen species and gaseous O2 [137]. The proposed different mechanisms suggested that surface lattice oxygen species at the metal/oxide interface could be activated by single metal atoms, thereby improving the catalytic oxidation of HCHO.…”