Synthesis, Structure And Catalytic Performance Of Single-Atom Silver Catalysts In The Complete Oxidation Of Formaldehyde

In this thesis, the synthesis, characterizations and complete oxidation of formaldehyde over the single-atom silver catalysts were systematically studied, and the obtained results were as follows:An "anti-Ostwald ripening" method was successfully applied to fabricate the single-atom silver catalysts. The metallic silver nanoparticles were initially supported on the{110} side-facets of a porous Hollandite-type Manganese Oxide (HMO) nanorods, and then diffused onto the HMO top-facet and finally anchored on the (001) facts by a simple thermal process to form catalytically active single-atom silver centers. The anti-Ostwald ripening method was effective for the fabrication of the single-atom silver catalysts, which was confirmed by synchrotron X-ray adsorption and X-ray diffraction spectroscopies.A metal-assisted Mar-van Krevelen mechanism for the oxygen activation over the single-atom silver catalysts in the complete oxidation of formaldehyde was proposed on the basis of various characterization techniques and catalytic activities. The activation of oxygen is often regarded as one of the rate-determining steps in the oxidation of formaldehyde. At the temperatures below 65℃ (T< 65℃), the oxygen atoms in the vicinity of single silver atoms participated in the oxidation reaction of formaldehyde, concomitant with the formation of oxygen defects, which were replenished by the gaseous oxygen to complete the cycle of the oxidation reaction. At the temperatures above 65℃ (T> 65℃), both oxygen at the perimeter of silver atoms and the neighboring oxygen around silver atoms could be involved in the complete oxidation of formaldehyde. Thus, the temperature-dependent metal-assisted Mars-van Krevelen oxygen activation mechanism was established for the complete oxidation of formaldehyde.The relationship between electronic density of states and catalytic activity of the single-atom catalysts in the complete oxidation of formaldehyde was established by using the difference X-ray absorption near-edge structure spectra. The results revealed that the density of states of the silver atoms of the single-atom catalysts was much closer to the Femi level than metallic silver nanoparticles or isolated silver atoms. The hybridization between oxygen and silver atoms led to the frontier d orbitals of silver catalytic sites with partial vacancy, which accelerated the oxidation of formaldehyde at low temperatures.The research results in the thesis have a potential application in controlling the emissions of volatile organic compounds such as formaldehyde.