Gold-based Core-shell Catalysts For Formaldehyde Catalytic Oxidation

Formaldehyde(HCHO),as one of the most common Volatile Organic Compounds(VOCs)indoors,has become the focus of people's treatment.HCHO is removed by a high-efficiency thermal catalytic oxidation method in this project.Among them,precious metal catalysts,such as gold(Au),are promising in the catalytic oxidation of HCHO.However,Au-based catalysts are easily sintered at high temperatures,so regulation of their structure has gradually attracted attention.In this paper,a series of Au@SiO2 catalysts with core-shell structure were prepared by soft-templated method.By adjusting the number of Au cores and the thickness of SiO2 shell,the structure-activity relationship between Au-based catalysts with core-shell structure and HCHO catalytic performance was first reported;and the reaction mechanism of HCHO on Au-based core-shell catalysts was systematically explored.The main conclusions are as follows:(1)The Au@SiO2 catalysts prepared by soft-templated method were regulated by reducing agents,and the effect of the type of reducing agent on the core-shell structure was studied.It is found that when using the aqueous ammonia as reducing agent to prepare the Au@SiO2 catalyst,the particle size distribution of Au nanoparticles generated by the adjustment of Au colloid stirring temperature and solution pH variable is not uniform,and there are still some structures of SiO2 shell without Au core;When using sodium borohydride as reducing agent is more conducive to the formation of Au cores with smaller particle size and higher dispersion,and the core-shell structure of Au@SiO2 catalyst is more uniform(2)In the process of preparing Au@SiO2 catalyst with sodium borohydride as reducing agent,the Au core morphology and SiO2 shell thickness were controlled by regulating Au colloid concentration and TEOS concentration,so as to further understand the role of core-shell structure in HCHO catalytic oxidation.It is proved that compared with single-core structure and multi-core structure,the coexisting structure of single-core and multi-core can significantly improve the HCHO catalytic performance.In addition,thinner SiO2 shell in Au@SiO2 catalyst makes it easier for HCHO reactant molecules to contact the active Au species,thereby reducing the HCHO complete conversion temperature.(3)Phase analysis was carried out on Au@SiO2 core-shell structure catalyst prepared with sodium borohydride as reducing agent,and it was related to its HCHO catalytic performance The structure-activity relationship results showed that because of the strong metal-support interaction in core-shell structure,Au cores transport electrons to the surface of SiO2 shell which promotes the formation of highly oxidized Au(Au+and Au3+).Moreover,the HCHO activity on Au3+ formed in single-core structure is much better than that of Au+ formed in multi-core structure.(4)The oxidation mechanism of HCHO catalytic oxidation over Au@SiO2 core-shell catalyst was investigated by in-situ infrared technique.It is indicated that in the HCHO adsorption process on Au@SiO2 catalyst,formate and methylene dioxy(DOM)are the main adsorption intermediates.Furthermore,the dissociation rate and form of formate are the key to HCHO complete conversion on Au@SiO2 core-shell catalyst.The catalyst has long-term stability and good development potential in practical application.