Controllable Preparation And Co Oxidation Performance Of Highly Dispersed Gold Catalysts

Supported nano-gold catalysts have excellent catalytic performance for CO catalytic oxidation.However,the controllable preparation of highly dispersed nano-gold catalysts has always been a difficulty in this research,and the stability of their catalytic reaction is also a problem that needs to be overcome.In particular,it is more difficult to control the preparation of highly dispersed and active Au catalysts with inert alumina as the carrier.In this paper,a series of Au/MO_x-Al₂O₃ nano-gold catalysts with excellent performance were prepared from the aspects of optimization of catalyst preparation parameters,selection of preparation methods,support surface modification and activation atmosphere treatment.The microstructure,catalytic reaction performance and possible reaction mechanism of the nano-gold catalysts were investigated by XRD,HADDF-STEM,In-situ FTIR,CO infrared ray analyzer and low-temperature dew point instrument,The effects of many factors on the CO catalytic oxidation reaction of nano Au catalyst were explored in order to provide theoretical reference for the preparation of high-performance nano-gold catalyst.The main results are as follows:1.The optimization of the preparation parameters of the catalyst,such as the nature of the support,the feeding sequence in the preparation process,the type of alkali added in the catalyst preparation process,the effect of ammonia immersion,the loading amount of gold and the effect of heat treatment,can significantly improve the activity and reaction stability of Au/Al₂O₃ catalyst.In particular,the pretreatment of Au/Al₂O₃ catalyst with different atmospheres has a significant impact on the catalytic activity trend.2.Compared with the traditional deposition method,the catalyst prepared by the improved one-pot deposition method has better activity and stability by optimizing the feeding sequence and treatment methods of each link of the traditional deposition method.The experimental results show that the influence of the content of doped transition metals on the catalytic performance is not completely positive correlation,and there are different optimal thresholds for different transition metals.Compared with other transition metals,the activity and stability of nano-gold catalyst prepared by Zn O doping are significantly improved.The nano-gold catalyst doped with Zn O does not have the spinel structure produced by traditional deposition precipitation calcination.The nano-gold has smaller particle size and higher dispersion.The main active center is Au⁰,and is more sensitive to the water vapor content in the feed gas.3.The catalytic activity of nano-gold catalysts treated with different activation atmospheres is obviously different.In situ infrared characterization results show that the supplement rate of hydroxyl content on the surface of the catalyst directly affects the different CO oxidation reaction paths.With the catalyst for H₂ reduction,the water vapor in the raw material is involved in the catalytic reaction,and the-oh transportation is a slow reaction as a rate control step.For the catalyst reduced by air,the adsorption of CO reaction gas in the reaction is a slow reaction,which is the rate control step.Different action paths lead to obvious differences in the activity of nano-gold catalysts.This study has certain theoretical significance for adjusting the catalytic performance by adjusting the pretreatment atmosphere and the water vapor content of the reaction feed gas.