Study Of Ruthenium Catalysts Based On Graphite For Ammonia Synthesis

For the ruthenium based ammonia synthesis catalyst, the graphitized carbon as a support has significant advantages. Activated carbon catalyst carrier methanation reaction occurs under the high temperature and high pressure, affecting the stability of the catalyst. Therefore, this paper attempts to explore influence of graphite on Ru catalysts. Pure graphite used as a support to study the activity and stability of catalyst support on graphite. and a series of characterization methods, such as H2-TPR, H2-TPD, N2-TPD, N2 physical adsorption, MS, GS; SEM, TEM, Raman are used to analyzes the influence of different modified means and additives on the stability and activity of the catalyst. Research the influence of the promoters and heat treatment on the activity of catalyst supported on HSAG, explore the role of the surface chemical properties of high surface area graphite in catalyst stability. This paper also made a preliminary exploration on preparation method of high surface area graphite and its application in ammonia synthesis catalyst. The main findings are as follows:Graphite magnesium oxide composite support prepared by the composite method, although the surface area and pore volume of the composite are smaller than the pure Magnesium Oxide, the activity of catalyst is high than the catalyst supported on the pure graphite and pure Magnesium Oxide. The reasons are as follows:composite support has strong alkalinity position, what’s more, the conductive graphite in the composite support is able to transfer electron. The research indicated that, the optimal quantity ratio of the graphite and the magnesia is 0.5:1. The roasting temperature can affect the alkalinity of the support, the higher the roasting temperature the stronger the alkalinity of the support, but higher temperatures will affect the physical properties of the support.Using commercial high surface area graphite HSAG300 (hereinafter referred to as HSAG) as a support, investigate how the promoter and Ruthenium precursor affect the activity of catalyst, promoter potassium and barium have different performance on catalytic, barium-promoted Ru/HSAG as long as 1wt% to achieve the best activity, 4wt% is required for potassium. Study of barium potassium double-promoted catalyst, the activity of catalyst changes with the content of barium in double promoters.Using heat treatment to change HSAG surface chemical properties, heat treatment in an inert atmosphere can remove the functional groups containing oxygen on the surface of HSAG, and nitric acid reflux will improve the functional groups containing oxygen, studied the effect of surface chemical properties on activity and stability. HSAG on catalyst activity after different heat treatments have little effect, but the higher processing temperature, improves stability of the catalyst.Magnetic grinding and ball grinding are used to prepare HSAG. In the magnetic grinding method, the magnetic grinding time and the ratio of graphite and magnetic needle were investigated. HSAG prepared by magnetic grinding method has a large surface area than commercial HSAG. After magnetic grinding processing, the oxygen-containing functional groups of graphite surface have become more abundant, the surface area of HSAG prepared by ball grinding is not obvious, but the activity of the catalyst have significantly improved. The high temperature treatment had little effect on the activity of the catalyst, but the stability of the catalyst improved. The activity of the catalyst increased after oxidation treatment of HSAG, its stability is reduced.