Studies On The Nitridation Of Silica Materials And Their Adsorption And Catalytic Properties

In recent decades, mesoporous silica materials have been rapidly developed dueto their high specific surface area and ordered pore structure. These silica materialsplayed a very important role in diverse areas such as catalysis, adsorption and so on.Although properties of these silica materials are stable, silanols groups on the surfaceof silica materials can be modified. Therefore, in order to promote furtherapplications of these materials, many studies have gradually focused on thefunctional treatment of their surface. Some researchers use the direct reaction ofsome metals to replace the silicon atoms, or use grafting method to introduce theorganic functional groups into the surface of silica materials. However, due to thelimitations of numbers of the incorporated atoms and the harsh conditions, themodification of silica materials has been limited. Based on these disadvantages,people tend to directly replace the oxygen atom in the skeleton of the siliconmaterials to achieve the functionalization of the surface of silicon materials.Currently, the most concern is the high-temperature nitriding method. The alkalineproperties by the substitution of N atom for the framework O atom in the siliconmaterials can be used in many fields.In this paper, the silicon oxynitride materials with different nitrogen contentwere prepared through high-temperature nitriding of the as-synthetic sphericalsilicon oxide and mesoporous molecular sieve SBA-15. Then, the nitridedmesoporous molecular sieve SBA-15was used as the support to make the silvercatalysts. The resultant products were systematically characterized by scanningelectron microscopy （SEM）, high-resolution transmission electron microscope（HRTEM）, elemental analysis （CNH）, X-ray photoelectron spectroscopy （XPS） andSi MAS NMR. Finally, spherical silicon oxynitride materials were used for theabsorption of carbon dioxide, and the catalytic activities of the silver catalysts loadedon the nitrided and non-nitrided carriers were evaluated for the CO selectiveoxidation reaction. Related research results are as follows:1. Using the high-temperature nitriding method, the high nitrogen contentsilicon oxynitride were prepared and the highest nitrogen content （mass fraction） wasup to9.48%. The as-syn silicon oxynitride material with the highest nitrogen content（SiO₂-N-1000） was used to study the absorption performance of carbon dioxide.Owing to the introduction of N atom in the silicon oxynitride material, it wasendowed a basic group which possesses the strong force with the acidic gas CO₂. Asa result, the nitrided silica materials exhibited perfect adsorption capacity compared to the non-nitrided silica materials, and the adsorption amount of CO₂increasedfrom3.08×10^-4g/g to6.71×10^-4g/g.2. Using the same high-temperature nitriding method, the mesoporous SBA-15was modified to obtain a series of the carriers with different N content, which wereused as a host to accommodate nano-silver into the channels. Then, the productswere used to the catalytic activity test of the CO selective oxidation reaction.According to the present experimental results, the regularity of nitrogen-incorporatedSBA-15was somehow destroyed due to the heat treatment, but it still maintained thetypical mesoporous structure. Additionally, the nitrogen content incorporated in theframework increased with the nitridation temperature and the silver particles wereuniformly dispersed in the host carrier for the interaction between the nitrogenspecies and silver particles. Therefore, the higher nitrogen content of the products,the higher catalytic activity and selectivity, and when the nitriding temperature was1000℃, the CO conversion of catalyst Ag/SBA-15-N-1000was up to70%or75%.