Ullmann Reaction Of Aqueous Medium Cleaning Efficient Referral Developed Its Catalytic Properties Of The Pore Structure Supported Palladium Catalyst

The green chemistry represents a new and strong trend in chemistry research and chemical engineerings. Green chemistry requires to avoid chemical pollutions from the original source, including the use of non-toxic and safety raw materials and catalysts, the design of clean reaction route, such as to avoid or decrease the use of organic solvents. Obviously, the catalyst plays a key role in realizing green chemistry. The superiority of mesoporous materials are uniform and tailored mesoporous diameter, stable framework, suitable size of wall thickness which is easy for modification owing to the high surface area and the plenty silanol groups on channnel surface. Supported metal catalysts with these mesoporous materials as support exhibit comparable activity and selectivity with their corresponding homogeneous catalysts. But they are more preferable in the industrial application owing to the easy separation and repetitive use. In this paper, pure and modified SiO₂ materials with different mesoporous structure, such as Ph-MCM-41, Ph-SBA-15, NH₂C₃H₆-MCM-41 and Ph-Al-MCM-41 etc., were synthesized by hydrothermal method and co-condention. Based on these supports, supported Pd catalysts were prepared by impregnation or coordination, followed by reduction in H₂/N₂ atmosphere. Their catalytic performances were evaluated by using aqueous iodobenzene Ullmann reactions as the probe, which could be considered as an example in green chemistry since water was used as reaction mediaum instead of traditionally used organic solvents. Based on various characterizations and kinetic studies, the relationship between the catalytic behaviors and structural characters of the as-prepared catalysts was discussed briefly, and the reaction mechanism over these catalysts was investigated. The followings are the details:1. MCM-41, Al-MCM-41, SBA-15 and SBA-12 with ordered hexagonal pore channels and KIT-5, MCM-48, SBA-16 with cubic pore channels have been prepared by hydrothermal method. The supported Pd catalysts with the 2d-hexagonal mesoporous materials as supports exhibited excellent activity and yield of diphenyl during iodobenzene Ullmann reactions in water medium. The introduction of Al...