Oxidation Of Cyclohexane Catalyzed By Two Kind Of Novel 2D Nano-materials Based On Nano Silver Modification

Catalytic oxidation of cyclohexane(CyH)to a mixture of cyclohexanone and cyclohexanol(KA oil)is one of the most important reaction in chemical industry.Despite extensive development efforts on developing novel catalyst and new process arrangement have been made,current commercial processes are still desirable to further decrease the economic and environmental costs in the oxidation procedures.We think that this problem is mainly resulted by the environmental differences of the active sites inside the catalyst and deep oxidation caused by harsh reaction conditions.Ultrathin two-dimensional(2D)nanostructure is considered as promising catalysts highly,due to their large surface-to-volume ratio,homogeneous catalytic environment and limited thickness on the atomic scale.On the other hand,metallic silver nanocrystal is utilized to some catalytic oxidation reactions with enhanced activity and known for its unique surface plasmon resonance(SPR)effect,which could dramatically enhance the absorption of visible light and provide new opportunities for developing high-performance photocatalysts.By the concept of combining with the advantage of ultrathin 2D nanostructures and silver nanocrystal,a series of catalysts based on graphene oxide(GO),WO3 nanosheets(WO3 NSs)and Ag nanocrystal have been prepared and applied for mild-condition oxidation of cyclohexane.The structure-activity relationship and reaction mechanism catalyzed by the above catalysts were systematically studied.The main research scope was carried out as following:1.The catalytic properties of metal-free functionalized GO in the selective oxidation of cyclohexane was investigated to understand the effects of structure,functional groups and oxygen-containing groups.Both GO sheets and nano graphene oxide(NGO)sheets possessed high cyclohexane conversions of 16.7%and 17.7%comparable to that of metal catalysts in the aerobic oxidation of cyclohexane.The higher catalytic activity of NGO sheets was caused by the smaller size and the higher content of-COOH.Within the oxygen-containing groups,the carboxylic acid groups on the surfaces of GO are supposed as the active site for the generation of ·O2-radical,which was the active oxygen species in this catalytic oxidation process.2.The catalytic properties of GO-Ag nanocrystals were investigated to understand the effects of the size and morphology in the selective oxidation of cyclohexane.The GO-Ag nanoparticle composites(GO-Ag NPs)with smaller size showed higher catalytic activity than those with bigger Ag nanoparticles,while GO-Ag nanorod composites(GO-Ag NRs)perform better catalytic property than GO-Ag NPs.The highest cyclohexane conversion of 37.0%with the selectivity of 94.0%to KA oil was obtained by using the photocatalysts of GO-Ag NRs under solar light irradiation at room temperature.The higher catalytic activity of GO-Ag NRs was caused by the stronger SPR effect of Ag NRs,and its facilitated generation of ·OH radicals.Both GO-Ag NPs and GO-Ag NRs possessed great durability without evident decline of conversion efficiency and selectivity after five repeated consecutive runs.3.The photocatalytic properties of Ag NPs coupled with tungsten oxide(WO3)nanocrystals were investigated to understand structural effects of the WO3 nanocrystals in selective oxidation of cyclohexane.The photocatalytic activity of monolayer hydrated WO3 nanosheet-Ag nanoparticle composites(WO3 NSs-Ag NPs)was 1.3 times higher than that of WO3 nanocube-Ag nanoparticle composites(WO3 NCs-Ag NPs).The highest cyclohexane conversion of 40.2%with KA oil selectivity of 97.0%was achieved by the photocatalyst of WO3 NSs-Ag NPs under solar-light irradiation at room temperature.The WO3 NSs-Ag NPs showed good photocatalytic stability without evident decline of catalytic activity after ten cycles.The improved photocatalytic activity in the oxidation of cyclohexane by WO3 NSs-Ag NPs was mainly due to the facilitated generation of high-reactive hydroxyl radical(·OH),which was caused by the enhanced light absorption by SPR effect of Ag NPs,and the effective charge transfer on the surface of WO3 monolayer structure.4.The catalytic properties of graphene oxide-Fe3O4 nanopaticles composites(GO-Fe3O4 NPs),GO-Ag NPs and WO3 NSs-Ag NPs were investigated to understand the differences in catalytic mechanism between ordinary transition metal NPs and noble metal NPs in the wet air oxidation of cyclohexane,which was of great importance for the catalysts design in photothermal heterogeneous oxidation of cyclohexane.Meanwhile,The comparative experiments among thermal and photothermal catalysis indicated that:(a)The conversion was facilitated by temperature rise,but high temperature caused less than 50%of selectivity to KA oil;(b)The photothermal form could decline the reaction conditions markedly comparing to the thermal catalysis,and the selectivity of KA oil was nearly 100%due to the controllable generation of reactive oxide species as well as the mild conditions.In the case,cyclohexane conversion of 8.2%with KA oil selectivity of 98.1%was obtained by WO3 NSs-Ag NPs in the photothermal oxidation of cyclohexane.And WO3 NSs-Ag NPs also showed great durability without evident decline of conversion efficiency and selectivity after five repeated consecutive runs.The concept of photothermal cooperation for partial oxidation of saturated C-H in this work may pave a way for the development of high-performance catalysts and green chemical production processes.