| Alcohols oxidation is of great importance in industrial applications, the products such as aldehyde or ketone are widely used in pharmaceutical, food, and perfume industries. Traditional methods based on oxidants, such as dichromate, potassium permanganate, manganese are expensive, polluting and solvent generous. In the last decade, it is a hotspot that greener and more effective reaction system such as liquid-phase oxidation or gas-phase oxidation adopts molecular oxygen or hydrogen peroxide as oxidant. So the investigation of alcohols oxidation is not only important in green chemistry but also industrial applications.The cheap, high active and high stable heteropoly acid is widely used in catalytic systems (homogeneous and heterogeneous systems), the acidity and oxidability of which could be regulated based on the element. Pd based catalyst is relatively cheaper among the noble metal catalysts. In the homogeneous system, the separation process of heteropoly acid and product is tedious. Graphene supported semi-heterogeneous heteropoly acid may solve separation problem. We have prepared the heterogeneous catalysts which adopt heteropoly acid and Pd as active sites and applied them into alcohols oxidation reaction in order to investigate their catalytic ability and structure-activity relationship. We adopt XRD to characterize crystal structure, TEM and SEM to characterize surface morphology, XPS to track the evolution behavior in the reaction. We have solved the problems, such as the structure of the catalysts, catalytic pathway, deactivation mechanism using control experiments and characterization methods (XRD, TEM, SEM, XPS, etc.). The concrete contents are as follows:1. Preparation, characterization of heteropoly acid/graphene oxide catalyst and its applications in the oxidation of benzyl alcoholThe novel carbon material graphene have been widely used industrial applications. We have prepared heteropoly acid/graphene oxide catalyst and applied it in alcohol oxidation reaction. The amount of graphene oxide is reduced because it is catalyst support other than oxidant. Compared with HPW/AC and HPW/RGO catalyst, the selectivity of aldehyde is much higher. We have investigated the effect of HPW content, reaction time and reaction temperature on the activity of the catalyst. XRD and Raman testify that charge transfer effect between HPW and APTES modified GO is obvious and HPW disperse on the support randomly. XPS and ICP testify that the deactivation is obvious because of the loss of HPW species, which is caused by the abscission of sp3 carbon in the reaction conditions. The possible catalytic pathway is: that the peroxide which is formed between H2O2 and HPW catalyze benzyl alcohol to benzaldehyde uner reaction conditions.2. Preparation, characterization of sulfur modified SBA-15 supported amphorous Pd catalyst and its applications in the oxidation of benzyl alcoholCompared with Au, Pt and Ru, the selectivity of aldehyde or ketone in alcohol oxidation is much higher using Pd based catalyst. However, the small Pd nanoparticles are liable to sinter and loss from support. The sintering problem could be solved using amorphous catalyst and the loss of active sites could be settled using N or S modified supports. We have prepared sulfur modified SBA-15 supported amphorous Pd catalysts and applied them in the oxidation of alcohols (aliphatic and aromatic alcohols). TEM, XRD and SEAD indicate that Pd is amorphous, which is not leached from the support as testified by ICP test. For the catalyst SBA-15SCCSPd and SBA-15SCCCSPd, the activity is much lower after 2 times use due to the reconstruction of Pd species, which is elucidated by XPS. For SBA-15SSPd, the activity is excellent and the Pd species is not reconstructed. The reaction pathway is confirmed by control experiments, XPS results and isotope experiment. Pd dimer which is formed between catalyst and molecular oxygen dissociate and aldehyde is formed. The cycle is accomplished because of the formation of the dimer between dissociated intermediate, base and molecular oxygen.3. Preparation, characterization of Pd/TiO2 and its application in gas phase alcohol oxidation reactionThe catalytic activity of amorphous Pd is excellent in alcohol oxidation reaction. However, the catalytic efficiency is low, which is a disadvantage in industrial applications. Anti-sintered large size Pd NPs is of great importance in catalytic applications. Anti-sintered Pd/TiO2 is prepared and applied into alcohols (aliphatic and aromatic alcohols) oxidation reaction. The particle size is 15 nm and Pd/TiO2-DP exhibits excellent activity compared with Pd/TiO2-IWI and Pd/TiO2-HDP. The particle size, textual properties and BET surface area of this series of the catalyst are close to each other, which are confirmed by XRD, TEM and BET. For Pd/TiO2-DP after use, Pd2+ reconstructs to Pd0 and the catalytic activity is nearly unchanged.4. Preparation, characterization of CuPd-Cu2O/Ti-powder catalyst and its application in gas phase alcohol oxidation reactionFor liquid phase oxidation of alcohols, the catalytic efficiency is low and the separation of catalyst and product is tedious. Cu based catalysts are widely used in alcohol oxidation, however, deactivation is inevitable. The catalyst-bed-temperature could be reduced in the gas phase oxidation of alcohols using metal supports. Hence, we have prepared CuPd-Cu2O/Ti-powder catalyst and applied it into alcohols (aliphatic and aromatic alcohols) oxidation reaction. The synergic effect between Cu and Pd is also investigated. The weight hourly space velocity is 20 h-1 and the heat-transfer effect is excellent using our catalyst. The active CuPd (alloy)-Cu2O site formed during reaction condition contributes to its activity and stability. The possible catalytic mechanism is catalytic dehydrogenation cycle and active Cu2O is stabilized by CuPd alloy. |
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