Preparation Of Surface Modified Nano Catalysts And Their Application In Catalytic Reactions

With the continuous development of society,as well as the increasing stringent environmental protection issues,precise synthesis of chemicals under mild conditions and the low emission of process waste are highly desired.Therefore,greater demands are being placed on the excellent performance of catalysts.P-Aminophenol(PAP)and benzaldehyde are extremely important organic compounds.The former is widely used in the pharmaceutical,rubber,dyestuff and other industries to synthesize acetaminophen,rubber antiagers and azo dyes,while benzaldehyde as an intermediate in medicine and dye industry,can be used to produce lauric acid,benzyl benzoate and other chemicals.Also,benzaldehyde is widely used in the production of spices due to its unique smell of almond.Until now,the synthesis routes of these two chemicals in industry have suffered from problems such as complicated reaction process,corrosive and hazardous production and large amount of toxic waste,etc.Previous work of our laboratory has made some pioneering progress in the design of novel catalysts used in the production process.We prepared carbon nitride with underlying nickel as a catalyst in the hydrogenation of nitrobenzene under acidic condition and PAP could be obtained one step with basically zero emission.In addition,for the green synthesis of benzaldehyde we also developed hexadecylphosphate-functionalized iron oxide nanoparticles and realized the exclusive generation of benzaldehyde through oxidation of toluene in a gas-liquid-solid three phase reaction system.Based on the large efforts of our laboratory above,in this paper we studied the performance of cobalt silicides and silicon carbide encapsulated cobalt for selective hydrogenation of nitrobenzene to PAP in sulfuric acid and the influence of electron transfer between semiconductor and metal on the performance of catalysts.Besides,we prepared nano palladium silicides modified with hexadecylphosphate and applied them in the catalytic oxidation’ of toluene to discuss the promotion impact of organic molecules on the selectivity to benzaldehyde.Effect of the silane treatment on the structural stability of catalyst was also studied and some innovative results have been achieved.The contents are summarized as following:(1)The hydrogenation of nitrobenzene in sulfuric acid to produce PAP,an important chemical intermediate involves partial hydrogenation of nitrobenzene to phenylhydroxylamine,followed by in-situ acid catalyzed Bamberger rearrangement.In this work,in order to increase the acid resistance of cobalt,silicon was inserted into the nano crystal structure to form cobalt silicides supported on active carbon.According to our previous work on the semiconductor/metal reverse heterojunction model,we prepared catalysts supported on active carbon with semiconductor SiC and metal Co in SiC/Co/AC.Structural characterization such as X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS)suggests that the electron transfer between SiC and Co enhances the hydrogenation reaction activity and inert SiC protects the catalyst from leaching in sulfuric acid.Catalysts prepared after the optimization showed excellent hydrogenation reaction activity,stability and selectivity to PAP.(2)As an important catalyst support,γ-Al2O3 was reported to be transformed to boehmite in the aqueous reactions,thus leading to the aggregation or loss of active species and reduction of catalyst stability.Our previous work on the catalytic oxidation of toluene in the mircoemulsion system proved that the modification of organic molecules could effectively control the way reactants contact the active sites and improve the selectivity to target product.In this paper,catalysts loaded onγ-Al2O3 with different content of nano metal palladium were prepared.After the silane treatment,the obtained palladium silicides were modified with different content of hexadecylphosphate on the surface to change the hydrophobicity/hydrophilicity and performance of catalysts.When the catalysts were applied in the aqueous oxidation of toluene under neutral condition,we found that proper modification of organic molecules contributed to the enhancement of catalytic performance and higher selectivity to benzaldehyde.Characterization such as X-ray dirraction(XRD)and Fourier Transform Infrared Spectroscopy(FTIR)indicates that silane treatment prevents the formation of boehmite as well as avoids the agglomeration or leaching of active species.Therefore,catalysts exhibited good structural and catalytic stability in the aqueous oxidation of toluene after silane treatment.