Research On Metal Nickel Embedded Porous Carbon Coated Honeycomb Ceramic Monolithic Catalysts

The monolithic catalyst compensates for the defects in the macrostructure of traditional powder and granular catalysts,and exhibits superior performance in multiphase continuous reactions.It is mainly composed of three parts:carrier,coating and active component.At present,the carbon coating obtained by coating with the synthetic polymer is firmly bonded to the carrier,and the porous carbon material is an excellent catalyst carrier.However,in the carbon coated monolithic catalyst prepared by the conventional method,a close relationship cannot be established between the metal active component and the carbon coating.As a result,the carbon-coated monolithic catalyst cannot fully exert its catalytic performance.Based on this,a new preparation method is crucial for carbon-coated monolithic catalysts.In this paper,furfuryl alcohol was used as the carbon source,nickel nitrate hexahydrate was used as the nickel source and added before the polymerization of furfuryl alcohol.After polymerization,a novel nickel embedded porous carbon-coated honeycomb ceramic monolithic catalyst(Ni@C)was obtained by one-step coating,and further prepared catalyst samples with different carbonization temperatures.At the same time,a nickel-supported porous carbon-coated honeycomb ceramic monolithic catalyst(NiO/C)was prepared by moisture impregnation.Then,the prepared catalysts were analyzed by XRF,elemental analysis,TG,Raman spectroscopy,N2-physical adsorption,FT-IR,TPD,TEM,XPS,XRD,TPR and other characterization methods.The effect of carbonization temperature on the physical-chemical properties of the embedded monolith catalyst was studied,and the performance differences between the embedded and supported monolithic catalysts were compared.Finally,the performance of the prepared catalyst was evaluated by the hydrogenation reaction of nitrobenzene and the selective hydrogenation of p-chloronitrobenzene.The reaction was carried out by a fixed bed reactor and adopts the method of gas-liquid multiphase continuous hydrogenation.The study found:In this new Ni@C structure,the extremely uniform nickel particles are uniformly fixed in the porous carbon structure,and the nickel particles migrate and agglomerate only when the porous carbon structure collapses under high temperature conditions.In the Ni@C structure formation process,the nickel precursor first decomposes to form NiO,which is then reduced to Ni~0 metal by the decomposition of the oxygen-containing functional group in the porous carbon structure,and the porous carbon structure can protect the Ni~0 metal from being oxidized by air.It shows that the mosaic structure limits and fixes the growth and migration of nickel particles on the one hand,and on the other hand forms a reducing chemical environment and stabilizes the chemical form of Ni~0.The optimum carbonization temperature is 600°C.However,at the same carbonization temperature,the properties of nickel-supported carbon-coated honeycomb ceramic monolithic catalyst[NiO/C(600)]prepared by traditional impregnation method are exactly the opposite.The size distribution of nickel particles is in a wide range.Meanwhile,nickel particles exist in the form of NiO and can not exist in air after reduction.Therefore,in the catalytic hydrogenation of nitrobenzene,the Ni@C(600)sample showed obvious advantages of activity and stability without pre reduction.Further applied to the selective hydrogenation of p-chloronitrobenzene,the Ni@C(600)sample exhibited high catalytic activity and selectivity,while the NiO/C(600)sample exhibited low catalytic activity and selectivity.At the same time,comparing the supported palladium catalyst[1%-Pd/C(600)],it was found that its catalytic activity was high,but dechlorination was also more serious.Therefore,it can be concluded that the embedded structure not only has the effect of inhibiting dechlorination in the reaction,but also further enhances the activity of the catalyst.In addition,the oxygen-containing functional groups on the surface of the carbon coating also promote its catalytic performance.The reduction of NiO/C(600)samples prior to use will result in a decrease in oxygen-containing functional groups and will not effectively utilize the oxygen-containing functional groups on the surface.Finally,by reducing the metal loading of the embedded catalyst[2.5%-Ni@C(600)],it was found that it still maintained superior performance and the catalytic activity exceeded that of the NiO/C(600)sample.This is also a strong testimony to the fact that the catalytic performance of embedded catalysts is indeed much better than that of conventional supported catalysts.