Amorphous Ni-Mo-P Alloy Modified Catalytic Hydrogenation Of Nitrobenzene And Aniline

The liquid-phase selective hydrogenation of nitrobenzene (NB) to aniline (AN) isa green synthesis route, and its core is the efficiently selective hydrogenation catalyst.Due to their unique isotropic nature, numerous coordinative unsaturated sites and highactive surface density, most amorphous alloys have better catalytic performance andstronger poison resistance than crystalline alloys. Thus, they have been classified as asort of novel catalytic material, which is not only highly effective, but alsoenvironmental friendly. However, their disadvantages such as small specific surfacearea and poor thermal stability limit their practical application.In this study, Ni-Mo-P amorphous catalysts were prepared by chemical reductionmethod with the assistance of ultrasonic, and the optimal ultrasonic condition wasinvestigated. Then, in order to further develop the thermal stability, layeredcompounds like potassium titanate, bentonite and expanded graphite were used, thendifferent modified Ni-Mo-P amorphous catalysts were prepared byimpregnation-chemical reduction method, respectively. After that, Ni-Mo-P-EGamorphous catalysts with different addition of expanded graphite (EG) were preparedby the method above with the assistance of ultrasonic.Meanwhile, the catalytic performance of the prepared catalysts was investigatedby the selective hydrogenation of nitrobenzene to aniline. Furthermore, the effect ofultrasonic and different layered materials on the structure, thermal stability, surfacearea, pore distribution, reducibility and hydrogen adsorption property, etc. wereresearched by the characterization of X-ray diffraction (XRD), surface area-poredistribution test (BET), thermogravimetric analysis (TG), temperature programmedreduction (TPR), temperature programmed desorption (TPD), scanning electronmicroscope (SEM) and X-ray photoelectron spectroscopy (XPS).The result shows that proper introduction of ultrasonic did not influence theamorphous structure of the catalyst. Besides, the cavatition caused by ultrasonic can greatly improve the specific surface area and disperse the active sites more evenly.After process of25min under the sonication power of70W, the surface area of thecatalyst reached313.5m2/g, and the conversion of NB and selectivity of ANincreased by21.4%and0.3%, respectively. On the contrary, with excessive ultrasonicprocess, the cavatition would cause partial high temperature and result in thecrystallization of fractional amorphous catalyst particles. Thus, the activity decreased.After the modification of different layered materials on Ni-Mo-P amorphouscatalyst, it was found that comparing with potassium titanate and bentonite, expandedgraphite performed better. As Ni-Mo-P amorphous catalyst particles can enter into thelayer and the micro pores of expanded graphite and form a sandwich structure;therefore, the specific surface area can be improved, and more active sites appeared.Owing to this peculiar structure and interacting with layered graphite, the activespecies could be stabilized, then, the thermal stability and activity of the catalystincreased.Moreover，it also indicates that appropriate addition of expanded graphite did notaffect the amorphous structure of the catalyst. However, with the increase of theexpanded graphite content, the activity dropped owing to the decrease of the activespecies on the unit mass of the catalyst, and the difficulty for the reduction of theamorphous alloy particles inside the graphite pores. The research shows that theoptimal addition of EG is8wt%, with the reaction temperature of110℃, hydrogenpressure of1.8MPa and reaction time of90min, the conversion of NB and selectivityof AN reached99.9%, respectively. After cycling use for6times, the conversion ofNB and selectivity ofAN still remained98.2%and98.4%, respectively.Catalytic hydrogenation, especially the selective hydrogenation is an importantchemical process, which requires the development of the catalyst. Therefore, it is anextremely significant project to apply expanded graphite into Ni-Mo-P amorphouscatalyst, which has lower cost and more environmental friendly. Since expandedgraphite is consisted of layered graphene, the excellent electronic conductionperformance of graphene might facilitate the transfer of the electron during the redox reaction. However, it exists a series of process to generate grapheme from expandedgraphite; hence, the synthesis of Ni-Mo-P-EG amorphous catalyst still need to beoptimized, and the modification mechanism need further development as well.