Research On Catalytic Stability Of In-Situ Liquid Htdrogenation

The in situ liquid phase catalytic hydrogenation was proposed by our group in2004, which is a new liquid phase hydrogenation without using extra H2source. The hydrogen atoms produced from the aqueous phase reforming of oxygenated hydrocarbons are used directly for the hydrogenation of halogenated nitro compounds, obviating the difficulty associated with the necessity of molecular hydrogen in liquid catalytic hydrogenation and overcoming the limit of low atomic utilization in the hydrogen-transfer reaction system.Halogenated anilines are important intermediates for the synthesis of fine chemicals like pesticides, rubbers and herbicide. The hydrogenation of halogenated aromatic nitro compound for the synthesis of anilines usually use metal catalysts, such as Pt、Pdd、Ru and Ni based supported catalyst. However, different metal based catalysts usually accompany with some drawbacks. In this dissertation, we have compared different metal based catalyst and emphasis the catalytic performance of them to the in situ liquid phase hydrogenation. However, for the purpose of industrial application, some in-depth studies on the catalytic stability were conducted in our programme.This dissertation mainly discuss the effects of reaction conditions on the in situ liquid catalytic hydrogenation, and we have investigated the effect of different synthetic factors on the catalytic performance. Reasons for the catalyst deactivation were studied, meanwhile, we have synthesized the desired catalyst with long lifespan and proposed several ways to regenerate the deactivated catalyst. By means of the study on the stability of in-situ liquid hydrogenation, we could improve their performance for industrial application, therefore creating great economic、 social and environmental benefits. The detailed points of this dissertation are listed as follows.1. The Ni、Co、Ru-based mono or bimetallic supported catalysts were synthesized by impregnation method and the Pt-based assembled catalyst were prepared by adsorption method, which were all applied in the in situ liquid catalytic hydrogenation of halogenated nitrobenzene to yield the corresponding aniline. The research results indicated that nickle or cobalt based supported catalysts exhibited relatively lower catalytic performance, with27.7%conversion of3,4-dichloronitrobenzene, while the catalytic activity and selectivity to3,4-dichloroaniline could reach100%and96.7%respectively using ruthenium as the active component. Meanwhile, the Ru-based catalyst exhibited lower activity when the liquid space velocity is higher, but the assembled Pt-Sn/γ-Al2O3catalyst could sustain high activity under the same conditions. The main byproducts were N-ethylidine-3,4-dichloroaniline、N-ethyl-3,4-dichloro-aniline、9,10-di-chloro-2-methylquinoline and9,10-dichloro-2-methyl-tetrahydroquinoline. The interconnection between different catalysts and their properties were systematically observed from the view of reaction mechanism and reaction condition.2. The Ru-Fe/y-Al2O3bimetallic catalysts were prepared by impregnation method and applied in the in-situ liquid catalytic hydrogenation of3,4-dichloronitrobenzene to yield3,4-dichloroaniline. The conversion and selectivity could reach100%and96.4%respectively, and the catalytic stability was significantly influenced by Fe content and could reach200h without obvious deactivation by controlling Ru and Fe content of2(wt)%and6(wt)%. The reforming of ethanol usually accompanies with the formation of CO and would cause catalyst deactivation, and the deactivated catalyst could be regenerated by Water-Gas-Shift (WGS) reaction and Fischer-Tropsch Synthesis (FTS) reaction, which employed Fe3O4promoted Ru/Al2O3as catalyst due to its high efficiency of CO transformation, thus enhance the quantity of active hydrogen atoms and increase the efficiency of-NO2hydrogenation.3. The Ru-Fe/γ-Al2O3catalyst were systematically characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), fourier transform infrared (FT-IR) spectroscopy, N2adsorption-desorption (BET) and X-ray photoelectron spectroscopy (XPS) with regard to the properties of nanoparticle size and distribution, metallic crystalline constitution, surface structure parameters and adsorption species, the results indicated that carbon deposition on the catalyst surface is the reason second to carbon monoxide poisoning, we used calcination to eliminate the carbon, and clear the absorbed CO through ethanol/water flushing and hydrogen reduction under high temperatures, the activity of regenerated Ru-Fe/γ-Al2O3catalyst could reach the pre-reaction level. Crystalline phase change、nanoparticle aggregation、 change of surface structure and loss of metal components may cause partial deactivation, while the reasons for deactivation and ways of regeneration are in progress.In conclusion, aromatic nitro compounds could be reduced to corresponding anilines with excellent activity and selectivity in the in situ liquid catalytic hydrogenation, and the lifespan could be prolonged by additive modification or catalyst reactivation. The in situ liquid catalytic hydrogenation shows higher atomic utilization, simple production process and has lower harm to the environment, which opens a new field in the liquid catalytic hydrogenation and shows wide applications in industry.