Preparation, Characterization Of Supported Ni₂P Catalysts And Their Catalytic Hydrogenation Activity

Transition metal phosphides have recently been reported as a new class ofhigh-activity hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) catalysts.Among them Ni2P has better HDS and HDN activity. The surface area ofunsupported Ni2P catalysts is rather low (< 1 m2/g). To increase the active surfacearea, the dispersion of Ni2P on a high-surface support is needed. SiO2 is widely usedas support of the Ni2P catalysts. TiO2 is commonly used as support of catalysts. Itcan cause strong interaction with metal, that facilitates disperse of active componentson its surface. Hydrogenation of aromatic hydrocarbons is of permanent interest inthe industrialized world because of toughening of environmental legislation. Inparticular, a high content of aromatics in diesel fuels results not only in lower fuelquality, but also in hazardous emission of exhaust gases. The conventional catalystsfor hydrogenation of aromatic hydrocarbons are sensitive to sulfur-containingcompounds, which leads to their irreversible deactivation. However, Ni2P catalystshave favorable sulfur resistance capability. Therefore, it is much significant thatsupported Ni2P catalysts were used in the hydrogenation reaction of aromatichydrocarbons.In this thesis, the catalytic behaviors of benzene hydrogenation and toluenehydrogenation over the supported Ni2P catalysts were systematically studied.A series of supported Ni2P catalysts on TiO2 were firstly prepared viatemperature-programmed reduction (H2-TPR). The structure characteristics ofsamples have been characterized by means of X-ray powder (XRD), N2 adsorption(BET) and X-ray photoelectron spectroscopy (XPS). Benzene hydrogenation waschosen as a model reaction to investigate the influences of Ni loading, initial Ni/Pmole ratio and precursor reduction conditions on catalytic activity. Results showedthat Ni2P is the main phase on the TiO2 supported catalysts. And there is Ni12P5phase on the Ni2P/TiO2catalysts with higher Ni loading, higher and lower P loadingwhich were prepared under higher final reduction temperature, lower reduction gas i南京工业大学硕士学位论文flow. Ni2P/TiO2 catalysts have high activity with 100% cyclohexane selectivity andexcellent stability in benzene hydrogenation reaction. The preparation factors havegreat effects on the activity of benzene hydrogenation. With the increase of Ni and Ploading, final reduction temperature, reduction time, reduction gas flow or reductiongas composition, the activity of the Ni2P/TiO2 catalyst increased firstly and thendecreased. Benzene conversion reaches a maximum with Ni loading of 12.0%, initialNi/P mole ratio of 1/1.0, final reduction temperature of 750℃, reduction time of 4h,reduction gas flow of 60ml/min and reduction gas composition of 10%H2/90%N2. Incomparison with Ni2P/SiO2, Ni/TiO2, Ni2P/TiO2 catalyst has much better activity andstability in benzene hydrogenation reaction.In addition, the catalytic activity of Ni2P/TiO2 for toluene hydrogenation wasstudied. Results show that the reaction conditions have great effects on the activityof toluene hydrogenation. With the increase of reaction temperature, the reactionactivity increased firstly and then decreased. Toluene conversion reaches a maximumwith reaction temperature of 250℃. With the increase of reaction H2 flow, tolueneconversion decreased. The activity and stability of the Ni2P/TiO2 catalysts are alsoaffected profoundly by Ni loading, P content. With the increase of Ni loading, theactivity of the catalyst increased firstly and then decreased. Toluene conversionreaches a maximum with Ni loading of 12.0%. With the increases of P content, thereaction stability is better, but the steady activity increased firstly and then decreased.Steady toluene conversion reaches a maximum with initial Ni/P mole ratio of 1/1.0.