Preparation, Characterization And Aromatic Hydrogenation Of Highly Active Nickel Supported On Montmorillonite Catalyst

Montmorillonite (MMT), a kind of layered aluminosilicate clay with theexcellent properties such as swelling, cation exchangeable, water absorption andadsorption, is extensively utilized in the field of catalyst industry. In this paper, theMMT was pretreated with acid, alkali and organic pillared, then Ni supported on thepretreated MMT catalysts were prepared. The performances of the different catalystsare evaluated by the micro autoclave reaction tests for hydrogenation of naphthalene.The catalysts were also characterized by N2adsorption (BET), X-ray diffraction(XRD), H2-TPD, FT-IR, UV-DRS and so on. The effects of the different treatments onthe specific surface area, pore structure, dispersion and the performance of Ni/MMTcatalysts were studied. Since transition metal phosphide had shown superior activitiesfor hydrodesulfurization and hydrodenitrogenation performance, transition metalphosphide was expected to become a new efficient hydrotreating catalyst for oilprocessing. The supported and unsupported nickel phosphide catalysts were alsoprepared using nickel metal as precursor by thermal decomposition of phosphate.The hydrogenation performances of nickel phosphide and nickel catalyst werecompared by hydrogenation of naphthalene with and without sulfur in the feed. Theresults show that:The performances of Ni/MMT catalysts were improved by pretreatment of MMTwith both sulfuric acid and acetic acid for hydrogenation of naphthalene. But thereasons for improvement of the catalyst pretreated with sulfuric acid and acetic acidwere different. Acetic acid treatment did not destroy the layered structure of MMT butincreased layer spacing, which was in favor of the nickel component into theinterlayer to improve the dispersion and hydrogenation performance of the catalyst.Sulfuric acid treatment destroyed the layered structure of MMT and the single chipcould be separated from the layered structure of MMT. Then the specific surface area,pore volume, dispersion and hydrogenation performance of the catalyst was enhancedgreatly. The hydrogenation activity of Ni/MMT catalyst pretreated with3M sulfuricacid was the highest, and was equal to that of Ni/SBA-15. The Ni/MMT prepared byliquid phase deposition-precipitation method showed even more excellentperformance of hydrogenation than Ni/SBA-15.The effects of the pretreatment with NaOH and ammonia water on theperformances of Ni/MMT were different. The specific surface, pore structure anddispersion of Ni/MMT were not improved, and the hydrogenation performance of Ni/MMT even declined as MMT being pretreated with NaOH. Ammonia treatmentdid not affect the layered structure of MMT interlayer. Ammonium ion was notintroduced into the interlayers of MMT yet. The specific surface area, pore volumeand dispersion of Ni/MMT catalyst pretreated by ammonia water were improvedmarkedly. Hydrogenation activity of the catalyst was also improved greatly. The effectand preparation efficiency for treatment of ammonia water were improved greatly bymicrowave.MMT pretreated with hexadecyl trimethyl ammonium bromide (CTAB)increased the interlayer spacing, which was in favor of nickel nitrate into theinterlayer of MMT. CTAB-pillared structure can form complexes with nickel ion andisolated nickel ion. It had a very good role in promoting the dispersion of nickelnitrate and Ni/MMT catalyst. At the same time, the particles of metal nickel interlayerof MMT, which not only can greatly increase the specific surface area of the catalyst,but also can form new porous structure. The pore volume of catalyst also increased,pore structure did not contain micropores substantially, which was in favor of masstransfer of naphthalene reactants and hydrogenation products. The hydrogenationactivity of Ni/MMT catalyst was significantly improved. The specific surface area,pore volume of Al2O3-pillared MMT also increased, but the pore structure contains acertain microporous. After supported nickel, though the dispersion of catalystincreased, some microporous were blocked by metal nickel, compared with the carrier,the specific surface area and micropore volume of the catalyst decreased significantly.Compared with the untreated catalyst in hydrogenation, Al2O3-pillared MMTsupported metal nickel catalysts can improve the naphthalene hydrogenationactivities,but the increase was far less than the CTAB-pillared catalyst.Metal nickel as nickel precursor to preparing nickel phosphide catalyst withhypophosphite thermal decomposition method, the reaction atmosphere、phosphorusnickel molar ratio、reaction temperature and time had important effects on thepreparation of nickel phosphide. It was suitable in argon or vacuum conditions, but thehydrogen atmosphere was not conducive to generate nickel phosphide. The optimalpreparation conditions prepared for unsupported nickel phosphide was that: Aratmosphere, P/Ni=3.0,250℃,1h.Unsupported nickel phosphide can also be preparedby nickel chloride precursor in this way, but the nickel oxide precursor was notsuitable. With metallic nickel and nickel chloride as precursor under this condition,Ni2P/MCM-41, Ni2P/MMT-CTAB and Ni2P/γ-Al2O3were successfully prepared. The hydrogenation results showed that：when the reaction system without sulfide,hydrogenation properties of metal nickel catalyst was better than that of nickelphosphide catalyst, but when the reaction system exist sulfide, the activity of metalnickel catalyst was decreased greatly, but the activity of nickel phosphide catalystdecrease was not obvious and it showed higher hydrogenation activity than the metalnickel catalyst. This suggested that the nickel phosphide catalyst had highperformance of resistance to sulfur poisoning.