ИСТИНА

The series of Ni/Al2O3 catalysts were synthesized by different methods in order to vary the degree of MSI. IMP-series: catalysts were prepared by wet impregnation method from Ni(NO3)2 water solution. CP-series: catalysts were prepared by co-precipitation from Ni(NO3)2 and Al(NO3)3 mixture by NaOH at pH 9. DP-series: catalysts were prepared by depositionprecipitation of Ni from Ni(NO3)2 by urea or ammonia. Catalysts precursors were calcined at different temperatures (110–600°C) and reduced with hydrogen at 330 or 450°C. CD-series: Ni was deposited on the alumina from colloid dispersion of 4-5 nm Ni0 particles. Catalysts were tested in the hydrodechlorination of chlorobenzene (HDC) at 50–350oC in the gas-phase flow type fixed-bed system. Catalysts after calcination, reduction and catalytic tests were studied by N2 physisorption, TEM, SEM, IR, and TPR. The influence of the calcination and reduction parameters on the active sites formation was revealed for the IMP-series. Calcination of the precursor at 400°C and higher temperatures leads to the strong bonding of Ni2+ species to the alumina surface because of the formation of spinel phase. With increasing the nickel content, the fraction of Ni2+ species reducible at temperatures 500–600°С increases. Calcination of the catalyst precursor at temperatures below 300°C leads to the formation of weakly bound Ni2+ species that are reduced to metallic nickel in a hydrogen stream at 300°C. The changes in the surface composition are reflected in the catalytic activity in gas-phase chlorobenzene HDC. Spinel forms of Ni are inactive in this reaction, but they react with hydrogen under the reaction conditions to form Ni0, which results in the increase in catalytic activity. The active sites formed by the reduction of weakly bound Ni2+ species are the most active and stable in chlorobenzene HDC.