Hydrodesulfurization NiMo catalysts supported on Co, Ni and B modified Al2O3 from Anderson heteropolymolybdates

AbstractRecent catalysts of hydrodesulfurization (HDS) reaction consist of CoMo and NiMo phase supported on gamma-Al2O3 support. The support was modified with cobalt nitrate, nickel nitrate, or boric acid and high loadings of Anderson type heteropolyoxomolybdate (NH4)3[Ni(OH)6Mo6O18].7H2O were deposited. Surface area (SBET) and sulfide phase dispersion of the catalysts were determined by N2 physisorption and O2 chemisorption, respectively. Samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, infrared and UV-Vis spectrometry, and temperature programmed reduction. The activity of catalyst was measured in HDS of 1-benzothiophene. The preliminary incorporation of Co, Ni and B into the support increased the HDS activity of the deposited NiMo phase. IR and UV-Vis DR data revealed the partial decomposition of the initial Anderson type NiMo complex with a formation of new surface compounds, including heteropolymolybdates and separated polymeric oxomolybdenum compounds. X-ray photoelectron spectroscopy showed that the degree of Mo sulfidation is the smallest for the catalysts prepared over unmodified alumina and boron-modified alumina. The highest degree of sulfidation was found for the catalysts supported over Co-and Ni-modified alumina. The nickel-modified alumina increased the HDS activity and dispersion of the NiMo phase the most, which was associated with the formation of the largest number of active sites

Redox properties of ceria-alumina oxides

A series of xCeO2-Al2O3 samples of different CeO2 loading (x = 1‒12 wt.%) were prepared by impregnation of γ-alumina with aqueous solution of (NH4)3[Ce(NO3)6]. The effect of CeO2 content on the structure, textural and redox properties of xCeO2-Al2O3 samples was studied by using N2 adsorption-desorption isotherms, XRD, and TPR. It was shown that the increase of CeO2 content leads to a decrease in surface area and pore volume of mixed oxides caused by filling the pores with cerium oxide particles. XRD measurements detected an increase of CeO2 average particle size on increasing ceria content. The redox properties of xCeO2-Al2O3 oxides were modified by a consecutive reduction and oxidation treatment, which was more evident for 6- and 12-wt.% CeO2 samples. An enhanced reducibility upon reduction-oxidation treatment of xCeO2-Al2O3 oxides was revealed by formation of a phase of high oxygen mobility reduced at a lower temperature.The authors kindly acknowledge financial support by the Bulgarian Science Fund through project FNI E02/16 as well as by bilateral collaborations of the Institute of Catalysis with Catholic University of Louvain la Neuve (Belgium) and Institute of Catalysis and Petrochemistry, Madrid (Spain).Peer Reviewe

Structure and surface properties of ceria-modified Ni-based catalysts for hydrogen production

Series of Ni catalysts supported on alumina and mixed xCeO2-Al2O3 oxides with different CeO2 content (1–12 wt%) were prepared by impregnation method. The effect of CeO2 loading on the structure and catalytic properties of supported Ni catalysts in dry methane reforming was studied. The texture, structure and surface properties of the catalysts in their calcined, reduced and used state were studied by using different techniques such as: adsorption-desorption isotherms, XRD, UV–vis DRS, XPS, Raman, H2-TPR, EPR, TPO and TEM. Variation in the electronic environments of the cerium and nickel as a function of the CeO2 content and pretreatment was observed for CeO2-containing Ni catalysts. The couples Ni2+/Nio and Ce3+/Ce4+ were detected in the oxidic, reduced and spent ceria-loaded Ni catalysts. CeO2-containing Ni catalysts exhibited higher activity and stability with time on stream relative to that of alumina-supported Ni. The obvious difference in the behaviors of Ni/xCeO2-Al2O3 and Ni/Al2O3 was related to the difference in their dispersions. Small nanoparticles of 4.7–6.3 nm were observed for CeO2-modified catalysts assuring their high activity and resistance to carbon deposition. The highest activity and stability of Ni catalyst with 6 wt.% CeO2 was due to the higher electron density and accessibility of the active sites caused by the close contact between nickel and cerium species. While, Ni/Al2O3 catalyst exhibited low activity and carbon resistant due to the agglomeration of nickel particles up to 20 nm