Effect of Chitosan Addition on NiMo/Al2O3 Catalysts for Dibenzothiophene Hydrodesulfurization

Abstract

A series of supported NiMo catalysts were prepared by impregnating ammonium heptamolybdate and nickel nitrate (at 12 and 3 wt% of Mo and Ni, respectively) over chitosan (Chi) modified Al2O3 carrier. Alumina substrate was first impregnated with the organic additive (in acidic aqueous HNO3 solution, given the insolubility of chitosan at neutral pH) at concentrations corresponding to Chi/Ni mol ratios of 0.5, 1 and 2. Lower Mo dispersion in materials prepared over Chi-modified alumina was observed by Raman spectroscopy. Also, in those samples formation of hardly reducible aluminum molybdates (due to acidic conditions used during chitosan deposition) was evidenced by thermal analysis. Sulfided (under H2S/H2 flow, at 400 °C) catalysts were tested in dibenzothiophene hydrodesulfurization (HDS, at 72.4 kg/cm2, 320 °C, batch reactor, n-hexadecane as solvent) where no improved activity (in pseudo first order kinetic constant basis) was registered for chitosan-modified samples. However, increased selectivity to the product from direct desulfurization route (biphenyl) suggested enhanced promotion of MoS2 phase (by Ni) in catalysts prepared with organic additive. CO adsorption at -173 °C (followed by infrared spectroscopy) showed lower concentration of NiMoS active sites over catalysts prepared over chitosan-impregnated alumina carrier pointing out to the existence of highly efficient sites, in spite of their lower surface concentration. The present investigation opens the possibility of using chitosan, a sub-product from seafood industry, as efficient HDS catalyst additive.

Effect of Chitosan on the Performance of NiMoP-Supported Catalysts for the Hydrodesulfurization of Dibenzothiophene

“…Our findings in the present study contrast with those published in a previous report [16] in which sulfided catalysts based on chitosan-modified NiMo supported on alumina did not increase the catalytic activity as compared to corresponding conventional materials with Al 2 O 3 carrier, regardless of the chitosan : Ni ratio used. It is worth mentioning that in those formulations the acid used to dissolve chitosan was HNO 3 and in the present case we used phosphoric one; thus, as mentioned above, phosphorylated chitosan could be formed [35], thereby leading to the formation of nickel complexes, sulfidation of Ni 2+ species being delayed, which accounts for improved DBT HDS.…”

“…In this line, we recently reported the effect of chitosan addition on NiMo/Al 2 O 3 catalysts for dibenzothiophene hydrodesulfurization [16], in which we varied the content of organic agent in various formulations. From that study we observed that the higher the concentration of chitosan, the lower the activity of the studied alumina-supported NiMo catalysts.…”

NiMo/alumina hydrodesulphurization catalyst modified by saccharose: Effect of addition stage of organic modifier

“…For instance, Mazoyer [47] found enhanced activity in both tetralin hydrogenation and 4,6-dimethyl-DBT HDS (about 33 and 48 %, respectively) of CoMo/Al 2 O 3 catalysts impregnated with diethyleneglycol n-butylether. Additionally, increased selectivity to products from the direct desulphuration route (Scheme 2) suggested better promotion of MoS 2 crystals by Co. [48,49] Further, according to Geantet et al, [9] an industrial calcined CoMoP catalyst impregnated with TEG in an aqueous solution increased its HDS activity by more than twice when tested in desulphurization of both 4,6-dimethyl-DBT and real feedstock (straight-run gas oil). Unfortunately, details about the annealing procedure at which these commercial formulations had been submitted were not provided.…”

“…NiMoI and NiMoII sulphided formulations converted DBT exclusively through the direct desulphurization route (Scheme 2) to biphenyl, suggesting good promotion of MoS 2 crystals by nickel. [48,49] The limited HDS activity over the former catalyst could be then related to a low amount of well-promoted sulphided phases which probably originated in decreased active phases dispersion, as evidenced in the corresponding UV-vis spectrum of Figure 7.…”

Efficient CoMoS Catalysts Supported on Bio‐Inspired Polymer Coated Alumina for Hydrotreating Reactions

“…As a result, more Co atoms are available to promote the MoS 2 crystallites formed during sulfidation. Coating the surface of alumina with carbon is another suitable option . Weakening the interaction with the support avoids the formation of catalytically inactive refractory species like CoAl 2 O 4 and Al(OH) 6 Mo 6 O 18 , but may also decrease the dispersion of the active phase.…”