The role of MgO in the formation of surface active phases of CoMo/Al2O3–MgO catalysts for hydrodesulfurization of dibenzothiophene

Hydrodesulfurization of dibenzothiophene using NiMoWS catalysts supported on Al–Mg and Ti–Mg mixed oxides

In this work, two series of trimetallic NiMoW sulfide catalysts supported on Al–Mg(x) and Ti–Mg(x) mixed oxides with different content of MgO (x = 5, 10, 15 and 20 wt.% of MgO) were synthesized. The mixed oxides and catalysts were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, N2 physisorption and Diffuse reflectance spectroscopy (DRS UV–Vis); and evaluated during the hydrodesulfurization (HDS) of dibenzothiophene (DBT) reaction. The NiMoW/Al–Mg catalysts showed a higher dispersion of Ni, Mo and W species than NiMoW/Ti–Mg catalysts resulting in higher catalytic activities. Catalysts with 10 wt.% of MgO showed the highest catalytic activity for both series of catalysts. Most of the synthesized catalysts exhibited higher activities than NiMoWS/Al–Ti reference catalyst. The present comparison study clearly showed that NiMoW/Al–Mg and NiMoW/Ti–Mg catalyst with 10 wt.% of MgO might be a promising and effective catalyst for the HDS-DBT reaction.

Comparative Study of Strategies for Enhancing the Performance of Co3O4/Al2O3 Catalysts for Lean Methane Combustion

Spinel-type cobalt oxide is a highly active catalyst for oxidation reactions owing to its remarkable redox properties, although it generally exhibits poor mechanical, textural and structural properties. Supporting this material on a porous alumina can significantly improve these characteristics. However, the strong cobalt–alumina interaction leads to the formation of inactive cobalt aluminate, which limits the activity of the resulting catalysts. In this work, three different strategies for enhancing the performance of alumina-supported catalysts are examined: (i) surface protection of the alumina with magnesia prior to the deposition of the cobalt precursor, with the objective of minimizing the cobalt–alumina interaction; (ii) coprecipitation of cobalt along with nickel, with the aim of improving the redox properties of the deposited cobalt and (iii) surface protection of alumina with ceria, to provide both a barrier effect, minimizing the cobalt–alumina interaction, and a redox promoting effect on the deposited cobalt. Among the examined strategies, the addition of ceria (20 wt % Ce) prior to the deposition of cobalt resulted in being highly efficient. This sample was characterized by a notable abundance of both Co3+ and oxygen lattice species, derived from the partial inhibition of cobalt aluminate formation and the insertion of Ce4+ cations into the spinel lattice.

Dibenzothiophene Hydrodesulfurization over P-CoMo on Sol-Gel Alumina Modified by La Addition. Effect of Rare-Earth Content

Alumina-lanthana (La at 1, 3, or 5 wt%) supports were prepared by sol-gel from Al alkoxide sol where La(NO3)3 was added. Annealed (550 °C) xerogels were characterized by N2 physisorption, thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy- energy dispersive spectroscopy (SEM-EDS), CO2-adsorption studied in IR region, Raman and ultraviolet-vis (UV-vis) spectroscopies. The texture of amorphous binary matrices of high La dispersion was adequate to applications in catalysts for middle distillates hydrodesulfurization (HDS). Generally, the amount and strength of surface basic sites increased with La content in solids. Mo (at 2.8 at. nm−2) and Co (at Co/(Co+Mo) = 0.3) were deposited over carriers by one-pot simultaneous impregnation in the presence of PO43− (P2O5/(NiO+MoO3) = 0.2 mass ratio). Calcined (400 °C) Co-Mo-P impregnated precursors had decreased basicity as to that of corresponding carriers, suggesting strong La-deposited species interaction. As La content in carriers increased Mo=O Raman stretching vibrations shifted to lower wave-numbers (949 to 935 cm−1) suggesting octahedral molybdates coordination change to tetrahedral. Although La at the lowest concentration (1 wt%) enhanced dibenzothiophene, HDS (~38% higher as to the Al2O3-supported formulation) desulfurization was significantly diminished at augmented content. Presence of hardly sulfidable tetrahedral Mo originated during impregnation at basic conditions in pores of La-modified carriers seemed to dictate observed behavior. Rare earth content in formulations enhanced selectivity to biphenyl.

Tuning the metal–support interaction in supported K-promoted NiMo catalysts for enhanced selectivity and productivity towards higher alcohols in CO hydrogenation

Ni–KMoS/MMO catalysts were obtained using encapsulated Mo-based precursors to tune metal–support interaction, and enhanced selectivity and productivity towards higher alcohols.