Diego Valencia

Effect of citrate addition in NiMo/SBA-15 catalysts on selectivity of DBT hydrodesulfurization

Abstract NiMo catalysts supported on SBA-15 were prepared by coimpregnation and successive impregnation methods with the addition of citric acid in the impregnation solutions. Addition of citric acid resulted in an increase in both catalysts’ activity in dibenzothiophene HDS and selectivity towards the direct desulfurization route, which was due to an increase in the MoS2 dispersion and in the amount of Ni-Mo-S species.

Topological and Electronic Structure of Heterocyclic Compounds Adsorbed on Hydrotreating Catalysts

We studied the electronic structure of the adsorption of S- and N-containing aromatic compounds present in crude oils on MoS2 and WS2 clusters by means of all-electron DFT methods. The aim of this work is to understand results related to the hydrotreating catalyst poisoning by quinoline. We studied the adsorption of the organic compounds by flat (π) and perpendicular (σ) adsorption on each cluster catalyst. The calculated adsorption energies indicated that π-adsorption was more favorable over σ-adsorption. In the σ mode, quinoline presented the largest adsorption energy, which led to understand the poisoning of the catalysts. We performed electron localization function (ELF) studies on the molecules adsorbed on a perpendicular orientation. We showed methyl-substituted compounds had a weaker S-{Mo,W} bond due to steric hindrance. Furthermore, atoms-in-molecules (AIM) calculations at the critical points (i.e. {S,N}-{Mo,W} interfaces) revealed a correlation between electron density and Laplacian of the electron density at this region and the adsorption energy. Ellipticity (ε) studies revealed structural information of binding at these sites, as well as the competition between S- and N-containing compounds. Similarly, ε showed that methyl-containing compounds had a very distinct character than non-substituted ones, thus revealing the importance of steric effects. Analytic tools such as ELF and AIM provide correlations between the experimental observations and properties. We find these studies can be further used to understand other catalytic phenomena.Graphical Abstract.