Hydrodesulfurization of 4,6-Dimethyldibenzothiophene and the Diesel Oil Fraction on NiMo Catalysts Supported over Proton-Exchanged AlMCM-41 and TiMCM-41 Extrudates

Karolina Jaroszewska,Gérald Djéga-Mariadassou,Jolanta Grzechowiak,Marek Lewandowski,Kinga Góra-Marek

doi:10.3390/catal11091086

Abstract

NiMo catalysts supported on mesoporous MCM-41 type materials shaped with binder were tested for activity in the hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and the diesel fuel fraction (0.92 wt% of sulfur). The aim of the investigation was to evaluate the effect of ion exchange with protons of Al- or Ti-substituted MCM-41 mesoporous supports. The subjected catalytic systems were NiMo/HAlMCM-41 and NiMo/HTiMCM-41, and for comparison purposes NiMo/AlMCM-41 and NiMo/TiMCM-41. The samples were characterized by N2 sorption (at 77 K), XRD, TEM, XPS, SEM and Py–IR. It was found that the functionalization of AlMCM-41 and TiMCM-41 with protons increased the conversion of 4,6-DMDBT and the pseudo-first-order rate constant. Correspondingly, 4,6-DMDBT HDS reactions over the NiMo/HTiMCM-41 catalyst proceeded to a similar extent via hydrogenation and direct desulfurization, whereas over the NiMo/HAlMCM-41 they proceeded mainly via direct desulfurization. Furthermore, the ion-exchanged catalysts displayed two-fold higher efficiency in direct desulfurization than their non-modified counterparts. The NiMo/HTiMCM-41 catalyst exhibited the highest catalytic efficiency in the HDS of 4,6-DMDBT and the diesel oil fraction. The high activity of the NiMo/HTiMCM-41 catalyst is mainly attributed to its appropriate acidity, as well as the metal–support interaction providing both the high dispersion of the active phase and the desirable multilayered stacking morphology of the active phase slabs.

Highlights

Environmental concerns have imposed stricter regulations on vehicle fuels in order to limit harmful emissions like SOx and NOx from exhaust gases
Fluorescence spectroscopy (Phillips PW 1400). This investigation attempted to determine the ways in which the modification of the MCM-41 sieves with Al- or Ti-substitution and proton incorporation affects the properties and activity of NiMo catalysts shaped with a binder
The activity of catalytic systems of NiMo/HAlMCM-41 and NiMo/HTiMCM-41 was compared in the HDS of 4,6dimethyldibenzothiophene (4,6-DMDBT) and diesel fuel with a 0.92 wt% sulfur concentration

Summary

Introduction

Environmental concerns have imposed stricter regulations on vehicle fuels in order to limit harmful emissions like SOx and NOx from exhaust gases. The differences observed in the catalyst performance were attributed to the structure and specific electronic properties of the supported active phases, due to a higher Lewis acidity than the Ti-free samples. The increase in the Lewis acid site concentration (NiMo/HAlMCM-41) or the preservation of this electron-acceptor function (NiMo/AlMCM-41, NiMo/HTiMCM-41, and NiMo/TiMCM41), besides undoubtedly covering the mesopore surface with the metal phase (Table 1), can be ascribed to the presence of highly exposed unsaturated Ni and Mo cations. The spectrum of the reduced NiMo/HTiMCM-41 sample in the Mo 3d region shows the presence of spectral lines at 234.7 and 237.3 eV (Figure 4(Bb)) In both cases, the values of BE are somewhat higher than those usually observed at for stoichiometric MoO3 (232.9 and 236.1 eV) [61], suggesting some interactions of molybdenum species with the support surface. The internal surface of the NiMo/HTiMCM-41 sample is well covered by molybdenum species

Catalytic Performance

Support and Catalyst Preparation

Characterization of Supports and Catalysts

Catalytic Activity Assessment

Findings

Conclusions