Showing papers by "Malcolm L. H. Green published in 2014"
TL;DR: The CBC method as discussed by the authors is based on an elementary molecular orbital analysis of the bonding involving the central atom (M), with the various interactions being classified according to the number of electrons that each neutral ligand contributes to the bonding orbital.
Abstract: The Covalent Bond Classification (CBC) method provides a means to classify covalent molecules according to the number and types of bonds that surround an atom of interest. This approach is based on an elementary molecular orbital analysis of the bonding involving the central atom (M), with the various interactions being classified according to the number of electrons that each neutral ligand contributes to the bonding orbital. Thus, with respect to the atom of interest (M), the ligand can contribute either two (L), one (X), or zero (Z) electrons to a bonding orbital. A normal covalent bond is represented as M–X, whereas dative covalent bonds are represented as either M←L or M→Z, according to whether the ligand is the donor (L) or acceptor (Z). A molecule is classified as [MLlXxZz] according to the number of L, X, and Z ligand functions that surround M. Not only does the [MLlXxZz] designation provide a formal classification of a molecule, but it also indicates the electron configuration, the valence, and t...
142 citations
TL;DR: In this paper, the authors examined the performance of a NiMo-urea redox solution deposited on tungsten oxide-modified alumina surface and showed that a subsequent impregnation with NiMourea solution produces an increase of the decomposition period of the metal oxide precursor and urea.
Abstract: The major challenge for deep hydrotreating of diesel fuels is the removal of refractory sulfur-containing compounds and reducing aromatics to meet the stringent environmental regulations. In the present study, the hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatization (HDA) reactions of various real feedstocks over alumina-supported NiMoW catalyst synthesized by impregnation solution-based combustion method have been examined in order to gain insight into the capability of this preparation method to produce deep hydrotreating catalysts. The results show that a single exothermic peak with an ignition temperature of 272 °C decomposes the NiMo-urea redox solution deposited on tungsten oxide-modified alumina surface, a subsequent impregnation with NiMo-urea solution produces an increase of the decomposition period of the metal oxide precursor and urea. Furthermore, the addition of Ni and Mo to WOx-modified alumina facilities the NiO–Mo (or W) Ox interaction and promotes MeOx reducibility. On the other hand, feed with lower density and higher end-boiling point (T95) shows lower HDS reactivity and hence more demanding operating conditions (i.e., high hydrogen pressure, high reaction temperature and low liquid contact time) are required to obtain diesel fuel with low aromatics, high cetane index and ultra low-S and -N concentrations. The strong inhibiting effect of N-containing compounds and weak effect of aromatics over the HDS reactivity of real feedstock is reflected on smaller HDS rate constant than HDN rate constant for γ-alumina-supported NiMo, NiMoW and even CoMo sulfide catalysts. The presence of tungsten in the NiMo catalyst selectively enhances the rates of the HDS reactions compared to the HDN reactions, particularly of refractory S compounds.
51 citations