Row Transition Metal Sulfides Research Articles

Second row transition metal sulfides for the hydrotreatment of coal derived naphtha III. Removal of individual nitrogen compounds

The disappearance of individual nitrogen compounds is followed during the hydrotreatment of a coal-derived naphtha containing a mixture of nitrogen-, sulfur- and oxygen-containing heteroatom compounds over bulk second row transition metal sulfides. The naphtha contains mainly three types of nitrogen compounds: pyridines, anilines and quinolines. While quinoline is the least reactive of the three simplest compounds in these compound classes, substituted anilines are the compounds most difficult to remove from the naphtha. The presence or absence of an alkyl substituent exerts a strong influence on the reactivity of individual compounds and can over-shadow the differences between compound types. The reactivity patterns of the methyl-substituted pyridines indicate a steric hindrance about the nitrogen atom. The order of reactivity between alkyl-substituted anilines is different over the various sulfides with steric hindrance about the nitrogen atom indicated for only the higher activity catalysts. Except for molybdenum sulfide, the reactivity of quinoline is less than or equal to that of methyl-substituted quinolines. The individual nitrogen compounds do not disappear according to a first order rate expression but indicate strong product inhibition of the reaction rate. The overall removal of nitrogen does not follow simple first, zero or second order kinetics and shows similar kinetic behavior as for the disappearance of individual nitrogen compounds.

Second row transition metal sulfides for the hydrotreatment of coal-derived naphtha II. Removal of individual sulfur compounds

The disappearance of individual sulfur compounds has been investigated during the hydrotreatment (simultaneous removal of sulfur, nitrogen and oxygen) of coal-derived naphtha over each of the bulk second row transition metal sulfides. The sulfur compounds in the naphtha mainly consist of thiols/sulfides, thiophene and substituted thiophenes. Thiols/sulfides are, in general, more easily converted than thiophenic compounds are. Lighter thiols/sulfides are intermediates in the conversion of higher boiling thiols/sulfides or thiophenes. Side chain alkyl CC bond breaking is predominant during the disappearance of thiophenes over the Zr and Nb catalysts while CS bond breaking is predominant over the other catalysts. Thiophenic compounds are hydrogenated prior to desulfurization over the Mo, Ru, Rh and Pd sulfides. Highly substituted thiophenes are the compounds most difficult to convert over the Mo, Ru, Rh and Pd sulfides. The substituted thiophenes exhibit different reactivity trends over molybdenum sulfide, on one hand, and the Group VIII sulfides, on the other, indicating different adsorption modes and surface mechanisms for their conversion over these catalysts. Individual sulfur compounds do not follow first order kinetics and the disappearance rate is limited by product inhibition. The overall removal of sulfur does not follow simple first or second order kinetics since the individual compounds do not react in parallel, independent or first order reactions.

Second row transition metal sulfides for the hydrotreatment of coal-derived naphtha I. Catalyst preparation, characterization and comparison of rate of simultaneous removal of total sulfur, nitrogen and oxygen

Naphtha derived from an Illinois No. 6 coal contains appreciable quantities of sulfur-, nitrogen- and oxygen-containing compounds. The hydrotreatment of this naphtha has been evaluated over unsupported transition metal sulfide catalysts of the second row in the Periodic Table. The catalysts were prepared by a room temperature precipitation reaction. Surface areas, crystalline phase and particle size distributions were determined by Brunauer-Emmet-Teller (BET), X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. A comparison of average particle sizes calculated from these three techniques has enabled the understanding of the morphology of the transition metal sulfides. The catalysts exhibit a so-called volcano plot for the HDS of dibenzothiophene. Similar so-called volcano plots are also exhibited for the simultaneous hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and the hydrodeoxygenation (HDO) of the coal-derived naphtha containing a mixture of heteroatoms. The order of reactivity of the transition metal catalysts is the same for all three of the processes. Ruthenium sulfide (RuS2) is the most active catalyst for HDS, HDN and HDO of the coal-derived naphtha.

Volcano plots, hydrodesulfurization and surface atom pair potentials

It is shown how a new parameter, the pair potential calculated between two adjacent sulfur atoms of a metal sulfide, correlate with the observed rates of the hydrodesulfurization reaction. The differences between the first row transition metal sulfides and their heavier conjeners is due to the different spin states of the metal.

The role of transition metal sulfides in hydrotreatment. III. Acidity, XPS and catalytic activity

Although, recently, most of the research on catalysis has been devoted to hydrotreatment, attention has been paid to hydrodesulfurization (HDS) but very little has been done on hydrodemetallization (HDM). This article is part of a systematic study directed towards defining the role of transition metal sulfides in hydrotreatment reactions [1,2]. We have considered catalysts supported on silica or alumina. Acidity has been evaluated using pyridine as probe molecule. This property can be attributed to the sulfide phase of the catalysts. The alumina supported catalysts were more acid than the silica supported catalysts. Since the acidity might exclusively be of Lewis type, the pattern observed through the first row transition metal sulfides reflects the trend of the electron-aceptor character of these sulfides. The XPS results indicate that catalysts are partially sulfided (at 400°C). At the same time, the results corroborate a better Me-support interaction on alumina than on silica. The HDM and HDS intrinsic activities, using a desalphalted (DAO) Morichal as feed were evaluated normalizing conversion in terms of the surface metal sites per surface area. The intrinsic activity patterns obtained for the first row transition metal sulfides, were very similar to those mentioned of acidity, reaffirming the importance of the electronic structure of the sulfide phase on its catalytic activity.

Hydrodenitrogenation of Decahydroquinoline Over Carbon‐Supported Transition Metal Sulfide Catalysts

AbstractThe catalytic properties of the first, second and third row transition metal sulfides supported on activated carbon (TMS/C) were investigated for the hydrodenitrogenation of decahydroquinoline in micro‐autoclaves at 50 bar total pressure and at 623 K or 653 K. Excluding vanadium sulfide, the first row TMS/C catalysts had very low activity and showed no periodic trend. On the other hand, second and third row TMS/C catalysts were quite active and showed volcano‐type periodic trends, with maxima at Rh and Ir sulfides respectively. These periodic trends were very similar to those observed earlier for the TMS/C catalysts in the hydrodenitrogenation of quinoline and in the hydrodesulfurisation of thiophene.

ChemInform Abstract: Catalysis by Transition Metal Sulfides

As supplies of clean petroleum feedstocks dwindle, industry will be called upon to process and upgrade “dirtier” feedstocks. Feedstocks of this type contain large amounts of sulfur and nitrogen which must be removed for utilization and further processing. Catalysts based on transition metal sulfides are currently used for such processes but fall considerably short of requirements for future use. In spite of the importance of these catalysts, little is understood regarding the general fundamental basis for and origin of their catalytic activity. This paper reports some of our recent studies of the fundamental properties of transition metal sulfide catalysts. The primary effect in the hydrodesulfurization (HDS) of dibenzothiophene by transition metal sulfides is “electronic”, i.e. it is related to the position the metal occupies in the periodic table. This effect, which determines the ability of the transition metal sulfides to catalyze the HDS reaction, varies over three orders of magnitude across the periodic table. The first row transition metal sulfides are relatively inactive, but the second and third row transition metals show maximum activity with Ru and Os. A secondary effect in HDS catalysis by transition metal sulfides is “geometric” in origin.

Catalysis by transition metal sulfides: The relation between calculated electronic trends and HDS activity

Recent measurements of the catalytic activity of a series of transition metal sulfides showed that the ability of a particular sulfide to catalyze the HDS reaction is related to the position of the transition metal in the periodic table (Pecoraro, T. A., and Chianelli, R. R., J. Catal. 67, 430 (1981)). In order to understand the specific origin of these periodic trends in activity, SCF-Xα calculations of the electronic structure of cluster models of the first and second row transition metal sulfides were carried out. The results of these calculations were used to identify several electronic factors which appear to be related to the catalytic activity of the transition metal sulfides. The computed quantities which measure these factors were combined to form an activity parameter for each sulfide. This parameter shows a direct correlation with the catalytic activity of the sulfides. A model for the binding of thiophenic molecules to the surface of the sulfide catalyst is suggested. This model is consistent both with the correlation between bulk electronic structure and catalytic activity of the sulfides and with the ligand properties of thiophene in transition metal complexes.

Carbon ‐ Supported Transition Metal Sulfides

AbstractFirst, second and third row transition metal sulfides ranging from group VI to group VIII c, supported on activated carbon were evaluated for their ability to catalyze the hydrodesulfurization of thiophene at atmospheric pressure. X‐ray photoelectron spectroscopy was used to measure the chemical state and to obtain an indication of the dispersion of the supported sulfide particles. Second and third row elements display volcano curves with catalytic activity varying over more than an order of magnitude and maxima occuring at Rh in the second and Ir in the third row. First row elements show a twin‐shaped pattern with maximum activity located at Cr and Co. The resemblance of these experimental activity trends with those previously reported for unsupported transition metal sulfides demonstrate the advantage of carbon supports in studies on the intrinsic catalytic properties of small sulfide particles. A correlation between the catalytic activity of second and third row elements and the shift in XPS binding energies between metal and metal sulfide phases was found. Superior catalysts have low binding energy shifts and preserve a high degree of metal character under sulfiding conditions.

Study structure of first and second row transition metal sulfides using SCF-SW- Xα cluster calculations

Energy levels and charge distributions for MS 6 ̋ − clusters M = TiNi and ZrPd) have been calculated using the SCF-SW-Xα method. Calculated binding energies for the clusters are compared with corresponding features in the XPS spectra of the metal sulfides. Trends in the energy levels and charge distributions indicate that the bonding in the second row transition metal sulfides is more covalent than in the first row sulfides. This results largely from the increased metal-sulfur d-pπ interactions which occur for the second row transition metals. Trends in the bonding in the metal sulfides are discussed in light of the activity of these materials as hydrodesulfurization catalysts.