Mohan S. Rana

Mixed oxide supported hydrodesulfurization catalysts—a review

Abstract Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al 2 O 3 containing mixed oxide supports, TiO 2 containing mixed oxide supports, ZrO 2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO 2 containing mixed oxides received maximum attention, especially TiO 2 –Al 2 O 3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication.

Characterization and evaluation of ZrO2 supported hydrotreating catalysts

A series of zirconia supported molybdenum catalysts were prepared and characterized by BETSA, XRD, TPR, FTIR, XPS and oxygen chemisorption. Thiophene, cyclohexene and tetrahydrofuran were taken as model compounds for evaluating their hydrodesulfurization (HDS), hydrogenation (HYD) and hydrodeoxygenation (HDO) activities, respectively. The XRD results indicate that Mo is present as a monolayer up to 6 wt.% loading, whereas MoO3 crystalline growth is observed beyond this loading. O2-uptake and catalytic activities also increase up to 6 wt.% Mo-loading but above this loading both start decreasing. There are good correlations between O2 uptake and all catalytic activities. TPR and FTIR results indicate that at lower loading, MoO3 is present as tetrahedra form and at moderate loading, both tetrahedral and octahedral forms are found. XPS results reveal that the electron transfer is taking place from support to molybdenum.

Studies on physico-chemical characterization and catalysis on high surface area titania supported molybdenum hydrotreating catalysts

A series of titania supported molybdenum catalysts were prepared by incipient wetness impregnation method and characterized by BET surface area, XRD, TPR, FTIR, ESCA, and low temperature oxygen chemisorption. Thiophene, cyclohexene and tetrahydrofuran were taken as model compounds for evaluating catalytic activities for hydrodesulfurization (HDS), hydrogenation (HYD), and hydrodeoxygenation (HDO) reactions, respectively. XRD results indicate that molybdenum oxide species are dispersed as a monolayer on the support up to 8 wt.% Mo and the formation of crystalline MoO 3 is observed above this loading. FTIR and TPR results showed that molybdenum oxide species were present predominantly in tetrahedral form at lower loading and polymeric octahedral forms are dominant at higher loading. Both oxygen chemisorption and rates of reaction were found to increase with increasing Mo loading up to 8 wt.% and then decrease with further increase in loading. HDS and HYD activities are more or less same but HDO activity is two times higher than HDS and HYD activities. The results are also interpreted with the help of other parameters, like dispersion, equivalent molybdenum surface area, surface coverage, crystalline size, quasi-turnover frequencies and intrinsic activities. ESCA results suggest that electron transfer is taking place from support to metal.

TiO2–ZrO2 mixed oxide as a support for hydrotreating catalyst

Pure TiO2, ZrO2 and TiO2–ZrO2 mixed oxides are prepared by urea hydrolysis. Hydrotreating catalysts containing 12 wt% molybdenum are prepared using these oxides and characterized by BET surface area, pore volume, XRD and oxygen chemisorption. It is observed that oxides produced by the method of urea hydrolysis have higher surface area as compared to those available commercially. With increasing zirconia content in the mixed oxide, the surface area increases and a maximum value is obtained for a mixed oxide having Ti and Zr molar ratio of 65/35. XRD results indicate that mixed oxides are poorly crystalline in nature. Thiophene hydrodesulfurization, cyclohexene hydrogenation and tetrahydrofuran hydrodeoxygenation are taken as model reactions for evaluating catalytic activities. It is found that both O2 uptake and catalytic activities increase with increasing zirconia content in mixed oxide and reach maximum values for the 12 wt% Mo/TiO2–ZrO2 (65/35) catalyst. With further increases in zirconia content, O2 uptake and catalytic activities decrease and the lowest values are observed for the pure ZrO2 supported catalyst.

Characterization and hydrodesulfurization catalysis on WS2 supported on mesoporous Al-HMS material

Abstract Hexagonal mesoporous silica (HMS) and Al–HMS materials with high surface area and mesoporous structure were synthesized following the neutral templating path way. These materials were used as a support for the first time in preparing W/HMS, and W/Al–HMS catalysts and their Co, and Ni promoted analogues. On Al–HMS support (Si/Al=35) the tungsten loading was varied from 10 to 25 wt.%. On a catalyst containing 21 wt.% W the promoter concentration was varied from 1 to 5 wt.%. Oxygen uptakes and crystallite sizes of WS 2 derived from it indicated that WS 2 is well dispersed at all the loadings studied. The hydrodesulfurization and hydrogenation activities varied in a similar manner to that of oxygen uptakes as a function of W loading indicating that there exists a correlation between oxygen chemisorption and catalytic sites. The HMS and Al–HMS mesoporous material supported WS 2 catalysts showed outstanding activities in comparison with WS 2 supported on γ-Al 2 O 3 .

Catalytic functionalities of TiO2 based SiO2, Al2O3, ZrO2 mixed oxide hydroprocessing catalysts

Thiophene HDS and cyclohexene HYD activities on three mixed oxides supported Mo and promoted by Co or Ni are presented. A comparative study indicated that Ti containing mixed oxide supports show outstanding activity for HDS. The trends of variation of activities indicated that the two functionalities originate from different set of catalytic sites on molybdenum sulfide phase.

Effect of Asphaltene Contained in Feed on Deactivation of Maya Crude Hydrotreating Catalyst

Abstract The effect of asphaltene contained in Maya heavy crude on the deactivation is studied. Different heavy feeds are prepared by the mixing of Maya with desulfurized diesel. A standard NiMo catalyst is used in a batch reactor to evaluate hydrodemetallation (HDM), hydrodesulphurization (HDS), and asphaltene (HDAsp) conversion. Textural properties of the spent catalysts are studied by pore size distribution and x-ray diffraction (XRD). Metals and coke deposition on the deactivated catalysts are also measured. It is found that HDM and HDAsp activities decrease with increasing concentration of asphaltene in feed, whereas the opposite trend is observed in the case of HDS. Both deposits of coke and vanadium on the catalysts surface increase with the concentration of asphaltene in feed. The presence of asphaltene is the main reason to decrease surface area and total pore volume and hence it causes deactivation.

Hydrotreating of Maya Crude Oil: I. Effect of Support Composition and Its Pore-diameter on Asphaltene Conversion

Abstract A systematic study for a concept governing support effect in heavy oil hydrotreating (HDT) catalysts is performed. Different Al2O3 and its mixed oxides supports were prepared and CoMo supported catalysts were tested for Maya heavy crude oil hydrotreating. Fresh and spent catalysts are characterized with N2 adsorption-desorption, element analysis, and scanning electron microscopy-energy dispersion analysis by x-ray (SEM-EDAX), which confirms that coke and metals deposition on the surface of catalyst is most probably near the pore mouth. It is also demonstrated from these results that asphaltene conversion depends on the pore diameter of the catalyst, while other hydrotreating conversions (hydrodesulfurization (HDS), hydrodenitogenation (HDN), and in some extent hydrodemetallization (HDM)) are more likely affected by the nature of active metal distribution. The evaluation of alumina mixed oxide (TiO2, ZrO2, B2O3, and MgO) supported catalysts indicates that supports with basic nature have better stability than the acid ones.

Hydrodesulfurization, Hydrodenitrogenation, Hydrodemetallization, and Hydrodeasphaltenization of Maya Crude over NiMo/Al2O3 Modified with Ti and P

Abstract The effect of adding Ti (4.5 wt%) and P (∼1.0 wt%) by several routes to a NiMo/ab Al2O3 catalyst on the hydrodesulfurization (HDS), hydrodenitrogenation (HDN), hydrodemetallization (HDM), and hydrodeasphaltenization (HDAs) of heavy Maya crude was investigated. The results show that not all the catalyst functionalities respond equally well to the addition of Ti and P to the catalyst formulation. There is not a single catalyst formulation that can achieve optimum performance in all the catalyst functionalities. For HDS, Ti incorporation increases activity but the route by which P is added afterwards can improve or be detrimental to HDS activity. For HDN, the incorporation of P to the catalyst can lead to significant improvements in catalytic activity and catalyst stability. Ti increases HDM activity but the addition of P to the catalyst is detrimental to this functionality. For the elimination of asphaltenes, the catalyst supported on pure alumina is the best. So for HDAs, no benefit is obtained by the addition of Ti or P to the catalyst. Textural properties are important and HDM and HDAs increase with catalyst average pore diameter. Hydrodemetallization activity increases with the acidity of the catalyst.

Hydrotreating of maya crude oil: II. Generalized relationship between hydrogenolysis and HDAs

Abstract Studies of hydrodeasphaltenization (HDAs) and hydrodemetallization (HDM) of Maya heavy crude oil at temperature of 380°C and pressure of 5.4 MPa have been carried out in a high pressure microreactor. Different pore diameter alumina CoMo-supported catalysts were prepared and their catalytic effect is estimated. The fresh and spent catalysts were characterized by textural properties; and the average pore diameter of a fresh catalyst was found to be proportional to the HDM and HDA conversions. The hydrogen elemental analysis of reactant and products indicated that asphaltene conversion is a combination of cracking and hydrogenation (HYD), since HDM correlated well with HDAs, which is due to the complex nature of both molecules (asphaltene and metals).