Synthesis of bulk and alumina-supported γ-Mo2N catalysts by a single-step complex decomposition method

A single-step complex decomposition method for the synthesis of bulk and alumina-supported γ-Mo₂N catalysts is described. The complex precursor (HMT)₂(NH₄)₄Mo₇O₂₄·2H₂O (HMT: hexamethylenetetramine) is converted to γ-Mo₂N under a flow of Ar in a temperature range of 823–1023 K. Furthermore, decomposition of the precursor in a NH₃ flow forms γ-Mo₂N in a temperature range of 723–923 K. Compared with direct decomposition of the precursor in Ar, the reaction in NH₃ shows obvious advantages that the nitride forms at a lower temperature. In addition, alumina-supported γ-Mo₂N catalysts with different nitride loadings can be prepared from the alumina-supported complex precursor in the Ar or NH₃ flow. The resultant catalysts exhibit good dibenzothiophene HDS activities, which are similar to the γ-Mo₂N/γ-Al₂O₃ prepared by traditional TPR method. The catalyst prepared by decomposition in an Ar flow exhibits highest activity. It proves that such a single-step complex decomposition method possesses the potential to be a general route for the preparation of molybdenum nitride catalysts.     

Highly dispersed NiW/γ-Al2O3 catalyst prepared by hydrothermal deposition method

This article describes a novel hydrothermal deposition method for preparing highly dispersed NiW/γ-Al₂O₃ catalysts and demonstrates its advantages over the conventional impregnation method. Via the hydrothermal precipitation reactions between sodium tungstate and hydrochloric acid and between nickel nitrate and urea, respectively, the active species W and Ni were deposited on γ-Al₂O₃. In the hydrothermal deposition of WO₃, a surfactant hexadecyltrimethyl ammonium bromide (CTAB) was used to prevent the aggregation of WO₃. The characterization results obtained by means of X-ray photoelectron spectroscopy (XPS), N₂ adsorption and high-resolution transmission electron microscopy (HRTEM) measurements showed that compared with the catalyst prepared by the conventional impregnation method, the catalyst with the same metal contents prepared by the hydrothermal deposition had much higher W and Ni dispersion, higher specific surface area, larger pore volume, the significantly decreased slab length and slightly increased stacking degree of sulfided W species, leading to the significantly enhanced dibenzothiophene (DBT) hydrodesulfurization (HDS) activity. The DBT HDS assessment results also revealed that the catalyst containing 17.7 wt% WO₃ and 2.4 wt% NiO prepared by the hydrothermal deposition method had the similar DBT HDS activity as a commercial NiW/γ-Al₂O₃ catalyst containing 23 wt% WO₃ and 2.6 wt% NiO, resulting in the greatly decreased amount of active metals for achieving the same HDS activity.     

Quantification of the in situ DRIFT spectra of Pt/K/γ-A12O3 NOx adsorber catalysts

A method to quantify DRIFT spectral features associated with the in situ adsorption of gases on a NO_x adsorber catalyst, Pt/K/Al₂O₃, is described. To implement this method, the multicomponent catalyst is analysed with DRIFT and chemisorption to determine that under operating conditions the surface comprised a Pt phase, a pure γ-Al₂O₃ phase with associated hydroxyl groups at the surface, and an alkalized-Al₂O₃ phase where the surface –OH groups are replaced by –OK groups. Both DRIFTS and chemisorption experiments show that 93–97% of the potassium exists in this form. The phases have a fractional surface area of 1.1% for the 1.7 nm-sized Pt, 34% for pure Al₂O₃ and 65% for the alkalized-Al₂O₃. NO₂ and CO₂ chemisorption at 250 °C is implemented to determine the saturation uptake value, which is observed with DRIFTS at 250 °C. Pt/Al₂O₃ adsorbs 0.087 μmol CO₂/m²and 2.0 μmol NO₂/m², and Pt/K/Al₂O₃ adsorbs 2.0 μmol CO₂/m²and 6.4 μmol NO₂/m². This method can be implemented to quantitatively monitor the formation of carboxylates and nitrates on Pt/K/Al₂O₃ during both lean and rich periods of the NO_x adsorber catalyst cycle.     

Hydroisomerization and hydrocracking of long chain n-alkanes on Pt/amorphous SiO2–Al2O3 catalyst

The hydroisomerization and hydrocracking of n-hexadecane, n-octacosane and n-hexatriacontane on a 0.3% platinum/amorphous silica–alumina (MSA/E) catalyst was investigated in a stirred microautoclave at 345, 360 and 380°C and between 2 and 13.1 MPa hydrogen pressure. For each n-paraffin, the reaction pathway and the kinetic parameters were determined. The results were used to elucidate the effect of chain length and operating conditions on isomerization and cracking selectivity. The conversion of the n-paraffins lead to the formation of a mixture of the respective isomers, as the main product, together with cracking products. At every temperature, the iso-alkane/n-alkane ratio of cracking products increased considerably with increasing conversion degree. At the same conversion level, higher reaction temperatures lead to cracking products characterized by a lower iso-alkane/n-alkane ratio. The conversion rate constants showed a considerable increase between n-C₁₆ and n-C₂₈, whereas a slight decrease between n-C₂₈ and n-C₃₆ was observed. The hydroisomerization selectivities showed a decrease as a function of chain length and with increasing conversion levels. The increase in reaction temperature leads to a small decrease in the isomerization selectivities only at low-medium conversion degrees and at the highest temperature investigated, while the effect of this parameter on the maximum yields achievable in iso-C16, iso-C28 and iso-C36 was negligible. The results indicate that the conversion of the n-paraffins follows a first-order kinetic in hydrocarbon while the order in hydrogen pressure was −1.1 ± 0.21 for n-C₁₆ and −0.66 ± 0.15 for n-C₂₈. Furthermore, an increase in hydroisomerization selectivity at higher hydrogen pressure for n-C₂₈ conversion was observed.     

Preparation, characterization and deactivation studies of Co–Mo/γ–Al2O3 deoxidizing catalyst

A deoxidizing catalyst was prepared in this paper. Several characterization techniques (XRD, SEM–EDS, TEM, TPD and TPR) were used to study its structure and properties. A normal pressure micro-reactor was built to study its deoxidizing performance. Results show that when inlet O₂ concentration was 0.1%, space velocity was 3000–12 000 h⁻¹ and operation temperature was above 80 °C, the outlet residual O₂ can be as low as 1.0 × 10⁻⁶ (v/v). 300 h continuous operation shows that its deoxidizing activity was stable. Through comparison of the deoxidizing activities for fresh and deactivated catalyst and by simulating the water vapor contents in system, the mechanism of deactivation and reactivation was studied.     

Effects of promoters on catalytic activity and carbon deposition of Ni/γ‐Al2O3 catalysts in CO2 reforming of CH4

Catalytic reforming of methane with carbon dioxide was studied in a fixed‐bed reactor using unpromoted and promoted Ni/γ‐Al₂O₃ catalysts. The effects of promoters, such as alkali metal oxide (Na₂O), alkaline‐earth metal oxides (MgO, CaO) and rare‐earth metal oxides (La₂O₃, CeO₂), on the catalytic activity and stability in terms of coking resistance and coke reactivity were systematically examined. CaO‐, La₂O₃‐ and CeO₂‐promoted Ni/γ‐Al₂O₃ catalysts exhibited higher stability whereas MgO‐ and Na₂O‐promoted catalysts demonstrated lower activity and significant deactivation. Metal‐oxide promoters (Na₂O, MgO, La₂O₃, and CeO₂) suppressed the carbon deposition, primarily due to the enhanced basicities of the supports and highly reactive carbon species formed during the reaction. In contrast, CaO increased the carbon deposition; however, it promoted the carbon reactivity. © 2000 Society of Chemical Industry     

Methylcyclohexane dehydrogenation on Rh/γ-Al2O3 catalysts

The influence of the Rh loading on the surface properties and catalytic behaviour of Rh/γ-Al₂O₃ catalysts has been studied. The series of catalysts presents differences in metal dispersion, reducibility, surface composition and catalytic activity. All the data reported suggest that the differences in catalytic behaviour in the methylcyclohexane dehydrogenation reaction can be explained in terms of electron-deficient rhodium clusters, essentially when the metal particle size becomes smaller than 15 Å.     

Influence of support acid pretreatment on the behaviour of CoOx/γ-alumina monolithic catalysts in the CH4-SCR reaction

The effect of treatment with different mineral acids (H₂SO₄, H₃PO₄, HNO₃ and HCl) on the activity of monolithic CoO_x/γ-Al₂O₃ catalysts in the reduction of nitric oxide with methane in the presence of oxygen (CH₄-SCR of NO_x) was studied. Their behaviour in the methane oxidation reaction in both the presence and absence of NO_x was determined in order to interpret the results in terms of intrinsic activity and competition between both processes. Depending on the nature of the acid used, significant differences were observed in the catalytic activities which were related to the textural states, surface acidities and the nature of the detected species. The best results were obtained after treatment with H₂SO₄, which increased the activity towards NO_x elimination compared to the other catalysts. This behaviour was attributed not only to an increase in surface acidity but also to the stabilisation of the active Co²⁺ species, thus avoiding the formation of Co₃O₄ spinel that is responsible for the strongly adsorbed NO_x species that lead to NO₂ formation which increase the rate of the undesired methane oxidation reaction at high temperatures.     

Acidity of dealuminated β-zeolites via coupled nh3-stepwise temperature programmed desorption (STPD) and FT-IR spectroscopy

Ammonia stepwise temperature programmed desorption (STPD) and FT-IR spectroscopy have been used to study the acidity of dealuminated β-zeolites with Si/Al ratios in the range of 14.5 to 132. A carefully optimized temperature profile starting at 150 °C (in order to exclude physisorbed NH₃) revealed five peaks at about 180 °C, 250 °C, 350 °C, 440 °C, and 540 °C. Our investigations indicate that the first two peaks correspond to Lewis-type acidity of low strength and that the last three peaks correspond to Brønsted-type acidity of increasing strength. A one-to-one relation between the total number of ammonia molecules desorbed in the above temperature range and that of the Al atoms exists. High strength Lewis sites were not observed probably because the extent of dehydroxylation in the above temperature range was minimal. By increasing the level of dealumination, it was found that the relative population of strong Brønsted sites increases in comparison with the weak ones. The present stepwise temperature programmed desorption experiments coupled with FT-IR provide a very accurate tool for the quantitative measurement of the strength of the zeolite acid sites.     

Influence of chlorine ions in Pt/A12O3 catalysts for methane total oxidation

Residual chlorine ions on a Pt/Al₂O₃ catalyst surface prepared from chlorine-containing precursors appear to inhibit the total oxidation of methane. At 450°C, as chlorine is eliminated with time on stream, the reaction rate increases despite the sintering of the platinum particles. The steady state reaction rate which is reached after 60 h is identical to that obtained with a catalyst prepared from a precursor containing no chlorine. Whether chlorine is present or not in the initial state of the catalyst does not appear to have an influence on the evolution of the platinum particle size.     

Desulfurization of commercial fuels by π-complexation: Monolayer CuCl/γ-Al2O3

Monolayer CuCl/γ-Al₂O₃ sorbent was studied for desulfurization of a commercial jet fuel (364.3 ppmw S) and a commercial diesel (140 ppmw S). The sorbent was prepared by means of spontaneous monolayer dispersion methods. Deep desulfurization (sulfur levels of <1 ppmw) was accomplished with this sorbent using a fixed-bed adsorber. The CuCl/γ-Al₂O₃ sorbent was capable of removing 6.4 and 11.2 mg of sulfur per gram for jet fuel at breakthrough (at <1 ppmw S) and saturation, respectively. The same sorbent was capable of removing 0.94 and 1.8 mg of sulfur per gram for BP diesel at breakthrough and saturation, respectively. The difference in sulfur capacities for jet fuel and diesel was apparently caused by the difference in concentrations of strongly binding compounds, such as nitrogen heterocycles, heavy (polynuclear) aromatics and fuel additives. In comparison with CuCl/γ-Al₂O₃, Cu(I)Y zeolite has higher sulfur capacities but is less stable and can be easily oxidized to Cu(II)Y by fuel additives (such as oxygenates) and moisture and consequently loses π-complexation ability. However, all these cuprous π-complexation sorbents selectively adsorb thiophenic compounds over aromatics and olefins (as predicted by the high separation factors), which resulted in the observed desulfurization capability. A feasibility study is shown for efficient regeneration of CuCl/γ-Al₂O₃ using ultrasound at ambient temperature. Possible problems associated with desulfurization using π-complexation sorbents for commercial fuels are discussed.     

Catalytic activity of Pt‐Re‐Pb/Al2O3 naphtha reforming catalysts

BACKGROUND: The main purpose of the naphtha reforming process is to obtain high octane naphtha, aromatic compounds and hydrogen. The catalysts are bifunctional in nature, having both acid and metal sites. The metal function is supplied by metal particles (Pt with other promoters like Re, Ge, Sn, etc.) deposited on the support. The influence of the addition of Pb to Pt‐Re/Al₂O₃ naphtha reforming catalysts was studied in this work. The catalysts were prepared by co‐impregnation and they were characterized by means of temperature programmed reduction, thermal programmed desorption of pyridine and several test reactions such as cyclohexane dehydrogenation, cyclopentane hydrogenolysis and n‐heptane reforming. RESULTS: It was found that Pb interacts strongly with the (Pt‐Re) active phase producing decay in the metal function activity. Hydrogenolysis is more affected than dehydrogenation. Part of the Pb is deposited over the support decreasing the acidity and the strength of the most acidic sites. CONCLUSION: The n‐heptane reforming reaction shows that Pb modifies the stability and selectivity of the Pt‐Re catalysts. Small Pb additions increase the stability and greatly improve the selectivity to C₇ isomers and aromatics while they decrease the formation of low value products such as methane and gases. Copyright © 2011 Society of Chemical Industry     

CoMo/MgO–Al2O3 supported catalysts: An alternative approach to prepare HDS catalysts

Three different supports were prepared with distinct magnesia–alumina ratio x = MgO/(MgO + Al₂O₃) = 0.01, 0.1 and 0.5. Synthesized supports were impregnated with Co and Mo salts by the incipient wetness method along with 1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid (CyDTA) as chelating agent. Catalysts were characterized by BET surface area, Raman spectroscopy, SEM-EDX and HRTEM (STEM) spectroscopy techniques. The catalysts were evaluated for the thiophene hydrodesulfurization reaction and its activity results are discussed in terms of using chelating agent during the preparation of catalyst. A comparison of the activity between uncalcined and calcined catalysts was made and a higher activity was obtained with calcined MgO–Al₂O₃ supported catalysts. Two different MgO containing calcined catalysts were tested at micro-plant with industrial feedstocks of heavy Maya crude oil. The effect of support composition was observed for hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodeasphaltenization (HDAs) and hydrodenitrogenation (HDN) reactions, which were reported at temperature of 380 °C, pressure of 7 MPa and space-velocity of 1.0 h⁻¹ during 204 h of time-on-stream (TOS).     

Kinetics of acetone hydrogenation over Pt/Al2O3 catalysts

The hydrogenation of acetone to isopropanol has been studied in the vapour phase over Pt/Al₂O₃ catalysts. The rate law obtained at a total pressure of 1 atm and temperatures between 303 and 363 K is of the form V=kP⁰_aP^1/2_H exp (-44 kJ mol^?1 RT^?1). The kinetic results are consistent with a Langmuir-Hinshelwood hydrogenation mechanism involving a half hydrogenated species and a non-competitive chemisorption of acetone and hydrogen on the platinum surface. The specific activity (calculated per platinum surface atom) has been found to be scarcely dependent on the platinum particle size. It is suggested that the chemisorption sites are made of a very small ensemble of platinum atoms.     

Catalytic Oxidative Decomposition of Hydrazine in Vapor Phase over Nanosized Au/γ‐Al2O3

The catalytic activity of nanosized Au/γ‐Al₂O₃, synthesized by a deposition‐precipitation process, on oxidative decomposition of hydrazine in air is discussed. The catalyst exhibited an excellent activity at low temperatures. The activity was strongly dependent upon the gold cluster size. The impacts of certain pertinent operating parameters including the particle size of the catalyst, temperature, hydrazine concentration, and feed flow rate on the extent of the reaction were investigated. The results were reproducible with a mean absolute deviation of 3 %. Deactivation of the catalyst during the reaction was found to be unlikely. Finally, a kinetic model based on the Eley‐Rideal formulation was proposed for the reaction and a correlation was made between the data predicted from the model and those determined experimentally.     

Effect of preparation methods on the hydrocracking performance of NiMo/Al2O3 catalysts

In this work, NiMo catalysts with various contents of MoO_3 were prepared through incipient wetness impregnation by a two-step method(NM-x A) and one-pot method(NM-xB). The catalysts were then characterized by XRD, XPS, NH_3-TPD, H_2-TPR, HR-TEM, and N2 adsorption–desorption technologies.The performance of the NiMo/Al_2O_3 catalysts was investigated by hydrocracking low-temperature coal tar. When the MoO_3 content was 15 wt%, the interaction between Ni species and Al_2O_3 on the NM-15 B catalyst was stronger than that on the NM-15 A catalyst, resulting in the poor performance of the former.When the MoO_3 content was 20 wt%, MoO_3 agglomerated on the surface of the NM-20 A catalyst, leading to decreased number of active sites and specific surface area and reduced catalytic performance. The increase in the number of MoS_2 stack layers strengthened the interaction between Ni and Mo species of the NM-20 B catalyst and consequently improved its catalytic performance. When the MoO_3 content reached 25 wt%, the active metals agglomerated on the surface of the NiMo catalysts, thereby directly decreasing the number of active sites. In conclusion, the two-step method is suitable for preparing catalysts with large pore diameter and low MoO_3 content loading, and the one-pot method is more appropriate for preparing catalysts with large specific surface area and high MoO_3 content. Moreover, the NMx A catalysts had larger average pore diameter than the NM-xB catalysts and exhibited improved desulfurization performance.     

Catalytic activities of Co(Ni)Mo/TiO2–Al2O3 catalysts in gasoil and thiophene HDS and pyridine HDN: effect of the TiO2–Al2O3 composition

The effect of the TiO₂–Al₂O₃ mixed oxide support composition on the hydrodesulfurization (HDS) of gasoil and the simultaneous HDS and hydrodenitrogenation (HDN) of gasoil+pyridine was studied over two series of CoMo and NiMo catalysts. The intrinsic activities for gasoil HDS and pyridine HDN were significantly increased by increasing the amount of TiO₂ into the support, and particularly over rich- and pure-TiO₂-based catalysts. It is suggested that the increase in activity be due to an improvement in reducing and sulfiding of molybdena over TiO₂. The inhibiting effect of pyridine on gasoil HDS was found to be similar for all the catalysts, i.e., was independent of the support composition. The ranking of the catalysts for the gasoil HDS test differed from that obtained for the thiophene test at different hydrogen pressures. In the case of gasoil HDS, the activity increases with TiO₂ content and large differences are observed between the catalysts supported on pure Al₂O₃ and pure TiO₂. In contrast, in the case of the thiophene test, the pure Al₂O₃-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also, in the thiophene test the difference in intrinsic activity between the pure Al₂O₃-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also in the thiophene test, the difference in intrinsic activity between the pure Al₂O₃- and pure TiO₂-based catalysts is relatively small and dependent on the H₂ pressure used. Such differences in activity trend among the gasoil and the thiophene tests are due to a different sensitivity of the catalysts (by different support or promoter) to the experimental conditions used. The results of the effect of the H₂ partial pressure on the thiophene HDS, and on the effect of H₂S concentration on gasoil HDS demonstrate the importance of these parameters, in addition to the nature of the reactant, to perform an adequate catalyst ranking.     

Separation of bovine serum albumin (BSA) using γ‐Al2O3–clay composite ultrafiltration membrane

BACKGROUND: Ceramic membranes have received more attention than polymeric membranes for the separation and purification of bio‐products owing to their superior chemical, mechanical and thermal properties. Commercially available ceramic membranes are too expensive. This could be overcome by fabricating membranes using low‐cost raw materials. The aim of this work is to fabricate a low‐cost γ‐Al₂O₃–clay composite membrane and evaluate its potential for the separation of bovine serum albumin (BSA) as a function of pH, feed concentration and applied pressure. To achieve this, the membrane support is prepared using low‐cost clay mixtures instead of very expensive alumina, zirconia and titania materials. The cost of the membrane can be further reduced by preparing a γ‐alumina surface layer on the clay support using boehmite sol synthesized from inexpensive aluminium chloride instead of expensive aluminium alkoxide using a dip‐coating technique. RESULTS: The pore size distribution of the γ‐Al₂O₃‐clay composite membrane varied from 5.4–13.6 nm. The membrane was prepared using stable boehmite sol of narrow particle size distribution and mean particle size 30.9 nm. Scanning electron microscopy confirmed that the surface of the γ‐Al₂O₃–clay composite membrane is defect‐free. The pure water permeability of the support and the composite membrane were found to be 4.838 × 10^?6 and 2.357 × 10^?7 m³ m^?2 s^?1 kPa^?1, respectively. The maximum rejection of BSA protein was found to be 95%. It was observed that the separation performance of the membrane in terms of flux and rejection strongly depends on the electrostatic interaction between the protein and charged membrane. CONCLUSION: The successively prepared γ‐Al₂O₃‐clay composite membrane proved to possess good potential for the separation of BSA with high yield and could be employed as a low cost alternate to expensive ceramic membranes. Copyright © 2009 Society of Chemical Industry