Hydrocracking Brazilian Marlim vacuum residue with natural limonite. Part 1: catalytic activity of natural limonite

An experimental study examined the catalytic effects of natural Australian (AL) and Brazilian (BL) limonites used in hydrocracking Brazilian Marlim vacuum residue (ML-VR). The catalytic behavior of the limonites was compared with a conventional NiO-MoO₃-Al₂O₃ (NiMo) catalyst. Diphenylmethane (DPM) and 1-methylnaphthalene (1-MN) were used as standards. The order in which coke and gas formation were suppressed during hydrocracking of ML-VR was NiMo>BL>AL, which is the same order as for the hydrogenation activity observed with the standard compounds. By contrast, the limonite catalysts exhibited relatively higher conversions and distillate yields in ML-VR hydrocracking than did the NiMo catalyst with the order of conversion and distillate yield (yield of the fraction with boiling point of 540 °C) being AL>BL>NiMo, which is the same order obtained for catalytic cracking of the two standards. Coke formation was effectively suppressed at high hydrogen pressures. The limonite catalysts showed lower activities for nitrogen and sulfur removal than did NiMo, but both proved to have a larger activity for nickel removal.     

Propane Reactions over Faujasite Structure Zeolites Type-X and USY: Effect of Zeolite Silica over Alumina Ratio, Strength of Acidity and Kind of Exchanged Metal Ion

In this work we prepared various zeolite-X and USY samples partially exchanged with copper, iron and platinum. These samples were characterized by XRD, Chemical Analysis, SEM-EDS, N₂-adsorption–desorption, ammonia-TPD, and tested as catalysts in high temperature (400 and 550 °C) propane transformation. The obtained results revealed the strong effect of Si/Al ratio in faujasite zeolite structure, the number and strength of acid sites and of the presence of different metal ions in countered ion sites, on the catalytic activity and selectivity of zeolite-X and USY. The highest propane dehydrogenation activity was achieved with the platinum-exchanged X zeolite (∼11.2% propylene yield, ∼31% selectivity). On the contrary USY zeolites showed high cracking capability and relatively low dehydrogenation activity excepting the platinum-exchanged sample which yielded notably high aromatization products.     

Efficient synthesis of glycerol carbonate from glycerol and urea with lanthanum oxide as a solid base catalyst

Lanthanum oxide catalyst prepared by precipitation method and calcined at 600 °C exhibited better catalytic activity in the catalytic synthesis of glycerol carbonate from glycerol and urea with TOF up to 1506 mmol/g·h. It was proposed that the lanthanum oxide catalyst with more strong basic sites (T_d > 400 °C) exhibited higher catalytic activity. Accordingly, the catalyst containing appropriate amount of La₂O₂CO₃ phase exhibited higher catalytic activity. Moreover, the recycling experiments demonstrated that the catalytic activity can be essentially preserved during the recycling tests investigated.     

Influence of Particle Size on Reaction Selectivity in Cyclohexene Hydrogenation and Dehydrogenation over Silica-Supported Monodisperse Pt Particles

The role of particle size during the hydrogenation/dehydrogenation of cyclohexene (10 Torr C₆H₁₀, 200–600 Torr H₂, and 273–650 K) was studied over a series of monodisperse Pt/SBA-15 catalysts. The conversion of cyclohexene in the presence of excess H₂ (H₂: C₆H₁₀ ratio = 20:60) is characterized by three regimes: hydrogenation of cyclohexene to cyclohexane at low temperature (<423 K), an intermediate temperature range in which both hydrogenation and dehydrogenation occur; and a high temperature regime in which the dehydrogenation of cyclohexene dominates (>573 K). The rate of both reactions demonstrated maxima with temperature, regardless of Pt particle size. For the hydrogenation of cyclohexene, a non-Arrhenius temperature dependence (apparent negative activation energy) was observed. Hydrogenation is structure insensitive at low temperatures, and apparently structure sensitive in the non-Arrhenius regime; the origin of the particle-size dependent reactivity with temperature is attributed to a change in the coverage of reactive hydrogen. Small particles were more active for dehydrogenation and had lower apparent activation energies than large particles. The selectivity can be controlled by changing the particle size, which is attributed to the structure sensitivity of both reactions in the temperature regime where hydrogenation and dehydrogenation are catalyzed simultaneously.     

Low Temperature Steam Reforming of Ethanol Over Supported Noble Metal Catalysts

The catalytic activity of M/Al₂O₃ catalysts for the reaction of steam reforming of ethanol has been investigated in the temperature range of 300–450 °C. It has been found that the catalytic performance varies in the order of Pt > Pd > Rh > Ru, with Pt exhibiting high activity and selectivity toward hydrogen production, as well as long term stability at low temperatures. It is shown that the reaction occurs in a bifunctional manner, with the participation of both the dispersed metallic phase and the support. Ethanol interacts strongly with the Al₂O₃ carrier, promoting mainly ethanol dehydration, while in the presence of Pt, catalytic activity is shifted toward lower temperatures. Ethanol decomposition and dehydrogenation reactions dominate at low temperatures, while reforming, water-gas shift and methanation contribute significantly to product distribution.     

Steam reforming of ethanol on Ni–CeO2–ZrO2 catalysts: Effect of doping with copper, cobalt and calcium

Steam reforming (SR) and oxidative steam reforming (OSR) of ethanol were investigated over undoped and Cu, Co and Ca doped Ni/CeO₂–ZrO₂ catalyst in the temperature range of 400–650 °C. The nickel loading was kept fixed at 30 wt.% and the loading of Cu and Co was varied from 2 to 10 wt% whereas the Ca loading was varied from 5 to 15 wt.%. The catalysts were characterized by various techniques, such as surface area, temperature programmed reduction, X-Ray diffraction and H₂ chemisorption. For Cu and Co doped catalyst, CuO and Co₃O₄ phases were detected at high loading whereas for Ca doped catalyst, no separate phase of CaO was found. The reducibility and the metal support interactions were different for doped catalysts and varied with the amount and nature of dopants. The hydrogen uptake, nickel dispersion and nickel surface area was reduced with the metal loading and for the Co loaded catalysts the dispersion of Ni and nickel surface area was very low. For Cu and Ca doped catalysts, the activity was increased significantly and the main products were H₂, CO, CH₄ and CO₂. However, the Co doped catalysts showed poor activity and a relatively large amount of C₂H₄, C₂H₆, CH₃CHO and CH₃COCH₃ were obtained. For SR, the maximum enhancement in catalytic activity was obtained with in the order of NCu5. For Cu–Ni catalysts, CH₃CHO decomposition and reforming reaction was faster than ethanol dehydrogenation reaction. Addition of Cu and Ca enhanced the water gas shift (WGS) and acetaldehyde reforming reactions, as a result the selectivity to CO₂ and H₂ were increased and the selectivity to CH₃CHO was reduced significantly. The maximum hydrogen selectivity was obtained for Catalyst N (93.4%) at 650 °C whereas nearly the same selectivity to hydrogen (89%) was obtained for NCa10 catalyst at 550 °C. In OSR, the catalytic activity was in the order N > NCu5 > NCa15 > NCo5. In the presence of oxygen, oxidation of ethanol was appreciable together with ethanol dehydrogenation. For SR reaction, the highest hydrogen yield was obtained on the undoped catalyst at 600 °C. However, with calcium doping the hydrogen yields are higher than the undoped catalyst in the temperature range of 400–550 °C.     

Novel nitrogen containing heterogeneous catalysts for oxidative dehydrogenation of light paraffins

Novel nitrogen contained catalyst CoN_x/Al₂O₃ yielded high performance in the oxidative dehydrogenation of propane and n-butane. 47.6 and 37.4 wt% yield of olefins at 82% butane and 76.7% propane conversion were measured at 600 °C. Ethylene and propylene were mainly formed at >400 °C via oxidative cracking of paraffins. XRD and XPS studies of the novel catalytic system indicate an essential modification of cobalt by nitrogen.     

Gas Phase Hydrogenation of Maleic Anhydride to γ-Butyrolactone by Cu–Zn–Ce Catalyst in the Presence of n-Butanol

A series of Cu–Zn–Ce catalysts were prepared by coprecipitation method and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, temperature programmed reduction, and N₂ adsorption. The catalytic activities of the Cu–Zn–Ce catalysts in gas phase hydrogenation of maleic anhydride in the presence of n-butanol were studied at 220–280 °C and 1 MPa. The conversion of maleic anhydride was more than 97%. After reduction, CuO species present in the calcined Cu–Zn–Ce catalysts were converted to metallic copper (Cu°). The presence of ZnO in the Cu–Zn–Ce catalysts was beneficial to stabilizing the catalytic activity in maleic anhydride hydrogenation to γ-butyrolactone. At the same time, n-butanol was dehydrogenated to butyl aldehyde, then to butyl butyrate via reactions, such as disproportionation and esterification. Cu–Zn–Ce catalysts are beneficial to the H₂ compensation in the coupling process of hydrogenation and dehydrogenation.     

Omega−3 fatty acid ethyl ester from a simple catalytic non-oxidative dehydrogenation of a biobased oleochemical

Essential fatty acids and derivatives, such as ethyl esters, have acquired an important interest, lately. The reactivity of ethyl linoleate (di-unsaturated fatty acid ethyl ester, FAEE), specially the catalytic reactions of non-oxidative dehydrogenation and isomerization, in a fixed bed reactor using active carbon as a catalyst has been studied. Active carbon presented dehydrogenation properties under non-oxidative conditions and in a temperature range of 70–120 °C. Omega−3 tri-unsaturated FAEE and aromatic FAEE were the detected dehydrogenation compounds. Mono-unsaturated FAEE and isomers of ethyl linoleate were the products of hydrogenation and isomerization reactions, respectively. The dehydrogenation activity of active carbon remained stable with time. The non-oxidative dehydrogenation to omega−3 tri-unsaturated FAEE becomes more important than the isomerization and hydrogenation reactions at lower temperatures such as 70 °C. Up to a 7.2% of omega−3 tri-unsaturated FAEE has been obtained synthetically for the first time.     

Gas phase hydrogenation of maleic anhydride to tetrahydrofuran by Cu/ZnO/TiO2 catalysts in the presence of n-butanol

Cu/ZnO/TiO₂ catalysts were prepared via the coprecipitation method. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectrometry, temperature programmed reduction, and N₂ adsorption. The catalytic activity of Cu/ZnO/TiO₂ catalyst in gas phase hydrogenation of maleic anhydride in the presence of n-butanol was studied at 235–280 °C and 1 MPa. The conversion of maleic anhydride was more than 95.7% and the selectivity of tetrahydrofuran was up to 92.7%. At the same time, n-butanol was converted to butyraldehyde and butyl butyrate via reactions, namely, dehydrogenation, disproportionation, and esterification. There were two kinds of CuO species present in the calcined Cu/ZnO/TiO₂ catalysts. At a lower copper content, the CuO species strongly interacted with ZnO and TiO₂; at a higher copper content, both the surface-anchored and bulk CuO species were present. The metallic copper (CuO) produced by the reduction of the surface-anchored CuO species favored the deep hydrogenation of maleic anhydride to tetrahydrofuran. The deep hydrogenation activity of Cu/ZnO/TiO₂ catalyst increased with the decrease of crystallite sizes of CuO and the increase of microstrain values. Compensations of reaction heat and H₂ in the coupling reaction of maleic anhydride hydrogenation and n-butanol dehydrogenation were distinct.     

Catalytic hydrogenation of alkenes on acidic zeolites: Mechanistic connections to monomolecular alkane dehydrogenation reactions

Brønsted acid sites in zeolites (H-FER, H-MFI, H-MOR) selectively hydrogenate alkenes in excess H₂ at high temperatures (>700 K) and at rates proportional to alkene and H₂ pressures. This kinetic behavior and the De Donder equations for non-equilibrium thermodynamics show that, even away from equilibrium, alkene hydrogenation and monomolecular alkane dehydrogenation occur on predominantly uncovered surfaces via microscopically reverse elementary steps, which involve kinetically-relevant (C–H–H)⁺ carbonium-ion-like transition states in both directions. As a result, rate constants, activation energies and activation entropies for these two reactions are related by the thermodynamics of the overall stoichiometric gas-phase reaction. The ratios of rate constants for hydrogenation and dehydrogenation reactions do not depend on the identity or reactivity of active sites; thus, sites within different zeolite structures (or at different locations within a given zeolite) that favor alkane dehydrogenation reactions, because of their ability to stabilize the required transition states, also favor alkene hydrogenation reactions to the exact same extent. These concepts and conclusions also apply to monomolecular alkane cracking and bimolecular alkane–alkene reaction paths on Brønsted acids and, more generally, to any forward and reverse reactions that proceed via the same kinetically-relevant step on vacant surfaces in the two directions, even away from equilibrium. The evidence shown here for the sole involvement of Brønsted acids in the hydrogenation of alkoxides with H₂ is unprecedented in its mechanistic clarity and thermodynamic rigor. The scavenging of alkoxides via direct H-transfer from H₂ indicates that H₂ can be used to control the growth of chains and the formation of unreactive deposits in alkylation, oligomerization, cracking and other acid-catalyzed reactions.     

Castor oil hydrogenation by a catalytic hydrogen transfer system using limonene as hydrogen donor

The hydrogenation of castor oil was investigated using a catalytic transfer hydrogenation system in which palladium on carbon was the catalyst and limonene was the solvent and hydrogen donor. The highest percentage of castor oil modification occurred at 178°C using 1% Pd/C and an oil/limonene ratio of 1∶3. The optimized system presented very good reproducibility and 100% conversion of the ricinoleate. GC using a mass spectrometer as detector and ¹H NMR spectra of the products indicated that hydrogenation was accompanied by dehydrogenation leading to a mixture of 12-hydroxy and 12-keto stearic derivatives.     

Establishment and maintenance of an optimal chiral surface in cinchona-modified 1% Pt/Al2O3 for enantioselective hydrogenation of α-keto esters

An optimal chiral surface in the cinchona-modified Pt/Al₂O₃ catalytic system is established for fast enantioselective hydrogenation of ethyl pyruvate. A makeup protocol is used to compensate for the destructive hydrogenation of the chiral modifier, thus maintaining the optimal chiral surface over the course of the hydrogenation reaction. Hydrogenation over the optimal surface (Pt_surface/modifier = 5–12) results in high enantioselectivity (94% ee) under mild conditions (5.8 bar and 17^°C) with high turnover frequency (4 s^-1) and turnover numbers (pyruvate/modifier>28,000, pyruvate/Pt_surface>5,500). This revised version was published online in June 2006 with corrections to the Cover Date.     

Valorization of α-olefins: Double bond shift and skeletal isomerization of 1-pentene and 1-hexene on zirconia-based catalysts

Several catalysts consisting of Pt supported on sulfated or tungstated zirconia (one of them supported on alumina) have been characterized by different techniques, such as elemental and XRD analyses, N₂ adsorption, TPD of ammonia, TPR and H₂ chemisorption. All these catalysts were active in the transformation of two α-olefins, 1-pentene and 1-hexene, both present in most of FCC naphthas, whose conversion to internal and branched olefins is of a great interest for their use in reformulated gasolines and as intermediate chemicals. At low reaction temperatures (200–250 °C), both hydrogenation and double bond shift compete to give n-paraffins and internal olefins, respectively. As the temperature rises (>350 °C) the catalytic activity for the isomerization reactions increases, yielding a higher amount of internal and branched olefins. The product composition depends on the particular catalyst and reaction conditions used. The high activity of the sulfated zirconia, is remarkable and clearly indicates the participation of acid sites in these reactions.     

Dehydrogenation of C3–C4 paraffin's to corresponding olefins over slit-SAPO-34 supported Pt-Sn-based novel catalyst

The objective of this work is to discuss the performance of Pt-Sn/slit-SAPO-34 novel catalyst for selective C₃–C₄ dehydrogenation to corresponding light olefins. The metallic contents, acidity, active metallic sites and metallic dispersion were determined using a number of physico-chemical techniques as it gives a justification for superior catalytic activity for dehydrogenation reaction. The Pt-Sn/slit-SAPO-34 catalyst was analyzed for dehydrogenation activity under optimized operating conditions; at atmospheric pressure, hydrogen to alkane (feed) molar ratio is 0.2, weight hourly space velocity 5 h^?1 and temperature 585 °C. Around 40% light alkane conversion and above 95% of total olefins selectivity with 94% propene, 92% n-butene and about 84% iso-butene selectivity were achieved over Pt-Sn/slit-SAPO-34 novel catalyst. The catalyst was parametrically characterized over the above said operating conditions and effects of operating conditions on product distribution were discussed. The coke formation was inherently related to catalyst activity in dehydrogenation reaction and related to surface intermetallic ensemble effects; and ultimately the prominent stakeholder in catalyst deactivation. The novel catalysts also showed very good hydrothermal stability in a continuous reaction–regeneration cycles due to silica-based acidic structure of support. The results obtained over Pt-Sn/slit-SAPO-34 novel catalyst were compared with other Pt-Sn-based ZSM-5 and SAPO-34 supported catalysts of similar active metallic content under identical operating conditions.     

Catalytic behaviour of nickel and iron metal contaminants of an FCC catalyst after oxidative and reductive thermal treatments

The catalytic effects of nickel and iron deposited on an FCC (fluidized catalytic cracking) catalyst via metal naphthenates were studied in a micro activity test (MAT) unit after both oxidative and reductive treatments of the catalyst samples.The dehydrogenation activity of nickel was found to be close to the dehydrogenation activity of vanadium – and not several times higher than that of vanadium as is often reported – when deposited on the commercial FCC catalyst used in this study followed by steam deactivation (oxidative treatment) at 760 °C. However, the dehydrogenation activity of nickel was significantly intensified after post-treatment with a CO/N₂ mixture at this temperature (reductive treatment).The results show that iron did not have a dehydrogenation activity after steaming, but had a significant dehydrogenation activity after steaming when followed by exposure to the CO/N₂ mixture at 760 °C. The results indicate that the presence of deposited iron was inducing an additional catalytic cracking activity for the FCC catalyst.It was observed that co-impregnation of equal loadings of nickel, iron and vanadium on the FCC catalyst led to a considerably higher dehydrogenation activity than could be expected from the catalytic behaviour of the separate elements. The dehydrogenation activity was however slightly reduced by the reductive treatment as the reduced dehydrogenation activity from the lower oxidation state of vanadium (V³⁺) more than compensated the increased dehydrogenation activity of iron and nickel. A slightly increased gasoline production after the reductive treatment of the co-impregnated sample was a result of the increased production of gasoline from the FCC catalyst itself, which more than compensated for the reduced gasoline production from nickel.     

Differences in coke burning-off from Pt–Sn/Al2O3 catalyst with oxygen or ozone

Pt–Sn/γ-Al₂O₃ catalysts with different Sn loadings were prepared by incipient wetness coimpregnation of γ-Al₂O₃ with H₂PtCl₆ and SnCl₂. The Pt–Sn interaction was tested by temperature-programmed reduction and the catalytic activity was measured by cyclohexane dehydrogenation. The catalysts were coked by cyclopentane at 500 °C and totally or partially decoked with O₂ at 450 °C or O₃ at 125 °C. Coke deposits were studied by TPO and the catalytic activity of coked catalysts, partially or totally regenerated, by cyclohexane dehydrogenation.The TPO with O₃ shows that coke combustion with O₃ starts at a low temperature and has a maximum at 150 °C, that is a compensation between the increase of the burning rate and the rate of O₃ decomposition when increasing the temperature. Meanwhile O₂ burns coke with a maximum at 500 °C. When performing partial decoking with O₃ (125 °C) the remaining coke is more oxygenated and easier to burn than the coke that remains after decoking with O₂ (450 °C).After burning with O₃ the dehydrogenation activity of the fresh catalyst is recovered, while after burning with O₂ the activity is higher than that of the fresh catalyst. The burning with O₃ practically does not change the original Pt–Sn interaction while the burning with O₂ produces a decrease in the interaction, producing free Pt sites with higher dehydrogenation capacity.The differences in coke combustion with O₃ and O₂ are due to the different form of generation of activated oxygen, the species that oxidizes the coke. O₃ is activated by the γ-Al₂O₃ support at low temperatures firstly eliminating coke from the support while O₂ is activated by Pt at temperatures higher than 450 °C and the coke removal starts on the metal. Then, the recovery of the Pt catalytic activity as a function of coke elimination is faster with O₂ than with O₃.     

Catalytic transfer hydrogenation on a hydrogen-absorbing alloy (CaNi5) using hydriding–dehydriding properties

By using the characteristics of a hydrogen-absorbing alloy, the hydrogen produced by catalytic dehydrogenation of saturated compounds can be absorbed to form metal hydrides, and, vice versa, the resulting metal hydrides are able to hydrogenate efficiently unsaturated compounds upon dehydriding. Gas-phase reactions between 2-butene and 2-propanol on a hydrogen-absorbing alloy CaNi₅ have been studied in the temperature range of 393–473 K. CaNi₅ showed interesting characteristics as an active catalyst for the catalytic transfer hydrogenation of butene from propanol as a hydrogen donor. 2-propanol was effectively dehydrogenated at 423 K to yield acetone in which the dissociated hydrogen was completely absorbed by CaNi₅ to form the metal hydride. When the alloy was hydrided to some extent, butene was hydrogenated by the absorbed hydrogen in the metal hydride to produce butane. The overall reaction on CaNi₅ was expressed as catalytic transfer hydrogenation of 2-butene from 2-propanol through intermediate formation of metal hydrides, rather than the direct reaction between butene and propanol on the alloy. Thus, CaNi₅ effectively repeated hydriding–dehydriding cycles: hydriding of CaNi₅ by 2-propanol dehydrogenation with subsequent dehydriding for the hydrogenation of 2-butene. The use of hydrogen-absorbing CaNi₅ provides a novel reaction system for the catalytic transfer hydrogenation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structures of the distillates obtained from hydrogenation and pyrolysis of Liddell coal

The structures of the distillable fractions (oils, b.p. >200 °C and volatile fractions, b.p. <200 °C) of the products from hydrogenation and pyrolysis of an Australian bituminous coal (Liddell) were investigated by gas chromatography-mass spectrometry (g.c.-m.s.) and nuclear magnetic resonance spectroscopy (n.m.r.). The distillable oil generated from hydrogenation of Liddell coal at 400 °C, using nickel molybdenum ortin (II) chloride as catalyst and tetralin or recycle oil as vehicle, consisted of a wide range of compounds. Long straight-chain alkanes were important components together with alkyl-substituted benzenes and tetralins, phenols and polycyclic material. When yields were low, as in the case of catalytic experiments with nickel molybdenum catalysts and no vehicle, isoprenoids could be identified. When a substantial proportion of the coal was converted to oil, branched-chain alkanes were not important components of the product. The replacement of tetralin and nickel molybdenum catalyst with stannous chloride reduced the amounts of methyl tetralins in the product. When tetralin was replaced by recycle oil, alkanes were more important components of the liquid products. Although alkenes were absent in oils generated by hydrogenation, they were important components of oils generated by pyrolysis. The highly volatile fractions (b.p. <200 °C) produced during hydrogenation consisted of alkyl-substituted benzenes, decalins, methylindan and straight-chain alkanes. Straight-chain alkanes were more abundant in those volatile fractions generated by hydrogenation with recycle vehicle than with tetralin. The Brown-Ladner method of estimating the fraction of aromatic carbon in distillable oils was adequate for less volatile fractions but was inadequate for the highly volatile fractions because of the large amounts of α-CH₃ and β-CH₃ alkyl groups present.     

Surface organometallic chemistry on metals. Application to chemicals and fine chemicals

Some applications of surface organometallic chemistry on metals to catalysis are presented, showing the great importance of the modification of a metallic surface by organometallic compounds on its catalytic properties. The selective hydrogenation of α–β unsaturated aldehydes such as citral (Z and E) can be achieved on rhodium–tin catalysts. While rhodium alone is relatively unselective, geraniol (and nerol) can be obtained selectively (> 98%) without a significant loss of activity by use of a rhodium–tin catalyst showing a typical ligand effect of the organotin fragment on the surface. Similarly, in the isomerization of (+) 3-carene into (+) 2-carene or the dehydrogenation of butan–2–ol into methyl ethyl ketone, the selectivity into the desired product is increased by introduction of small amounts of tin which will form adatoms poisoning unselective sites. An alloying effect of tin is also presented in the dehydrogenation reaction of isobutane in isobutene. This revised version was published online in June 2006 with corrections to the Cover Date.