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Applied Catalysis A, General (v.326, #2)
1-Heptyne semihydrogenation catalized by palladium or rhodium complexes by M.E. Quiroga; D.A. Liprandi; E.A. Cagnola; P.C. L’ Argentière (pp. 121-129).
[RhCl(NH2(CH2)12CH3)3], [RhCl(NH2(CH2)5CH3)3], [PdCl2(NH2(CH2)12CH3)2] and [PdCl2(NH2(CH2)5CH3)2] were obtained and tested as catalysts in different conditions for the 1-heptyne semi-hydrogenation. All of the catalytic systems exhibited a better performance than the Lindlar catalyst, except [PdCl2(NH2(CH2)5CH3)2]. The best catalytic system was [RhCl(NH2(CH2)12CH3)3]/γAl2O3, containing an electron-rich metal and an electron-donating ligand (NH2(CH2)12CH3). This behaviour could be explained by means of electronic and geometric effects. The figure shows the conversion to 1-heptene (%) vs total 1-heptyne conversion (%) for the Rh complexes in homogeneous and heterogeneous conditions and Lindlar catalyst.▪[RhCl(TDA)3], [RhCl(HA)3], [PdCl2(TDA)2] and [PdCl2(HA)2] (TDA=tridecylamine, HA=hexylamine) were synthesized and tested as catalysts in homogeneous and heterogeneous condition for the 1-heptyne semihydrogenation, using γ-alumina as support. The Lindlar catalyst was used as a reference. XPS, FTIR and Atomic Absorption results showed that the active catalytic species in each case is the complex itself. All of the catalytic systems exhibited a better performance than the Lindlar catalyst, with the exception of [PdCl2(HA)2]. The analysis of activity and selectivity values allowed to say that the best system is [RhCl(TDA)3]/Al2O3, an heterogeneous catalyst with an electron-rich transition metal and an electron-donating ligand (TDA) containing a long-chain hydrocarbon substituent. The complex system catalytic behaviour could be explained by means of electronic and geometric effects.
Keywords: 1-Heptyne semihydrogenation; Rh/Pd complexes; Coordination sphere; Homo/heterogeneous condition
Pd catalysts supported on MgO, ZrO2 or MgO-ZrO2: Preparation, characterization and study in hexane conversion by Dragos Ciuparu; Alain Ensuque; François Bozon-Verduraz (pp. 130-142).
MgO-rich supports favour high selectivities in aromatization whereas zirconia-rich supports favour isomerization, especially when Pd is photodeposed in basic medium. A new bifunctionality of zirconia supported catalysts, involving the role of point defects (oxygen vacancies, Zr3+ ions) is proposed. ▪High surface area zirconia and MgO–ZrO2 composites are prepared and used as supports of Pd catalysts. Amorphous zirconia is prepared via precipitation and digestion of zirconium oxyhydroxide in hydrazine. Composite MgO–ZrO2 oxides are obtained by (i) grafting of zirconium acetylacetonate on MgO and (ii) coprecipitation of a mixed gel of zirconium oxyhydroxide and magnesium hydroxide. Several methods of palladium deposition are investigated: multi- step processes such as anchoring and impregnation of Pd acetylacetonate, single- step processes such as electroless and photodeposition in acidic or basic medium (for zirconia only). These catalysts are tested in hexane conversion at 753K. In continuous flow reactor measurements, only aromatic, cracking and isomerization products are detected, with only very low amounts of methylcyclopentane.Deposition of Pd via anchoring of Pd(acac)2 leads to the smallest metal particle size (4–5nm) whatever the support. The basic MgO support favours strongly aromatization (near 90% selectivity) but limits conversion (around 12%). Introduction of small quantities of zirconia on MgO increases the conversion without loss of aromatization selectivity. Conversely, zirconia-rich supports favour isomerization at the expense of aromatization but increase the conversion (around 22%). With pure zirconia, the conversion suffers a marked decrease with time. The cracking selectivity is low (≤10%) for all anchored catalysts.The method of palladium deposition on zirconia has a marked influence on the catalytic performances. The significant differences in conversion at stationary state (electroless≪photodeposition in acidic medium
Keywords: Zirconia; MgO; Palladium catalysts; Photodeposition; Hexane conversion
Structural changes and surface activities of ethylbenzene dehydrogenation catalysts during deactivation by Morteza Baghalha; Omid Ebrahimpour (pp. 143-151).
Industrial dehydrogenation of ethylbenzene to styrene is performed using potassium-promoted iron oxide catalyst. Previous attempts on deactivation mechanisms are based on the chemical differences between the fresh and used catalysts. In the present work, in addition to the chemical changes, the effect of structural changes of internal areas of the catalyst on its activity before and after deactivation are considered.▪Industrial dehydrogenation of ethylbenzene to styrene is performed using potassium-promoted iron oxide catalyst. Many attempts have been made to understand the deactivation mechanism of the catalyst based on the chemical differences between the fresh and used catalysts. In the present work, in addition to the effect of chemical changes, the effect of structural changes of the internal areas on the catalyst activity was investigated. A fresh and used commercial catalyst from an industrial reactor which had been continuously used for two years under severe conditions (LHSV=1h−1, T=610°C, mass ratio of steam to ethylbenzene=1.2, P=1.2atm) was studied. Nitrogen adsorption, Hg porosimetry, X-ray diffractometer (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), FT-IR, Leco carbon analysis, and wet chemical analysis were performed on both fresh and used catalysts. The catalyst activity tests were performed in a lab-scale continuous fixed bed reactor, maintained at fixed temperature using an electrically heated furnace. It was found that micro and mesopores ( d<50nm), that make 5% of the total catalyst porosity (21%), were completely filled with carbon deposits in the used catalyst (holding 1.1wt.% carbon). This caused a surface area reduction of 29%, as measured by Brunauer–Emmett–Teller (BET) method. The remaining 95% of the pores were macropores that were slightly covered with carbon (holding only 0.6wt.% carbon). Based on a variety of activity tests, it is proposed that the surface catalytic activity for ethylbenzene dehydrogenation follows the order: KFeO2>Fe2O3/Fe3O4>carbon (at 562°C). At higher temperature of 639°C, however, this trend reverses and carbon surface becomes more active than KFeO2 surface.
Keywords: Ethylbenzene; Dehydrogenation; Catalyst; Styrene; Characterization
Conversion of syngas to higher alcohols over nanosized LaCo0.7Cu0.3O3 perovskite precursors by Nguyen Tien-Thao; M. Hassan Zahedi-Niaki; Houshang Alamdari; Serge Kaliaguine (pp. 152-163).
This article provides a systematic study of the synthesis of higher alcohols over nanocrystalline La(Co, Cu)O3 perovskite precursors. The optimum parameters for catalyst preparation and for alcohol synthesis were determined. Under the optimal reaction conditions, the alcohol productivity is in a broad range of 70–140mg/gcat/h and the selectivity towards alcohols is about 40–45wt.%. The catalyst morphology of the ground perovskite has strong effects on the catalyst stability as well as productivity.▪Two LaCo0.7Cu0.3O3 perovskite catalysts synthesized by reactive grinding and by the citrate complex method have been characterized by X-ray diffraction (XRD), BET, SEM, H2-temperature-programmed reduction (TPR) and tested for the synthesis of higher alcohols and hydrocarbons from syngas. The ground sample shows a rather high surface area and nanometric particles. The coexistence of copper and cobalt in the perovskite lattice provides a highly dispersed bimetallic phase after pretreatment under hydrogen. Both samples were reduced in situ prior to being tested for the synthesis of alcohols and hydrocarbons. The catalytic activity and product distribution depend strongly on the process variables, alkali promoter, preparation method, and catalyst morphology. While the ground perovskite is rather selective for the synthesis of higher alcohols, the citrate-derived precursor produces mainly methane and light hydrocarbons in addition to 10–15wt.% of alcohols. The optimum parameters for catalyst preparation and for alcohol synthesis were determined. Under the optimal reaction conditions, the alcohol productivity is in a broad range of 70–140mg/gcat/h and the selectivity towards alcohols is about 40–45wt.%. Both alcohols and hydrocarbons produced obey a classical Anderson–Schulz–Flory (ASF) plot carbon number distribution.The nanocrystalline perovskite precursor shows a better catalytic performance compared to the citrate-derived sample in terms of both alcohol selectivity and productivity. The catalytic stability of the ground perovskite is dependent not only on the crystal domain size (or the size of nanoparticles) and the amount of remnant sodium ions, but also strongly on the compactness of nanoparticles. The existence of slit-shaped spaces between primary nanoparticles and/or grain boundaries hinders the formation of long carbon chains, which are precursors for the formation of coke on the catalyst surface.
Keywords: La-Co-Cu; Higher-alcohols; Co-Cu metal; Syngas; Stability; Perovskite
Effect of cobalt carboxylate precursor chain length on Fischer-Tröpsch cobalt/alumina catalysts by Kalala Jalama; Neil J. Coville; Diane Hildebrandt; David Glasser; Linda L. Jewell (pp. 164-172).
The synthesis of a series of Co carboxylate alumina supported catalysts in which the carboxylate chain length has been varied has been shown to impact on the catalytic activity of the catalysts in the Fischer-Tröpsch reaction. ▪The effect of the cobalt carboxylate chain length (C2, C5 and C9) on the preparation of alumina supported cobalt catalysts has been studied by TPR, XRD and hydrogen chemisorption techniques. The activity and selectivity of the prepared catalysts have been evaluated for Fischer-Tröpsch (FT) activity in a stirred basket reactor. It is shown that for catalysts with Co content of 10wt.% the activity increases as the carboxylate chain length increases while the selectivity towards methane and light hydrocarbons decreases with the carboxylate chain length. This change relates to the effect of the chain length on the catalyst particle size. The catalyst prepared using cobalt acetate was found to present the highest metal–support interaction and the poorest performance for the Fischer-Tröpsch reaction. When the metal content was increased to 15 and 20wt.% Co, respectively, the metal–support interaction for the catalyst particles prepared from cobalt acetate significantly decreased making it a better catalyst for the FT reaction compared to the catalyst particles prepared from C5 and C9 cobalt carboxylates.
Keywords: Fischer-Tröpsch synthesis; Cobalt catalyst; Carboxylate chain length; Activity; Selectivity
The effect of reduction temperature on Co-Mo/Al2O3 catalysts for carbon nanotubes formation by Siang-Piao Chai; Sharif Hussein Sharif Zein; Abdul Rahman Mohamed (pp. 173-179).
Catalyst reduction temperature was observed to affect the yield and diameter uniformity of carbon nanotubes (CNTs) produced on Co-Mo/Al2O3 catalysts. The results show that on the whole, the reduced catalysts gave higher carbon yield. The CNTs obtained from the unreduced catalyst and the catalysts reduced at 400, 550, and 700°C had diameters of 9.0±1.4, 11.0±1.8, 11.2±1.8, and 12.1±2.7nm, respectively, showing that an increase in catalyst reduction temperature produced a slightly larger average diameter and wider diameter distribution. Raman spectra further elucidate that better-graphitized CNTs were produced on the catalysts reduced with increasing reduction temperatures.Catalyst reduction temperature was observed to affect the yield and diameter uniformity of carbon nanotubes (CNTs) produced on Co-Mo/Al2O3 catalysts. The results show that on the whole, the reduced catalysts gave higher carbon yield. An increase in catalyst reduction temperature produced a slightly larger average diameter and wider diameter distribution. Raman spectra further elucidate that better-graphitized CNTs were produced on the catalysts reduced with increasing reduction temperatures. ▪
Keywords: Carbon nanotubes; Methane decomposition; Catalyst reduction; Co-Mo/Al; 2; O; 3; catalysts
High-active nickel catalyst of NiB/SiO2 for citral hydrogenation at low temperature by Shu-Jen Chiang; Chao-Hsing Yang; Yin-Zu Chen; Biing-Jye Liaw (pp. 180-188).
A high-active supported nickel catalyst of 5% NiB/SiO2 for citral hydrogenation was prepared by impregnation-chemical reduction method. The 5% NiB/SiO2 catalyst was much more active than 5% Ni/SiO2, a conventional supported nickel catalyst reduced by H2. A high yield of citronellal/citronellol of about 98% and a yield of citronellal of about 84% over 5% NiB/SiO2 were obtained at a low temperature of 30°C.▪A high-active supported nickel catalyst of NiB/SiO2 was obtained by impregnation-chemical reduction for liquid-phase hydrogenation. The precursor salt of nickel was mounted on SiO2 by impregnating, drying and calcination at an appropriate temperature without being decomposed, and then reduced with aqueous NaBH4 solution. The factors that governed the preparation of NiB/SiO2 catalysts were examined by the hydrogenation of butyraldehyde. The NiB/SiO2 catalysts were characterized as an ultrafine and amorphous structure, which were much more active than NiB and Ni/SiO2, a conventional supported nickel catalyst reduced by H2. The optimal catalyst of 5% NiB/SiO2 was used to hydrogenate citral to citronellal and citronellol, which was about 14 times as active as NiB, but less selective than NiB. Nevertheless, the reaction could be performed at room temperature to promote the selectivity. A high yield of citronellal/citronellol of about 98% and a yield of citronellal of about 84% over 5% NiB/SiO2 were obtained at a low temperature of 30°C.
Keywords: Amorphous catalyst; Chemical reduction; NiB/SiO; 2; Hydrogenation; Citral
Highly selective synthesis of 2,6-Dimethylnaphthanlene by green catalysts— N-alkyl-pyridinium halides-aluminum chloride ionic liquids by Wei Wu; Guang Wu; Minlin Zhang (pp. 189-193).
Under mild conditions, the transalkylation of 2-methylnaphthanlene with 1,2,4,5-tetramethylbenzene high selective synthesised 2,6-dimethylnaphthalene in N-alkyl-pyridinium halides-aluminum chloride ionic liquids as acid catalysts. The 2,6-DMN selectivity of 100% and 2-MN conversion of 7.9% are observed within 3h of the reaction.▪The transalkylation of 2-methylnaphthanlene (2-MN) with 1,2,4,5-tetramethylbenzene (TeMB) for highly selective synthesis of 2,6-dimethylnaphthalene (2,6-DMN) was performed in N-alkyl-pyridinium halides-aluminum chloride ionic liquids ([C nPy]Cl-AlCl3IL's) as acid catalysts. The influences of length of alkyl group at organic cation, of acid strength of the ionic liquids, as well as reaction time and temperature were studied. Due to its appropriate acidity, the [BuPy]Cl-AlCl3 IL's ( x=0.71) reveals higher activity and selectivity to 2,6-DMN in the reaction under mild conditions when both isomerization of 2,6-DMN and disproportionation of 2-MN are substantively restrained. The selectivity to 2,6-DMN and 2,6-/2,7-DMN ratio reach maximum values of 80.5% and 4.13, respectively, relatively to the thermodynamic value of 2,6-/2,7-DMN ratio ≈l usually obtained with other acid catalysts. After 3h of the reaction the selectivity to 2,6-DMN reaches 100% at 7.9% conversion. The mechanism of transalkylation of 2-MN with TeMB in [C nPy]Cl-AlCl3 IL's is proposed. It is believed that Al2Cl7− is probably the active catalytic species of the reaction. The re-using of the acidic ionic liquids has been investigated. The main reason for deactivation of the catalysts is found to be a leaching of the active Al2Cl7− species as a result of the hydrolysis.
Keywords: Ionic liquid; Selectivity; Transalkylation; 2,6-Dimethylnaphthalene; Deactivation
Methanol oxidation catalysis and substructure of PtRu bimetallic nanoparticles by Hiroaki Nitani; Takashi Nakagawa; Hideo Daimon; Yukiko Kurobe; Takahiro Ono; Yusuke Honda; Akiko Koizumi; Satoshi Seino; Takao A. Yamamoto (pp. 194-201).
PtRu nanoparticles catalyst supported on carbon was synthesized and analyzed. The results indicated a clear correlation between the catalytic activity and Pt–Ru atomic pair frequency occurring on the particle surface, which support the “bi-functional mechanism”. ▪Catalytic material of PtRu nanoparticles supported on carbon (PtRu/C) for direct methanol fuel cells was synthesized by a polyol reduction method. Addition of phosphorus was effective for downsizing PtRu particles and improving their catalytic activity. The activity obtained was six times of that of a commercial catalysis. The samples were analyzed by techniques of X-ray absorption fine structure (XAFS) at Pt LIII-edge and Ru K-edge, transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF). These results indicated a core–shell structure consisting of a Pt-rich core and Ru-rich shell. By examining coordination numbers determined by XAFS analysis, we found a clear correlation between the catalytic activity and the Pt–Ru atomic pair frequency occurring on the particle surface, which supports the “bi-functional mechanism”.
Keywords: PtRu bimetallic catalyst; DMFC; Bi-functional mechanism; EXAFS; Core–shell structure
Mechanistic studies on the Ru(III)-catalyzed oxidation of some aromatic primary diamines by chloramine-T in hydrochloric acid medium: A kinetic approach by K.N. Shivananda; B. Lakshmi; R.V. Jagadeesh; Puttaswamy; K.N. Mahendra (pp. 202-212).
The kinetics of ruthenium(III) chloride (Ru(III))-catalyzed oxidation of aromatic primary diamines viz., 4,4′-diaminodiphenyl methane (DDM), 4,4′-diaminodiphenyl sulfone (DDS) and 4,4′-diaminodiphenyl ether (DDE) by sodium N-chloro- p-toluenesulfonamide or chloramine-T (CAT) in HCl medium have been investigated at 298K. Scheme 1 has been proposed for the Ru(III) catalyzed oxidation of aromatic primary diamines by CAT in acid medium to substantiate the observed kinetics.▪Here, n=2 for DDM and 1 for DDE. In Scheme 1, X and X′ represent the complex intermediate species.Above scheme leads to the following rate law:Rate=K1K2k3[CAT]t[Amine][H+][Ru(III)]1+K1[H+]+K1K2[Amine][H+]The derived rate law and proposed mechanism are consistent with all the experimental kinetic results.The kinetics of ruthenium(III) chloride (Ru(III))-catalyzed oxidation of aromatic primary diamines viz., 4,4′-diaminodiphenyl methane (DDM), 4,4′-diaminodiphenyl sulfone (DDS) and 4,4′-diaminodiphenyl ether (DDE), by sodium N-chloro- p-toluenesulfonamide or chloramine-T (CAT) in HCl medium have been investigated at 298K. Under comparable experimental conditions, the three oxidation reactions follow identical kinetics with first-order dependence both on [oxidant]0 and [Ru(III)], and less than unity order dependence on [Amine]0 and on [H+]. The stoichiometry for each reaction was found and the oxidation products were identified through GC–MS analysis. The reactions were subjected to changes in (a) ionic strength, (b) p- toluenesulfonamide, (c) dielectric permittivity, (d) halide ions, (e) solvent isotope and (f) temperature effect. The reaction mixture fails to initiate the polymerization of acrylonitrile. The activation parameters for the overall reaction were deduced from Arrhenius plots. Under comparable experimental conditions, the relative reactivity of these amines towards CAT is in the order: DDS>DDE>DDM. This reactivity trend may be attributed to electronic factors. The isokinetic temperature ( β) of 350K calculated from enthalpy–entropy relationships and the Exner criterion was much higher than the experimental temperature of 298K employed in the present study, indicating that the reaction is under enthalpy control. Under the identical set of experimental conditions, the kinetics of Ru(III)- catalyzed oxidation of amines by CAT has been compared with those of uncatalyzed reactions; the catalyzed reactions are found to be about 5-fold faster. The catalytic constant ( KC) has been calculated for each amine at different temperatures. The values of activation parameters with respect to Ru(III)-catalyst have been evaluated from the plots of log KC versus 1/ T. The protonated species CH3C6H4SO2N+H2Cl has been postulated as the reactive oxidizing species of CAT. The observed results have been explained by a plausible mechanism and the related rate law has been deduced.
Keywords: Ru(III) catalysis; Oxidation-kinetics; Aromatic diamines; Chloramine-T
Selective CO methanation catalysts for fuel processing applications by Robert A. Dagle; Yong Wang; Guan-Guang Xia; James J. Strohm; Jamelyn Holladay; Daniel R. Palo (pp. 213-218).
Selective CO methanation as a strategy for CO removal in fuel processing applications was investigated over Ru-based catalysts. Ru metal loading and crystallite size were shown to affect catalyst performance. We present the effects of metal loading, preparation method, and crystallite size on performance for Ru-based catalysts in the selective methanation of CO in the presence of H2 and CO2.▪Selective CO methanation as a strategy for CO removal in fuel processing applications was investigated over Ru-based catalysts. Ru metal loading and crystallite size were shown to affect catalyst activity and selectivity. Even operating at a gas-hourly-space-velocity as high as 13,500h−1, a 3% Ru/Al2O3 catalyst with a 34.2nm crystallite was shown to be capable of reducing CO in a reformate to less than 100ppm over a wide temperature range from 240 to 280°C, while keeping hydrogen consumption below 10%. We present the effects of metal loading, preparation method, and crystallite size on performance for Ru-based catalysts in the selective methanation of CO in the presence of H2 and CO2.
Keywords: Methanation; CO removal; Ru/Al; 2; O; 3; catalysts; Fuel processing; Microreactor
Rhodium catalyzed hydroformylation of monoterpenes containing a sterically encumbered trisubstituted endocyclic double bond under mild conditions by José G. da Silva; Humberto J.V. Barros; Angelica Balanta; Alberto Bolaños; Maria L. Novoa; Marisela Reyes; Ricardo Contreras; J. Carles Bayón; Elena V. Gusevskaya; Eduardo N. dos Santos (pp. 219-226).
The rhodium catalyzed hydroformylation 2-carene (1), 3-carene (2), and α-pinene (3), in the presence of PPh3 or various diphosphines and phosphites has been studied. The use of a bulky P(O- o-tBuPh)3 ligand both improves the selectivity, and increases significantly the hydroformylation rate under relatively mild reaction conditions (80–100°C, 40–80atm).▪The rhodium catalyzed hydroformylation of endocyclic monoterpenes, that is, 2-carene (1), 3-carene (2), and α-pinene (3), in the presence of PPh3 or various diphosphines and phosphites has been studied. The unmodified Rh catalyst promotes an intense isomerization of both carenes whose hydroformylation occurs rather slowly, and results in a complex mixture of aldehydes and alcohols. The addition of PPh3, diphosphines or P(OPh)3 in a P/Rh ratio as high as 20, efficiently prevents the isomerization, but the activity for hydroformylation is drastically reduced. On the other hand, the use of a bulky P(O- o-tBuPh)3 ligand both reduces the isomerization, and significantly increases the hydroformylation rate. All three sterically crowded olefins1–3 have been efficiently hydroformylated under relatively mild reaction conditions (80–100°C, 40–80atm) to a main aldehyde (2-formylcarane, 4-formylcarane, and 3-formylpinene, respectively) with good chemo- and regioselectivity, and almost 100% stereoselectivity for the trans isomers.
Keywords: 2-Carene; 3-Carene; α-Pinene; Hydroformylation; Rhodium catalyst; Bulky phosphite
Carbon-supported low-loading rhodium sulfide electrocatalysts for oxygen depolarized cathode applications by Andrea F. Gullá; Lajos Gancs; Robert J. Allen; Sanjeev Mukerjee (pp. 227-235).
The loading of Rh xS y on Vulcan was studied in terms of morphological characteristics and ORR activity for the depolarised electrolysis of hydrochloric acid. Optimal Rh xS y loading was found to be at 15wt.%, two times lower than the commercially available material. We report a significant development in terms of materials and material employment for the oxygen depolarized electrolysis of HCl.▪Noble metal chalcogens are the preferred choice of electrocatalyst materials over pure metals and metal alloys in many industrial processes involving operation in highly corrosive environment. The depolarised electrolysis of hydrochloric acid represents one of such processes; in this case, rhodium sulfide is incorporated into gas diffusion electrode structure for use as oxygen-consuming cathode. An increased dispersion of the rhodium/sulfur compound is an evident goal to obtain highly active catalyst systems while maintaining similar activity. In studying the effect of Rh xS y loading on carbon on oxygen reduction reaction activity, it is paramount to understand and optimize the structure sensitivity of the reaction. Doing so will not only aid in determining the optimal metal loading but more importantly will control the commercial viability of the electrocatalyst. In the present work, the Rh xS y loading on Vulcan XC72-R was studied in terms of morphological characteristics and ORR activity. Physicochemical characterization suggests that the preparation methodology of such chalcogens plays a fundamental role in terms of chemical structure. ORR kinetics was addressed using a series of rotating disk electrode experiments in 1M HCl electrolyte, in which the optimal Rh xS y loading was found to be at 15wt.%, a value two times lower with respect to the commercially available 30wt.% material. Any higher dispersion results in no significant increase in the overall electrocatalytic performance. Based on the increased Rh utilization and enhanced activity found for the low-loading Rh xS y/C samples, we report a significant development in terms of materials and material employment for the oxygen depolarized electrolysis of HCl.
Keywords: Hydrochloric acid electrolysis; Oxygen-depolarized cathode; Oxygen reduction reaction; Rhodium sulfide
Effect of sulphiding agents on the hydrodeoxygenation of aliphatic esters on sulphided catalysts by O.İ. Şenol; T.-R. Viljava; A.O.I. Krause (pp. 236-244).
The effects of H2S and CS2 on the hydrodeoxygenation (HDO) of aliphatic oxygenates were investigated on sulphided NiMo/γ-Al2O3 and CoMo/γ-Al2O3 catalysts. Unlike CS2, H2S had a promoting effect on the HDO. The use of H2S as sulphiding agent in the HDO of aliphatic oxygenates was concluded to be more beneficial than the use of CS2.▪In hydrodeoxygenation (HDO) on sulphided hydrotreating catalysts, addition of a sulphiding agent is typically required to maintain the catalyst activity. The effects of H2S and CS2 on the HDO of aliphatic esters on sulphided NiMo/γ-Al2O3 and CoMo/γ-Al2O3 catalysts were investigated in a fixed-bed flow reactor. The model compounds studied were methyl heptanoate, ethyl heptanoate, heptanol and heptanoic acid. The HDO produced C7 and C6 hydrocarbons in reactions where oxygen- and sulphur-containing compounds were formed as intermediates. Unlike CS2, H2S had a promoting effect on the HDO of the aliphatic oxygenates. The addition of H2S stabilised the selectivities as a function of time, and shifted the main products from C7 to C6 hydrocarbons, but did not prevent catalyst deactivation. The promoting effect of H2S was attributed to the increased catalyst acidity, which enhanced the acid-catalysed reactions (hydrolysis, esterification, dehydration, E2 elimination and SN2 nucleophilic substitution). Both H2S and CS2 suppressed the hydrogenation reactions on the NiMo catalyst but did not affect them significantly on the CoMo catalyst. H2S induced less hydrogen consumption and coke formation than CS2, but the carbon efficiency suffered in the presence of H2S. Thus, the use of H2S as sulphiding agent in the HDO of the aliphatic oxygenates was concluded to be more beneficial than the use of CS2.
Keywords: Bio-oil; Hydrodeoxygenation; Sulphided catalyst; Hydrogen sulphide; Carbon disulphide; Aliphatic ester