Applied Catalysis A, General (v.361, #1-2)
Editorial Board (CO2).
Modeling, simulation and analysis of heavy oil hydroprocessing in fixed-bed reactors employing liquid quench streams by Anton Alvarez; Jorge Ancheyta; José A.D. Muñoz (1-12).
This work presents the modeling and analysis of heavy oil hydroprocessing with liquid quenching. The model showed to predict quite well the experimental data. The analysis was extended to simulate the commercial process. It was determined that the liquid quenching scheme reduces the consumption of utilities and equipment requirements, and thereby total costs, without affecting product quality.This work presents the modeling and analysis of heavy oil hydroprocessing in a fixed-bed reactor system with liquid quenching. Hydroprocessing tests at various operating conditions were conducted in a multi-reactor pilot plant, with inter-bed injection of quench gas or liquid. Based on the experimental information, a heterogeneous plug-flow reactor model was developed to simulate the behavior of the process with both gas and liquid quenching. Major reactions such as hydrodesulfurization (HDS), hydrodenitrogenation (HDN), hydrodemetallization (HDM), hydrodeasphaltenization (HDAs), and hydrocracking (HCR) are considered. The model showed to predict quite well the experimental data in the range of the studied operating conditions. The analysis was extended to simulate the commercial process and to analyze different quenching schemes from an economical point of view. It was determined that the liquid quenching scheme reduces the consumption of utilities and equipment requirements, and thereby total costs, without affecting product quality.
Keywords: Heavy oil hydroprocessing; Fixed-bed reactor; Liquid quenching;
Comparison of redox isotherms for vanadia supported on zirconia and titania by P.R. Shah; I. Baldychev; J.M. Vohs; R.J. Gorte (13-17).
The thermodynamic redox properties of zirconia- and titania-supported vanadia were characterized by coulometric titration in order to understand the impact that these properties have on methanol oxidation and propane ODH.Zirconia- and titania-supported vanadia catalysts were characterized by coulometric titration, Raman spectroscopy, and rate measurements for methanol oxidation and propane oxidative dehydrogenation (ODH). Redox isotherms obtained at 748 K by coulometric titration of a titania-supported vanadia catalyst with a loading of 2.9 V/nm2 showed that reduction occurred in a single step at a P O 2 of 10−22 atm, corresponding to a ΔG of oxidation of −300 kJ/mol; however, reduction of the sample caused changes in the isotherm obtained during re-oxidation consistent with formation of bulk V2O5, which requires higher P O 2 for oxidation. With vanadia-zirconia catalysts, increasing the calcination temperature from 748 to 873 K caused changes in both the Raman spectra and in the 748-K redox isotherm consistent with formation of bulk ZrV2O7. Rate measurements for methanol oxidation and propane ODH on vanadia-titania, vanadia-zirconia, bulk V2O5, and ZrV2O7 showed relatively small differences in specific rates.
Keywords: Coulometric titration; Vanadia; Titania; Zirconia; Methanol oxidation; Propane oxidative dehydrogenation;
Hydrodesulfurization of 4,6-dimethyldibenzothiophene over high surface area metal phosphides by Rui Wang; Kevin J. Smith (18-25).
High surface area MoP (139 m2/g), Ni2P (216 m2/g) and a series of Ni x MoP (121–16 m2/g) catalysts were synthesized by adding citric acid (CA) to precursor salt solutions prior to drying, calcination and reduction. Their HDS TOFs decreased in the order Ni2P > Ni x MoP > MoP and for the Ni x MoP catalysts, the observed TOF increased with Ni content.Unsupported monometallic phosphides (MoP and Ni2P), as well as a series of bimetallic nickel molybdenum phosphides (Ni x MoP), were synthesized with high surface area by adding citric acid (CA) to precursor metal salt solutions prior to drying, calcination and temperature-programmed reduction (TPR). The resulting MoP and Ni2P catalysts had surface areas of 139 and 216 m2/g, respectively. The surface areas of the Ni x MoP catalysts decreased with increased Ni content and ranged from 121 to 16 m2/g. In all cases, the catalyst surface area was greater than that obtained when a conventional preparation procedure was followed that did not use CA. The activity of the catalysts for the hydrodesulfurization (HDS) of a feed containing 3000 ppm 4,6-dimethyldibenzothiophene (4,6-DMDBT) in toluene was measured at 583 K and 3.0 MPa. The resulting catalysts were highly active and among the studied phosphides, Ni2P exhibited the highest HDS activity with a conversion of 87.7% at a WHSV of 26 h−1 and a H2/liquid feed ratio of 625 (v/v). The HDS TOF decreased in the order Ni2P > Ni x MoP > MoP and for the Ni x MoP catalyst, the observed TOF increased with Ni content.
Keywords: Catalyst; Hydrodesulfurization; Metal phosphide; Nickel phosphide; Molybdenum phosphide; 4,6-Dimethyldibenzothiophene; Citric acid;
Transesterification between dimethyl carbonate and phenol in the presence of (NH4)8Mo10O34 as a catalyst precursor by Yong Tae Kim; Eun Duck Park (26-31).
The novel catalyst system (NH4)8Mo10O34 was found to be active for transesterification between dimethyl carbonate and phenol based on the comparisons of performance over Sn-, Pb- and Mo-based metal complexes. X-ray diffraction (XRD), inductively coupled plasma–atomic emission spectroscopy (ICP–AES), the temperature-programmed desorption (TPD) with mass spectroscopy, thermogravimetic analysis (TGA), Infrared spectroscopy (FT-IR), and Raman spectroscopy were conducted to characterize the catalysts. (NH4)8Mo10O34 can be formed from (NH4)6Mo7O24·4H2O through calcinations at ∼423 K. The Mo species dissolved from (NH4)8Mo10O34 appeared to play the main part in this reaction. This homogeneous catalyst showed the superior turnover frequency to those of the homogeneous lead complexes obtained from PbO. The activation energy was determined to be 87.1 kJ mol−1.The novel catalyst system (NH4)8Mo10O34 was found to be active for transesterification between dimethyl carbonate and phenol based on the comparisons of performance over Sn-, Pb- and Mo-based metal complexes. X-ray diffraction (XRD), inductively coupled plasma–atomic emission spectroscopy (ICP–AES), the temperature-programmed desorption (TPD) with mass spectroscopy, thermogravimetic analysis (TGA), Infrared spectroscopy (FT-IR), and Raman spectroscopy were conducted to characterize the catalysts. (NH4)8Mo10O34 can be formed from (NH4)6Mo7O24·4H2O through calcinations at ∼423 K. The Mo species dissolved from (NH4)8Mo10O34 appeared to play the main part in this reaction. This homogeneous catalyst showed the superior turnover frequency to those of the homogeneous lead complexes obtained from PbO. The activation energy was determined to be 87.1 kJ mol−1.
Keywords: Transesterification; Dimethyl carbonate (DMC); Methylphenyl carbonate (MPC); Diphenyl carbonate (DPC); (NH4)8Mo10O34;
Synthesis, characterization and photocatalytic activity of M x Ce1−x VO4 (M = Li, Ca and Fe) by Sudarshan Mahapatra; R. Vinu; Dipankar Saha; T.N. Guru Row; Giridhar Madras (32-41).
Li x Ce1−x VO4 was synthesized by the solid-state technique. Particle sizes were in the range of 600–800 nm, as observed by scanning electron microscopy. The photocatalytic activity of these compounds was investigated for the first time for the degradation of different dyes and organics, the oxidation of cyclohexane and the hydroxylation of benzene.Non-stoichiometric substituted cerium vanadates, M x Ce1−x VO4 (M = Li, Ca and Fe), were synthesized by solid-state reactions. The crystal structure was analyzed by powder X-ray diffraction and it exhibits a tetragonal zircon structure, crystallizing in the space group I41/amd with a = 7.3733(4) and c = 6.4909(4) Å and Z = 4. Particle sizes were in the range of 600–800 nm, as observed by scanning electron microscopy. The thermal analysis of the compounds showed phase stability up to 1100 °C. The UV diffuse reflectance spectra indicated that the compounds have band gaps in the range of 2.6–2.9 eV. The photocatalytic activity of these compounds was investigated for the first time for the degradation of different dyes, and organics, the oxidation of cyclohexane and the hydroxylation of benzene. The degradation of dyes was modeled using the Langmuir–Hinshelwood kinetics, while the oxidation of cyclohexane and hydroxylation of benzene were modeled using a free radical mechanism and a series reaction mechanism, respectively.
Keywords: Photocatalysis; Photo-oxidation; Orthovanadates; Synthesis;
Soybean oil and beef tallow alcoholysis by acid heterogeneous catalysis by Rafael A. Soldi; Angelo R.S. Oliveira; Luiz P. Ramos; Maria Aparecida F. César-Oliveira (42-48).
Sulfonated polystyrene compounds (SPS) were synthesized, leading catalytically active polymeric materials with high sulfonation degree. Catalyst performance was evaluated in beef tallow and soybean oil transesterification reactions. The SPS leading to conversion of 85 and 75% for soybean oil and beef tallow in to ethyl esters, respectively, and 94% of the soybean oil methyl esters. Therefore, sulfonated polymeric compounds obtained from linear polystyrene are efficient catalysts.Sulfonated polystyrene compounds (SPS) were synthesized from linear polystyrene (PS), leading to catalytically active polymeric materials with sulfonation degrees between 5.0 and 6.2 mmol SO3H/g of dry polymer. Catalyst performance was evaluated in beef tallow and soybean oil transesterification with ethanol and methanol. The SPS were used at 20 mol% of –SO3H groups in relation to the oil mass. Methanol:oil molar ratios of 3:1, 6:1, 9:1, and 100:1 were employed, and the reactions lasted between 3 and 18 h. The SPS samples were insoluble in the reaction media and led to conversions of 85 and 75% of refined soybean oil and beef tallow with a 53 mg KOH/g acid number, respectively. There was an increase in ester production for reactions carried out at higher methanol:oil molar ratio and, in some cases, products with as much as 94% methyl ester content were obtained. Therefore, sulfonated polymeric compounds obtained from linear polystyrene are efficient catalysts for the alcoholysis of refined vegetable oils and raw materials containing high acid numbers.
Keywords: Heterogeneous polymeric catalyst; Sulfonated polystyrene; Biodiesel; Methanolysis;
Ethanol dehydrogenation by gold catalysts: The effect of the gold particle size and the presence of oxygen by Yejun Guan; Emiel J.M. Hensen (49-56).
A range of silica-supported gold nanoparticle catalysts between 1.7 and 15 nm have been synthesized by varying the support (ordered mesoporous silicas, silicas with and without aluminium impurities) and the gold loading procedure. A strong influence of the gold particle size on the non-oxidative dehydrogenation of ethanol is noted: gold nanoparticles of about 6 nm show a much higher activity than smaller or larger particles. This optimal catalytic activity is attributed to the existence of surface steps with a suitable geometry for the removal of β-H atoms from adsorbed ethoxide. In the presence of oxygen, the rate for dehydrogenation is much higher because of the presence of an adsorbed oxygen species, but the selectivity becomes lower as combustion starts to contribute. The intrinsic activity is constant up to about 7 nm and then increases for larger particles.A range of silica-supported gold nanoparticle catalysts have been synthesized on various silica supports. The particle size was varied between 1.7 and 15 nm by varying the support (ordered mesoporous silicas, silicas with and without aluminium impurities) and the gold loading procedure. A strong influence of the gold particle size on the non-oxidative dehydrogenation of ethanol is noted: gold nanoparticles of about 6 nm show a much higher activity than smaller or larger particles. This optimal catalytic activity is attributed to the existence of surface steps with a suitable geometry for the removal of β-H atoms from adsorbed ethoxide. Such stepped sites are expected to be present with maximum density for intermediate particle size. In the presence of oxygen, the rate for dehydrogenation is much higher because of the presence of an adsorbed oxygen species, but the selectivity becomes lower as combustion starts to contribute. The intrinsic activity is constant up to about 7 nm and then increases for larger particles. The larger gold nanoparticles may contain strongly adsorbed oxygen adatoms, which are much scarcer on smaller gold particles. Infrared spectroscopy shows that, already at room temperature, adsorbed ethoxide reacts with molecular oxygen, whereas C–H bond cleavage to produce acetaldehyde requires at least a temperature of 75 °C. The reaction rate is first order with respect to ethanol in both cases.
Keywords: Gold; Particle size effect; Ethanol; Dehydrogenation; Oxidation;
The oxidative dehydrogenation of n-hexane over Ni–Mo–O catalysts by Bavani Pillay; Mfanuwenkosi R. Mathebula; Holger B. Friedrich (57-64).
The effect of chemical composition on nickel–molybdenum catalysts in the oxidative dehydrogenation of n-hexane was studied. The catalysts consisted of the following phases: nickel oxide, molybdenum trioxide, nickel molybdate (α-NiMoO4 and β-NiMoO4) and a solid solution of nickel in a lattice of nickel molybdate. Characterization of the catalysts was carried out using ICP-OES, BET, XRD, FTIR, SEM, TPR and XPS techniques. The effect of phase composition of the catalysts on their catalytic activity and selectivity to the products obtained in the temperature range 300–500 °C was also studied. The most selective catalyst for the synthesis of hexenes was the pure β-NiMoO4, which gave 25% selectivity to 1-hexene and 10% selectivity to 2-hexenes and 3-hexenes at 9% conversion. The pure phases NiO and MoO3, although active in hexane ODH, showed poor selectivity to hexenes, particularly to 1-hexene at comparable conversions suggesting that they are not responsible for the catalytic activity of the NiO–MoO3 system. The pure β-phase was more selective towards the hexenes than the α-phase with the difference in the molybdenum coordination believed to be the reason for the different activities and selectivities of the two modifications of NiMoO4. The α-phase with MoO3 was more active, suggesting that a synergetic effect plays an important role in modifying catalytic activity.Catalysts consisting of the following phases: nickel oxide, molybdenum trioxide, nickel molybdate (α-NiMoO4 and β-NiMoO4) and a solid solution of nickel in a lattice of nickel molybdate were investigated in the oxidation/oxidative dehydrogenation of n-hexane. Pure β-NiMoO4 gave the highest selectivity to hexenes, predominantly 1-hexene.
Keywords: NiMoO4; n-Hexane; Oxidation; In situ characterization;
Selective hydrogenation of α,β-unsaturated aldehydes over Au/Mg x AlO hydrotalcite catalysts by Kuen-Jiun You; Ching-Tu Chang; Biing-Jye Liaw; Ching-Tsuen Huang; Yin-Zu Chen (65-71).
Gold dispersed on a solid base of Mg x AlO hydrotalcite could selectively hydrogenate α,β-unsaturated aldehydes (UALs) to α,β-unsaturated alcohols (UOLs). A high selectivity of UOL was obtained at the complete conversion. A correlation between the gold states (Au3+/Au0) and the activity and selectivity was found. Increasing the Au3+/Au0 ratio of the catalyst increased the activity and selectivity of UAL to UOL.Liquid-phase reduction of α,β-unsaturated aldehydes (UALs) to the corresponding α,β-unsaturated alcohols (UOLs) was investigated on gold catalysts supported on a solid base of Mg x AlO hydrotalcite (x = Mg/Al molar ratio). The Au/Mg x AlO catalysts were prepared using a modified deposition precipitation method without adjusting the pH of the initial HAuCl4 solution. The effects of various parameters involved in preparation of catalysts were also studied, including the Mg/Al molar ratio and the calcination temperatures of the Mg x AlO support and Au/Mg x AlO catalyst. The Mg/Al ratio of Mg x AlO affected the pH of the final solution, and determined the actual gold loading in the catalyst. Calcination temperatures of the Mg x AlO support and Au/Mg x AlO catalyst determined the ratio of gold states (Au3+/Au0) on the catalyst. A correlation between the gold states (Au3+/Au0) and the activity and selectivity of UAL to UOL was found. Increasing the Au3+/Au0 ratio of the catalysts increased the activity and selectivity of UAL to UOL. The different performances of the Au/Mg x AlO catalysts from Group VIII metals due to the effects of temperature, pressure and steric structures of UALs were discussed.
Keywords: Gold catalysts; Hydrotalcite; Mg x AlO; Selective hydrogenation; α,β-Unsaturated aldehyde;
Oxidation of methanol and total reduced sulfur compounds with ozone over V2O5/TiO2 catalyst: Effect of humidity by E. Sahle-Demessie; Venu Gopal Devulapelli (72-80).
The purpose of this study was to investigate the feasibility of using ozone-enhanced catalytic oxidation for the treatment of high volume, low concentration (HVLC) waste gas streams at a Kraft pulp and paper mill that contain hazardous air pollutants such as methanol (CH3OH), reduced sulfur compounds (TRS), including dimethyl sulfide (DMS), dimethyl disulfide (DMDS), methanethiol (MT), hydrogen sulfide (H2S), and saturated with moisture. This paper reports that ozone-enhance V2O5-TiO2 catalyzed oxidation is a stable and effective process to remove methanol and TRS compounds in the presence of moisture that has composition similar to the effluent stream coming out of a pulp mill blow tank.The effect of moisture on the oxidation of CH3OH, MT and DMS was studied using V2O5/TiO2 as a catalyst at different feed compositions (Cmethanol: 1000 and 7500 ppm; CDMS: 250 and 1000 ppm; and CMT: 250 and 1000 ppm) and gas hourly space velocities (37,000–150,000 h−1) at 250 °C and O3-to-substrate mole ratio of 2.1. Conversions of methanol and TRS compounds were high and the main products were CO2, CO and SO2 with small amounts of partial oxidation products. Increasing the relative humidity of the gas stream from zero to 18,000 ppm reduced the conversion of methanol, whereas the conversion of TRS compounds was not affected, although the selectivity for partial oxidation products of TRS compounds decreased. High moisture levels have inhibition effect on the reactions because of competitive adsorption of methanol and water on to the same sites. The increase in the complete oxidation of TRS products could be due to forming hydroxyl ion radicals in presence of ozone and water molecules. Possible reaction mechanisms have been proposed for the complete oxidation of methanol and TRS compounds with ozone based on the product distribution.Oxidation of air pollutants with ozone over V2O5/TiO2 offers the advantage of performing reactions at low temperatures, resulting in a cost-effective advanced oxidation technology and does not generate secondary pollutants. The effects of humidity and feed compositions on the catalytic activity, reaction pathway and product distribution of methanol and total reduced sulfur (TRS) compounds was studied. Scheme represents reaction mechanism for the oxidation of methanol and TRS with ozone over V2O5/TiO2 catalyst.
Keywords: Catalytic oxidation; Ozone; Methanol; Dimethyl sulfide; Methanethiol; Effect of humidity;
Large scale hydroisomerization reactions of n-heptane on partially reduced MoO3/TiO2 by H. Al-Kandari; F. Al-Kharafi; A. Katrib (81-85).
Hydroisomerization of n-heptane was carried out on the bifunctional MoO2(H x )ac phase deposited on TiO2 at the bench scale level. Experimental conditions comparable to those carried out in industry such as hydrogen pressure, reaction temperature, and hydrogen flow rate. Space velocity and the catalyst stability were employed. High conversion and isomerization selectivity were obtained at 623 K, 5 bar and 0.8 h−1 LHSV.Hydroisomerization of n-heptane on the bifunctional molybdenum MoO2−x (OH) y phase has been carried out at industrial conditions in terms of temperature, pressure and space velocity. A conversion of 78% and 82% in isomerization selectivity were obtained at 623 K, 5 bar pressure, 30 SLPH and 0.8 h−1 LHSV using 15 g of the catalyst. Complete transformation of n-heptane to isomerization products was observed below the saturation limit of n-heptane reactant to the available active sites at 0.8 h−1 LHSV. Time on stream experiments for 70 h did not show any changes in neither the conversion nor the isomerization selectivity. The stability and the resistance of the catalytic systems towards poisoning by hydrocarbon species are attributed to the particular position of Mo atoms placed along the C-axis of the deformed rutile structure of this phase.
Keywords: MoO3; TiO2; Bifunctional catalyst; Isomerization of n-heptane; LHSV;
Perovskites with cotton-like morphology consisting of nanoparticles and nanorods: Their synthesis by the combustion method and their NO x adsorption behavior by Md. Hasan Zahir; Toshio Suzuki; Yoshinobu Fujishiro; Masanobu Awano (86-92).
The perovskites La0.8A0.2MnO3 (A = Cs) and La0.8A0.2Mn0.8B0.2O3 (A = Cs and B = Ga) have been synthesized by a solution-combustion method using metal nitrates, urea and glucose as the fuel materials. The perovskite products have been tested as catalysts for NO + NO2 (NO x ) adsorption. Rapid adsorption of NO x by the perovskites with cotton-like morphology consisting of nanoparticles and nanorods was highly effective for NO x removal from the gas phase.The perovskites La0.8A0.2MnO3 (A = Cs) and La0.8A0.2Mn0.8B0.2O3 (A = Cs and B = Ga) have been synthesized by a solution-combustion method using metal nitrates, urea and glucose as the fuel materials. The structures of the synthesized products were studied by XRD, FT-IR, SEM, and BET analyses. The morphology of La0.8Cs0.2MnO3 (LCM) was cotton-like whereas the product of La0.8Cs0.2Mn0.8Ga0.2O3 (LCMG) was comprised of rather voluminous cotton-like morphology coexisting with nanorods. The nanorods are quite long, straight, and round and have a much smoother surface structure. The perovskite products have been tested as catalysts for NO + NO2 (NO x ) adsorption. The formation of various species during the adsorption of NO x , issuing from a synthetic, lean-burn exhaust gas upon LCM and LCMG was studied using FT-IR. Rapid adsorption of NO x by the perovskites with cotton-like morphology consisting of nanoparticles and nanorods was highly effective for NO x removal from the gas phase.
Keywords: NO x trap catalyst; Lean-burn; Perovskites; Nanorods;
Additional Brønsted acid sites in [Ga]HZSM-5 formed by the presence of water by Artit Ausavasukhi; Tawan Sooknoi (93-98).
GaO(OH) is formed by chemisorbed water on GaO+. This GaO(OH) can be readily inserted into the framework by reactions with defect hydroxyls (>300 °C) forming additional acid sites. Upon heating, the GaO(OH) can either: (i) react with the Brønsted acid sites to form GaO+ back or (ii) become dehydrated to form smaller clusters of Ga2O3 (>450 °C).The incorporation of Ga(NO3)3 into HZSM-5 zeolite results in additional Brønsted acid sites evidenced by 1H MAS NMR and FTIR. Such acid sites are proposed to arise from the incorporated Ga extra-framework (GaO(OH)) and insertion of such species with defect hydroxyls into the zeolite framework (GaOHSi). These additional Brønsted acid sites are particularly formed under steaming and may well be responsible for the change in the catalytic behaviour of [Ga]HZSM-5 when water is present in the reaction stream. In the reaction using ethylene as a feed, higher hydrocarbons, namely aromatics, can be produced over “reduced Ga species”. In contrast, the conversion of ethanol over [Ga]HZSM-5 showed an increased activity in a manner similar to that over a typical HZSM-5, but with higher acidity. The formation of the additional acid sites is readily reversible at high temperature (>450 °C) and hence the steam treatment can be used for re-dispersing the incorporated Ga species.
Keywords: 1H MAS NMR; GaHZSM-5; Brønsted acid; Water; Ethanol;
Conversion of methylesters to hydrocarbons over an H-ZSM5 zeolite catalyst by Tanate Danuthai; Siriporn Jongpatiwut; Thirasak Rirksomboon; Somchai Osuwan; Daniel E. Resasco (99-105).
The conversion of methyl octanoate on H-ZSM5 yields a variety of hydrocarbons (C1–C7), with significant amounts of aromatics. Octanoic acid and heavy products, particularly 8-pentadecanone are formed as primary products via acid-catalyzed hydrolysis and condensation, respectively. Both octanoic acid and the condensation products undergo further reaction producing aromatics as secondary products.The conversion of methyl octanoate on an H-ZSM5 zeolite catalyst has been investigated as a model reaction for the production of hydrocarbon fuels and chemicals from biodiesel. The reactivity of methyl octanoate on H-ZSM5 is higher than that observed with a linear alkane of the same chain length as the ester, n-octane. The enhanced activity may be due to the strong adsorption of the ester group on the zeolite sites. The deoxygenation of methyl octanoate yielded a variety of hydrocarbons (C1–C7), with significant amounts of aromatics. Octanoic acid and heavy products, particularly 8-pentadecanone, were formed as primary products from methyl octanoate via acid-catalyzed hydrolysis and condensation, respectively. Both octanoic acid and the condensation products undergo further reaction, producing aromatics. The comparison conducted with n-octane as a feed indicates that aromatics can be formed through a series of reactions, namely cracking, oligomerization, and cyclization. A small amount of ethylbenzene and o-xylene at low conversion of methyl octanoate indicates that direct dehydrocyclization may also take place, but this path was not evident when the feed was n-octane.
Keywords: Biofuels; Methyl ester conversion; Alkane conversion; Aromatization; H-ZSM5;
Modification of Co–Mn–Al mixed oxide with potassium and its effect on deep oxidation of VOC by K. Jirátová; J. Mikulová; J. Klempa; T. Grygar; Z. Bastl; F. Kovanda (106-116).
Catalytic activity of the Co4MnAl mixed oxide catalyst modified with various amounts of potassium was examined in total oxidation of toluene and ethanol. The highest activity in toluene oxidation was achieved with the catalyst containing ca. 1 wt% K, while in ethanol oxidation the catalysts activity gradually increased with increasing potassium content up to 3 wt% K.Catalytic activity of the Co–Mn–Al mixed oxide catalyst (Co:Mn:Al molar ratio of 4:1:1) modified with various amounts of potassium (0–3 wt%) was examined in total oxidation of toluene and ethanol. The prepared catalysts were characterized by chemical analysis (AAS), powder X-ray diffraction (XRD), surface area measurements, temperature programmed techniques (TPR, TPD), voltammetry of microparticles, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The non-modified catalyst was composed of spinel-like Co–Mn–Al mixed oxide as the only XRD crystalline phase. The surface concentrations of metal components obtained by XPS were different from the bulk ones determined by chemical analysis and the segregation of the metal components depended on the actual potassium content. The low K additions changed mainly the surface acid–base properties of the catalyst. According to XRD and voltammetry measurements, Mn oxides segregated from the original spinel-like phase at high concentration of potassium (2.7 and 3.0 wt%); XPS showed an enrichment of the catalysts surface with Mn. The K addition caused significant changes in the catalyst efficiency. The highest conversion in toluene oxidation was achieved with the catalyst containing about 1 wt% K; no reaction by-products were observed beside H2O and CO2. In ethanol oxidation, the catalysts activity gradually increased with increasing potassium content up to about 3 wt% K, but the presence of excess potassium in the Co–Mn–Al catalyst negatively affected formation of reaction by-products: acetaldehyde production steeply increased with potassium concentration higher than 1 wt%.
Keywords: Layered double hydroxides; Mixed oxide catalysts; VOC; Potassium promoter;
Single-step conversion of cellulose to 5-hydroxymethylfurfural (HMF), a versatile platform chemical by Yu Su; Heather M. Brown; Xiwen Huang; Xiao-dong Zhou; James E. Amonette; Z. Conrad Zhang (117-122).
A new catalytic pathway is revealed for the rapid conversion of cellulose to sugars and further to 5-hydroxymethylfurfural (HMF) in a single-step process under mild temperatures (80–120 °C). Paired CuCl2/CrCl2 catalysts in 1-ethyl-3-methyl-imidazolium chloride solvent exhibited remarkably high activity for hydrolytic cellulose depolymerization. The product selectivity can be tuned by simply varying the CuCl2/CrCl2 ratio.The ability to use cellulosic biomass as feedstock for the large-scale production of liquid fuels and chemicals depends critically on the development of effective low temperature processes. One promising biomass-derived platform chemical is 5-hydroxymethylfurfural (HMF), which is suitable for alternative polymers or for liquid biofuels. While HMF can currently be made from fructose and glucose, the ability to synthesize HMF directly from raw natural cellulose would remove a major barrier to the development of a sustainable HMF platform. Here we report a single-step catalytic process where cellulose as the feed is rapidly depolymerized and the resulting glucose is converted to HMF under mild conditions. A pair of metal chlorides (CuCl2 and CrCl2) dissolved in 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) at temperatures of 80–120 °C collectively catalyze the single-step process of converting cellulose to HMF with an unrefined 96% purity among recoverable products (at 55.4 ± 4.0% HMF yield). After extractive separation of HMF from the solvent, the catalytic performance of recovered [EMIM]Cl and the catalysts was maintained in repeated uses. Cellulose depolymerization occurs at a rate that is about one order of magnitude faster than conventional acid-catalyzed hydrolysis. In contrast, single metal chlorides at the same total loading showed considerably less activity under similar conditions.
Keywords: 5-Hydroxymethylfurfural; HMF; Ionic liquid; 1-Alkyl-3-methylimidazolium chloride; 1-Ethyl-3-methyl-imidazolium chloride; Glucose; Cellobiose; Maltose; Cellulose conversion; Paired metal chlorides; CuCl2; CrCl2;
Remediation of actual groundwater polluted with nitrate by the catalytic reduction over copper–palladium supported on active carbon by Yi Wang; Yoshinori Sakamoto; Yuichi Kamiya (123-129).
Ozone-treatment of actual groundwater polluted with NO3 − substantially helped to maintain the catalytic activity of Cu–Pd/active carbon due to removal of organic compounds in the groundwater. While Cl− in the groundwater caused the decrease in the activity and selectivity, a process of ozone pre-treatment, catalytic reduction using Cu–Pd/active carbon, and ion-exchange with Na-mordenite remediated the actual groundwater.Catalytic reduction of nitrate (NO3 −) in groundwater over a Cu–Pd catalyst supported on active carbon was investigated in a gas–liquid co-current flow system at 298 K. Although Cu–Pd/active carbon, in which the Cu/Pd molar ratio was more than 0.66, showed high activity, high selectivity for the formation of N2 and N2O (98%), and high durability for the reduction of 100 ppm NO3 − in distilled water, the catalytic performance decreased during the reduction of NO3 − in groundwater. The catalyst also irreversibly deactivated during the reaction in groundwater. The organic species in the groundwater caused the decrease in the catalytic performance and the irreversible catalyst deactivation. Ozone-treatment of the groundwater to remove the organic species substantially helped to maintain the catalytic activity and to halt the irreversible deactivation of the catalyst. Chloride ion (Cl−) in the groundwater also caused the decrease in the activity and selectivity, but the effects of Cl− were reversible. Sulfate ion (SO4 2−) and cations, including Mg2+, Ca2+ and K+, had little or no effect on the catalytic performance of Cu–Pd/active carbon, though they were present in the groundwater sample. More than an allowable level of NH3 (NH4 +) was formed during the catalytic reduction of NO3 − in the groundwater, but was completely removed by the cation-exchange process using Na-mordenite.
Keywords: Nitrate; Groundwater; Catalytic reduction; Copper–palladium bimetal catalyst; Humic acid; Ion-exchange;
Liquid phase trans-stilbene epoxidation over catalytically active cobalt substituted TUD-1 mesoporous materials (Co-TUD-1) using molecular oxygen by Xian-Yang Quek; Qinghu Tang; Shuangquan Hu; Yanhui Yang (130-136).
The unique pore structure of Co-TUD-1 catalyst is suggested to be beneficial for the epoxidation of bulky alkene molecules, e.g., trans-stilbene with molecular oxygen, comparing with other well-established catalysts, e.g., Co-MCM-41 and Co2+-NaX. Microwave irradiation can significantly shorten the reaction time, whereas high conversion and epoxide selectivity remained.A series of framework substituted Co-TUD-1 catalysts, prepared by direct hydrothermal synthesis, were characterized using X-ray diffraction, nitrogen physisorption, transmission electron microscopy and UV–vis and Raman spectroscopies. These catalysts showed high conversion and selectivity towards trans-stilbene oxide in liquid phase trans-stilbene epoxidation with molecular oxygen as oxidant in the absence of a sacrificial reductant. The conversion and selectivity did not remarkably differentiate for fresh and recycled catalyst after four reaction runs. The unique pore structure of Co-TUD-1 catalyst is suggested to be beneficial for the epoxidation of bulky alkene molecules comparing with other well-established catalysts, e.g., Co-MCM-41 and Co2+-NaX. Microwave irradiation can significantly shorten the reaction time, whereas high conversion and epoxide selectivity remained.
Keywords: Co-TUD-1; trans-Stilbene; Epoxidation; Molecular oxygen; Microwave;
Group 11 (Cu, Ag, Au) promotion of 15%Co/Al2O3 Fischer–Tropsch synthesis catalysts by Gary Jacobs; Mauro C. Ribeiro; Wenping Ma; Yaying Ji; Syed Khalid; Paulo T.A. Sumodjo; Burtron H. Davis (137-151).
Co/Al2O3 FT catalysts promoted with Group 11 metals were characterized by EXAFS/XANES and enhanced Co reducibility was observed. With 0.83% and 2.76% Ag and 1.51%Au, significant gains in Co active site densities were achieved resulting in improved CO conversion levels relative to the unpromoted catalyst in CSTR testing. Slight decreases in light product selectivity and slight increases in C5+ selectivity were also achieved.Co/Al2O3 Fischer–Tropsch synthesis catalysts promoted with different quantities of Group 11 metals (Cu, Ag, Au) were characterized and tested. The presence of relatively small quantities of such metals enhanced Co reducibility and, in the cases of Ag and Au, improved the surface Co metal active site densities. EXAFS experiments with the most loaded catalyst samples show that only Co–Co and Me–Me (Me = Cu, Ag and Au) coordination could be observed. This suggests that the greater fraction of the metals form different phases. However, the reduction promoting effect of the Group 11 metal is severely hampered once the catalyst receives a mild passivation treatment following primary reduction. An explanation in terms of promoter segregation during primary reduction is proposed. At lower promoter levels (0.83%Ag and 1.51%Au) and higher Ag levels (2.76%), significant gains in Co active site densities were achieved resulting in improved CO conversion levels relative to the unpromoted catalyst. Moreover, slight decreases in light product (e.g., CH4) selectivity and slight increases in C5+ selectivity were achieved. At high Au loading (5.05%), however, too much Au was loaded which, although significantly increasing the fraction of Co reduced, blocked Co surface sites and resulted in decreased CO conversion rates. While Cu facilitated Co reduction, the increased fraction of reduced Co did not translate to improved active site densities. It appears that a fraction of Cu tended to cover the rim of Co clusters, resulting in decreases in CO conversion rates and detrimental increases in light product selectivity.
Keywords: Co; Cobalt; Cu; Copper; Ag; Silver; Au; Gold; Al2O3; Alumina; Syngas; Synthesis gas; Fischer–Tropsch synthesis; FT; Gas to liquids; GTL; Promoters; Reducibility; EXAFS; XANES;
Jacobsen catalyst immobilized on chitosan membrane as interface catalyst in organic/aqueous system for alkene oxidation by T.C.O. Mac Leod; V. Palaretti; V.P. Barros; A.L. Faria; T.A. Silva; Marilda D. Assis (152-159).
The Jacobsen catalyst was immobilized in chitosan membrane and characterized by different techniques. The new catalyst was used in a biphasic system, as a catalytic barrier between two different phases: an organic substrate phase and an aqueous solution of oxidants, dismissing the need for phase transfer agents, and leading to better product yields compared with the catalyst in homogeneous medium.The Jacobsen catalyst, Mn(salen), was immobilized in chitosan membrane. The obtained Mn(salen)-Chit was characterized by thermogravimetric analysis (TG), differential thermal analysis (DTA), differential scanning calorimetry (DSC), infrared spectroscopy (FT-IR), degree of N-acetylation by 1H NMR, and UV–vis spectroscopy. The UV–vis absorption spectrum of the encapsulated catalyst displayed the typical bands of the Jacobsen catalyst, and the FT-IR presented an absorption band characteristic of the imines present in the Jacobsen catalyst. The chitosan membranes were available, in a biphasic system, as a catalytic barrier between two different phases: an organic substrate phase (cyclooctene or styrene) and an aqueous solution of either m-CPBA, t-BuOOH or H2O2, and dismissing the need for phase transfer agents and leading to better product yields compared with the catalyst in homogeneous medium. This new catalyst did not leach from the support and was reused many times, leading to high turnover frequencies.
Keywords: Catalysis; Salen complexes; Alkene oxidation; Chitosan;
Preferential oxidation of CO by CuO x /CeO2 nanocatalysts prepared by SACOP. Mechanisms of deactivation under the reactant stream by Gregorio Marbán; Irene López; Teresa Valdés-Solís (160-169).
CuO x /CeO2 nanocatalysts were synthesized using the silica aquagel co-precipitation (SACOP) technique and tested for the preferential oxidation of CO (PROX). In spite of their high catalytic activity and selectivity they suffer from some deactivation. The deactivation mechanism comprises the formation of surface carbonates (the main cause of deactivation) and the partial sintering of copper (by the aggregation of dispersed Cu2+ in CuO clusters), both of which are a function of the gas concentration, temperature and reaction time.CuO x /CeO2 nanocatalysts were synthesized using the silica aquagel co-precipitation (SACOP) technique and tested for the preferential oxidation of CO (PROX). In spite of their high catalytic activity and selectivity, it was found that deactivation restricted their utilization in practical conditions, as is the case for most copper-based catalysts analyzed in the PROX process. In order to determine the causes of deactivation exhaustive analyses of the evolution of the composition of the catalyst surface during the reaction were performed by means of spectroscopic techniques (XPS and FTIR). Moreover step–response experiments under different atmospheres were carried out in order to establish the deactivating potential of the different gases present in the reactant stream. The deactivation mechanism comprises the formation of surface carbonates (the main cause of deactivation) and the partial sintering of copper (by the aggregation of dispersed Cu2+ in CuO clusters), both of which are a function of the gas concentration, temperature and reaction time.
Keywords: Preferential oxidation of CO; Deactivation; Sintering; Carbonates; CuO x /CeO2;