Effect of preparation and operation conditions on the catalytic performance of cobalt-based catalysts for light olefins production

Cobalt-based catalysts were prepared by precipitation method. This research investigated the effects of different supports cobalt loading, promoters, loading of promoters and calcination conditions on the catalytic performance of cobalt catalysts for Fisher-Tropsch synthesis (FTS). It was found that the catalyst containing 40 wt.% Co/TiO₂ promoted with 6 wt.% Zn was an optimal catalyst for the conversion of synthesis gas to hydrocarbons especially light olefins. The activity and selectivity of optimal catalyst were studied in different operational conditions. The results showed that the best operational conditions were the H₂/CO = 2/1 molar feed ratio at 240 °C and GHSV = 1100 h⁻¹ under atmospheric pressure. Characterization of catalysts were carried out by using X-ray diffraction (XRD), thermal gravimetric analysis (TGA), hydrogen temperature program reduction (H₂-TPR), N₂ physisorption measurements such as Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods.     

Effects of promoters and calcination conditions on the catalytic performance of iron-manganese catalysts for Fischer-Tropsch synthesis

The effects of [Fe]/[Mn] molar ratios, promoters, loading of optimal promoter and calcination conditions on the catalytic performance of iron-manganese catalysts for the Fisher-Tropsch synthesis (FTS) were investigated. It was found that the 50%Fe/50%Mn catalyst that was promoted with 6 wt.% K is an optimal catalyst for the conversion of synthesis gas to hydrocarbons especially light olefins. The effects of calcination behaviors and operational conditions on the catalytic performance of optimal catalyst were investigated. The results are shown that the best operational conditions are the H₂/CO = 2/1 molar feed ratio at 280 °C and GHSV = 1400 h^− 1 under 3 bar total pressure. Characterization of catalysts were carried out using X-ray diffraction (XRD), temperature program reduction (TPR), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC), and the N₂ adsorption-desorption measurements such as Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods.     

Transesterification of sunflower oil catalyzed by flyash-based solid catalysts

Flyash-based base catalyst was used in the transesterification of sunflower oil with methanol to methyl esters in a heterogeneous manner. Catalyst preparation variables such as, the KNO₃ loading amount and calcination temperature were optimized. The catalysts were characterized by powder XRD. The catalyst prepared by loading of 5 wt.% KNO₃ on flyash followed by its calcination at 773 K has exhibited maximum oil conversion (87.5 wt.%). The influence of various reaction parameters such as % catalyst loading, methanol to oil molar ratio, reaction time, temperature, reusability of the catalyst on the catalytic activity was investigated. K₂O derived from KNO₃ might be an essential component in the catalyst for its efficiency.     

Fischer–Tropsch synthesis on mono- and bimetallic Co and Fe catalysts supported on carbon nanotubes

An extensive study of Fischer–Tropsch synthesis (FTS) on carbon nanotubes (CNTs)-supported bimetallic cobalt/iron catalysts is reported. Up to 4 wt.% of iron is added to the 10 wt.% Co/CNT catalyst by co-impregnation. The physico-chemical properties, FTS activity and selectivity of the bimetallic catalysts were analyzed and compared with those of 10 wt.% monometallic cobalt and iron catalysts at similar operating conditions (H₂/CO = 2:1 molar ratio, P = 2 MPa and T = 220 °C). The metal particles were distributed inside the tubes and the rest on the outer surface of the CNTs. For iron loadings higher than 2 wt.%, Co–Fe alloy was revealed by X-ray diffraction (XRD) techniques. 0.5 wt.% of Fe enhanced the reducibility and dispersion of the cobalt catalyst by 19 and 32.8%, respectively. Among the catalysts studied, cobalt catalyst with 0.5% Fe showed the highest FTS reaction rate and percentage CO conversion. The monometallic iron catalyst showed the minimum FTS and maximum water–gas shift (WGS) rates. The monometallic cobalt catalyst exhibited high selectivity (85.1%) toward C₅+ liquid hydrocarbons, while addition of small amounts of iron did not significantly change the product selectivity. Monometallic iron catalyst showed the lowest selectivity for 46.7% to C₅+ hydrocarbons. The olefin to paraffin ratio in the FTS products increased with the addition of iron, and monometallic iron catalyst exhibited maximum olefin to paraffin ratio of 1.95. The bimetallic Co–Fe/CNT catalysts proved to be attractive in terms of alcohol formation. The introduction of 4 wt.% iron in the cobalt catalyst increased the alcohol selectivity from 2.3 to 26.3%. The Co–Fe alloys appear to be responsible for the high selectivity toward alcohol formation.     

Effect of magnesium addition on catalytic performance of PtSnK/γ-Al2O3 catalyst for isobutane dehydrogenation

The effect of magnesium addition on the catalytic properties of PtSnK/γ-Al₂O₃ catalyst for isobutane dehydrogenation has been investigated by reaction tests and some physicochemical characterizations such as nitrogen adsorption, TEM, H₂ chemisorption, TPR, H₂-TPD, and TPO. It was found that with the suitable addition of magnesium (0.2 and 0.4 wt.%), the platinum dispersion increased, while the carbon depositions decreased. The presence of Mg in the PtSnMgK/γ-Al₂O₃ catalysts could not only strengthen the Sn-Al₂O₃ interaction, but also stabilize the oxidation states of Sn species, which resulted in the increased reaction activity and stability. However, when the content of magnesium was excessive (0.6 and 0.8 wt.%), the character of platinum and the interfacial properties between the metal and the support changed evidently, which was disadvantageous to the reaction. In our experiments, addition of 0.4 wt.% Mg to PtSnK/Al₂O₃ catalyst showed the best catalytic performance. After reaction for 6 h, selectivity toward isobutene of higher than 94% was achieved with the corresponding conversion value of about 29.0%.     

Enhancement of pyrolysis gasoline hydrogenation over Pd-promoted Ni/SiO2-Al2O3 catalysts

Pyrolysis gasoline upgrading by hydrogenation and ring opening was investigated over highly loaded Ni catalysts supported on amorphous silica-alumina and incorporating promoters as Pd, seeking a higher aromatic reduction of this feedstock in order to meet stringent fuel regulations. The effect of Ni loading and Pd component on the activity of those systems was evaluated in a fixed bed reactor under the following operating conditions: T = 573 and 673 K, H₂:PyGas molar ratio = 10, P = 5.0 MPa, WHSV = 4 h⁻¹. The catalyst properties, measured by several characterization techniques (ICP-AES, XRD, N₂ adsorption-desorption isotherms, TPR, H₂-TPD, CO chemisorption, XPS, FTIR spectroscopy of adsorbed pyridine and NH₃-TPD), were related to their catalytic activity and selectivity. Interestingly, the increase in Ni loading from 24.4 to 33.2 Ni wt.% has a negative effect on both hydrogenation and ring opening activities, as it causes a drop in the BET surface area and a decrease in metal-support interaction, with a negative bearing on catalyst stability. On the other hand, the addition of Pd has a positive effect for hydrogenation, linked with the higher electronegativity of Pd⁰ species compared to those of Ni⁰, as well as with a greater stability of Pd-promoted catalysts during on-stream conditions. A linear correlation has been found between the total amount of desorbed H₂, as determined from H₂-TPD experiments on freshly reduced catalysts, and the initial turnover frequency.     

Effects of Co dopants and flame conditions on the formation of Co/ZrO2 nanoparticles by flame spray pyrolysis and their catalytic properties in CO hydrogenation

The Co/ZrO₂ catalysts with various Co loadings (5–10 wt.%) were prepared by one-step flame spray pyrolysis (FSP) under different flame conditions. As revealed by XRD and TEM, all the resulting Co/ZrO₂ nanoparticles were composed of single-crystalline particles exhibiting the characteristic tetragonal structure of ZrO₂. Varying the amount of Co dopants during FSP synthesis did not alter the primary particle size of ZrO₂ which was determined to be ca. 14 nm. On the other hand, increasing precursor feed rate from 3 to 8 ml/min resulted in an increase of ZrO₂ crystallite size from 10 to 19 nm. The higher precursor feed rate produced higher enthalpy of flame and longer residence times, which increased coalescence and sintering of the particles. Compared to the Co/ZrO₂ prepared by conventional impregnation method, the catalytic activities of the FSP-made catalysts were much higher. Moreover, the hydrogenation rates of the FSP-made Co/ZrO₂ catalysts were increased with increasing Co loading and precursor feed rate. According to H₂ chemisorption and H₂ temperature program reduction results, the improvement of catalytic activity and C₂–C₆ selectivities of the FSP-made catalysts in the CO hydrogenation was attributed to the higher number of Co metal active sites and lower interaction between Co/CoO and ZrO₂ support obtained via the FSP synthesis.     

Electrochemical behaviour of propane-fed solid oxide fuel cells based on low Ni content anode catalysts

Two different low Ni content (10 wt.%) anode catalysts were investigated for intermediate temperature (800 °C) operation in solid oxide fuel cells fed with dry propane. Both catalysts were prepared by the impregnation of a Ni-precursor on different oxide supports, i.e. gadolinia doped ceria (CGO) and La_0.6Sr_0.4Fe_0.8Co_0.2O₃ perovskite, and thermal treated at 1100 °C for 2 h. The Ni-modified perovskite catalyst was mixed with a CGO powder and deposited on a CGO electrolyte to form a composite catalytic layer with a proper triple-phase boundary. Anode reduction was carried out in-situ in H₂ at 800 °C for 2 h during cell conditioning. Electrochemical performance was recorded at different times during 100 h operation in dry propane. The Ni-modified perovskite showed significantly better performance than the Ni/CGO anode. A power density of about 300 mW cm⁻² was obtained for the electrolyte supported SOFC in dry propane at 800 °C. Structural investigation of the composite anode layer after SOFC operation indicated a modification of the perovskite structure and the occurrence of a La₂NiO₄ phase. The occurrence of metallic Ni in the Ni/CGO system caused catalyst deactivation due to the formation of carbon deposits.     

Biomass to hydrogen via catalytic steam reforming of bio-oil over Ni-supported alumina catalysts

Production of hydrogen (H₂) from catalytic steam reforming of bio-oil was investigated in a fixed bed tubular flow reactor over nickel/alumina (Ni/Al₂O₃) supported catalysts at different conditions. The features of the steam reforming of bio-oil, including the effects of metal content, reaction temperature, W_bHSV (defined as the mass flow rate of bio-oil per mass of catalyst) and S/C ratio (the molar ratio of steam to carbon fed) on the hydrogen yield were investigated. Carbon conversion (moles of carbon in the outlet gases to moles of the carbon feed) was also studied, and the outlet gas distributions were obtained. It was revealed that the Al₂O₃ with 14.1% Ni content gave the highest yield of hydrogen (73%) among the catalysts tested, and the best carbon conversion was 79% under the steam reforming conditions of S/C = 5, W_bHSV = 13 1/h and temperature = 950 °C. The H₂ yield increased with increasing temperature and decreasing W_bHSV; whereas the effect of the S/C ratio was less pronounced. In the S/C ratio range of 1 to 2, the hydrogen yield was slightly increased, but when the S/C ratio was increased further, it did not have an effect on the H₂ production yield.     

Catalytic performance and characterization of cobalt-nickel nano catalysts for CO hydrogenation

A series of Co-Ni nano catalysts were prepared by co-precipitation method. We investigated the effect of Co/Ni molar ratios precipitate and calcination conditions on the catalytic performance of cobalt nickel catalysts for Fisher-Tropsch synthesis (FTS). The catalyst containing 90%Co/10%Ni was found to be optimal for the conversion of synthesis gas to light olefins. The activity and selectivity of the optimal catalyst were studied in different operational conditions. The results show that the best operational conditions are the H₂/CO=2/1 molar feed ratio at 310 °C and GHSV=1,200 h^?1 under 5 bar of pressure. The prepared catalysts were characterized by powder X-ray diffraction (XRD), N2 adsorption-desorption measurements such as BET and BJH methods, transmission electron microscopy (TEM) and thermal gravimetric analysis (TGA).     

Catalytic dehydration of methanol to dimethyl ether over mordenite catalysts

The conversion of methanol to dimethyl ether was carried out over various commercial mordenite and ion-exchanged catalysts to evaluate the catalytic performance of mordenite catalysts with different pore structures and acidities. These catalysts were compared for their catalytic properties in a fixed-bed reactor at 1 atm, 573 K and LHSV of 2.84 h^− 1. The catalysts were characterized by BET, ICP, NH₃-TPD, XRD, TGA and FT-IR techniques. The ion-exchanged mordenite showed higher activity, selectivity and good stability in dehydration of methanol due to the addition of medium acid sites. Also, the effect of water on catalyst deactivation was investigated over two selected catalysts in order to develop a suitable catalyst for synthesis of dimethyl ether. It was found that the H-mordenite catalyst supplied by Süd-chemie Co., (MCDH-1) was more active and less deactivated than another one in a feed containing 20 wt.% water.     

Effect of heat treatment on the performance of TiO2-Pt/CNT catalysts for methanol electro-oxidation

TiO₂-Pt/CNT catalysts before and after heat treatment were prepared. Their catalytic activities for methanol and CO electro-oxidation were studied in detail. The results showed that the proper amount of hydrous TiO₂ in TiO₂-Pt/CNTs (e.g. heated at 200 °C for 2 h) was favorable for enhancing the catalytic activity of Pt/CNTs, which provided evidence for bi-functional mechanism. The studies on the catalysts with different TiO₂/Pt molar ratio displayed that the optimum molar ratio varied with the increase of heat treatment temperature. It was found that the optimum molar ratio of TiO₂/Pt was at 1:2 for the catalysts without heat treatment and was at 1:1 for the catalysts by heat treatment at 500 °C. This fact was ascribed to the difference in compact degree between TiO₂ and Pt/CNTs before and after heat treatment. Considering the influence of heating temperature, it was found that TiO₂-Pt/CNT catalyst heated at 200 °C for 2 h had better catalytic activity for methanol oxidation.     

Hydrogen production by aqueous-phase reforming of glycerol over nickel catalysts supported on CeO2

Nickel catalysts supported on CeO₂ were prepared and evaluated in aqueous-phase reforming of glycerol. Three different methodologies of synthesis were used: wet impregnation, co-precipitation and combustion, and the catalysts were characterized by chemical composition, textural analysis, crystalline structure and reducibility. The reaction was carried out in a batch reactor with solution of 1 and 10 wt.% glycerol, at 523 and 543 K. A maximum glycerol conversion of 30% was achieved by the catalyst prepared by combustion at 543 K using solution 1% glycerol. In the gas phase, the molar fraction of H₂ was always higher than 70% and formation of CH₄ was very low (< 1%). The increase in glycerol concentration decreases the conversion and H₂ formation.     

Modeling and operating conditions optimization of Fischer–Tropsch synthesis in a fixed-bed reactor

The effect of a range of operation variables such as pressure, low temperature and H₂/CO molar feed ration the catalytic performance of 80%Co/20%Ni/30 wt% La₂O₃/1 wt% Cs catalyst was investigated. It was found that the optimum operating conditions is a H₂/CO = 2/1 molar feed ratio at 260 °C temperature and 2 bar pressure. Reaction rate equations were derived on the basis of the Langmuir–Hinshelwood–Hougen–Watson (LHHW) type models for the Fischer–Tropsch reactions. The activation energy obtained was 59.69 kJ/mol for optimal kinetic model.     

Aqueous-phase catalytic process for production of pentane from furfural over nickel-based catalysts

Supported nickel catalysts for aqueous-phase catalytic hydrogenation/dehydration of furfural were prepared using impregnation method with different supporting materials. Effects of supporting materials, nickel loading and reaction temperature on conversion rate of furfural as well as selectivity for desired product C₅ were systematically studied. Experiments showed that catalytic activity of Ni/SiO₂-Al₂O₃ was obviously higher than that of Ni/γ-Al₂O₃. The conversion of furfural over 14 wt.%Ni/SiO₂-Al₂O₃ catalyst was 62.99% under the temperature of 140 °C and the cold pressure of H₂ 3.0 MPa, while that was 19.19% over 14 wt.%Ni/γ-Al₂O₃ under the same conditions. Conversion rate of furfural increased with temperature, but selectivity for desired product decreased with temperature. Tentative reaction mechanisms of hydrogenation/dehydration were proposed. In order to investigate catalyst recyclability, a batch of Ni/SiO₂-Al₂O₃ was reused three times and analyzed by Thermogravimetry (TG). It was found that considerable amount of coke formed on Ni/SiO₂-Al₂O₃ surface and deteriorated its activity dramatically after second use.     

Inhibition of CoMo/HMS catalyst deactivation in the HDS of 4,6-DMDBT by support modification with phosphate

A series of CoMoS catalysts supported on hexagonal mesoporous silica (HMS) modified with different amounts of phosphate (0.5, 1.0, 1.5 and 2.0 wt.%) were prepared in order to study the influence of phosphate on catalyst deactivation. The catalysts were characterized by a variety of techniques (X-ray fluorescence, N₂ adsorption-desorption at 77 K, FT-IR study of the framework vibration and NO adsorption, NH₃-TPD, H₂-TPR, XPS, ³¹P NMR and TPO/TGA). The sulfided catalysts were tested in the deep hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) performed in a fixed-bed flow reactor at 598 K, P = 5.0 MPa and WHSV = 46.4 h⁻¹. The catalyst with the largest phosphate content (2.0 wt.%) showed the best catalytic response linked with its low deactivation during on-stream reaction and a larger sulfidation degree of Co species. It was found that coking behavior is closely related with the location of the active sites in the support structure being a lower coke formation on the catalysts having active phases located within support structure. The catalysts modified with a large amount of phosphorous (1.5 and 2.0 wt.% of P₂O₅) were more susceptible to coking and produced a more polymerized coke than P-free sample, as confirmed by TPO/TGA experiments. The presence of P₂O₅ favours the sulfidation degree of Co species and the creation of medium strength acid sites leading to the enhancement of the 4,6-DMDBT HDS reaction toward the isomerization route.     

Catalytic gasification of coal using eutectic salts: reaction kinetics with binary and ternary eutectic catalysts

Kinetic studies of the catalytic steam gasification of Illinois No. 6 coal were carried out using binary and ternary eutectic salt mixtures in a fixed-bed reactor. The effects of major process variables such as temperature, pressure, catalyst loading and steam flow rate were evaluated for the binary 29% Na₂CO₃-71% K₂CO₃ and ternary 43.5% Li₂CO₃-31.5% Na₂CO₃-25% K₂CO₃ eutectic catalyst systems. A Langmuir-Hinshelwood rate expression was developed to explain the reaction mechanism for steam gasification using the binary and ternary catalysts. The activation energy of the ternary catalyst (98 kJ/mol) was less than that of the binary catalyst (201 kJ/mol) or single salt such as K₂CO₃ (170 kJ/mol). The molar heats of adsorption for the ternary and binary catalysts were exothermic and about 180 and 92 kJ/mol, respectively. The molten nature of the ternary eutectic at the gasification temperatures and its lower activation energy favored higher gasification rates compared to the single and binary alkali metal salts.     

Development and reactivity tests of Ce-Zr-based Claus catalysts for coal gas cleanup

Claus reaction (2H₂S + SO₂ ↔ 3/nS_n + 2H₂O) was used to clean the gasified coal gas and the reactivity of several metal oxide-based catalysts on Claus reaction was investigated at various operating conditions. In order to convert H₂S contained in the gasified coal gas to elemental sulfur during Claus reaction, the catalysts having the high activity under the highly reducing condition with the moisture should be developed. CeO₂, ZrO₂, and Ce_1−xZr_xO₂ catalysts were prepared for Claus reaction and their reactivity changes due to the existence of the reducing gases and H₂O in the fuel gas was investigated in this study. The Ce-based catalysts shows that their activity was deteriorated by the reduction of the catalyst due to the reducing gases at higher than 220 °C. Meanwhile, the effect of the reducing gases on the catalytic activity was not considerable at low temperature. The activities of all three catalysts were degraded on the condition that the moisture existed in the test gas. Specifically, the Ce-based catalysts were remarkably deactivated by their sulfation. The Ce-Zr-based catalyst had a high catalytic activity when the reducing gases and the moisture co-existed in the simulated fuel gas. The deactivation of the Ce-Zr-based catalyst was not observed in this study. The lattice oxygen of the Ce-based catalyst was used for the oxidation of H₂S and the lattice oxygen vacancy on the catalyst was contributed to the reduction of SO₂. ZrO₂ added to the Ce-Zr-based catalyst improved the redox properties of the catalyst in Claus reaction by increasing the mobility of the lattice oxygen of CeO₂.     

Carbon infiltration of carbon-fiber preforms by catalytic CVI

Experimental studies were conducted to assess catalytic chemical vapor infiltration processing for preparing carbon/carbon composites as a potential improvement to conventional one. The catalyst was introduced into the carbon fiber preforms by wet impregnation. Using C₃H₆/Ar/H₂ as the original gas, catalytic carbon was formed at 500-1000 °C for 1-3 h. It was found that carbon filaments were formed as the preparing temperatures were 500-700 °C, and carbon particles could be obtained at 800-1000 °C. The increasing rate of density was up to 0.916 g/ml/h when the sample was formed at 600 °C for 1 h with the catalytic of 0.7 wt.% Ni, and the carbon yield arrived to 90 wt.% . According to the micrographs of catalytic carbon, the forming mechanism of carbon filaments agreed with that of carbon filaments due to a metal catalyst. The weighted average interlayer spacing of C/C composites with catalytic carbon decreased to 0.341.     

Methane reforming reaction with carbon dioxide over SBA-15 supported Ni-Mo bimetallic catalysts

A series of mesoporous molecular sieves SBA-15 supported Ni-Mo bimetallic catalysts (xMo1Ni, Ni = 12 wt.%, Mo/Ni atomic ratio = x, x = 0, 0.3, 0.5, 0.7) were prepared using co-impregnation method for carbon dioxide reforming of methane. The catalytic performance of these catalysts was investigated at 800 °C, atmospheric pressure, GHSV of 4000 ml·g_cat^− 1·h^− 1 and a V(CH₄)/(CO₂) ratio of 1 without dilute gas. The result indicated that the Ni-Mo bimetallic catalysts had a little lower initial activity compared with Ni monometallic catalyst, but it kept very stable performance under the reaction conditions. In addition, the Ni-Mo bimetallic catalyst with Mo/Ni atomic ratio of 0.5 showed high activity, superior stability and the lowest carbon deposition rate (0.00073g_c·g_cat^− 1·h^− 1) in 600-h time on stream. The catalysts were characterized by power X-ray diffraction, N₂-physisorption, H₂-TPR, CO₂-TPD, TG and TEM. The results indicate that the Ni-Mo bimetallic catalysts have smaller metal particle, higher metal dispersion, stronger basicity, metal-support interaction and Mo₂C species. It is concluded that Mo species in the Ni-Mo bimetallic catalysts play important roles in reducing effectively the amount of carbon deposition, especially the amount of shell-like carbon deposition.