Direct synthesis of middle iso-paraffins from synthesis gas on hybrid catalysts

This paper focuses on the synthesis of iso-paraffin-rich hydrocarbons by Fischer–Tropsch synthesis (FTS) over silica gel supported Co catalyst (Co/SiO₂). The basic concept is to isomerize and/or hydrocrack the primary FTS hydrocarbon products. A physical mixture consisting of a small amount of zeolite or Pd/zeolite mixed with Co/SiO₂ enhanced the formation of C₄–C₁₀ iso-paraffins while suppressing the formation of higher molecular hydrocarbons, probably because of the selective cracking of these hydrocarbons on them. In separate experiments, a two-reactor system was used. The first reactor contained a physical mixture of Co/SiO₂ and zeolite, and the second reactor contained zeolites or Pd-supported zeolites. The two-reactor system gave sharp C-number distribution within C₃–C₆ and iso-paraffins-rich products. The hydrocracking of n-octane and n-decane (model compound simulating products of the FTS reaction) over mixed catalysts composed of various compositions of Pd/SiO₂ and ZSM-5 in the presence of gaseous hydrogen showed high and stable activity, and produced primarily iso-paraffin-rich hydrocarbons. The isomerization was favored for mixtures rich in Pd/SiO₂. The role of Pd was thought to be the inlet of hydrogen spillover to the zeolite surface.     

Selective removal of H2S from coke oven gas

The catalytic performance of some metal oxides in the selective oxidation of H₂S in the stream containing water vapor and ammonia was investigated in this study. Among the catalysts tested, V₂O₅/SiO₂ and Fe₂O₃/SiO₂ catalyst showed good conversion of H₂S with very low selectivity to undesired SO₂. Hydrogen sulfide could be recovered as harmless solid products (elemental sulfur and various ammonium salts), and distribution of solid products was varied with types of catalyst and compositions of reactant. XRD and FT-IR analysis revealed that the salt was mixture of ammonium–sulfur–oxygen compounds. It was noteworthy that V₂O₅/SiO₂ catalyst produced elemental sulfur and ammonium thiosulfate, and that elemental sulfur was principal product on Fe₂O₃/SiO₂ catalyst. Small amount of ammonium sulfate was obtained with the Fe₂O₃/SiO₂ catalyst. In order to elucidate the reaction path, the effects of O₂/H₂S ratio and concentration of NH₃ and H₂O are also studied with the V₂O₅/SiO₂ catalyst.     

Catalytic synthesis of methanethiol from hydrogen sulfide and carbon monoxide over vanadium-based catalysts

The direct synthesis of methanethiol, CH₃SH, from CO and H₂S was investigated using sulfided vanadium catalysts based on TiO₂ and Al₂O₃. These catalysts yield high activity and selectivity to methanethiol at an optimized temperature of 615 K. Carbonyl sulfide and hydrogen are predominant products below 615 K, whereas above this temperature methane becomes the preferred product. Methanethiol is formed by hydrogenation of COS, via surface thioformic acid and methylthiolate intermediates. Water produced in this reaction step is rapidly converted into CO₂ and H₂S by COS hydrolysis.

Titania was found to be a good catalyst for methanethiol formation. The effect of vanadium addition was to increase CO and H₂S conversion at the expense of methanethiol selectivity. High activities and selectivities to methanethiol were obtained using a sulfided vanadium catalyst supported on Al₂O₃. The TiO₂, V₂O₅/TiO₂ and V₂O₅/Al₂O₃ catalysts have been characterized by temperature programmed sulfidation (TPS). TPS profiles suggest a role of V₂O₅ in the sulfur exchange reactions taking place in the reaction network of H₂S and CO.     

Investigation of CoNiMo/Al2O3 catalysts: Relationship between H2S adsorption and HDS activity

Sulfidation of trimetallic CoNiMo/Al₂O₃ catalysts was studied by thermogravimetry at 400 °C under flow and pressure conditions. Results were compared with those obtained on prepared and industrial CoMo/Al₂O₃ and NiMo/Al₂O₃ catalysts. The amount of sorbed H₂S on the sulfided solids was measured at 300 °C in the H₂S pressure range 0–3.5 MPa at constant H₂ pressure (3.8 MPa). The adsorption isotherms were simulated using a model featuring dissociated adsorption of H₂S on supported metal sulfides and bare alumina. The amount of sulfur-vacancy sites could thus be determined under conditions close to industrial practice. A relationship with activity results for thiophene HDS and benzene hydrogenation was sought for.     

Tetralin hydrogenation catalyzed by Mo2C/Al2O3 and WC/Al2O3 in the presence of H2S

Supported molybdenum and tungsten carbides were synthesized by temperature-programmed reactions. These materials were characterized by XRD, EDS analysis, HRTEM and CO chemisorption. Hydrogenation of tetralin was carried out at a total pressure of 4 MPa (3.06 MPa of H₂), at 573 K, without or with sulfur (200 ppm of sulfur as DMDS). The resulting activities were compared with those of MoS₂/Al₂O₃ and Pt (1% (w/w) metal loading) supported on Al₂O₃ or SiO₂. In the absence of sulfur, WC/Al₂O₃ showed an initial activity similar to that of Pt/SiO₂, higher than that of MoS₂/Al₂O₃ but lower than that of Pt/Al₂O₃. In the presence of H₂S, WC/Al₂O₃ showed a steady-state activity similar to that of Pt/Al₂O₃ (which suffered a marked deactivation). Post-reaction characterization did not show any sulfur poisoning of the supported carbides. Therefore the supported carbides are sulfur-tolerant and promising catalysts for the hydrogenation of aromatics in diesel fuels in the presence of small amounts of S-containing compounds.     

Semi-indirect synthesis of LPG from syngas: Conversion of DME into LPG

Efficient conversion of dimethyl ether (DME) into liquefied petroleum gas (LPG) with a hybrid catalyst is a novel method for semi-indirect synthesis of LPG fuel from syngas. The hybrid catalysts consisting of zeolite and hydrogenation catalyst were investigated in a fixed bed reactor. Experimental results demonstrated that the hybrid catalyst consisting of (Pd/SiO₂) and USY efficiently converted DME into LPG and restrained decomposition of DME into CO and H₂. With that catalyst, the one through conversion of DME reached about 100%, almost no CO and CO₂ were produced and selectivity for LPG was more than 65%.     

合成气费托合成制重质烃Ru-Co/SiC催化剂的制备及性能

费托合成是以合成气生产清洁燃料和其他化学品的重要途径。传统费托合成产物遵循A-S-F分布,只有甲烷和重质烃的选择性没有极限值。因此,费托合成研究以最大程度地合成重质烃,提高合成产物中重质烃的选择性为目标。基于此,首先详细探究了Al₂O₃、SiO₂和SiC载体对费托反应性能的影响。结果表明 Co/SiC催化剂具有最高的CO转化率（83.5%）和C₅₊选择性（80.3%）。与浸渍法相比,原位还原法更为有效地引入Ru到Co/SiC催化剂,将C₅₊选择性提高至90.1%。Ru助剂能在保持较高催化活性不变的前提下,有效提高Co/SiC催化剂C₅₊选择性。催化剂表征（XRD、H₂-TPR、XPS、H₂-化学吸附和TEM）结果表明,Ru能与Co发生相互作用,提高了催化剂的可还原性和活性组分的分散性,进而改善了Co/SiC催化剂重质烃的选择性。     

化学链燃烧中H2S对NiFe2O4氧载体活性的影响机理

采用密度泛函理论方法研究H₂S与NiFe₂O₄（001）完整表面和氧缺陷表面的相互作用机理。结果表明,H₂S在NiFe₂O₄氧载体表面Ni原子位的吸附能比其在Fe原子位的吸附能大。氧缺陷的形成会使H₂S在氧载体表面金属原子位的吸附能增大,并且Ni原子位吸附H₂S的吸附能增加更为明显。因而,NiFe₂O₄氧载体表面的Ni原子位是H₂S的主要吸附位。同时采用热力学方法进一步研究含H₂S的合成气与NiFe₂O₄氧载体之间的反应,发现H₂S与氧载体的反应产物与氧载体的还原程度密切相关。由于铁氧化物的深度还原过程受到热力学限制,H₂S与NiFe₂O₄氧载体反应的主要产物为Ni₃S₂。密度泛函理论方法与热力学方法研究结果均表明H₂S倾向于与NiFe₂O₄氧载体中Ni发生相互作用,这将对NiFe₂O₄氧载体的反应性能产生不利影响。     

Attrition resistance of spray-dried iron F–T catalysts: Effect of activation conditions

The focus of the research reported herein was to investigate the effects of phase changes, as occur during Fe catalyst activation and Fischer–Tropsch synthesis, on Fe catalyst attrition resistance. Different activation conditions (CO, H₂ or syngas) were applied prior to attrition testing to a selected spray-dried Fe catalyst containing 9.1 wt.% binder SiO₂, which had been shown to have the highest attrition resistance in our early study of calcined catalysts. Although, XRD indicated that different Fe phase compositions resulted in the differently activated catalyst samples, chemical attrition was not observed for any of the samples. The BET surface areas of the activated samples were smaller than that of the calcined precursor but no significant changes in pore volume and particle size were found. The attrition resistances of the differently activated catalyst samples were found to be similar to that of the calcined catalyst for this spray-dried Fe catalyst. Attrition resistance was found previously to be governed by catalyst particle density, which has been shown earlier to relate to the SiO₂ network in catalysts. It is therefore suggested that the type and concentration of SiO₂ that is incorporated during the preparation of spray-dried Fe catalysts have a much more significant impact on catalyst attrition than Fe phase change during activation in the presence of CO, H₂ or H₂+CO.     

Resistance to sulfur poisoning of hot gas cleaning catalysts for the removal of tar from the pyrolysis of cedar wood

In the partial oxidation of tar derived from the pyrolysis of cedar wood, the effect of H₂S addition was investigated over non-catalyst, steam reforming Ni catalyst, and Rh/CeO₂/SiO₂ using a fluidized bed reactor. In the non-catalytic gasification, the product distribution was not influenced by the presence of H₂S. Steam reforming Ni catalyst was effective for the tar removal without H₂S addition, however, the addition of H₂S deactivated drastically. In contrast, Rh/CeO₂/SiO₂ exhibited higher and more stable activity than the Ni catalyst even under the presence of high concentration of H₂S (280 ppm). On the Ni catalyst, the adsorption of sulfur was observed by XPS and Ni species was oxidized during the partial oxidation of tar. In the case of Rh/CeO₂/SiO₂, the adsorption of sulfur was below the detection limit of XPS. This can be related to the self-cleaning of catalyst surface during the circulation in the fluidized bed reactor for the partial oxidation of tar derived from cedar pyrolysis.     

不同氧化锰载体对费托钴基催化剂合成低碳烯烃的影响

制备不同的Co/MnO_x (Co/MnO、Co/MnO₂、Co/Mn₂O₃、Co/Mn₃O₄) 催化剂,并利用XRD、SEM、TEM、BET、TPR、DRIFTS、XPS表征手段分析催化剂的理化性质,比较不同氧化锰载体对催化性能的影响,考察催化剂对低碳烯烃(C₂⁼～C₄⁼)的选择性影响。结果表明催化剂Co/MnO和Co/Mn₃O₄更容易还原,并且CO的吸附量较大,有利于实现较高的CO转化率;Co/Mn₂O₃和Co/Mn₃O₄中CO桥式吸附更高,有利于生成更多的-CH₂-物种。综合考虑催化剂的活性和C₂⁼～C₄⁼选择性,Co/Mn₃O₄的费托合成(FTS)性能最好,其中C₂⁼～C₄⁼选择性为50.91%,烯烷比(O/P)为3.40。     

Kinetics of dibenzothiophene hydrodesulfurization over MoS2 supported catalysts: modelization of the H2S partial pressure effect

The influence of H₂S partial pressure over the catalytic activity of MoS₂, supported on three different oxides: Al₂O₃, TiO₂ and ZrO₂, was studied in the hydrodesulfurization of dibenzothiophene (DBT). A complex inhibiting effect is observed and two orders of reaction relative to H₂S were determined: −1/2 and 0, as a function of H₂S partial pressure. The experimental results are in good agreement with the kinetic models whereby the DBT transformation takes place through a dihydrogenated intermediate (DH-DBT). The associated mechanism considers that the heterolytic dissociative adsorption of H₂ and H₂S occurs over an unsaturated Mo ion and over a stable sulfur ion.     

CO hydrogenation over a rhodium vanadate catalyst: Reduction and regeneration of RhVO4 on SiO2

The hydrogenation of CO over an Rh vanadate (RhVO₄) catalyst supported on SiO₂ (RhVO₄/SiO₂) has been investigated after H₂ reduction at 500°C, and the results are compared with those of vanadia-promoted (V₂O₅–Rh/SiO₂) and unpromoted Rh/SiO₂ catalysts. The mean size of Rh particles, which were dispersed by the decomposition of RhVO₄ after the H₂ reduction, was smaller (41 Å) than those (91–101 Å) of V₂O₅–Rh/SiO₂ and Rh/SiO₂ catalysts. The RhVO₄/SiO₂ catalyst showed higher activity and selectivity to C₂ oxygenates than the unpromoted Rh/SiO₂ catalyst after the H₂ pretreatment. The CO conversion of the RhVO₄/SiO₂ catalyst was much higher than that of V₂O₅–Rh/SiO₂ catalyst, and the yield of C₂ oxygenates increased. We also found that the RhVO₄/SiO₂ catalyst can be regenerated by calcination or O₂ treatment at high temperature after the reaction.     

In situ XAFS analysis of Pd–Pt catalysts during hydrotreatment of model oil

Supported Pd–Pt catalysts are efficient for hydrodesulfurization (HDS) and hydrodearomatization (HDA) reactions of diesel fuel and their activity varied with the kinds of supports. Concerning HDA, alumina supported catalysts showed four times higher TOF (turn over frequency) than silica supported one. In order to elucidate the difference in activity, the structural analysis of the active phase was performed. After reduction pretreatment, relatively uniform and large metallic alloy Pd–Pt particles were formed on SiO₂, whereas, Pd and Pt atoms formed rather segregated particles on Al₂O₃. Subsequent X-ray absorption of fine structure (XAFS) analysis under HDS conditions showed no contribution of sulfur for SiO₂ supported catalyst, whereas, formation of sulfided metal species was observed in XAFS spectra for the Al₂O₃ supported catalyst. It is suggested that on Pd–Pt/SiO₂, thin sulfide layer on the metal cluster surface blocked the active sites and lowered the HDA activity. Presence of partially sulfided phase originated from rather segregated structure like Pd–Pt/Al₂O₃ is thought to be requisite for high HDA activity.     

High performance Pd/beta catalyst for the production of gasoline-range iso-paraffins via a modified Fischer–Tropsch reaction

The direct synthesis of gasoline-range iso-paraffins from synthesis gas (CO + H₂, syngas) via a modified Fischer–Tropsch (FT) reaction was intensively studied under a wide range of reaction conditions by the combination of Co/SiO₂ and Pd/beta in a consecutive dual reactor system. Results indicate that high selectivity of gasoline-range iso-paraffins (iso-paraffins relative to C₄+ hydrocarbons was about 80%) could be achieved with the presence of Pd/beta catalyst in the lower reactor. Moreover, the performance of the Pd/beta catalyst for the titled reaction and the product composition can be significantly regulated by independently changing the reaction conditions such as catalyst amount, reaction temperature, and hydrogen partial pressure in the lower reactor. It was found that the Pd/beta catalyst used in this work was very active and stable even at a reaction temperature as low as 503 K. With the increase of hydrogen partial pressure in the lower reactor, the long-term stability of the Pd/beta catalyst was significantly enhanced.     

Catalytic reduction of SO2 over supported transition-metal oxide catalysts with C2H4 as a reducing agent

This work investigates performances of supported transition-metal oxide catalysts for the catalytic reduction of SO₂ with C₂H₄ as a reducing agent. Experimental results indicate that the active species, the support, the feed ratio of C₂H₄/SO₂, and pretreatment are all important factors affecting catalyst activity. Fe₂O₃/γ-Al₂O₃ was found to be the most active catalyst among six γ-Al₂O₃-supported metal oxide catalysts tested. With Fe₂O₃ as the active species, of the supports tested, CeO₂ is the most suitable one. Using this Fe₂O₃/CeO₂ catalyst, we found that the optimal Fe content is 10 wt.%, the optimal feed ratio of C₂H₄/SO₂ is 1:1, and the catalyst presulfidized by H₂+H₂S exhibits a higher performance than those pretreated with H₂ or He. Although the feed concentrations of C₂H₄:SO₂ being 3000:3000 ppm provide a higher conversion of SO₂, the sulfur yield decreases drastically at temperatures above 300 °C. With higher feed concentrations, maximum yield appears at higher temperatures. The C₂H₄ temperature-programmed desorption (C₂H₄-TPD) and SO₂-TPD desorption patterns illustrate that Fe₂O₃/CeO₂ can adsorb and desorb C₂H₄ and SO₂ more easily than can Fe₂O₃/γ-Al₂O₃. Moreover, the SO₂-TPD patterns further show that Fe₂O₃/γ-Al₂O₃ is more seriously inhibited by SO₂. These findings may properly explain why Fe₂O₃/CeO₂ has a higher activity for the reduction of SO₂.     

New supported ruthenium catalyst for hydrodesulfurization reaction

The effect of the kind of ruthenium precursor {Ru₃(CO)₁₂ or RuCl₃·nH₂O} and the activation conditions on the performance of Ru/MgF₂ preparations in thiophene hydrodesulfurization has been studied. The highest activity, higher than that of the commercially available system CoMo/Al₂O₃, was revealed by the Ru/MgF₂ catalyst sulfided in the 50% H₂S/He atmosphere. According to the results of TPR study, this preparation was characterized by exceptionally high content of RuS₂, which seems to be responsible for its high activity. As follows from the product distribution of thiophene HDS, the activation in the H₂S/He atmosphere mainly leads to the formation of saturated products (butane), while the activation in the atmosphere of H₂S/H₂, to the formation of unsaturated products (butene-1, cis- and trans-butene-2).     

Effect of palladium on sulfur resistance in Pt–Pd bimetallic catalysts

The interactions of H₂ and H₂S molecules with Pt–Pd bimetallic catalysts were investigated at the molecular level using a DFT (density functional theory) approach to better understand the structures and properties of active sites, and the relations between structural changes and sulfur resistance. It was found that when alloying the Pt catalyst with a small amount of Pd at a particular surface atomic ratio range, both H₂ and H₂S showed different adsorption properties compared to those on monometallic Pt or Pd catalyst. The adsorptions of both H₂ and H₂S were enhanced, but the adsorption energy of H₂ increased more than that of H₂S, indicating that the adsorption of H₂S became less favorable compared with H₂ on the bimetallic Pt–Pd catalyst surface. The desorption energy of hydrogen from monometallic Pt or Pd, as well as bimetallic Pt–Pd supported on zeolite, were calculated by temperature-programmed desorption (TPD), the values were compared against the DFT results to explain experimentally and theoretically why the bimetallic Pt–Pd catalyst has better sulfur resistance than monometallic Pt catalyst.     

Fischer–Tropsch synthesis over Re-promoted Co supported on Al2O3, SiO2 and TiO2: Effect of water

The activity and selectivity of rhenium promoted cobalt Fischer–Tropsch catalysts supported on Al₂O₃, TiO₂ and SiO₂ have been studied in a fixed-bed reactor at 483 K and 20 bar. Exposure of the catalysts to water added to the feed deactivates the Al₂O₃ supported catalyst, while the activity of the TiO₂ and SiO₂ supported catalysts increased. However, at high concentrations of water both the SiO₂ and TiO₂ supported catalyst deactivated. Common for all catalysts was an increase in C₅₊ selectivity and a decrease in the CH₄ selectivity by increasing the water partial pressure. The catalysts have been characterized by scanning transmission electron microscope (STEM), BET, H₂ chemisorption and X-ray diffraction (XRD).     

Hydrodeoxygenation of aliphatic esters on sulphided NiMo/γ-Al2O3 and CoMo/γ-Al2O3 catalyst: The effect of water

Water formed during hydrotreating of oxygen-containing feeds has been found to affect the performance of sulphided catalysts in different ways. The effect of water on the activity of sulphided NiMo/γ-Al₂O₃ and CoMo/γ-Al₂O₃ catalysts in hydrodeoxygenation (HDO) of aliphatic esters was investigated in a tubular reactor by varying the amount of water in the feed. In additional experiments, H₂S was added to the feed, alone and simultaneously with water.

Under the same conditions, the NiMo catalyst exhibited a higher activity than the CoMo catalyst. The ester conversions decreased with increase in the amount of added water. When H₂S and water were added simultaneously, the conversion increased to the same level as without water addition on the NiMo catalyst and reached a higher value on the CoMo catalyst. The conversions were highest, however, when only H₂S was added. Unfortunately, the conversions decreased with time under all conditions. On both catalysts, the total yield of the C₇ and C₆ hydrocarbons decreased with the amount of added water, while the concentrations of the oxygen-containing intermediates increased. The presence of H₂S improved the total hydrocarbon yield and shifted the main products towards the C₆ hydrocarbons. Thus, the addition of H₂S effectively compensated the inhibition by water.