Carbon Monoxide Hydrogenation over Zirconia Supported Ni and Co-Ni Bimetallic Catalysts

Zirconia supported nickel and cobalt-nickel bimetallic catalysts were prepared and characterized for various physico-chemical properties. The hydrogenation of carbon monoxide was studied over these catalysts in the pressure range of 101.3–1654kPa, temperature range of 513–533K, weight hourly space velocity range of 8–14h^–1 and H2/CO mole ratio of 2. Catalysts containing both Co and Ni were found to give higher C₅₊ hydrocarbons selectivity compared to that containing only Ni. A maximum C₅₊ hydrocarbons selectivity of 55wt% was obtained at 655kPa pressure, 523K and 9.6h^–1 of WHSV with catalyst containing 4.03wt% Co and 2.64wt% Ni. The C₂ and C₃ olefin contents of the products decreased with increase in pressure. Improved deactivation behavior of the catalysts was observed when operated at high pressure.     

Selective synthesis of light olefins from syngas over potassium-promoted molybdenum carbide catalysts

In the hydrogenation of CO at atmospheric pressure, unsupported molybdenum carbide catalyst produced mostly C₁-C₅ paraffins. Promotion of the catalyst with K₂CO₃ yielded C₂-C₅ hydrocarbons consisting of 80–100% olefins and reduced the methane selectivity. The selectivity of C₂-C₅ olefins among all hydrocarbon products was 50–70 wt% at CO conversions up to 70%.This work has been supported by Korean Science and Engineering Foundation through a contract 88-03-1302.     

Confined Iron Nanoparticles on Mesoporous Ordered Silica for Fischer–Tropsch Synthesis

Iron oxide particles were deposited in an ordered mesoporous material (SBA-15) with the aim of studying its behavior in the catalytic hydrogenation of CO (Fischer–Tropsch Synthesis). Bulk iron oxide, and iron supported on porous silica with different textural properties (Aerosil^®-200) were used for comparison. The characterization of the materials showed that in the Fe@SBA-15 material, iron nanoparticles were confined inside the mesopores of the SBA-15 support (pore diameter ~?8 nm), and Fe@Aerosil^®-200 material also presented iron oxide nanoparticles highly dispersed on the material. In situ Synchrotron radiation XRD studies were performed in order to study the evolution of iron phases in the Fe@SBA-15 and the bulk iron oxide under hydrogen and hydrogen/carbon monoxide conditions. DFT calculations were performed on bare Fe(100) and a Fe₁₆ cluster in CO activation and C_xH_y hydrogenation. Catalytic microactivity tests, performed at conversions of ~?6–8%, showed important differences in the selectivity of the materials. Higher selectivity to methane and light hydrocarbons were observed in the supported catalysts (Fe@SBA-15 and Fe@Aerosil^®-200) than in bulk Fe catalyst. Moreover, the supported catalysts showed selectivity to ethylene (Fe@SBA-15) and propylene (Fe@Aerosil^®-200), products that were not observed in the bulk iron catalyst. On the other hand, bulk iron showed a major selectivity to higher hydrocarbons (C₅–C₉) and oxygenates.

     

Selective production of methanol from syngas over LaTi1−xCuxO3 mixed oxides

Carbon monoxide hydrogenation was studied over partially substituted copper-containing LaTi_1–xCu_xO₃ oxides and on copper supported on La₂O₃. The unsubstituted (x = 0) oxide was weakly active for CO hydrogenation, whereas all the other oxides were more active and exhibited high selectivity to methanol. Particularly, for substitutions x = 0.5–0.6, where the perovskite structure was observed, CO conversions close to 22% and selectivity close to 80% were found. Cu/La₂O₃ was, however, less active and yielded CO₂ and hydrocarbons as the major products. Using X-ray photoelectron spectroscopy it was determined that under reaction conditions copper exists as reduced species. The L₃VV X-ray induced Auger transition at 1849.2 eV observed for a representative LaMn_0.5Cu_0.5O₃ catalyst prereduced and used in CO hydrogenation at 573 K, suggests that Cu⁺ species dominates in spent catalyst. These Cu⁺ species are believed to be stable under reaction conditions in the perovskite structure, only a slight Cu enrichment occurs on the topmost layer of catalysts.     

Effect of Vanadium Promotion on Activated Carbon-Supported Cobalt Catalysts in Fischer–Tropsch Synthesis

The effect of vanadium promotion on activated carbon (AC)-supported cobalt catalysts in Fischer–Tropsch synthesis has been studied by means of XRD, TPR, CO-TPD, H₂-TPSR of chemisorbed CO and F-T reaction. It was found that the CO conversion could be significantly increased from 38.9 to 87.4% when 4 wt.% V was added into Co/AC catalyst. Small amount of vanadium promoter could improve the selectivity toward C₁₀–C₂₀ fraction and suppress the formation of light hydrocarbon. The results of CO-TPD and H₂-TPSR of adsorbed CO showed that the addition of vanadium increased the concentration of surface-active carbon species by enhancing CO dissociation and further improved the selectivity of long chain hydrocarbons. However, excess of vanadium increased methane selectivity and decreased C₅⁺ selectivity.     

K/LaFeMnO3 Perovskite-Type Oxide Catalyst for the Production of C2–C4 Olefins via CO Hydrogenation

LaBO₃ (B?=?Fe, Mn, and FeMn) perovskite-type oxides were prepared by sol–gel method and then used as catalysts in CO hydrogenation for light olefins. The catalysts were characterized using XRD, H₂-TPR, SEM, CO (CO₂)-TPD, and XPS. The results showed that the lattice oxygen migration and oxygen vacancies promoted oxygen mobility by doping Mn²⁺ at the B site, Moreover, the presence of manganese as a promoter in the catalyst increased olefin selectivity compared with the olefin selectivity of the catalyst containing iron at the B-site and exhibited resistance to carbon deposition; while reducing the metal elements. In CO hydrogenation, potassium-promoted LaFeMnO₃ catalysts afforded high catalytic activity and C₂⁼–C₄⁼ selectivity. An O/P value of 5.0 and a C₂⁼–C₄⁼ fraction of 54% were achieved for all hydrocarbons with low methane selectivity.

Graphic Abstract

     

Selective oxidation of methane with air over silica catalysts

Partial oxidation of methane by oxygen to form formaldehyde, carbon oxides, and C₂ products (ethane and ethene) has been studied over silica catalyst supports (fumed Cabosil and Grace 636 silica gel) in the 630–780 °C temperature range under ambient pressure. The silica catalysts exhibit high space time yields (at low conversions) for methane partial oxidation to formaldehyde, and the C₂ hydrocarbons were found to be parallel products with formaldehyde. Short residence times enhanced both the C₂ hydrocarbons and formaldehyde selectivities over the carbon oxides even within the differential reactor regime at 780 °C. This suggests that the formaldehyde did not originate from methyl radicals, but rather from methoxy complexes formed upon the direct chemisorption of methane at the silica surface at high temperature. Very high formaldehyde space time yields (e.g., 812 g/kg cat h at the gas hourly space velocity = 560 000 (NTP)/kg cat h) could be obtained over the silica gel catalyst at 780 °C with a methane/air mixture of 1.5/1. These yields greatly surpass those reported for silicas earlier, as well as those over many other catalysts. Low CO₂ yields were observed under these reaction conditions, and the selectivities to formaldehyde and C₂ hydrocarbons were 28.0 and 38.8%, respectively, at a methane conversion of 0.7%. A reaction mechanism was proposed for the methane activation over the silica surface based on the present studies, which can explain the product distribution patterns (specifically the parallel formation of formaldehyde and C₂ hydrocarbons).     

Selective synthesis of alcohols from syngas and hydroformylation of ethylene over supported cluster-derived cobalt catalysts

Hydroformylation of ethylene and CO hydrogenation were studied over cobalt-based catalysts derived from reaction of Co₂(CO)₈ with ZnO, MgO and La₂O₃ supports. At 433 K a similar activity sequence was reached for both reactions: Co/ ZnO > Co/La₂O₃ > Co/MgO. This confirms the deep analogy between hydroformylation and CO hydrogenation into alcohols. In the CO hydrogenation the selectivity towards alcohol mixture (C₁-C₃) was found to be near 100% at 433 K for a conversion of 6% over the Co/ZnO catalyst; this catalyst showed oxo selectivity higher than 98% in the hydroformylation of ethylene. Magnetic experiments showed that no metallic cobalt particles were formed at 433 K. It is suggested that the active site for the step that is common to both reactions is related to the surface homonuclear Co²⁺/[Co(CO)₄]^– ion-pairing species.     

Potassium and nickel doped β-Mo2C catalysts for mixed alcohols synthesis via syngas

Potassium and nickel doped β-Mo₂C catalysts were prepared and their performances of CO hydrogenation were investigated. The main products over β-Mo₂C catalyst were hydrocarbons, and only few alcohols were obtained. The potassium promoter resulted in remarkable selectivity shift from hydrocarbons to alcohols over β-Mo₂C. Moreover, it was found that the potassium promoter enhanced the ability of chain propagation of β-Mo₂C catalyst and resulted in a higher selectivity to C₂₊OH. When doped by potassium and nickel, β-Mo₂C catalyst showed high activity and selectivity for mixed alcohols synthesis, the Ni promoter further enhanced the whole chain propagation to produce alcohols especially for the step of C₁OH–C₂OH. From the XPS analysis, it had been proved that the formation of higher alcohols might be attributable to the presence of Mo^IV species, whereas the formation of hydrocarbons was closely associated with the presence of Mo^II species on the surface of the catalysts.     

Carbon Monoxide Hydrogenation on Cobalt/Zeolite Catalysts

The synthesis of hydrocarbons from catalytic hydrogenation of CO/H₂ was investigated over Co/zeolite catalysts at 1 atm, 493–553 K, H₂/CO = 2, and GHSV = 1200. Various zeolites, such as NaA, NaX, NaY, KL and NaMordenite, were used as the supports. The catalysts were prepared by impregnation and were characterized by H₂/CO chemisorption and temperature-programmed reduction (TPR). Based on TPD measurements, the CO/H₂ adsorption ratio can be used as an index for the extent of metal-zeolite interaction. The stronger the metal-zeolite interaction is, the higher the Co/H₂ adsorption ratio on metal is. The activity and selectivity of cobalt supported in zeolites were affected by complex factors such as framework structure, Si/Al ratio, and the complementary cations. The activity of the catalyst is in the order: Co/KL > Co/NaX > Co/NaY > Co/NaMordenite > Co/NaA. All of the Co/zeolite catalysts had a very high selectivity to C₂–C₄ olefins, which would decrease with increasing reaction temperature. Cobalt oxide supported in zeolite was difficult to reduce. Increasing the reduction temperature could increase the reducibility of cobalt and resulted in the increase of activity.     

Hydrogenation of carbon dioxide over alumina supported Fe-K catalysts

The hydrogenation of CO₂ has been studied over Fe/alumina and Fe-K/alumina catalysts. The addition of potassium increases the chemisorption ability of CO₂ but decreases that of H₂. The catalytic activity test at high pressure (20 atm) reveals that remarkably high activity and selectivity toward light olefins and C₂₊ hydrocarbons can be achieved with Fe-K/alumina catalysts containing high concentration of K (K/Fe molar ratio = 0.5, 1.0). In the reaction at atmospheric pressure, the highly K-promoted catalysts give much higher CO formation rate than the unpromoted catalyst. It is deduced that the remarkable catalytic properties in the presence of K are attributable to the increase in the ability of CO₂ chemisorption and the enhanced activity for CO formation, which is the preceding step of C₂₊ hydrocarbon formation.     

Slurry-phase CO2 hydrogenation to hydrocarbons over a precipitated Fe-Cu-Al/K catalyst: Investigation of reaction conditions

The hydrogenation of CO₂ to hydrocarbons over a precipitated Fe-Cu-Al/K catalyst was studied in a slurry reactor for the first time. Reducibility of the catalyst and effect of reaction variables (temperature, pressure and H₂/CO₂ ratio of the feed gas) on the catalytic reaction performance were investigated. The reaction results indicated that the Fe-Cu-Al/K catalyst showed a good CO₂ hydrogenation performance at a relatively low temperature (533 K). With the increase of reaction temperature CO₂ conversion and olefin to paraffin (O/P) ratio in C₂-C₄ hydrocarbons as well as the selectivity to C₂-C₄ fraction increased, while CO and CH₄ selectivity showed a reverse trend. With the increase in reaction pressure, CO₂ conversion and the selectivity to hydrocarbons increased, while the CO selectivity and O/P ratio of C₂-C₄ hydrocarbons decreased. The investigation of H2/CO₂ ratio revealed that CO₂ conversion and CH₄ selectivity increased while CO selectivity and O/P ratio of C₂-C₄ decreased with increasing H₂/CO₂ ratio.     

Fischer-Tropsch Synthesis: Reaction Pathways for 14C-Labeled Acetic Acid

Reaction pathways for ¹⁴C labeled acetic acid (at both carboxylic and methyl positions) added during Fischer-Tropsch synthesis over a doubly promoted fused iron catalysts were studied in a CSTR at 100 psig, 270 °C and ca. 90% CO conversion. The addition of acetic acid slightly affected the CO conversion but results in a significant reduction in H₂ conversion. Both the unlabeled and labeled acetic acid addition caused a large decrease in the alkene ratio for C₂ hydrocarbons as compared to an increase for the C₃ and C₄ hydrocarbons suggesting a direct formation pathway of ethane from added acetic acid. The 1-alkene/2-alkene fraction was found to increase significantly when acetic acid was added and returned to the original value once the addition is terminated, indicating inhibition of hydrogenation activity of the catalyst by acetic acid. Distribution of ¹⁴C suggests some C–C bond rupture and direct formation of ethane from labeled acetic acid. In the case of 1-¹⁴C labeled acetic acid addition, the gradual increase of the relative molar activity (¹⁴C content per mole) with carbon number reveals that ¹⁴C containing part of acetic acid initiate chain growth and also participates in the chain propagation for hydrocarbon formation in FTS. When acetic acid labeled at methyl position was added, the results indicated that ¹⁴C containing part of acetic acid participates in chain initiation only. The addition of acetic acid decreases methane and methanol selectivity while it increases ethanol, acetaldehyde and acetone selectivity in FTS. Reaction of acetic acid during FTS was found to produce products like ethyl butanoate, ethylene glycol, and its ether, 1,2-diethoxyethane which are not generally observed in the normal FTS product spectrum. The results indicate that acetic acid is not a significant intermediate in FTS with an iron catalyst. ¹⁴C-distribution in most of the labeled oxygenate compounds are consistent with the hydrogenation of the acetic acid to acetaldehyde and/or ethanol as primary products followed by secondary reaction of these two primary oxygenate products.     

Hydrogenation of carbon dioxide by hybrid catalysts,direct synthesis of aromatics from carbon dioxide and hydrogen

Direct synthesis of aromatics from carbon dioxide hydrogenation was investigated in a single stage reactor using hybrid catalysts composed of iron catalysts and HZSM-5 zeolite. Carbon dioxide was first converted to CO by the reverse water gas shift reaction, followed by the hydrogenation of CO to hydrocarbons on iron catalyst, and finally the hydrocarbons were converted to aromatics in HZSM-5. Under the operating conditions of 350°C, 2100 kPa, and CO₂/H₅ = 1/2, the maximum aromatic selectivity obtained was 22% with a CO₂ conversion of 38% using fused iron catalyst combined with the zeolite. Together with the kinetic studies, thermodynamic analysis of the CO₂ hydrogenation was also conducted. It was found that unlike Fischer Tropsch synthesis, the formation of hydrocarbons from CO₂ may not be thermodynamically favored at higher temperatures.     

Comparative Study on CO2 Hydrogenation to Higher Hydrocarbons over Fe-Based Bimetallic Catalysts

This paper reports on notable promotion of C₂ ⁺ hydrocarbons formation from CO₂ hydrogenation induced by combining Fe and a small amount of selected transition metals. Al₂O₃-supported bimetallic Fe–M (M = Co, Ni, Cu, Pd) catalysts as well as the corresponding monometallic catalysts were prepared, and examined for CO₂ hydrogenation at 573 K and 1.1 MPa. Among the monometallic catalysts, C₂ ⁺ hydrocarbons were obtained only with Fe catalyst, while Co and Ni catalysts yielded higher CH₄ selectively than other catalysts. The combination of Fe and Cu or Pd led to significant bimetallic promotion of C₂ ⁺ hydrocarbons formation from CO₂ hydrogenation, in addition to Fe–Co formulation discovered in our previous work. CO₂ conversion on Ni catalyst nearly reached equilibrium for CO₂ methanation which makes this catalyst suitable for making synthetic natural gas. Fe–Ni bimetallic catalyst was also capable of catalyzing CO₂ hydrogenation to C₂ ⁺ hydrocarbons, but with much lower Ni/(Ni+Fe) atomic ratio compared to other bimetallic catalysts. The addition of a small amount of K to these bimetallic catalysts further enhanced CO₂ hydrogenation activity to C₂ ⁺ hydrocarbons. K-promoted Fe–Co and Fe–Cu catalysts showed better performance for synthesizing C₂ ⁺ hydrocarbons than Fe/K/Al₂O₃ catalyst which has been known as a promising catalyst so far.     

Neopentane cracking catalyzed by iron- and manganese-promoted sulfated zirconia

Cracking of neopentane was catalyzed by a sulfated oxide of zirconium promoted with iron and manganese. Reaction at 300–450°C, atmospheric pressure, and neopentane partial pressures of 0.00025–0.005 bar gave methane as the principal product, along with C₂ and C₃ hydrocarbons, butenes, and coke. The order of reaction in neopentane was determined to be 1, consistent with a monomolecular reaction mechanism and with the formation of methane andt-butyl cations; the latter was presumably converted into several products, including only little isobutylene. At 450°C and a neopentane partial pressure of 0.005 bar, the rate of cracking at 5 min onstream was 5×10^–8 mol/(g of catalyst s). Under the same conditions, the rates observed for unpromoted sulfated zirconia and USY zeolite were 3×10^–8 and 6×10^–9 mol/ (g of catalyst s), respectively. The observation that the promoted sulfated zirconia is not much more active than the other catalysts is contrasted to published results showing that the former catalyst is more than two orders of magnitude more active than the others forn-butane isomerization at temperatures <100°C. The results raise a question about whether the superacidity attributed to sulfated zirconia as a low-temperature butane isomerization catalyst pertains at the high temperatures of cracking.     

Study on an iron–manganese Fischer–Tropsch synthesis catalyst prepared from ferrous sulfate

A systematic study was undertaken to investigate the effects of the initial oxidation degree of iron on the bulk phase composition and reduction/carburization behaviors of a Fe–Mn–K/SiO₂ catalyst prepared from ferrous sulfate. The catalyst samples were characterized by powder X-ray diffraction (XRD), Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS) and H₂ (or CO) temperature-programmed reduction (TPR). The Fischer–Tropsch synthesis (FTS) performance of the catalysts was studied in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that the fresh catalysts are mainly composed of α-Fe₂O₃ and Fe₃O₄, and the crystallite size of iron oxides is decreased with the increase of the initial oxidation degree of iron. The catalyst with high content of α-Fe₂O₃ in its as-prepared state has high content of iron carbides after being reduced in syngas. However, the catalyst with high content of Fe₃O₄ in its as-prepared state cannot be easily carburized in CO and syngas. FTS reaction study indicates that Fe-05 (Fe³⁺/Fe_total = 1.0) has the highest CO conversion, whereas Fe-03 (Fe³⁺/Fe_total = 0.55) has the lowest activity. The catalyst with high CO conversion has a high selectivity to gaseous hydrocarbons (C₁–C₄) and low selectivity to heavy hydrocarbons (C₅₊).     

Promotion effect of K2O and MnO additives on the selective production of light alkenes via syngas over Fe/silicalite-2 catalysts

The addition of K₂O and MnO promoters enhances catalyst activity and selectivity to light alkenes during CO hydrogenation over silicate-2 (Si-2) supported Fe catalysts. The results of CO hydrogenation and CO-TPD, CO/H₂-TPSR, C₂H₄/H₂-TPSR and C₂H₄/H₂ pulse reaction over Fe/Si-2 catalysts with and without promoters clearly show that the MnO promoter mainly prohibits the hydrogenation of C₂H₄ and C₃H₆. Therefore, it enhances the selectivity to C₂H₄ and C₃H₄ products. Meanwhile further incorporating the K₂O additive into the FeMn/ Si-2 catalyst leads to a remarkable increase in both the capacity and strength of the strong CO adspecies. These produce much more [C_ad] via their dissociation and disproportionation at higher temperatures. This results in an increase in the CO conversion and the selectivity to light olefins. Moreover, the K₂O additive modifies the hydrogenating reactivity of [C_ad] and suppresses the disproportionation of C₂H₄ that occurs as a side-reaction. Both K₂O and MnO promoters play key roles for enhancing the selective production of light alkenes from CO hydrogenation over Fe/Si-2 catalyst.     

Catalysts with noble metals based on super-cross-linked polystyrene for the hydrogenation of aromatic hydrocarbons

A series of catalysts containing noble metals on a super-cross-linked polystyrene (SCP) support with a developed specific surface area (>1000 m²/g) and high thermal stability are prepared and studied to develop an effective catalyst for the low-temperature hydrogenation of aromatic hydrocarbons. A study of Pt- and Pd-containing catalysts based on SCP, carbon supports, and alumina in the hydrogenation of simple (benzene, toluene), branched (n-butylbenzene) and polycyclic (terphenyl) aromatic compounds is conducted. In the hydrogenation of aromatic hydrocarbons, the activity of the catalysts on SCP is comparable to or surpasses analogous catalysts based on Al₂O₃ and Sibunit in the content of noble metals; it is established that catalysts on SCP have greater selectivity in the hydrogenation of benzene in a benzene-toluene mixture. The electronic state of metals in the Pt(Pd)/SCP catalysts is studied by the IR spectroscopy of adsorbed CO. In testing the catalysts in the hydrogenation of terphenyl, it is found that Pt-containing catalyst on the SCP can operate in reversible hydrogenation-dehydrogenation cycles (terphenyl-tercyclohexane); this is promising for the use of such catalyst systems in creating composite materials for hydrogen storage.     

Porous MoxCy/SiO2 Material for CO2 Hydrogenation

The synthesis and characterization of an inexpensive porous Mo_xC_y/SiO₂ material is presented, which was obtained by mixing ammonium hexamolybdate, sucrose, and a mesoporous silica (SBA-15), with a subsequent heat treatment under inert atmosphere. This porous material presented a specific surface area of 170 m²/g. The catalytic behavior in CO₂ hydrogenation was compared with that of Mo₂C and α-MoC_1?x obtained from ammonium hexamolybdate and sucrose, using different Mo/C ratios. CO₂ hydrogenation tests were performed at moderate (100 kPa) and high pressures (2.0 MPa), and it was found that only CO, H₂O and CH₄ are formed at moderate pressures by the three materials, while at higher pressures, methanol and hydrocarbons (C₂H₆, C₃H₈) are also obtained. Differences in selectivity were observed at the high pressure tests. Mo₂C presented higher selectivity to CO and methanol compared with MoC_1?x, which showed preferential selectivity to hydrocarbons (CH₄, C₂H₆). The porous Mo_xC_y/SiO₂ material showed the highest CO₂ hydrogenation activity at high temperatures (270 and 300 °C), being a promising material for the conversion of CO₂ to CO and CH₄.