CO Conversion Levels Research Articles

Direct Conversion of Syngas to Higher Alcohols via Tandem Integration of Fischer-Tropsch Synthesis and Reductive Hydroformylation.

The selective conversion of syngas to higher alcohols is an attractive albeit elusive route in the quest for effective production of chemicals from alternative carbon resources. We report the tandem integration of solid cobalt Fischer–Tropsch and molecular hydroformylation catalysts in a one‐pot slurry‐phase process. Unprecedented selectivities (>50 wt %) to C2+ alcohols are achieved at CO conversion levels >70 %, alongside negligible CO2 side‐production. The efficient overall transformation is enabled by catalyst engineering, bridging gaps in operation temperature and intrinsic selectivity which have classically precluded integration of these reactions in a single conversion step. Swift capture of 1‐olefin Fischer–Tropsch primary products by the molecular hydroformylation catalyst, presumably within the pores of the solid catalyst is key for high alcohol selectivity. The results underscore that controlled cooperation between solid aggregate and soluble molecular metal catalysts, which pertain to traditionally dichotomic realms of heterogeneous and homogeneous catalysis, is a promising blueprint toward selective conversion processes.

Direct Conversion of Syngas to Higher Alcohols via Tandem Integration of Fischer–Tropsch Synthesis and Reductive Hydroformylation

AbstractThe selective conversion of syngas to higher alcohols is an attractive albeit elusive route in the quest for effective production of chemicals from alternative carbon resources. We report the tandem integration of solid cobalt Fischer–Tropsch and molecular hydroformylation catalysts in a one‐pot slurry‐phase process. Unprecedented selectivities (>50 wt %) to C2+ alcohols are achieved at CO conversion levels >70 %, alongside negligible CO2 side‐production. The efficient overall transformation is enabled by catalyst engineering, bridging gaps in operation temperature and intrinsic selectivity which have classically precluded integration of these reactions in a single conversion step. Swift capture of 1‐olefin Fischer–Tropsch primary products by the molecular hydroformylation catalyst, presumably within the pores of the solid catalyst is key for high alcohol selectivity. The results underscore that controlled cooperation between solid aggregate and soluble molecular metal catalysts, which pertain to traditionally dichotomic realms of heterogeneous and homogeneous catalysis, is a promising blueprint toward selective conversion processes.

Manganese promotion of a cobalt Fischer-Tropsch catalyst to improve operation at high conversion

The addition of manganese to cobalt-based Fischer-Tropsch catalysts increases activity and significantly improves liquid fuel yield by decreasing CO2 and CH4 selectivity. These effects are particularly noticeable at high CO conversions where the catalyst is exposed to high H2O, and low CO and H2, partial pressures. Under these conditions, manganese-promotion causes a shift in the maximum liquid fuel yield from 61 C-% to 79 C-% (at CO-conversion levels of 78% and 91%, respectively), thus enabling once-through operation. Our CO-TPD and DFT studies show that manganese promotion cannot to be linked to enhanced CO adsorption nor promotion of the C-O bond cleavage (both typically postulated mechanisms). Rather, our DFT-calculations indicate that manganese promotion modelled as a manganese oxide cluster on Co(111) is associated with improved oxygen removal from the catalytically active surface, explaining the reduced selectivity towards CO2 at high conversion and, thus, reduced methane selectivity and improved liquid fuel yield.

Influence of Cs Loading on Pt/m-ZrO2 Water–Gas Shift Catalysts

Certain alkali metals (Na, K) at targeted loadings have been shown in recent decades to significantly promote the LT-WGS reaction. This occurs at alkali doping levels where a redshift in the C-H band of formate occurs, indicating electronic weakening of the bond. The C-H bond breaking of formate is the proposed rate-limiting step of the formate associative mechanism, lending support to the occurrence of this mechanism in H2-rich environments of the LT-WGS stage of fuel processors. Continuing in this vein of research, 2%Pt/m-ZrO2 was promoted with various levels of Cs in order to explore its influence on the rate of formate intermediate decomposition, as well as that of LT-WGS in a fixed bed reactor. In situ DRIFTS experiments revealed that Cs promoter loadings of 3.87% to 7.22% resulted in significant acceleration of the forward formate decomposition in steam at 130 °C. Of all of the alkali metals tested to date, the redshift in the formate ν(CH) band with the incorporation of Cs was the greatest. XANES difference experiments at the Pt L2 and L3 edges indicated that the electronic effect was not likely due to an enrichment of electronic density on Pt. CO2 TPD experiments revealed that, unlike Na and K promoters, Cs behaves more like Rb in that the decomposition of the second intermediate in LT-WGS, carbonate species, is hindered due to (1) increased basicity of Cs, (2) the tendency of Cs to cover Pt sites that facilitate CO2 decomposition, and (3) the tendency of Cs to increase Pt particle size as shown by EXAFS results, resulting in fewer Pt sites that facilitate CO2 decomposition. As such, the LT-WGS rate was hindered overall and the rate-limiting step shifted to carbonate decomposition (CO2 removal). Like its Rb counterpart, low levels of added Cs (e.g., 0.72%Cs) were found to improve the stability of the catalyst relative to the unpromoted catalyst; the stability comparison was made at similar CO conversion level as well as similar space velocity.

Highly dispersed Co nanoparticles embedded in a carbon matrix as a robust and efficient Fischer–Tropsch synthesis catalyst under harsh conditions

Series of catalysts with Co nanoparticles embedded in matrix of porous carbon is directly synthesized via a unique melting approach. No obvious deactivation is observed at high operating temperature and high CO conversion levels.

Tuning direct CO hydrogenation reaction over Fe-Mn bimetallic catalysts toward light olefins: Effects of Mn promotion

Highly dispersed FeMn bimetallic nanoparticles prepared by a low-temperature co-precipitation method were employed for direct CO hydrogenation for light olefins (C2∼C4=). An outstanding selectivity (60.6 %) for light olefins at a CO conversion level of 7.6 % was obtained over FeMn (4:1) catalyst activated by syngas (5%CO/5%H2). Characterization indicated that a strong interaction between Fe and Mn resulted in significant effects on stabilization of Fe1-xMnxO phase during activation period. Responding to the morphology effect, Mn decreased the surface energy of nanocrystals and weakened the agglomeration of nanoparticles, thus resulted in a decrease in particle size of Mn-promoted catalysts. The combined effects of inhibited carburization and improved metal dispersion contributed to the volcano pattern in the catalytic activity of Mn-promoted catalysts. In addition, Mn may act as an effective electron donor to Fe, enhancing CO dissociative adsorption while inhibiting secondary hydrogenation of olefins, thus giving rise to high olefin selectivity in CO hydrogenation.

Inverse CeO2/CuO WGS catalysts: Influence of the presence of oxygen in the reactant mixture

Three catalysts based on inverse configuration of copper-ceria catalysts, i.e. CeO2/CuO and two others in which the copper oxide phase is doped with Mn and Zn, respectively, are examined with respect to their performance for the water-gas shift reaction (WGS) and the influence of oxygen and/or hydrogen presence in the reaction mixture. Multitechnique characterization of the catalysts evidence the inverse configuration of the catalysts prepared by microemulsion method, which are basically constituted by small ceria particles of 4–5 nm supported onto larger copper oxide particles of 12–20 nm. Doping with Mn or Zn enhances the WGS performance of the catalyst. The presence of small amounts of oxygen in the reaction mixture importantly enhances the CO conversion as a consequence of the competing CO oxidation reaction. However, oxygen promotion of the WGS activity is only observed for the undoped catalyst at relatively low temperature and high CO/O2 ratio. The catalysts display high CO conversion levels even in the presence of hydrogen and oxygen, suggesting the feasibility of carrying out WGS and CO-PROX in a single step using them.

Catalytic assessment of Fe-La-Zr trimetallic mixed oxides in the Fischer-Tropsch synthesis using bio-syngas

H2/CO/CO2 gaseous mixtures obtained by biomass gasification (bio-syngas) could be used to obtain hydrocarbons by the Fischer-Tropsch synthesis (FTS). In this work, trimetallic Fe–La–Zr mixed oxides prepared by coprecipitation with oxalic acid were studied in the synthesis of hydrocarbons from bio-syngas at 300 °C and 10 bar. Catalysts obtained by calcination at 700 °C are activated by the bio-syngas and the one that contains 30 wt% of Fe attains steady CO conversion levels of 75% and a total hydrocarbon yield of 34%–36%. A liquid product containing hydrocarbons in the range C5–C13 is formed together with C1–C4 products. Potassium promotion (6 wt%) allows to increase CO conversion (∼89%) and hydrocarbons yield (∼44%). Catalysts obtained by calcination at 900 °C display higher activation times due to their crystalline structure, although they attain final activity levels close to the amorphous ones obtained by calcination at 700 °C.

Fischer–Tropsch Synthesis at High Conversions on Al2O3-Supported Co Catalysts with Different H2/CO Levels

Fischer–Tropsch experiments with different H2/CO ratios at high CO conversions have been carried out over an alumina-supported 20 wt % Co–0.5 wt % Re catalyst in a stainless steel fixed-bed reactor at 210 °C and 20 bar and with H2/CO ratios between 1.04 and 2.56. The results indicate that for H2/CO ratios above 2.1, CO conversion levels up to at least 85% can be obtained without significant short-term deactivation or loss of selectivity toward heavier hydrocarbons. Except for very low conversion anomalies, the data collapse into a single trendline for selectivity to C5+ products versus average hydrogen partial pressure in the reactor irrespective of the H2/CO feed ratio. The present results are important for development of small-scale biomass to liquid fuel plants based on a once-through process concept in order to avoid recycle streams.

Measurement of the Influence of the Microstructure of Alumina‐Supported Cobalt Catalysts on their Activity and Selectivity in Fischer–Tropsch Synthesis by using Steady‐State and Transient Kinetics

AbstractFive alumina‐supported Co catalysts with different particle sizes and structures were synthesized. The catalysts showed different activities during long‐term Fischer–Tropsch experiments. Steady‐state isotopic transient kinetic analysis (SSITKA) 12CO/H2→13CO/H2 experiments were performed during these long‐term runs. The number of active sites for CO adsorption and activation was estimated through the summation of all surface intermediates derived from the SSITKA results. Rather than comparing turnover frequencies, a kinetic analysis was performed. A simple kinetic rate equation based on the in situ number of active sites described the steady‐state CO conversion over the five catalysts adequately. Thus the difference in the catalytic performance could not be attributed to a difference in particle size, phase orientation (face‐centered cubic or hexagonal close packed), or Pt‐promotion effect but instead was only because of the number of reduced Co atoms exposed during the reaction. Similarly, the selectivity depended on the CO conversion level and temperature and not on the catalyst structure.

Fischer-Tropsch synthesis: Effect of carbonyl sulfide poison over a Pt promoted Co/alumina catalyst

The effect of carbonyl sulfide (COS) impurity present in syngas on the performance of a traditional cobalt catalyst (0.5%Pt-25%Co/Al2O3) was investigated for Fischer-Tropsch synthesis (FTS) using a continuously stirred tank reactor (CSTR). Reports about the use of COS as sulfur carrier for the poisoning of cobalt catalysts for FTS are scarce. The S-poisoned and un-poisoned catalysts were tested at industrially relevant FTS conditions and also compared at the same CO conversion level in order to evaluate the effect of sulfur on catalyst activity and product selectivity. The COS (1.8 ppmv) addition caused a significant irreversible effect on the activity. At similar CO conversion level, the COS poisoned catalyst exhibited higher methane and C2–C4 selectivities and lower C5+ selectivity compared to the clean or un-poisoned catalyst. The COS poisoned catalysts were characterized by X-ray adsorption near edge structure (XANES) analysis to find out the reason for the deactivation and altering of the product selectivities. The sulfur K-edge XANES results clearly indicate the formation of cobalt sulfide, which is known to enhance the hydrogenation ability. The olefin/paraffin ratio of the COS poisoned catalyst was found to be lower than that of the clean catalyst, providing further indication of the higher hydrogenation activity of the COS poisoned catalyst.

Effects of Co Particle Size on the Stability of Co/Al2O3 and Re–Co/Al2O3 Catalysts in a Slurry-Phase Fischer-Tropsch Reactor

The stability of a series of Co/Al2O3 and Re–Co/Al2O3 Fischer–Tropsch (FT) catalysts, with varying Co particle size, was measured in a continuous flow, stirred tank reactor operated at 220 °C, 2.1 MPa and with a H2/CO = 2/1 synthesis gas for periods up to 190 h time-on-stream (TOS). Results showed that catalyst stability was dependent upon the Co particle size, the degree-of-reduction (DOR) of the catalyst precursor, and the CO conversion. At the chosen operating conditions, carbon deposition was the main cause of catalyst deactivation and the initial rate of carbon deposition per active Co site increased with increased Co particle size (dCo = 2–22 nm) when measured at approximately the same CO conversion level. On the 15 wt % Co/Al2O3 catalyst the initial rate of carbon deposition increased with CO conversion (CO conversion ≤40%) whereas, on the 1.2 wt %Re-12 wt %Co/Al2O3 catalyst, the initial rate of carbon deposition decreased with increased CO conversion (CO conversions >60%) due to high concentration...

The activities of Cu-based Mg–Al layered double oxide catalysts in the water gas shift reaction

In this work, three preparation methods (an incipient wetness impregnation on Mg–Al hydrotalcite, co-precipitation (CP) and double-step-co-precipitation) were employed to prepare Cu-based Mg–Al layered double oxides for the water–gas shift reaction. The Cu0.15Mg3Al-CP300 catalyst formed by CP had a higher reducing the CO level with a lower H2 consumption. Varying Mg/Al molar ratios from 1 to 4, the Cu0.15Mg3Al-CP300 showed the lowest reduction temperature and highest catalytic activity. Increasing the calcination temperature from 300 °C to 500 °C resulted in a higher CO conversion level. Increasing the Cu/(Cu + Mg + Al) molar ratio from 0.15 to 0.30 reduced the crystallite sizes of the periclase phase with a markedly enhanced catalytic activity at temperatures below 350 °C. No marked deactivation of the Cu0.30Mg3Al-CP500 catalyst was found over a period test even though adding CO2 in the feed. After regeneration, the catalytic activity of the spent catalyst was the same as the fresh catalyst.

Microreactors technology for hydrogen purification: Effect of the catalytic layer thickness on CuOx/CeO2-coated microchannel reactors for the PROX reaction

Two blocks of microreactors composed by 100 microchannels and coated, respectively, with 150 and 300mg of a CuOx/CeO2 catalyst, were prepared and tested in the preferential oxidation of CO in presence of H2 (PROX). The deposition of different amount of catalyst resulted in different catalytic layer thicknesses thus modifying the catalytic performances of the microreactor. The evaluation of the main reaction variables (the space velocity, the O2-to-CO ratio and the presence of H2O and/or CO2 in the stream) was performed over both microreactors and compared to that of the parent powder catalyst. The least loaded microreactor, with a coating thickness around 10μm, presented the highest CO conversion and selectivity levels at temperatures below 160°C. This result evidences (i) the improvement of the catalytic performances got by the structuration of the powder catalyst and (ii) the importance of the selection of the adequate thickness of the catalytic layer on the microreactor, which have not to exceed and optimal value. An adequate coating thickness allows minimizing the mass and heat transport limitations, thus resulting in the enhancement of the catalytic performance during the PROX reaction.

Syngas Conversion to Hydrocarbons on Zirconia-Supported Iron Catalysts

The hydrogenation of CO to hydrocarbons is investigated over zirconia iron-based catalysts prepared by co-precipitation. These catalysts, in which the Fe-content varied between 0 and 100 %, were tested in the CO hydrogenation reaction under fixed reaction conditions (H2/CO = 2, T = 250 °C, P = 20 bar, GHSV = 0.0083 L/g.s.). The resulting activity data indicated that CO conversion is strongly dependent on the iron contents of the catalysts. The lowest CO conversion (<5 %) was obtained using Zr-rich catalysts (15Fe and 5Fe), and the highest CO conversion was obtained using Zr-free (100Fe) catalysts. For this catalyst, the CO conversion level reaches 38.5 %, with selectivities for the C2–C4 and C5+ hydrocarbons of 49.7 and 27.7 %, respectively. However, the activity profile of this catalyst slightly decreases with the time on-stream, indicating that it is progressively deactivated. If the activity is normalized to the iron content, the 95Fe and 85Fe catalysts display slightly better performances and are relatively stable for on stream periods of at least 48 h.

Selectivity control of Cu promoted iron-based Fischer-Tropsch catalyst by tuning the oxidation state of Cu to mimic K

The effect of activation gas on the Fischer-Tropsch synthesis (FTS) performance of copper and potassium promoted precipitated iron-based catalysts was investigated in an earlier study [Catal. Lett. 144 (2014) 1624-1635]. In that study, CO and syngas (H2/CO=0.7) activation methods were tested after varying the copper promoter loading (0, 2, and 5%, atomic ratios relative to iron). At similar CO conversion level, the selectivities for the CO-activated catalysts were identical for the various copper loaded catalysts, whereas for the syngas activated catalysts, light hydrocarbon (methane and C2–C4) selectivities decreased and higher hydrocarbon (C5+) selectivities increased with increasing copper loading. To understand the reason for that behavior, the catalyst samples were characterized by XANES/EXAFS spectroscopy following each activation procedure before and after exposure to FTS conditions. Cu K-edge normalized XANES results indicate that for the syngas activated catalyst copper is present primarily in the Cu1+ state, whereas for CO activated catalyst the copper is more reduced (greater fraction in the Cu0 state). The Cu1+ in the syngas activated catalyst behaved like K1+; therefore, the C5+ selectivity was enhanced and light hydrocarbon selectivity was suppressed.

Caso clínico 4. ¿Cuál sería su abordaje diagnóstico y terapéutico?

The effect of activation gas on the Fischer-Tropsch synthesis (FTS) performance of copper and potassium promoted precipitated iron-based catalysts was investigated in an earlier study [Catal. Lett. 144 (2014) 1624-1635]. In that study, CO and syngas (H2/CO = 0.7) activation methods were tested after varying the copper promoter loading (0, 2, and 5%, atomic ratios relative to iron). At similar CO conversion level, the selectivities for the CO-activated catalysts were identical for the various copper loaded catalysts, whereas for the syngas activated catalysts, light hydrocarbon (methane and C2–C4) selectivities decreased and higher hydrocarbon (C5+) selectivities increased with increasing copper loading. To understand the reason for that behavior, the catalyst samples were characterized by XANES/EXAFS spectroscopy following each activation procedure before and after exposure to FTS conditions. Cu K-edge normalized XANES results indicate that for the syngas activated catalyst copper is present primarily in the Cu1+ state, whereas for CO activated catalyst the copper is more reduced (greater fraction in the Cu0 state). The Cu1+ in the syngas activated catalyst behaved like K1+; therefore, the C5+ selectivity was enhanced and light hydrocarbon selectivity was suppressed.

Effective activation of montmorillonite and its application for Fischer-Tropsch synthesis over ruthenium promoted cobalt

The natural Na-type montmorillonite (Na-MMT) suspended in the 20wt.% HNO3 aqueous solution at concentrations between 2-20wt.% was activated at 70–104°C for a period, respectively. The thus obtained materials were abbreviated as acid-MMT-m-t/T, where m, t and T are the concentration of Na-MMT suspension (wt.%), time (h), and temperature (°C) during the acid activation, respectively. The Co-Ru/acid-MMT (20wt.% Co and 0.1wt.% Ru) was prepared by the incipient impregnation method. The materials were characterized by XRD, FT-IR, XRF, N2 adsorption-desorption at low temperature, H2-TPR, H2-TPD, oxygen titration, and NH3-TPD techniques. In comparison to the results of the Na-MMT, the structural, textural, and acidic properties of the acid-MMTs were clearly changed, the extent of which is strongly dependent on the acid activation conditions. For the first time, the acid-MMT with desired properties were obtained using a high ratio of Na-MMT suspension, such as 10wt.%, leading to a significantly improved process efficiency of the acid activation. The structural and compositional changes of acid-MMTs gave significant impacts on the reduction behavior of Co-Ru/acid-MMT catalysts. Moreover, the addition of Ru to Co/acid-MMTs decreased the peak temperatures of the two-step reduction of Co3O4 to Co via the CoO intermediate, leading to an increased extent of reduction of cobalt. The catalysts were comparatively investigated for Fischer-Tropsch (FT) synthesis in a fixed-bed reactor under the conditions of H2/CO =2, W/F =5.0g·h·mol−1, 235°C, and 1.0MPa. Results showed that the CO conversion was decreased in the order of Co-Ru/acid-MMT-2-12/104>Co-Ru/acid-MMT-10-12/104>Co-Ru/acid-MMT-20-12/104 ≫Co-Ru/acid-MMT-2-12/70>Co-Ru/acid-MMT-2-4/70>Co/acid-MMT-2-4/70. Moreover, all of the Co-Ru/acid-MMT catalysts showed clearly higher selectivity of C5-C12 hydrocarbons and lower selectivity of C21+ hydrocarbons compared with Co/SiO2 catalyst. The Co-Ru/acid-MMT-2-12/70 showed about 46% C5-C12 selectivity at a reasonable CO conversion level.

Fischer–Tropsch Synthesis: Effect of Activation Gas After Varying Cu Promoter Loading Over K-Promoted Fe-Based Catalyst

The effects of activation gas and copper promoter loading on the Fischer–Tropsch synthesis performance of potassium promoted precipitated iron-based catalysts were investigated using a continuously stirred tank reactor. In this study, CO and syngas (H2/CO = 0.7) activated catalysts were tested after varying the copper promoter loading (0, 2 and 5 %, atomic ratios relative to iron). After attaining a steady-state conversion for the CO-activated catalysts, similar or slightly higher CO conversions were exhibited with increasing copper loading, and the induction period was reduced with increasing copper loading. Partial pressure of hydrogen in the activation gas influenced the resulting activity of the catalysts. For syngas activated catalysts, CO conversion was found to increase with increasing copper loading up to 2 %, and slightly decrease with further increases in copper (5 %) loading. For similar CO conversion levels, the selectivities were similar for the CO activated catalysts, whereas for the syngas activated catalysts, the selectivity varied with copper loading. With increasing copper loading, lower hydrocarbon (methane and C2–C4) selectivities decreased and the corresponding higher hydrocarbon (C5+) selectivity increased.

Fischer–Tropsch Synthesis: Kinetics and Water Effect on Methane Formation over 25%Co/γ-Al2O3Catalyst

The kinetics and the effect of indigenous and externally added water on methane formation during Fischer–Tropsch synthesis (FTS) was studied over Co based catalysts using a 1 L continuously stirred tank reactor (CSTR). The water cofeeding study (10% water) was conducted over a 0.27%Ru–25%Co/Al2O3 catalyst at a low CO conversion level of 19% at 220 °C in order to lessen the effect of catalyst aging during the addition of water, while the kinetic experiment was conducted over 25%Co/γ-Al2O3 at the conditions of 205–230 °C, 1.4–2.5 MPa, H2/CO = 1.0–2.5, and 3–16 (NL/gcat)/h (XCO < 60%). Indigenous and externally added water decreases methane formation by a kinetic effect. The addition of 10% water led to a decrease in the CH4 rate by 12% (3.5 → 3.0 (mmol/gcat)/h), while little catalyst deactivation was observed during water addition. Increases in indigenous water partial pressure also lowered the CH4 rate and its selectivity. Kinetic analysis was performed using a group of 220 °C data collected between 365 and 918 h when the deactivation rate was very low. An empirical CH4 kinetic model, with a water effect term (PH2O/PH2), (rCH4 = kPCO aPH2b/(1 + mPH2O/PH2)) was used to fit kinetic data. The CH4 kinetic results suggest a negative water effect on CH4 formation during FTS on the unpromoted cobalt catalyst, consistent with the water effect results. The final methane kinetics (rCH4) equation obtained at 220 °C over 25%Co/γ-Al2O3 is as follows: rCH4/[(mol/gcat)/h] = 0.001053{PCO–0.86PH21.32/[1 + 0.46(PH2O/PH2)]}. Meanwhile, a methane selectivity model at 220 °C for the 25%Co/Al2O3 catalyst was also developed: SCH4 = 0.0792PCO–0.55PH20.44[(1 – 0.24PH2O/PH2)/(1 + 0.46PH2O/PH2)]. The CH4 selectivity model provided a good prediction of CH4 selectivities under the experimental conditions used. Furthermore, our empirical CH4 kinetic results on the cobalt catalyst are consistent with literature kinetic models that were derived from carbide mechanisms; high CH4 selectivity from the cobalt catalyst is found to be mainly due to a high CH4 reaction rate constant.