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41.
Unusual selectivity of oxygenate synthesis: Formation of acetic acid from syngas over unpromoted Rh in NaY zeolite 总被引:1,自引:0,他引:1
Syngas conversion over Rh/zeolite-NaY catalysts at high-pressure lead to high yields of acetic acid. This unusual selectivity toward one oxygenate in the absence of any catalyst promoter is most pronounced at lower temperature; the apparent activation energy for overall CO-hydrogenation is 23.7 kcal/mol, but for the formation of acetic acid it is 11.9 kcal/mol. The selectivity is little affected by the protons formed during the reduction of Rh. In stiu FT-IR measurement reveals that changes in activity and selectivity during the start-up period are caused by thorough catalyst reconstruction, converting the original Rh0 clusters to multinuclear Rh6(CO)16 and CH3Rhy(CO)x and/or mononuclear CH3Rh(CO)x carbonyl complexes, and smaller Rh0 clusters. Stable acetate groups, but not the surface bound acetyls, are formed and detected by FT-IR. Most of the cooperating Rh species survive when the pressure is lowered from 1.0 to 0.1 MPa, maintaining a high acetic acid selectivity that is vastly superior to that of the fresh catalyst. 相似文献
42.
The Fe2O3/Al2O3 catalyst was studied to selectively synthesize mixed alcohols from syngas in a continuously stirred slurry reactor with the oxygenated solvent Polyethylene Glycol-400 (PEG-400). The selectivity of mixed alcohols in the products reached as high as 95 wt.% and the C2+ alcohols (mainly ethanol) was more than 40 wt.% in the total alcohol products at the reaction conditions of 250 °C, 3.0 MPa, H2/CO = 2 and space velocity = 360 ml/gcat h. The hydrogen temperature programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) measurements of the catalyst confirmed that the FeO phase was responsible for the high selectivity to mixed alcohols in the process. And the oxygenated solvent PEG-400 was also necessary for the selective synthesis of mixed alcohols in the reaction system. 相似文献
43.
《International Journal of Hydrogen Energy》2023,48(28):10566-10578
The low quality municipal solid wastes (MSW) derived char has a potential to be used as a methanation catalyst to achieve low-cost methanation of the syngas derived from MSW, and its performance with varying reaction parameters should be explored for better application. In this study, a MSW char supported Ni-based catalyst (Ni-MSWC) was prepared by impregnation; the influences of CO2 and CH4 impurities in the raw syngas on methanation and the feasibility of conducting methanation in a low-pressure condition were investigated, then the catalyst's response to the changing parameters was identified. The results showed that the presence of low concentration CO2 in the H2-rich syngas is favorable to the gasification of the char carrier and activates Ni-MSWC catalyst. However, it also promotes F–T synthesis reaction and leads to a decrease in the methane yield (YCH4). The decrease in reaction pressure causes a decrease in YCH4 and results in coke formation; but inhibits F–T synthesis reaction and increases methane selectivity (SCH4). A higher reaction pressure increases system complexity and accelerates char carrier consumption. Moreover, presence of methane by 2.8% (vol.) promotes the methanation of CO2 through the methane dry reforming reaction, but it inevitably causes coke formation and affects the catalyst's stability. Based on YCH4 and Ni-MSWC's responses, CO:CO2 ≥ 3:2 and reaction pressure of 1 MPa (gauge pressure) are recommended, which help to inhibit the side reactions and maintain a high YCH4 (>95%). 相似文献
44.
《International Journal of Hydrogen Energy》2023,48(60):22909-22920
This study aims to investigate the gasification potential of olive pomace with using different fixed-bed gasifier systems. Olive pomace as a dried form was supplied from a chemical industry plant working on olive oil soap, located in Izmir, Türkiye. After a complete characterization of olive pomace, gasification experiments by using fixed bed reactor systems were done at three different gasifier temperatures as 700, 800 and 900 °C. As a gasification agent, dry air was used with four different flowrates (0.4, 0.2, 0.1, 0.05 L/min) while pure oxygen experiments were carried out with a flow rate of 0.01 L/min. Syngas with H2 content of 48% and 45% (volumetric) were obtained in updraft and downdraft gasifiers, respectively, by using dried air as a gasifying agent. Heating value of syngas was around 12.4 MJ/Nm3. In the pure oxygen atmosphere, H2 contents of the syngas were measured as 53% and 39%vol. In the updraft and downdraft gasifiers. This paper presents the research results on the olive pomace gasification study as a part of a large-scale research project and discuss them in the context of hydrogen production from the fixed bed reactors. 相似文献
45.
V.A. Vorontsov A.G. Gribovskiy L.L. Makarshin D.V. Andreev V.Y. Ylianitsky V.N. Parmon 《International Journal of Hydrogen Energy》2014
Partial oxidation of methane (POM) has been tested in an asymmetric microchannel reactor with different inlet configurations. One inlet of the reactor provided successive splitting of an inlet flow into parallel channels, whereas the opposite inlet allowed the inlet flow to enter the parallel channels simultaneously. It was found that concentrations of carbon monoxide and carbon dioxide changed by 20–30% and the conversion of methane changed by 5–20%, depending on the rate and direction of the inlet flow. The hydrogen production rate practically did not depend on the inlet configuration and equaled 15 l/h at the inlet flow rates from 600 to 1400 cm3/min and at the methane conversion of 80%. The data obtained demonstrated that the use of different operating modes of the asymmetric microreactor allows changing the composition of produced syngas. 相似文献
46.
Andres A. Amell Hernando A. YepesFrancisco J. Cadavid 《International Journal of Hydrogen Energy》2014
The laminar burning velocity of syngas mixtures has been studied by various researches. However, most of these studies have been conducted in atmospheric conditions at sea level. In the present study, the effect of sub atmospheric pressure was evaluated on the laminar burning velocity for a mixture of H2, CO and N2 (20:20:60 vol%) in real sub atmospheric condition. The measurements was conducted in an altitude of 2130 m.a.s.l (0.766 atm) and 21 m.a.s.l (0.994 atm) to evaluate the effect of pressure, the temperature and relative humidity were controlled using an air conditioning unit and was maintained in 295 ± 1 K and 62.6 ± 2.7% respectively. The Flames were generated using contoured slot-type nozzle burner, and an ICCD camera was used to capture chemiluminescence emitted by OH∗-CH∗ radicals present in the flame and thus obtain the flame front and determinate the laminar burning velocity using the angle method. The experimental results were compared with numerical calculations, conducted using the detailed mechanisms of Li et al. and the GRI-Mech 3.0. It was found that the laminar burning velocity increases at lower pressure, for an equivalence ratio of 1.1, the laminar burning velocity increases by almost 23% respect to the sea level conditions. 相似文献
47.
A study on the effect of CO2 and H2O dilution on the laminar burning characteristics of CO/H2/air mixtures was conducted at elevated pressures using spherically expanding flames and CHEMKIN package. Experimental conditions for the CO2 and H2O diluted CO/H2/air/mixtures of hydrogen fraction in syngas from 0.2 to 0.8 are the pressures from 0.1 to 0.3 MPa, initial temperature of 373 K, with CO2 or H2O dilution ratios from 0 to 0.15. Laminar burning velocities of the CO2 and H2O diluted CO/H2/air/mixtures were measured and calculated using the mechanism of Davis et al. and the mechanism of Li et al. Results show that the discrepancy exists between the measured values and the simulated ones using both Davis and Li mechanisms. The discrepancy shows different trends under CO2 and H2O dilution. Chemical kinetics analysis indicates that the elementary reaction corresponding to peak ROP of OH consumption for mixtures with CO/H2 ratio of 20/80 changes from reaction R3 (OH + H2 = H + H2O) to R16 (HO2+H = OH + OH) when CO2 and H2O are added. Sensitivity analysis was conducted to find out the dominant reaction when CO2 and H2O are added. Laminar burning velocities and kinetics analysis indicate that CO2 has a stronger chemical effect than H2O. The intrinsic flame instability is promoted at atmospheric pressure and is suppressed at elevated pressure for the CO2 and H2O diluted mixtures. This phenomenon was interpreted with the parameters of the effective Lewis number, thermal expansion ratio, flame thickness and linear theory. 相似文献
48.
Solid Oxide Electrolyzer Cells (SOECs) are promising energy devices for the production of syngas (H2/CO) by H2O and/or CO2 electrolysis. Here we developed a Cu–Ce0.9Gd0.1O2−δ/Ce0.8Gd0.2O2−δ/Ba0.5Sr0.5Co0.8Fe0.2O3−δ-Ce0.8Gd0.2O2−δ cell and performed H2O and CO2 electrolysis experiments in the intermediate temperature range (600°C–700 °C). As a baseline, the cell was first tested in fuel cell operation mode; the sample shows a maximum power density peak of 104 mW cm−2 at 700 °C under pure hydrogen and air. H2O electrolysis testing revealed a steady production of hydrogen with a Faraday's efficiency of 32% at 700 °C at an imposed current density of −78 mA cm−2. CO production was observed during CO2 electrolysis but higher cell voltages were required. A lower efficiency of about 4% was obtained at 700 °C at an imposed current density of −660 mA cm−2. These results confirm that syngas production is feasible by water and carbon dioxide electrolysis but further improvements from both the manufacturing and the electrocatalytic aspects are needed to reach higher yields and efficiencies. 相似文献
49.
A self-sustained electrochemical promotion (SSEP) catalyst is synthesized for partial oxidation reforming (POXR) of CH4 to produce syngas (H2 and CO) at a relatively low temperature ranging from 350 to 650 °C. The SSEP catalyst is comprised of 4 components: microscopic Ni/Cu/CeO2 anode, La0.9Sr0.1MnO3 cathode, copper as electron conductor, and yttria-stabilized-zirconia as oxygen ion conductor, which form microscopic electrochemical cells to enable the self-sustained electrochemical promotion for the POXR process. The SSEP catalyst exhibited much better catalytic performance in POXR of CH4 than a Ni–Cu–CeO2 catalyst and a commercial Pt–CeO2 catalyst. The CH4 conversion over the SSEP catalyst is 29.4% at 350 °C and reaches 100% at 550 °C and the maximum selectivity to H2 is on the level of 90% at 450–650 °C under a GHSV of 42,000 h−1. The mechanism of the SSEP is discussed. 相似文献
50.
Isotopic transient tracer techniques have been employed to study heterogeneous hydroformylation on Rh/SiO2 and Mn–Rh/SiO2. Pulse injection of D2 and
allowed tracing of the deuterium and CO incorporation pathway into the aldehyde product. The d1- and d2-propionaldehyde responses showed a double-peak, or two-hump, response to the D2 pulse, while
showed a single-hump response to the
pulse. Analysis of the product responses to the D2 pulse in CO/H2/C2H4 and CO/H2/C2H4/C2H5CHO suggests that the first hump of the d1- and d2-propionaldehyde responses was due to rapid H/D exchange with adsorbed propionaldehyde via enol intermediates. The decay of the second hump was due to reaction of adsorbed acyl with spillover hydrogen/deuterium. The
response was due to CO insertion followed by acyl hydrogenation. Compartment modeling of the product responses from the
and D2 pulse inputs allowed determination of residence times of adsorbed intermediates, surface coverages of adsorbed intermediates, and the elementary rate constants for acyl hydrogenation and CO insertion. Elementary rate constants for acyl hydrogenation determined from this study were consistent with the value calculated by transition state theory (TST). The addition of Mn promoter to Rh/SiO2 increased coverages of
,
, and
and shifted the rate-limiting step for propionaldehyde formation. Acyl hydrogenation is the rate-limiting step on Rh/SiO2 while CO insertion and acyl hydrogenation are both kinetically significant on Mn–Rh/SiO2. 相似文献