Synthesis Of C2 Oxygenates Research Articles

CO Hydrogenation to C2 Oxygenates over SiO2 Supported Rh-Based Catalyst: The Effect of pH Value of Impregnation Solution

The synthesis of C2 oxygenates including ethanol directly from coal-derived syngas is significant from both academic and practical points of view and SiO2 supported Rh-based catalysts are very effective for this conversion. However, the high price of Rh requires the improvement of its dispersion to maximize Rh efficiency. The adjustment of impregnation solution pH value can modify effectively the metal dispersion over the support. Herein, we reported the pH effect on catalytic performance of Rh-Mn-Li/SiO2 for CO hydrogenation to C2 oxygenates for the first time. A series of catalysts were prepared from different pH values of impregnation solutions, and were characterized by various techniques. With the increasing of solution pH value above zero point of charge (ZPC) of silica, Rh particle sizes increased with much wider size distribution and reduction of Rh species was restrained over the prepared catalysts owing to the stronger interaction between Rh and support. As a result, the active sites for CO insertion, especially for CO or H2 dissociation was lowered, leading to the depletion of the activity for the formation of C2 oxygenates from CO hydrogenation, and larger Rh particle size with wider size distribution favors the production of long chain hydrocarbons. On the contrary, when the catalyst was prepared using solution with pH below ZPC of silica, the dispersion and the reduction of Rh were promoted due to suitable Rh-support interaction, and in the CO hydrogenation reaction, the space time yield and selectivity of C2 oxygenates reached 679.4 g/kg-cat/h and 73.3%, respectively. The pH value of impregnating solution regulate the metal-support interaction and thus Rh particle sizes and its reduction, which effects strongly CO hydrogenation activity and selectivity.

Mechanism insights into direct conversion of syngas into C2 oxygenates via key intermediate C2O2 over Ni-Supported graphene

A critical step toward the rational design of new catalyst that achieve selective and efficient synthesis of C2+ oxygenates from syngas (CO/H2) by Fischer-Tropsch synthesis (FTS) is to determine the detailed reaction mechanism. Herein, the mechanism of two gaseous CO monomers coupling into a chemisorbed ethylene dione (O∗C∗CO) and subsequent hydrogenation of O∗C∗CO on the chainmail catalyst of nickel-supported graphene surface is reported. The results show that two gaseous CO monomers can be coupled into a two-atom-chemisorbed O∗C∗CO via a metastable intermediate of O∗CCO single-atom-chemisorbed on Ni-supported on graphene with the barrier energy of 0.85 eV and a strong exothermicity of 1.45 eV. The key intermediate of O∗C∗CO can be stably chemisorbed on the Ni-supported-graphene surface by riveting two coupled C atoms on the ortho-, meta-, or para-position of graphene six-membered ring, forming four-, five-, and six-membered ring with the carbon atoms of graphene, respectively. Then, the potential energy surfaces of chemisorbed O∗C∗CO hydrogenation indicates that glycol-aldehyde (HOH2C–CHO) would be preferred to form by the kinetically favorable initial C-hydrogenation due to the low rate-limiting barrier of 0.46 eV, while the glyoxal (OHC=CHO) is a considerably competitive product because its rate-limiting barrier is only 0.18 eV higher than that of the glycol-aldehyde. These results suggest that the chainmail catalyst of nickel-supported graphene could be a potential and high-efficient catalyst for synthesis of C2 oxygenates from syngas, which also provides a fundamental insight into the new reaction mechanism of Fischer-Tropsch synthesis.

The effects of the nature of TiO2 supports on the catalytic performance of Rh–Mn/TiO2 catalysts in the synthesis of C2 oxygenates from syngas

Four types of TiO2 with different rutile/anatase crystalline phase compositions were used as supports, and the effect of the TiO2 phase composition on the catalytic properties of supported Rh catalysts in the synthesis of C2 oxygenates from syngas was studied.

Insight into size dependence of C2 oxygenate synthesis from syngas on Cu cluster: The effect of cluster size on the selectivity

Size dependence of C2 oxygenate formation from syngas on Cu cluster has been investigated to qualitatively probe into the effect of Cu cluster size on the selectivity of C2 oxygenates, which includes two key steps: CHx and C2 oxygenate formations; Cu13, Cu38 and Cu55 clusters have been employed to model different sizes of Cu cluster. Here, density functional theory method has been performed. Our results show that the adsorption ability of the species involving in C2 oxygenate formation decreases with the increasing of Cu cluster size; Cu cluster size significantly affects the dominant existence forms of CHx(x=1–3) species and C2 oxygenates. Among three Cu clusters, Cu13 cluster exhibits the highest selectivity toward C2 oxygenates compared to other two clusters, suggesting that Cu cluster size can affect the selectivity toward C2 oxygenates, moreover, the smaller Cu cluster size is, the higher the selectivity of C2 oxygenates is. That is probably related to the high concentration of low-coordinated defect sites on small size Cu cluster, which results in the higher activity and selectivity toward C2 oxygenates. The identification of higher intrinsic selectivity of C2 oxygenates, active sites, and stronger cluster size effect would be valuable for developing more efficient and stable Cu catalyst with higher selectivity toward C2 oxygenate in syngas conversion.

C2-oxygenates synthesis through CO hydrogenation on SiO2-ZrO2 supported Rh-based catalyst: The effect of support

Rh-Mn-Li catalysts supported on SiO2, ZrO2 and SiO2-ZrO2 mixed oxides with various molar ratios of Si/Zr were prepared and tested for the synthesis of C2-oxygenates from syngas. Compared with pure SiO2 and ZrO2 supported catalysts, catalysts supported on SiO2-ZrO2 mixed oxides showed higher activity and C2-oxygenates selectivity, in which Rh-Mn-Li/SiO2-ZrO2 (molar ratio of Si/Zr=1:3) exhibited the best yield of C2-oxygenates. The effect of the support on the performance of the Rh-based catalysts was investigated comprehensively by XRD, N2 adsorption-desorption, H2 and CO uptakes, FT-IR, XPS, H2-TPR, TPSR and CO-TPD techniques. The results indicated that the chemical state of Rh, CO adsorption species, dispersion of Rh and the ability of CO hydrogenation varied over catalysts supported on SiO2, ZrO2 and SiO2-ZrO2 mixed oxides, which led to the diverse catalytic activity toward C2-oxygenates synthesis.

Synthesis of C2 oxygenates from syngas over monodispersed SiO2 supported Rh-based catalysts: Effect of calcination temperature of SiO2

The effect of calcination temperature of the monodispersed SiO2 synthesized by the Stöber method on the catalytic performance of RhMnLi/SiO2 for CO hydrogenation to C2 oxygenates was investigated. The means of N2 adsorption-desorption, in-situ FT-IR, H2-TPD, H2-TPR, CO-TPD, and TPSR were used to characterize the physico-chemical properties of SiO2 supports and the corresponding RhMnLi/SiO2 catalysts. The results showed that the amount of surface Si-OH groups on SiO2 affects the Rh dispersion and RhMn interaction. The increase in the number of SiOH groups on the SiO2 was favorable for the Rh dispersion and CO adsorption, further enhanced the activity of the catalyst. In addition, an appropriate amount of surface SiOH groups on the SiO2 calcined at 350°C can gain a moderate RhMn interaction. This interaction is conducive to achieve the right hydrogenation ability, which is favorable for the CO insertion into metal-CHx band, and ultimately increases the selectivity of C2 oxygenates.

The effect of Fe on the catalytic performance of Rh–Mn–Li/SiO2 catalyst: A DRIFTS study

Different amounts of Fe promoted Rh–Mn–Li/SiO2 catalysts were prepared and investigated for the synthesis of C2 oxygenates from syngas. The results showed that the low amount of Fe (≤ 0.1 wt.%) improved the reactivity and yield of C2+ oxygenates, but an opposite effect appeared at high content of Fe (> 0.1 wt.%). Diffuse reflectance infrared Fourier transform spectroscopy was used to probe the effects of Fe on CO adsorption and hydrogenation, and two opposing effects were evidenced. Moreover, it is proposed that the facile transformation of dicarbonyl Rh+(CO)2 into H–Rh–CO is responsible for high selectivity of C2+ oxygenates.

Enhanced C2 oxygenate synthesis by CO hydrogenation over Rh-based catalyst supported on a novel SiO2

Abstract A novel SiO 2 synthesized by the Stober method was studied as the support for Rh–Mn–Li catalyst, and better performance for C 2 oxygenate synthesis via CO hydrogenation was achieved compared with the counterpart using commercial SiO 2 as the support. The investigation based on the catalytic performance and characterizations of the catalysts suggests that the hydroxyl–metal interaction over the catalyst supported on SiO 2 prepared by the Stober method results in a change in the CO adsorption on Rh particles, which promotes the CO dissociation and CO insertion, leading to higher CO conversion and C 2 oxygenate selectivity.

Synthesis of C2-oxygenates from syngas over Rh-based catalyst supported on SiO2, TiO2 and SiO2–TiO2 mixed oxide

Abstract SiO 2 , TiO 2 and SiO 2 –TiO 2 mixed oxide were synthesized by sol–gel method and used as supports for Rh-based catalysts. The effect of support on the performance of Rh-based catalysts for C 2 -oxygenates synthesis from syngas was investigated by XRD, N 2 adsorption-desorption, FT-IR, H 2 -TPD, H 2 -TPR and TPSR techniques. The results indicated that SiO 2 –TiO 2 supported catalyst had higher dispersion of Rh and thus more Rh + sites, better capability for CO adsorption and dissociation, and moderate ability for hydrogenation. As a result, SiO 2 –TiO 2 supported Rh-based catalyst exhibited higher activity and C 2 oxygenates selectivity compared with counterparts supported on TiO 2 and SiO 2 .

ChemInform Abstract: Investigation of the Reactions of Acetaldehyde on Promoted Rhodium Catalysts.

Abstract The reactions of acetaldehyde and ethanol on a series of supported rhodium catalysts have been investigated under different experimental conditions. The results show that pure rhodium is a poor catalyst for the hydrogenation of acetaldehyde especially in CO/H2 mixtures. In contrast, iron oxide promoted rhodium is an extremely efficient catalyst for the hydrogenation of acetaldehyde even in the presence of carbon monoxide at low temperatures. The results are consistent with the suggestion that in the synthesis of C2-oxygenates from CO/H2 mixtures on rhodium catalysts, acetaldehyde is a primary product from which ethanol is easily produced in a secondary hydrogenation reaction. Evidence from experiments using physical mixtures of Rh/SiO2 and Fe/SiO2 show a clear synergy in the hydrogenation of acetaldehyde. It is concluded that in CO/H2 reactions ethanol may be produced either by the hydrogenation of a surface species related to adsorbed acetaldehyde or by hydrogenation of acetaldehyde at isolated iron oxide sites. In the former case, sites at the Rh/oxide promoter interface are likely to be of importance, while in the latter case hydrogen spillover from rhodium to iron oxide sites is thought to be necessary for rapid hydrogenation of acetaldehyde to occur. Infrared measurements using an in situ cell show that the nature of the adsorbed species present on the rhodium surface under reaction conditions is affected by the promoter. When acetaldehyde is injected over the pure Rh/SiO2 catalyst, no adsorbed ethanol is detected, whereas with the iron oxide promoted catalyst strong bands due to adsorbed ethanol are observed. It is concluded that the hydrogenation of acetaldehyde, or equivalent adsorbed species, is controlled by the availability of surface hydrogen. One function of the oxide promoter may be to increase the amount of available hydrogen by acting as a reservoir for spillover hydrogen.

CO Hydrogenation to C2-oxygenates over Rh–Mn–Li/SiO2 Catalyst: Effects of Support Pretreatment with nC1–C5 Alcohols

The effects of support pretreatment with nC1–C5 alcohols on the performance of Rh–Mn–Li/SiO2 catalyst in the synthesis of C2-oxygenates from syngas have been investigated by CO hydrogenation reaction, transmission electron microscopy (TEM), pulse adsorption of CO and H2, and Fourier Transform infrared (FT-IR) spectroscopy. The catalysts prepared from the pretreated silica supports exhibited higher space time yields of C2-oxygenates (STYC2-oxy) and selectivities towards C2-oxygenates (SC2-oxy) than that prepared from the untreated silica support. The enhancement in the hydrophobicity of the pretreated silica supports would be favorable for increasing Rh dispersion and ratio of Rh+/Rh0 sites, therefore increasing the number of active sites, especially the active sites for CO insertion. Such variations are responsible for the improvements in the catalytic performance of the Rh–Mn–Li/SiO2 catalyst.

The Performance of C2 Oxygenates Synthesis from Syngas over Rh−Mn−Li−Fe/SiO2 Catalysts with Various Rh Loadings

The promotion effect of additives on Rh−Mn−Li−Fe/SiO2 catalyst was investigated by means of an in-situ FTIR technique. IR results suggested that the additives Fe, Mn, and Li might be in close contact with Rh, and form new active sites, which promoted CO activation over Rh surface and favored the formation of C2-oxygenated intermediates. The catalysts with rhodium loading of 1.0−5.0 wt % were tested by CO hydrogenation to find the optimized rhodium loading. The results showed that the high-rhodium-loading catalysts exhibited high activity and selectivity toward C2 oxygenates at low temperature, but the selectivity was very sensitive to reaction temperature, low-rhodium-loading catalysts showed low activity, while the selectivity was not so sensitive to reaction temperature, therefore high space time yield (STY) of C2 oxygenates can be obtained by increasing the reaction temperature. Among the catalysts investigated, the 1.5 wt % rhodium catalyst exhibited the highest selectivity and relative higher rhodium efficiency for the synthesis of C2 oxygenates.

Role of Vanadium Promoter in Rh-V/SiO 2 Catalysts for the Synthesis of C 2-Oxygenates from Syngas

Role of Vanadium Promoter in Rh-V/SiO 2 Catalysts for the Synthesis of C 2-Oxygenates from Syngas

Investigation of the reactions of acetaldehyde on promoted rhodium catalysts

Abstract The reactions of acetaldehyde and ethanol on a series of supported rhodium catalysts have been investigated under different experimental conditions. The results show that pure rhodium is a poor catalyst for the hydrogenation of acetaldehyde especially in CO/H2 mixtures. In contrast, iron oxide promoted rhodium is an extremely efficient catalyst for the hydrogenation of acetaldehyde even in the presence of carbon monoxide at low temperatures. The results are consistent with the suggestion that in the synthesis of C2-oxygenates from CO/H2 mixtures on rhodium catalysts, acetaldehyde is a primary product from which ethanol is easily produced in a secondary hydrogenation reaction. Evidence from experiments using physical mixtures of Rh/SiO2 and Fe/SiO2 show a clear synergy in the hydrogenation of acetaldehyde. It is concluded that in CO/H2 reactions ethanol may be produced either by the hydrogenation of a surface species related to adsorbed acetaldehyde or by hydrogenation of acetaldehyde at isolated iron oxide sites. In the former case, sites at the Rh/oxide promoter interface are likely to be of importance, while in the latter case hydrogen spillover from rhodium to iron oxide sites is thought to be necessary for rapid hydrogenation of acetaldehyde to occur. Infrared measurements using an in situ cell show that the nature of the adsorbed species present on the rhodium surface under reaction conditions is affected by the promoter. When acetaldehyde is injected over the pure Rh/SiO2 catalyst, no adsorbed ethanol is detected, whereas with the iron oxide promoted catalyst strong bands due to adsorbed ethanol are observed. It is concluded that the hydrogenation of acetaldehyde, or equivalent adsorbed species, is controlled by the availability of surface hydrogen. One function of the oxide promoter may be to increase the amount of available hydrogen by acting as a reservoir for spillover hydrogen.

Synthesis of C2-oxygenates from syngas over Co-Re-Sr/SiO2 catalysts - Preparation of catalysts.

Synthesis of C2-oxygenates from syngas over Co-Re-Sr/SiO2 catalysts - Preparation of catalysts.

SELECTIVE SYNTHESIS OF C2-OXYGENATES BY CO HYDROGENATION OVER SILICA-SUPPORTED Co–Ir CATALYST

Abstract Silica-supported Co–Ir bimetallic catalyst was effective for the selective synthesis of C2-oxygenates such as ethanol, acetaldehyde, and acetic acid by vapor-phase CO hydrogenation at 280–320 °C and 51 atm. It is suggested that Co–Ir catalyst may form an active species responsible for the synthesis of C2-oxygenates.

ＣＯ合成化学の発展 Ｉ

Recent many publications concerning the organic synthesis with carbon monixide (synthesis gas) are reviewed according to the following items.(1) Synthesis and utilization of methanol (methanol synthesis; conversion of methanol to gasoline; acetic acid production by methanol carbonylation; ethanol and ethylene from methanol).(2) Methanation(3) Fischer-Tropsch and related synthesis (Fischer-Tropsch synthesis; synthesis of C2-oxygenates; synthesis of higher alcohols; synthesis of paraffin waxes-polymethylene; isosynthesis process; aromatics production; hydrocarbons from carbon monoxide and steam; alkylamines synthesis; production of lower olefins-ethylene; production of glycols).