A Cu/Zn/Al/Zr Fibrous Catalyst that is an Improved CO<Subscript>2</Subscript> Hydrogenation to Methanol Catalyst

A series of Cu/Zn/Al/Zr CO₂ hydrogenation to methanol catalysts containing different ratios of Al/Zr were prepared using a co-precipitation procedure. SEM, TEM, and XRD characterization showed that all the catalysts comprised crystallites in a fibrous structure and their Cu/Zn crystallite dispersions were better than that of a commercial (COM) catalyst. It is suggested that the high dispersion and stability of the Cu/Zn crystallites due to the fibrous structure enhanced CO₂ hydrogenation, and the added Zr component further improved the catalyst. A 5% Zr addition gave a methanol space time yield 80% higher than that on the COM catalyst.     

The difference in the active sites for CO2 and CO hydrogenations on Cu/ZnO-based methanol synthesis catalysts

The effect of Zn in copper catalysts on the activities for both CO₂ and CO hydrogenations has been examined using a physical mixture of Cu/SiO₂+ZnO/SiO₂ and a Zn-containing Cu/SiO₂ catalyst or (Zn)Cu/SiO₂. Reduction of the physical mixture with H₂ at 573–723 K results in an increase in the yield of methanol produced by the CO₂ hydrogenation, while no such a promotion was observed for the CO hydrogenation, indicating that the active site is different for the CO₂ and CO hydrogenations. However, the methanol yield by CO hydrogenation is significantly increased by the oxidation treatment of the (Zn)Cu/SiO₂ catalyst. Thus it is concluded that the Cu–Zn site is active for the CO₂ hydrogenation as previously reported, while the Cu–O–Zn site is active for the CO hydrogenation.     

In Situ Hydrogenation of CO2 by Al/Fe and Zn/Cu Alloy Catalysts under Mild Conditions

The development of efficient metal catalysts for in situ hydrogenation of CO₂ in water under mild conditions has gained considerable attention. Three Al alloys (Al/Fe, Al/Fe/Cu, Al/Cu) and three Zn/Cu alloys for in situ hydrogenation of CO₂ in aqueous bicarbonate solutions were investigated. Hydrogen was generated by reaction of Al, Fe, and Zn in the alloys with water. In situ hydrogenation of CO₂ was likely to be catalyzed by intermetallic compounds and generated metal oxides. Al alloys catalyzed the hydrogenation to methane while Zn/Cu alloys produced CO and formic acid. Zn/Cu5 possessed the highest catalytic activity, which was attributed to the CuZn5 crystal planes in the alloys. Insights are provided into the importance of compositions and structures of alloys for the selectivity for in situ hydrogenation of CO₂ in aqueous bicarbonate solutions.     

Fluorine-modified Cu/Zn/Al/Zr catalysts via hydrotalcite-like precursors for CO2 hydrogenation to methanol

Fluorine-modified Cu/Zn/Al/Zr catalysts were prepared by calcination of the fluorine-containing Cu/Zn/Al/Zr hydrotalcite-like compounds and tested for CO₂ hydrogenation to methanol. The results revealed that the CH₃OH selectivity was greatly improved by the remarkable increase of the proportion of strongly basic sites, while the CO₂ conversion decreased slightly. It is also found that the activity of catalysts is closely related to the synergy between the Cu and basic sites. The CH₃OH yield for the fluorine-modified Cu/Zn/Al/Zr catalysts was higher than that for the fluorine-free catalysts; thus, the introduction of fluorine favored the methanol formation.     

Influence of titania on zirconia promoted Cu/SiO2 catalysts for methanol synthesis from CO/H2 and CO2/H2

The effects of adding mixtures of titania and zirconia on the methanol synthesis activity and selectivity of Cu/SiO₂ were investigated. The synthesis of methanol from both CO/H₂ and CO₂/H₂ mixtures was examined at 0.65 MPa and temperatures between 448 and 573 K. For CO hydrogenation, the addition of ZrO₂ alone increased the methanol synthesis activity of Cu/SiO₂ by up to three-fold. Substitution of a portion of the ZrO₂ by TiO₂ decreased the methanol synthesis activity of the catalyst relative to that observed when only ZrO₂ is added. ZrO₂ addition also enhanced the methane synthesis activity by as much as seven fold. In the case of CO₂ hydrogenation, the maximum methanol synthesis activity is achieved when a 50/50 wt% mixture of ZrO₂ and TiO₂ is added to Cu/SiO₂. Neither the presence of the oxide additive nor its composition had any effect on the activity of the reverse water–gas-shift reaction, which suggests that this reaction proceeds only on Cu. The observed effects of ZrO₂ and TiO₂ on the catalytic activity of methanol synthesis from CO and CO₂, and methane synthesis from CO, are interpreted in terms of the strength and concentration of acidic and basic groups on the surface of the dispersed oxide.     

Cu/ZnO/AlOOH catalyst for methanol synthesis through CO<Subscript>2</Subscript> hydrogenation

Catalytic conversion of CO₂ to methanol is gaining attention as a promising route to using carbon dioxide as a new carbon feedstock. AlOOH supported copper-based methanol synthesis catalyst was investigated for direct hydrogenation of CO₂ to methanol. The bare AlOOH catalyst support was found to have increased adsorption capacity of CO₂ compared to conventional Al₂O₃ support by CO₂ temperature-programmed desorption (TPD) and FT-IR analysis. The catalytic activity measurement was carried out in a fixed bed reactor at 523 K, 30 atm and GHSV 6,000 hr^?1 with the feed gas of CO₂/H₂ ratio of 1/3. The surface basicity of the AlOOH supported Cu-based catalysts increased linearly according to the amount of AlOOH. The optimum catalyst composition was found to be Cu : Zn : Al=40 : 30 : 30 at%. A decrease of methanol productivity was observed by further increasing the amount of AlOOH due to the limitation of hydrogenation rate on Cu sites. The AlOOH supported catalyst with optimum catalyst compositions was slightly more active than the conventional Al₂O₃ supported Cu-based catalyst.     

Selective Hydrogenation of Soybean Oil on Copper Catalysts as a Tool Towards Improved Bioproducts

The liquid-phase soybean oil hydrogenation was studied on silica-supported Cu and ternary Cu–Zn–Al catalysts. Cu/SiO₂ samples were prepared by incipient-wetness impregnation (Cu/SiO₂-Imp) and chemisorption-hydrolysis (Cu/SiO₂-CH), while two Cu–Zn–Al mixed oxides containing 8 (Cu(8)–Zn–Al) and 15?% Cu (Cu(15)–Zn–Al), respectively, were prepared by coprecipitation. Copper dispersion (D _Cu) was 23?% on Cu/SiO₂-CH, and this sample showed a high activity for soybean oil hydrogenation; in contrast, Cu/SiO₂-Imp was inactive, probably because Cu was poorly dispersed (D _Cu?=?2?%). The oil hydrogenation activity on Cu(15)–Zn–Al (D _Cu?=?9?%) was lower than on Cu/SiO₂-CH, while Cu(8)–Zn–Al (D _Cu?=?23?%) was inactive. Citral hydrogenation used as a test reaction showed that the intrinsic Cu⁰ activity was not significantly changed by the kind of support or the catalyst preparation method. These latter results suggested that the observed differences in soybean oil hydrogenation may be explained as changes in accessibility of the triglyceride molecules to Cu active sites. In ternary Cu–Zn–Al samples, access to catalytic sites was hampered by the narrower pore structure of the catalyst. Copper exhibited unique properties for obtaining proper lubricants from soybean oil hydrogenation because selectively hydrogenated unsaturated linolenic (C18:3) and linoleic (C18:2) fatty acids to unsaturated oleic acid (C18:1) without forming saturated stearic acid (C18:0).     

Effects of zirconia promotion on the activity of Cu/SiO2 for methanol synthesis from CO/H2 and CO2/H2

The effect of zirconia promotion on Cu/SiO₂ for the hydrogenation of CO and CO₂ at 0.65 MPa has been investigated at temperatures between 473 and 573 K. With increasing zirconia loading, the rate of methanol synthesis is greatly enhanced for both CO and CO₂ hydrogenation, but more significantly for CO hydrogenation. For example, at 533 K the methanol synthesis activity of 30.5 wt% zirconia-promoted Cu/SiO₂ is 84 and 25 times that of unpromoted Cu/SiO₂ for CO and CO₂ hydrogenation, respectively. For all catalysts, the rate of methanol synthesis from CO₂/H₂ is higher than that from CO/H₂. The apparent activation energy for methanol synthesis from CO decreases from 22.5 to 17.5 kcal/mol with zirconia addition, suggesting that zirconia alters the reaction pathway. For CO₂ hydrogenation, the apparent activation energies (~12 kcal/mol) for methanol synthesis and the reverse water-gas shift (RWGS) reaction are not significantly affected by zirconia addition. While zirconia addition greatly increases the methanol synthesis rate for CO₂ hydrogenation, the effect on the RWGS reaction activity is comparatively small. The observed effects of zirconia are interpreted in terms of a mechanism which zirconia serves to adsorb either CO or CO₂, whereas Cu serves to adsorb H₂. It is proposed that methanol is formed by the hydrogenation of the species adsorbed on zirconia.     

Reaction between methanol and acetic acid catalyzed by SiO2‐supported V‐P‐O catalyst in oxygen atmosphere

SiO₂‐supported V‐P‐O catalysts prepared by the incipient‐wetness impregnation method beginning with ammonium metavanadate and phosphoric acid were used in the catalytic reaction between methanol and acetic acid in an oxygen atmosphere. The SiO₂‐supported V‐P‐O catalysts were composed of VOPO₄ and (VO)₂P₂O₇ phases. Both the acidic and alkaline sites were co‐present in the catalysts. The vanadium species catalyzed the oxidation of methanol to formaldehyde. The V‐P‐O(20–30 wt%)/SiO₂ catalysts with a P/V mole ratio of 2:1 exhibited higher catalytic activity for the formation of acrylic acid and methyl acrylate with a total selectivity of ～28 % at 380 °C. The acid sites of the catalysts also catalyzed the formation of methyl acetate with a selectivity of ～65 %. Methanol can be an alternative to formaldehyde for the synthesis of both acrylic acid and methyl acrylate through the aldol condensation reaction.     

An in situ high pressure FT-IR study of CO2/H2 interactions with model ZnO/SiO2, Cu/SiO2 and Cu/ZnO/SiO2 methanol synthesis catalysts

In situ FT-IR spectroscopy allows the methanol synthesis reaction to be investigated under actual industrial conditions of 503 K and 10 MPa. On Cu/SiO₂ catalyst formate species were initially formed which were subsequently hydrogenated to methanol. During the reaction a steady state concentration of formate species persisted on the copper. Additionally, a small quantity of gaseous methane was produced. In contrast, the reaction of CO₂ and H₂ on ZnO/SiO₂ catalyst only resulted in the formation of zinc formate species: no methanol was detected. The interaction of CO₂ and H₂ with Cu/ZnO/SiO₂ catalyst gave formate species on both copper and zinc oxide. Methanol was again formed by the hydrogenation of copper formate species. Steady-state concentrations of copper formate existed under actual industrial reaction conditions, and copper formate is the pivotal intermediate for methanol synthesis. Collation of these results with previous data on copper-based methanol synthesis catalysts allowed the formulation of a reaction mechanism.     

Production of Synthesis Gas via Dry Reforming of Methane over Co‐Based Catalysts: Effect on H2/CO Ratio and Carbon Deposition

The effect of support type on synthesis gas production using Co‐based catalysts supported over TiO₂‐P25, Al₂O₃, SiO₂, and CeO₂ was investigated. The catalysts were prepared by the incipient wet impregnation method and characterized by various techniques for comparison. Experiments were performed in a micro tubular reactor. The results revealed that all Co‐supported catalysts produced synthesis gas ratios of 1 and below and, thus, proved to be well‐suited for methanol and Fischer‐Tropsch syntheses. Co catalysts supported over TiO₂‐P25 and Al₂O₃ provided better synthesis gas ratios and stability performances. The promotion of a Co/TiO₂‐P25 catalyst with Ce had a substantial influence on its catalytic activity and the amount of carbon deposit. A Ce‐promoted catalyst diminished markedly the extent of carbon deposition and thus boosted the performance towards better activity and stability.     

Hydrogenation of m‐dinitrobenzene to m‐phenylenediamine over La2O3‐promoted Ni/SiO2 catalysts

BACKGROUND: Liquid‐phase catalytic hydrogenation of m‐dinitrobenzene is an environmentally friendly routine for m‐phenylenediamine production. The key to increasing product yield is to develop catalysts with high catalytic performance. In this work, La₂O₃‐modified Ni/SiO₂ catalysts were prepared and applied to the hydrogenation of m‐dinitrobenzene to m‐phenylenediamine. The effect of La₂O₃ loading on the properties of Ni/SiO₂ was investigated. The reaction kinetic study was performed in ethanol over Ni/3%La₂O₃–SiO₂ catalyst, in order to clarify the reaction mechanism of m‐dinitrobenzene hydrogenation. RESULTS: It was found that the activity of the silica supported nickel catalysts is obviously influenced by La₂O₃ loading. Ni/3%La₂O₃–SiO₂ catalyst exhibits high activity owing to its well dispersed nickel species, with conversion of m‐dinitrobenzene and yield of m‐phenylenediamine up to 97.1% and 94%, respectively. The results also show that Ni/3%La₂O₃–SiO₂ catalyst can be reused at least six times without significant loss of activity. CONCLUSION: La₂O₃ shows strong promotion of the effect of Ni/SiO₂ catalyst for liquid‐phase hydrogenation of m‐dinitrobenzene. La₂O₃ loading can affect the properties of Ni/SiO₂ catalyst. Based on the study of m‐dinitrobenzene hydrogenation kinetics over Ni/3%La₂O₃–SiO₂ catalyst, a possible reaction mechanism is proposed. Copyright © 2009 Society of Chemical Industry     

Gold dispersed on TiO2 and SiO2: adsorption properties and catalytic behavior in hydrogenation reactions

Titania-supported Au catalysts were given both low temperature reduction and high temperature reduction at 473 and 773 K, respectively, and their adsorption and catalytic properties were compared to identically pretreated Pt/TiO₂ catalysts and pure TiO₂ samples as well as Au/SiO₂ catalysts. This was done to determine whether a reaction model proposed for methanol synthesis over metals dispersed on Zn, Sr and Th oxides could also explain the high activities observed in hydrogenation reactions over MSI (Metal-Support Interaction) catalysts such as Pt/TiO₂. This model invokes O vacancies on the oxide support surface, formed by electron transfer from the oxide to the metal across Schottky junctions established at the metal-support interface, as the active sites in this reaction. The similar work functions of Pt and Au should establish similar vacancy concentrations, and O₂ chemisorption indicated their presence. However, these Au catalysts were completely inactive for CO and acetone hydrogenation, and ethylene hydrogenation rates were lower on the supported Au catalysts than on the supports alone. Consequently, this model cannot explain the high rate of the two former reactions over TiO₂-supported Pt although it does not contradict models invoking specialinterfacial sites.     

Characterization of some perovskite oxides based on YBa2Cu3O7 − x in relation to their use in methanol production

The oxidized and weakly reducible perovskite oxide YBa₂Cu₃O_{7 − x} (YBCO) has been prepared as a catalyst, supported on γ‐Al₂O₃. It was further modified by (i) impregnation with Ru and Pd and (ii) cobalt incorporation via co‐precipitation. All the catalysts were either 20% (w/w) YBCO/γ‐Al₂O₃ or 2% (w/w) Ru, Pd or Co/20% (w/w) YBCO/γ‐Al₂O₃. The catalysts were characterized using temperature programmed reduction (TPR), surface area measurements and X‐ray diffraction (XRD) studies before and after various treatments. They were studied as catalysts in the pressure range 20–50 atmospheres and in the temperature range 523–573 K in an autoclave equipped with a spinning basket catalyst container. The Pd‐, Ru‐ and Co‐modified catalysts gave predominantly methanation products, along with some C₂–C₄ hydrocarbons. However the YBCO/γ‐Al₂O₃ catalyst exhibited significant methanol selectivity at 50 atmospheres and at 523 K X‐ray diffraction studies revealed the presence of Cu(0), Cu(I) and Cu(II) after reduction and the species Cu(0) and Cu(I) are probably essential to CH₃OH production. © 2000 Society of Chemical Industry     

CO2 Hydrogenation to Methanol Over Cu/ZnO/Al2O3 Catalysts Prepared by a Novel Gel-Network-Coprecipitation Method

A novel gel-network-coprecipitation process has been developed to prepare ultrafine Cu/ZnO/Al₂O₃ catalysts for methanol synthesis from CO₂ hydrogenation. It is demonstrated that the gel-network-coprecipitation method can allow the preparation of the ultrafine Cu/ZnO/Al₂O₃ catalysts by homogeneous coprecipitation of the metal nitrate salts in the gel network formed by gelatin solution, which makes the metallic copper in the reduced catalyst exist in much smaller crystallite size and exhibit a much higher metallic copper-specific surface area. The effect of the gel concentration of gelatin on the structure, morphology and catalytic properties of the Cu/ZnO/Al₂O₃ catalysts for methanol synthesis from hydrogenation of carbon dioxide was investigated. The Cu/ZnO/Al₂O₃ catalysts prepared by the gel-network-coprecipitation method exhibit a high catalytic activity and selectivity in CO₂ hydrogenation to methanol.     

Methanol synthesis over Cu/SiO2 catalysts

The rates of CO and CO/CO₂ hydrogenation at 4.2 MPa and 523 K are reported for a series of Cu/SiO₂ catalysts containing 2 to 88 wt.% Cu. These catalysts were prepared on a variety of silica sources using several different Cu deposition techniques. In CO/CO₂ hydrogenation, the rate of methanol formation is proportional to the exposed Cu surface area of the reduced catalyst precursor, as determined by N₂O frontal chromatography. The observed rate, 4.2×10^–3 mole CH₃OH/Cu site-sec, is within a factor of three of the rates reported by others over Cu/ZnO and Cu/ZnO/Al₂O₃ catalysts under comparable conditions. These results suggest that the ZnO component is only a moderate promoter in methanol synthesis. Hydrogenation of CO over these catalysts also gives methanol with high selectivity, but the synthesis rate is not proportional to the Cu surface area. This implies that another type of site, either alone or in cooperation with Cu, is involved in the synthesis of methanol from CO.     

Liquid‐phase hydrogenation of cinnamaldehyde over Cu‐Au/SiO2 catalysts

The synthesis, characterization, and application of silica‐supported Cu‐Au bimetallic catalysts in selective hydrogenation of cinnamaldehyde are described. The results showed that Cu‐Au/SiO₂ bimetallic catalysts were superior to monometallic Cu/SiO₂ and Au/SiO₂ catalysts under identical conditions. Adding a small amount of gold (6Cu‐1.4Au/SiO₂ catalyst) afforded eightfold higher catalytic reaction rate compared to Cu/SiO₂ along with the high selectivity (53%, at 55% of conversion) toward cinnamyl alcohol. Characterization techniques such as x‐ray diffraction, H₂ temperature‐programmed reduction, ultraviolet‐visible spectroscopy, transmission electron microscopy, Fourier‐transform infrared spectra of chemisorbed CO, and x‐ray photoelectron spectroscopy were employed to understand the origin of the catalytic activity. A key genesis of the high activity of the Cu‐Au/SiO₂ catalyst was ascribed to the synergistic effect of Cu and Au species: the Au sites were responsible for the dissociative activation of H₂ molecules, and Cu⁰ and Cu⁺ sites contributed to the adsorption‐activation of C?C and C?O bond, respectively. A combined tuning of particle dispersion and its surface electronic structure was shown as a consequence of the formation of Au‐Cu alloy nanoparticles, which led to the significantly enhanced synergy. A plausible reaction pathway was proposed based on our results and the literature. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3300–3311, 2014     

Activated Carbon‐Supported Mo‐Co‐K Sulfide Catalysts for Synthesizing Higher Alcohols from CO2

Activated carbon‐supported Mo‐Co‐K sulfide catalysts, prepared by stepwise impregnation, were used in the synthesis of higher alcohols via CO₂ hydrogenation. The catalysts with varying Mo contents and defined K/Mo and Co/Mo molar ratios exhibited relatively high CO₂ conversions and high selectivity to total alcohols and C₂₊ alcohols. Moreover, the influence of calcination conditions on the sulfidation states and catalytic performance was studied. The surface sulfur runoff of the supported catalysts can be effectively suppressed by online calcination. As a result, the selectivity to total alcohols and C₂₊ alcohols can be improved.     

CO2 hydrogenation reactivity and structure of Rh/SiO2 catalysts prepared from acetate,chloride and nitrate precursors

Silica-supported Rh catalysts (Rh/SiO₂) were prepared from acetate, chloride and nitrate precursors by an impregnation method and were applied to CO₂ hydrogenation reaction. CO₂ conversion over the catalyst prepared from chloride precursor was lower than that over acetate or nitrate one, because of fewer active sites on catalysts, as estimated by H₂ chemisorption. The main product was CO over the catalysts prepared from acetate and nitrate, but it was CH₄ over the catalyst prepared from chloride precursor. Characterization of catalysts by TEM, FT-IR and XPS was carried out in order to elucidate the effect of metal precursor on the CO₂ hydrogenation reactivity. The results of XPS showed that the O atomic ratio to Rh on surface hydroxyl groups increased in the order: chloride<nitrate<acetate precursor. The ratio of hydroxyl groups to Rh particles on SiO₂ surface was expected to have a significant influence on the reactivity.     

Influence of rare-earth elements (La,Ce, Nd and Pr) on the performance of Cu/Zn/Zr catalyst for CH3OH synthesis from CO2

A series of Cu/Zn/Zr (CZZ) catalysts with different rare earth elements (La, Ce, Nd and Pr) were prepared by co-precipitation method and tested for CO₂ hydrogenation to methanol. The influence of modifier (La, Ce, Nd and Pr) on the physicochemical properties of CZZ catalysts was studied. The results of catalytic test reveal that CO₂ conversion was correlated to the introduction of different promoters. The introduction of La and Ce favors the production of methanol, and Nd and Pr modified CZZ catalysts show relative low activity compared with the reference CZZ catalyst.