CO2 hydrogenation over Pd-modified methanol synthesis catalysts

The effect of palladium incorporation on the performance of Cu–ZnO(Al₂O₃) during the hydrogenation of carbon dioxide has been assessed. Temperature-programmed reduction profiles and X-ray photoelectron spectra of copper revealed that Pd enhances copper oxide reduction. Carbon dioxide conversion and methanol yield were found to increase on Pd-loaded catalysts. The importance of the palladium incorporated to the base Cu–ZnO(Al₂O₃) catalyst in determining the catalytic activity is discussed in terms of the relative ease with which hydrogen is dissociated on the Pd particles and then spilt over the Cu–ZnO phase of the base catalyst.     

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.     

CO2 hydrogenation to methanol over Cu/ZnO/ZrO2 catalysts prepared via a route of solid-state reaction

Cu/ZnO/ZrO₂ catalysts were prepared by a route of solid-state reaction and tested for the synthesis of methanol from CO₂ hydrogenation. The effects of calcination temperature on the physicochemical properties of as-prepared catalysts were investigated by N₂ adsorption, XRD, TEM, N₂O titration and H₂-TPR techniques. The results show that the dispersion of copper species decreases with the increase in calcination temperature. Meanwhile, the phase transformation of zirconia from tetragonal to monoclinic was observed. The highest activity was achieved over the catalyst calcined at 400 °C. This method is a promising alternative for the preparation of highly efficient Cu/ZnO/ZrO₂ catalysts.     

Active sites in Cu/ZnO/ZrO2 catalysts for methanol synthesis from CO/H2

Among various Cu/ZnO/ZrO₂ catalysts with the Cu/Zn ratio of 3/7, the one with 15 wt.% of ZrO₂ obtains the best activity for methanol synthesis by hydrogenation of CO. The TPR, TPO and XPS analyses reveal that a new copper oxide phase is formed in the calcined Cu/ZnO/ZrO₂ catalysts by the dissolution of zirconium ions in copper oxide. In addition, the Cu/ZnO/ZrO₂ catalyst with 15 wt.% of ZrO₂ turns out to contain the largest amount of the new copper oxide phase. When the Cu/ZnO/ZrO₂ catalysts is reduced, the Cu²⁺ species present in the ZrO₂ lattice is transformed to Cu⁺ species. This leads to the speculation that the addition of ZrO₂ to Cu/ZnO catalysts gives rise to the formation of Cu⁺ species, which is related to the methanol synthesis activity of Cu/ZnO/ZrO₂ catalyst in addition to Cu metal particles. Consequently, the ratio of Cu⁺/Cu⁰ is an important factor for the specific activity of Cu/ZnO/ZrO₂ catalyst for methanol synthesis.     

Synergism in methanol synthesis from carbon dioxide over gold catalysts supported on metal oxides

Gold deposited on various oxides with high dispersion was found to be active for the hydrogenation of CO₂ at temperatures between 150 and 400°C. Product selectivities greatly depended on the nature of support oxide. Acidic oxides like TiO₂ gave higher CO₂ conversions but low methanol yields. Zinc oxide component was indispensable for selective methanol synthesis. Significantly, large particle size effect of gold was observed and smaller gold particles gave higher methanol productivity per exposed surface area of gold. This can be explained by an increase in the perimeter area of gold particles with a decrease in particle size. Methanol yield was greatly enhanced in a Au/ZnO---TiO₂ catalyst probably due to an increase in gold-zinc oxide interface.     

Comparative study of synthesis of methylamines from carbon oxides and ammonia over Cu/A12O3

Methylamines have been synthesized from carbon dioxide, hydrogen and ammonia using Cu/Al₂O₃ catalysts with different copper loading. The reaction was performed in a fixed-bed micro reactor in the temperature range 473–573 K and at 0.6 MPa total pressure. The product amines were mono-, di- and trimethylamine (MMA, DMA, TMA). The distribution of the amines depended mainly on the reaction temperature and the NH₃/CO₂ ratio in the feed gas. At elevated temperatures and higher NH₃ concentrations methanol synthesis is suppressed and MMA is the main amine product, reaching a ratio of MMA:DMA:TMA of 1:0.23:0.07. Conversion and product distribution were compared to that of the corresponding reaction starting from CO or methanol instead of CO₂. With CO conversion was lower but the selectivity to MMA was higher. If CO₂ was replaced by methanol, conversion increased and TMA was the main product. In all experiments a change of space velocity had relatively little influence on both conversion and distribution of amines.     

Catalytic performance for CO2 conversion to methanol of gallium-promoted copper-based catalysts: influence of metallic precursors

This study reports new gallium-promoted copper-based catalysts prepared by co-impregnation of methoxide–acetylacetonate (acac) precursors from methanolic solutions onto silica and zinc oxide supports. Catalyst performance in the CO₂ hydrogenation to methanol was investigated at 2 MPa and temperatures between 523 and 543 K. A high activity and selectivity for ZnO-supported catalysts was found, which also showed a high stability in terms of both activity and selectivity. The maximum value for the activity was 378 g MeOH/kg cat h at 543 K, with a selectivity of 88% towards methanol production. The high performance of these materials in the CO₂ hydrogenation is related to the presence of Ga₂O₃ promoter and highly dispersed Cu⁺ species on the surface, determined by XPS and Auger on used catalysts.     

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.     

Cr2O3 promoted skeletal Cu catalysts for the reactions of methanol steam reforming and water gas shift

Promotional effects of chromia on the structure and activity of skeletal copper catalysts for methanol steam reforming and water gas shift have been studied. Catalysts were prepared by leaching CuAl₂ alloy particles in aqueous NaOH solutions containing sodium chromate at various concentrations. XPS spectra showed that the surface of the resulting catalysts mainly consisted of Cr³⁺ compounds and Cu⁰. Cu⁺ and/or Cu²⁺ were not observed by XPS.

Increasing the concentration of chromate in the leach liquor resulted in decreases in pore diameter and copper crystallite size but significant enhancement of BET surface area was observed while the total pore volume was maintained. The addition of small amounts of chromate to the leach liquor significantly enhanced the Cu surface area. However, higher concentrations of chromate in the leach liquor decreased the Cu surface areas although the total surface areas increased.

The activities of Cr₂O₃ promoted skeletal copper catalysts for both methanol steam reforming and water gas shift reactions were determined separately. The results indicated that deposition of Cr₂O₃ on skeletal copper catalysts significantly improved the specific activities for these reactions. Chromia is found to act as a structural and catalytic promoter for these reactions.     

Methanol synthesis from CO2 over Cu/ZnO catalysts prepared from various coprecipitated precursors

Various precursors of Cu/ZnO catalysts were prepared by coprecipitation methods. By varying the conditions of coprecipitation, precursors having different structures (aurichalcite, malachite, hydrozincite, or their mixture) were obtained at given Cu/Zn ratios, ranging from 30/70 to 70/30. In a wide range of the Cu/Zn ratios, the catalysts derived from the precursors containing aurichalcite exhibited high performance in the methanol synthesis from CO₂.     

Measurement of concentration profiles over ZnO–Cr2O3/CeO2–ZrO2 monolithic catalyst in oxidative steam reforming of methanol

Oxidative steam reforming of methanol (OSRM) reaction was investigated over a novel monolithic ZnO–Cr₂O₃/CeO₂–ZrO₂ catalyst developed in our laboratory. A novel flat-bed reactor was designed to measure the concentration profiles of the monolithic catalyst beds under different operation conditions: water-to-methanol mole ratio (W/M) between 1 and 1.5; oxygen-to-methanol mole ratio (O/M) in the range of 0.1–0.3; space velocity ranging from 1840 to 2890 h^− 1; and reaction temperature in the scale of 400–440 °C. On the basis of these results, reaction pathways for the OSRM were discussed. It is indicated that only three independent reactions dominate in our reaction system, namely, the partial oxidation of methanol, the steam reforming of methanol and the methanol decomposition reaction, whereas the water–gas shift and the reverse water–gas shift reactions should be ignored. In addition, the steam reforming of methanol proceeds along all the catalyst bed, whereas methanol decomposition and oxidation reactions occur mainly at the entrance of the catalyst bed.     

Low-temperature catalytic combustion of methanol and its decomposed derivatives over supported gold catalysts

Gold can be compared favorably with Pd and Pt in the catalytic combustion of CH₃OH, HCHO and HCOOH when it is deposited on some reducible metal oxides (-Fe₂O₃, TiO₂, etc.). While the supported gold catalysts are less active in H₂ oxidation, they exhibit much higher activities in CO oxidation. For Au/TiO₂, the effect of catalyst preparation was further investigated. Since the activity for CO oxidation of the gold catalysts is not depressed but enhanced by moisture, they are practically applicable to CO removal from air at room temperature. Gold supported on manganese oxide is especially effective in the selective CO removal from hydrogen, indicating its potential applicability to polymer electrolyte fuel cells using the reformed gas of methanol.     

Hydrogenation of carbon dioxide over copper-pyrochlore/zeolite composite catalysts

The hydrogenation of CO₂ was studied over composite catalysts obtained by mixing Cu-based methanol synthesis catalyst and HY zeolite. A mechanism associating methanol synthesis and MTG (methanol to gasoline) reaction allowed the formation of C₁-C₄ hydrocarbons. It was found that the catalytic behaviors of the composite catalysts were favorably influenced by the characteristics of the methanol synthesis catalysts. The Cu-La₂Zr₂O₇ catalyst we recently developed associated with HY zeolite exhibited interesting performances in hydrocarbon synthesis. The addition of ZrO₂ to Cu---La₂Zr₂O₇/HY enhanced the ability to produce hydrocarbons. Comparing composite catalyst systems prepared with different Cu-based methanol synthesis catalysts, the effect of Na contamination on methanol and hydrocarbon formation over composite catalysts were also discussed.     

机械研磨燃烧法制备Cu/ZnO/Al2O3甲醇合成催化剂

引言Cu/ZnO/Al2O3催化剂近年来广泛应用于低压甲醇合成、二甲醚合成和水煤气变换等领域[1-2],该催化体系具有活性高、使用寿命长、反应温度及     

CeO2改性Ni/γ-Al2O3催化剂上顺酐加氢制备丁二酸酐

采用等体积浸渍法制备CeO₂改性Ni/γ-Al₂O₃催化剂,通过BET、XRD、H₂-TPR和SEM等对催化剂结构及物化性能进行表征,考察Ni-CeO₂/γ-Al₂O₃催化剂对顺酐催化加氢制备丁二酸酐催化性能的影响。结果表明,引入适量CeO₂可提高催化剂活性组分Ni的分散度,增加催化剂比表面积,提高催化剂热稳定性。采用负载CeO₂质量分数5%的Ni-CeO₂/γ-Al₂O₃催化剂,在反应温度120 ℃、反应压力2.0 MPa和空速0.6 h^-1条件下,顺酐转化率为99.5%,丁二酸酐选择性为99.4%。     

Influence of chlorine ions in Pt/A12O3 catalysts for methane total oxidation

Residual chlorine ions on a Pt/Al₂O₃ catalyst surface prepared from chlorine-containing precursors appear to inhibit the total oxidation of methane. At 450°C, as chlorine is eliminated with time on stream, the reaction rate increases despite the sintering of the platinum particles. The steady state reaction rate which is reached after 60 h is identical to that obtained with a catalyst prepared from a precursor containing no chlorine. Whether chlorine is present or not in the initial state of the catalyst does not appear to have an influence on the evolution of the platinum particle size.     

Enhancement of pyrolysis gasoline hydrogenation over Pd-promoted Ni/SiO2-Al2O3 catalysts

Pyrolysis gasoline upgrading by hydrogenation and ring opening was investigated over highly loaded Ni catalysts supported on amorphous silica-alumina and incorporating promoters as Pd, seeking a higher aromatic reduction of this feedstock in order to meet stringent fuel regulations. The effect of Ni loading and Pd component on the activity of those systems was evaluated in a fixed bed reactor under the following operating conditions: T = 573 and 673 K, H₂:PyGas molar ratio = 10, P = 5.0 MPa, WHSV = 4 h⁻¹. The catalyst properties, measured by several characterization techniques (ICP-AES, XRD, N₂ adsorption-desorption isotherms, TPR, H₂-TPD, CO chemisorption, XPS, FTIR spectroscopy of adsorbed pyridine and NH₃-TPD), were related to their catalytic activity and selectivity. Interestingly, the increase in Ni loading from 24.4 to 33.2 Ni wt.% has a negative effect on both hydrogenation and ring opening activities, as it causes a drop in the BET surface area and a decrease in metal-support interaction, with a negative bearing on catalyst stability. On the other hand, the addition of Pd has a positive effect for hydrogenation, linked with the higher electronegativity of Pd⁰ species compared to those of Ni⁰, as well as with a greater stability of Pd-promoted catalysts during on-stream conditions. A linear correlation has been found between the total amount of desorbed H₂, as determined from H₂-TPD experiments on freshly reduced catalysts, and the initial turnover frequency.     

Characterization and catalytic activity of Pd/V2O5/Al2O3 catalysts on benzene total oxidation

The role of vanadium oxide and palladium on the benzene oxidation reaction over Pd/V₂O₅/Al₂O₃ catalysts was investigated. The Pd/V₂O₅/Al₂O₃ catalysts were more active than V₂O₅/Al₂O₃ and Pd/Al₂O₃ catalysts. The increase of vanadium oxide content decreased the Pd dispersion and increased the benzene conversion. A strong Pd particle size effect on benzene oxidation reaction was observed. Although the catalysts containing high amount of V⁴⁺ species were more active, the Pd particle size effect was responsible for the higher activity.     

Direct synthesis of organic carbonates from the reaction of CO2 with methanol and ethanol over CeO2 catalysts

The catalytic properties of CeO₂ catalysts in direct synthesis of dimethyl carbonate (DMC) from CH₃OH and CO₂ were investigated. The formation rate of DMC over the catalysts calcined at 873 K and above was almost proportional to the surface area of catalysts. However, CeO₂ calcined at 673 K showed lower activity than expected from the surface area. From the results of catalyst characterization, CeO₂ calcined at 673 K contained considerable amount of amorphous phase. In contrast, the ratio of amorphous phase decreased on the catalysts calcined at 873 K and above. This suggests that stable crystallite surface is active for the reaction.

In the CH₃OH + C₂H₅OH + CO₂ reaction at low temperature, ethyl methyl carbonate (EMC) was formed, and selectivity of EMC formation was comparable to that of DMC. The formation route is discussed by the comparison with transesterification reaction.     

Synthesis of methanol and isobutanol from syngas over ZrO2-based catalysts

The effects of reaction conditions on the synthesis of isobutanol and methanol from syngas over Zr---K and Zr---Mn---K catalysts have been investigated, with the reactions carried out at pressures between 8 and 16 MPa, temperatures between 380 and 440 °C, and gas hourly space velocity (GHSV) between 3 000 and 8 000 h⁻¹. It was found that the Zr---K catalyst exhibited the highest activity and selectivity at 420 °C, 10.0 MPa, and 5 000 h⁻¹, and that the Mn-promoted catalyst increased the yield of isobutanol with the corresponding optimum temperature being 400 °C. Moreover, the higher pressure and GHSV favored isobutanol synthesis. At 16. 0 MPa, 400 °C, 5 000 h⁻¹, the space time yield of isobutanol was about 21.5 ml per ml cat. h⁻¹, and selectivity reached 98% over the Zr---Mn---K catalyst.