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.     

Comparison of the activity of Ru and Pt catalysts for the oxidation of carbon by NO2

The role of two catalysts Pt/Al₂O₃ and Ru/NaY on the oxidation of carbon by NO₂ was investigated in the temperature range 300–400 °C. In the case of Pt/Al₂O₃ no significant catalytic effect on the carbon oxidation rate is observed although decomposition of NO₂ takes place on the noble metal and leads to the formation of NO. This result suggests that the amount of the oxygen atoms transferred from the metallic surface sites to the carbon surface to form C(O) complex is negligible. In contrast, in presence of Ru/NaY the oxidation rate of carbon by NO₂ is markedly increased. Hence, a significant part of the formed O through catalytic decomposition of NO₂ on Ru surface sites is transferred to the carbon surface leading to a larger amount of C(O) complexes on the carbon surface. Thus, the ruthenium surface is a generator of active oxygen species that are spilled over on the carbon surface at 350 °C.     

CO hydrogenation over potassium-promoted Fe/carbon catalysts

The effects of potassium on the catalytic behavior in CO hydrogenation over K-promoted Fe/carbon catalysts having low K/Fe ratios were investigated. Even though the doses of potassium were low the promotional effects were pronounced, especially on the olefin-to-paraffin ratio, and theC ₃ toC ₄ olefin selectivities of the K-promoted catalysts were as high as 51 to 66 mol%. Over the catalysts having no or low potassium content the olefin-to-paraffin ratio and the ratio of the CO₂ formation rate to the rate of CO conversion to hydrocarbons remained roughly the same regardless of temperature, while over the K-promoted catalysts having higher potassium content they increased with temperature. Formation of significant amounts of filamentous carbon was observed in the K-promoted catalysts; however, the carbon deposition did not appear to affect the inherent activity and selectivity of the K-promoted catalysts.     

担载钌催化剂的CO吸附和加氢反应性能

通过ＣＯ脉冲化学吸附以及对吸附态ＣＯ和ｃｏ＋Ｈ＿２反应进行程序升温表面反应（ＴＰＳＲ），发现１％Ｒｕ／ｓｉＯ＿２和１％Ｒｕ／ＡＬ＿２Ｏ＿３催化剂的ＣＯ吸附量随焙烧温度的升高而降低。且根据５１３Ｋ和室温吸附ｃｏ的ＴＰＳＲ不同，认为存在两类不同活性中心。Ⅰ类中心：金属钌与载体的相互作用弱，易吸附ＣＯ；Ⅱ类中心：金属与载体的相互作用强，较难吸附ＣＯ。随焙烧温度升高，金属与载体作用增强，Ⅱ类中心增多。在微型流动反应器上ＣＯ中压加氢发现经６７３Ｋ焙烧的样品的活性及长链烃的生成量和烯／烷比均大于１２０℃烘干的样品，因此认为，Ⅰ类中心为加氢中心，Ⅱ类中心为链增长中心。     

Hydrogenation of carbon dioxide to methanol over palladium-promoted Cu/ZnO/A12O3 catalysts

The effect of Pd on a Cu/ZnO/A1₂O₃ catalyst for methanol synthesis from CO₂/H₂ has been investigated. Activities of impregnated catalysts and physical mixtures were studied in an internal recycle reactor under 5 MPa, 250°C and a range of conversions. In all cases, the promotion of methanol production was greater at higher flow rates (lower conversions). The promotion achieved by use of Pd/A1₂O₃+ Cu/ZnO/Al₂O₃ physical mixtures was found to increase with Pd content. Greater promotion was observed over the Pd impregnated Cu/ZnO/Al₂O₃ catalysts, although this was insensitive to the particular Pd loadings used. The results are consistent with the proposal that hydrogen spillover is responsible for the observed promotion. The effectiveness of Pd as a promoter for the reduction of CuO in the catalysts was studied by TPR and was found to be related to the level of promotion in methanol production.     

Hydrogenation of dimethyl succinate over monolithic catalysts

Hydrogenation of dimethyl succinate over monolithic copper and nickel catalysts was studied using a semibatch reactor in which liquid was circulated, while hydrogen was continuously passed through the mixture. Flow rates of both phases were adjusted, so the system operated in the Taylor flow regime. The process was investigated at 150–240°C and 3–7 MPa. A nickel catalyst was active, but was insufficiently selective. Higher loaded copper catalysts were active and selective with respect to γ-butyrolactone at relatively low conversions. Catalyst activity (initial rates) was similar to that for the liquid phase hydrogenation of maleic anhydride over conventional catalysts previously reported. The catalysts deactivated, but unlike the nickel catalyst, activity of copper catalyst was easily restored by high temperature treatment in hydrogen.     

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.     

Comparative study of Au/ZrO2 catalysts in CO oxidation and 1,3-butadiene hydrogenation

This work investigates the effects of Au³⁺/Au⁰ ratio or distribution of gold oxidation states in Au/ZrO₂ catalysts of different gold loadings (0.01–0.76% Au) on CO oxidation and 1,3-butadiene hydrogenation by regulating the temperature of catalyst calcination (393–673 K) and pre-reduction with hydrogen (473–523 K). The catalysts were prepared by deposition–precipitation and were characterized with elemental analysis, nitrogen adsorption/desorption, TEM, XPS and TPR. The catalytic data showed that the exposed metallic Au⁰ atoms at the surface of Au particles were not the only catalytic sites for the two reactions, isolated Au³⁺ ions at the surface of ZrO₂, such as those in the catalysts containing no more than 0.08% Au were more active by TOF. For 0.76% Au/ZrO₂ catalysts having coexisting Au³⁺ and Au⁰, the catalytic activity changed differently with varying the Au³⁺/Au⁰ ratio in the two reactions. The highest activity for the CO oxidation reaction was observed over the catalyst of Au³⁺/Au⁰ = 0.33. However, catalyst with a higher Au³⁺/Au⁰ ratio showed always a higher activity for the hydrogenation reaction; co-existance of Au⁰ with Au³⁺ ions lowered the catalyst activity. Moreover, the coexisting Au particles changed the product selectivity of 1,3-butadiene hydrogenation to favor the formation of more trans-2-butene and butane. It is thus suggested that for better control of the catalytic performance of Au catalyst the effect of Au³⁺/Au⁰ ratio on catalytic reactions should be investigated in combination with the particle size effect of Au.     

Activation of carbon dioxide on Fe-catalysts

Development and evaluation of novel catalysts capable of activating CO₂ especially in CO₂ hydrogenation have been investigated. Several catalysts have been prepared, and characterized by CO₂ TPD. Their performance has been evaluated at 300 °C and 10 bar. All catalysts were active in CO₂ hydrogenation reaction with conversions of approximately 15–30% at 24 h time on stream. Potassium was found to enhance chain growth and to decrease the formation of methane. Ru promoter did not provide any benefit in activity or selectivity. Zr-promoted catalyst materials exhibited enhanced CO₂ adsorption and improved hydrocarbon yields.     

CO_2 methanation over TiO_2–Al_2O_3 binary oxides supported Ru catalysts

TiO_2 modified Al_2O_3 binary oxide was prepared by a wet-impregnation method and used as the support for ruthenium catalyst. The catalytic performance of Ru/TiO_2–Al_2O_3catalyst in CO_2 methanation reaction was investigated. Compared with Ru/Al_2O_3 catalyst, the Ru/TiO_2–Al_2O_3catalytic system exhibited a much higher activity in CO_2 methanation reaction. The reaction rate over Ru/TiO_2–Al_2O_3 was 0.59 mol CO_2·(g Ru)1·h-1, 3.1 times higher than that on Ru/Al_2O_3[0.19 mol CO_2·(gRu)-1·h-1]. The effect of TiO_2 content and TiO_2–Al_2O_3calcination temperature on catalytic performance was addressed. The corresponding structures of each catalyst were characterized by means of H_2-TPR, XRD, and TEM. Results indicated that the averaged particle size of the Ru on TiO_2–Al_2O_3support is 2.8 nm, smaller than that on Al_2O_3 support of 4.3 nm. Therefore, we conclude that the improved activity over Ru/TiO_2–Al_2O_3catalyst is originated from the smaller particle size of ruthenium resulting from a strong interaction between Ru and the rutile-TiO_2 support, which hindered the aggregation of Ru nanoparticles.     

C,CO and CO2 hydrogenation on cobalt foil model catalysts: evidence for the need of CoO reduction

The hydrogenation of C, CO, and CO₂ has been studied on polycrystalline cobalt foils using a combination of UHV studies and atmospheric pressure reactions in temperature range from 475 to 575 K at 101 kPa total pressure. The reactions produce mainly methane but with selectivities of 98, 80, and 99 wt% at 525 K for C, CO, and CO₂, respectively. In the C and CO₂ hydrogenation the rest is ethane, whereas in CO hydrogenation hydrocarbons up to C₄ were detected. The activation energies of methane formation are 57, 86, and 158 kJ/mol from C, CO, and CO₂, respectively. The partial pressure dependencies of the CO and CO₂ hydrogenation indicate roughly first order dependence on hydrogen pressure (1.5 and 0.9), negative first order on CO (–0.75) and zero order on CO₂ (–0.05). Post reaction spectroscopy revealed carbon deposition from CO and oxygen deposition from CO₂ on the surface above 540 K. The reduction of cobalt oxide formed after dissociation of C-O bonds on the surface is proposed to be the rate limiting step in CO and CO₂ hydrogenation.     

CO2加氢合成甲醇催化剂的研究进展

随着大气中CO₂浓度的增加,温室效应导致的全球变暖问题日益严重。CO₂加氢合成甲醇是CO₂循环利用的有效途径,在环保、能源等领域具有重要意义,其中高效催化剂的研制是实现该过程工业化的关键。本文从催化剂组成、制备方法及反应机理等方面对CO₂加氢催化剂的研究进展进行了评述。分析了催化剂中活性中心的状态,归纳了载体和助剂的作用,比较了制备方法的优劣,并对催化反应机理进行了讨论。针对当前存在的问题,指出反应机理的深入探讨和催化剂制备方法的革新是今后的研究重点和主要方向。     

Economic Assessment of the Hydrogenation of CO2 to Liquid Fuels and Petrochemical Feedstock

To remove high concentrations of CO₂ from the off‐gas of coal‐driven power plants, a new process was proposed. The catalytic hydrogenation of the CO₂ leads to the production of C₂ – C₄ (petrochemical feedstock) and liquid C₅₊ hydrocarbons (fuel). Thus, environmentally harmful CO₂ may be converted sustainably to useful products. On the basis of a process flow sheet, the costs for processing the CO₂ are estimated for different plant sizes. The price of hydrogen contributes significantly to the overall production costs. Further price reductions may be achieved by final engineering optimization of the process as a whole and specific unit operations.     

Highly effective conversion of carbon dioxide to valuable compounds on composite catalysts

The highly effective catalytic conversion of CO₂ into valuable compounds was investigated by multi-functional catalysts composed of base-metal oxides as the main components promoted by a low concentration of precious metals and gallium oxide. The desired reduced state of catalyst metal oxides for exhibiting the optimum catalytic performance could be controlled by both the hydrogen spillover on the precious metal parts and the inverse-spillover from the Ga parts. By applying those principal concepts in the catalyst structure-design, the rapid CO₂ reforming of methane, the rapid CO₂ methanation, the effective synthesis of methanol and/or ethanol from CO₂ and H₂, and selective syntheses of high quality gasoline and/or light olefins by means of one-pass conversion of CO₂-H₂ mixture via methanol as the intermediate product, were respectively realized. Those novel catalytic reactions would have a high potential to moderate the accumulation of CO₂ come from fossil fuel combustion, while compensating the cost of hydrogen as the reducing reagent.     

丁辛醇加氢催化技术进展

介绍了丁辛醇工业流程中加氢部分的工艺及国外催化剂研制情况,同时对加氢催化剂的国产化进程作了重点介绍,认为丙烯氢甲酰化研究与开发项目中加氢部分的催化剂的选择完全可以立足国内.     

The Influence of Supercritical Carbon Dioxide (SC‐CO2) on Electrolytes and Hydrogenation of Soybean Oil

The electrochemical hydrogenation of soybean oil with supercritical carbon dioxide (SC‐CO₂) has been studied to seek ways for substantial reduction of the trans fatty acids (TFA). The solubility of CO₂ in electrolytes and the conductivity of electrolytes were investigated using a self‐made electrochemical hydrogenation reactor. The optimum hydrogenation parameters were assessed. Both the solubility of CO₂ in electrolytes and the conductivity of electrolytes increased with increasing CO₂ pressure. When the pressure reached a critical point of CO₂, the solubility of CO₂ expressed as a mole fraction was 0.42 in cathode electrolyte and 0.1 in anode electrolyte. At 8 MPa, the conductivity of electrolytes was 1.5 times higher than that at 2 MPa. When the pressure was higher than the critical point of CO₂, the solubility of CO₂ in electrolytes and the conductivity of electrolytes reached a stable value. The optimum condition for electrochemical hydrogenation of soybean oil in SC‐CO₂ were reaction pressure (8 MPa), reaction temperature (48 °C), current (125 mA), agitation speed (300 rpm), and reaction time (8 h). Fatty acid profile, iodine value, and TFA content were evaluated at the optimum parameters. This investigation showed that the electrochemical hydrogenation of soybean oil in SC‐CO₂ was improved. The reaction time was shortened by 4 h, and TFA content was reduced by 35.8% compared to traditional hydrogenation process.     

Selective methanation of CO over supported Ru catalysts

The catalytic performance of supported ruthenium catalysts for the selective methanation of CO in the presence of excess CO₂ has been investigated with respect to the loading (0.5–5.0 wt.%) and mean crystallite size (1.3–13.6 nm) of the metallic phase as well as with respect to the nature of the support (Al₂O₃, TiO₂, YSZ, CeO₂ and SiO₂). Experiments were conducted in the temperature range of 170–470 °C using a feed composition consisting of 1%CO, 50% H₂ 15% CO₂ and 0–30% H₂O (balance He). It has been found that, for all catalysts investigated, conversion of CO₂ is completely suppressed until conversion of CO reaches its maximum value. Selectivity toward methane, which is typically higher than 70%, increases with increasing temperature and becomes 100% when the CO₂ methanation reaction is initiated. Increasing metal loading results in a significant shift of the CO conversion curve toward lower temperatures, where the undesired reverse water–gas shift reaction becomes less significant. Results of kinetic measurements show that CO/CO₂ hydrogenation reactions over Ru catalysts are structure sensitive, i.e., the reaction rate per surface metal atom (turnover frequency, TOF) depends on metal crystallite size. In particular, for Ru/TiO₂ catalysts, TOFs of both CO (at 215 °C) and CO₂ (at 330 °C) increase by a factor of 40 and 25, respectively, with increasing mean crystallite size of Ru from 2.1 to 4.5 nm, which is accompanied by an increase of selectivity to methane. Qualitatively similar results were obtained from Ru catalysts supported on Al₂O₃. Experiments conducted with the use of Ru catalyst of the same metal loading (5 wt.%) and comparable crystallite size show that the nature of the metal oxide support affects significantly catalytic performance. In particular, the turnover frequency of CO is 1–2 orders of magnitude higher when Ru is supported on TiO₂, compared to YSZ or SiO₂, whereas CeO₂- and Al₂O₃-supported catalysts exhibit intermediate performance. Optimal results were obtained over the 5%Ru/TiO₂ catalyst, which is able to completely and selectively convert CO at temperatures around 230 °C. Addition of water vapor in the feed does not affect CO hydrogenation but shifts the CO₂ conversion curve toward higher temperatures, thereby further improving the performance of this catalyst for the title reaction. In addition, long-term stability tests conducted under realistic reaction conditions show that the 5%Ru/TiO₂ catalyst is very stable and, therefore, is a promising candidate for use in the selective methanation of CO for fuel cell applications.     

Bifunctional pathways in the carbon dioxide reforming of methane over MgO-promoted Ru/C catalysts

The addition of MgO to a ruthenium catalyst dispersed on an inert activated carbon is found to improve the catalyst selectivity and stability in the dry reforming of methane to syngas. Steady-state and isotopic transient kinetic experiments carried out in a TAP reactor have revealed a cooperative interaction between the metal and the basic oxide in the CO₂/CH₄ reaction via a bifunctional mechanism. This specific effect is proposed to explain the discovered promoting effect. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrodenitrogenation of pyridine over activated carbon-supported sulfided Mo and NiMo catalysts. Effects of hydrogen sulfide and oxidation of the support

The hydrodenitrogenation (HDN) of pyridine over activated carbon-supported Mo and NiMo sulfided catalysts was studied. Without H₂S in the feed the catalysts showed a high conversion of pyridine and of piperidine to C₅ hydrocarbons at the beginning of reaction, followed by a strong deactivation. A large increase in the conversion of pyridine was observed when H₂S was added to the feed at H₂S/H₂0.006. The conversion of piperidine to C₅ hydrocarbons was enhanced by H₂S and it increased as the H₂S pressure increases up to H₂S/H₂0.006. The promotion effect of Ni was operative only when H₂S was present and it increased with the H₂S/H₂ ratio. Without H₂S, the degree of surface oxidation of the support affected the deactivation of the catalysts. When H₂S was added to the feed, the conversion of pyridine was stable and independent of the acid treatment of the support. A more oxidized support enhanced the C-N bond breaking reaction.     

Isoprene formation from CO and H2 over CeO2 catalysts

The CO-H₂ reaction over CeO₂ catalysts at around 623 K and 67 kPa forms isoprene with about 20% and 70% selectivities in total and C₅ hydrocarbons, respectively. The formation of dienes may be due to the low and high activity of CeO₂ for alkene and CO hydrogenation, respectively.