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.     

Selective oxidehydrogenation of ethane with CO2 over CeO2-based catalysts

Ceria catalysts were found active and selective to the oxidehydrogenation of ethane (ODE) with CO₂ and the actual contribution for C₂H₄ formation from heterogeneous catalysis was 75–55% in the range 953–993 K. The presence of calcium ions in solid solution in the ceria crystalline network increased significatively the selectivity to ethene and the efficiency of CO₂ as oxidant in the heterogeneous reaction.     

TiO2基催化剂还原CO2研究进展

能源危机和环境污染是当今世界发展面临的两大挑战,如何有效缓解煤、石油等不可再生化石资源过度消耗所引发的能源危机,以及由此造成CO₂过量排放引起的温室效应问题,是当前人类发展亟待解决的重大科学问题之一。基于此,本文综述了近年来以TiO₂为光催化剂,以绿色、清洁的太阳光能催化还原CO₂成低价态含碳燃料(如CH₄、CH₃OH、HCHO、HCOOH、C₂H₅OH等)研究进展。在TiO₂光还原CO₂机理基础上,对元素掺杂、半导体复合与染料敏化、高活性晶面调控、低维纳米结构设计、助催化剂、Z型结构设计和单原子催化等方法来提高光还原CO₂反应效率和选择性进行分析,并指出目前研究存在的关键问题和未来CO₂光还原的发展方向。     

Co/CeO2-ZrO2 catalysts prepared by impregnation and coprecipitation for ethanol steam reforming

Co/CeO₂-ZrO₂ catalysts for the ethanol steam reforming were prepared by wet incipient impregnation and coprecipitation methods. These catalysts were characterized by nitrogen adsorption, TEM-EDX, XRD, H₂-TPR, and CO chemisorption techniques. It was found that the catalyst reducibility was influenced by the preparation methods; catalysts with different reduction behaviors in the pre-reduction showed different catalytic activities toward hydrogen production. The H₂-TPR studies suggested the presence of metal–support interactions in Co/CeO₂-ZrO₂ catalysts during their hydrogen pre-reduction, a necessary treatment process for catalysts activation. These interactions were influenced by the preparation methods, and the impregnation method is a favorable method to induce a proper metal–support effect that allows only partial reduction of the cobalt species and leads to a superior catalytic activity for the hydrogen production through ethanol steam reforming. At 450 °C, the impregnated catalyst gives a hydrogen production rate of 147.3 mmol/g-s at a WHSV of 6.3 h⁻¹ (ethanol) and a steam-to-carbon ratio of 6.5.     

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.     

Preparation of Cu/ZrO2 catalysts for methanol synthesis from CO2/H2

Cu/ZrO₂ catalysts for methanol synthesis from CO₂/H₂ were respectively prepared by deposition coprecipitation (DP) and solid state reaction (SR) methods. There is an intimate interaction between copper and zirconia, which strongly affects the reduction property and catalytic performance of the catalysts. The stronger the interaction, the lower the reduction temperature and the better the performance of the catalysts. Surface area, pore structure and crystal structure of the catalysts are mainly controlled by preparation methods and alkalinity of synthesis system. The conversion of CO₂ and selectivity of methanol are higher for DP catalysts than for SP catalysts.     

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.     

Tri-reforming of CH4 using CO2 for production of synthesis gas to dimethyl ether

In general, there are three processes for production of synthesis gas; steam reforming, CO₂ reforming and partial oxidation of methane or natural gas. In the present work, we refer to tri-reforming of methane to synthesize syngas with desirable H₂/CO ratios by simultaneous oxy-CO₂-steam reforming of methane. In this study, we report the results obtained on tri-reforming of methane over the Ni/ZrO₂ based catalyst in order to restrain the carbon deposition and to evaluate the catalytic performance. Results of tri-reforming of CH₄ by three catalysts (Ni/Ce–ZrO₂, Ni/ZrO₂ and Haldor Topsoe R67-7H) are showed that the coke on the reactor wall and the surface of catalyst were reduced dramatically. It was found that the weak acidic site, basic site and redox ability of Ce–ZrO₂ play an important role in tri-reforming of methane conversion. Carbon deposition depends not only on the nature of support, but also on the oxidant as like steam or oxygen. Therefore, the process optimization by reactant ratios is important to manufacture the synthesis gas from natural gas and carbon dioxide.     

Potential of zeolite supported rhodium catalysts for the CO2 reforming of CH4

Zeolite Y supported rhodium catalysts were prepared by ion-exchange starting from an aqueous solution of [Rh[(NH₃)₅Cl]Cl₂·6H₂0]. Previous work in this laboratory had shown that this procedure results in a Rh dispersion of near 100%. The catalysts were tested for their activity in the CO₂ reforming of CH₄. They were found to combine extraordinary stability with high activity and selectivity. At 923 K, 90 mol-% of the CH₄ was converted giving a H₂/CO ratio near unity. A weight loading of 0.5 to 0.93% Rh gives the highest turnover frequencies. Thermodynamic equilibrium is reached near 873 K. With a given Rh loading, the zeolite supports are superior to amorphous supports and NaY is superior to the HY. No deactivation was observed in tests of 30 h time on stream at atmospheric pressure or after repeated thermal cycles. No coke deposition was detected by temperature programmed oxidation of used catalysts. Temperature programmed reduction indicates the presence of three discernible Rh species.     

H2 production through steam reforming of ethanol over Pt/ZrO2, Pt/CeO2 and Pt/CeZrO2 catalysts

The effect of the support nature and metal dispersion on the performance of Pt catalysts during steam reforming of ethanol was studied. H₂ and CO production was facilitated over Pt/CeO₂ and Pt/CeZrO₂, whereas the acetaldehyde and ethene formation was favored on Pt/ZrO₂. According to the reaction mechanism, determined by temperature-programmed desorption (TPD) and Diffuse Reflectance Infrared Spectroscopy (DRIFTS) analysis, some reaction pathways are favored depending on the support nature, which can explain the differences observed on the resulting product distribution.     

Hydrocarbon synthesis through CO2 hydrogenation over CuZnOZrO2/zeolite hybrid catalysts

Direct syntheses of hydrocarbons from CO₂ hydrogenation were investigated over hybrid catalysts consisting of methanol synthesis catalyst (CuZnOZrO₂) and zeolites (MFI and SAPO). The yield of hydrocarbons was strongly depending upon the amount of zeolite's acid sites as measured by NH₃ TPD, while the product distributions were hardly affected by the change of acidity. The main product was ethane in the case of MFI hybrid catalyst and C₃ or C₄ hydrocarbon in the case of SAPO hybrid catalyst. This difference in product distribution was attributed to different mechanism of hydrocarbon formation. Investigation based on the ethene co-reaction suggested that the consecutive mechanism operated for HZSM-5 and the carbon pool mechanism for SAPO.     

Oxidative dehydrogenation of ethylbenzene to styrene with CO2 over SnO2–ZrO2 mixed oxide nanocomposite catalysts

SnO₂–ZrO₂ nanocomposite catalysts with different compositions ranging from 0 to 100% of SnO₂ were prepared at room temperature by co-precipitation method using aqueous ammonia as a hydrolyzing agent. X-ray diffraction, transmission electron microscopic characterization revealed the SnO₂–ZrO₂ nanocomposite behavior. Acid–base properties of these catalysts were ascertained by temperature-programmed desorption (TPD) of NH₃ and CO₂. Both acidic and basic sites distribution of the nanocomposite catalysts is quite different from those of respective single oxides (SnO₂ or ZrO₂). Catalytic activity of these nanocomposite catalysts for ethylbenzene dehydrogenation (EBD) to styrene in the presence of excess CO₂ was evaluated. The change in the acid–base bi-functionality of the nanocomposite catalysts in comparison with single oxides had profound positive influence in enhancing the catalytic activity.     

Niobium sulfide as a dopant for Mo/TiO2 catalysts

Mo/TiO₂ catalysts were modified with Nb by two different methods, sol–gel and surface deposition, in order to study the effect of Nb incorporation on the thiophene HDS activity. The results show that the formation of Nb–Ti mixed oxides leads to catalysts with poor HDS activity while the deposition of Nb oxide species on the surface of TiO₂ leads to catalysts with activities larger than those of Mo/Al₂O₃ and Mo/TiO₂. This increase in activity was attributed to the formation of a larger population of Mo sulfur anionic vacancies when Nb was surface deposited on the TiO₂.     

Effects of small MoO3 additions on the properties of nickel catalysts for the steam reforming of hydrocarbons III. Reduction of Ni-Mo/Al2O3 catalysts

Ni/Al₂O₃ catalyst modified by small amounts of Mo show unusual properties in the steam reforming of hydrocarbons. There are no data about the effect of small amounts of molybdenum on reduction of the Ni-Mo supported catalysts. The properties of these very complex systems depend on the conditions of successive preparation stages (calcination, reduction) or the process conditions.

A series of Ni/Al₂O₃ catalysts modified by Mo were prepared in order to investigate the influence of promoter amounts and preparation sequence on their properties. Temperature programmed reduction (TPR) has been employed to study the reducibility of Ni-Mo/Al₂O₃ catalysts. Catalysts were further characterized by BET area, H₂ chemisorption and X-ray diffraction measurements.

The TPR curves of Ni-Mo/Al₂O₃ catalysts are very complex. Mo addition leads to the decrease of catalysts reducibility. However, complete reduction of NiO and MoO₃ can be achieved at 800 °C. The reduction course depends on the sequence of nickel and molybdenum addition into the support. Precise measurements of Ni peaks positions in the XRD pattern of Ni/Al₂O₃ and Ni-Mo/Al₂O₃ samples show the possibility of Ni-Mo solid solution formation.     

Methanol synthesis from CO2-rich syngas over a ZrO2 doped CuZnO catalyst

ZrO₂-doped CuZnO catalyst prepared by successive-precipitation method was investigated by ICP-AES, BET, TEM, XRD, EXAFS, H₂-TPR and CO/CO₂ hydrogenation. The active phase of copper in CuZnO catalyst prepared by co-precipitation method was well-crystallized. The presence of ZrO₂ led to a high copper dispersion, which was distinctive from CuZnO. Though the activity for carbon monoxide hydrogenation was little lower than that of CuZnO catalyst, ZrO₂-doped CuZnO catalyst showed much higher activity and selectivity towards methanol synthesis from carbon dioxide hydrogenation. Moreover, ZrO₂-doped CuZnO catalyst showed high performance for methanol synthesis from CO₂-rich syngas.     

Catalytic conversion of methane and CO2 to synthesis gas over a La2O3-modified SiO2 supported Ni catalyst in fluidized-bed reactor

In this contribution, a commercial spherical SiO₂ was modified with different amounts of La₂O₃, and used as the support of Ni catalysts for autothermal reforming of methane in a fluidized-bed reactor. Nitrogen adsorption, XRD and H₂-TPR analysis indicated that La₂O₃-modified SiO₂ had higher surface area, strengthened interaction between Ni and support, and improved dispersion of Ni. CO₂-TPD found that La₂O₃ increased the alkalescence of SiO₂ and improved the activation of CO₂. Coking reaction (via both temperature-programmed surface reaction of CH₄ (CH₄-TPSR) and pulse decomposition of CH₄) disclosed that La₂O₃ reduced the dehydrogenation ability of Ni. CO₂-TPO, O₂-TPO (followed after CH₄-TPSR) confirmed that only part amount of carbon species derived from methane decomposition could be removed by CO₂, and O₂ in feed played a crucial role for the gasification of the inactive surface carbons. Ni/xLa₂O₃-SiO₂ (x = 10, 15, 30) possessed high activity and excellent stability for autothermal reforming of methane in a fluidized-bed reactor.     

Development of high performance Raney Cu-based catalysts for methanol synthesis from CO2 and H2

Catalytic hydrogenation of CO₂ into methanol has been investigated over Raney Cu-based catalysts. The Raney catalysts leached in NaOH/ZnO solutions showed high activities and selectivities for methanol synthesis. The deposition of Zn on the surface of Cu particles increased the surface area and the specific activity of Raney Cu–M. Raney Cu–Zr developed was significantly more active than a commercial catalyst.     

The behaviour of Ru/Fe2O3 catalysts and Fe2O3 supports in the TPR and TPO conditions

The texture of Fe₂O₃ support and Ru/Fe₂O₃ catalysts supported on iron oxides obtained from β-FeOOH (B) or δ-FeOOH (D) and their catalytic activity in WGSR were studied. Also their susceptibilities to reduction and reoxidation, were studied by TPR, using H₂ or CO and TPO methods. In the case of TPR_CO the composition of the reducing mixture containing traces of H₂O enabled investigation of water gas shift reaction (WGSR).

The catalysts from series D were found more readily reducible and oxidised than those from series B. The supported ruthenium enhanced the redox effects and caused the appearance of additional effects related directly to its presence. Depending on the kind of support and on ruthenium presence considerable differences in temperatures of WGSR onset were found. It is suggested that the susceptibility of the catalysts to reduction and oxidation is responsible for their activity in the WGSR.     

The role of the oxidic support on the deactivation of Pt catalysts during the CO2 reforming of methane

Pt supported on γ-Al₂O₃, TiO₂ and ZrO₂ are active catalysts for the CO₂ reforming of methane to synthesis gas. The stability of the catalysts increased in the order Pt/γ-A1₂O₃ < Pt/TiO₂ < Pt/ZrO₂. For all catalysts, the decrease in activity with time on stream is caused by carbon formation, which blocks the active metal sites for reaction. With Pt/TiO₂ and Pt/ZrO₂, deactivation started immediately after the start of the reaction, while the Pt/γ-A1₂O₃ catalyst showed an induction period during which carbon was accumulated without affecting the catalytic activity.     

甲醇和乙醇合成异丁醛La-V/TiO_2-SiO_2催化剂的制备及其催化性能

以V_2O_5为活性组分,通过对催化剂活性组分、载体结构和助剂等因素的研究,制备La-V/TiO_2-SiO_2催化剂,在n(甲醇)∶n(乙醇)=4∶1、空速1.5 h-1、氮气流量120 m L·min~(-1)、反应温度360℃和常压条件下,乙醇转化率84%,异丁醛选择性67%。