Effect of a promoter on the properties of the 20% Co-M/CoAl<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> catalytic system in the synthesis of hydrocarbons from CO and H<Subscript>2</Subscript>

The 20% Co-M/CoAl _x O _y catalytic systems promoted with Ru, Pd, and Re, in which cobalt is not only an active component but also a constituent of the support, were studied in this work. The effects of the addition and concentration of a promoter on the catalytic properties of the resulting system in the synthesis of hydrocarbons from CO and H₂ was studied. It was found that the introduction of rhenium into the composition of the 20% Co/CoAl _x O _y catalyst considerably increased the yield of C₅₊ hydrocarbons with a minimum methane formation in the synthesis of hydrocarbons from CO and H₂.     

Hydrocarbon synthesis from CO and H<Subscript>2</Subscript>: Promotion of Co/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts with noble metals

The effect of promotion of Co catalysts with noble metals on their activity and selectivity in the synthesis of hydrocarbons from CO and H₂ has been studied. Platinum at a content of (0.05–0.10)% has been found to be best promoter.     

Effect of thermal pretreatment conditions on the properties of a cobalt catalyst in hydrocarbon synthesis from CO and H<Subscript>2</Subscript>

The effect of the conditions of the thermal pretreatment of a cobalt catalyst based on zeolite β (Co/Hβ) on the synthesis of hydrocarbons from CO and H₂ was studied. The physicochemical and catalytic properties of Co/Hβ samples were studied and the synthesis products were analyzed in order to determine the most favorable regime for the thermal treatment of this catalytic system. It was found that double calcination at 250°C was an optimum temperature regime. It is likely that a large amount of catalytic centers for polymerization was formed on the surface of the catalytic system under these conditions.     

Effect of the regeneration conditions of a cobalt-zeolite catalyst on its properties in the synthesis of hydrocarbons from CO and H<Subscript>2</Subscript>

The effect of the hydrogen regeneration conditions of a 20% Co/Hβ cobalt-zeolite catalyst on its properties in the synthesis of hydrocarbons from CO and H₂ was studied. It was found that regeneration with hydrogen was most effective at 400°C. In this case, the productivity of the catalyst was as high as 305 × 10³ g/m³ Cat/h at a maximum synthesis-gas space velocity (5000 h⁻¹).     

Synthesis of alcohols from CO and H<Subscript>2</Subscript> on iron catalysts containing carbon fiber

It was found that alcohols can be synthesized from CO and H₂ at 3 MPa and 280–300°C in the presence of Fe catalysts containing an activated fibrous carbon material (AFCM) as a support. It was established that 20% Fe/AFCM catalysts possess an extremely high specific activity in the conversion of carbon monoxide (∼1 × 10⁻⁴ mol CO (mol Fe)⁻¹ s⁻¹), which is higher than the activity of traditional bulk iron catalysts by almost an order of magnitude. The values of CO conversion and selectivity for alcohols obtained for these catalysts are close to the parameters of industrial processes (Synol process, Oxyl process, and synthesis according to Bashkirov); however, they are obtained under milder conditions in a single run rather than with the use of a recycle. The Fe/AFCM catalysts make it possible to obtain monohydric alcohols in yields to ∼50 g/m³ (to a 50% concentration in synthesis water) upon the almost complete conversion of CO. In this case, the fraction of C₂-C₄ alcohols was as high as 55–60%.     

Preferential CO Oxidation on Bimetallic Pt<Subscript>0.5</Subscript>M<Subscript>0.5</Subscript> Catalysts (M = Fe,Co, Ni) Prepared from Double Complex Salts

Properties of Pt_0.5M_0.5 nanopowders (M = Fe, Co, Ni) of alloys obtained via the decomposition of double complex salts [Pt(NH₃)₅Cl][Fe(C₂O₄)₃] ? 4H₂O, [Pt(NH₃)₄][Co(C₂O₄)₂(H₂O)₂] ? 2H₂O, and [Pt(NH₃)₄][Ni(C₂O₄)₂(H₂O)₂] ? 2H₂O, respectively, are studied in the reaction of preferential CO oxidation. It is shown that bimetallic Pt_0.5M_0.5 catalysts (M = Fe, Co, Ni) are much more active in the low temperature range than Pt nanopowder. The activity of the catalysts decreases in the order Pt_0.5M_0.5 ≥ Pt_0.5M_0.5 > Pt_0.5M_0.5 @ Pt. The higher activity of bimetallic Pt0.5M0.5 catalysts in the reaction of preferential CO oxidation in the low-temperature range under conditions of dense Pt surface coverage by adsorbed CO molecules is most likely caused by the activation of CO on Pt atoms, the activation of O₂ on atoms of the second metal (Fe, Co, Ni), and the reaction that occurs at the sites of contact between the atoms of platinum and the atoms of the second metal on the surfaces of the alloy’s nanoparticles. The bimetallic systems investigated in this work can be used to improve catalysts of practically important preferential CO oxidation reaction. These systems have considerable potential in the afterburning reactions of CO and hydrocarbons; hydrogenation reactions; electrochemical reactions; and many others. The means used in the preparation of bimetallic nanopowders based on the decomposition of double complex salts is simple, does not require the use of expensive or complex reagents, and can be easily adapted to produce supported catalysts containing Pt_0.5M_0.5 metal alloys (M = Fe, Co, Ni).     

Separation characteristics of tetrapropylammoniumbromide templating silica/alumina composite membrane in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>/H<Subscript>2</Subscript> and CH<Subscript>4</Subscript>/H<Subscript>2</Subscript> systems

Nanoporous silica membrane without any pinholes and cracks was synthesized by organic templating method. The tetrapropylammoniumbromide (TPABr)-templating silica sols were coated on tubular alumina composite support ( γ-Al₂O₃/ α-Al₂O₃ composite) by dip coating and then heat-treated at 550 °C. By using the prepared TPABr templating silica/alumina composite membrane, adsorption and membrane transport experiments were performed on the CO₂/N₂, CO₂/H₂ and CH₄/H₂ systems. Adsorption and permeation by using single gas and binary mixtures were measured in order to examine the transport mechanism in the membrane. In the single gas systems, adsorption characteristics on the α-Al₂O₃ support and nanoporous unsupport (TPABr templating SiO₂/ γ-Al₂O₃ composite layer without α-Al₂O₃ support) were investigated at 20–40 °C conditions and 0.0–1.0 atm pressure range. The experimental adsorption equilibrium was well fitted with Langmuir or/and Langmuir-Freundlich isotherm models. The α-Al₂O₃ support had a little adsorption capacity compared to the unsupport which had relatively larger adsorption capacity for CO₂ and CH₄. While the adsorption rates in the unsupport showed in the order of H₂> CO₂> N₂> CH₄ at low pressure range, the permeate flux in the membrane was in the order of H₂≫N₂> CH₄> CO₂. Separation properties of the unsupport could be confirmed by the separation experiments of adsorbable/non-adsorbable mixed gases, such as CO₂/H₂ and CH₄/H₂ systems. Although light and non-adsorbable molecules, such as H₂, showed the highest permeation in the single gas permeate experiments, heavier and strongly adsorbable molecules, such as CO₂ and CH₄, showed a higher separation factor (CO₂/H₂=5-7, CH₄/H₂=4-9). These results might be caused by the surface diffusion or/and blocking effects of adsorbed molecules in the unsupport. And these results could be explained by surface diffusion. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Pretreatment of cobalt catalysts for hydrocarbon synthesis from CO and H<Subscript>2</Subscript>

The effects of the preimpregnation of reduced cobalt catalysts with liquid hydrocarbons on hydrocarbon synthesis from CO and H₂ are considered. The preimpregnation of the catalysts shortens their reduction time. This effect is likely due to the fact that the impregnated catalyst sooner comes to a steady-state operating regime because of the enhanced mass transfer in the catalyst pellets during the process.     

CO oxidation from syngas (CO and H<Subscript>2</Subscript>) using nanoporous Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

The concept of “waste-to-wealth” is spreading awareness to prevent global warming and recycle the restrictive resources. To contribute towards sustainable development, hydrogen energy is obtained from syngas (CO and H₂) generated from waste gasification, followed by CO oxidation and CO₂ removal. In H₂ generation, it is key to produce more purified H₂ from syngas using heterogeneous catalysts. In this respect, we prepared Pt/Al₂O₃ catalyst with nanoporous structure using precipitation method, and compared its catalytic activity with commercial alumina (Degussa). Based on the results of XRD and TEM, it was found that metal particles did not aggregate on the alumina surface and showed high dispersion. Optimum condition for CO conversion was 1.5 wt% Pt loaded on Al₂O₃ support, and pure hydrogen was obtained after removal of CO₂ gas.     

Synergism Between Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Au/TiO<Subscript>2</Subscript> in the Low Temperature Oxidation of Propene

CO impedes the low temperature (<170 °C) oxidation of C₃H₆ on supported Pt. Supported Au catalysts are very effective in the removal of CO by oxidation, although it has little propene oxidation activity under these conditions. Addition of Au/TiO₂ to Pt/Al₂O₃ either as a physical mixture or as a pre-catalyst removes the CO and lowers the light-off temperature (T ₅₀) for C₃H₆ oxidation compared with Pt catalyst alone by ~54 °C in a feed of 1% CO, 400 ppm C₃H₆, 14% O₂, 2% H₂O.     

Effect of pressure on the activity and selectivity of cobalt-zeolite catalysts for the synthesis of hydrocarbons from CO and H<Subscript>2</Subscript>

The effect of pressure (0.5–2.5 MPa) on the synthesis of hydrocarbons from CO and H₂ on Co-zeolite catalysts in a fixed-bed flow reactor was studied. It was found that productivity and selectivity for liquid hydrocarbons increased with pressure, whereas the selectivity of methane formation did not increase. The isoparaffin content of the products of catalysis was inversely proportional to the amount of heavy fractions in the products.     

The nature of surface species on modified Pt-based catalysts for the SCR of NO by C<Subscript>3</Subscript>H<Subscript>6</Subscript> under lean-burn condition

The catalytic activity behavior for the selective catalytic reduction of NO by C₃H₆ under excess oxygen and the nature of surface species on the active sites of Pt/Al₂O₃ catalyst after adding a second metal (Fe, Sn, Co, Cr or W) were investigated. It has been found that an important role of second metals is on TONs of C₃H₆ and NO conversions and the nature of surface species produced on the catalyst surface at low temperature instead of the catalytic activity behavior towards the temperature programmed reaction. Although the introduction of each second metal distinctly disturbs the characteristic of surface species, the reaction mechanism is presumably similar. The observation of few surface species and the investigation about their reactivity indicate that few mechanisms are simultaneously proceeding at the same reaction condition.     

Kinetic models of Fischer-Tropsch synthesis reaction over granule-type Pt-promoted Co/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

Kinetic models of CO hydrogenation to paraffinic hydrocarbons through Fischer-Tropsch synthesis (FTS) reaction were studied by using Langmuir-Hinshelwood Hougen-Watson (LHHW) model of 16 different reaction steps with a pseudo steady-state assumption (PSSA) on the prototype Pt-promoted Co/Al₂O₃ catalyst having a granule size of ～1 mm of spherical γ-Al₂O₃ support (surface area of 149m²/g). The derived kinetic models from ten sets of experimental data by altering the reaction conditions such as temperatures, pressures, space velocities and H₂/CO molar ratios were found to be well fitted with reasonable kinetic parameters and small errors of conversion of CO and hydrocarbon distributions in terms of mean absolute relative residual (MARR) and relative standard deviation error (RSDE). The derived reaction rates and CO activation energy of -86 kJ/mol well correspond to the our previously reported results using power-type catalysts. Based on the LHHW model with PSSA, the possible chemical intermediates on the granule ball-type Co-Pt/Al₂O₃ surfaces were precisely considered to explain the typical adsorption, initiation, propagation and termination steps of FTS reaction as well as to derive elementary reaction rates with their kinetic parameters and hydrocarbon distributions. The derived kinetic models were further used to verify temperature-profiles in a pilot-scale fixed-bed tubular FTS reactor with a packing depth of 100 cm catalyst, and it confirmed that the temperature gradients were less than 10 °C in a length of reactor by effectively removing the generated heat by an exothermic FTS reaction.     

Method of estimating absolute concentrations of C<Subscript>2</Subscript>H<Subscript>5</Subscript> and H radicals in hydrocarbon diffusion flames

A method for estimating absolute concentrations of C₂H₅ and H radicals in hydrocarbon diffusion flames is proposed and substantiated. Concentration profiles of C₂H₅ and H on the flame axis are obtained. In the method proposed, the concentration of C₂H₅ is determined from the equality of two quantities — the rate of loss of n-butane by diffusion and the rate of its formation by recombination of two C₂H₅ radicals. The concentration of H radicals is determined from the relation between the ratio C₂H₅/H and experimental profiles of C₂H₄, C₂H₆, and O₂. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 13–20, November–December, 2007.     

Partial oxidation of methane over Ni/Ce-Zro<Subscript>2</Subscript>/θ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The catalytic behavior of Ni/Ce-ZrO₂/θ-Al₂O₃ has been investigated in the partial oxidation of methane (POM) toward synthesis gas. The catalyst showed high activity and selectivity due to the heat treatment of the support and the promotional effect of Ce-ZrO₂. It is suggested that the support was stabilized through the heat treatment of γ-Al₂O₃ and the precoating of Ce-ZrO₂, on which a protective layer was formed. Moreover, sintering of the catalyst was greatly suppressed for 24 h test. Pulse experiments of CH₄, O₂ and/or CH₄/O₂ with a molar ratio of 2 were systematically performed over fresh, partially reduced and well reduced catalyst. Results indicate that CH₄ can be partially oxidized to CO and H₂ by the reactive oxygen in complex NiO_x species existing over the fresh catalyst. It is demonstrated that POM over Ni/Ce-ZrO₂/θ-Al₂O₃ follows the pyrolysis mechanism, and both the carbonaceous materials from CH₄ decomposition over metallic nickel and the reactive oxygen species present on NiO_x and Ce-ZrO₂ are intermediates for POM.     

Photocatalytic Generation of H<Subscript>2</Subscript> Gas from Neat Ethanol over Pt/TiO<Subscript>2</Subscript> Nanotube Catalysts

TiO₂ nanotubes promoted with Pt metal were prepared and tested to be the photocatalytic dehydrogenation catalyst in neat ethanol for producing H₂ gas (C₂H₅OHC₃CHO +H₂). It was found that the ability to produce H₂, the liquid phase product distribution and the catlyst stability of these promoted nano catalysts all depended on the Pt loading and catalyst preparation procedure. These Pt/TiO₂ catalysts with TiO₂ nanotubes washed with diluted H₂SO₄ solution produced 1, 2-diethoxy ethane (acetal) as the major liquid phase product, while over those washed with diluted HCl solution or H₂O, acetaldehyde was the major liquid phase product.     

The promotional effect of K on the catalytic activity of Ni/MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> for the combined H<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> reforming of coke oven gas for syngas production

A K-promoted 10Ni-(x)K/MgAl₂O₄ catalyst was investigated for the combined H₂O and CO₂ reforming (CSCR) of coke oven gas (COG) for syngas production. The 10Ni-(x)K/MgAl₂O₄ catalyst was prepared by co-impregnation, and the K content was varied from 0 to 5 wt%. The BET, XRD, H₂-chemisorption, H₂-TPR, and CO₂-TPD were performed for determining the physicochemical properties of prepared catalysts. Except under the condition of a K/Ni=0.1 (wt%/wt%), the Ni crystal size and dispersion decreased with increasing K/Ni. The coke resistance of the catalyst was investigated under conditions of CH₄: CO₂: H₂: CO:N₂=1 : 1 : 2 : 0.3 : 0.3, 800 °C, 5 atm. The coke formation on the used catalyst was examined by SEM and TG analysis. As compared to the 10Ni/MgAl₂O₄ catalyst, the Kpromoted catalyst exhibited superior activity and coke resistance, attributed to its strong interaction with Ni and support, and the improved CO₂ adsorption characteristic. The 10Ni-1K/MgAl₂O₄ catalyst exhibited optimum activity and coke resistance with only 1wt% of K.     

The effect of ethane on the performance of commercial polyphenylene oxide and Cardo-type polyimide hollow fiber membranes in CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> separation applications

Impurities such as hydrogen sulfide, water vapor and heavy hydrocarbons in natural gas have considerable effects on the membrane performance. Small amounts of condensable and polymer soluble components in the feed gas cause swelling or plasticization of glassy membranes, leading to a reduction in membrane selectivity. In the present research the influence of ethane was investigated on the permeance and selectivity of two commercially available hollow fiber membranes, namely Cardo-type polyimide and PPO hollow fibers for CO₂/CH₄ separations. It was concluded that the gas mixture permeation rate was increased in the presence of C₂H₆. However, the CO₂/CH₄ separation factors remained almost the same in the presence and absence of the C₂H₆.     

Chemical Vapor Deposition of Pd(C<Subscript>3</Subscript>H<Subscript>5</Subscript>)(C<Subscript>5</Subscript>H<Subscript>5</Subscript>) to Synthesize Pd@MOF-5 Catalysts for Suzuki Coupling Reaction

Abstract  

The highly porous metal organic framework MOF-5 was loaded with the metal–organic compound [Pd(C₃H₅)(C₅H₅)] by metal–organic chemical vapor deposition (MOCVD) method. The inclusion compound [Pd(C₃H₅)(C₅H₅)]@MOF-5 was characterized by powder X-ray diffraction (PXRD), Fourier-transform infrared (FT-IR) spectroscopy, and solid-state nuclear magnetic resonance spectroscopy. It was found that the host lattice of MOF-5 remained intact upon precursor insertion. The –C₃H₅ ligand in the precursor is easier to lose due to the interaction between palladium and the benzenedicarboxylate linker in MOF-5, providing a possible explanation for the irreversibility of the precursor adsorption. Pd nanoparticles of about 2–5 nm in size was formed inside the cavities of MOF-5 by hydrogenolysis of the inclusion compound [Pd(C₃H₅)(C₅H₅)]@MOF-5 at room temperature. N₂ sorption of the obtained material confirmed that high surface area was retained. In the Suzuki coupling reaction the Pd@MOF-5 materials showed a good activity in the first catalytic run. However, the crystal structure of MOF-5 was completely destroyed during the following reaction runs, as confirmed by PXRD, which caused a big loss of the activity.     

CeO<Subscript>2</Subscript>-La<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZSM-5 sorbents for high-temperature H<Subscript>2</Subscript>S removal

Performance of CeO₂-La₂O₃/ZSM-5 sorbents for sulfur removal was examined at temperature ranging from 500 oC to 700 oC. The sulfur capacity of 5Ce5La/ZSM-5 was much bigger than that of CeO₂/ZSM-5. H₂ had a negative impact on the sulfidation; however, CO had little influence on sulfur removal. The characterization results showed that CeO₂ and La₂O₃ were well dispersed on ZSM-5 because of the intimate admixing of La₂O₃ and CeO₂, the major sulfidation products were Ce₂O₂S and La₂O₂S, the XRD and SEM results revealed that ZSM-5 structure could remain intact during preparation and sulfidation process, the H₂-TPR showed that the reducibility of CeO₂ can be remarkably enhanced by addition of La.