Reduction of NO by CH4 with Microwave Heating

The reduction of NO by CH₄ in the presence of excess O₂ over Co/HZSM-5, Ni/HZSM-5 and Mn/HZSM-5 catalysts with microwave heating was studied. By comparing the activities of the catalysts in the microwave heating mode with that in the conventional reaction mode, it was demonstrated that microwave heating could greatly reduce the reaction temperature, and could clearly expand the temperature window of the catalysts. Especially for the Co/HZSM-5 catalyst, the maximum conversion of NO to N₂ in the conventional reaction mode was consistent with that in the microwave heating mode. However, the temperature window for the maximum conversion in the microwave heating mode was from 260 to 360 °C instead of a temperature of 420 °C in the conventional reaction mode. The results suggest that microwave heating has a novel effect in the reduction of NO.     

Catalytic decomposition of TCE under microwave

The decomposition of trichloroethylene (TCE) by hydrogen over Co/γ-Al₂O₃ and Ni/γ-Al₂O₃ catalysts under microwave heating was studied. The comparison between the catalytic activity in the microwave heating mode and that in the conventional thermal mode demonstrated that the microwave heating could greatly reduce the reaction temperature, accelerate the TCE decomposition speed and improve the TCE decomposition ratio. The results suggest that the microwave heating has a novel effect in the decomposition of TCE.     

Role of cobalt on γ-Al2O3 based NO x storage catalyst

Co/Pt/Ba/γ-Al₂O₃, Co/Ba/γ-Al₂O₃, Pt/Ba/γ-Al₂O₃, Co/Pt/γ-Al₂O₃, Ba/γ-Al₂O₃, Pt/γ-Al₂O₃, and Co/γ-Al₂O₃ type catalysts were prepared by a conventional impregnation method, and their NO _x storage capacities were evaluated by colorimetric assay. Co-containing catalysts had a higher NO _x storage capacity than that of Co-free counterparts. The role of each component, especially Co, for the catalysts prepared was investigated by using in-situ FTIR. The high NO _x storage for Co-containing catalysts including Co/Ba/γ-Al₂O₃ and Co/Pt/Ba/γ-Al₂O₃ is mainly due to the formation of Co₃O₄ on the catalyst surface identified by XAFS.     

A study on the catalytic performance of Pd/γ-Al2O3, prepared by microwave calcination, in the direct synthesis of dimethylether

A series of Pd/γ-Al₂O₃ hybrid catalysts were prepared by impregnation and subsequent calcination under microwave irradiation. The catalysts were used for direct synthesis of dimethylether (DME) from syngas. The results show that calcination under microwave irradiation improved both the activity and selectivity of the catalysts for DME synthesis. The optimum power of the microwave was determined to be 420 W. Under such optimum conditions, CO conversion, DME selectivity and time space yield of DME were 60.1%, 67.0%, and 21.5 mmol·mL⁻¹·h⁻¹, respectively. Based on various characterizations such as nitrogen physisorption, X-ray diffraction, CO-temperature- programmed desorption, and Fourier transform infrared spectral analysis, the promotional effect of the microwave irradiation on the catalytic property was mainly attributed to both the higher dispersion of Pd and the significant increase in the adsorption on the CO-bridge of Pd. Microwave irradiation with very high power led to the increase in CO-bridge adsorption and thereby decreased the catalytic activity, whereas the coverage by metallic Pd of the active sites on acidic γ-Al₂O₃ significantly occurred under microwave irradiation with very low power, resulting in a decrease in the selectivity to DME.     

Methane conversion over nanostructured Pt/γAl2O3 catalysts in dielectric-barrier discharge

Spherical nanostructured γ-Al₂O₃ granules were prepared by combining the modified Yoldas process and oil-drop method, followed by the Pt impregnation inside mesopores of the granules by incipient wetness method. Prepared Pt/γ-Al₂O₃ catalysts were reduced by novel method using plasma, which was named plasma assisted reduction (PAR), and then used for methane conversion in dielectric-barrier discharge (DBD). The effect of Pt loading, calcination temperature on methane conversion, and selectivities and yields of products were investigated. Prepared Pt/γ-Al₂O₃ catalysts were successfully reduced by PAR. The main products of methane conversion were the light alkanes such as C₂H₆, C₃H₈ and C₄H₁₀ when the catalytic plasma reaction was carried out with Pt/γ-Al₂O₃ catalyst. Methane conversion was in the range of 38–40% depending on Pt loading and calcination temperature. The highest yield of C₂H₆ was 12.7% with 1 wt% Pt/γ-Al₂O₃ catalysts after calcinations at 500 ‡C.     

Pt–Ni/γ-Al2O3 catalyst for the preferential CO oxidation in the hydrogen stream

The preferential CO oxidation (PROX) in the presence of excess hydrogen was studied over Pt–Ni/γ-Al₂O₃. CO chemisorption, X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy and temperature-programmed reduction were conducted to characterize active catalysts. The co-impregnated Pt–Ni/γ-Al₂O₃ was superior to Pt/Ni/γ-Al₂O₃ and Ni/Pt/γ-Al₂O₃ prepared by a sequential impregnation of each component on alumina support. The PROX activity was affected by the reductive pretreatment condition. The pre-reduction was essential for the low-temperature PROX activity. As the reduction temperature increased above 423 K, the CO₂ selectivity decreased and the atomic percent of Ni in the bimetallic phase of Pt–Ni increased. This catalyst exhibited the high CO conversion even in the presence of 2% H₂O and 20% CO₂ over a wide reaction temperature. The bimetallic phase of Pt–Ni seems to give rise to high catalytic activity for the PROX in H₂-rich stream.     

Sulfur production from smelter off-gas using CO–H2 gas mixture as the reducing agent over modified Fe/γ-Al2O3 catalysts

A series of modified γ-Al₂O₃ supported iron-based catalysts (M-Fe/γ-Al₂O₃) was developed to reduce SO₂ in actual smelter off-gases using CO–H₂ gas mixture as reducing agent for sulfur production. Used as modifiers, three metal additives — Ni, Co, and Ce were added to Fe/γ-Al₂O₃ catalysts. Changes in catalyst structure and active phase were characterized with X-ray diffraction, XPS, SEM, and EDS. The reduction ability of catalysts was exhibited via CO-TPR. The prepared catalysts only need to be pre-reacted for a period of time, eliminating the need for presulfidation treatment. Reaction conditions were optimized in a fixed bed reactor to achieve high SO₂ conversion and sulfur selectivity. XRD characterization was carried out to verify the resulting sulfur products. Combining in situ infrared characterization and catalyst evaluation of support and active component, the reaction mechanism was investigated and proposed.     

Deactivation and coke formation on palladium and platinum catalysts in vegetable oil hydrogenation

Deactivation of palladium and platinum catalysts due to coke formation was studied during hydrogenation of methyl esters of sunflower oil. The supported metal catalysts were prepared by impregnating γ-alumina with either palladium or platinum salts, and by impregnating α-alumina with palladium salt. The catalysts were reused for several batch experiments. The Pd/γ-Al₂O₃ catalyst lost more than 50% of its initial activity after four batch experiments, while the other catalysts did not deactivate. Samples of used catalysts were cleaned from remaining oil by repeated extractions with methanol, and the amount of coke formed on the catalysts was studied by temperature-programmed oxidation. The deactivation of the catalyst is a function of both the metal and the support. The amount of coke increased on the Pd/γ-Al₂O₃ catalyst with repeated use, but the amount of coke remained approximately constant for the Pt/γ-Al₂O₃ catalyst. Virtually no coke was detected on the Pd/α-Al₂O₃ catalyst. The formation of coke on Pd/α-Al₂O₃ may be slower than on the Pd/γ-Al₂O₃ owing to the carrier’s smaller surface area and less acidic character. The absence of deactivation for the Pt/γ-Al₂O₃ catalyst may be explained by slower formation of coke precursors on platinum compared to palladium.     

Carbon Nanofiber Supported Cobalt Catalysts for Fischer–Tropsch Synthesis with High Activity and Selectivity

Platelet and fishbone carbon nanofibers (CNFs) have been used as supports for cobalt Fischer–Tropsch catalysts. The activity and selectivity of the CNF supported catalysts have been studied at 483 K, 20 bar, and H₂/CO = 2.1, and compared with corresponding activity and selectivity for α-Al₂O₃ and γ-Al₂O₃ supported cobalt catalysts. The platelet CNF supported catalyst has demonstrated high activity and high selectivity to C₅₊ hydrocarbons, with activity comparable with Co/γ-Al₂O₃ and selectivity comparable with Co/α-Al₂O₃.     

Reduction of NO by H2 and CO on PdO-MoO3/γ-Al2O3 of low molybdena loading

The activity and selectivity in the catalytic reduction of NO by a mixture of CO and H₂ of three PdO-MoO₃/-Al₂O₃ catalysts are compared in the presence of varying amounts of oxygen at reaction temperatures from 100 to 550°C. The catalysts were prepared by different methods and contain about 2% Mo and 2% Pd. Results are compared with those for PdO/-Al₂O₃, PdO-MoO₃/-Al₂O₃ containing 2% Pd and 20% Mo, and a commercial Pt-Rh catalyst. The PdO-MoO₃/-Al₂O₃ catalysts are more active for the selective reduction of NO to N₂ and N₂O than PdO/-Al₂O₃ under slightly oxidizing conditions at temperatures from 300 to 550°C. At these reaction conditions, the fresh PdO-MoO₃/-Al₂O₃ catalysts are comparable with a commercial Pt-Rh catalyst. The improved activity of PdO-MoO₃/-Al₂O₃ relative to PdO/-Al₂O₃ is believed to be due to the interaction between Pd and Mo. The effect of O₂ on the activity and selectivity of these catalysts is different in the reduction of NO by H₂, by CO, and by a mixture of H₂ and CO. The results using the mixture of reductants cannot be inferred from the results with the single reductants.     

Conversion of natural gas to C2 product,hydrogen and carbon black using a catalytic plasma reaction

In the microwave and RF plasma catalytic reaction at room temperature, the decomposition of natural gas over Pd–NiO/γ-Al₂O₃ was carried out. The decomposition of methane is caused by collision by excitation of unstable electronic state. Measuring the flow rate and plasma power can represent kinetic data and mechanism. The conversion of C₂ hydrocarbons was increased from 47% to 63.7% in the microwave plasma catalytic reaction within electric field. Comparing the activities of catalysts, Pd–NiO/γ-Al₂O₃ bimetallic catalyst was more active than Pt–Sn/γ-Al₂O₃ catalyst because of modifying the surface of catalysts by carbon formation. In RF plasma catalytic reaction, we obtained high C₂ yield of 72%, in which the conversion and selectivity of C₂ hydrocarbons were related to the applied power and feed rate of natural gas.     

Reduction of NO by H2 on PdO-MoO3/γ-Al2O3 of low molybdena loading

The catalytic activity and selectivity of three PdO-MoO₃/-Al₂O₃ catalysts containing about 2% Pd and 2% Mo were studied for the reduction of NO by h₂ in the presence of varying amounts of oxygen at temperatures from 50 to 550 °C. The results are compared with those for PdO/-Al₂O₃, PdO-MoO₃/-Al₂O₃ containing 2% Pd and 20% Mo, and a commercial Pt-Rh catalyst. In the absence of oxygen, the conversion of NO to N₂ and N₂O is higher on the three catalysts than it is on PdO/-Al₂O₃ at 500 and 550 °C. In the presence of oxygen, the yields of N₂ and N₂O are generally lower on two of the PdO-MoO₃/-Al₂O₃ catalysts than on PdO/-Al₂O₃.     

Microwave-assisted epoxidation of styrene with molecular O2 over sulfated Co–Y–ZrO2 solid catalyst

The microwave-assisted styrene epoxidation reaction with molecular O₂ as an oxidant was studied over a sulfated Co–Y-doped ZrO₂ solid catalyst. The microwave irradiation (400 W) resulted in similar styrene conversion and styrene oxide selectivity, in reduced time, as compared to conventional thermal heating. Higher power (800 W) of microwave irradiation decreased the styrene oxide selectivity as well as leading to the formation of styrene glycol. DMF was found to be the most suitable solvent for epoxidation of styrene with molecular O₂ under microwave irradiation and yielded maximum oxide selectivity (91%) at 120 °C. The microwave-assisted oxidation reaction resulted in time saving and is energy conserving method.     

Hydrogenation of CO on supported cobalt γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst in fixed bed and slurry bubble column reactors

Fischer-Tropsch synthesis for the production of C₅+ hydrocarbons from syngas was carried out in a tubular fixed bed reactor (TFBR) and in a slurry bubble column reactor (SBCR). The Co-based catalysts for FTS were prepared by the conventional wet-impregnation of γ-Al₂O₃. Effects of operating conditions such as GHSV (1,000–4,000 ml/g·hr), reaction temperature (220–250°C) and pressure (0.5–3.0MPa) on the CO conversion and product selectivity of Co/γ-Al₂O₃ catalyst were examined in the TFBR and SBCR. The C₅+ selectivity and olefin selectivity in an SBCR were found to be higher than that in a TFBR, whereas C₂–C₄ selectivity showed a reverse trend. The CO conversion and product distribution in an SBCR were less sensitive than that in a TFBR with variations of reaction conditions.     

Epoxidation of Styrene by Anhydrous H2O2 over TS-1 and γ-Al2O3 Catalysts: Effect of Reaction Water, Poisoning of Acid Sites and Presence of Base in the Reaction Mixture

The styrene conversion and product (viz. styrene oxide, phenyl acetaldehyde, benzaldehyde) selectivity in the liquid-phase epoxidation of styrene by H₂O₂ (H₂O₂/styrene = 2) over TS-1 (Si/Ti = 80) and -Al₂O₃ are strongly influenced by the presence of water and/or base (viz. urea and pyridine) in the reaction mixture. The TS-1 showed high styrene conversion activity but no epoxide selectivity in the absence of any base. When anhydrous H₂O₂ (24% H₂O₂ in ethyl acetate), with the continuous removal of the reaction water (using the DeanStark trap), was used instead of 50% aqueous H₂O₂, both the conversion and epoxide yield are increased drastically for the -Al₂O₃, whereas for the TS-1, the increase in the conversion was quite small and there was also no improvement in the epoxide selectivity and/or yield. However, when urea or pyridine was added in the reaction mixture, the epoxide selectivity for both the catalysts was increased depending on the concentration of the base added; the increase in the selectivity was very large for the TS-1 but small for the -Al₂O₃. Poisoning of the acid sites of the -Al₂O₃ by the chemisorbed ammonia or pyridine (at 100 °C) caused a small decrease in the conversion, but it also caused a large decrease in the epoxide selectivity. However, the pyridine poisoning of the TS-1 caused a little beneficial effect, a small increase in the epoxide selectivity. The ammonia poisoning of the TS-1, however, resulted in a small decrease in the conversion with no improvement in the epoxide selectivity. As compared to the TS-1, the -Al₂O₃ catalyst showed a much better performance in the epoxidation by anhydrous H₂O₂ with the continuous removal of the reaction water. However, the reaction water, if not removed continuously, is detrimental to the -Al₂O₃, causing a large decrease in the catalytic activity and selectivity for styrene oxide but an increase in the selectivity for benzaldehyde.     

Role of La2O3 in Pd-Supported Catalysts for Methanol Decomposition

Systems of Pd supported on various La₂O₃-modified -Al₂O₃ and CeO₂–Al₂O₃ catalysts were tested for catalytic methanol decomposition and characterized by means of XRD, BET, TPR, H₂-chemisorption and CO–FTIR. The addition of lanthanum significantly improved the selectivity of CO and H₂ for all the catalysts but showed a different influence on the catalytic activity in two systems. Methanol conversion decreased on La₂O₃-modified Pd/-Al₂O₃ catalysts, in line with the reduction of Pd dispersion, while the addition of La₂O₃ improved the dispersion of Pd and reinforced Pd–CeO₂ interaction for La₂O₃-modified Pd/CeO₂–Al₂O₃ catalysts, which resulted in a high production rate of CO and H₂. Thus, a synergistic effect between CeO₂ and La₂O₃ was observed on -Al₂O₃-supported Pd catalyst for methanol decomposition.     

Selective CO oxidation in the presence of hydrogen over supported Pt catalysts promoted with transition metals

Selective CO oxidation in the presence of excess hydrogen was studied over supported Pt catalysts promoted with various transition metal compounds such as Cr, Mn, Fe, Co, Ni, Cu, Zn, and Zr. CO chemisorption, XRD, TPR, and TPO were conducted to characterize active catalysts. Among them, Pt-Ni/γ-Al₂O₃ showed high CO conversions over wide reaction temperatures. For supported Pt-Ni catalysts, Alumina was superior to TiO₂ and ZrO₂ as a support. The catalytic activity at low temperatures increased with increasing the molar ratio of Ni/Pt. This accompanied the TPR peak shift to lower temperatures. The optimum molar ratio between Ni and Pt was determined to be 5. This Pt-Ni/γ A1₂O₃ showed no decrease in CO conversion and CO₂ selectivity for the selective CO oxidation in the presence of 2 vol% H₂O and 20 vol% CO₂. The bimetallic phase of Pt-Ni seems to give rise to stable activity with high CO₂ selectivity in selective oxidation of CO in H₂-rich stream.     

Hydrodesulfurization of dibenzothiophene over supported and unsupported molybdenum carbide catalysts

A series of γ-Al₂O₃ supported molybdenum carbides [carbided Mo/γ-Al₂O₃ (MCS), Co-Mo/γ-Al₂O₃ (CMCS), and Ni-Mo/γ-Al₂O₃ (NMCS)] and unsupported molybdenum carbide (MCUS) were prepared by the temperature-programmed carburization of their corresponding molybdenum nitrides with 20 % CH₄/H₂. XRD and SEM studies show that unsupported molybdenum carbide catalyst possesses a typical crystalline Mo₂C (FCC structure), while supported molybdenum carbide catalysts possess highly dispersed surface molybdenum carbide species on an alumina oxide support. The results of dibenzothiophene (DBT) hydrodesulfurization over molybdenum carbide catalysts show that the reactivity is strongly dependent on the type of catalyst. Supported molybdenum carbide catalysts possess a higher reactivity than the unsupported molybdenum carbide catalyst. In addition, Co or Ni promoted, supported molybdenum carbide catalyst possesses a higher reactivity than the unpromoted, supported molybdenum carbide catalyst. The reactivity, which is also dependent on the reaction conditions, increases with increasing reaction temperature and pressure and contact time. The CO uptakes of the molybdenum carbide catalysts correlate well with overall activity (total rate) for DBT hydrodesulfurization. The major reaction product is biphenyl, with cyclohexylbenzene next in abundance regardless of the type of catalysts and reaction conditions. It was also found that the molybdenum carbide catalysts exhibit stable initial reactivity due to the stable and weak acidic characteristics of these catalysts.     

H2/CO2 separation characteristics of γ-Al2O3 membrane by aging stage in sol-gel process

γ-AlO(OH) sol solution was prepared by aluminum isopropoxide as an initial material. γ-Al₂O₃ membrane on the α-Al₂O₃ support was continuously made through coating and thermal treatment from the α-AlO(OH) sol. Previous work [Yoo et al., 1997] has shown that the aging stage in the sol preparation process mainly affects the characterization of γ-Al₂O₃ particles as well as γ-AlO(OH) sol. Based on this fact, the γ-Al₂O₃ membrane was prepared with two aging conditions in the present study. The separation characteristics experiment of the H₂/CO₂ mixture was performed on these membranes. As a result of the study, the mechanism of gas transport on the two membranes was proved as Knudsen diffusion. The ideal separation factor was reached at the value of the calculated Knudsen separation factor; however, permeability increased and selectivity decreased selectivity according to the aging.     

A role of molybdenum and shape selectivity of catalysts in simultaneous reactions of hydrocracking and hydrodesulfurization

The hydrocracking and hydrodesulfurization (HDS) of n-heptane containing 0.2 mole% dibenzothiophene (DBT) were performed simultaneously using NiPtMo catalysts supported on HZSM-5, LaY and γ-Al₂O₃ in a high pressure fixed bed reactor. Molybdenum played an important role in both hydrocracking and hydrodesulfurization (HDS). We found that the sulfur compound, dibenzothiophene (DBT). in the reactant was adsorbed on a molybdenum site and converted to hydrogen sulfide so that the active sites of the catalysts for hydrocracking were less poisoned by DBT and the conversion of n-heptane over molybdenum impregnated catalyst was higher than that over molybdenum-free catalyst. The crystal structures of the molybdenum supported on the zeolite and γ-Al₂O₃ were mainly MoO_2.5 (OH)_0.5[021] and MoO₃[210] respectively as shown by XRD analysis. The structure of MoO_2.5(OH)_0.5 was easily reduced to MoS₂[003] during the reaction. After the reaction of 100 hours over the catalyst supported on γ-Al₂O₃ the crystal structure of MoO₃[210] partially changed to MoO₃[300] and the structure of MoS₂[003] was not observed. Because of the reactant shape selectivity of zeolite, the acid and the metal sites in the intracrystalline of the catalysts supported on zeolites were less poisoned by DBT. Therefore, both hydrocracking and HDS using n-heptane containing 0.2 mole% of DBT were successfully demonstrated over the prepared catalysts.