Ryuichiro Ohnishi

Selective hydrodechlorination of CFC-113 on Bi- and Tl-modified palladium catalysts

Abstract More than 80% selectivity in the hydrodechlorination of 1,1,2-trichlorotrifluoroethane (CFC-113) has been observed over palladium catalysts containing selected metal additives such as Ag, Bi, Cd, Cu, Hg, In, Pb, Sn, Tl to chlorotrifluoroethene (3FCl) and trifluoroethene (3FH). In particular, a bismuth modified palladium catalyst supported on SiO 2 and a thallium modified catalyst on active carbon provided 3FH and 3FC1 with more than 90% yield at 520-600 K. Kinetic studies suggest that the reaction route is CFC-113→ 3FC1→ 3FH and that the role of the metal additives is to suppress the hydrodechlorination of 3FC1 to 3FH or further hydrogenation of 3FH. The thermodynamic estimations imply that the modifier plays another role in the inhibition of hydrodefluorination. The IR studies of carbon monoxide chemisorption on the modified palladium catalysts show that the addition of bismuth or thallium leads to a drastic suppression of bridged carbon monoxide on palladium and to the enhancement of linear carbon monoxide. This shift indicates that the addition of the promoter results in the breaking the ensembles of palladium atoms. Further evidence for this mechanism comes from the temperature-programmed reduction spectra, where a reduction peak shifts to higher temperature. X-ray diffraction spectra, where a broad peak based on palladium shifted to low angle of 2θ by the addition of thallium, indicates the formation of Tl-Pd alloy or intermetallic compound.

Methanol electrooxidation on platinum directly bonded to a solid polymer electrolyte membrane

Abstract Methanol electrooxidation in perchloric acid solution was performed on platinum directly bonded to a solid polymer electrolyte (Pt-SPE) membrane. The initial catalytic activity of platinum on either a cation or anion-exchange membrane of the SPE was comparable with that of platinized platinum(pt-Pt). After an initial sharp deactivation in a short time at the polarization, the Pt-SPE was found to retain high activity for a long duration, whereas the pt-Pt showed a considerable decrease in the activity during the polarization. A surface mediator action of Pt 0 and Pt 2+ was stressed as essential for the durability of a high catalytic activity of Pt-SPE, and it was suggested that the matrix stabilized the platinum at a higher oxidation state, Pt 2+

Pronounced catalytic activity and selectivity of MgO–SiO2–Na2O for synthesis of buta-1,3-diene from ethanol

MgO–SiO2(molar ratio = 1 : 1)prepared from ethyl orthosilicate and magnesium nitrate and promoted with 0.1 wt% Na2O exhibited a high catalytic activity (100%) and selectively (87%) for formation of buta-1,3-diene at 350 °C.

Novel rhenium-based catalysts for dehydrocondensation of methane with CO/CO2 towards ethylene and benzene

A new family of rhenium‐based catalysts bearing HZSM‐5 zeolite exhibits remarkable performances for the catalytic dehydrocondensation of methane with CO/CO2 towards ethylene, benzene, and naphthalene in high selectivity of above 90% at 1–3 atm and 973–1023 K. In contrast to Mo/HZSM‐5 catalysts, the EXAFS and TG/DTA/Mass studies reveal that the metallic Re on HZSM‐5 zeolite is a catalytically active and stable phase for the reaction.

Studies of the selective reduction of nitric oxide by carbon monoxide in the presence and absence of hydrogen over Au/NaY catalysts

The selective reduction of NO with CO in the presence and absence of hydrogen over Au/NaY catalysts has been studied by in situ FTIR spectroscopy and under steady-state conditions in a flow mode in the temperature range 473–723 K. The NCO intermediates found by FTIR absorption at 2280–2240 cm–1 after contacting, at 423–573 K, an Au/NaY catalyst with an NO–CO–H2 mixture shows a dependence on the presence of H2 which functions in N—O dissociation in this temperature region. Removal of NCO groups from the catalyst with time at 473 K, proposed to be limited by the prerequisite reaction between adsorbed NCO and NO in the gas phase, to form N2 and CO2 is accelerated with increasing temperatures. The effect of adding H2 to an NO–CO–He stream on the conversions of both NO and CO to, respectively, N2 and CO2 were found to be consistent with a temperature-dependent mechanism. The yields of N2 and CO2 were increased in the presence of hydrogen, when NCO complexes were present on the gold catalyst, up to 573 K. Above this temperature, where direct NO + CO is the only competing reaction, the presence of hydrogen reduced conversion. The activities of the gold catalysts were maintained even at temperatures as high as 723 K, suggesting that a large fraction of partially charged AuI cations were stabilized by the framework of NaY zeolite. This species, after pumping off the reacting mixture gases at 473 K and collecting the spectra on cooling the gold catalyst, gave a characteristic carbonyl IR absorption band at 2188 cm–1, reasonably assigned to a CO vibration of carbonyl coordinated to AuI.

Marked Enhancement of the Methane Dehydrocondensation Toward Benzene Using Effective Pd Catalytic Membrane Reactor with Mo/ZSM-5

Steady state product formation rates of benzene, hydrogen, naphthalene, toluene in methane dehydrocondensation reaction on 3 wt% Mo loaded ZSM-5 catalyst was enhanced 2–10 times by the removal of hydrogen using Pd membrane for 100 h at 883 K. The amount of permeated hydrogen through the Pd membrane was measured before and during the methane dehydrocondensation reaction. About 50–60% of hydrogen from the total hydrogen produced during the methane dehydrocondensation was selectively removed by the Pd membrane, owing to which the equilibrium of the methane dehydrocondensation was shifted toward the product side.

Improved methane dehydrocondensation reaction on HMCM-22 and HZSM-5 supported rhenium and molybdenum catalysts

As one of a few possible catalysts for the methane dehydrocondensation reaction towards benzene and naphthalene, novel Re/HMCM-22 was investigated. Results were compared with those from other HMCM-22 and HZSM-5 supported rhenium and molybdenum catalysts. Re/HMCM-22 was similarly active and selective catalyst for the reaction as Mo/HZSM-5, Re/HZSM-5 and Mo/HMCM-22 catalysts. The catalytic performances of HMCM-22 supported rhenium and molybdenum catalysts were characteristic of higher benzene selectivities and lower naphthalene selectivities as well as of higher catalytic stability than those of HZSM-5 supported catalysts. The differences of catalytic behavior between HMCM-22 and HZSM-5 supported catalysts are mainly related to their different channel structures, where HMCM-22 has large cavities and slit-like pore openings. The catalytic stabilities of HMCM-22 and HZSM-5 supported catalysts were improved greatly by the addition of a few percent of carbon dioxide in methane feed and by the acid-reflux pre-dealumination of HMCM-22 and HZSM-5 supports, owing to the effective suppression in the formation of carbonaceous deposit, which was revealed by the temperature-programmed oxidation (TPO) study of used catalysts. The analysis of solid-state aluminum and proton NMR studies shows that Bronsted acid sites on zeolite support promotes the formation of harmful carbonaceous deposit on the catalyst surface and, hence, that the partial reduction of the Bronsted acid sites by acid-reflux treatment enhances their catalytic stabilities. Extended X-ray absorption fine structure (EXAFS) analysis reveals that both molybdenum carbide and metallic rhenium on HMCM-22 are responsible for the methane activation, similar to the case of supporting on HZSM-5.

Catalytic dehydroaromatization of methane with CO/CO2 towards benzene and naphthalene on bimetallic Mo/zeolite catalysts : Bifunctional catalysis and dynamic mechanism

In recent years a great challenge and intriguing problem in hetergogeneous catalysis is the catalytic dehydrocondensation of natural gas into useful petrochemical feed stocks such as ethylene by the oxidative coupling of methane over Li/MgO and Sm 2 O 3 catalysts and the lower hydrocarbons by the two-step conversion of methane on Co and Ru catalysts, while they have not been feasible yet due to the lower yields and selectivities.

Highly Stable Performance of Methane Dehydroaromatization on Mo/HZSM-5 Catalyst with a Small Amount of H2 Addition into Methane Feed

With a small amount of H2 (3 ∼ 6%) addition into methane feed, coke formation on 6 wt% Mo catalyst during the methane dehydroaromatization reaction was effectively suppressed and the catalyst stability was increased evidently under the reaction conditions of 1023K, 0.3MPa and 2520 mL g-MFI-1 h-1 of methane space velocity.

Stable and Selective Dehydrocondensation of Methane Towards Benzene on Modified Mo/HMCM-22 Catalyst by the Dealumination Treatment

A modified Mo/HMCM-22 catalyst by the dealumination treatment (Mo/HMCM-22-D) exhibited remarkable performance for the catalytic dehydrocondensation of methane with a higher selectivity of benzene and a lower selectivity of coke, in comparison with the same Mo catalyst supported on parent HMCM-22 (Mo/HMCM-22). Excellent catalytic stability as well as a high benzene formation rate of 1500 nmol/(g-cat·s) was obtained on a 6%Mo/HMCM-22-D catalyst at 1023 K, 3 atm and 2700 ml/(g·h) owing to the efficient suppression of coke formation. Dealumination of the HMCM-22 zeolite was characterized by XRD, 27Al and 1H MAS NMR and NH3-TPD techniques. It was found that the dealumination treatment of HMCM-22 zeolite resulted in an effective suppression of acid sites, particularly the Brønsted acid sites (proton form in Al--O--Si) owing to the removal of tetrahedral framework aluminum, while the microporous structure and the zeolite framework remained unchanged. It was suggested that the stable and selective dehydrocondensation of methane towards benzene is based on the suppression of coke formation owing to the effective decrease of strong Brønsted acid sites by the dealumination treatment of the HMCM-22 zeolite.