Na-oki Ikenaga

Oxidative dehydrogenation of ethylbenzene with carbon dioxide

Abstract An attempt to use carbon dioxide as a diluent and oxidant in the dehydrogenation of ethylbenzene to styrene was carried out over an activated carbon-supported iron catalyst ( Fe 17 wt.-% ) at 773–973 K, CO2/ethylbenzene= 50-70 mol/mol and W/F= 30–120 g h/mol. An addition of 20–30 mol-% lithium nitrate to iron resulted in a significant increase in the catalytic activity. The highest yield of styrene (40–45%) with more than 90% selectivity was obtained at a ratio of lithium to iron of 0.1–0.2 (mol/mol). In addition to styrene, carbon monoxide and water were formed as products. This indicated that the reaction proceeds via an oxidative dehydrogenation mechanism. Added lithium nitrate was converted into lithium ferrite during the treatment of an iron-lithium co-loaded activated carbon catalyst under carbon dioxide at 973 K. Lithium ferrite thus formed would be an active center of the reaction.

Promoting effect of carbon dioxide on the dehydrogenation and aromatization of ethane over gallium-loaded catalysts

Ga2O3 and Ga2O3/TiO2 catalysts were found to be effective agents for the dehydrogenation of ethane to ethene in the presence of carbon dioxide at 650 °C. The activity of the Ga2O3 and Ga2O3/TiO2 catalysts in the presence of CO2 was 2–4 times higher than that without CO2. Ethene yields reached ca. 20–25% and selectivity was ca. 70–90% at 650°C in the 17% ethane and 83% CO2 feed at an SV of 9,000 ml/(g‐cat h). The presence of CO2 markedly promoted dehydrogenation of ethane over Ga2O3 and Ga2O3/TiO2 catalysts. Furthermore, the promoting effect of CO2 on the aromatization of ethane and ethene over a Ga2O3+H/ZSM‐5 catalyst was also observed above 650 °C. Aromatics yields were higher than those without CO2.

Dehydrogenation of light alkanes over oxidized diamond-supported catalysts in the presence of carbon dioxide

Oxidized diamond demonstrated excellent support for the dehydrogenation of light alkanes to alkenes in the presence of CO 2 . Oxidized diamond-supported Cr 2 O 3 and V 2 O 5 catalysts exhibited comparatively higher catalytic activities in the dehydrogenation of lower alkanes in the presence of CO 2 . In the dehydrogenation of propane, the oxidized diamond-supported Cr 2 O 3 and V 2 O 5 catalysts in the presence of CO 2 afforded nearly twofold higher activities than that in the absence of CO 2 . The activity of the oxidized diamond-supported V 2 O 5 catalyst in the dehydrogenation of propane increased with increasing reaction temperatures. Furthermore, in the dehydrogenation of n-butane and iso-butane, a promoting effect of CO 2 on butane conversion and butenes yields was observed over the oxidized diamond-supported Cr 2 O 3 and V 2 O 5 catalysts, though the promotion effect was small. UV-Vis analyses of the fresh and the reacted catalysts in the presence and absence of CO 2 revealed that CO 2 kept the surface V 2 O 5 and Cr 2 O 3 in a state of oxidation slightly higher than that in the absence of CO 2 .

Effect of support on the conversion of methane to synthesis gas over supported iridium catalysts

A partial oxidation of methane was carried out using iridium catalysts supported on several metal oxides. The productivity of the synthesis gas from methane was strongly affected by the choice of support oxides for the catalysts. The synthesis gas production proceeded basically via a two-step reaction consisting of methane combustion to give H2O and CO2, followed by the reforming of methane from CO2 and steam. Although the combustion and the reforming of methane from steam did not depend upon the catalyst support, a large variation in the catalytic activity for the reforming of methane from CO2 was observed over Ir catalysts with different supports. The support activity order in the reforming of methane from CO2 with iridium catalysts was as follows: TiO2≧ZrO2≧Y2O3>La2O3>MgO≧Al2O3>SiO2. The same order was observed in the synthesis gas production from the partial oxidation of methane.

Reaction mechanisms of carbon dioxide reforming of methane with Ru-loaded lanthanum oxide catalyst

Abstract A pulsed reaction technique was applied to discuss the effect of support on the activities and mechanisms in the CO2 reforming of methane over Ru catalyst. The reaction was carried out using a fixed bed reactor equipped with an on-line mass spectrometer. Four supports: La2O3, Y2O3 and ZrO2 which showed high activity and Al2O3, commonly used one in the reforming reaction, were compared when loaded with Ru. After feeding CO2 at 600°C, we introduced a pulse of CH4 over Ru/La2O3 catalyst under Ar steady flow. We observed the response of CO which was generated from the reaction with CHx on the ruthenium and the Ru–Ox formed during CO2 treatment or during the reaction of Ru–CHx with adsorbed CO2 onto the La2O3. Over Ru/Al2O3 catalyst, however, very small response of CO was observed. A pulse of 13 CO 2 was introduced under CH4 steady flow over Ru/La2O3, Ru/Y2O3 and Ru/ZrO2 catalysts. Symmetrical 13 CO responses were observed, but a small response of 12 CO from 12 CH x continued to evolve after generation of 13 CO from 13 CO 2 ceased. The following reaction cycle is believed to occur in the CO2 reforming of methane on active supports: A part of metallic ruthenium reacted with CH4 to give Ru–CHx; simultaneously ruthenium metal could be oxidized with CO2 to give Ru–Ox and CO; and then, oxygen transfer from Ru–Ox to Ru–CHx took place to give CO and metallic ruthenium. Distinct temperature increases in the catalyst bed for La2O3, Y2O3 and ZrO2 supports were observed with the introduction of CO2 pulses under Ar flow. On the other hand, a very small increase in the temperature of the catalyst bed was observed on Al2O3. These results indicate that CO2 reforming of CH4 with ruthenium loaded catalysts was strongly assisted by the activation of CO2 adsorbed on the basic sites.

Role of lattice oxygen of metal oxides in the dehydrogenation of ethylbenzene under a carbon dioxide atmosphere.

The mechanism for the dehydrogenation of ethylbenzene over V, Cr, and Fe oxides loaded on activated carbon, powdered diamond, Al(2)O(3), and MgO was studied in the presence of CO(2). Vanadium oxide-loaded catalysts provided higher styrene yields under CO(2) than Ar flow. The transient response method was carried out to understand the reaction behaviors of lattice oxygen of various metal oxides on the support. The results showed that lattice oxygen of vanadium oxide (V=O) was consumed in the dehydrogenation reaction and that reduced vanadium oxide was reoxidized with CO(2). A similar redox cycle was observed on iron oxide-loaded activated carbon catalyst. Spectroscopic characterization revealed that vanadium oxide and iron oxide on the support were reduced to a low valence state during the dehydrogenation reaction, and that CO(2) could oxidize the reduced metal oxides. In contrast, chromium(III) oxide was not reduced during dehydrogenation. From these findings, the redox cycle over vanadium oxide- and iron oxide-loaded catalysts was concluded to be an important factor in promoting the catalytic activity with CO(2).

Catalytic activity of iron compounds for coal liquefaction

Abstract The catalytic activity of pyrite and synthesized α-FeOOH in coal liquefaction was investigated using batch autoclaves with the aim of developing an industrial iron catalyst. The results indicate that the presence of H 2 S helps gaseous hydrogen transferring and prevents deactivation so that the catalyst promotes hydrocracking of coal and hydrogenation of the products. The activity converges with excess H 2 S and sulfur addition equivalent to an S/Fe molar ratio of 2.0 being reasonable for the activation. The active site is located on the outer surface, with finely divided catalysts exhibiting high activity. Both pulverized pyrite and synthesized α-FeOOH are sufficiently fine as to exhibit high activity in the process. Pulverized pyrite is an industrially feasible iron catalyst for coal liquefaction process, because it is inexpensive and does not require sulfur addition.

Transient response of catalyst bed temperature in the pulsed reaction of partial oxidation of methane to synthesis gas over supported group VIII metal catalysts

Mechanisms of partial oxidation of methane to synthesis gas were studied using a pulsed reaction technique and temperature jump measurement. Catalyst bed temperatures were directly measured by introducing 1 and 3 ml pulses of a mixture of CH 4 and O 2 (2/1). With Ir, Pt and Ni/TiO 2 catalysts, a sudden temperature increase at the front edge of the catalyst bed was observed upon introduction of the pulse. The synthesis gas production basically proceeded via two-step paths consisting of highly exothermic complete methane oxidation to give H 2 O and CO 2 , followed by the endothermic reforming of methane with H 2 O and CO 2 . In contrast, with the Rh and Pd/TiO 2 catalysts, the temperature at the front edge of the catalyst bed decreased upon introduction of the CH 4 /O 2 (2/1) pulse and a small increase in the temperature at the rear end was observed. Initially, the endothermic decomposition of CH 4 to H 2 and deposited carbon or CH x probably took place at the front edge of the catalyst bed, after which the deposited carbon or generated CH x species would be oxidized into CO x . When the Ru/TiO 2 catalyst was used, a temperature increase at the front edge of the catalyst bed was observed upon introduction of the 3 ml pulse of CH 4 /O 2 . In contrast, the temperature drop at the front edge of the catalyst bed was observed for a 1 ml pulse of CH 4 /O 2 . These results seemed to exhibit two possibilities for a synthesis gas formation route over the Ru/TiO 2 catalyst. The reaction pathway of the partial oxidation of methane with group VIII metal-loaded catalysts depended strongly upon the metal species and reaction conditions.

Partial Oxidation of Methane to Synthesis Gas Over Ru-Loaded Y2O3 Catalyst

Ru-loaded Y2O3 catalyst was investigated for the partial oxidation of methane to synthesis gas. Ru(0.5 wt%)/Y2O3 catalyst afforded a high CH4 conversion of 27% at a CH4:O2 ratio of 5 to give nearly a 1:2 ratio of CO and H2 with a selectivity of 75% at 873 K. Ru(0.5 wt%)/Y2O3 catalyst maintained high catalytic activity over 10 h in the partial oxidation of methane. Carbon deposition of the catalyst surface in the reaction of CH4 was examined by thermogravimetric analyses, and it was found that no carbon deposition occurred on the Ru(0.5 wt%)/Y2O3 catalyst. The synthesis-gas production proceeded basically via a two-step reaction consisting of methane combustion to give H2O and CO2, followed by the reforming of methane from CO2 and steam.

Diamond-Supported Metal Catalyst: A Novel Medium for Hydrogen Production from Methanol Decomposition

Oxidized diamond-supported Ni catalysts gave the best performance among the oxidized diamond-supported various metal catalysts for the decomposition of methanol to synthesis gas. Ni (5 wt%)/oxidized diamond afforded 82.5% conversion of methanol to give a CO to H2 ratio of 1.7 at 573 K.