Yasuyuki Matsumura

The influence of the support on the activity and selectivity of Pd in CO hydrogenation

Abstract Catalytic hydrogenation of carbon monoxide was studied over Pd supported on Al2O3, SiO2, TiO2, and ZrO2. Both the activity and the selectivity of the catalysts were strongly affected by the nature of the support. As a major product, Pd/Al2O3 produces dimethyl ether, Pd/SiO2 favors methanol formation, Pd/TiO2 produces CH4, and Pd/ZrO2 yields methanol. Higher CO conversions over Pd/ZrO2 and Pd/TiO2 were ascribed to the presence of cationic palladium species formed through the metal–support interaction. Significant dimethyl ether formation over Pd/Al2O3 was attributed to the acidity of the support metal oxide. The catalytic natures of Pd catalysts were discussed based on the results of catalyst characterization by XPS, TEM, and temperature-programmed reduction and desorption.

Photocatalytic decomposition of NO at 275 K on titanium oxide catalysts anchored within zeolite cavities and framework

Abstract Titanium oxide species prepared in the Y-zeolite cavities via an ion-exchange method and those of the Ti-silicalite catalyst prepared hydrothermally exhibit high photocatalytic reactivity for the direct decomposition of NO into N2, O2 and N2O at 275 K with a high selectivity for the formation of N2. The in situ photoluminescence and XAFS investigations indicate that these titanium oxide species are highly dispersed and exist in a tetrahedral coordination in the zeolite cavities and its framework. The charge transfer excited state of these titanium oxide species plays a significant role in the direct decomposition of NO with a high selectivity for the formation of N2, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species and the bulk powdered TiO2 catalyst mainly produce N2O.

Decomposition of methanol on Pt-loaded ceria

Abstract Methanol was decomposed to carbon monoxide and hydrogen on supported precious metals. Among the precious metals examined the performance of Pt was found to be the best, and ceria was the best support. Pt/CeO2 decomposed methanol completely at 230°C with 99.2% and 94.6% of selectivities to H2 and CO, respectively. TEM, ESCA, and XAFS analyses showed that Pt interacted very strongly with ceria, indicating the possibility of the formation of Pt–O–Ce bond and the penetration of Pt into the bulk ceria. The reaction mechanism was discussed on the basis of the kinetic analysis.

Low-temperature decomposition of methanol to carbon monoxide and hydrogen with low activation energy over Pd/ZrO2 catalyst

Palladium nano-particles in 2 wt% Pd/ZrO2 prepared by the deposition-precipitation method interact strongly with zirconium oxide. The catalyst is significantly active to the methanol decomposition to carbon monoxide and hydrogen at less than 500 K with the apparent activation energy of ca. 80 kJ mol-1 compared with 2 wt% Pd/ZrO2 prepared by the impregnation technique which produces the activation energy of ca. 100 kJ mol-1.

Catalytic methanol decomposition to carbon monoxide and hydrogen over nickel supported on silica

Abstract The decomposition of methanol to carbon monoxide and hydrogen can be catalyzed at 250°C over nickel supported on silica. The activity of the catalyst prepared by a sol–gel method increases with an increase in the content of nickel up to 40 wt.% while that for the sample prepared by an impregnation technique almost reaches a plateau at the nickel content of 10 wt.%. The activity does not relate simply to the nickel surface area of the sample, but it depends on the amounts of carbon monoxide and hydrogen strongly adsorbed on the catalyst. Small nickel particles are disadvantageous in the reaction.

Selective dehydrogenation of ethanol over highly dehydrated silica

Abstract Silica dehydrated above ca. 1000 K selectively converts ethanol to acetaldehyde, and the dehydrogenation proceeds according to Langmuir-Hinshelwood kinetics. Measurement of phosphorescence spectra confirmed that new sites are formed on silica by preheating above ca. 1000 K, but the dehydrated silica showed no acidity or basicity which might have been responsible for the dehydrogenation activity. Infrared spectra indicated dissociative adsorption of ethanol on the dehydrated silica and we infer that the adsorption site is an active SiOSi oxygen bridge formed by the dehydration of silica at high temperature, and that the reaction intermediate is formed by the dissociative adsorption of ethanol accompanying cleavage of that oxygen bridge.

Interaction between palladium and the support in Pd/CeO2 prepared by deposition-precipitation method and the catalytic activity for methanol decomposition

Abstract Adsorption of carbon monoxide on cerium oxide at room temperature can proceed over 3 wt.% Pd/CeO 2 prepared by a deposition–precipitation method. The quantity of carbon monoxide adsorbed is largely excessive to the content of palladium in the sample while the amount of carbon monoxide adsorbed on 3 wt.% Pd/CeO 2 prepared by the conventional impregnation technique is small. The catalyst prepared by deposition–precipitation is highly active for the methanol decomposition to carbon monoxide and hydrogen at 160°C–220°C compared with the impregnated sample. Analyses by XPS show presence of cationic palladium species in the former catalyst after the reaction while only metallic species can be found in the latter, appearing that there is strong interaction between the palladium species and the support in the catalyst prepared by deposition–precipitation.

Methanol synthesis from carbon monoxide and hydrogen catalyzed over Pd/CeO2 prepared by the deposition–precipitation method

Ceria‐supported palladium catalysts prepared by the deposition–precipitation method are highly active for the methanol synthesis from carbon monoxide and hydrogen in comparison with the catalyst prepared by the conventional impregnation method. Analyses by EXAFS show that palladium particles can be dispersed very well on the surface of ceria by both the methods, implying that the higher activity of the catalysts prepared by deposition–precipitation is not simply due to the particle size of palladium. Cationic palladium species are present in the samples prepared by deposition–precipitation after reduction with hydrogen at 300 °C, suggesting that the active species are produced by strong contact between palladium particles and the support.

Oxidative methane conversion to carbon monoxide and hydrogen at low reactor wall temperatures over ruthenium supported on silica

Oxidative methane conversion to carbon monoxide and hydrogen is catalyzed over ruthenium supported on silica at reactor wall temperatures as low as 400° C when the flow rate of reactants (methane and oxygen) is significantly high. The conversion of methane and the yields of carbon monoxide and hydrogen increase with increase in the flow rate of the reactants while oxygen is always completely consumed. Addition of carbon dioxide to the reactant flow can increase the yield of carbon monoxide in the reaction, suggesting that carbon dioxide functions as an oxidant and the actual surface temperature of the catalyst is sufficiently high that thermal conversion of methane via carbon dioxide and water can take place.

Low-temperature methanol decomposition to carbon monoxide and hydrogen catalysed over cationic palladium species in Pd/CeO2

Methanol can be selectively decomposed to carbon monoxide and hydrogen at a reaction temperature as low as 433 K over ceria-supported palladium catalysts prepared by deposition–precipitation and by impregnation methods, with the former method resulting in the higher catalytic activity. Cationic palladium species can be present in the catalyst prepared by deposition–precipitation even after reduction with hydrogen at 773 K. On the other hand, metallic palladium is the major species in the impregnated catalyst. A largely excessive amount of carbon monoxide over the palladium content is adsorbed at room temperature on the deposition–precipitation samples when reduced at 573 K, however, this phenomenon does not occur with the impregnation method. This suggests that the cationic palladium species enhance the transfer of carbon monoxide from the palladium sites to the ceria surface at room temperature. The adsorption strength of carbon monoxide on the cationic species is probably weaker than on the metallic surface, this may be advantageous in the methanol decomposition, which is suppressed in the presence of carbon monoxide.