Pulse Surface Reaction Rate Analysis Research Articles

CH4/CD4 isotope effect on the reaction of adsorbed hydrocarbon species in CO2-reforming over Ni/Al2O3 catalyst

By replacing CH4 with CD4, the isotope effect on the reaction of adsorbed hydrocarbon species with CO2 over Ni/Al2O3 catalyst was studied using pulse surface reaction rate analysis (PSRA). The first-order rate constant for this step was 1.45 times larger for CH4 than for CD4. The observed isotope effect suggests that the reaction of adsorbed hydrocarbon species with CO2 (or adsorbed oxygen) is rate-controlling for the reforming of CH4.

Kinetics, intermediates and mechanism for the CO2-reforming of methane on supported nickel catalysts

The nature and the reactivity of an intermediate hydrocarbon species, CHx, ads, have been determined for the CO2-reforming of CH4 over supported Ni catalysts by using pulse surface reaction rate analysis (PSRA). When a small amount of CH4 pulse was injected into flowing gas mixture of CO2 and He, it was immediately adsorbed on the catalyst and then gradually reacted with CO2 to CO and H2. Analysis of the dynamic behaviour of the produced CO enabled us to determine the first-order rate constant for the reaction between adsorbed CH4 and CO2. It was found from the dynamics of the H2 produced that two steps were responsible for H2 production: the dissociative adsorption of CH4 to produce (4 –x)/2 H2 and CHx, ads and the simultaneous production of x/2 H2 together with CO from the CHx, ads species. Separation of the amount of H2 between these two steps led us to determine the average number of hydrogen atoms involved in the hydrogen-deficient adsorbed hydrocarbon species, i.e. 2.7 for Ni/MgO, 2.4 for Ni/Al2O3, 1.9 for Ni/TiO2 and 1.0 for Ni/SiO2. The reactivity of the intermediate species was not correlated with the number of hydrogen atoms involved. The highest activity on Ni/TiO2 and almost the same activity on Ni/MgO, Ni/Al2O3 and Ni/SiO2 were observed both for the pulse reaction and for the steady-state reaction, suggesting that the reaction of CHx, ads with CO2(or Oads) is the rate-determining step in CO2-reforming.

Highly hydrogen-deficient hydrocarbon species for the CO2-reforming of CH4 on Co/Al2O3 catalyst

The dynamics of produced CO and H2, measured by pulse surface reaction rate analysis (PSRA), revealed that the intermediate hydrocarbon species for the CO2-reforming of CH4 was highly hydrogen-deficient (CH0.75) on supported Co/Al2O3 catalyst. It was also found that the species was more reactive than the less hydrogen-deficient one (CH2.4) on Ni/Al2O3 catalyst.

Promotion effect of metal oxides on C-O bond dissociation in CO hydrogenation over Rh/SiO2 Catalyst — possible role of partially reduced state cations

In CO hydrogenation over Rh/SiO2 catalysts, the effect of additive metal oxides on C-O bond dissociation was studied by using pulse surface reaction rate analysis (PSRA). The addition of oxides of Al, Ti, Cr, V, and Mn resulted in an increase in the rate constant for the dissociation according to this sequence, while the oxides of Cu, Zn, and Ag added decreased the rate constant to almost the same extent. In contrast to these metal oxides, MoO3 and WO3 did not change the dissociation activity. CO adsorption measurement indicated that all of the added metal oxides covered a considerable portion of the Rh metal surface, although the efficiency of covering was different from one metal oxide to another. Covering the Rh metal surface with an added metal oxide should decrease the rate constant of C-O bond dissociation, because ensemble sites, consisting of a group of surface Rh atoms and considered necessary for the dissociation, were destroyed. The suppression effect resulted from the destruction of the ensemble sites by adding the oxides of Cu, Zn, and Ag. For other metal oxides, temperature-programmed reduction (TPR) or O2 uptake measurement revealed that the added oxides, especially those existing on the Rh metal surface, were in a partially reduced state under reaction conditions. Owing to its high affinity for an oxygen atom, the cation in a partially reduced state participated in the reaction in such a way that the oxygen end of adsorbed CO species was bound to the cation so as to dissociate the C-O bond, which resulted in promotion of the dissociation. The observed promotion was explained in terms of the enhancement owing to the high affinity sufficient to overcome the suppression caused by destroying ensemble sites. Lack of the promotion effect of MoO3 and WO3 might result from a balance between promotion due to the high affinity of the partially reduced Mo or W and suppression caused by destroying ensemble sites. Excellent correlation was observed between the intrinsic activity increase, from which the suppression effect was excluded, and the heat of formation of metal oxide including MoO3 and WO3. Since the heat of formation of metal oxide is considered to be a measure of the affinity, this correlation supports the idea that the high affinity of additive cations for an oxygen atom is of primary importance in the promotion of C-O bond dissociation in CO hydrogenation.

Intermediate hydrocarbon species for the CO2-CH4 reaction on supported Ni catalysts

By using pulse surface reaction rate analysis (PSRA), the detailed structure of the intermediate hydrocarbon species was revealed by measuring the dynamic behavior of both CO and H2 produced from the CO2-CH4 reaction on supported Ni catalysts. It was found that the number of hydrogen atoms involved in the intermediate was different from one catalyst support to another: 2.7 for MgO, 2.5 for ZnO, 2.4 for Al2O3,1.9 for TiO2, and 1.0 for SiO2.

Reactivity of CO on vanadium-promoted rhodium catalysts as studied with transient techniques

The effect of vanadium promotion on the kinetics of CO methanation on silica-based rhodium catalysts was probed. Transient model experiments employing temperature-programmed surface reaction spectroscopy and pulse surface reaction rate analysis were used to unravel changes in rates of elementary reaction steps. CO dissociation is the rate-limiting step in the overall methanation reaction. The rate of CO dissociation is found to be enhanced by vanadium. The activation energy is lowered from 90 kJ/mol for Rh/SiO 2 to 65 kJ/mol for the promoted catalyst. The activation energy for CO dissociation is not dependent on the hydrogen partial pressure, while it is a strong function of the CO surface coverage. CO adsorption at temperatures above 250°C results in very reactive surface carbonaceous intermediates. Even at −15°C methane formation was observed upon hydrogenation. This reactive surface carbon can be incorporated in higher hydrocarbons. This process is favoured by vanadium promotion.

Rate constant for CO insertion in the hydroformylation of ethene on Rh/SiO2 as determined by pulse surface reaction rate analysis

A new method of pulse surface reaction rate analysis (PSRA) was proposed for determining the rate constant of the step of CO insertion in ethene hydroformylation. On pulsing ethene onto Rh/SiO2 via the continuous flow of a mixture of CO and H2, propanal was found to be produced gradually. It is revealed here that rate analysis of the dynamic behavior of produced propanal allows the determination of the rate constant for CO insertion. The effect of metal carbonate and oxides, added to the catalyst, on CO insertion was discussed in terms of the rate constant determined.

Electronic effect on surface reaction rates in the carbon monoxide hydrogenation over rhodium catalysts

The promoting effect of potassium on supported Rh catalysts was studied through the rate constants for the dissociation of C-O bond and for the hydrogenation of surface carbon species determined by pulse surface reaction rate analysis (PSRA). The potassium added, which was mainly present on the support surface but not on Rh metal, varied these two rate constants in a similar fashion. With increasing amount of the potassium added, both rate constants decreased on Rh/Al{sub 2}O{sub 3} and Rh/TiO{sub 2}, while they first increased and then decreased on Rh/SiO{sub 2}. The IR absorption of adsorbed CO was also influenced by potassium in a way that the band position shifted downward with the increase in its amount. It was concluded that the role of the potassium added was to increase the electron density of a supported Rh metal, by which the dissociation of C-O bond and the hydrogenation of surface carbon species were influenced.

Design of a potassium-promoted Rh/Al2O3 catalyst for synthesis of C 2 oxygenates by pulse surface reaction rate analysis

For the synthesis of C 2 oxygenates from carbon monoxide hydrogenation, a promoted Rh/Al 2O 3 catalyst was logically designed on the basis of a working hypothesis that appropriate suppression of both C O bond dissociation and hydrogenation of the resulting surface carbon species leads to an increase in selectivity. The application of pulse surface reaction rate analysis to determine the rate constants for these two steps indicated that among unpromoted catalysts, both rate constants were relatively small on a highly dispersed Rh/Al 2O 3 catalyst. Such a catalyst yielded an IR absorption for adsorbed carbon monoxide that appeared at lower wavenumber owing to the high electron density in the rhodium metal. This led us to except substantial promotion on adding potassium carbonate to the highly dispersed Rh/Al 2O 3 catalyst, because potassium carbonate had been found to increase the electron density in metal catalysts. Good performance of the catalyst was confirmed by continuous flow hydrogenation of carbon monoxide under pressure.

Absence of the Enhanced Methanation Activity of Ni/TiO2 in the SMSI State as Examined with Pulse Surface Reaction Rate Analysis

Abstract From rate measurements with pulse surface reaction rate analysis, it was found that the methanation activity of Ni/TiO2 was the same both in the SMSI and in the normal states.

Effect of strong metal-support interaction on the rate of hydrogenation of adsorbed carbon monoxide over titania-supported noble metal catalysts as revealed by pulse surface reaction rate analysis

On the basis of the rate constant per active site determined by pulse surface reaction rate analysis (PSRA), the effect of the strong metal-support interaction (SMSI) on the hydrogenation of adsorbed CO was studied for titania-supported noble metal catalysts. Reduction at 773 K resulted in a drastic decrease in the amount of CO adsorbed on all noble metals examined. The observed suppression of CO chemisorption resulted mainly from SMSI, because the chemisorption ability was restored considerably by heating these catalysts in an O 2 atmosphere and then reducing at 523 K. It was found that the effect of SMSI on the hydrogenation of adsorbed CO was different from one noble metal to another, although its effect on CO chemisorption was common to all titania-supported noble metals. Pt and Pd exhibited a much higher hydrogenation activity in their SMSI state than in their normal state, whereas Rh, Ru, and Ir exhibited almost the same activity in both states. By heating titania-supported Pt and Pd in O 2 and then reducing at 523 K, concomitant with destruction of the SMSI state, the high hydrogenation activity disappeared to near each original value. Subsequent reduction at 773 K again brought these catalysts to the SMSI state, accompanied by an increase in their activity. From these results, a possible cause is discussed for the high activity on Pt and Pd in the SMSI state and for its absence on Rh, Ru, and Ir in the SMSI state.

Support effect on surface reaction rates in carbon monoxide hydrogenation over supported rhodium catalysts

The effect of the support and dispersion on the rate of surface reaction of CO hydrogenation over Rh catalyst was investigated by pulse surface reaction rate analysis (PSRA). TiO{sub 2}, Al{sub 2}O{sub 3}, and SiO{sub 2} were used as the supports, and the dispersion of Rh was varied over a wide range by changing the Rh loading. The rate constants of C-O bond dissociation and the hydrogenation of the surface carbon species varied with the support and dispersion. The wavenumber of the IR absorption band due to linearly adsorbed CO also varied with the support and dispersion. The results are discussed in the light of more essential factors, such as the structure sensitivity, the electron property of Rh, and the pair site of metal-support suboxide. It was concluded that the electronic state of Rh is the predominant factor leading to the changes in the surface reaction rate constants with the support and dispersion.

Activity enhancement for the hydrogenation of CO adsorbed on Pt/Al2O3 and Pd/Al2O3 induced by high-temperature reduction

On the basis of the rate constant per active site determined by pulse surface reaction rate analysis (PSRA), the effect of the reduction temperature on the hydrogenation of adsorbed CO was studied for alumina-supported noble metal catalysts. It was found that the reduction temperature influenced the hydrogenation of adsorbed CO in a different way from one noble metal to another. The rate constant on Pt prepared from H2PtCl6 was more than five times larger on reduction at 773 K than at 523 K. Heating the catalyst, exhibiting the enhanced activity, in an O2 atmosphere at 723 K followed by reduction at 523 K resulted in a decrease in the rate constant to near its original value. The rate constant on Pd also varied with heat treatments in a way similar to that for Pt, although the activity enhancement was less pronounced. In contrast, no activity enhancement was observed on Rh and Ru. It was also found that the activity enhancement strongly depended on the metal precursor or preparation conditions : the Pt catalyst prepared from [Pt(NH3)4]Cl2 did not exhibit enhanced activity even after reduction at 773 K. Compared with the effect on the hydrogenation of adsorbed CO, the reduction temperature hardly influenced CO chemisorption for all noble metals examined. On the basis of the results obtained, a possible cause is discussed for the enhanced activity on Pt and Pd and for the absence of enhancement on Rh and Ru.

Design of Fischer-Tropsch catalysts by pulse surface reaction rate analysis: Part III. Optimum Amount of Vanadium Oxide Added to Ruthenium/Alumina Catalyst for Liquid Fuel Production

For the selective production of liquid fuels from carbon monoxide hydrogenation, the effect of the amount of vanadium oxide added to Ru/Al 2O 3 catalyst was investigated. In the continuous flow carbon monoxide hydrogenation under pressure, the highest selectivity for production of a liquid fuel fraction was obtained using a catalyst with a very low vanadium oxide content. Such a favorable condition was also shown from rate measurements by pulse surface reaction rate analysis (PSRA) for the dissociation of the C O bond and for the hydrogenation of the surface carbon species produced therefrom; the ratio of these two rate constants can be a measure of the relative concentation of the surface carbon species, the larger value of which leads to higher selectivity for liquid fuels. The optimum amount of vanadium oxide added was discussed in terms of the relative numbers of Ru Ru, Ru V, and V V pair sites and also of the dispersion of vanadium oxide on the ruthenium metal surface, both of which were evaluated from chemisorption measurements of carbon monoxide and hydrogen.

Design of fischer-tropsch catalysts by pulse surface reaction rate analysis: II. Selective Production of Liquid Fuel Fraction on Ruthenium/Alumina Catalyst Promoted by Rare Earth Oxides

For selective production of liquid fuels, Fischer-Tropsch catalysts were designed by adding rare earth oxides to ruthenium/alumina on the basis of the following working hypothesis; the redox property should lead to the enhancement of the dissociation of the C O bond and accordingly to high activity and selectivity, and the basic property should further improve the selectivity. PSRA (pulse surface reaction rate analysis) measurements revealed that in the hydrogenation of carbon monoxide on ruthenium/alumina, probably due to the redox property, rare earth oxide increased the rate constant for the dissociation of the C O bond and decreased that for the hydrogenation of the resulting surface carbon species. In the continuous flow hydrogenation of carbon monoxide under pressure, it was found that the addition of rare earth oxides resulted in an increase in the turnover frequency, as expected from the enhanced C O bond dissociation. Consistent with the results obtained from PSRA experiments, rare earth oxide also increased the selectivity for the production of higher hydrocarbons. The selectivity improvement was more pronounced than that by the oxides of vanadium, niobium, molybdenum and tungsten, which may be ascribable to the basic property of rare earth oxides.

Another strong metal–support interaction: high intrinsic methanation activity of an alumina-supported platinum catalyst after high temperature reduction without loss of chemisorption ability

It has been found from pulse surface reaction rate analysis measurements that the intrinsic methanation activity of an alumina-supported platinum catalyst was increased by high temperature reduction without a marked reduction in its chemisorption ability.

Absence of high methanation activity of titania-supported rhodium, ruthenium and iridium catalysts in their strong metal–support interaction state

From pulse surface reaction rate analysis measurements, it was found that the high intrinsic methanation activity of titania-supported rhodium, ruthenium, and iridium catalysts was absent in their strong metal–support interaction state.

ChemInform Abstract: Rate Constants of Surface Reactions in Methanation over Ru/Al2O3 Catalyst As Determined by Pulse Surface Reaction Rate Analysis.

Chemischer InformationsdienstVolume 17, Issue 19 Preparative Organic ChemistryToken Access ChemInform Abstract: Rate Constants of Surface Reactions in Methanation over Ru/Al2O3 Catalyst As Determined by Pulse Surface Reaction Rate Analysis. T. MORI, Search for more papers by this authorA. MIYAMOTO, Search for more papers by this authorH. NIIZUMA, Search for more papers by this authorN. TAKAHASHI, Search for more papers by this authorT. HATTORI, Search for more papers by this authorY. MURAKAMI, Search for more papers by this author T. MORI, Search for more papers by this authorA. MIYAMOTO, Search for more papers by this authorH. NIIZUMA, Search for more papers by this authorN. TAKAHASHI, Search for more papers by this authorT. HATTORI, Search for more papers by this authorY. MURAKAMI, Search for more papers by this author First published: May 13, 1986 https://doi.org/10.1002/chin.198619097AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume17, Issue19May 13, 1986 RelatedInformation

High activity of strong metal–support interaction catalysts for carbon monoxide hydrogenation revealed by pulse surface reaction rate analysis

By use of pulse surface reaction rate analysis, it was found that the active sites on titania-supported Pt and Pd catalysts for methanation were much more active in the strong metal–support interaction state than in the normal state.

Rate constants of surface reactions in methanation over ruthenium/alumina catalyst as determined by pulse surface reaction rate analysis

By use of a new PSRA (pulse surface reaction rate analysis) apparatus equipped with an emissionless infrared diffuse reflectance spectrometer (EDR) and a flame ionization detector (FID), the dynamics of both adsorbed CO and produced CH/sub 4/ were simultaneously measured in the CO hydrogenation over Ru/Al/sub 2/O/sub 3/ catalyst. When a CO pulse was introduced to the catalyst via the H/sub 2/ at temperatures above 405 K, an IR absorption band assignable to a linearly adsorbed CO appeared at 2040 cm/sup -1/. At the same time an FID response of CH/sub 4/ quickly increased. It was found that k/sub CH/sub x// is more than 50 times larger than k/sub CO/, indicating that on the Ru/Al/sub 2/O/sub 3/ catalyst the formation of (CH/sub x/)/sub ad/ from adsorbed CO is much slower than its hydrogenation to CH/sub 4/. Furthermore, an H/sub 2/-D/sub 2/ inverse isotope effect was observed for k/sub CO/, suggesting that hydrogen atoms play an important role in the C-O bond dissociation in the CO hydrogenation. A mechanism of the C-O bond dissociation was also discussed on the basis of these results for k/sub CO/. 7 references, 17 figures, 2 tables.