A Transient Kinetic Study of the Carbon Dioxide Reforming of Methane over Supported Ru Catalysts

Ferreira-Aparicio, Paloma; Márquez‐Álvarez, Carlos; Rodrı́guez-Ramos, I.; Schuurman, Y.; Guerrero-Ruı́z, A.; Mirodatos, C.

doi:10.1006/jcat.1999.2439

Cited by 100 publications

(66 citation statements)

References 25 publications

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“…The 13 C content corresponds to complete chemical and isotopic equilibration between CO and CO 2 , even at CH 4 chemical conversion levels (6.4%) far from equilibrium (η ) 0.06). These data indicate that CO 2 activation steps are much faster than kinetically relevant CH 4 dissociation steps, and that steps (12) and (14) occur in both directions many times in the time required for a CH 4 chemical conversion turnover. Thus, CO 2 activation steps are reversible and quasi-equilibrated during CH 4 -CO 2 reactions and by kinetic analogy also during CH 4 -H 2 O reactions at similar reaction conditions.…”

Section: Reforming Reactionsmentioning

confidence: 82%

“…Steps (12) and (14)-(19) in Scheme 1 describe the reverse water-gas shift reaction, which must, in view of the equilibrated nature of its component steps, also be quasi-equilibrated during CH 4 reforming reactions on Ru-based catalyst (Figure 2). Indeed, we find that the approach to equilibrium for this reaction, estimated from the prevalent concentrations of all reactants and products, is near unity at all conditions ( Figure 2).…”

Section: Reforming Reactionsmentioning

confidence: 99%

“…Ru clusters with a range of dispersion were prepared by varying the metal content, the reduction temperature, and the identity of the support. Turnover rates were calculated from forward rates normalized by the number of exposed Ru atoms; they are shown for CH 4 12 Portugal et al, 18 and Solymosi et al 3 on Ru-based catalysts are also shown in Table 1. We have corrected these literature rates for approach to equilibrium and extrapolated to our reaction conditions (873 K, 20 kPa CH 4 ) using a first-order CH 4 dependence and the activation energies reported in each literature report (92.5 kJ/ mol, Solymosi et al 3 ; 106 kJ/mol, Bradford et al 2 ).…”

Section: Reforming Reactionsmentioning

confidence: 99%

“…Fischer 12,17 NaY, 18 and carbon 2,19 effectively catalyze these reactions. The relevant elementary steps and the effects of metal dispersion and support on reaction rates have not been unequivocally established on supported Ru catalysts.…”

Section: Introductionmentioning

confidence: 99%

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Reaction Pathways and Site Requirements for the Activation and Chemical Conversion of Methane on Ru−Based Catalysts

2004

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Kinetic and isotopic tracer and exchange measurements were used to determine the identity and reversibility of elementary steps required for CH 4 reforming reactions on Ru-based catalyst. These studies provide a simple mechanistic picture and a unifying kinetic treatment for CH 4 /CO 2 and CH 4 /H 2 O reforming reactions and CH 4 decomposition. Forward kinetic rates were measured from net rates by correcting for the approach to equilibrium, after ruling out transport artifacts using pellet and bed dilution tests. The kinetic processes involved are exclusively limited by C-H bond activation, and CH 4 reaction rates are unaffected by the identity or the concentration of co-reactants (H 2 O, CO 2 ). Similar normal kinetic isotopic effects (k C-H /k C-D ) 1.40-1.51) were measured for CO 2 reforming, H 2 O reforming, and CH 4 decomposition, consistent with kinetically relevant C-H bond activation steps. The ratio of CH 4 /CD 4 cross-exchange to methane chemical conversion rates during the reaction of CO 2 reforming with CH 4 -CD 4 mixtures was 0.05, suggesting that steps involving C-H bond activation are essentially irreversible. Binomial D-atom distributions in dihydrogen and water were obtained during reactions of CH 4 /CO 2 /D 2 mixtures, and their D-contents were identical to those expected from complete equilibration between D 2 and H-atoms from reacted CH 4 , indicating that H-OH and H-H recombination steps are quasi-equilibrated. Reactions of 12 CH 4 / 12 CO 2 / 13 CO mixtures gave identical 13 C contents in CO and CO 2 , even far away from the CO 2 reforming equilibrium; thus, CO 2 activation is reversible and quasi-equilibrated during CO 2 reforming on Ru-based catalysts, as expected from the kinetic irrelevance of co-reactant activation steps. These conclusions suggest that water-gas shift reactions are also equilibrated, as confirmed by chemical analyses of reaction products. Forward CH 4 turnover rates increased with increasing Ru dispersion, but they were essentially unaffected by the identity of the support. This behavior reflects the higher reactivity of coordinatively unsaturated surface atoms, prevalent in small Ru clusters, for C-H bond activation reactions, as previously inferred from the effect of crystal orientation on CH 4 activation rates.

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Section: Reforming Reactionsmentioning

confidence: 82%

Section: Reforming Reactionsmentioning

confidence: 99%

Section: Reforming Reactionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Reaction Pathways and Site Requirements for the Activation and Chemical Conversion of Methane on Ru−Based Catalysts

2004

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“…After the oxidizing pre-treatment, two weak bands can be observed at 1590 and 1460 cm À1 (A). As soon as CH 4 reaches the catalyst (B), some gaseous CO 2 (CO 2(g) ) is produced, as shown by the growth of the double peak located around 2300 cm À1 [14,17,[44][45][46][47][48][49][50][51][52][53][54]; the intense peak with shoulders centred at 1304 cm À1 is due to gaseous CH 4 (CH 4(g) ) [45,47,50,51,55]. After 45 min under CH 4 , CO 2 production almost disappears and a broad peak located around 1900 cm À1 appears (C); this feature remains for at least 50 min under CH 4 (D).…”

Section: Resultsmentioning

confidence: 99%

Investigation of the behaviour of a Pd/γ-Al2O3 catalyst during methane combustion reaction using in situ DRIFT spectroscopy

Demoulin

Navez

Ruíz

2005

Applied Catalysis A: General

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Rapid catalytic reforming of methane with CO2 and its application to other reactions

Inui

2001

Appl. Organometal. Chem.

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First, indispensable requisites of the catalytic technologies for moderating the CO 2 problems are enumerated. Among various conditions, high conversion rates to treat a huge amount of the feed and high tolerance against coke deposit are most important. In spite of many advantages, CO 2 reforming of methane has the following general problem. Different from steam reforming, the deposited coke due to the disproportionation reaction of CO and the cracking of methane in CO 2 reforming cannot be volatilized by the reaction with steam. Based on the mechanisms of the coke formation mentioned above, a number of methods to reduce or prevent the coke deposit have been tried by many researchers. Many of them compared the results by using different kinds of catalyst components and their supports. Taking into account the catalytic performance and cost of catalyst materials, nickel supported on alkaline earth oxides and rare earth oxides, especially magnesia, were studied extensively. Sufficient stability to magnesia supported catalysts was observed; however, the conversion rate is still not high enough. Steam-CO 2 co-reforming and other approaches involving membrane reactors were also investigated; however, these results were basically affected by the intrinsic performance of the catalysts used and limit of diffusion in the case of the membrane. Another essential approach has been done by the author and coworkers. A nickel-based four-component composite catalyst was designed for high promotion of hydrogen spillover during the reaction progressing with high rates. Plenty of hydrogen on the catalyst surface prevented coke deposition and achieved an extraordinarily high reaction rate and high tolerance due to no covering of coke on the active catalytic sites. The large endothermic reaction heat of CO 2 reforming of methane could be compensated by simultaneous combination of catalytic combustion of a low concentration of easily combustible hydrocarbons.In this plenary lecture, almost all the studies on CO 2 reforming done in the recent decade were surveyed and summarized in the light of the above requisites to contribute to the further improvement in the catalysts and their reaction processes of CO 2 reforming of methane and/or natural gas.

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A Transient Kinetic Study of the Carbon Dioxide Reforming of Methane over Supported Ru Catalysts

Cited by 100 publications

References 25 publications

Reaction Pathways and Site Requirements for the Activation and Chemical Conversion of Methane on Ru−Based Catalysts

Reaction Pathways and Site Requirements for the Activation and Chemical Conversion of Methane on Ru−Based Catalysts

Investigation of the behaviour of a Pd/γ-Al2O3 catalyst during methane combustion reaction using in situ DRIFT spectroscopy

Rapid catalytic reforming of methane with CO2 and its application to other reactions

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