Evidence of surface-reaction segregation in cyclohexene hydrogenation and dehydrogenation over supported platinum

Sermon, Paul A.; Georgiades, G.; Vong, M. S. W.; Martín-Luengo, Maria Ángeles; Reyes, Patricio

doi:10.1098/rspa.1987.0043

Cited by 13 publications

(2 citation statements)

References 39 publications

(13 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In early works, the dehydrogenation of cyclohexene was intensively studied in the absence of oxygen, with emphasis on the adsorption mechanism and kinetics depending on the nature of the catalysts, , and special attention was paid to precious metals as active sites. − Adsorption and reaction studies on Pt (111) surface by Gland et al . showed that the dehydrogenation of cyclohexene intermediate is kinetically limited during the dehydrogenation of cyclohexane under 150 °C, whereas the dehydrogenation of cyclohexadiene intermediate to benzene occurs rapidly.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Low-Temperature Selective Oxidative Dehydrogenation of Cyclohexene by Titania-Supported Nanostructured Pd, Pt, and Pt–Pd Catalytic Films

Vaidulych,

Yeh,

Hoehner

et al. 2024

J. Phys. Chem. C

View full text Add to dashboard Cite

Films of titania-supported monometallic Pd, Pt, and bimetallic Pt−Pd catalysts made of metallic nanoparticles were prepared by magnetron sputtering and studied in the oxidative dehydrogenation (ODH) of cyclohexene. Pd/TiO x and Pt−Pd/TiO x were found active at as low temperature as 150 °C and showed high catalytic activity with high conversion (up to 81%) and benzene selectivity exceeding 97% above 200 °C. In turn, the Pt/TiO x catalyst performed poorly with the onset of benzene production at 200 °C only and conversions not exceeding 5%. The activity of bimetallic Pt−Pd catalysts far exceeded all of the other investigated catalysts at temperatures below 250 °C. However, the production of benzene significantly dropped with a further temperature increase due to the enhanced combustion of CO 2 at the expense of benzene formation. As in situ NAP-XPS measurement of the Pt−Pd/TiO x catalyst in the reaction conditions of the ODH of cyclohexene revealed Pd surface enrichment during the first temperature ramp, we assume that Pd surface enrichment is responsible for enhanced activity at low temperatures in the bimetallic catalyst. At the same time, the Pt constituent contributes to stronger cyclohexene adsorption and oxygen activation at elevated temperatures, leading to changes in conversion and selectivity with a drop in benzene formation and increased combustion to CO 2 . Both the monometallic Pd and the Pt−Pd-based catalysts produced a small amount of the second valuable product, cyclohexadiene, and below 250 °C produced only a negligible amount of CO 2 (<0.2%). To summarize, Pd-and Pt−Pd-based catalysts were found to be promising candidates for highly selective low-temperature dehydrogenation of cyclic hydrocarbons that showcased reproducibility and stability after the temperature activation. Importantly, these catalysts were fabricated by utilizing proven methods suitable for large-scale production on extended surfaces.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Low-Temperature Selective Oxidative Dehydrogenation of Cyclohexene by Titania-Supported Nanostructured Pd, Pt, and Pt–Pd Catalytic Films

Vaidulych,

Yeh,

Hoehner

et al. 2024

J. Phys. Chem. C

View full text Add to dashboard Cite

show abstract

IR-Emissionsanalyse der Temperaturprofile von Pt/SiO2-Katalysatoren bei exothermen Reaktionen

1987

View full text Add to dashboard Cite

show abstract

IR Emission Analysis of Temperature Profiles in Pt/SiO₂ Catalysts during Exothermic Reactions

Georgiades

Self

Sermon

1987

Angew. Chem. Int. Ed. Engl.

View full text Add to dashboard Cite

Although the excess temperature of the active sites in supported catalysts during catalysis could be several hundred degrees higher than that measured by a thermocouple,fi1 theoretical and experimental results have been contradictory. Indirect evidence may come from cataiyst sinteringl2I (attributed to local heating and consequent Pt mobility during oxidation-reduction) and the fact that in CO oxidation a Pd/Si02 catalyst without external heating remained at 150-190 K above the temperature of the reactant stream.[31 Unfortunately, 150-K temperature excursions of Pt/Si02 are probably representative of the support rather than the active sites (see Ref. 141).lnfrared emission can, however, provide direct evidence of the temperature of the more important supported phase if at the relevant wavelengths the "black" active metal emits more strongly than the support. It has been shown that (1) the temperature of Ni crystallites exhibits an average transient increase of 165 K above that of the silica support within 3 s on O2 chernisorption,['I (2) during CO oxidation at 573 K the temperature of Pd is at least 190 K above that of its SiO, support,[31 and ( 3 ) temperature variations of 28 K exist across Pt/A1203 catalysts during H2 oxidation.[" However, it is now necessary to concentrate on temperature profiles produced under flow conditions using porous impregnated catalysts, operating in flow reactors with residence times of a few seconds, at partial pressures close to the stoichiometric composition of reactant^ '^] and to consider their significance for analysis of the kinetics of heterogeneous reactions.@I We report here on the Pt/Si02-catalyzed oxidation of H, and hydrogenation of cyclohexene.This particular catalyst (see Experimenfal Procedure) was selected because (1) the size of its pores might be large enough to reduce pore diffusion limitation, (2) the support would increase thermal and chemical isolation of the Pt active sites, (3) the activity of Pt was high and well known in the reactions selected, and (4) the Pt was finely dispersed (i.e., hydrogen chemisorption revealedfIol that it existed as 4-nm particles) throughout the internal pore structure of the support with sizes much smaller than the support pore size, thereby possibly allowing relatively ready access of reactants and release of products.Platinum is one of the most active metals for H2 oxidation"" (-AH=241.8 kJ/mol H20) and has been studied in the unsupported'"' and supported['31 states. On supported catalysts a thermal feedback from the heat generated by the reaction may affect the chemical rate and cause oscillations and bi~tability."~. Interestingly, the higher activity for smaller SiO,-supported Pt particles during H2 oxidation"31 could not be explained by their heating up more than the larger ones. In cyclohexene hydrogenation (-AH= 117.8 kJ/molf161) supported and unsupported Pt have been found["-201 to show structure insensitivity (i.e., the turnover numbers remained constant at 2-3 cyclohexane molecules produced per Pt site per second12'] a...

show abstract

Evidence of surface-reaction segregation in cyclohexene hydrogenation and dehydrogenation over supported platinum

Cited by 13 publications

References 39 publications

Low-Temperature Selective Oxidative Dehydrogenation of Cyclohexene by Titania-Supported Nanostructured Pd, Pt, and Pt–Pd Catalytic Films

Low-Temperature Selective Oxidative Dehydrogenation of Cyclohexene by Titania-Supported Nanostructured Pd, Pt, and Pt–Pd Catalytic Films

IR-Emissionsanalyse der Temperaturprofile von Pt/SiO2-Katalysatoren bei exothermen Reaktionen

IR Emission Analysis of Temperature Profiles in Pt/SiO₂ Catalysts during Exothermic Reactions

Contact Info

Product

Resources

About

Evidence of surface-reaction segregation in cyclohexene hydrogenation and dehydrogenation over supported platinum

Cited by 13 publications

References 39 publications

Low-Temperature Selective Oxidative Dehydrogenation of Cyclohexene by Titania-Supported Nanostructured Pd, Pt, and Pt–Pd Catalytic Films

Low-Temperature Selective Oxidative Dehydrogenation of Cyclohexene by Titania-Supported Nanostructured Pd, Pt, and Pt–Pd Catalytic Films

IR-Emissionsanalyse der Temperaturprofile von Pt/SiO2-Katalysatoren bei exothermen Reaktionen

IR Emission Analysis of Temperature Profiles in Pt/SiO2 Catalysts during Exothermic Reactions

Contact Info

Product

Resources

About

IR Emission Analysis of Temperature Profiles in Pt/SiO₂ Catalysts during Exothermic Reactions