Surface synergisms between copper and its oxides in catalytic isopropanol/acetone interconversions at 430-523 K

Cunningham, Joseph; Al-Sayyed, Ghassan; Cronin, John A.; Healy, C.; Hirschwald, W.

doi:10.1016/s0166-9834(00)81229-4

Cited by 33 publications

(10 citation statements)

References 13 publications

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“…In the case of 5Cu, 20Cu, and Cu-1800P, a small amount (<1%) of a light gaseous product (possibly a light hydrocarbon) was observed during the first few minutes on stream, whereas for 0.5Cu and Cu powder, isopropyl alcohol was the only detectable product throughout the duration of the reaction. This is consistent with other studies of acetone hydrogenation in which the only reported product was isopropyl alcohol, ,− although in one case aldol condensation-type products were reported at temperatures above 473 K …”

Section: Resultssupporting

confidence: 92%

Influence of Crystallite Size on Acetone Hydrogenation over Copper Catalysts

2004

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Acetone hydrogenation was studied over a family of Cu/SiO2 catalysts as well as UHP Cu powder and a Cu chromite catalyst. Oxygen chemisorption via dissociative N2O adsorption was used to count surface Cu atoms and calculate crystallite sizes, and a microwave absorption technique was used to measure the electrical conductivity of these Cu particles. Under differential reaction conditions at 423 K and 1 atm, all catalysts exhibited deactivation on stream and activities were typically 10-20% of their initial values after 3-4 h on stream. However, initial turnover frequencies (TOFs) varied from 0.056 s(-1) on the most highly dispersed Cu catalyst to 0.50 s(-1) on Cu powder, with the highest TOF of 2.4 s(-1) occurring on 110 nm crystallites. A similar trend with a broader (80-fold) variation was observed in the "steady-state" TOF values. Apparent activation energies varied between 11 and 14 kcal/mol. These initial TOF values are in good agreement with previous results, and a correlation exists between TOF and Cu crystallite size in this reaction, which appears to be structure sensitive. In addition, the electrical conductivity of these dispersed Cu nanoparticles, which was always less than that of bulk Cu, also increased with increasing Cu crystallite size; consequently, the change in this parameter may offer a possible explanation for the increase in TOF.

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Section: Resultssupporting

confidence: 92%

Influence of Crystallite Size on Acetone Hydrogenation over Copper Catalysts

2004

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“…Another striking feature of the behavior of the alloys studied is the marked difference found between the chemical states of copper of Cu−Ti and the other two alloys. According to literature data, either metallic copper (Cu 0 ) , is involved in the dehydrogenation of alcohols to carbonyl compounds or the coexistence of metallic and oxidized copper species , is required. On the basis of these observations as well as the inactivity of Cu−Ti alloy in such dehydrogenations, the lack of surface Cu 0 could be predicted …”

Section: Discussionmentioning

confidence: 99%

Surface Characterization of Cu−M (M = Ti, Zr, or Hf) Alloy Powder Catalysts

Molnár¹,

and²,

Szépvölgyi³

et al. 1998

J. Phys. Chem. B

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X-ray photoelectron spectroscopy was used for surface characterization of amorphous Cu−M alloy powders (Cu40Ti60, Cu50Zr50, and Cu65Hf35) produced by mechanical alloying of the constituents. When used as catalyst in the dehydrogenation of alcohols Cu−Zr and Cu−Hf were found to undergo structural changes resulting in surface copper enrichment with a substantial fraction of copper being in fully reduced, metallic (Cu0) state. This result accounts for the high and stable catalytic activity of Cu−Zr and Cu−Hf in the transformations of alcohols. In contrast, when Cu−Ti is used in inert atmosphere, surface enrichment of titanium is observed. Although segregation of copper occurs in the presence of hydrogen, only oxidized copper species are detected on the surface. In either case, the catalytic activity of Cu−Ti is inferior to the other two alloy samples. TiH2 is shown by XRD to be the characteristic species formed under hydrogen. This is stable in the presence of hydrogen and, therefore, Cu acts as an oxygen scavenger and forms oxidized surface species that do not show catalytic activity.

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“…This table shows that: (i) increasing the reaction temperature increases the selectivity towards acetone formation and decreases the selectivity towards condensation product formation. The increase in the selectivity towards acetone formation with increasing the reaction temperature is explained on the light of the dehydrogenation reaction of isopropyl alcohol yielding acetone is endothermic reaction [31]. Dehydrogenation process over copper species did not proceed at low exposures of iso-propanol, but the dehydrogenation activity enhanced by pretreatments or treatments on stream or by coexistence of copper (in oxidized and reduced form) [32].…”

Section: Effect Of the Precursor And Preparation Conditions Of The Sumentioning

confidence: 97%