TL;DR: The mechanism of cyclohexanol and cycloenanone adsorption and the kinetics and mechanism of dehydrogenation to cycloenhexanone over Cu 0 and Cu + catalysts were studied by IR spectroscopy and kinetic methods as discussed by the authors.
Abstract: The mechanism of cyclohexanol and cyclohexanone adsorption and the kinetics and mechanism of cyclohexanol dehydrogenation to cyclohexanone over Cu 0 catalysts (on Cu–Mg) and Cu + catalysts (on Cu–Zn–Al) were studied by IR spectroscopy and kinetic methods. In situ IR spectroscopy data demonstrated that cyclohexanol is adsorbed onto monovalent copper at room temperature, forming molecularly adsorbed cyclohexanol and cyclohexanol alcoholate of Cu + . Cyclohexanol alcoholate species were considered as intermediates for cyclohexanone formation on monovalent copper sites. Unlike in the case of Cu + , the dissociative adsorption of cyclohexanol on Cu 0 was observed only at temperatures of 50 °C or higher. Cyclohexanol adsorption on Cu 0 was accompanied by formation of a cyclohexanol alcoholate species and a phenolate species. The existence of the two adsorbed species on Cu 0 explains the low selectivity of catalysts with this active site. In the case of dehydrogenation on Cu + copper the kinetics suggests that the reaction proceeds by abstraction of the hydroxyl hydrogen from adsorbed cyclohexanol and formation of the cyclohexanol alcoholate of Cu + . Hydroxyl hydrogen abstraction was considered to be the rate-determining (rds) step of the reaction. For dehydrogenation of cyclohexanol on Cu 0 , the IR and kinetic data were consistent with a dissociative adsorption of cyclohexanol and formation of cyclohexanol alcoholate of Cu 0 . The removal of the second nonhydroxyl hydrogen was hypothesized to be the rate-determining step of reaction on Cu 0 . The proposed kinetic models for dehydrogenation on the catalysts with Cu + and Cu 0 sites give a satisfactory fit to the reaction rate data and provide physically meaningful values for enthalpies and entropies of cyclohexanol and cyclohexanone adsorption.
TL;DR: In this article, the performance of Pd catalysts supported on SiO2, Al2O3 and ZrO2 for the HDO of phenol has been compared in the gas phase, at 300 °C and 1 atm using a fixed bed reactor.
Abstract: The performance of Pd catalysts supported on SiO2, Al2O3 and ZrO2 for the hydrodeoxygenation (HDO) of phenol has been compared in the gas phase, at 300 °C and 1 atm using a fixed bed reactor. While Pd supported on SiO2 and Al2O3 exhibits high selectivity to cyclohexanone, when supported on an oxophilic support such as ZrO2, it favors the selectivity toward benzene, reducing the formation of ring-hydrogenated products, cyclohexanone and cyclohexanol. Diffuse reflectance infrared Fourier transform spectroscopy experiments support the participation of a keto-tautomer intermediate (2,4-cyclohexadienone) in the reaction. This intermediate can be hydrogenated in two different pathways. If the ring is hydrogenated, cyclohexanone and cyclohexanol are dominant products, as in the case of Pd/SiO2 and Pd/Al2O3 catalysts. By contrast, if the carbonyl group of the keto-intermediate tautomer is hydrogenated, benzene is directly formed via rapid dehydration of the unstable cyclohexadienol intermediate. This is observed ...
TL;DR: In this paper, the vapor phase reaction of triols and diols was performed over copper metal catalysts, and a reaction mechanism for the dehydration of glycerol to form hydroxyacetone was proposed.
Abstract: The vapor-phase reaction of triols and diols was performed over copper metal catalysts. Triols, such as 1,2,3-propanetriol (glycerol) and 1,2,3- and 1,2,4-butanetriols, were dehydrated to afford corresponding hydroxyketones, while 1,2-propanediol was dehydrogenated to form hydroxyacetone. Supported copper as well as pure copper metal was an effective catalyst for the dehydration of glycerol to produce hydroxyacetone under inert conditions. In hydrogen flow, however, copper catalyzed the hydrogenation of hydroxyacetone as well as hydrogenolysis to produce ethylene glycol. Alumina-supported copper showed the highest catalytic activity with hydroxyacetone selectivity of >90 mol% at ambient pressure of nitrogen and 250 °C. Copper metal provides an active site for the dehydration of glycerol. We propose a reaction mechanism for the dehydration of glycerol to form hydroxyacetone.
TL;DR: A series of CuO/Al(2)O(3)-ZrO( 2) catalysts with Cu loadings varying from 1.0 to 20 wt % were prepared and characterized by X-ray diffraction, temperature-programmed reduction (TPR), temperature- programmed desorption (TPD), electron spin resonance (ESR), and Brunauer-Emmett-Teller surface area measurements.
Abstract: A series of CuO/Al(2)O(3)-ZrO(2) catalysts with Cu loadings varying from 10 to 20 wt % were prepared and characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD) of CO(2) and NH(3), electron spin resonance (ESR), and Brunauer-Emmett-Teller surface area measurements The dispersion and metal area of copper were determined by the N(2)O decomposition method XRD results suggest that the copper oxide is present in a highly dispersed amorphous state at copper loadings < 10 wt % and as a crystalline CuO phase at higher Cu loadings ESR results suggest the presence of two types of copper species on the Al(2)O(3)-ZrO(2) support TPR results suggest well-dispersed copper oxide species at low Cu loadings and crystalline copper oxide species at high Cu loadings Well-dispersed copper oxide species were reduced more easily than large copper oxide species by H(2) The results of CO(2) TPD suggest that the basicity of the catalysts was found to increase with an increase of copper loading up to 50 wt % and decreases with a further increase of copper loading The results of NH(3) TPD suggest that the acidity of the catalysts was found to decrease with an increase of copper loading up to 50 wt % and increases with a further increase of copper loading The catalytic properties were evaluated for the vapor-phase dehydrogenation of cyclohexanol to cyclohexanone and correlated with the results of CO(2) TPD measurements and the dispersion of Cu on the Al(2)O(3)-ZrO(2) support
TL;DR: In this article, NiCu single atom alloy (SAA) nanoparticles supported on silica are reported to catalyze the non-oxidative dehydrogenation of ethanol, selectively to acetaldehyde and hydrogen products by facilitating the C H bond cleavage.
Abstract: NiCu single atom alloy (SAA) nanoparticles supported on silica are reported to catalyze the non-oxidative dehydrogenation of ethanol, selectively to acetaldehyde and hydrogen products by facilitating the C H bond cleavage. The activity and selectivity of the NiCu SAA catalysts were compared to monometallic copper and to PtCu and PdCu single atom alloys, in a flow reactor at moderate temperatures. In-situ DRIFTS showed that the silica support facilitates the O H bond cleavage of ethanol to form ethoxy intermediates over all the supported alloy catalysts. However, these remain unreactive up to 250 °C for the Cu/SiO2 monometallic nanoparticles, while in the NiCu SAA, acetaldehyde is formed at much lower temperatures, below 150 °C. In situ DRIFTS was also used to identify the C H activation step as the rate determining step of this reaction on all the copper catalysts we examined. The presence of atomically dispersed Ni in Cu significantly lowers the C H bond activation barrier, whereas Pt and Pd atoms were found less effective. This work provides direct evidence that the C H bond cleavage is the rate determining step in ethanol dehydrogenation over this type catalyst.
TL;DR: In this article, a novel coupling route highlighting the combination of hydrogenation of furfural and dehydrogenation of cyclohexanol in vapor phase conditions over Cu-MgO-Cr 2 O 3 catalyst is presented.
Abstract: A novel coupling route highlighting the combination of hydrogenation of furfural and dehydrogenation of cyclohexanol in vapor phase conditions over Cu-MgO-Cr 2 O 3 catalyst is highly advantageous in terms of avoiding external pumping of H 2 and maintaining the formation of furfuryl alcohol and cyclohexanone, the desired products, respectively, in good amounts at atmospheric pressure. The catalytic activity of this catalyst is compared with a Cu-MgO coprecipitated catalyst and a copper chromite (commercial Cu-1800P supplied by M/s. Engelhard Corp., USA) catalyst. Cu-MgO-Cr 2 O 3 catalyst is prepared by coprecipitation method using tetraethyl ammonium hydroxide as precipitating agent. All the catalysts are characterized by BET surface area, temperature programmed reduction, XRD and XPS. The BET surface area of Cu-MgO-Cr 2 O 3 catalyst is higher indicating the presence of smaller Cu particles. XRD results also indicate the presence of smaller particles of Cu in Cu-MgO-Cr 2 O 3 catalyst. XPS results indicate the presence of Cu species (Cu 0 /Cu + ) at the surface of Cu-MgO-Cr 2 O 3 catalyst. The higher yields of the products over the Cu-MgO-Cr 2 O 3 catalyst in independent and combined reactions compared to the other two catalysts may be attributed to the promotional effect of Cr 2 O 3 , smaller Cu particle size and more number of Cu 0 /Cu + species at the surface.