Copper dispersion

Similar experiments with copper dispersed on AI2O3 did not show any unusual behavior of the Al(ls) or Cu(2p) photolines. In this case, the copper could be easily cycled between CuO under oxidative conditions, to Cu metal during reducing conditions. We observed only a slight shift (<0.4 eV) of the aluminum (Is) line upon initial heating, which was attributed to the loss of water in the alumina matrix. 

Homogeneous, nanosized, copper-loaded anatase titania was synthesized by an improved sol-gel method [197], These titania composite photocatalysts were applied to the photoreduction of carbon dioxide to evaluate their photocatalytic performance. Methanol was found to be the primary hydrocarbon product [198], Under calcination conditions, small copper particles are well dispersed on the surface of anatase titania. According to XAS and XPS analysis, the oxidation state of Cu(I) was suggested to be the active species for C02 photoreduction [199], Higher copper dispersion and smaller copper particles on the titania surface are responsible for a great improvement in the performance of C02 photoreduction. 

Carbon dioxide [124-38-9] M 44.0, sublimes at -78.5 . Passed over CuO wire at 800° to oxidise CO and other reducing impurities (such as H2), then over copper dispersed on Kieselguhr at 180° to remove oxygen. Drying at -78° removed water vapour. Final purification was by vacuum distn at liquid nitrogen temperature to remove non-condensable gases [Anderson, Best and Dominey JCS 3498 1962]. 

Now the influence of water or ammonia on copper catalysts is being investigated. Previously A. BAIKER and coll, have shown that ammonia could modify the catalytic properties of copper catalysts used in the amination of alcohols (9). These authors noticed the formation of copper nitride after NH3 exposure at a temperature of about 300°C which is the reaction temperature of our study. The first results that we obtained in our study showed that both H2O and NH3 decrease significantly the copper dispersion in unpromoted catalysts and that this modification is less significant when Ca or Mn are added to the Cu-Cr catalyst. We are now studying what are the superfical modifications consecutive to the addition of promoters or/and water and ammonia. 

Without zinc, silicon diffusion to the surface is slow under MCS conditions. Furthermore, when only tin is used as a promoter, no Cu is observed at the surface. Table 3 shows the elemental concentration under various conditions. Under MCS reaction conditions, when zinc was present silicon was not depleted from the subsurface, and when zinc was absent the subsurface was depleted in silicon. Zinc causes the rate of silicon diffusion and copper dispersion to increase. Zinc accumulates at grain boundaries and lowers the free energy of CU3SL Tin and zinc appear to work synergistically but tin does not enhance silicon diffusion on its own. Tin does appear to lower the surface energy of silicon/copper. 

Oh, S.T., Sando, M., Sekino, T. and Niihara, K., Processing and properties of copper dispersed alumina matrix nanocomposites , NanostructuredMater, 1998 10 267-272. 

In CO2 hydrogenation over Cu/ZrOj based catalysts, the methanol formation activity could be correlated with copper dispersion. The reaction intermediates of methanol synthesis were carbonate, formate, formaldehyde and/or methoxy, and the rate determining step for methanol synthesis seems to be the conversion of formate into formaldehyde or methoxy. 

Although methanol synthesis from COj hydrogenation over supported copper catalysts has been widely investigated, there are still controversies concerning the methanol synthesis mechanism and the effect of copper on the catalytic activity[l-6]. In this work, the influence of the copper dispersion in Cu/ZrO catalyst on the catalytic activity in COj hydrogenation was investigated. In order to understand the reaction mechanism, FT-IR spectroscopy under reaction conditions and TPD of adsorbed methanol were performed. 

Among copper based binary catalyst systems, CuO/ZrOj was proved to be the most reactive toward methanol synthesis. The methanol synthesis activity of the CuO/ZrOj catalyst was greatly affected by the copper dispersion (or copper crystallite size) the smaller the crystallite size, the higher the rate of methanol synthesis (Table 1). When some components of Ce, Cr, Pd, K, V and Zn were added as promoters into CuO/ZrOj, the crystallite size of copper particles changed significantly. CeOj increased the copper crystallite size significantly, while ZnO made the copper crystallite size much smaller than those of the Cu/ZrOj samples. 

Figure 4.9 Interaction between ruthenium and copper dispersed on silica, as illustrated by the marked difference in the EXAFS envelope functions derived from EXAFS data associated with the K-absorption edge of copper in silica-supported copper and ruthenium-copper catalysts (31). (Reprinted with permission from the American Institute of Physics.)...

K, we observed the dispersion of copper decreased in the absence of barium while the modification was less important in the presence of barium. Therefore in the presence of barium, the copper dispersion was higher and copper oxide was not totally reduced even after the reduction treatment. 

Z. Chajar, M. Primet, H. Praliaud, M. Chevrier, C. Gauthier, F. Mathis and E.S. Lox "Influence of the Copper Dispersion on the Selective Reduction of Nitric Oxide over CU/AI2O3 Catalysts Nature of the Active Sites", Proc. 3rd Intern. Symp. CAPOC III, Bnissels (1994)... 

INFLUENCE OF THE COPPER DISPERSION ON THE SELECTIVE REDUCTION OF NITRIC OXIDE OVER CU/AI2O3 NATURE OF THE ACTIVE SITES. 

G. Casella, T.R.I. Cataldi, A. Guerrieri, and E. Desimoni, Copper dispersed into polyanihne films as an amperometric sensor in alkaline solutions of amino acids and polyhydric compounds, Analyt. Chim. Acta, 335, 217-225 (1996). 

Andrade et al. [10] reported composition effect on the WGS activity of Cu-Zn-Al203 catalysts. They proposed that the interaction between the catalyst components in the calcined samples led to a synergy between the Cu-rich and the Al-rich Zn-containing compositions and for Zn-rich samples, ZnO may play the role of a copper dispersion agent. There was found a defined correlation between the catalytic activity and the amount of reduced free CuO in the sample. They also proposed that a high Cu, Zn and Al surface interdispersion is necessary in order to attain a high catalytic activity. Li et al. [11] investigated the effect of Al content on the WGS activity of Cu/Zn/Al catalysts. 12% Al composition catalyst shows better activity than other catalysts. 

The effects of ultrasound on the reactivity of copper metal as a stoichiometric reagent have been documented in the literature in two cases, the Ullmann coupling 2 and the reaction with salicylidene-aniline to form uncharacterized copper complexes.33 These reactions are discussed in Ch. 5 (pp. 171 and 208). In addition, ultrasound has been used to enhance the reduction of Cu salts by alkali metals to form highly reactive copper dispersions. ... 

Sharma, P.K., and Hickey, G.S., A comparison of the oxygen uptake characteristics of copper-exchanged zeolite with copper dispersed on a silica support. Gas Sep. Purif. 7(3), 141-146 (1993). 

For La-M-Cu-ZnO (M = Y, Ce, Mg, or Zr) catalysts derived from perov-sldtes [16], CO2 conversion varies between 6.4 and 12.6% (5 MPa, 250 °C, CO2/ H2 = 3, and GHSV = 3600 h ) depending of M but is always related to the Cu° sur a.ce area. The nature of M is then demonstrated to impact only the copper dispersion it does not affect the Intrinsic activity of the catalysts. Selectivity to methanol remains poor (52.5-59.6% methanol 33-46% CO 1.7-2.5% CH4), but it has been seen that as the binding energy of Cu Auger peak (a) shifts to lower value, higher methanol selectivity is observed. 

The production of methanol at industrial scale takes place in the presence of H2, CO, and CO2 mixtures at pressures close to 50 bar in the 550 to 640 K temperature range. The catalyst of choice is copper dispersed on the surface of zinc oxide [20-22]. Recent studies on CO2 hydrogenation have received much attention in an attempt to rekindle interest in the role of CO2 in industrial conditions of methanol synthesis. This issue is closely related to the fact that kinetic experiments, using isotope-labeled carbon oxides [22] and spectroscopic experiments [23], have demonstrated that under industrial conditions methanol is produced by the hydrogenation of CO2, CO merely providing a source of CO2 and acting as... 

Kusy R, Comeiiussen R (1975) The thermal conductivity of nickel and copper dispersed in poly(vinyl chloride). Polym Eng Sci 15 107-112... 

The hydrogenation of CDT catalysed by copper dispersed on different oxides, in the initial step of the reaction, follows in all cases a first order kinetic respect to CDT concentration. 

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