The greatest promotion for the oxidation of EG was observed on Pd 28 Cu 72 /C (7 times faster), for PG was on Pd 11 Cu 89 /C (12 times), and for G was on Pd 63 Cu 37 /C (14 times). We observe a decrease in density of states near the Fermi level with increasing amount of Cu and a shift of the d-band center away from the Fermi energy. This surface electronic perturbation could be one of the factors affecting the oxidation of the polyalcohols. A second factor could be the bi-functional effect as we also observe an increase in hydroxyl adsorption at lower potentials on all PdCu/C compared to Pd/C. Therefore, we suggest that the combination of both of these effects, electronic and bifunctional, contributes to the promotion of the oxidation of these polyalcohols. Furthermore, the ratio of Cu to Pd appears to play an important role in the oxidation rate.
Palladium is an efficient monoatomic catalyst for the electrochemical oxidation of polyalcohols in alkaline media, yet the oxidation rate is still slow compared to other smaller molecules. In order to improve the oxidation rate, Ni was mixed with Pd for synthesis of PdNi/C nanoparticles. The oxidation rates of ethylene glycol (EG), propylene glycol (PG), and glycerol (G) on Pd/C were compared to the oxidation rates on Pd16Ni84/C, Pd53Ni47/C, and Pd68Ni32/C. The oxidation rate of PG was enhanced by the presence of Ni as much as 14 times (Pd53Ni47/C). The oxidation rate of EG was enhanced 2.3 times on Pd68Ni32/C, and G was improved 2.9 times on Pd53Ni47/C. A significant shift in d‐band center was also observed (as high as +0.11 eV in Pd53Ni47/C) on each PdNi/C catalyst compared to that of Pd/C due to the presence of Ni. The correlation between increased oxidation rate and shift in d‐band center is indicative of the presence of an electronic effect, which is particularly strong for PG.
SynopsisTwo-level fractional factorial designs were employed to study the solution polymerization of butadiene in a batch reactor using cobalt octoate/DEAC/water as catalyst. Conversion and molecular weight data obtained as functions of time were used to develop a kinetic model, and the estimated kinetic parameters were correlated empirically with four operating variables: temperature and concentrations of cobalt octoate, DEAC, and water. The experimental data indicate that a t high water concentration a significant amount of oligomers is formed during early stages of polymerization, and the molecular weight of polymer increases with time. Analysis of the data suggests instantaneous initiation, first order propagation with cobalt and monomer, and transfer to monomer. Models which do not take account of the branching are shown to be incapable of fitting data for both a,, and Mu. The catalyst decay seems to follow a first-order mechanism, but the evidence is somewhat inconclusive. INTRODUCTIONCis-polybutadiene can be prepared using Ziegler-Natta catalysts of titanium or cobalt compounds with aluminum alkyls. A cobalt catalyst usually has the advantage of high solubility in organic solvents and as a result is more efficient in terms of polymer yield per unit mass of catalyst used.Several different cobalt salts have been reported to be effective for the 1,4-cis addition polymerization of butadiene, and cobalt salts of fatty acids have been used successfully in the commercial production of polybutadiene. The most common of these is cobalt octoate with diethyl aluminum chloride (DEAC) and water as cocatalysts. Despite its practical significance, however, the kinetics of this catalyst system have not been studied extensively.Among the few publications on this subject appearing in the open literature is Gippin's' investigation of the kinetic behavior of cobalt octoate and the effects of water and its substitutes, such as cumene hydroperoxide, elemental bromine, and tert-butyl alcohol, on the activity of the catalyst and the quality of polymer produced after 19 h of reaction at 5°C. Gippin believed that part of the DEAC reacts with water or its substitutes to produce higher acid derivatives. A possible reaction of DEAC with those compounds is the dialkylation of DEAC by the substitution of a reactive electronegative group for one ethyl group.Recently Honig et a1.2.S reported kinetic data on butadiene polymerization with a cobalt octoate-DEAC catalyst. The results and the proposed mechanism formed the basis for a kinetic model developed by Hamielec and co-worker~,~ who used an empirical factor to take account of the efficiency of In this work a batch reactor was used for polymerization. Under preselected operating conditions experiments were carried out according to two-level fractional factorial designs. The rate and average molecular weights were measured as functions of time to develop a kinetic model and estimate its kinetic parameters. The effects of temperature and concentration of DEAC, and of water, on those parame...
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