234
Ind. Eng. Chem. Fundam., Vol. 17, No. 3, 1978
CORRESPONDENCE
Catalytic Oxidation of Phenol in Aqueous Solution over Copper Oxide
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Sir: We have recently discovered that copper from the supported CuO catalyst used by Sadana and Katzer (1974a) is leached out of the catalyst by phenol in the reaction mixture. In our studies, cupric ion concentrations were measured by \means of an atomic absorption spectrometer, in milliliter-sized liquid samples withdrawn from the reactor during reaction. In one run in which we used the same type of catalyst as Sadana and Katzer, namely, 10%CuO on y-alumina (Harshaw Cu-0803T 118) at 150 “C, using an initial oxygen partial pressure of 10.6 atm, 6.5 g of catalyst, and an initial concentration of phenol of 4400 g/L, a curve of phenol concentration vs. time was determined. Two other phenol concentration vs. time curves were obtained for runs performed: (1)at identical conditions in the presence of no catalyst (called the “background” reaction curve), and (2) a t identical conditions, but with solid catalyst replaced by cupric ion at a concentration of 148 g/L. This is approximately the concentration of cupric ion found to have been leached out of the sample of fresh Harshaw catalyst when the phenol concentration had fallen to half of its original value. By comparing the slopes of these three curves at this concentration of phenol it was found that the “background” rate was approximately 9% of the total rate measured with the Harshaw catalyst, and the homogeneous catalytic component of reaction attributable to cupric ion was approximately 20% of the total. In other runs (Njiribeako, 1977) performed with CuO on
Sir: Since we reported on our initial studies of aqueousphase phenol oxidation over supported copper oxide (Sadana and Katzer, 1974a,b),we have been investigating the stability and durability of supported transition metal catalysts under aqueous-phase oxidation conditions. Our previous studies were aimed at determining the catalytic behavior of a supported base metal oxide catalyst under aqueous-phase oxidation conditions. The results reported by Njiribeako et al. (1978) confirm our results (Bansal, 1977). We have shown that with commercial copper-containing catalysts copper concentrations as high as 100 ppm can occur in solution, which may contribute to homogeneous reaction. We have shown that by stabilizing such a catalyst so as to reduce the aqueous-phase copper ion concentration by a factor of about 100-fold the observed activity was reduced by 15-20%. This is as would be expected if the
0019-7874/78/1017-0234$01.00/0
silica catalyst (Girdler T-1506),the homogeneous component of reaction attributable to cupric ion was found to be as high as 40% of the total reaction rate. Although we have not studied this phenomenon extensively, it is clear that the homogeneous catalytic component due to the leached cupric ion in batch reaction varies with time as well as reaction conditions. In view of the large and variable homogeneous catalytic reaction component caused by the leaching of copper from the heterogeneous catalyst, we suggest that the interpretation of the reaction mechanism given by Sadana and Katzer (1974a,b) is open to question and demands careful experimental reexamination. Literature Cited Njiribeako. A. I., M.A.Sc. Thesis, Chemical Engineering, University of Waterloo, Waterloo, Ont., Canada, 1977. Sadana, A., Katzer, J. R., Ind. Eng. Chem. Fundam., 13, 127 (1974a). Sadana, A,, Katzer, J. R., J. Catal., 35, 140 (1974b).
Department of Chemical Engineering Queen’s University Kingston, Ontario Department of Chemical Engineering Uniuersity of Waterloo Waterloo, Ontario, Canada N2L 3Gl
Adolphus I. Njiribeako Robert R. Hudgins* Peter L. Silveston
Receiued for review November 7,1977 Accepted April 13,1978
extent of homogeneous reaction due to leached copper were 20% of the total rate as reported by Njiribeako et al. (1978). The concentrations of cupric ion that we have found have never approached the value of 148 g/L as reported by Njiribeako et al. (1978); we frankly do not see how such concentrations could occur. Literature Cited Bansal. R., M.Ch.E. Thesis, Chem. Eng., University of Delaware, Newark, Del., 1977. Njiribeako, A. J., Hudgins, R. R., Silveston, P. L., Ind. Eng. Chem. Fundam., preceding correspondence in this issue, 1978. Sadana, A., Katzer, J. R., Ind. Eng. Chem. Fundam., 13, 127 (1974a). Sadana, A., Katzer, J. R., J. Catal., 35, 140 (1974b).
Department of Chemical Engineering Uniuersity of Delaware Newark, Delaware 19711
0 1978 American Chemical Society
James R. Katzer
