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The so-called IFP catalyst is well-known as a non-Rh catalyst for direct alcohol synthesis from syngas. In order to elucidate the reaction mechanism, catalysts of various combinations of three main elements, Cu, Co, Cr, in the IFP catalyst were prepared. The structures of the combinations were studied using XRD, TPR, STEM-EDX, etc., and the active species of the catalysts were discussed together with the results of activity tests.The oxide structures of one- and two-component catalysts were determined by XRD analysis and summarized in Table 1. The XRD spectra of a Cu•Co•Cr threecomponent catalyst, calcined at 450°C or at 600°C, are shown in Fig. 1. Based on the spectra, it turned out to be a mixture of CuO and unknown (A) which had a structure similar to Co•Cr spinel oxide. The increase in crystallinity was observed in the oxide calcined at 600°C. In order to determine the structure of (A), both the TEM observation (Fig. 2) and STEMEDX analysis (Table 2) were carried out. The oxide was composed of dark part and pale part as shown in Fig. 2. It is assumed based on the STEM-EDX analysis that CuO exists mainly in the dark part while (A) exists mainly in the pale part. The structure of (A) was deduced to be [Cu(II)aCo(II)1-a] [Co(III)(a+1)/2 Cr(III)(3-a)/2]O4(O_??_a_??_0.9).The reduction states of the catalyst components under the reaction conditions were discussed using the results of the TPR experiments (Fig. 3, Table 3). In the three-component catalyst, copper was reduced mostly to its metallic state, cobalt to Co(II) and chromium stayed as Cr(III). It is probable that the copper in spinel (A) is not completely reduced but exists as Cu (I), whereas CuO is reduced to copper.The results of atmospheric reaction are shown in Table 4. Cu, Cu•Co and Cu•Co•Cr effected the conversion of carbon monoxide to a measurable extent, but they showed poor selectivity for oxygenates. In order to understand the effect of K, atmospheric reaction tests using catalysts containing K were carried out (Table 5). The addition of K decreased the total activity while it increased the selectivity for oxygenates.A reaction test under 9.8 atm using a Cu•Co catalyst was made to observe the effect of reaction pressure (Table 6). Although the total activity was somewhat lower than that obtained under atmospheric pressure, the selectivity for oxygenates was higher.Concerning the active species of IFP type catalysts, the molecular adsorption of CO is probably effected by the Cu(I) present in the spinel, while both the dissociative adsorption of CO and the formation of the C-C bond are brought about by Co. The hydrogenation is catalysed by Co or Cr. Both reducibility and dispersion are controlled by the spinel formation of Cr with Cu and Co.
- 公益社団法人 石油学会の論文
公益社団法人 石油学会 | 論文
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