The Kolbel Engelhardt synthesis : catalysis by supported cobalt and copper systems

A suite of alumina (Al\\(_2\\)O\\(_3\\)) and silica (SiO\\(_2\\)4O‚àövñ) supported Co and Cu catalysts, physical mixes of the single metal catalysts, and mixed metal hybrid catalysts were investigated by temperature programmed reduction (TPR) and assessed in terms of their Kolbel Engelhardt (KE) activities. By comparison of the results from the different preparations it was shown that mixed non-stoichiometric Co/Cu oxides occurred on the calcined hybrids, which were reduced to interactive Co\\(^o\\) and Cu\\(^o\\) particles. This metal species distribution was associated with the production of high aromatic yields relative to aliphatic analogues. The most interesting sample was a Co/Cu on silica supported catalyst with Co and Cu to support ratios both of 10 on a weight percent basis (Co/Cu/SiO\\(_2\\)40‚àövñ; 10:10:100). This sample was screened in a series of CO/H\\(_2\\)O feeds of varying CO:H\\(_2\\)O ratios. There were two regimes of feed composition, defined as the CO rich regime and the H\\(_2\\)O rich regime. The performance of Co/Cu/SiO\\(_2\\)40‚àövñ; 10:10:100 was entirely different in each. Within the CO rich regime carbon deposition via the Boudouard reaction was the predominant cause of CO conversion at high temperature (300¬¨‚àûC, 325¬¨‚àûC), whereas in the H\\(_2\\)O rich regime substantial excess H\\(_2\\) was produced. The most favourable product distributions were given at a CO:H\\(_2\\)O feed ratio of 1:1. The Co/Cu/SiO\\(_2\\)40‚àövñ; 10:10:100 catalyst and the physical mix analogue, Co/SiO\\(_2\\)40‚àövñ; 10:100 + Cu/SiO\\(_2\\)40‚àövñ; 10:100, were characterised in detail using techniques including X-ray diffraction (XRD), electron probe microanalysis, and thermogravimetry. On the calcined hybrid sample Cu occurred as Cu\\(^{2+}\\) surface networks and Co as Co\\(_3\\)O\\(_4\\). These species were reduced totally during the activation procedure. The interaction between Co and Cu, suggested by TPR and screening evidence, was caused by the close proximity of the two metals rather than the formation of mixed metal stoichiometric oxides or alloys. Mechanistic studies using infrared (IR) spectroscopy indicated that CO adsorbed to Co/Cu/SiO\\(_2\\)40‚àövñ; 10:10:100 on Cu\\(^o\\) particles and at Co\\(^o\\)/Cu\\(^o\\) crystallite interfaces. When water was introduced a formate type species and polyene were observed. The formate species was probably a water gas shift reaction (WGSR) intermediate, and the polyene a common intermediate to the formation of coke and aromatic products. Reactivity experiments involving ethene conversion and coke stripping with H\\(_2\\)O and H\\(2\\) confirmed the role of polyene as an intermediate.