UV Raman spectroscopic study of V/δ-Al₂O₃ catalysts in butane dehydrogenation

The increasing demand for light olefins and the insufficient capacity from current production by steam and catalytic cracking are the driving forces to seek alternative ways to manufacture these chemicals. The most feasible processes on a commercial scale at present are catalytic dehydrogenation (DH) and oxidative dehydrogenation (ODH) of light alkanes. Raman spectroscopy was used to investigate the structural changes of surface VO_x and the coke formation process during butane DH over V/δ-Al₂O₃ catalysts with various surface VO_x densities. A better understanding of coke formation chemistry and the role of different VO_x species in coke formation could facilitate optimization of catalysts and possible reduction of side reactions leading to coke. Raman spectra from 1,3-butadiene DH on 1.2 V sample showed some different features from other olefins and butane at reaction temperatures below 573 K. These two bands were readily formed upon room temperature adsorption of 1,3-butadiene on the 1.2 V sample and persisted from reaction temperature ≤ 773 K. The two bands observed at room temperature could be removed after heating in He at 573 K, suggesting they were due to adsorbed 1,3-butadiene on the V/δ-Al₂O₃ sample. The two bands at ∼ 850 and 1006/cm observed upon the reaction of C₄ olefins and butane on VO_x samples were related to a -CH=CH₂ structure but not exactly 1,3-butadiene. Coke species formed on polymerized VO_x were more easily removed than on isolated VO_x. This is an abstract of a paper presented at the ACS Fuel Chemistry Meeting (San Diego, CA Spring 2005).