(617gq) Catalytic Activity and Sulfur Dependence of Co/Mo Nanoparticle Catalysts in WGS Reaction

The global interest in water-gas shift (WGS) reaction to produce pure hydrogen from fossil resources increased significantly in recent years. However, conventional WGS catalysts are easily deactivated by sulfur compounds which are ubiquitous in syngas. On the other hand, MoS₂ is a sulfur-dependent phase that shows WGS and HDS (Hydrodesulfurization) activity. Relatively low WGS activity of pure MoS₂ can be improved by adding Co as a structural promoter. In addition, promoted nanoparticles possessing different crystal sizes are expected to show differences not only in the WGS activity, but also sulfur dependence.

Several different size of Co/Mo catalysts were synthesized in our laboratory and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermo gravimetric analysis (TGA), physic- and chemisorption, and temperature programmed reduction (TPR) in H₂. The XPS analysis was performed to determine the oxidation states and chemical composition in the surface region. The Raman spectrum was employed to characterize the nature of bulk phases (ordered and disordered) present in fresh and used catalysts. The CO chemisorption was used to detemine active metal surface areas, while the TPR analysis probed whether the addition of Co facilitated the reduction of active metals at lower temperatures. The TGA analysis was employed to study the interactions between Co, Mo and support as a function of particle size and composition ratios for the Co/Mo nanoparticles. The XRD was employed to estimate the size and phase composition of Co/Mo nanoparticles. The size and shape of supported Co/Mo nanoparticles was further probed by TEM. The WGS catalytic activity of these catalysts was evaluated in the WGS reaction at 398-823 K under atmospheric pressure in a fixed-bed micro reactor employing the feed of 10% CO and 20% H₂O (balance He). The Co/Mo catalysts were pre-activated in H₂S abundant atmosphere (1 vol. % H₂S balanced by H₂) for 8 hours. The improvements in the WGS catalytic activity was correlated to the size, shape and the composition ratios of the Co/Mo nanoparticles.