Alcohol Dehydration over Zr-KIT-6: Lewis Acidic Zr-Incorporated Mesoporous Silicates

Dehydration of alcohols over a solid acid catalyst is a key step in producing alkenes from bioalcohols obtained by fermentation and C-C coupling using either Guerbet synthesis or hydroformylation. The common solid acid catalysts used for dehydration in industry are zeolites [1]. However, their microporous structure induces pore diffusion limitations with either progressively longer chain alcohols or sugar alcohols such as glycerol, rendering them susceptible to deactivation by fouling [2]. MCM-type zeolites with a mesoporous structure have been attempted to address this problem [3], but low hydrothermal stability and structural reproducibility are significant drawbacks [4]. To address these disadvantages, we have developed a solid Lewis acidic catalyst with a tunable pore size by incorporating Zr into the mesoporous silicate structure KIT-6. Characterization of the catalyst shows a narrow pore size distribution (with mean pore size ~7 nm) with a high number of medium-strength acid sites depending on Zr content [4]. Zr-KIT-6 has been tested for dehydration of linear C₂-C₄ alcohols. In the 190-300 °C temperature range, the Zr-KIT-6 catalysts showed > 98% selectivity to propene. The intrinsic rate constants obtained in the absence of mass transfer limitations scale with the number of acid sites in the various Zr-KIT-6 samples. The intrinsic activation energy was ~49 kJ/mol and the catalyst activity was stable for several days during continuous runs in a fixed-bed reactor [5]. These results along with those from the dehydration of other alcohols such as ethanol will be presented.

References

1. Tanabe, K., Hölderich, W.F., 1999. Industrial application of solid acid–base catalysts. Applied Catalysis A: General 181, 399–434.

2. Wilson, K., Clark, J.H., 2000. Solid acids and their use as environmentally friendly catalysts in organic synthesis. Pure and Applied Chemistry 72, 1313–1319.

3. Haishi, T., Kasai, K., Iwamoto, M., 2011. Fast and Quantitative Dehydration of Lower Alcohols to Corresponding Olefins on Mesoporous Silica Catalyst. Chemistry Letters 40, 614–616.

4. Ramanathan, A., Subramaniam, B., Maheswari, R., Hanefeld, U., 2013. Synthesis and characterization of Zirconium incorporated ultra large pore mesoporous silicate, Zr–KIT-6. Microporous and Mesoporous Materials 167, 207–212.

5. Pan, Q., Ramanathan, A., Snavely, W.K., Chaudhari, R.V., Subramaniam, B., 2013. Synthesis and Dehydration Activity of Novel Lewis Acidic Ordered Mesoporous Silicate: Zr-KIT-6. Ind. Eng. Chem. Res.