287606 Ethanol Conversion On ZrO2: The Role of Brönsted and Lewis Acidic Sites

Tuesday, October 30, 2012: 10:10 AM
322 (Convention Center )
Changjun Liu1, Junming Sun1, Colin Smith1 and Yong Wang1,2, (1)The Gene & Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA, (2)Pacific Northwest National Lab, Richland, WA

Ethanol Conversion On ZrO2: The role of Brönsted and Lewis acidic sites

Changjun Liu, Junming Sun, Colin Smith, Yong Wang*†‡

The Gene & Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman Washington 99164, United States

Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States

Abstract

As one of the sustainable natural resources, biomass has attracted increased attentions for its conversion into valuable chemicals in recent decades1. The increased availability and reduced cost of bioethanol2 provides the potential to make value-added chemicals from ethanol in large scale. Direct conversion of bioethanol into ethylene, propene has been studied over wide range of acidic catalyst like zeolites. More recently the direct conversion of bioethanol into isobutene over nanosized ZnxZryOz catalyst has also been reported3. Ethylene is considered as the intermediate in conversion bioethanol to propene4 while it is considered as one of the major byproduct in isobutene production. Generally either the production of propene or isobutene from bioethanol are conducted at the temperature above 400 oC over various acidic catalysts. Although, ethanol conversion to ethylene has been studied extensively at a temperature range of 150 oC to 300 oC, the investigation on the intrinsic catalytic behavior of acidic sites of different nature and varied strength under different temperature ranges are still rare. In this work, the ethanol dehydration at a wide temperature ranges (200-500 oC) have been studied on ZrO2 catalysts with controlled Brönsted and Lewis acidic sites. Specifically, the effect of Brönsted and Lewis acidic sites on the reaction pathway in ethanol dehydration has been investigated (Figure 1.).

a)        ZrO2 with Lewis acidic site

b)      ZrO2 with Brönsted and Lewis acidic sites

Figure 1. Ethanol conversion and main products distribution at various reaction temperatures

At low temperature range (T<300 oC), Brönsted acid site is mainly responsible for the intermolecular dehydration of ethanol to diethyl ether. While only intramolecular dehydration of ethanol to ethylene was observed on Lewis acidic site at the whole temperature range studied albeit it's low activity. Dehydrogenation of ethanol was significant at lower temperature with Lewis acidic sites being more selective. At higher temperature (T>300 oC), the intramolecular dehydration started taking over with intermolecular dehydration of ethanol being largely suppressed on the Brönsted acidic sites. Interestingly, ethylene dimerization to 1-butene was also observed, and its selectivity increased with reaction temperature; whereas, no dimerization was observed on Lewis acidic sites. The possible reaction mechanisms regarding Brönsted and Lewis acidic sites a catalyzed different reaction was discussed in details.

* Corresponding author

Reference

1.      Serrano-Ruiz, J. C.; Luque, R.; Sepulveda-Escribano, A., Transformations of biomass-derived platform molecules: from high added-value chemicals to fuels via aqueous-phase processing. Chem. Soc. Rev. 2011, 40 (11), 5266-5281.

2.      Deluga, G. A.; Salge, J. R.; Schmidt, L. D.; Verykios, X. E., Renewable Hydrogen from Ethanol by Autothermal Reforming. Science 2004, 303 (5660), 993-997.

3.      Sun, J.; Zhu, K.; Gao, F.; Wang, C.; Liu, J.; Peden, C. H. F.; Wang, Y., Direct Conversion of Bio-ethanol to Isobutene on Nanosized ZnxZryOz Mixed Oxides with Balanced Acid¨CBase Sites. J. Am. Chem. Soc. 2011, 133 (29), 11096-11099.

4.      (a) Oikawa, H.; Shibata, Y.; Inazu, K.; Iwase, Y.; Murai, K.; Hyodo, S.; Kobayashi, G.; Baba, T., Highly selective conversion of ethene to propene over SAPO-34 as a solid acid catalyst. Applied Catalysis A: General 2006, 312 (0), 181-185; (b) Xia, W.; Takahashi, A.; Nakamura, I.; Shimada, H.; Fujitani, T., Study of active sites on the MFI zeolite catalysts for the transformation of ethanol into propylene. J. Mol. Catal. A: Chem. 2010, 328 (1¨C2), 114-118.


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