(195e) Ethanol Conversion On ZrO2: The Role of Brönsted and Lewis Acidic Sites

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 Zn_xZr_yO_z 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.).

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

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