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Lehigh University logo
Lehigh University logo

Xu "George" Yan

Combined theoretical and experimental study of ethanol to 1,3-butadiene over MgO/SiO2

Department: Chemical and Biomolecular Engineering
Advisor: Jonas Baltrusaitis

Abstract:
We explored the mechanism and active sites for the conversion of ethanol to butadiene over a MgO/SiO2 catalyst, a catalyst besides ZrO2/SiO2 that also support the process. We studied this reaction using a fixed bed reactor (FBR) to test for reactivity, diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) to observe the catalyst surface during reaction and to find the active sites, and density functional theory (DFT) calculations to build a mechanistic model to support experimental data. FBR data has shown that butadiene forms at 400-450 oC over the catalyst at 50-60% yield, and one of the initiation steps is the formation of acetaldehyde. Further reactivity testing showed that acetaldehyde begins to emerge at temperatures as low as 200 oC. In-situ DRIFTS data shows that acetaldehyde and adsorbed ethoxide are the dominant surface species at 400-450 oC, suggesting that ethanol dehydrogenation may be the rate-determing step (RDS). Further DRIFTS testing with CO2 and pyridine as surface probes showed that the catalyst contains basic and Lewis acid sites; surface basic sites are active for acetaldehyde production. DFT calculations supported our claim of the RDS and showed that the reaction could possibly follow two competitive mechanisms, the aldol condensation mechanism and the Prins condensation. In-situ DRIFTS of intermediates for both reactions have also shown that both mechanisms are possible. Future work will focus on identifying other surface features responsible for the reaction and temperature program desorption (TPD) of surface probes.

About Xu "George" Yan:
George Yan is a senior at Lehigh University pursuing a BS in chemical engineering with a minor in applied mathematics. He has been assisting in research in Professor Baltrusaitis’s lab since late November 2014 on various projects regarding the mechanism and active sites of catalytic reactions. His research uses mostly experimental and some theoretical techniques. Under the leadership and guidance of Professor Baltrusaitis and Ph. D. Candidate William Taifan, we hope to provide concrete evidence for the mechanism and active sites for the conversion of ethanol to 1,3-butadiene over the classic MgO/SiO2 catalyst, as a sustainable pathway to produce synthetic rubber. After graduation, George Yan will pursue a Ph. D. in chemical engineering.