Alumina Graphene Catalytic Condenser for Programmable Solid Acids



Precise control of electron density at catalyst active sites enables regulation of surface chemistry for optimal rate and selectivity to products. Here, an ultrathin catalytic film of amorphous alumina (4 nm) was integrated into a catalytic condenser device that enabled tunable electron depletion from the alumina active layer and correspondingly stronger Lewis acidity. The catalytic condenser had the following structure: amorphous alumina/graphene/HfO2 dielectric (70 nm)/p-type Si. Application of positive voltages up to +3 V between graphene and the p-type Si resulted in electrons flowing out of the alumina; positive charge accumulated in the catalyst. Temperature programmed surface reaction of thermocatalytic isopropanol dehydration to propene on the charged alumina surface revealed a shift in the propene formation peak temperature of up to ΔT(peak)~50 ⁰C relative to the uncharged film, consistent with a 16 kJ/mol (0.17 eV) reduction in the apparent activation energy. Electrical characterization of the thin amorphous alumina film by ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling microscopy (STM) indicates the film is a defective semiconductor with an appreciable density of in-gap electronic states. Density functional theory calculations of isopropanol binding on the pentacoordinate aluminum active sites indicate significant binding energy changes (ΔBE) up to 60 kJ/mol (0.62 eV) for 0.125 e- depletion per active site, supporting the experimental findings. Overall, the results indicate that continuous and fast electronic control of thermocatalysis can be achieved with the catalytic condenser device.


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Supplementary material

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Supporting Information for Alumina Graphene Catalytic Condenser for Programmable Solid Acids
The Supporting Information contains descriptions of: Catalytic condenser fabrication methods, TEM and SEM characterization, reactor setup, reaction process and control experiments, electronic characterization, X-Ray diffraction, Redhead analysis of temperature programmed surface reactions, and additional references

Supplementary weblinks

Dauenhauer Group Research Page
Description of the Paul Dauenhauer research group at the University of Minnesota