Alumina Graphene Catalytic Condenser for Programmable Solid Acids

Precise control of electron density at catalyst active sites enables regulation of surface chemistry for the 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 (IPA) dehydration to propene on the charged alumina surface revealed a shift in the propene formation peak temperature of up to Delta T-peak similar to 50 degrees C relative to the uncharged film, consistent with a 16 kJ mol(-1) (0.17 eV) reduction in the apparent activation energy. Electrical characterization of the thin amorphous alumina film by ultraviolet photoelectron spectroscopy and scanning tunneling microscopy indicates that the film is a defective semiconductor with an appreciable density of in-gap electronic states. Density functional theory calculations of IPA binding on the pentacoordinate aluminum active sites indicate significant binding energy changes (Delta BE) up to 60 kJ mol(-1) (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.

Automated summary

Precise control of electron density at catalyst active sites enables regulation of surface chemistry for optimal rate and selectivity. In this study, an ultrathin catalytic film of amorphous alumina was integrated into a catalytic condenser device, allowing tunable electron depletion from the alumina active layer and increased Lewis acidity. Experimental results showed that the charged alumina surface exhibited a shift in propene formation peak temperature and a reduction in activation energy, supporting the findings from density functional theory calculations. These findings demonstrate that continuous and fast electronic control of thermocatalysis can be achieved with the catalytic condenser device.