Effects of tunable acidity and basicity of Nb-KIT-6 catalysts on ethanol conversion: Experiments and kinetic modeling

The relative amounts of acidic and basic sites in niobium-containing ordered mesoporous silicates (Nb-KIT-6) are tunable with metal loading. The acidity and basicity change from 0.11 to 0.34 mmol NH3-equiv./g cat. and 0.17 to 0.31 mmol CO2-equiv./g cat., respectively, as the Nb loading is increased from 1.5 to 10.9%. This work harnesses this unique feature to better understand acidity and basicity effects on ethanol conversion activity and product selectivity. It is shown that the yields of ethylene and acetaldehyde, the dominant products, are tuned with Nb loading. Catalyst characterization results and designed kinetic experiments provide evidence of acid-base pairs involved in the formation of various products. A macrosite kinetic model based on these observations and published mechanistic pathways fits the data for formation of the major products (ethylene, acetaldehyde, diethyl ether, and ethane) remarkably well. These results provide guidance for the rational design of bifunctional mesoporous materials exhibiting tunable acidity and basicity. (c) 2017 American Institute of Chemical Engineers AIChE J, 63: 2888-2899, 2017