(30h) Tuning Solid Acids for the Target Catalytic Reactions

Solid acids facilitate cleaner and much easier reactions and thus have replaced toxic, corrosive, and unrecyclable liquid mineral acids in many catalytic applications, the most prominent being the cracking and refining of a billion tons of crude oil into useful chemical components. Brønsted and Lewis acid sites on solid acids have different functions and initiate catalytic reactions via proton transfer or hydride abstraction. By ion-exchange of parent zeolites with multivalent metal cations in solution, the type, strength, and concentration of acid sites could be tuned on zeolite via various dehydration temperatures. Amorphous silica/alumina (SA) is another popular solid acid that normally provide moderate Brøsted acidity, albeit weaker than that of zeolites. Via the homogeneous composition from precursors and formation of Al-O-Si bonds, the acidity of SAs can be tuned from moderate to zeolitic acid strength depending on the aluminum content. For the activation of C-H bonds of hydrocarbons, in-situ MAS NMR investigations indicated that Brønsted acid sites prefer to protonate aromatic rings of alkyl benzene with low activation energies of about 40 kJ/mol. Lewis acid sites are selectively activating the alkyl group by hydride abstraction with high activation energies of about 200 kJ/mol. Therefore, we tuned acidic properties of zeolites to switch on/off the petrochemical processes for target reaction intermediates, which normally have very short life time. To active the carbonyl groups for the fine-chemical synthesis or bio-oil upgrading, Brønsted and Lewis acid sites always contribute to the different reaction pathways and final products. Lots of efforts had been done to keep one type acid site only in the reaction to avoid competition and enhance the acid strength using expansive precursors to promote the conversion. However, we developed a cooperative catalysis system between Brønsted and Lewis acid sites for commercial catalysts, two acid centers can work together to promote desired reactions.