In situ DRIFTS investigations on the evolution of surface and catalysis properties of alumina-promoted sulfated zirconia during n-butane isomerization

The changes in surface-structure properties of aluminum-promoted sulfated zirconia (SZA) during NH3 ad/desorption and n-butane isomerization were investigated by in situ DRIFTS experiments. Different from water ad/desorption, the adsorption of ammonia, n-butane, and pyridine on SZA surface not only occupies the acid sites, but also decreases the oxidizing ability of S=O bonds, leading to a decrease in the catalytic activity. For the first time, the coexistence and interaction mechanism of oxidative activation and superacid catalyzed protolytic activation routes are proposed. As an efficient activation pathway, the protonation of n-butane on superacidic sites needs to overcome a high energy barrier and this pathway deactivates quickly at the beginning of reaction, while the ODH route is limited by reaction equilibrium and occurs during the whole deactivation stage. The water and butene formed via ODH decrease the strength of acid sites and the oxidizing ability of the sulfated species, which causes deactiv...