N-dodecane hydroisomerization over Pt/ZSM-22: Controllable microporous Brönsted acidity distribution and shape-selectivity

The controllable acidity distribution in micropore for ZSM-22 zeolites is successfully tailored by using a new template protective NH4+ exchange strategy. The location and density of microporous Brönsted acidity is tailored by controlling the degree of detemplation and the concentration of NH4+ aqueous solution, respectively. The distribution of microporous Brönsted acidity of these Pt/ZSM-22 catalysts obviously affects the shape-selectivity in the hydroisomerization of n-dodecane. Weak microporous acidity leads to the formation of centrally mono-branched isomers, while strong microporous Brönsted acidity near the pore mouth favors the formation of multi-branched isomers, and strong microporous Brönsted acidity deep inside the pore mouth favors cracking through (s, p) β-scission. By selectively tailoring microporous Brönsted acidity near the pore mouth with lower acid density, the isomer yield over Pt/ZSM-22 was increased from 40.7% to 63.7%. This enhanced catalytic performance comes from the preferable formation of centrally mono-branched isomers and multi-branched isomers through key-lock model.