• • RSXRD at the Al K-edge resolves Al siting in ZSM-5 with 12 T atoms, distinguishing single Al at T8 and Al pairs at T4/T6—critical for predicting catalytic selectivity in commercial zeolites where Si/Al ratio alone fails to correlate with performance.
• • Probe molecules (trimethylphosphorus oxide, acetone, pyridinium) adsorb preferentially at T8 (straight pore) and T6 (cross-pore), while T4 in cross-pore channels shows negligible adsorption, indicating steric hindrance that reduces accessibility by >80% compared to T8.
• • The integration of RSXRD with neutron powder diffraction, solid-state NMR, and DFT achieves atomic-scale localization of Al, overcoming the ~0.1 Å resolution limit of conventional XRD for Al/Si discrimination.
• • Industrial ZSM-5 catalysts with identical Si/Al ratios can exhibit up to 10-fold variations in activity due to Al distribution; this method provides a validated protocol for quality control and rational catalyst design.